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Raman spectroscopy
NITISH KUMARMPHARM (ANALYSIS)
2015-2016
GT Road (NH-95) Ghal Kalan Moga(142001) Punjab India
2
INTRODUCTIONbull Raman spectroscopy is the measurement of the
wavelength and intensity of inelastically scattered light from molecules The Raman scattered light occurs at wavelengths that are shifted from the incident light by the energies of molecular vibrations
bull Raman spectroscopy is used to determine the molecular motions especially the vibrational one
3
Time lap
bull 1923 ndash Inelastic light scattering is predicted by A Smekelbull 1928 ndash Landsberg and Mandelstam see unexpected frequency shifts in
scattering from quartz
bull 1928 ndash CV Raman and KS Krishnan see ldquofeeble fluorescencerdquo from neat solvents
bull 1930 ndash CV Raman wins Nobel Prize in Physics
bull 1961 ndash Invention of laser makes Raman experiments reasonablebull 1977 ndash Surface-enhanced Raman scattering (SERS) is discoveredbull 1997 ndash Single molecule SERS is possible
4
OVERVIEW
bull A vibrational spectroscopy
- IR and Raman are the most common vibrational spectroscopes for assessing molecular motion and fingerprinting species
- Based on inelastic scattering of a monochromatic excitation source
- Routine energy range 200 - 4000 cmndash1
bull Complementary selection rules to IR spectroscopy
- Selection rules dictate which molecular vibrations are probed
- Some vibrational modes are both IR and Raman active
bull Great for many real-world samples
- Minimal sample preparation (gas liquid solid)
- Compatible with wet samples and normal ambient
- Achilles Heal is sample fluorescence
5
Raman spectrometerrsquos mechanismWhen a substances (in any state) is irradiated with a monochromatic light of
definite frequency(v)the light scattered at right angle to the incident light contains lines of 1 Incident frequency and 2Also of lower frequency
Sometimes lines of higher frequency are also obtained that of the incident beam will be scattered It is called Raman scattering
The line with lower frequency are called Stokersquos lines
Also the line with higher frequency are called Antistokersquos lines
The line with the same frequency as that of the incident light is called Rayleigh line
6
Frequency -
This difference is called Raman frequency or Raman shift
8
bull It may be noted that raman frequencies for a particular substances are characteristic of that substances
bull The various observation made by raman are called raman effect
bull Also the spectrum obtained is called raman spectrum
9
Classical theory of raman effect
bull According to the classical theory of electromagnetic radiation electric and magnetic fields oscillating at a given frequency are able to give out electromagnetic radiation of the same frequency One could use electromagnetic radiation theory to explain light scattering phenomena
bull For a majority of systems only an induced electric dipole moment μ is taken into consideration This dipole moment which is induced by the electric field E could be expressed by the power series
μ=μ(1)+μ(2)+μ(3)+⋯whereμ(1)=α Esdotμ(2)=12β EEsdotμ(3)=16γ EEEsdot
α is termed the polarizability tensor It is a second-rank tensor with all the components in the unit of CV-1m2 Typically orders of magnitude
for components in α β and γ are as follows α 10-40 CV-1m2
β 10-50 CV-2m3 and γ 10-61 CV-3m4
According to the values the contributions of μ(2)and μ(3) are quite small unless electric field is very high Since Rayleigh and Raman scattering are observed quite readily with very much lower electric field intensities one may expect to explain Rayleigh and Raman scattering in terms of μ(1) only
10
Classical theory of raman effecty of Raman Effect
Colthup et al Introduction to Infrared and Raman Spectroscopy 3rd ed Academic Press Boston 1990
mind = aE
polarizability
11
ElectronicGround State
1st ElectronicExcited State
Exci
tatio
n En
ergy
s (c
mndash1
)
Vibstates
4000
25000
0
fluor
esce
nce
IRs
s semit
2nd ElectronicExcited State
Raman∆s=semit-s
s ∆sflu
ores
cenc
eIm
purit
y
Fluorescence = Trouble
Raman Spectroscopy Absorption Scattering and Fluorescence
Stokes Anti-Stokes
12
Raman Spectroscopy Classical Treatment
bull Number of peaks related to degrees of freedom
DoF = 3N - 6 (bent) or 3N - 5 (linear) for N atomsbull Energy related to harmonic oscillator
bull Selection rules related to symmetry Rule of thumb symmetric=Raman active asymmetric=IR active
Raman 1335 cmndash1
IR 2349 cmndash1
IR 667 cmndash1
CO2
s or s c
2k(m1m2)
m1m2
Raman + IR 3657 cmndash1
Raman + IR 3756 cmndash1
Raman + IR 1594 cmndash1
H2O
13
Theory of raman spectraTwo cases may arise depending upon whether a collision between a photon and molecules In itrsquos ground state is elastic or inelastic in natureCase 1- if the collision is elastic ndash this lead to the appearance of unmodified lines (or unmodified frequency of light) in the scattered beam and this explain rayleigh scatteringCase 2 - if the collision is inelastic ndash there will be exchange or transfer of energy between the scattering molecules and the incident photonThe frequency of scattered light and the incident photon which is either higher or lower than that of the incident photon is called raman frequency
Total energy before collision = total energy after collision
14
Presentation of Raman Spectra
lex = 1064 nm = 9399 cm-1
Breathing mode9399 ndash 992 = 8407 cm-1
Stretching mode9399 ndash 3063 = 6336 cm-1
15
Rayleigh Scattering- Occurs when incident EM radiation induces an oscillating dipole in a molecules which is re-radiated at the same frequency
Eugene Hecht Optics Addison-Wesley Reading MA 1998
bullElastic (l does not change)
bullRandom direction of emission
bullLittle energy lossbullof emission
bullLittle energy loss
4 2 20
4 2
8 ( ) (1 cos )( )sc
EE
d a
l
16
Raman ScatteringOccurs when monochromatic light is scattered light has been weakly modulated
by the characteristic frequencies of the molecules Raman spectroscopy measures the differences between the wavelengths of the
incident radiation and the scatted radiation
max 0
max max 0
max max 0
( ) cos 21 cos 2 ( )21 cos 2 ( )2
equilz zz
zzvib
zzvib
t E td r E tdr
d r E tdr
m a a
a
Selection rule v = plusmn1Overtones v = plusmn2 plusmn3 hellip
Must also have a change in polarizability
Classical Description does not suggest any difference between Stokes and Anti-Stokes intensities
1
0
vibhkTN e
N
17
The Raman polarization
The Raman Polarization is a property of waves that can oscillate with more than one orientation EMR or waves such as light and gravitational wave exhibit polarization
Polarization state - the shape traced out in a fixed plane by the electric vector as such a plane wave passes over it is a description of the polarization
Eg linear polarization circular polarization
elliptical polarization orthogonally polarization
Polarization changes are necessary to form the virtual state and hence the Raman effect
18
Condition for raman spectroscopyVibrational modes that are more polarizable are more Raman-active Examples ndash N2 (dinitrogen) symmetric stretch cause no change in dipole (IR-inactive) cause a change in the polarizability of the bond ndash as the bond gets longer it is more easily deformed (Raman -active)
ndash CO2 asymmetric stretch cause a change in dipole (IR-active) Polarizability change of one C=O bond lengthening is cancelled by the shortening of the other ndash no net polarizability (Raman-inactive) Some modes may be both IR and Raman-active others may be one or the other
19
Condition for raman spectroscopy
Raman spectra occurs as a result of oscillation of a dipole moment induced in a molecules by the oscillating electric field of an incident wave
As the induced dipole moment is directly proportional to the polarisability of the molecules the molecules must possess anisotropic polarisability which should change during molecular rotation or vibration for vibrational or rotational-vibrational raman spectra
Anisotropic polarisability depends upon the orientation of the molecules
In the presence of an electric field the electron cloud of an atom or molecules is distorted or polarised
20
Mutual Exclusion Principle
For molecules with a center of symmetry no IR active transitions are Raman active and vice versa
THORNSymmetric molecules IR-active vibrations are not Raman-active Raman-active vibrations are not IR-active
O = C = O O = C = O
Raman active Raman inactive IR inactive IR active
21
Raman Instrumentation
22
There are following component involves
1 Laser or source of light 2 Filter3 Sample holder 4 detector
23
The block design dispersive Raman scattering system
Radiation sources
Sample Wavelength
selector
Detector InGaAs or
Ge
RecorderDetector InGaAs or
Ge
RecorderDetector
InGaAs or Ge
Recorder
Block diagram
90
24
Flow diagram dispersive Raman scattering system
25
Schematic diagram dispersive raman scattering system
26
1 Laser or source of light
bull Lasers are generally the only source strong enough to scatter lots of light and lead to detectable raman scattering
bull Lasers operate using the principle of stimulated emission
bull Electronic population inversion is required to achieve gain via stimulated emission (before the fluorescence lifetime is reached)
bull Population inversion is achieved by ldquopumpingrdquo using lots of photons in a variety of laser gain media
27
List of Various laser source
SNo Laser wavelength01 NdYAG 1064nm
02 HeNe 633nm
03 Argon ion 488nm
04 GaAlAs diode 785nm
05 Co2 10600nm
06 Ti-Sapphire 800nm
28
A - HeNe laserbull Filled with 71 He amp Ne gas optimum output of 6328 Aring
bull High voltage excitation is preferred
B - NdYAG Systembull A typical laser system ndashthe neodymium-doped yttrium aluminum garnet or Nd+3
bull YAG is a cubic crystalline material
bull Crystal field splitting causes electronic energy level splitting
bull NdYAG laser are optically pumped using a flash tube or laser diodes
bull These are the one of the most common type of laser
bull It emits 1064 nm wavelength
29
2Filter bull It is therefore essential to have monochromatic radiations
bull For getting monochromatic radiations filters are used
bull They may be made of nickel oxide glass or quartz glass
bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator
30
3Sample holder bull For the study of raman effect the type of sample holder to be used
depends upon the intensity of sources the nature and availability of the sample
bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids
bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be
used for the study of raman spectra
bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy
31
4detectorbull Researchers traditionally used single points detectors such as
photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality
bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)
bull Sensitivity amp performance of modern CCD detectors are high
32
APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling
33
bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and
gypsum illustrating how Raman can be used for fast mineral ID
bull Gemstone and mineral identification
bull Fluid inclusions
bull Mineral and phase distribution in rock sections
bull Phase transitions
bull Mineral behavior under extreme conditions
34
Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance
35
Semiconductors
bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width
bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis
36
Life Sciences
bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level
bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure
37
Differences between IR and Raman methodsSNo Raman IR
01 It is due to the scattering of light by the vibrating molecules
It is the result of absorption of light by vibrating molecules
02 The vibration is Raman active if it causes a change in polarisability
Vibration is IR active if there is change in dipole moment
03 The molecule need not possess a permanent dipole moment
The vibration concerned should have a change in dipole moment due to that vibration
04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR
05 Sample preparation is not very elaborate it can be in any state
Sample preparation is elaborateGaseous samples can rarely be used
06 Gives an indication of covalent character in the molecule
Gives an indication of ionic character in the molecule
07 Cost of instrumentation is very high
Comparatively inexpensive
38
Advantages of Raman over IR
bull Water can be used as solvent bull Very suitable for biological samples in native state (because water
can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral
overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power
39
Advantages of IR over Ramanbull Simpler and cheaper instrumentation
bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio
bull Lower detection limit than (normal) Raman
bull Background fluorescence can overwhelm Raman
bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)
40
Several variations of Raman spectroscopy
1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal
bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)
bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977
bull A comprehensive theory of the effect was given by Lombardi and Birke
41
2 Resonance Raman spectroscopy The excitation wavelength is matched to an
electronic transition of the molecule or crystal so that vibrational modes associated with the excited electronic state are greatly enhanced This is useful for studying large molecules such as polypeptides which might show hundreds of bands in conventional Raman spectra It is also useful for associating normal modes with their observed frequency shifts
42
3 Surface-enhanced resonance Raman spectroscopy (SERRS) ndash A combination of SERS and resonance Raman spectroscopy that uses proximity to a surface to increase Raman intensity and excitation wavelength matched to the maximum absorbance of the molecule being analysed
4 Coherent anti-Stokes Raman spectroscopy (CARS) ndash
Two laser beams are used to generate a coherent anti-Stokes frequency beam which can be enhanced by resonance
43
5 Raman optical activity (ROA) ndash Measures vibrational optical activity by means of a small difference in the intensity of Raman scattering from chiral molecules in right- and left-circularly polarized incident light or equivalently a small circularly polarized component in the scattered light
6 Spatially offset Raman spectroscopy (SORS)
7 Spontaneous Raman spectroscopy (SRS) 8 Optical tweezers Raman spectroscopy (OTRS)
44
9 Angle-resolved Raman spectroscopy10 Inverse Raman spectroscopy11 Tip-enhanced Raman spectroscopy
(TERS) 12 Surface plasmon polariton enhanced
Raman scattering (SPPERS)13 Stand-off Remote Raman ndash 14 Fourier-transform Rama spectroscopyapplied
to photobiological systems
45
2
INTRODUCTIONbull Raman spectroscopy is the measurement of the
wavelength and intensity of inelastically scattered light from molecules The Raman scattered light occurs at wavelengths that are shifted from the incident light by the energies of molecular vibrations
bull Raman spectroscopy is used to determine the molecular motions especially the vibrational one
3
Time lap
bull 1923 ndash Inelastic light scattering is predicted by A Smekelbull 1928 ndash Landsberg and Mandelstam see unexpected frequency shifts in
scattering from quartz
bull 1928 ndash CV Raman and KS Krishnan see ldquofeeble fluorescencerdquo from neat solvents
bull 1930 ndash CV Raman wins Nobel Prize in Physics
bull 1961 ndash Invention of laser makes Raman experiments reasonablebull 1977 ndash Surface-enhanced Raman scattering (SERS) is discoveredbull 1997 ndash Single molecule SERS is possible
4
OVERVIEW
bull A vibrational spectroscopy
- IR and Raman are the most common vibrational spectroscopes for assessing molecular motion and fingerprinting species
- Based on inelastic scattering of a monochromatic excitation source
- Routine energy range 200 - 4000 cmndash1
bull Complementary selection rules to IR spectroscopy
- Selection rules dictate which molecular vibrations are probed
- Some vibrational modes are both IR and Raman active
bull Great for many real-world samples
- Minimal sample preparation (gas liquid solid)
- Compatible with wet samples and normal ambient
- Achilles Heal is sample fluorescence
5
Raman spectrometerrsquos mechanismWhen a substances (in any state) is irradiated with a monochromatic light of
definite frequency(v)the light scattered at right angle to the incident light contains lines of 1 Incident frequency and 2Also of lower frequency
Sometimes lines of higher frequency are also obtained that of the incident beam will be scattered It is called Raman scattering
The line with lower frequency are called Stokersquos lines
Also the line with higher frequency are called Antistokersquos lines
The line with the same frequency as that of the incident light is called Rayleigh line
6
Frequency -
This difference is called Raman frequency or Raman shift
8
bull It may be noted that raman frequencies for a particular substances are characteristic of that substances
bull The various observation made by raman are called raman effect
bull Also the spectrum obtained is called raman spectrum
9
Classical theory of raman effect
bull According to the classical theory of electromagnetic radiation electric and magnetic fields oscillating at a given frequency are able to give out electromagnetic radiation of the same frequency One could use electromagnetic radiation theory to explain light scattering phenomena
bull For a majority of systems only an induced electric dipole moment μ is taken into consideration This dipole moment which is induced by the electric field E could be expressed by the power series
μ=μ(1)+μ(2)+μ(3)+⋯whereμ(1)=α Esdotμ(2)=12β EEsdotμ(3)=16γ EEEsdot
α is termed the polarizability tensor It is a second-rank tensor with all the components in the unit of CV-1m2 Typically orders of magnitude
for components in α β and γ are as follows α 10-40 CV-1m2
β 10-50 CV-2m3 and γ 10-61 CV-3m4
According to the values the contributions of μ(2)and μ(3) are quite small unless electric field is very high Since Rayleigh and Raman scattering are observed quite readily with very much lower electric field intensities one may expect to explain Rayleigh and Raman scattering in terms of μ(1) only
10
Classical theory of raman effecty of Raman Effect
Colthup et al Introduction to Infrared and Raman Spectroscopy 3rd ed Academic Press Boston 1990
mind = aE
polarizability
11
ElectronicGround State
1st ElectronicExcited State
Exci
tatio
n En
ergy
s (c
mndash1
)
Vibstates
4000
25000
0
fluor
esce
nce
IRs
s semit
2nd ElectronicExcited State
Raman∆s=semit-s
s ∆sflu
ores
cenc
eIm
purit
y
Fluorescence = Trouble
Raman Spectroscopy Absorption Scattering and Fluorescence
Stokes Anti-Stokes
12
Raman Spectroscopy Classical Treatment
bull Number of peaks related to degrees of freedom
DoF = 3N - 6 (bent) or 3N - 5 (linear) for N atomsbull Energy related to harmonic oscillator
bull Selection rules related to symmetry Rule of thumb symmetric=Raman active asymmetric=IR active
Raman 1335 cmndash1
IR 2349 cmndash1
IR 667 cmndash1
CO2
s or s c
2k(m1m2)
m1m2
Raman + IR 3657 cmndash1
Raman + IR 3756 cmndash1
Raman + IR 1594 cmndash1
H2O
13
Theory of raman spectraTwo cases may arise depending upon whether a collision between a photon and molecules In itrsquos ground state is elastic or inelastic in natureCase 1- if the collision is elastic ndash this lead to the appearance of unmodified lines (or unmodified frequency of light) in the scattered beam and this explain rayleigh scatteringCase 2 - if the collision is inelastic ndash there will be exchange or transfer of energy between the scattering molecules and the incident photonThe frequency of scattered light and the incident photon which is either higher or lower than that of the incident photon is called raman frequency
Total energy before collision = total energy after collision
14
Presentation of Raman Spectra
lex = 1064 nm = 9399 cm-1
Breathing mode9399 ndash 992 = 8407 cm-1
Stretching mode9399 ndash 3063 = 6336 cm-1
15
Rayleigh Scattering- Occurs when incident EM radiation induces an oscillating dipole in a molecules which is re-radiated at the same frequency
Eugene Hecht Optics Addison-Wesley Reading MA 1998
bullElastic (l does not change)
bullRandom direction of emission
bullLittle energy lossbullof emission
bullLittle energy loss
4 2 20
4 2
8 ( ) (1 cos )( )sc
EE
d a
l
16
Raman ScatteringOccurs when monochromatic light is scattered light has been weakly modulated
by the characteristic frequencies of the molecules Raman spectroscopy measures the differences between the wavelengths of the
incident radiation and the scatted radiation
max 0
max max 0
max max 0
( ) cos 21 cos 2 ( )21 cos 2 ( )2
equilz zz
zzvib
zzvib
t E td r E tdr
d r E tdr
m a a
a
Selection rule v = plusmn1Overtones v = plusmn2 plusmn3 hellip
Must also have a change in polarizability
Classical Description does not suggest any difference between Stokes and Anti-Stokes intensities
1
0
vibhkTN e
N
17
The Raman polarization
The Raman Polarization is a property of waves that can oscillate with more than one orientation EMR or waves such as light and gravitational wave exhibit polarization
Polarization state - the shape traced out in a fixed plane by the electric vector as such a plane wave passes over it is a description of the polarization
Eg linear polarization circular polarization
elliptical polarization orthogonally polarization
Polarization changes are necessary to form the virtual state and hence the Raman effect
18
Condition for raman spectroscopyVibrational modes that are more polarizable are more Raman-active Examples ndash N2 (dinitrogen) symmetric stretch cause no change in dipole (IR-inactive) cause a change in the polarizability of the bond ndash as the bond gets longer it is more easily deformed (Raman -active)
ndash CO2 asymmetric stretch cause a change in dipole (IR-active) Polarizability change of one C=O bond lengthening is cancelled by the shortening of the other ndash no net polarizability (Raman-inactive) Some modes may be both IR and Raman-active others may be one or the other
19
Condition for raman spectroscopy
Raman spectra occurs as a result of oscillation of a dipole moment induced in a molecules by the oscillating electric field of an incident wave
As the induced dipole moment is directly proportional to the polarisability of the molecules the molecules must possess anisotropic polarisability which should change during molecular rotation or vibration for vibrational or rotational-vibrational raman spectra
Anisotropic polarisability depends upon the orientation of the molecules
In the presence of an electric field the electron cloud of an atom or molecules is distorted or polarised
20
Mutual Exclusion Principle
For molecules with a center of symmetry no IR active transitions are Raman active and vice versa
THORNSymmetric molecules IR-active vibrations are not Raman-active Raman-active vibrations are not IR-active
O = C = O O = C = O
Raman active Raman inactive IR inactive IR active
21
Raman Instrumentation
22
There are following component involves
1 Laser or source of light 2 Filter3 Sample holder 4 detector
23
The block design dispersive Raman scattering system
Radiation sources
Sample Wavelength
selector
Detector InGaAs or
Ge
RecorderDetector InGaAs or
Ge
RecorderDetector
InGaAs or Ge
Recorder
Block diagram
90
24
Flow diagram dispersive Raman scattering system
25
Schematic diagram dispersive raman scattering system
26
1 Laser or source of light
bull Lasers are generally the only source strong enough to scatter lots of light and lead to detectable raman scattering
bull Lasers operate using the principle of stimulated emission
bull Electronic population inversion is required to achieve gain via stimulated emission (before the fluorescence lifetime is reached)
bull Population inversion is achieved by ldquopumpingrdquo using lots of photons in a variety of laser gain media
27
List of Various laser source
SNo Laser wavelength01 NdYAG 1064nm
02 HeNe 633nm
03 Argon ion 488nm
04 GaAlAs diode 785nm
05 Co2 10600nm
06 Ti-Sapphire 800nm
28
A - HeNe laserbull Filled with 71 He amp Ne gas optimum output of 6328 Aring
bull High voltage excitation is preferred
B - NdYAG Systembull A typical laser system ndashthe neodymium-doped yttrium aluminum garnet or Nd+3
bull YAG is a cubic crystalline material
bull Crystal field splitting causes electronic energy level splitting
bull NdYAG laser are optically pumped using a flash tube or laser diodes
bull These are the one of the most common type of laser
bull It emits 1064 nm wavelength
29
2Filter bull It is therefore essential to have monochromatic radiations
bull For getting monochromatic radiations filters are used
bull They may be made of nickel oxide glass or quartz glass
bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator
30
3Sample holder bull For the study of raman effect the type of sample holder to be used
depends upon the intensity of sources the nature and availability of the sample
bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids
bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be
used for the study of raman spectra
bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy
31
4detectorbull Researchers traditionally used single points detectors such as
photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality
bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)
bull Sensitivity amp performance of modern CCD detectors are high
32
APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling
33
bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and
gypsum illustrating how Raman can be used for fast mineral ID
bull Gemstone and mineral identification
bull Fluid inclusions
bull Mineral and phase distribution in rock sections
bull Phase transitions
bull Mineral behavior under extreme conditions
34
Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance
35
Semiconductors
bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width
bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis
36
Life Sciences
bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level
bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure
37
Differences between IR and Raman methodsSNo Raman IR
01 It is due to the scattering of light by the vibrating molecules
It is the result of absorption of light by vibrating molecules
02 The vibration is Raman active if it causes a change in polarisability
Vibration is IR active if there is change in dipole moment
03 The molecule need not possess a permanent dipole moment
The vibration concerned should have a change in dipole moment due to that vibration
04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR
05 Sample preparation is not very elaborate it can be in any state
Sample preparation is elaborateGaseous samples can rarely be used
06 Gives an indication of covalent character in the molecule
Gives an indication of ionic character in the molecule
07 Cost of instrumentation is very high
Comparatively inexpensive
38
Advantages of Raman over IR
bull Water can be used as solvent bull Very suitable for biological samples in native state (because water
can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral
overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power
39
Advantages of IR over Ramanbull Simpler and cheaper instrumentation
bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio
bull Lower detection limit than (normal) Raman
bull Background fluorescence can overwhelm Raman
bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)
40
Several variations of Raman spectroscopy
1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal
bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)
bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977
bull A comprehensive theory of the effect was given by Lombardi and Birke
41
2 Resonance Raman spectroscopy The excitation wavelength is matched to an
electronic transition of the molecule or crystal so that vibrational modes associated with the excited electronic state are greatly enhanced This is useful for studying large molecules such as polypeptides which might show hundreds of bands in conventional Raman spectra It is also useful for associating normal modes with their observed frequency shifts
42
3 Surface-enhanced resonance Raman spectroscopy (SERRS) ndash A combination of SERS and resonance Raman spectroscopy that uses proximity to a surface to increase Raman intensity and excitation wavelength matched to the maximum absorbance of the molecule being analysed
4 Coherent anti-Stokes Raman spectroscopy (CARS) ndash
Two laser beams are used to generate a coherent anti-Stokes frequency beam which can be enhanced by resonance
43
5 Raman optical activity (ROA) ndash Measures vibrational optical activity by means of a small difference in the intensity of Raman scattering from chiral molecules in right- and left-circularly polarized incident light or equivalently a small circularly polarized component in the scattered light
6 Spatially offset Raman spectroscopy (SORS)
7 Spontaneous Raman spectroscopy (SRS) 8 Optical tweezers Raman spectroscopy (OTRS)
44
9 Angle-resolved Raman spectroscopy10 Inverse Raman spectroscopy11 Tip-enhanced Raman spectroscopy
(TERS) 12 Surface plasmon polariton enhanced
Raman scattering (SPPERS)13 Stand-off Remote Raman ndash 14 Fourier-transform Rama spectroscopyapplied
to photobiological systems
45
3
Time lap
bull 1923 ndash Inelastic light scattering is predicted by A Smekelbull 1928 ndash Landsberg and Mandelstam see unexpected frequency shifts in
scattering from quartz
bull 1928 ndash CV Raman and KS Krishnan see ldquofeeble fluorescencerdquo from neat solvents
bull 1930 ndash CV Raman wins Nobel Prize in Physics
bull 1961 ndash Invention of laser makes Raman experiments reasonablebull 1977 ndash Surface-enhanced Raman scattering (SERS) is discoveredbull 1997 ndash Single molecule SERS is possible
4
OVERVIEW
bull A vibrational spectroscopy
- IR and Raman are the most common vibrational spectroscopes for assessing molecular motion and fingerprinting species
- Based on inelastic scattering of a monochromatic excitation source
- Routine energy range 200 - 4000 cmndash1
bull Complementary selection rules to IR spectroscopy
- Selection rules dictate which molecular vibrations are probed
- Some vibrational modes are both IR and Raman active
bull Great for many real-world samples
- Minimal sample preparation (gas liquid solid)
- Compatible with wet samples and normal ambient
- Achilles Heal is sample fluorescence
5
Raman spectrometerrsquos mechanismWhen a substances (in any state) is irradiated with a monochromatic light of
definite frequency(v)the light scattered at right angle to the incident light contains lines of 1 Incident frequency and 2Also of lower frequency
Sometimes lines of higher frequency are also obtained that of the incident beam will be scattered It is called Raman scattering
The line with lower frequency are called Stokersquos lines
Also the line with higher frequency are called Antistokersquos lines
The line with the same frequency as that of the incident light is called Rayleigh line
6
Frequency -
This difference is called Raman frequency or Raman shift
8
bull It may be noted that raman frequencies for a particular substances are characteristic of that substances
bull The various observation made by raman are called raman effect
bull Also the spectrum obtained is called raman spectrum
9
Classical theory of raman effect
bull According to the classical theory of electromagnetic radiation electric and magnetic fields oscillating at a given frequency are able to give out electromagnetic radiation of the same frequency One could use electromagnetic radiation theory to explain light scattering phenomena
bull For a majority of systems only an induced electric dipole moment μ is taken into consideration This dipole moment which is induced by the electric field E could be expressed by the power series
μ=μ(1)+μ(2)+μ(3)+⋯whereμ(1)=α Esdotμ(2)=12β EEsdotμ(3)=16γ EEEsdot
α is termed the polarizability tensor It is a second-rank tensor with all the components in the unit of CV-1m2 Typically orders of magnitude
for components in α β and γ are as follows α 10-40 CV-1m2
β 10-50 CV-2m3 and γ 10-61 CV-3m4
According to the values the contributions of μ(2)and μ(3) are quite small unless electric field is very high Since Rayleigh and Raman scattering are observed quite readily with very much lower electric field intensities one may expect to explain Rayleigh and Raman scattering in terms of μ(1) only
10
Classical theory of raman effecty of Raman Effect
Colthup et al Introduction to Infrared and Raman Spectroscopy 3rd ed Academic Press Boston 1990
mind = aE
polarizability
11
ElectronicGround State
1st ElectronicExcited State
Exci
tatio
n En
ergy
s (c
mndash1
)
Vibstates
4000
25000
0
fluor
esce
nce
IRs
s semit
2nd ElectronicExcited State
Raman∆s=semit-s
s ∆sflu
ores
cenc
eIm
purit
y
Fluorescence = Trouble
Raman Spectroscopy Absorption Scattering and Fluorescence
Stokes Anti-Stokes
12
Raman Spectroscopy Classical Treatment
bull Number of peaks related to degrees of freedom
DoF = 3N - 6 (bent) or 3N - 5 (linear) for N atomsbull Energy related to harmonic oscillator
bull Selection rules related to symmetry Rule of thumb symmetric=Raman active asymmetric=IR active
Raman 1335 cmndash1
IR 2349 cmndash1
IR 667 cmndash1
CO2
s or s c
2k(m1m2)
m1m2
Raman + IR 3657 cmndash1
Raman + IR 3756 cmndash1
Raman + IR 1594 cmndash1
H2O
13
Theory of raman spectraTwo cases may arise depending upon whether a collision between a photon and molecules In itrsquos ground state is elastic or inelastic in natureCase 1- if the collision is elastic ndash this lead to the appearance of unmodified lines (or unmodified frequency of light) in the scattered beam and this explain rayleigh scatteringCase 2 - if the collision is inelastic ndash there will be exchange or transfer of energy between the scattering molecules and the incident photonThe frequency of scattered light and the incident photon which is either higher or lower than that of the incident photon is called raman frequency
Total energy before collision = total energy after collision
14
Presentation of Raman Spectra
lex = 1064 nm = 9399 cm-1
Breathing mode9399 ndash 992 = 8407 cm-1
Stretching mode9399 ndash 3063 = 6336 cm-1
15
Rayleigh Scattering- Occurs when incident EM radiation induces an oscillating dipole in a molecules which is re-radiated at the same frequency
Eugene Hecht Optics Addison-Wesley Reading MA 1998
bullElastic (l does not change)
bullRandom direction of emission
bullLittle energy lossbullof emission
bullLittle energy loss
4 2 20
4 2
8 ( ) (1 cos )( )sc
EE
d a
l
16
Raman ScatteringOccurs when monochromatic light is scattered light has been weakly modulated
by the characteristic frequencies of the molecules Raman spectroscopy measures the differences between the wavelengths of the
incident radiation and the scatted radiation
max 0
max max 0
max max 0
( ) cos 21 cos 2 ( )21 cos 2 ( )2
equilz zz
zzvib
zzvib
t E td r E tdr
d r E tdr
m a a
a
Selection rule v = plusmn1Overtones v = plusmn2 plusmn3 hellip
Must also have a change in polarizability
Classical Description does not suggest any difference between Stokes and Anti-Stokes intensities
1
0
vibhkTN e
N
17
The Raman polarization
The Raman Polarization is a property of waves that can oscillate with more than one orientation EMR or waves such as light and gravitational wave exhibit polarization
Polarization state - the shape traced out in a fixed plane by the electric vector as such a plane wave passes over it is a description of the polarization
Eg linear polarization circular polarization
elliptical polarization orthogonally polarization
Polarization changes are necessary to form the virtual state and hence the Raman effect
18
Condition for raman spectroscopyVibrational modes that are more polarizable are more Raman-active Examples ndash N2 (dinitrogen) symmetric stretch cause no change in dipole (IR-inactive) cause a change in the polarizability of the bond ndash as the bond gets longer it is more easily deformed (Raman -active)
ndash CO2 asymmetric stretch cause a change in dipole (IR-active) Polarizability change of one C=O bond lengthening is cancelled by the shortening of the other ndash no net polarizability (Raman-inactive) Some modes may be both IR and Raman-active others may be one or the other
19
Condition for raman spectroscopy
Raman spectra occurs as a result of oscillation of a dipole moment induced in a molecules by the oscillating electric field of an incident wave
As the induced dipole moment is directly proportional to the polarisability of the molecules the molecules must possess anisotropic polarisability which should change during molecular rotation or vibration for vibrational or rotational-vibrational raman spectra
Anisotropic polarisability depends upon the orientation of the molecules
In the presence of an electric field the electron cloud of an atom or molecules is distorted or polarised
20
Mutual Exclusion Principle
For molecules with a center of symmetry no IR active transitions are Raman active and vice versa
THORNSymmetric molecules IR-active vibrations are not Raman-active Raman-active vibrations are not IR-active
O = C = O O = C = O
Raman active Raman inactive IR inactive IR active
21
Raman Instrumentation
22
There are following component involves
1 Laser or source of light 2 Filter3 Sample holder 4 detector
23
The block design dispersive Raman scattering system
Radiation sources
Sample Wavelength
selector
Detector InGaAs or
Ge
RecorderDetector InGaAs or
Ge
RecorderDetector
InGaAs or Ge
Recorder
Block diagram
90
24
Flow diagram dispersive Raman scattering system
25
Schematic diagram dispersive raman scattering system
26
1 Laser or source of light
bull Lasers are generally the only source strong enough to scatter lots of light and lead to detectable raman scattering
bull Lasers operate using the principle of stimulated emission
bull Electronic population inversion is required to achieve gain via stimulated emission (before the fluorescence lifetime is reached)
bull Population inversion is achieved by ldquopumpingrdquo using lots of photons in a variety of laser gain media
27
List of Various laser source
SNo Laser wavelength01 NdYAG 1064nm
02 HeNe 633nm
03 Argon ion 488nm
04 GaAlAs diode 785nm
05 Co2 10600nm
06 Ti-Sapphire 800nm
28
A - HeNe laserbull Filled with 71 He amp Ne gas optimum output of 6328 Aring
bull High voltage excitation is preferred
B - NdYAG Systembull A typical laser system ndashthe neodymium-doped yttrium aluminum garnet or Nd+3
bull YAG is a cubic crystalline material
bull Crystal field splitting causes electronic energy level splitting
bull NdYAG laser are optically pumped using a flash tube or laser diodes
bull These are the one of the most common type of laser
bull It emits 1064 nm wavelength
29
2Filter bull It is therefore essential to have monochromatic radiations
bull For getting monochromatic radiations filters are used
bull They may be made of nickel oxide glass or quartz glass
bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator
30
3Sample holder bull For the study of raman effect the type of sample holder to be used
depends upon the intensity of sources the nature and availability of the sample
bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids
bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be
used for the study of raman spectra
bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy
31
4detectorbull Researchers traditionally used single points detectors such as
photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality
bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)
bull Sensitivity amp performance of modern CCD detectors are high
32
APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling
33
bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and
gypsum illustrating how Raman can be used for fast mineral ID
bull Gemstone and mineral identification
bull Fluid inclusions
bull Mineral and phase distribution in rock sections
bull Phase transitions
bull Mineral behavior under extreme conditions
34
Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance
35
Semiconductors
bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width
bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis
36
Life Sciences
bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level
bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure
37
Differences between IR and Raman methodsSNo Raman IR
01 It is due to the scattering of light by the vibrating molecules
It is the result of absorption of light by vibrating molecules
02 The vibration is Raman active if it causes a change in polarisability
Vibration is IR active if there is change in dipole moment
03 The molecule need not possess a permanent dipole moment
The vibration concerned should have a change in dipole moment due to that vibration
04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR
05 Sample preparation is not very elaborate it can be in any state
Sample preparation is elaborateGaseous samples can rarely be used
06 Gives an indication of covalent character in the molecule
Gives an indication of ionic character in the molecule
07 Cost of instrumentation is very high
Comparatively inexpensive
38
Advantages of Raman over IR
bull Water can be used as solvent bull Very suitable for biological samples in native state (because water
can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral
overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power
39
Advantages of IR over Ramanbull Simpler and cheaper instrumentation
bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio
bull Lower detection limit than (normal) Raman
bull Background fluorescence can overwhelm Raman
bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)
40
Several variations of Raman spectroscopy
1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal
bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)
bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977
bull A comprehensive theory of the effect was given by Lombardi and Birke
41
2 Resonance Raman spectroscopy The excitation wavelength is matched to an
electronic transition of the molecule or crystal so that vibrational modes associated with the excited electronic state are greatly enhanced This is useful for studying large molecules such as polypeptides which might show hundreds of bands in conventional Raman spectra It is also useful for associating normal modes with their observed frequency shifts
42
3 Surface-enhanced resonance Raman spectroscopy (SERRS) ndash A combination of SERS and resonance Raman spectroscopy that uses proximity to a surface to increase Raman intensity and excitation wavelength matched to the maximum absorbance of the molecule being analysed
4 Coherent anti-Stokes Raman spectroscopy (CARS) ndash
Two laser beams are used to generate a coherent anti-Stokes frequency beam which can be enhanced by resonance
43
5 Raman optical activity (ROA) ndash Measures vibrational optical activity by means of a small difference in the intensity of Raman scattering from chiral molecules in right- and left-circularly polarized incident light or equivalently a small circularly polarized component in the scattered light
6 Spatially offset Raman spectroscopy (SORS)
7 Spontaneous Raman spectroscopy (SRS) 8 Optical tweezers Raman spectroscopy (OTRS)
44
9 Angle-resolved Raman spectroscopy10 Inverse Raman spectroscopy11 Tip-enhanced Raman spectroscopy
(TERS) 12 Surface plasmon polariton enhanced
Raman scattering (SPPERS)13 Stand-off Remote Raman ndash 14 Fourier-transform Rama spectroscopyapplied
to photobiological systems
45
4
OVERVIEW
bull A vibrational spectroscopy
- IR and Raman are the most common vibrational spectroscopes for assessing molecular motion and fingerprinting species
- Based on inelastic scattering of a monochromatic excitation source
- Routine energy range 200 - 4000 cmndash1
bull Complementary selection rules to IR spectroscopy
- Selection rules dictate which molecular vibrations are probed
- Some vibrational modes are both IR and Raman active
bull Great for many real-world samples
- Minimal sample preparation (gas liquid solid)
- Compatible with wet samples and normal ambient
- Achilles Heal is sample fluorescence
5
Raman spectrometerrsquos mechanismWhen a substances (in any state) is irradiated with a monochromatic light of
definite frequency(v)the light scattered at right angle to the incident light contains lines of 1 Incident frequency and 2Also of lower frequency
Sometimes lines of higher frequency are also obtained that of the incident beam will be scattered It is called Raman scattering
The line with lower frequency are called Stokersquos lines
Also the line with higher frequency are called Antistokersquos lines
The line with the same frequency as that of the incident light is called Rayleigh line
6
Frequency -
This difference is called Raman frequency or Raman shift
8
bull It may be noted that raman frequencies for a particular substances are characteristic of that substances
bull The various observation made by raman are called raman effect
bull Also the spectrum obtained is called raman spectrum
9
Classical theory of raman effect
bull According to the classical theory of electromagnetic radiation electric and magnetic fields oscillating at a given frequency are able to give out electromagnetic radiation of the same frequency One could use electromagnetic radiation theory to explain light scattering phenomena
bull For a majority of systems only an induced electric dipole moment μ is taken into consideration This dipole moment which is induced by the electric field E could be expressed by the power series
μ=μ(1)+μ(2)+μ(3)+⋯whereμ(1)=α Esdotμ(2)=12β EEsdotμ(3)=16γ EEEsdot
α is termed the polarizability tensor It is a second-rank tensor with all the components in the unit of CV-1m2 Typically orders of magnitude
for components in α β and γ are as follows α 10-40 CV-1m2
β 10-50 CV-2m3 and γ 10-61 CV-3m4
According to the values the contributions of μ(2)and μ(3) are quite small unless electric field is very high Since Rayleigh and Raman scattering are observed quite readily with very much lower electric field intensities one may expect to explain Rayleigh and Raman scattering in terms of μ(1) only
10
Classical theory of raman effecty of Raman Effect
Colthup et al Introduction to Infrared and Raman Spectroscopy 3rd ed Academic Press Boston 1990
mind = aE
polarizability
11
ElectronicGround State
1st ElectronicExcited State
Exci
tatio
n En
ergy
s (c
mndash1
)
Vibstates
4000
25000
0
fluor
esce
nce
IRs
s semit
2nd ElectronicExcited State
Raman∆s=semit-s
s ∆sflu
ores
cenc
eIm
purit
y
Fluorescence = Trouble
Raman Spectroscopy Absorption Scattering and Fluorescence
Stokes Anti-Stokes
12
Raman Spectroscopy Classical Treatment
bull Number of peaks related to degrees of freedom
DoF = 3N - 6 (bent) or 3N - 5 (linear) for N atomsbull Energy related to harmonic oscillator
bull Selection rules related to symmetry Rule of thumb symmetric=Raman active asymmetric=IR active
Raman 1335 cmndash1
IR 2349 cmndash1
IR 667 cmndash1
CO2
s or s c
2k(m1m2)
m1m2
Raman + IR 3657 cmndash1
Raman + IR 3756 cmndash1
Raman + IR 1594 cmndash1
H2O
13
Theory of raman spectraTwo cases may arise depending upon whether a collision between a photon and molecules In itrsquos ground state is elastic or inelastic in natureCase 1- if the collision is elastic ndash this lead to the appearance of unmodified lines (or unmodified frequency of light) in the scattered beam and this explain rayleigh scatteringCase 2 - if the collision is inelastic ndash there will be exchange or transfer of energy between the scattering molecules and the incident photonThe frequency of scattered light and the incident photon which is either higher or lower than that of the incident photon is called raman frequency
Total energy before collision = total energy after collision
14
Presentation of Raman Spectra
lex = 1064 nm = 9399 cm-1
Breathing mode9399 ndash 992 = 8407 cm-1
Stretching mode9399 ndash 3063 = 6336 cm-1
15
Rayleigh Scattering- Occurs when incident EM radiation induces an oscillating dipole in a molecules which is re-radiated at the same frequency
Eugene Hecht Optics Addison-Wesley Reading MA 1998
bullElastic (l does not change)
bullRandom direction of emission
bullLittle energy lossbullof emission
bullLittle energy loss
4 2 20
4 2
8 ( ) (1 cos )( )sc
EE
d a
l
16
Raman ScatteringOccurs when monochromatic light is scattered light has been weakly modulated
by the characteristic frequencies of the molecules Raman spectroscopy measures the differences between the wavelengths of the
incident radiation and the scatted radiation
max 0
max max 0
max max 0
( ) cos 21 cos 2 ( )21 cos 2 ( )2
equilz zz
zzvib
zzvib
t E td r E tdr
d r E tdr
m a a
a
Selection rule v = plusmn1Overtones v = plusmn2 plusmn3 hellip
Must also have a change in polarizability
Classical Description does not suggest any difference between Stokes and Anti-Stokes intensities
1
0
vibhkTN e
N
17
The Raman polarization
The Raman Polarization is a property of waves that can oscillate with more than one orientation EMR or waves such as light and gravitational wave exhibit polarization
Polarization state - the shape traced out in a fixed plane by the electric vector as such a plane wave passes over it is a description of the polarization
Eg linear polarization circular polarization
elliptical polarization orthogonally polarization
Polarization changes are necessary to form the virtual state and hence the Raman effect
18
Condition for raman spectroscopyVibrational modes that are more polarizable are more Raman-active Examples ndash N2 (dinitrogen) symmetric stretch cause no change in dipole (IR-inactive) cause a change in the polarizability of the bond ndash as the bond gets longer it is more easily deformed (Raman -active)
ndash CO2 asymmetric stretch cause a change in dipole (IR-active) Polarizability change of one C=O bond lengthening is cancelled by the shortening of the other ndash no net polarizability (Raman-inactive) Some modes may be both IR and Raman-active others may be one or the other
19
Condition for raman spectroscopy
Raman spectra occurs as a result of oscillation of a dipole moment induced in a molecules by the oscillating electric field of an incident wave
As the induced dipole moment is directly proportional to the polarisability of the molecules the molecules must possess anisotropic polarisability which should change during molecular rotation or vibration for vibrational or rotational-vibrational raman spectra
Anisotropic polarisability depends upon the orientation of the molecules
In the presence of an electric field the electron cloud of an atom or molecules is distorted or polarised
20
Mutual Exclusion Principle
For molecules with a center of symmetry no IR active transitions are Raman active and vice versa
THORNSymmetric molecules IR-active vibrations are not Raman-active Raman-active vibrations are not IR-active
O = C = O O = C = O
Raman active Raman inactive IR inactive IR active
21
Raman Instrumentation
22
There are following component involves
1 Laser or source of light 2 Filter3 Sample holder 4 detector
23
The block design dispersive Raman scattering system
Radiation sources
Sample Wavelength
selector
Detector InGaAs or
Ge
RecorderDetector InGaAs or
Ge
RecorderDetector
InGaAs or Ge
Recorder
Block diagram
90
24
Flow diagram dispersive Raman scattering system
25
Schematic diagram dispersive raman scattering system
26
1 Laser or source of light
bull Lasers are generally the only source strong enough to scatter lots of light and lead to detectable raman scattering
bull Lasers operate using the principle of stimulated emission
bull Electronic population inversion is required to achieve gain via stimulated emission (before the fluorescence lifetime is reached)
bull Population inversion is achieved by ldquopumpingrdquo using lots of photons in a variety of laser gain media
27
List of Various laser source
SNo Laser wavelength01 NdYAG 1064nm
02 HeNe 633nm
03 Argon ion 488nm
04 GaAlAs diode 785nm
05 Co2 10600nm
06 Ti-Sapphire 800nm
28
A - HeNe laserbull Filled with 71 He amp Ne gas optimum output of 6328 Aring
bull High voltage excitation is preferred
B - NdYAG Systembull A typical laser system ndashthe neodymium-doped yttrium aluminum garnet or Nd+3
bull YAG is a cubic crystalline material
bull Crystal field splitting causes electronic energy level splitting
bull NdYAG laser are optically pumped using a flash tube or laser diodes
bull These are the one of the most common type of laser
bull It emits 1064 nm wavelength
29
2Filter bull It is therefore essential to have monochromatic radiations
bull For getting monochromatic radiations filters are used
bull They may be made of nickel oxide glass or quartz glass
bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator
30
3Sample holder bull For the study of raman effect the type of sample holder to be used
depends upon the intensity of sources the nature and availability of the sample
bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids
bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be
used for the study of raman spectra
bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy
31
4detectorbull Researchers traditionally used single points detectors such as
photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality
bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)
bull Sensitivity amp performance of modern CCD detectors are high
32
APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling
33
bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and
gypsum illustrating how Raman can be used for fast mineral ID
bull Gemstone and mineral identification
bull Fluid inclusions
bull Mineral and phase distribution in rock sections
bull Phase transitions
bull Mineral behavior under extreme conditions
34
Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance
35
Semiconductors
bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width
bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis
36
Life Sciences
bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level
bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure
37
Differences between IR and Raman methodsSNo Raman IR
01 It is due to the scattering of light by the vibrating molecules
It is the result of absorption of light by vibrating molecules
02 The vibration is Raman active if it causes a change in polarisability
Vibration is IR active if there is change in dipole moment
03 The molecule need not possess a permanent dipole moment
The vibration concerned should have a change in dipole moment due to that vibration
04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR
05 Sample preparation is not very elaborate it can be in any state
Sample preparation is elaborateGaseous samples can rarely be used
06 Gives an indication of covalent character in the molecule
Gives an indication of ionic character in the molecule
07 Cost of instrumentation is very high
Comparatively inexpensive
38
Advantages of Raman over IR
bull Water can be used as solvent bull Very suitable for biological samples in native state (because water
can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral
overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power
39
Advantages of IR over Ramanbull Simpler and cheaper instrumentation
bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio
bull Lower detection limit than (normal) Raman
bull Background fluorescence can overwhelm Raman
bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)
40
Several variations of Raman spectroscopy
1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal
bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)
bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977
bull A comprehensive theory of the effect was given by Lombardi and Birke
41
2 Resonance Raman spectroscopy The excitation wavelength is matched to an
electronic transition of the molecule or crystal so that vibrational modes associated with the excited electronic state are greatly enhanced This is useful for studying large molecules such as polypeptides which might show hundreds of bands in conventional Raman spectra It is also useful for associating normal modes with their observed frequency shifts
42
3 Surface-enhanced resonance Raman spectroscopy (SERRS) ndash A combination of SERS and resonance Raman spectroscopy that uses proximity to a surface to increase Raman intensity and excitation wavelength matched to the maximum absorbance of the molecule being analysed
4 Coherent anti-Stokes Raman spectroscopy (CARS) ndash
Two laser beams are used to generate a coherent anti-Stokes frequency beam which can be enhanced by resonance
43
5 Raman optical activity (ROA) ndash Measures vibrational optical activity by means of a small difference in the intensity of Raman scattering from chiral molecules in right- and left-circularly polarized incident light or equivalently a small circularly polarized component in the scattered light
6 Spatially offset Raman spectroscopy (SORS)
7 Spontaneous Raman spectroscopy (SRS) 8 Optical tweezers Raman spectroscopy (OTRS)
44
9 Angle-resolved Raman spectroscopy10 Inverse Raman spectroscopy11 Tip-enhanced Raman spectroscopy
(TERS) 12 Surface plasmon polariton enhanced
Raman scattering (SPPERS)13 Stand-off Remote Raman ndash 14 Fourier-transform Rama spectroscopyapplied
to photobiological systems
45
5
Raman spectrometerrsquos mechanismWhen a substances (in any state) is irradiated with a monochromatic light of
definite frequency(v)the light scattered at right angle to the incident light contains lines of 1 Incident frequency and 2Also of lower frequency
Sometimes lines of higher frequency are also obtained that of the incident beam will be scattered It is called Raman scattering
The line with lower frequency are called Stokersquos lines
Also the line with higher frequency are called Antistokersquos lines
The line with the same frequency as that of the incident light is called Rayleigh line
6
Frequency -
This difference is called Raman frequency or Raman shift
8
bull It may be noted that raman frequencies for a particular substances are characteristic of that substances
bull The various observation made by raman are called raman effect
bull Also the spectrum obtained is called raman spectrum
9
Classical theory of raman effect
bull According to the classical theory of electromagnetic radiation electric and magnetic fields oscillating at a given frequency are able to give out electromagnetic radiation of the same frequency One could use electromagnetic radiation theory to explain light scattering phenomena
bull For a majority of systems only an induced electric dipole moment μ is taken into consideration This dipole moment which is induced by the electric field E could be expressed by the power series
μ=μ(1)+μ(2)+μ(3)+⋯whereμ(1)=α Esdotμ(2)=12β EEsdotμ(3)=16γ EEEsdot
α is termed the polarizability tensor It is a second-rank tensor with all the components in the unit of CV-1m2 Typically orders of magnitude
for components in α β and γ are as follows α 10-40 CV-1m2
β 10-50 CV-2m3 and γ 10-61 CV-3m4
According to the values the contributions of μ(2)and μ(3) are quite small unless electric field is very high Since Rayleigh and Raman scattering are observed quite readily with very much lower electric field intensities one may expect to explain Rayleigh and Raman scattering in terms of μ(1) only
10
Classical theory of raman effecty of Raman Effect
Colthup et al Introduction to Infrared and Raman Spectroscopy 3rd ed Academic Press Boston 1990
mind = aE
polarizability
11
ElectronicGround State
1st ElectronicExcited State
Exci
tatio
n En
ergy
s (c
mndash1
)
Vibstates
4000
25000
0
fluor
esce
nce
IRs
s semit
2nd ElectronicExcited State
Raman∆s=semit-s
s ∆sflu
ores
cenc
eIm
purit
y
Fluorescence = Trouble
Raman Spectroscopy Absorption Scattering and Fluorescence
Stokes Anti-Stokes
12
Raman Spectroscopy Classical Treatment
bull Number of peaks related to degrees of freedom
DoF = 3N - 6 (bent) or 3N - 5 (linear) for N atomsbull Energy related to harmonic oscillator
bull Selection rules related to symmetry Rule of thumb symmetric=Raman active asymmetric=IR active
Raman 1335 cmndash1
IR 2349 cmndash1
IR 667 cmndash1
CO2
s or s c
2k(m1m2)
m1m2
Raman + IR 3657 cmndash1
Raman + IR 3756 cmndash1
Raman + IR 1594 cmndash1
H2O
13
Theory of raman spectraTwo cases may arise depending upon whether a collision between a photon and molecules In itrsquos ground state is elastic or inelastic in natureCase 1- if the collision is elastic ndash this lead to the appearance of unmodified lines (or unmodified frequency of light) in the scattered beam and this explain rayleigh scatteringCase 2 - if the collision is inelastic ndash there will be exchange or transfer of energy between the scattering molecules and the incident photonThe frequency of scattered light and the incident photon which is either higher or lower than that of the incident photon is called raman frequency
Total energy before collision = total energy after collision
14
Presentation of Raman Spectra
lex = 1064 nm = 9399 cm-1
Breathing mode9399 ndash 992 = 8407 cm-1
Stretching mode9399 ndash 3063 = 6336 cm-1
15
Rayleigh Scattering- Occurs when incident EM radiation induces an oscillating dipole in a molecules which is re-radiated at the same frequency
Eugene Hecht Optics Addison-Wesley Reading MA 1998
bullElastic (l does not change)
bullRandom direction of emission
bullLittle energy lossbullof emission
bullLittle energy loss
4 2 20
4 2
8 ( ) (1 cos )( )sc
EE
d a
l
16
Raman ScatteringOccurs when monochromatic light is scattered light has been weakly modulated
by the characteristic frequencies of the molecules Raman spectroscopy measures the differences between the wavelengths of the
incident radiation and the scatted radiation
max 0
max max 0
max max 0
( ) cos 21 cos 2 ( )21 cos 2 ( )2
equilz zz
zzvib
zzvib
t E td r E tdr
d r E tdr
m a a
a
Selection rule v = plusmn1Overtones v = plusmn2 plusmn3 hellip
Must also have a change in polarizability
Classical Description does not suggest any difference between Stokes and Anti-Stokes intensities
1
0
vibhkTN e
N
17
The Raman polarization
The Raman Polarization is a property of waves that can oscillate with more than one orientation EMR or waves such as light and gravitational wave exhibit polarization
Polarization state - the shape traced out in a fixed plane by the electric vector as such a plane wave passes over it is a description of the polarization
Eg linear polarization circular polarization
elliptical polarization orthogonally polarization
Polarization changes are necessary to form the virtual state and hence the Raman effect
18
Condition for raman spectroscopyVibrational modes that are more polarizable are more Raman-active Examples ndash N2 (dinitrogen) symmetric stretch cause no change in dipole (IR-inactive) cause a change in the polarizability of the bond ndash as the bond gets longer it is more easily deformed (Raman -active)
ndash CO2 asymmetric stretch cause a change in dipole (IR-active) Polarizability change of one C=O bond lengthening is cancelled by the shortening of the other ndash no net polarizability (Raman-inactive) Some modes may be both IR and Raman-active others may be one or the other
19
Condition for raman spectroscopy
Raman spectra occurs as a result of oscillation of a dipole moment induced in a molecules by the oscillating electric field of an incident wave
As the induced dipole moment is directly proportional to the polarisability of the molecules the molecules must possess anisotropic polarisability which should change during molecular rotation or vibration for vibrational or rotational-vibrational raman spectra
Anisotropic polarisability depends upon the orientation of the molecules
In the presence of an electric field the electron cloud of an atom or molecules is distorted or polarised
20
Mutual Exclusion Principle
For molecules with a center of symmetry no IR active transitions are Raman active and vice versa
THORNSymmetric molecules IR-active vibrations are not Raman-active Raman-active vibrations are not IR-active
O = C = O O = C = O
Raman active Raman inactive IR inactive IR active
21
Raman Instrumentation
22
There are following component involves
1 Laser or source of light 2 Filter3 Sample holder 4 detector
23
The block design dispersive Raman scattering system
Radiation sources
Sample Wavelength
selector
Detector InGaAs or
Ge
RecorderDetector InGaAs or
Ge
RecorderDetector
InGaAs or Ge
Recorder
Block diagram
90
24
Flow diagram dispersive Raman scattering system
25
Schematic diagram dispersive raman scattering system
26
1 Laser or source of light
bull Lasers are generally the only source strong enough to scatter lots of light and lead to detectable raman scattering
bull Lasers operate using the principle of stimulated emission
bull Electronic population inversion is required to achieve gain via stimulated emission (before the fluorescence lifetime is reached)
bull Population inversion is achieved by ldquopumpingrdquo using lots of photons in a variety of laser gain media
27
List of Various laser source
SNo Laser wavelength01 NdYAG 1064nm
02 HeNe 633nm
03 Argon ion 488nm
04 GaAlAs diode 785nm
05 Co2 10600nm
06 Ti-Sapphire 800nm
28
A - HeNe laserbull Filled with 71 He amp Ne gas optimum output of 6328 Aring
bull High voltage excitation is preferred
B - NdYAG Systembull A typical laser system ndashthe neodymium-doped yttrium aluminum garnet or Nd+3
bull YAG is a cubic crystalline material
bull Crystal field splitting causes electronic energy level splitting
bull NdYAG laser are optically pumped using a flash tube or laser diodes
bull These are the one of the most common type of laser
bull It emits 1064 nm wavelength
29
2Filter bull It is therefore essential to have monochromatic radiations
bull For getting monochromatic radiations filters are used
bull They may be made of nickel oxide glass or quartz glass
bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator
30
3Sample holder bull For the study of raman effect the type of sample holder to be used
depends upon the intensity of sources the nature and availability of the sample
bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids
bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be
used for the study of raman spectra
bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy
31
4detectorbull Researchers traditionally used single points detectors such as
photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality
bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)
bull Sensitivity amp performance of modern CCD detectors are high
32
APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling
33
bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and
gypsum illustrating how Raman can be used for fast mineral ID
bull Gemstone and mineral identification
bull Fluid inclusions
bull Mineral and phase distribution in rock sections
bull Phase transitions
bull Mineral behavior under extreme conditions
34
Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance
35
Semiconductors
bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width
bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis
36
Life Sciences
bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level
bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure
37
Differences between IR and Raman methodsSNo Raman IR
01 It is due to the scattering of light by the vibrating molecules
It is the result of absorption of light by vibrating molecules
02 The vibration is Raman active if it causes a change in polarisability
Vibration is IR active if there is change in dipole moment
03 The molecule need not possess a permanent dipole moment
The vibration concerned should have a change in dipole moment due to that vibration
04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR
05 Sample preparation is not very elaborate it can be in any state
Sample preparation is elaborateGaseous samples can rarely be used
06 Gives an indication of covalent character in the molecule
Gives an indication of ionic character in the molecule
07 Cost of instrumentation is very high
Comparatively inexpensive
38
Advantages of Raman over IR
bull Water can be used as solvent bull Very suitable for biological samples in native state (because water
can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral
overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power
39
Advantages of IR over Ramanbull Simpler and cheaper instrumentation
bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio
bull Lower detection limit than (normal) Raman
bull Background fluorescence can overwhelm Raman
bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)
40
Several variations of Raman spectroscopy
1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal
bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)
bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977
bull A comprehensive theory of the effect was given by Lombardi and Birke
41
2 Resonance Raman spectroscopy The excitation wavelength is matched to an
electronic transition of the molecule or crystal so that vibrational modes associated with the excited electronic state are greatly enhanced This is useful for studying large molecules such as polypeptides which might show hundreds of bands in conventional Raman spectra It is also useful for associating normal modes with their observed frequency shifts
42
3 Surface-enhanced resonance Raman spectroscopy (SERRS) ndash A combination of SERS and resonance Raman spectroscopy that uses proximity to a surface to increase Raman intensity and excitation wavelength matched to the maximum absorbance of the molecule being analysed
4 Coherent anti-Stokes Raman spectroscopy (CARS) ndash
Two laser beams are used to generate a coherent anti-Stokes frequency beam which can be enhanced by resonance
43
5 Raman optical activity (ROA) ndash Measures vibrational optical activity by means of a small difference in the intensity of Raman scattering from chiral molecules in right- and left-circularly polarized incident light or equivalently a small circularly polarized component in the scattered light
6 Spatially offset Raman spectroscopy (SORS)
7 Spontaneous Raman spectroscopy (SRS) 8 Optical tweezers Raman spectroscopy (OTRS)
44
9 Angle-resolved Raman spectroscopy10 Inverse Raman spectroscopy11 Tip-enhanced Raman spectroscopy
(TERS) 12 Surface plasmon polariton enhanced
Raman scattering (SPPERS)13 Stand-off Remote Raman ndash 14 Fourier-transform Rama spectroscopyapplied
to photobiological systems
45
6
Frequency -
This difference is called Raman frequency or Raman shift
8
bull It may be noted that raman frequencies for a particular substances are characteristic of that substances
bull The various observation made by raman are called raman effect
bull Also the spectrum obtained is called raman spectrum
9
Classical theory of raman effect
bull According to the classical theory of electromagnetic radiation electric and magnetic fields oscillating at a given frequency are able to give out electromagnetic radiation of the same frequency One could use electromagnetic radiation theory to explain light scattering phenomena
bull For a majority of systems only an induced electric dipole moment μ is taken into consideration This dipole moment which is induced by the electric field E could be expressed by the power series
μ=μ(1)+μ(2)+μ(3)+⋯whereμ(1)=α Esdotμ(2)=12β EEsdotμ(3)=16γ EEEsdot
α is termed the polarizability tensor It is a second-rank tensor with all the components in the unit of CV-1m2 Typically orders of magnitude
for components in α β and γ are as follows α 10-40 CV-1m2
β 10-50 CV-2m3 and γ 10-61 CV-3m4
According to the values the contributions of μ(2)and μ(3) are quite small unless electric field is very high Since Rayleigh and Raman scattering are observed quite readily with very much lower electric field intensities one may expect to explain Rayleigh and Raman scattering in terms of μ(1) only
10
Classical theory of raman effecty of Raman Effect
Colthup et al Introduction to Infrared and Raman Spectroscopy 3rd ed Academic Press Boston 1990
mind = aE
polarizability
11
ElectronicGround State
1st ElectronicExcited State
Exci
tatio
n En
ergy
s (c
mndash1
)
Vibstates
4000
25000
0
fluor
esce
nce
IRs
s semit
2nd ElectronicExcited State
Raman∆s=semit-s
s ∆sflu
ores
cenc
eIm
purit
y
Fluorescence = Trouble
Raman Spectroscopy Absorption Scattering and Fluorescence
Stokes Anti-Stokes
12
Raman Spectroscopy Classical Treatment
bull Number of peaks related to degrees of freedom
DoF = 3N - 6 (bent) or 3N - 5 (linear) for N atomsbull Energy related to harmonic oscillator
bull Selection rules related to symmetry Rule of thumb symmetric=Raman active asymmetric=IR active
Raman 1335 cmndash1
IR 2349 cmndash1
IR 667 cmndash1
CO2
s or s c
2k(m1m2)
m1m2
Raman + IR 3657 cmndash1
Raman + IR 3756 cmndash1
Raman + IR 1594 cmndash1
H2O
13
Theory of raman spectraTwo cases may arise depending upon whether a collision between a photon and molecules In itrsquos ground state is elastic or inelastic in natureCase 1- if the collision is elastic ndash this lead to the appearance of unmodified lines (or unmodified frequency of light) in the scattered beam and this explain rayleigh scatteringCase 2 - if the collision is inelastic ndash there will be exchange or transfer of energy between the scattering molecules and the incident photonThe frequency of scattered light and the incident photon which is either higher or lower than that of the incident photon is called raman frequency
Total energy before collision = total energy after collision
14
Presentation of Raman Spectra
lex = 1064 nm = 9399 cm-1
Breathing mode9399 ndash 992 = 8407 cm-1
Stretching mode9399 ndash 3063 = 6336 cm-1
15
Rayleigh Scattering- Occurs when incident EM radiation induces an oscillating dipole in a molecules which is re-radiated at the same frequency
Eugene Hecht Optics Addison-Wesley Reading MA 1998
bullElastic (l does not change)
bullRandom direction of emission
bullLittle energy lossbullof emission
bullLittle energy loss
4 2 20
4 2
8 ( ) (1 cos )( )sc
EE
d a
l
16
Raman ScatteringOccurs when monochromatic light is scattered light has been weakly modulated
by the characteristic frequencies of the molecules Raman spectroscopy measures the differences between the wavelengths of the
incident radiation and the scatted radiation
max 0
max max 0
max max 0
( ) cos 21 cos 2 ( )21 cos 2 ( )2
equilz zz
zzvib
zzvib
t E td r E tdr
d r E tdr
m a a
a
Selection rule v = plusmn1Overtones v = plusmn2 plusmn3 hellip
Must also have a change in polarizability
Classical Description does not suggest any difference between Stokes and Anti-Stokes intensities
1
0
vibhkTN e
N
17
The Raman polarization
The Raman Polarization is a property of waves that can oscillate with more than one orientation EMR or waves such as light and gravitational wave exhibit polarization
Polarization state - the shape traced out in a fixed plane by the electric vector as such a plane wave passes over it is a description of the polarization
Eg linear polarization circular polarization
elliptical polarization orthogonally polarization
Polarization changes are necessary to form the virtual state and hence the Raman effect
18
Condition for raman spectroscopyVibrational modes that are more polarizable are more Raman-active Examples ndash N2 (dinitrogen) symmetric stretch cause no change in dipole (IR-inactive) cause a change in the polarizability of the bond ndash as the bond gets longer it is more easily deformed (Raman -active)
ndash CO2 asymmetric stretch cause a change in dipole (IR-active) Polarizability change of one C=O bond lengthening is cancelled by the shortening of the other ndash no net polarizability (Raman-inactive) Some modes may be both IR and Raman-active others may be one or the other
19
Condition for raman spectroscopy
Raman spectra occurs as a result of oscillation of a dipole moment induced in a molecules by the oscillating electric field of an incident wave
As the induced dipole moment is directly proportional to the polarisability of the molecules the molecules must possess anisotropic polarisability which should change during molecular rotation or vibration for vibrational or rotational-vibrational raman spectra
Anisotropic polarisability depends upon the orientation of the molecules
In the presence of an electric field the electron cloud of an atom or molecules is distorted or polarised
20
Mutual Exclusion Principle
For molecules with a center of symmetry no IR active transitions are Raman active and vice versa
THORNSymmetric molecules IR-active vibrations are not Raman-active Raman-active vibrations are not IR-active
O = C = O O = C = O
Raman active Raman inactive IR inactive IR active
21
Raman Instrumentation
22
There are following component involves
1 Laser or source of light 2 Filter3 Sample holder 4 detector
23
The block design dispersive Raman scattering system
Radiation sources
Sample Wavelength
selector
Detector InGaAs or
Ge
RecorderDetector InGaAs or
Ge
RecorderDetector
InGaAs or Ge
Recorder
Block diagram
90
24
Flow diagram dispersive Raman scattering system
25
Schematic diagram dispersive raman scattering system
26
1 Laser or source of light
bull Lasers are generally the only source strong enough to scatter lots of light and lead to detectable raman scattering
bull Lasers operate using the principle of stimulated emission
bull Electronic population inversion is required to achieve gain via stimulated emission (before the fluorescence lifetime is reached)
bull Population inversion is achieved by ldquopumpingrdquo using lots of photons in a variety of laser gain media
27
List of Various laser source
SNo Laser wavelength01 NdYAG 1064nm
02 HeNe 633nm
03 Argon ion 488nm
04 GaAlAs diode 785nm
05 Co2 10600nm
06 Ti-Sapphire 800nm
28
A - HeNe laserbull Filled with 71 He amp Ne gas optimum output of 6328 Aring
bull High voltage excitation is preferred
B - NdYAG Systembull A typical laser system ndashthe neodymium-doped yttrium aluminum garnet or Nd+3
bull YAG is a cubic crystalline material
bull Crystal field splitting causes electronic energy level splitting
bull NdYAG laser are optically pumped using a flash tube or laser diodes
bull These are the one of the most common type of laser
bull It emits 1064 nm wavelength
29
2Filter bull It is therefore essential to have monochromatic radiations
bull For getting monochromatic radiations filters are used
bull They may be made of nickel oxide glass or quartz glass
bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator
30
3Sample holder bull For the study of raman effect the type of sample holder to be used
depends upon the intensity of sources the nature and availability of the sample
bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids
bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be
used for the study of raman spectra
bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy
31
4detectorbull Researchers traditionally used single points detectors such as
photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality
bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)
bull Sensitivity amp performance of modern CCD detectors are high
32
APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling
33
bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and
gypsum illustrating how Raman can be used for fast mineral ID
bull Gemstone and mineral identification
bull Fluid inclusions
bull Mineral and phase distribution in rock sections
bull Phase transitions
bull Mineral behavior under extreme conditions
34
Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance
35
Semiconductors
bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width
bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis
36
Life Sciences
bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level
bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure
37
Differences between IR and Raman methodsSNo Raman IR
01 It is due to the scattering of light by the vibrating molecules
It is the result of absorption of light by vibrating molecules
02 The vibration is Raman active if it causes a change in polarisability
Vibration is IR active if there is change in dipole moment
03 The molecule need not possess a permanent dipole moment
The vibration concerned should have a change in dipole moment due to that vibration
04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR
05 Sample preparation is not very elaborate it can be in any state
Sample preparation is elaborateGaseous samples can rarely be used
06 Gives an indication of covalent character in the molecule
Gives an indication of ionic character in the molecule
07 Cost of instrumentation is very high
Comparatively inexpensive
38
Advantages of Raman over IR
bull Water can be used as solvent bull Very suitable for biological samples in native state (because water
can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral
overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power
39
Advantages of IR over Ramanbull Simpler and cheaper instrumentation
bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio
bull Lower detection limit than (normal) Raman
bull Background fluorescence can overwhelm Raman
bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)
40
Several variations of Raman spectroscopy
1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal
bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)
bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977
bull A comprehensive theory of the effect was given by Lombardi and Birke
41
2 Resonance Raman spectroscopy The excitation wavelength is matched to an
electronic transition of the molecule or crystal so that vibrational modes associated with the excited electronic state are greatly enhanced This is useful for studying large molecules such as polypeptides which might show hundreds of bands in conventional Raman spectra It is also useful for associating normal modes with their observed frequency shifts
42
3 Surface-enhanced resonance Raman spectroscopy (SERRS) ndash A combination of SERS and resonance Raman spectroscopy that uses proximity to a surface to increase Raman intensity and excitation wavelength matched to the maximum absorbance of the molecule being analysed
4 Coherent anti-Stokes Raman spectroscopy (CARS) ndash
Two laser beams are used to generate a coherent anti-Stokes frequency beam which can be enhanced by resonance
43
5 Raman optical activity (ROA) ndash Measures vibrational optical activity by means of a small difference in the intensity of Raman scattering from chiral molecules in right- and left-circularly polarized incident light or equivalently a small circularly polarized component in the scattered light
6 Spatially offset Raman spectroscopy (SORS)
7 Spontaneous Raman spectroscopy (SRS) 8 Optical tweezers Raman spectroscopy (OTRS)
44
9 Angle-resolved Raman spectroscopy10 Inverse Raman spectroscopy11 Tip-enhanced Raman spectroscopy
(TERS) 12 Surface plasmon polariton enhanced
Raman scattering (SPPERS)13 Stand-off Remote Raman ndash 14 Fourier-transform Rama spectroscopyapplied
to photobiological systems
45
8
bull It may be noted that raman frequencies for a particular substances are characteristic of that substances
bull The various observation made by raman are called raman effect
bull Also the spectrum obtained is called raman spectrum
9
Classical theory of raman effect
bull According to the classical theory of electromagnetic radiation electric and magnetic fields oscillating at a given frequency are able to give out electromagnetic radiation of the same frequency One could use electromagnetic radiation theory to explain light scattering phenomena
bull For a majority of systems only an induced electric dipole moment μ is taken into consideration This dipole moment which is induced by the electric field E could be expressed by the power series
μ=μ(1)+μ(2)+μ(3)+⋯whereμ(1)=α Esdotμ(2)=12β EEsdotμ(3)=16γ EEEsdot
α is termed the polarizability tensor It is a second-rank tensor with all the components in the unit of CV-1m2 Typically orders of magnitude
for components in α β and γ are as follows α 10-40 CV-1m2
β 10-50 CV-2m3 and γ 10-61 CV-3m4
According to the values the contributions of μ(2)and μ(3) are quite small unless electric field is very high Since Rayleigh and Raman scattering are observed quite readily with very much lower electric field intensities one may expect to explain Rayleigh and Raman scattering in terms of μ(1) only
10
Classical theory of raman effecty of Raman Effect
Colthup et al Introduction to Infrared and Raman Spectroscopy 3rd ed Academic Press Boston 1990
mind = aE
polarizability
11
ElectronicGround State
1st ElectronicExcited State
Exci
tatio
n En
ergy
s (c
mndash1
)
Vibstates
4000
25000
0
fluor
esce
nce
IRs
s semit
2nd ElectronicExcited State
Raman∆s=semit-s
s ∆sflu
ores
cenc
eIm
purit
y
Fluorescence = Trouble
Raman Spectroscopy Absorption Scattering and Fluorescence
Stokes Anti-Stokes
12
Raman Spectroscopy Classical Treatment
bull Number of peaks related to degrees of freedom
DoF = 3N - 6 (bent) or 3N - 5 (linear) for N atomsbull Energy related to harmonic oscillator
bull Selection rules related to symmetry Rule of thumb symmetric=Raman active asymmetric=IR active
Raman 1335 cmndash1
IR 2349 cmndash1
IR 667 cmndash1
CO2
s or s c
2k(m1m2)
m1m2
Raman + IR 3657 cmndash1
Raman + IR 3756 cmndash1
Raman + IR 1594 cmndash1
H2O
13
Theory of raman spectraTwo cases may arise depending upon whether a collision between a photon and molecules In itrsquos ground state is elastic or inelastic in natureCase 1- if the collision is elastic ndash this lead to the appearance of unmodified lines (or unmodified frequency of light) in the scattered beam and this explain rayleigh scatteringCase 2 - if the collision is inelastic ndash there will be exchange or transfer of energy between the scattering molecules and the incident photonThe frequency of scattered light and the incident photon which is either higher or lower than that of the incident photon is called raman frequency
Total energy before collision = total energy after collision
14
Presentation of Raman Spectra
lex = 1064 nm = 9399 cm-1
Breathing mode9399 ndash 992 = 8407 cm-1
Stretching mode9399 ndash 3063 = 6336 cm-1
15
Rayleigh Scattering- Occurs when incident EM radiation induces an oscillating dipole in a molecules which is re-radiated at the same frequency
Eugene Hecht Optics Addison-Wesley Reading MA 1998
bullElastic (l does not change)
bullRandom direction of emission
bullLittle energy lossbullof emission
bullLittle energy loss
4 2 20
4 2
8 ( ) (1 cos )( )sc
EE
d a
l
16
Raman ScatteringOccurs when monochromatic light is scattered light has been weakly modulated
by the characteristic frequencies of the molecules Raman spectroscopy measures the differences between the wavelengths of the
incident radiation and the scatted radiation
max 0
max max 0
max max 0
( ) cos 21 cos 2 ( )21 cos 2 ( )2
equilz zz
zzvib
zzvib
t E td r E tdr
d r E tdr
m a a
a
Selection rule v = plusmn1Overtones v = plusmn2 plusmn3 hellip
Must also have a change in polarizability
Classical Description does not suggest any difference between Stokes and Anti-Stokes intensities
1
0
vibhkTN e
N
17
The Raman polarization
The Raman Polarization is a property of waves that can oscillate with more than one orientation EMR or waves such as light and gravitational wave exhibit polarization
Polarization state - the shape traced out in a fixed plane by the electric vector as such a plane wave passes over it is a description of the polarization
Eg linear polarization circular polarization
elliptical polarization orthogonally polarization
Polarization changes are necessary to form the virtual state and hence the Raman effect
18
Condition for raman spectroscopyVibrational modes that are more polarizable are more Raman-active Examples ndash N2 (dinitrogen) symmetric stretch cause no change in dipole (IR-inactive) cause a change in the polarizability of the bond ndash as the bond gets longer it is more easily deformed (Raman -active)
ndash CO2 asymmetric stretch cause a change in dipole (IR-active) Polarizability change of one C=O bond lengthening is cancelled by the shortening of the other ndash no net polarizability (Raman-inactive) Some modes may be both IR and Raman-active others may be one or the other
19
Condition for raman spectroscopy
Raman spectra occurs as a result of oscillation of a dipole moment induced in a molecules by the oscillating electric field of an incident wave
As the induced dipole moment is directly proportional to the polarisability of the molecules the molecules must possess anisotropic polarisability which should change during molecular rotation or vibration for vibrational or rotational-vibrational raman spectra
Anisotropic polarisability depends upon the orientation of the molecules
In the presence of an electric field the electron cloud of an atom or molecules is distorted or polarised
20
Mutual Exclusion Principle
For molecules with a center of symmetry no IR active transitions are Raman active and vice versa
THORNSymmetric molecules IR-active vibrations are not Raman-active Raman-active vibrations are not IR-active
O = C = O O = C = O
Raman active Raman inactive IR inactive IR active
21
Raman Instrumentation
22
There are following component involves
1 Laser or source of light 2 Filter3 Sample holder 4 detector
23
The block design dispersive Raman scattering system
Radiation sources
Sample Wavelength
selector
Detector InGaAs or
Ge
RecorderDetector InGaAs or
Ge
RecorderDetector
InGaAs or Ge
Recorder
Block diagram
90
24
Flow diagram dispersive Raman scattering system
25
Schematic diagram dispersive raman scattering system
26
1 Laser or source of light
bull Lasers are generally the only source strong enough to scatter lots of light and lead to detectable raman scattering
bull Lasers operate using the principle of stimulated emission
bull Electronic population inversion is required to achieve gain via stimulated emission (before the fluorescence lifetime is reached)
bull Population inversion is achieved by ldquopumpingrdquo using lots of photons in a variety of laser gain media
27
List of Various laser source
SNo Laser wavelength01 NdYAG 1064nm
02 HeNe 633nm
03 Argon ion 488nm
04 GaAlAs diode 785nm
05 Co2 10600nm
06 Ti-Sapphire 800nm
28
A - HeNe laserbull Filled with 71 He amp Ne gas optimum output of 6328 Aring
bull High voltage excitation is preferred
B - NdYAG Systembull A typical laser system ndashthe neodymium-doped yttrium aluminum garnet or Nd+3
bull YAG is a cubic crystalline material
bull Crystal field splitting causes electronic energy level splitting
bull NdYAG laser are optically pumped using a flash tube or laser diodes
bull These are the one of the most common type of laser
bull It emits 1064 nm wavelength
29
2Filter bull It is therefore essential to have monochromatic radiations
bull For getting monochromatic radiations filters are used
bull They may be made of nickel oxide glass or quartz glass
bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator
30
3Sample holder bull For the study of raman effect the type of sample holder to be used
depends upon the intensity of sources the nature and availability of the sample
bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids
bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be
used for the study of raman spectra
bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy
31
4detectorbull Researchers traditionally used single points detectors such as
photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality
bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)
bull Sensitivity amp performance of modern CCD detectors are high
32
APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling
33
bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and
gypsum illustrating how Raman can be used for fast mineral ID
bull Gemstone and mineral identification
bull Fluid inclusions
bull Mineral and phase distribution in rock sections
bull Phase transitions
bull Mineral behavior under extreme conditions
34
Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance
35
Semiconductors
bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width
bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis
36
Life Sciences
bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level
bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure
37
Differences between IR and Raman methodsSNo Raman IR
01 It is due to the scattering of light by the vibrating molecules
It is the result of absorption of light by vibrating molecules
02 The vibration is Raman active if it causes a change in polarisability
Vibration is IR active if there is change in dipole moment
03 The molecule need not possess a permanent dipole moment
The vibration concerned should have a change in dipole moment due to that vibration
04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR
05 Sample preparation is not very elaborate it can be in any state
Sample preparation is elaborateGaseous samples can rarely be used
06 Gives an indication of covalent character in the molecule
Gives an indication of ionic character in the molecule
07 Cost of instrumentation is very high
Comparatively inexpensive
38
Advantages of Raman over IR
bull Water can be used as solvent bull Very suitable for biological samples in native state (because water
can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral
overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power
39
Advantages of IR over Ramanbull Simpler and cheaper instrumentation
bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio
bull Lower detection limit than (normal) Raman
bull Background fluorescence can overwhelm Raman
bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)
40
Several variations of Raman spectroscopy
1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal
bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)
bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977
bull A comprehensive theory of the effect was given by Lombardi and Birke
41
2 Resonance Raman spectroscopy The excitation wavelength is matched to an
electronic transition of the molecule or crystal so that vibrational modes associated with the excited electronic state are greatly enhanced This is useful for studying large molecules such as polypeptides which might show hundreds of bands in conventional Raman spectra It is also useful for associating normal modes with their observed frequency shifts
42
3 Surface-enhanced resonance Raman spectroscopy (SERRS) ndash A combination of SERS and resonance Raman spectroscopy that uses proximity to a surface to increase Raman intensity and excitation wavelength matched to the maximum absorbance of the molecule being analysed
4 Coherent anti-Stokes Raman spectroscopy (CARS) ndash
Two laser beams are used to generate a coherent anti-Stokes frequency beam which can be enhanced by resonance
43
5 Raman optical activity (ROA) ndash Measures vibrational optical activity by means of a small difference in the intensity of Raman scattering from chiral molecules in right- and left-circularly polarized incident light or equivalently a small circularly polarized component in the scattered light
6 Spatially offset Raman spectroscopy (SORS)
7 Spontaneous Raman spectroscopy (SRS) 8 Optical tweezers Raman spectroscopy (OTRS)
44
9 Angle-resolved Raman spectroscopy10 Inverse Raman spectroscopy11 Tip-enhanced Raman spectroscopy
(TERS) 12 Surface plasmon polariton enhanced
Raman scattering (SPPERS)13 Stand-off Remote Raman ndash 14 Fourier-transform Rama spectroscopyapplied
to photobiological systems
45
9
Classical theory of raman effect
bull According to the classical theory of electromagnetic radiation electric and magnetic fields oscillating at a given frequency are able to give out electromagnetic radiation of the same frequency One could use electromagnetic radiation theory to explain light scattering phenomena
bull For a majority of systems only an induced electric dipole moment μ is taken into consideration This dipole moment which is induced by the electric field E could be expressed by the power series
μ=μ(1)+μ(2)+μ(3)+⋯whereμ(1)=α Esdotμ(2)=12β EEsdotμ(3)=16γ EEEsdot
α is termed the polarizability tensor It is a second-rank tensor with all the components in the unit of CV-1m2 Typically orders of magnitude
for components in α β and γ are as follows α 10-40 CV-1m2
β 10-50 CV-2m3 and γ 10-61 CV-3m4
According to the values the contributions of μ(2)and μ(3) are quite small unless electric field is very high Since Rayleigh and Raman scattering are observed quite readily with very much lower electric field intensities one may expect to explain Rayleigh and Raman scattering in terms of μ(1) only
10
Classical theory of raman effecty of Raman Effect
Colthup et al Introduction to Infrared and Raman Spectroscopy 3rd ed Academic Press Boston 1990
mind = aE
polarizability
11
ElectronicGround State
1st ElectronicExcited State
Exci
tatio
n En
ergy
s (c
mndash1
)
Vibstates
4000
25000
0
fluor
esce
nce
IRs
s semit
2nd ElectronicExcited State
Raman∆s=semit-s
s ∆sflu
ores
cenc
eIm
purit
y
Fluorescence = Trouble
Raman Spectroscopy Absorption Scattering and Fluorescence
Stokes Anti-Stokes
12
Raman Spectroscopy Classical Treatment
bull Number of peaks related to degrees of freedom
DoF = 3N - 6 (bent) or 3N - 5 (linear) for N atomsbull Energy related to harmonic oscillator
bull Selection rules related to symmetry Rule of thumb symmetric=Raman active asymmetric=IR active
Raman 1335 cmndash1
IR 2349 cmndash1
IR 667 cmndash1
CO2
s or s c
2k(m1m2)
m1m2
Raman + IR 3657 cmndash1
Raman + IR 3756 cmndash1
Raman + IR 1594 cmndash1
H2O
13
Theory of raman spectraTwo cases may arise depending upon whether a collision between a photon and molecules In itrsquos ground state is elastic or inelastic in natureCase 1- if the collision is elastic ndash this lead to the appearance of unmodified lines (or unmodified frequency of light) in the scattered beam and this explain rayleigh scatteringCase 2 - if the collision is inelastic ndash there will be exchange or transfer of energy between the scattering molecules and the incident photonThe frequency of scattered light and the incident photon which is either higher or lower than that of the incident photon is called raman frequency
Total energy before collision = total energy after collision
14
Presentation of Raman Spectra
lex = 1064 nm = 9399 cm-1
Breathing mode9399 ndash 992 = 8407 cm-1
Stretching mode9399 ndash 3063 = 6336 cm-1
15
Rayleigh Scattering- Occurs when incident EM radiation induces an oscillating dipole in a molecules which is re-radiated at the same frequency
Eugene Hecht Optics Addison-Wesley Reading MA 1998
bullElastic (l does not change)
bullRandom direction of emission
bullLittle energy lossbullof emission
bullLittle energy loss
4 2 20
4 2
8 ( ) (1 cos )( )sc
EE
d a
l
16
Raman ScatteringOccurs when monochromatic light is scattered light has been weakly modulated
by the characteristic frequencies of the molecules Raman spectroscopy measures the differences between the wavelengths of the
incident radiation and the scatted radiation
max 0
max max 0
max max 0
( ) cos 21 cos 2 ( )21 cos 2 ( )2
equilz zz
zzvib
zzvib
t E td r E tdr
d r E tdr
m a a
a
Selection rule v = plusmn1Overtones v = plusmn2 plusmn3 hellip
Must also have a change in polarizability
Classical Description does not suggest any difference between Stokes and Anti-Stokes intensities
1
0
vibhkTN e
N
17
The Raman polarization
The Raman Polarization is a property of waves that can oscillate with more than one orientation EMR or waves such as light and gravitational wave exhibit polarization
Polarization state - the shape traced out in a fixed plane by the electric vector as such a plane wave passes over it is a description of the polarization
Eg linear polarization circular polarization
elliptical polarization orthogonally polarization
Polarization changes are necessary to form the virtual state and hence the Raman effect
18
Condition for raman spectroscopyVibrational modes that are more polarizable are more Raman-active Examples ndash N2 (dinitrogen) symmetric stretch cause no change in dipole (IR-inactive) cause a change in the polarizability of the bond ndash as the bond gets longer it is more easily deformed (Raman -active)
ndash CO2 asymmetric stretch cause a change in dipole (IR-active) Polarizability change of one C=O bond lengthening is cancelled by the shortening of the other ndash no net polarizability (Raman-inactive) Some modes may be both IR and Raman-active others may be one or the other
19
Condition for raman spectroscopy
Raman spectra occurs as a result of oscillation of a dipole moment induced in a molecules by the oscillating electric field of an incident wave
As the induced dipole moment is directly proportional to the polarisability of the molecules the molecules must possess anisotropic polarisability which should change during molecular rotation or vibration for vibrational or rotational-vibrational raman spectra
Anisotropic polarisability depends upon the orientation of the molecules
In the presence of an electric field the electron cloud of an atom or molecules is distorted or polarised
20
Mutual Exclusion Principle
For molecules with a center of symmetry no IR active transitions are Raman active and vice versa
THORNSymmetric molecules IR-active vibrations are not Raman-active Raman-active vibrations are not IR-active
O = C = O O = C = O
Raman active Raman inactive IR inactive IR active
21
Raman Instrumentation
22
There are following component involves
1 Laser or source of light 2 Filter3 Sample holder 4 detector
23
The block design dispersive Raman scattering system
Radiation sources
Sample Wavelength
selector
Detector InGaAs or
Ge
RecorderDetector InGaAs or
Ge
RecorderDetector
InGaAs or Ge
Recorder
Block diagram
90
24
Flow diagram dispersive Raman scattering system
25
Schematic diagram dispersive raman scattering system
26
1 Laser or source of light
bull Lasers are generally the only source strong enough to scatter lots of light and lead to detectable raman scattering
bull Lasers operate using the principle of stimulated emission
bull Electronic population inversion is required to achieve gain via stimulated emission (before the fluorescence lifetime is reached)
bull Population inversion is achieved by ldquopumpingrdquo using lots of photons in a variety of laser gain media
27
List of Various laser source
SNo Laser wavelength01 NdYAG 1064nm
02 HeNe 633nm
03 Argon ion 488nm
04 GaAlAs diode 785nm
05 Co2 10600nm
06 Ti-Sapphire 800nm
28
A - HeNe laserbull Filled with 71 He amp Ne gas optimum output of 6328 Aring
bull High voltage excitation is preferred
B - NdYAG Systembull A typical laser system ndashthe neodymium-doped yttrium aluminum garnet or Nd+3
bull YAG is a cubic crystalline material
bull Crystal field splitting causes electronic energy level splitting
bull NdYAG laser are optically pumped using a flash tube or laser diodes
bull These are the one of the most common type of laser
bull It emits 1064 nm wavelength
29
2Filter bull It is therefore essential to have monochromatic radiations
bull For getting monochromatic radiations filters are used
bull They may be made of nickel oxide glass or quartz glass
bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator
30
3Sample holder bull For the study of raman effect the type of sample holder to be used
depends upon the intensity of sources the nature and availability of the sample
bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids
bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be
used for the study of raman spectra
bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy
31
4detectorbull Researchers traditionally used single points detectors such as
photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality
bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)
bull Sensitivity amp performance of modern CCD detectors are high
32
APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling
33
bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and
gypsum illustrating how Raman can be used for fast mineral ID
bull Gemstone and mineral identification
bull Fluid inclusions
bull Mineral and phase distribution in rock sections
bull Phase transitions
bull Mineral behavior under extreme conditions
34
Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance
35
Semiconductors
bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width
bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis
36
Life Sciences
bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level
bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure
37
Differences between IR and Raman methodsSNo Raman IR
01 It is due to the scattering of light by the vibrating molecules
It is the result of absorption of light by vibrating molecules
02 The vibration is Raman active if it causes a change in polarisability
Vibration is IR active if there is change in dipole moment
03 The molecule need not possess a permanent dipole moment
The vibration concerned should have a change in dipole moment due to that vibration
04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR
05 Sample preparation is not very elaborate it can be in any state
Sample preparation is elaborateGaseous samples can rarely be used
06 Gives an indication of covalent character in the molecule
Gives an indication of ionic character in the molecule
07 Cost of instrumentation is very high
Comparatively inexpensive
38
Advantages of Raman over IR
bull Water can be used as solvent bull Very suitable for biological samples in native state (because water
can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral
overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power
39
Advantages of IR over Ramanbull Simpler and cheaper instrumentation
bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio
bull Lower detection limit than (normal) Raman
bull Background fluorescence can overwhelm Raman
bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)
40
Several variations of Raman spectroscopy
1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal
bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)
bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977
bull A comprehensive theory of the effect was given by Lombardi and Birke
41
2 Resonance Raman spectroscopy The excitation wavelength is matched to an
electronic transition of the molecule or crystal so that vibrational modes associated with the excited electronic state are greatly enhanced This is useful for studying large molecules such as polypeptides which might show hundreds of bands in conventional Raman spectra It is also useful for associating normal modes with their observed frequency shifts
42
3 Surface-enhanced resonance Raman spectroscopy (SERRS) ndash A combination of SERS and resonance Raman spectroscopy that uses proximity to a surface to increase Raman intensity and excitation wavelength matched to the maximum absorbance of the molecule being analysed
4 Coherent anti-Stokes Raman spectroscopy (CARS) ndash
Two laser beams are used to generate a coherent anti-Stokes frequency beam which can be enhanced by resonance
43
5 Raman optical activity (ROA) ndash Measures vibrational optical activity by means of a small difference in the intensity of Raman scattering from chiral molecules in right- and left-circularly polarized incident light or equivalently a small circularly polarized component in the scattered light
6 Spatially offset Raman spectroscopy (SORS)
7 Spontaneous Raman spectroscopy (SRS) 8 Optical tweezers Raman spectroscopy (OTRS)
44
9 Angle-resolved Raman spectroscopy10 Inverse Raman spectroscopy11 Tip-enhanced Raman spectroscopy
(TERS) 12 Surface plasmon polariton enhanced
Raman scattering (SPPERS)13 Stand-off Remote Raman ndash 14 Fourier-transform Rama spectroscopyapplied
to photobiological systems
45
10
Classical theory of raman effecty of Raman Effect
Colthup et al Introduction to Infrared and Raman Spectroscopy 3rd ed Academic Press Boston 1990
mind = aE
polarizability
11
ElectronicGround State
1st ElectronicExcited State
Exci
tatio
n En
ergy
s (c
mndash1
)
Vibstates
4000
25000
0
fluor
esce
nce
IRs
s semit
2nd ElectronicExcited State
Raman∆s=semit-s
s ∆sflu
ores
cenc
eIm
purit
y
Fluorescence = Trouble
Raman Spectroscopy Absorption Scattering and Fluorescence
Stokes Anti-Stokes
12
Raman Spectroscopy Classical Treatment
bull Number of peaks related to degrees of freedom
DoF = 3N - 6 (bent) or 3N - 5 (linear) for N atomsbull Energy related to harmonic oscillator
bull Selection rules related to symmetry Rule of thumb symmetric=Raman active asymmetric=IR active
Raman 1335 cmndash1
IR 2349 cmndash1
IR 667 cmndash1
CO2
s or s c
2k(m1m2)
m1m2
Raman + IR 3657 cmndash1
Raman + IR 3756 cmndash1
Raman + IR 1594 cmndash1
H2O
13
Theory of raman spectraTwo cases may arise depending upon whether a collision between a photon and molecules In itrsquos ground state is elastic or inelastic in natureCase 1- if the collision is elastic ndash this lead to the appearance of unmodified lines (or unmodified frequency of light) in the scattered beam and this explain rayleigh scatteringCase 2 - if the collision is inelastic ndash there will be exchange or transfer of energy between the scattering molecules and the incident photonThe frequency of scattered light and the incident photon which is either higher or lower than that of the incident photon is called raman frequency
Total energy before collision = total energy after collision
14
Presentation of Raman Spectra
lex = 1064 nm = 9399 cm-1
Breathing mode9399 ndash 992 = 8407 cm-1
Stretching mode9399 ndash 3063 = 6336 cm-1
15
Rayleigh Scattering- Occurs when incident EM radiation induces an oscillating dipole in a molecules which is re-radiated at the same frequency
Eugene Hecht Optics Addison-Wesley Reading MA 1998
bullElastic (l does not change)
bullRandom direction of emission
bullLittle energy lossbullof emission
bullLittle energy loss
4 2 20
4 2
8 ( ) (1 cos )( )sc
EE
d a
l
16
Raman ScatteringOccurs when monochromatic light is scattered light has been weakly modulated
by the characteristic frequencies of the molecules Raman spectroscopy measures the differences between the wavelengths of the
incident radiation and the scatted radiation
max 0
max max 0
max max 0
( ) cos 21 cos 2 ( )21 cos 2 ( )2
equilz zz
zzvib
zzvib
t E td r E tdr
d r E tdr
m a a
a
Selection rule v = plusmn1Overtones v = plusmn2 plusmn3 hellip
Must also have a change in polarizability
Classical Description does not suggest any difference between Stokes and Anti-Stokes intensities
1
0
vibhkTN e
N
17
The Raman polarization
The Raman Polarization is a property of waves that can oscillate with more than one orientation EMR or waves such as light and gravitational wave exhibit polarization
Polarization state - the shape traced out in a fixed plane by the electric vector as such a plane wave passes over it is a description of the polarization
Eg linear polarization circular polarization
elliptical polarization orthogonally polarization
Polarization changes are necessary to form the virtual state and hence the Raman effect
18
Condition for raman spectroscopyVibrational modes that are more polarizable are more Raman-active Examples ndash N2 (dinitrogen) symmetric stretch cause no change in dipole (IR-inactive) cause a change in the polarizability of the bond ndash as the bond gets longer it is more easily deformed (Raman -active)
ndash CO2 asymmetric stretch cause a change in dipole (IR-active) Polarizability change of one C=O bond lengthening is cancelled by the shortening of the other ndash no net polarizability (Raman-inactive) Some modes may be both IR and Raman-active others may be one or the other
19
Condition for raman spectroscopy
Raman spectra occurs as a result of oscillation of a dipole moment induced in a molecules by the oscillating electric field of an incident wave
As the induced dipole moment is directly proportional to the polarisability of the molecules the molecules must possess anisotropic polarisability which should change during molecular rotation or vibration for vibrational or rotational-vibrational raman spectra
Anisotropic polarisability depends upon the orientation of the molecules
In the presence of an electric field the electron cloud of an atom or molecules is distorted or polarised
20
Mutual Exclusion Principle
For molecules with a center of symmetry no IR active transitions are Raman active and vice versa
THORNSymmetric molecules IR-active vibrations are not Raman-active Raman-active vibrations are not IR-active
O = C = O O = C = O
Raman active Raman inactive IR inactive IR active
21
Raman Instrumentation
22
There are following component involves
1 Laser or source of light 2 Filter3 Sample holder 4 detector
23
The block design dispersive Raman scattering system
Radiation sources
Sample Wavelength
selector
Detector InGaAs or
Ge
RecorderDetector InGaAs or
Ge
RecorderDetector
InGaAs or Ge
Recorder
Block diagram
90
24
Flow diagram dispersive Raman scattering system
25
Schematic diagram dispersive raman scattering system
26
1 Laser or source of light
bull Lasers are generally the only source strong enough to scatter lots of light and lead to detectable raman scattering
bull Lasers operate using the principle of stimulated emission
bull Electronic population inversion is required to achieve gain via stimulated emission (before the fluorescence lifetime is reached)
bull Population inversion is achieved by ldquopumpingrdquo using lots of photons in a variety of laser gain media
27
List of Various laser source
SNo Laser wavelength01 NdYAG 1064nm
02 HeNe 633nm
03 Argon ion 488nm
04 GaAlAs diode 785nm
05 Co2 10600nm
06 Ti-Sapphire 800nm
28
A - HeNe laserbull Filled with 71 He amp Ne gas optimum output of 6328 Aring
bull High voltage excitation is preferred
B - NdYAG Systembull A typical laser system ndashthe neodymium-doped yttrium aluminum garnet or Nd+3
bull YAG is a cubic crystalline material
bull Crystal field splitting causes electronic energy level splitting
bull NdYAG laser are optically pumped using a flash tube or laser diodes
bull These are the one of the most common type of laser
bull It emits 1064 nm wavelength
29
2Filter bull It is therefore essential to have monochromatic radiations
bull For getting monochromatic radiations filters are used
bull They may be made of nickel oxide glass or quartz glass
bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator
30
3Sample holder bull For the study of raman effect the type of sample holder to be used
depends upon the intensity of sources the nature and availability of the sample
bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids
bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be
used for the study of raman spectra
bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy
31
4detectorbull Researchers traditionally used single points detectors such as
photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality
bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)
bull Sensitivity amp performance of modern CCD detectors are high
32
APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling
33
bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and
gypsum illustrating how Raman can be used for fast mineral ID
bull Gemstone and mineral identification
bull Fluid inclusions
bull Mineral and phase distribution in rock sections
bull Phase transitions
bull Mineral behavior under extreme conditions
34
Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance
35
Semiconductors
bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width
bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis
36
Life Sciences
bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level
bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure
37
Differences between IR and Raman methodsSNo Raman IR
01 It is due to the scattering of light by the vibrating molecules
It is the result of absorption of light by vibrating molecules
02 The vibration is Raman active if it causes a change in polarisability
Vibration is IR active if there is change in dipole moment
03 The molecule need not possess a permanent dipole moment
The vibration concerned should have a change in dipole moment due to that vibration
04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR
05 Sample preparation is not very elaborate it can be in any state
Sample preparation is elaborateGaseous samples can rarely be used
06 Gives an indication of covalent character in the molecule
Gives an indication of ionic character in the molecule
07 Cost of instrumentation is very high
Comparatively inexpensive
38
Advantages of Raman over IR
bull Water can be used as solvent bull Very suitable for biological samples in native state (because water
can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral
overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power
39
Advantages of IR over Ramanbull Simpler and cheaper instrumentation
bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio
bull Lower detection limit than (normal) Raman
bull Background fluorescence can overwhelm Raman
bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)
40
Several variations of Raman spectroscopy
1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal
bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)
bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977
bull A comprehensive theory of the effect was given by Lombardi and Birke
41
2 Resonance Raman spectroscopy The excitation wavelength is matched to an
electronic transition of the molecule or crystal so that vibrational modes associated with the excited electronic state are greatly enhanced This is useful for studying large molecules such as polypeptides which might show hundreds of bands in conventional Raman spectra It is also useful for associating normal modes with their observed frequency shifts
42
3 Surface-enhanced resonance Raman spectroscopy (SERRS) ndash A combination of SERS and resonance Raman spectroscopy that uses proximity to a surface to increase Raman intensity and excitation wavelength matched to the maximum absorbance of the molecule being analysed
4 Coherent anti-Stokes Raman spectroscopy (CARS) ndash
Two laser beams are used to generate a coherent anti-Stokes frequency beam which can be enhanced by resonance
43
5 Raman optical activity (ROA) ndash Measures vibrational optical activity by means of a small difference in the intensity of Raman scattering from chiral molecules in right- and left-circularly polarized incident light or equivalently a small circularly polarized component in the scattered light
6 Spatially offset Raman spectroscopy (SORS)
7 Spontaneous Raman spectroscopy (SRS) 8 Optical tweezers Raman spectroscopy (OTRS)
44
9 Angle-resolved Raman spectroscopy10 Inverse Raman spectroscopy11 Tip-enhanced Raman spectroscopy
(TERS) 12 Surface plasmon polariton enhanced
Raman scattering (SPPERS)13 Stand-off Remote Raman ndash 14 Fourier-transform Rama spectroscopyapplied
to photobiological systems
45
11
ElectronicGround State
1st ElectronicExcited State
Exci
tatio
n En
ergy
s (c
mndash1
)
Vibstates
4000
25000
0
fluor
esce
nce
IRs
s semit
2nd ElectronicExcited State
Raman∆s=semit-s
s ∆sflu
ores
cenc
eIm
purit
y
Fluorescence = Trouble
Raman Spectroscopy Absorption Scattering and Fluorescence
Stokes Anti-Stokes
12
Raman Spectroscopy Classical Treatment
bull Number of peaks related to degrees of freedom
DoF = 3N - 6 (bent) or 3N - 5 (linear) for N atomsbull Energy related to harmonic oscillator
bull Selection rules related to symmetry Rule of thumb symmetric=Raman active asymmetric=IR active
Raman 1335 cmndash1
IR 2349 cmndash1
IR 667 cmndash1
CO2
s or s c
2k(m1m2)
m1m2
Raman + IR 3657 cmndash1
Raman + IR 3756 cmndash1
Raman + IR 1594 cmndash1
H2O
13
Theory of raman spectraTwo cases may arise depending upon whether a collision between a photon and molecules In itrsquos ground state is elastic or inelastic in natureCase 1- if the collision is elastic ndash this lead to the appearance of unmodified lines (or unmodified frequency of light) in the scattered beam and this explain rayleigh scatteringCase 2 - if the collision is inelastic ndash there will be exchange or transfer of energy between the scattering molecules and the incident photonThe frequency of scattered light and the incident photon which is either higher or lower than that of the incident photon is called raman frequency
Total energy before collision = total energy after collision
14
Presentation of Raman Spectra
lex = 1064 nm = 9399 cm-1
Breathing mode9399 ndash 992 = 8407 cm-1
Stretching mode9399 ndash 3063 = 6336 cm-1
15
Rayleigh Scattering- Occurs when incident EM radiation induces an oscillating dipole in a molecules which is re-radiated at the same frequency
Eugene Hecht Optics Addison-Wesley Reading MA 1998
bullElastic (l does not change)
bullRandom direction of emission
bullLittle energy lossbullof emission
bullLittle energy loss
4 2 20
4 2
8 ( ) (1 cos )( )sc
EE
d a
l
16
Raman ScatteringOccurs when monochromatic light is scattered light has been weakly modulated
by the characteristic frequencies of the molecules Raman spectroscopy measures the differences between the wavelengths of the
incident radiation and the scatted radiation
max 0
max max 0
max max 0
( ) cos 21 cos 2 ( )21 cos 2 ( )2
equilz zz
zzvib
zzvib
t E td r E tdr
d r E tdr
m a a
a
Selection rule v = plusmn1Overtones v = plusmn2 plusmn3 hellip
Must also have a change in polarizability
Classical Description does not suggest any difference between Stokes and Anti-Stokes intensities
1
0
vibhkTN e
N
17
The Raman polarization
The Raman Polarization is a property of waves that can oscillate with more than one orientation EMR or waves such as light and gravitational wave exhibit polarization
Polarization state - the shape traced out in a fixed plane by the electric vector as such a plane wave passes over it is a description of the polarization
Eg linear polarization circular polarization
elliptical polarization orthogonally polarization
Polarization changes are necessary to form the virtual state and hence the Raman effect
18
Condition for raman spectroscopyVibrational modes that are more polarizable are more Raman-active Examples ndash N2 (dinitrogen) symmetric stretch cause no change in dipole (IR-inactive) cause a change in the polarizability of the bond ndash as the bond gets longer it is more easily deformed (Raman -active)
ndash CO2 asymmetric stretch cause a change in dipole (IR-active) Polarizability change of one C=O bond lengthening is cancelled by the shortening of the other ndash no net polarizability (Raman-inactive) Some modes may be both IR and Raman-active others may be one or the other
19
Condition for raman spectroscopy
Raman spectra occurs as a result of oscillation of a dipole moment induced in a molecules by the oscillating electric field of an incident wave
As the induced dipole moment is directly proportional to the polarisability of the molecules the molecules must possess anisotropic polarisability which should change during molecular rotation or vibration for vibrational or rotational-vibrational raman spectra
Anisotropic polarisability depends upon the orientation of the molecules
In the presence of an electric field the electron cloud of an atom or molecules is distorted or polarised
20
Mutual Exclusion Principle
For molecules with a center of symmetry no IR active transitions are Raman active and vice versa
THORNSymmetric molecules IR-active vibrations are not Raman-active Raman-active vibrations are not IR-active
O = C = O O = C = O
Raman active Raman inactive IR inactive IR active
21
Raman Instrumentation
22
There are following component involves
1 Laser or source of light 2 Filter3 Sample holder 4 detector
23
The block design dispersive Raman scattering system
Radiation sources
Sample Wavelength
selector
Detector InGaAs or
Ge
RecorderDetector InGaAs or
Ge
RecorderDetector
InGaAs or Ge
Recorder
Block diagram
90
24
Flow diagram dispersive Raman scattering system
25
Schematic diagram dispersive raman scattering system
26
1 Laser or source of light
bull Lasers are generally the only source strong enough to scatter lots of light and lead to detectable raman scattering
bull Lasers operate using the principle of stimulated emission
bull Electronic population inversion is required to achieve gain via stimulated emission (before the fluorescence lifetime is reached)
bull Population inversion is achieved by ldquopumpingrdquo using lots of photons in a variety of laser gain media
27
List of Various laser source
SNo Laser wavelength01 NdYAG 1064nm
02 HeNe 633nm
03 Argon ion 488nm
04 GaAlAs diode 785nm
05 Co2 10600nm
06 Ti-Sapphire 800nm
28
A - HeNe laserbull Filled with 71 He amp Ne gas optimum output of 6328 Aring
bull High voltage excitation is preferred
B - NdYAG Systembull A typical laser system ndashthe neodymium-doped yttrium aluminum garnet or Nd+3
bull YAG is a cubic crystalline material
bull Crystal field splitting causes electronic energy level splitting
bull NdYAG laser are optically pumped using a flash tube or laser diodes
bull These are the one of the most common type of laser
bull It emits 1064 nm wavelength
29
2Filter bull It is therefore essential to have monochromatic radiations
bull For getting monochromatic radiations filters are used
bull They may be made of nickel oxide glass or quartz glass
bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator
30
3Sample holder bull For the study of raman effect the type of sample holder to be used
depends upon the intensity of sources the nature and availability of the sample
bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids
bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be
used for the study of raman spectra
bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy
31
4detectorbull Researchers traditionally used single points detectors such as
photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality
bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)
bull Sensitivity amp performance of modern CCD detectors are high
32
APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling
33
bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and
gypsum illustrating how Raman can be used for fast mineral ID
bull Gemstone and mineral identification
bull Fluid inclusions
bull Mineral and phase distribution in rock sections
bull Phase transitions
bull Mineral behavior under extreme conditions
34
Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance
35
Semiconductors
bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width
bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis
36
Life Sciences
bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level
bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure
37
Differences between IR and Raman methodsSNo Raman IR
01 It is due to the scattering of light by the vibrating molecules
It is the result of absorption of light by vibrating molecules
02 The vibration is Raman active if it causes a change in polarisability
Vibration is IR active if there is change in dipole moment
03 The molecule need not possess a permanent dipole moment
The vibration concerned should have a change in dipole moment due to that vibration
04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR
05 Sample preparation is not very elaborate it can be in any state
Sample preparation is elaborateGaseous samples can rarely be used
06 Gives an indication of covalent character in the molecule
Gives an indication of ionic character in the molecule
07 Cost of instrumentation is very high
Comparatively inexpensive
38
Advantages of Raman over IR
bull Water can be used as solvent bull Very suitable for biological samples in native state (because water
can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral
overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power
39
Advantages of IR over Ramanbull Simpler and cheaper instrumentation
bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio
bull Lower detection limit than (normal) Raman
bull Background fluorescence can overwhelm Raman
bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)
40
Several variations of Raman spectroscopy
1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal
bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)
bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977
bull A comprehensive theory of the effect was given by Lombardi and Birke
41
2 Resonance Raman spectroscopy The excitation wavelength is matched to an
electronic transition of the molecule or crystal so that vibrational modes associated with the excited electronic state are greatly enhanced This is useful for studying large molecules such as polypeptides which might show hundreds of bands in conventional Raman spectra It is also useful for associating normal modes with their observed frequency shifts
42
3 Surface-enhanced resonance Raman spectroscopy (SERRS) ndash A combination of SERS and resonance Raman spectroscopy that uses proximity to a surface to increase Raman intensity and excitation wavelength matched to the maximum absorbance of the molecule being analysed
4 Coherent anti-Stokes Raman spectroscopy (CARS) ndash
Two laser beams are used to generate a coherent anti-Stokes frequency beam which can be enhanced by resonance
43
5 Raman optical activity (ROA) ndash Measures vibrational optical activity by means of a small difference in the intensity of Raman scattering from chiral molecules in right- and left-circularly polarized incident light or equivalently a small circularly polarized component in the scattered light
6 Spatially offset Raman spectroscopy (SORS)
7 Spontaneous Raman spectroscopy (SRS) 8 Optical tweezers Raman spectroscopy (OTRS)
44
9 Angle-resolved Raman spectroscopy10 Inverse Raman spectroscopy11 Tip-enhanced Raman spectroscopy
(TERS) 12 Surface plasmon polariton enhanced
Raman scattering (SPPERS)13 Stand-off Remote Raman ndash 14 Fourier-transform Rama spectroscopyapplied
to photobiological systems
45
12
Raman Spectroscopy Classical Treatment
bull Number of peaks related to degrees of freedom
DoF = 3N - 6 (bent) or 3N - 5 (linear) for N atomsbull Energy related to harmonic oscillator
bull Selection rules related to symmetry Rule of thumb symmetric=Raman active asymmetric=IR active
Raman 1335 cmndash1
IR 2349 cmndash1
IR 667 cmndash1
CO2
s or s c
2k(m1m2)
m1m2
Raman + IR 3657 cmndash1
Raman + IR 3756 cmndash1
Raman + IR 1594 cmndash1
H2O
13
Theory of raman spectraTwo cases may arise depending upon whether a collision between a photon and molecules In itrsquos ground state is elastic or inelastic in natureCase 1- if the collision is elastic ndash this lead to the appearance of unmodified lines (or unmodified frequency of light) in the scattered beam and this explain rayleigh scatteringCase 2 - if the collision is inelastic ndash there will be exchange or transfer of energy between the scattering molecules and the incident photonThe frequency of scattered light and the incident photon which is either higher or lower than that of the incident photon is called raman frequency
Total energy before collision = total energy after collision
14
Presentation of Raman Spectra
lex = 1064 nm = 9399 cm-1
Breathing mode9399 ndash 992 = 8407 cm-1
Stretching mode9399 ndash 3063 = 6336 cm-1
15
Rayleigh Scattering- Occurs when incident EM radiation induces an oscillating dipole in a molecules which is re-radiated at the same frequency
Eugene Hecht Optics Addison-Wesley Reading MA 1998
bullElastic (l does not change)
bullRandom direction of emission
bullLittle energy lossbullof emission
bullLittle energy loss
4 2 20
4 2
8 ( ) (1 cos )( )sc
EE
d a
l
16
Raman ScatteringOccurs when monochromatic light is scattered light has been weakly modulated
by the characteristic frequencies of the molecules Raman spectroscopy measures the differences between the wavelengths of the
incident radiation and the scatted radiation
max 0
max max 0
max max 0
( ) cos 21 cos 2 ( )21 cos 2 ( )2
equilz zz
zzvib
zzvib
t E td r E tdr
d r E tdr
m a a
a
Selection rule v = plusmn1Overtones v = plusmn2 plusmn3 hellip
Must also have a change in polarizability
Classical Description does not suggest any difference between Stokes and Anti-Stokes intensities
1
0
vibhkTN e
N
17
The Raman polarization
The Raman Polarization is a property of waves that can oscillate with more than one orientation EMR or waves such as light and gravitational wave exhibit polarization
Polarization state - the shape traced out in a fixed plane by the electric vector as such a plane wave passes over it is a description of the polarization
Eg linear polarization circular polarization
elliptical polarization orthogonally polarization
Polarization changes are necessary to form the virtual state and hence the Raman effect
18
Condition for raman spectroscopyVibrational modes that are more polarizable are more Raman-active Examples ndash N2 (dinitrogen) symmetric stretch cause no change in dipole (IR-inactive) cause a change in the polarizability of the bond ndash as the bond gets longer it is more easily deformed (Raman -active)
ndash CO2 asymmetric stretch cause a change in dipole (IR-active) Polarizability change of one C=O bond lengthening is cancelled by the shortening of the other ndash no net polarizability (Raman-inactive) Some modes may be both IR and Raman-active others may be one or the other
19
Condition for raman spectroscopy
Raman spectra occurs as a result of oscillation of a dipole moment induced in a molecules by the oscillating electric field of an incident wave
As the induced dipole moment is directly proportional to the polarisability of the molecules the molecules must possess anisotropic polarisability which should change during molecular rotation or vibration for vibrational or rotational-vibrational raman spectra
Anisotropic polarisability depends upon the orientation of the molecules
In the presence of an electric field the electron cloud of an atom or molecules is distorted or polarised
20
Mutual Exclusion Principle
For molecules with a center of symmetry no IR active transitions are Raman active and vice versa
THORNSymmetric molecules IR-active vibrations are not Raman-active Raman-active vibrations are not IR-active
O = C = O O = C = O
Raman active Raman inactive IR inactive IR active
21
Raman Instrumentation
22
There are following component involves
1 Laser or source of light 2 Filter3 Sample holder 4 detector
23
The block design dispersive Raman scattering system
Radiation sources
Sample Wavelength
selector
Detector InGaAs or
Ge
RecorderDetector InGaAs or
Ge
RecorderDetector
InGaAs or Ge
Recorder
Block diagram
90
24
Flow diagram dispersive Raman scattering system
25
Schematic diagram dispersive raman scattering system
26
1 Laser or source of light
bull Lasers are generally the only source strong enough to scatter lots of light and lead to detectable raman scattering
bull Lasers operate using the principle of stimulated emission
bull Electronic population inversion is required to achieve gain via stimulated emission (before the fluorescence lifetime is reached)
bull Population inversion is achieved by ldquopumpingrdquo using lots of photons in a variety of laser gain media
27
List of Various laser source
SNo Laser wavelength01 NdYAG 1064nm
02 HeNe 633nm
03 Argon ion 488nm
04 GaAlAs diode 785nm
05 Co2 10600nm
06 Ti-Sapphire 800nm
28
A - HeNe laserbull Filled with 71 He amp Ne gas optimum output of 6328 Aring
bull High voltage excitation is preferred
B - NdYAG Systembull A typical laser system ndashthe neodymium-doped yttrium aluminum garnet or Nd+3
bull YAG is a cubic crystalline material
bull Crystal field splitting causes electronic energy level splitting
bull NdYAG laser are optically pumped using a flash tube or laser diodes
bull These are the one of the most common type of laser
bull It emits 1064 nm wavelength
29
2Filter bull It is therefore essential to have monochromatic radiations
bull For getting monochromatic radiations filters are used
bull They may be made of nickel oxide glass or quartz glass
bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator
30
3Sample holder bull For the study of raman effect the type of sample holder to be used
depends upon the intensity of sources the nature and availability of the sample
bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids
bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be
used for the study of raman spectra
bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy
31
4detectorbull Researchers traditionally used single points detectors such as
photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality
bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)
bull Sensitivity amp performance of modern CCD detectors are high
32
APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling
33
bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and
gypsum illustrating how Raman can be used for fast mineral ID
bull Gemstone and mineral identification
bull Fluid inclusions
bull Mineral and phase distribution in rock sections
bull Phase transitions
bull Mineral behavior under extreme conditions
34
Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance
35
Semiconductors
bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width
bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis
36
Life Sciences
bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level
bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure
37
Differences between IR and Raman methodsSNo Raman IR
01 It is due to the scattering of light by the vibrating molecules
It is the result of absorption of light by vibrating molecules
02 The vibration is Raman active if it causes a change in polarisability
Vibration is IR active if there is change in dipole moment
03 The molecule need not possess a permanent dipole moment
The vibration concerned should have a change in dipole moment due to that vibration
04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR
05 Sample preparation is not very elaborate it can be in any state
Sample preparation is elaborateGaseous samples can rarely be used
06 Gives an indication of covalent character in the molecule
Gives an indication of ionic character in the molecule
07 Cost of instrumentation is very high
Comparatively inexpensive
38
Advantages of Raman over IR
bull Water can be used as solvent bull Very suitable for biological samples in native state (because water
can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral
overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power
39
Advantages of IR over Ramanbull Simpler and cheaper instrumentation
bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio
bull Lower detection limit than (normal) Raman
bull Background fluorescence can overwhelm Raman
bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)
40
Several variations of Raman spectroscopy
1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal
bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)
bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977
bull A comprehensive theory of the effect was given by Lombardi and Birke
41
2 Resonance Raman spectroscopy The excitation wavelength is matched to an
electronic transition of the molecule or crystal so that vibrational modes associated with the excited electronic state are greatly enhanced This is useful for studying large molecules such as polypeptides which might show hundreds of bands in conventional Raman spectra It is also useful for associating normal modes with their observed frequency shifts
42
3 Surface-enhanced resonance Raman spectroscopy (SERRS) ndash A combination of SERS and resonance Raman spectroscopy that uses proximity to a surface to increase Raman intensity and excitation wavelength matched to the maximum absorbance of the molecule being analysed
4 Coherent anti-Stokes Raman spectroscopy (CARS) ndash
Two laser beams are used to generate a coherent anti-Stokes frequency beam which can be enhanced by resonance
43
5 Raman optical activity (ROA) ndash Measures vibrational optical activity by means of a small difference in the intensity of Raman scattering from chiral molecules in right- and left-circularly polarized incident light or equivalently a small circularly polarized component in the scattered light
6 Spatially offset Raman spectroscopy (SORS)
7 Spontaneous Raman spectroscopy (SRS) 8 Optical tweezers Raman spectroscopy (OTRS)
44
9 Angle-resolved Raman spectroscopy10 Inverse Raman spectroscopy11 Tip-enhanced Raman spectroscopy
(TERS) 12 Surface plasmon polariton enhanced
Raman scattering (SPPERS)13 Stand-off Remote Raman ndash 14 Fourier-transform Rama spectroscopyapplied
to photobiological systems
45
13
Theory of raman spectraTwo cases may arise depending upon whether a collision between a photon and molecules In itrsquos ground state is elastic or inelastic in natureCase 1- if the collision is elastic ndash this lead to the appearance of unmodified lines (or unmodified frequency of light) in the scattered beam and this explain rayleigh scatteringCase 2 - if the collision is inelastic ndash there will be exchange or transfer of energy between the scattering molecules and the incident photonThe frequency of scattered light and the incident photon which is either higher or lower than that of the incident photon is called raman frequency
Total energy before collision = total energy after collision
14
Presentation of Raman Spectra
lex = 1064 nm = 9399 cm-1
Breathing mode9399 ndash 992 = 8407 cm-1
Stretching mode9399 ndash 3063 = 6336 cm-1
15
Rayleigh Scattering- Occurs when incident EM radiation induces an oscillating dipole in a molecules which is re-radiated at the same frequency
Eugene Hecht Optics Addison-Wesley Reading MA 1998
bullElastic (l does not change)
bullRandom direction of emission
bullLittle energy lossbullof emission
bullLittle energy loss
4 2 20
4 2
8 ( ) (1 cos )( )sc
EE
d a
l
16
Raman ScatteringOccurs when monochromatic light is scattered light has been weakly modulated
by the characteristic frequencies of the molecules Raman spectroscopy measures the differences between the wavelengths of the
incident radiation and the scatted radiation
max 0
max max 0
max max 0
( ) cos 21 cos 2 ( )21 cos 2 ( )2
equilz zz
zzvib
zzvib
t E td r E tdr
d r E tdr
m a a
a
Selection rule v = plusmn1Overtones v = plusmn2 plusmn3 hellip
Must also have a change in polarizability
Classical Description does not suggest any difference between Stokes and Anti-Stokes intensities
1
0
vibhkTN e
N
17
The Raman polarization
The Raman Polarization is a property of waves that can oscillate with more than one orientation EMR or waves such as light and gravitational wave exhibit polarization
Polarization state - the shape traced out in a fixed plane by the electric vector as such a plane wave passes over it is a description of the polarization
Eg linear polarization circular polarization
elliptical polarization orthogonally polarization
Polarization changes are necessary to form the virtual state and hence the Raman effect
18
Condition for raman spectroscopyVibrational modes that are more polarizable are more Raman-active Examples ndash N2 (dinitrogen) symmetric stretch cause no change in dipole (IR-inactive) cause a change in the polarizability of the bond ndash as the bond gets longer it is more easily deformed (Raman -active)
ndash CO2 asymmetric stretch cause a change in dipole (IR-active) Polarizability change of one C=O bond lengthening is cancelled by the shortening of the other ndash no net polarizability (Raman-inactive) Some modes may be both IR and Raman-active others may be one or the other
19
Condition for raman spectroscopy
Raman spectra occurs as a result of oscillation of a dipole moment induced in a molecules by the oscillating electric field of an incident wave
As the induced dipole moment is directly proportional to the polarisability of the molecules the molecules must possess anisotropic polarisability which should change during molecular rotation or vibration for vibrational or rotational-vibrational raman spectra
Anisotropic polarisability depends upon the orientation of the molecules
In the presence of an electric field the electron cloud of an atom or molecules is distorted or polarised
20
Mutual Exclusion Principle
For molecules with a center of symmetry no IR active transitions are Raman active and vice versa
THORNSymmetric molecules IR-active vibrations are not Raman-active Raman-active vibrations are not IR-active
O = C = O O = C = O
Raman active Raman inactive IR inactive IR active
21
Raman Instrumentation
22
There are following component involves
1 Laser or source of light 2 Filter3 Sample holder 4 detector
23
The block design dispersive Raman scattering system
Radiation sources
Sample Wavelength
selector
Detector InGaAs or
Ge
RecorderDetector InGaAs or
Ge
RecorderDetector
InGaAs or Ge
Recorder
Block diagram
90
24
Flow diagram dispersive Raman scattering system
25
Schematic diagram dispersive raman scattering system
26
1 Laser or source of light
bull Lasers are generally the only source strong enough to scatter lots of light and lead to detectable raman scattering
bull Lasers operate using the principle of stimulated emission
bull Electronic population inversion is required to achieve gain via stimulated emission (before the fluorescence lifetime is reached)
bull Population inversion is achieved by ldquopumpingrdquo using lots of photons in a variety of laser gain media
27
List of Various laser source
SNo Laser wavelength01 NdYAG 1064nm
02 HeNe 633nm
03 Argon ion 488nm
04 GaAlAs diode 785nm
05 Co2 10600nm
06 Ti-Sapphire 800nm
28
A - HeNe laserbull Filled with 71 He amp Ne gas optimum output of 6328 Aring
bull High voltage excitation is preferred
B - NdYAG Systembull A typical laser system ndashthe neodymium-doped yttrium aluminum garnet or Nd+3
bull YAG is a cubic crystalline material
bull Crystal field splitting causes electronic energy level splitting
bull NdYAG laser are optically pumped using a flash tube or laser diodes
bull These are the one of the most common type of laser
bull It emits 1064 nm wavelength
29
2Filter bull It is therefore essential to have monochromatic radiations
bull For getting monochromatic radiations filters are used
bull They may be made of nickel oxide glass or quartz glass
bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator
30
3Sample holder bull For the study of raman effect the type of sample holder to be used
depends upon the intensity of sources the nature and availability of the sample
bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids
bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be
used for the study of raman spectra
bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy
31
4detectorbull Researchers traditionally used single points detectors such as
photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality
bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)
bull Sensitivity amp performance of modern CCD detectors are high
32
APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling
33
bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and
gypsum illustrating how Raman can be used for fast mineral ID
bull Gemstone and mineral identification
bull Fluid inclusions
bull Mineral and phase distribution in rock sections
bull Phase transitions
bull Mineral behavior under extreme conditions
34
Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance
35
Semiconductors
bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width
bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis
36
Life Sciences
bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level
bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure
37
Differences between IR and Raman methodsSNo Raman IR
01 It is due to the scattering of light by the vibrating molecules
It is the result of absorption of light by vibrating molecules
02 The vibration is Raman active if it causes a change in polarisability
Vibration is IR active if there is change in dipole moment
03 The molecule need not possess a permanent dipole moment
The vibration concerned should have a change in dipole moment due to that vibration
04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR
05 Sample preparation is not very elaborate it can be in any state
Sample preparation is elaborateGaseous samples can rarely be used
06 Gives an indication of covalent character in the molecule
Gives an indication of ionic character in the molecule
07 Cost of instrumentation is very high
Comparatively inexpensive
38
Advantages of Raman over IR
bull Water can be used as solvent bull Very suitable for biological samples in native state (because water
can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral
overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power
39
Advantages of IR over Ramanbull Simpler and cheaper instrumentation
bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio
bull Lower detection limit than (normal) Raman
bull Background fluorescence can overwhelm Raman
bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)
40
Several variations of Raman spectroscopy
1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal
bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)
bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977
bull A comprehensive theory of the effect was given by Lombardi and Birke
41
2 Resonance Raman spectroscopy The excitation wavelength is matched to an
electronic transition of the molecule or crystal so that vibrational modes associated with the excited electronic state are greatly enhanced This is useful for studying large molecules such as polypeptides which might show hundreds of bands in conventional Raman spectra It is also useful for associating normal modes with their observed frequency shifts
42
3 Surface-enhanced resonance Raman spectroscopy (SERRS) ndash A combination of SERS and resonance Raman spectroscopy that uses proximity to a surface to increase Raman intensity and excitation wavelength matched to the maximum absorbance of the molecule being analysed
4 Coherent anti-Stokes Raman spectroscopy (CARS) ndash
Two laser beams are used to generate a coherent anti-Stokes frequency beam which can be enhanced by resonance
43
5 Raman optical activity (ROA) ndash Measures vibrational optical activity by means of a small difference in the intensity of Raman scattering from chiral molecules in right- and left-circularly polarized incident light or equivalently a small circularly polarized component in the scattered light
6 Spatially offset Raman spectroscopy (SORS)
7 Spontaneous Raman spectroscopy (SRS) 8 Optical tweezers Raman spectroscopy (OTRS)
44
9 Angle-resolved Raman spectroscopy10 Inverse Raman spectroscopy11 Tip-enhanced Raman spectroscopy
(TERS) 12 Surface plasmon polariton enhanced
Raman scattering (SPPERS)13 Stand-off Remote Raman ndash 14 Fourier-transform Rama spectroscopyapplied
to photobiological systems
45
14
Presentation of Raman Spectra
lex = 1064 nm = 9399 cm-1
Breathing mode9399 ndash 992 = 8407 cm-1
Stretching mode9399 ndash 3063 = 6336 cm-1
15
Rayleigh Scattering- Occurs when incident EM radiation induces an oscillating dipole in a molecules which is re-radiated at the same frequency
Eugene Hecht Optics Addison-Wesley Reading MA 1998
bullElastic (l does not change)
bullRandom direction of emission
bullLittle energy lossbullof emission
bullLittle energy loss
4 2 20
4 2
8 ( ) (1 cos )( )sc
EE
d a
l
16
Raman ScatteringOccurs when monochromatic light is scattered light has been weakly modulated
by the characteristic frequencies of the molecules Raman spectroscopy measures the differences between the wavelengths of the
incident radiation and the scatted radiation
max 0
max max 0
max max 0
( ) cos 21 cos 2 ( )21 cos 2 ( )2
equilz zz
zzvib
zzvib
t E td r E tdr
d r E tdr
m a a
a
Selection rule v = plusmn1Overtones v = plusmn2 plusmn3 hellip
Must also have a change in polarizability
Classical Description does not suggest any difference between Stokes and Anti-Stokes intensities
1
0
vibhkTN e
N
17
The Raman polarization
The Raman Polarization is a property of waves that can oscillate with more than one orientation EMR or waves such as light and gravitational wave exhibit polarization
Polarization state - the shape traced out in a fixed plane by the electric vector as such a plane wave passes over it is a description of the polarization
Eg linear polarization circular polarization
elliptical polarization orthogonally polarization
Polarization changes are necessary to form the virtual state and hence the Raman effect
18
Condition for raman spectroscopyVibrational modes that are more polarizable are more Raman-active Examples ndash N2 (dinitrogen) symmetric stretch cause no change in dipole (IR-inactive) cause a change in the polarizability of the bond ndash as the bond gets longer it is more easily deformed (Raman -active)
ndash CO2 asymmetric stretch cause a change in dipole (IR-active) Polarizability change of one C=O bond lengthening is cancelled by the shortening of the other ndash no net polarizability (Raman-inactive) Some modes may be both IR and Raman-active others may be one or the other
19
Condition for raman spectroscopy
Raman spectra occurs as a result of oscillation of a dipole moment induced in a molecules by the oscillating electric field of an incident wave
As the induced dipole moment is directly proportional to the polarisability of the molecules the molecules must possess anisotropic polarisability which should change during molecular rotation or vibration for vibrational or rotational-vibrational raman spectra
Anisotropic polarisability depends upon the orientation of the molecules
In the presence of an electric field the electron cloud of an atom or molecules is distorted or polarised
20
Mutual Exclusion Principle
For molecules with a center of symmetry no IR active transitions are Raman active and vice versa
THORNSymmetric molecules IR-active vibrations are not Raman-active Raman-active vibrations are not IR-active
O = C = O O = C = O
Raman active Raman inactive IR inactive IR active
21
Raman Instrumentation
22
There are following component involves
1 Laser or source of light 2 Filter3 Sample holder 4 detector
23
The block design dispersive Raman scattering system
Radiation sources
Sample Wavelength
selector
Detector InGaAs or
Ge
RecorderDetector InGaAs or
Ge
RecorderDetector
InGaAs or Ge
Recorder
Block diagram
90
24
Flow diagram dispersive Raman scattering system
25
Schematic diagram dispersive raman scattering system
26
1 Laser or source of light
bull Lasers are generally the only source strong enough to scatter lots of light and lead to detectable raman scattering
bull Lasers operate using the principle of stimulated emission
bull Electronic population inversion is required to achieve gain via stimulated emission (before the fluorescence lifetime is reached)
bull Population inversion is achieved by ldquopumpingrdquo using lots of photons in a variety of laser gain media
27
List of Various laser source
SNo Laser wavelength01 NdYAG 1064nm
02 HeNe 633nm
03 Argon ion 488nm
04 GaAlAs diode 785nm
05 Co2 10600nm
06 Ti-Sapphire 800nm
28
A - HeNe laserbull Filled with 71 He amp Ne gas optimum output of 6328 Aring
bull High voltage excitation is preferred
B - NdYAG Systembull A typical laser system ndashthe neodymium-doped yttrium aluminum garnet or Nd+3
bull YAG is a cubic crystalline material
bull Crystal field splitting causes electronic energy level splitting
bull NdYAG laser are optically pumped using a flash tube or laser diodes
bull These are the one of the most common type of laser
bull It emits 1064 nm wavelength
29
2Filter bull It is therefore essential to have monochromatic radiations
bull For getting monochromatic radiations filters are used
bull They may be made of nickel oxide glass or quartz glass
bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator
30
3Sample holder bull For the study of raman effect the type of sample holder to be used
depends upon the intensity of sources the nature and availability of the sample
bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids
bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be
used for the study of raman spectra
bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy
31
4detectorbull Researchers traditionally used single points detectors such as
photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality
bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)
bull Sensitivity amp performance of modern CCD detectors are high
32
APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling
33
bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and
gypsum illustrating how Raman can be used for fast mineral ID
bull Gemstone and mineral identification
bull Fluid inclusions
bull Mineral and phase distribution in rock sections
bull Phase transitions
bull Mineral behavior under extreme conditions
34
Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance
35
Semiconductors
bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width
bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis
36
Life Sciences
bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level
bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure
37
Differences between IR and Raman methodsSNo Raman IR
01 It is due to the scattering of light by the vibrating molecules
It is the result of absorption of light by vibrating molecules
02 The vibration is Raman active if it causes a change in polarisability
Vibration is IR active if there is change in dipole moment
03 The molecule need not possess a permanent dipole moment
The vibration concerned should have a change in dipole moment due to that vibration
04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR
05 Sample preparation is not very elaborate it can be in any state
Sample preparation is elaborateGaseous samples can rarely be used
06 Gives an indication of covalent character in the molecule
Gives an indication of ionic character in the molecule
07 Cost of instrumentation is very high
Comparatively inexpensive
38
Advantages of Raman over IR
bull Water can be used as solvent bull Very suitable for biological samples in native state (because water
can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral
overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power
39
Advantages of IR over Ramanbull Simpler and cheaper instrumentation
bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio
bull Lower detection limit than (normal) Raman
bull Background fluorescence can overwhelm Raman
bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)
40
Several variations of Raman spectroscopy
1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal
bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)
bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977
bull A comprehensive theory of the effect was given by Lombardi and Birke
41
2 Resonance Raman spectroscopy The excitation wavelength is matched to an
electronic transition of the molecule or crystal so that vibrational modes associated with the excited electronic state are greatly enhanced This is useful for studying large molecules such as polypeptides which might show hundreds of bands in conventional Raman spectra It is also useful for associating normal modes with their observed frequency shifts
42
3 Surface-enhanced resonance Raman spectroscopy (SERRS) ndash A combination of SERS and resonance Raman spectroscopy that uses proximity to a surface to increase Raman intensity and excitation wavelength matched to the maximum absorbance of the molecule being analysed
4 Coherent anti-Stokes Raman spectroscopy (CARS) ndash
Two laser beams are used to generate a coherent anti-Stokes frequency beam which can be enhanced by resonance
43
5 Raman optical activity (ROA) ndash Measures vibrational optical activity by means of a small difference in the intensity of Raman scattering from chiral molecules in right- and left-circularly polarized incident light or equivalently a small circularly polarized component in the scattered light
6 Spatially offset Raman spectroscopy (SORS)
7 Spontaneous Raman spectroscopy (SRS) 8 Optical tweezers Raman spectroscopy (OTRS)
44
9 Angle-resolved Raman spectroscopy10 Inverse Raman spectroscopy11 Tip-enhanced Raman spectroscopy
(TERS) 12 Surface plasmon polariton enhanced
Raman scattering (SPPERS)13 Stand-off Remote Raman ndash 14 Fourier-transform Rama spectroscopyapplied
to photobiological systems
45
15
Rayleigh Scattering- Occurs when incident EM radiation induces an oscillating dipole in a molecules which is re-radiated at the same frequency
Eugene Hecht Optics Addison-Wesley Reading MA 1998
bullElastic (l does not change)
bullRandom direction of emission
bullLittle energy lossbullof emission
bullLittle energy loss
4 2 20
4 2
8 ( ) (1 cos )( )sc
EE
d a
l
16
Raman ScatteringOccurs when monochromatic light is scattered light has been weakly modulated
by the characteristic frequencies of the molecules Raman spectroscopy measures the differences between the wavelengths of the
incident radiation and the scatted radiation
max 0
max max 0
max max 0
( ) cos 21 cos 2 ( )21 cos 2 ( )2
equilz zz
zzvib
zzvib
t E td r E tdr
d r E tdr
m a a
a
Selection rule v = plusmn1Overtones v = plusmn2 plusmn3 hellip
Must also have a change in polarizability
Classical Description does not suggest any difference between Stokes and Anti-Stokes intensities
1
0
vibhkTN e
N
17
The Raman polarization
The Raman Polarization is a property of waves that can oscillate with more than one orientation EMR or waves such as light and gravitational wave exhibit polarization
Polarization state - the shape traced out in a fixed plane by the electric vector as such a plane wave passes over it is a description of the polarization
Eg linear polarization circular polarization
elliptical polarization orthogonally polarization
Polarization changes are necessary to form the virtual state and hence the Raman effect
18
Condition for raman spectroscopyVibrational modes that are more polarizable are more Raman-active Examples ndash N2 (dinitrogen) symmetric stretch cause no change in dipole (IR-inactive) cause a change in the polarizability of the bond ndash as the bond gets longer it is more easily deformed (Raman -active)
ndash CO2 asymmetric stretch cause a change in dipole (IR-active) Polarizability change of one C=O bond lengthening is cancelled by the shortening of the other ndash no net polarizability (Raman-inactive) Some modes may be both IR and Raman-active others may be one or the other
19
Condition for raman spectroscopy
Raman spectra occurs as a result of oscillation of a dipole moment induced in a molecules by the oscillating electric field of an incident wave
As the induced dipole moment is directly proportional to the polarisability of the molecules the molecules must possess anisotropic polarisability which should change during molecular rotation or vibration for vibrational or rotational-vibrational raman spectra
Anisotropic polarisability depends upon the orientation of the molecules
In the presence of an electric field the electron cloud of an atom or molecules is distorted or polarised
20
Mutual Exclusion Principle
For molecules with a center of symmetry no IR active transitions are Raman active and vice versa
THORNSymmetric molecules IR-active vibrations are not Raman-active Raman-active vibrations are not IR-active
O = C = O O = C = O
Raman active Raman inactive IR inactive IR active
21
Raman Instrumentation
22
There are following component involves
1 Laser or source of light 2 Filter3 Sample holder 4 detector
23
The block design dispersive Raman scattering system
Radiation sources
Sample Wavelength
selector
Detector InGaAs or
Ge
RecorderDetector InGaAs or
Ge
RecorderDetector
InGaAs or Ge
Recorder
Block diagram
90
24
Flow diagram dispersive Raman scattering system
25
Schematic diagram dispersive raman scattering system
26
1 Laser or source of light
bull Lasers are generally the only source strong enough to scatter lots of light and lead to detectable raman scattering
bull Lasers operate using the principle of stimulated emission
bull Electronic population inversion is required to achieve gain via stimulated emission (before the fluorescence lifetime is reached)
bull Population inversion is achieved by ldquopumpingrdquo using lots of photons in a variety of laser gain media
27
List of Various laser source
SNo Laser wavelength01 NdYAG 1064nm
02 HeNe 633nm
03 Argon ion 488nm
04 GaAlAs diode 785nm
05 Co2 10600nm
06 Ti-Sapphire 800nm
28
A - HeNe laserbull Filled with 71 He amp Ne gas optimum output of 6328 Aring
bull High voltage excitation is preferred
B - NdYAG Systembull A typical laser system ndashthe neodymium-doped yttrium aluminum garnet or Nd+3
bull YAG is a cubic crystalline material
bull Crystal field splitting causes electronic energy level splitting
bull NdYAG laser are optically pumped using a flash tube or laser diodes
bull These are the one of the most common type of laser
bull It emits 1064 nm wavelength
29
2Filter bull It is therefore essential to have monochromatic radiations
bull For getting monochromatic radiations filters are used
bull They may be made of nickel oxide glass or quartz glass
bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator
30
3Sample holder bull For the study of raman effect the type of sample holder to be used
depends upon the intensity of sources the nature and availability of the sample
bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids
bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be
used for the study of raman spectra
bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy
31
4detectorbull Researchers traditionally used single points detectors such as
photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality
bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)
bull Sensitivity amp performance of modern CCD detectors are high
32
APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling
33
bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and
gypsum illustrating how Raman can be used for fast mineral ID
bull Gemstone and mineral identification
bull Fluid inclusions
bull Mineral and phase distribution in rock sections
bull Phase transitions
bull Mineral behavior under extreme conditions
34
Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance
35
Semiconductors
bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width
bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis
36
Life Sciences
bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level
bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure
37
Differences between IR and Raman methodsSNo Raman IR
01 It is due to the scattering of light by the vibrating molecules
It is the result of absorption of light by vibrating molecules
02 The vibration is Raman active if it causes a change in polarisability
Vibration is IR active if there is change in dipole moment
03 The molecule need not possess a permanent dipole moment
The vibration concerned should have a change in dipole moment due to that vibration
04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR
05 Sample preparation is not very elaborate it can be in any state
Sample preparation is elaborateGaseous samples can rarely be used
06 Gives an indication of covalent character in the molecule
Gives an indication of ionic character in the molecule
07 Cost of instrumentation is very high
Comparatively inexpensive
38
Advantages of Raman over IR
bull Water can be used as solvent bull Very suitable for biological samples in native state (because water
can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral
overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power
39
Advantages of IR over Ramanbull Simpler and cheaper instrumentation
bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio
bull Lower detection limit than (normal) Raman
bull Background fluorescence can overwhelm Raman
bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)
40
Several variations of Raman spectroscopy
1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal
bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)
bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977
bull A comprehensive theory of the effect was given by Lombardi and Birke
41
2 Resonance Raman spectroscopy The excitation wavelength is matched to an
electronic transition of the molecule or crystal so that vibrational modes associated with the excited electronic state are greatly enhanced This is useful for studying large molecules such as polypeptides which might show hundreds of bands in conventional Raman spectra It is also useful for associating normal modes with their observed frequency shifts
42
3 Surface-enhanced resonance Raman spectroscopy (SERRS) ndash A combination of SERS and resonance Raman spectroscopy that uses proximity to a surface to increase Raman intensity and excitation wavelength matched to the maximum absorbance of the molecule being analysed
4 Coherent anti-Stokes Raman spectroscopy (CARS) ndash
Two laser beams are used to generate a coherent anti-Stokes frequency beam which can be enhanced by resonance
43
5 Raman optical activity (ROA) ndash Measures vibrational optical activity by means of a small difference in the intensity of Raman scattering from chiral molecules in right- and left-circularly polarized incident light or equivalently a small circularly polarized component in the scattered light
6 Spatially offset Raman spectroscopy (SORS)
7 Spontaneous Raman spectroscopy (SRS) 8 Optical tweezers Raman spectroscopy (OTRS)
44
9 Angle-resolved Raman spectroscopy10 Inverse Raman spectroscopy11 Tip-enhanced Raman spectroscopy
(TERS) 12 Surface plasmon polariton enhanced
Raman scattering (SPPERS)13 Stand-off Remote Raman ndash 14 Fourier-transform Rama spectroscopyapplied
to photobiological systems
45
16
Raman ScatteringOccurs when monochromatic light is scattered light has been weakly modulated
by the characteristic frequencies of the molecules Raman spectroscopy measures the differences between the wavelengths of the
incident radiation and the scatted radiation
max 0
max max 0
max max 0
( ) cos 21 cos 2 ( )21 cos 2 ( )2
equilz zz
zzvib
zzvib
t E td r E tdr
d r E tdr
m a a
a
Selection rule v = plusmn1Overtones v = plusmn2 plusmn3 hellip
Must also have a change in polarizability
Classical Description does not suggest any difference between Stokes and Anti-Stokes intensities
1
0
vibhkTN e
N
17
The Raman polarization
The Raman Polarization is a property of waves that can oscillate with more than one orientation EMR or waves such as light and gravitational wave exhibit polarization
Polarization state - the shape traced out in a fixed plane by the electric vector as such a plane wave passes over it is a description of the polarization
Eg linear polarization circular polarization
elliptical polarization orthogonally polarization
Polarization changes are necessary to form the virtual state and hence the Raman effect
18
Condition for raman spectroscopyVibrational modes that are more polarizable are more Raman-active Examples ndash N2 (dinitrogen) symmetric stretch cause no change in dipole (IR-inactive) cause a change in the polarizability of the bond ndash as the bond gets longer it is more easily deformed (Raman -active)
ndash CO2 asymmetric stretch cause a change in dipole (IR-active) Polarizability change of one C=O bond lengthening is cancelled by the shortening of the other ndash no net polarizability (Raman-inactive) Some modes may be both IR and Raman-active others may be one or the other
19
Condition for raman spectroscopy
Raman spectra occurs as a result of oscillation of a dipole moment induced in a molecules by the oscillating electric field of an incident wave
As the induced dipole moment is directly proportional to the polarisability of the molecules the molecules must possess anisotropic polarisability which should change during molecular rotation or vibration for vibrational or rotational-vibrational raman spectra
Anisotropic polarisability depends upon the orientation of the molecules
In the presence of an electric field the electron cloud of an atom or molecules is distorted or polarised
20
Mutual Exclusion Principle
For molecules with a center of symmetry no IR active transitions are Raman active and vice versa
THORNSymmetric molecules IR-active vibrations are not Raman-active Raman-active vibrations are not IR-active
O = C = O O = C = O
Raman active Raman inactive IR inactive IR active
21
Raman Instrumentation
22
There are following component involves
1 Laser or source of light 2 Filter3 Sample holder 4 detector
23
The block design dispersive Raman scattering system
Radiation sources
Sample Wavelength
selector
Detector InGaAs or
Ge
RecorderDetector InGaAs or
Ge
RecorderDetector
InGaAs or Ge
Recorder
Block diagram
90
24
Flow diagram dispersive Raman scattering system
25
Schematic diagram dispersive raman scattering system
26
1 Laser or source of light
bull Lasers are generally the only source strong enough to scatter lots of light and lead to detectable raman scattering
bull Lasers operate using the principle of stimulated emission
bull Electronic population inversion is required to achieve gain via stimulated emission (before the fluorescence lifetime is reached)
bull Population inversion is achieved by ldquopumpingrdquo using lots of photons in a variety of laser gain media
27
List of Various laser source
SNo Laser wavelength01 NdYAG 1064nm
02 HeNe 633nm
03 Argon ion 488nm
04 GaAlAs diode 785nm
05 Co2 10600nm
06 Ti-Sapphire 800nm
28
A - HeNe laserbull Filled with 71 He amp Ne gas optimum output of 6328 Aring
bull High voltage excitation is preferred
B - NdYAG Systembull A typical laser system ndashthe neodymium-doped yttrium aluminum garnet or Nd+3
bull YAG is a cubic crystalline material
bull Crystal field splitting causes electronic energy level splitting
bull NdYAG laser are optically pumped using a flash tube or laser diodes
bull These are the one of the most common type of laser
bull It emits 1064 nm wavelength
29
2Filter bull It is therefore essential to have monochromatic radiations
bull For getting monochromatic radiations filters are used
bull They may be made of nickel oxide glass or quartz glass
bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator
30
3Sample holder bull For the study of raman effect the type of sample holder to be used
depends upon the intensity of sources the nature and availability of the sample
bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids
bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be
used for the study of raman spectra
bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy
31
4detectorbull Researchers traditionally used single points detectors such as
photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality
bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)
bull Sensitivity amp performance of modern CCD detectors are high
32
APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling
33
bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and
gypsum illustrating how Raman can be used for fast mineral ID
bull Gemstone and mineral identification
bull Fluid inclusions
bull Mineral and phase distribution in rock sections
bull Phase transitions
bull Mineral behavior under extreme conditions
34
Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance
35
Semiconductors
bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width
bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis
36
Life Sciences
bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level
bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure
37
Differences between IR and Raman methodsSNo Raman IR
01 It is due to the scattering of light by the vibrating molecules
It is the result of absorption of light by vibrating molecules
02 The vibration is Raman active if it causes a change in polarisability
Vibration is IR active if there is change in dipole moment
03 The molecule need not possess a permanent dipole moment
The vibration concerned should have a change in dipole moment due to that vibration
04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR
05 Sample preparation is not very elaborate it can be in any state
Sample preparation is elaborateGaseous samples can rarely be used
06 Gives an indication of covalent character in the molecule
Gives an indication of ionic character in the molecule
07 Cost of instrumentation is very high
Comparatively inexpensive
38
Advantages of Raman over IR
bull Water can be used as solvent bull Very suitable for biological samples in native state (because water
can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral
overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power
39
Advantages of IR over Ramanbull Simpler and cheaper instrumentation
bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio
bull Lower detection limit than (normal) Raman
bull Background fluorescence can overwhelm Raman
bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)
40
Several variations of Raman spectroscopy
1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal
bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)
bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977
bull A comprehensive theory of the effect was given by Lombardi and Birke
41
2 Resonance Raman spectroscopy The excitation wavelength is matched to an
electronic transition of the molecule or crystal so that vibrational modes associated with the excited electronic state are greatly enhanced This is useful for studying large molecules such as polypeptides which might show hundreds of bands in conventional Raman spectra It is also useful for associating normal modes with their observed frequency shifts
42
3 Surface-enhanced resonance Raman spectroscopy (SERRS) ndash A combination of SERS and resonance Raman spectroscopy that uses proximity to a surface to increase Raman intensity and excitation wavelength matched to the maximum absorbance of the molecule being analysed
4 Coherent anti-Stokes Raman spectroscopy (CARS) ndash
Two laser beams are used to generate a coherent anti-Stokes frequency beam which can be enhanced by resonance
43
5 Raman optical activity (ROA) ndash Measures vibrational optical activity by means of a small difference in the intensity of Raman scattering from chiral molecules in right- and left-circularly polarized incident light or equivalently a small circularly polarized component in the scattered light
6 Spatially offset Raman spectroscopy (SORS)
7 Spontaneous Raman spectroscopy (SRS) 8 Optical tweezers Raman spectroscopy (OTRS)
44
9 Angle-resolved Raman spectroscopy10 Inverse Raman spectroscopy11 Tip-enhanced Raman spectroscopy
(TERS) 12 Surface plasmon polariton enhanced
Raman scattering (SPPERS)13 Stand-off Remote Raman ndash 14 Fourier-transform Rama spectroscopyapplied
to photobiological systems
45
17
The Raman polarization
The Raman Polarization is a property of waves that can oscillate with more than one orientation EMR or waves such as light and gravitational wave exhibit polarization
Polarization state - the shape traced out in a fixed plane by the electric vector as such a plane wave passes over it is a description of the polarization
Eg linear polarization circular polarization
elliptical polarization orthogonally polarization
Polarization changes are necessary to form the virtual state and hence the Raman effect
18
Condition for raman spectroscopyVibrational modes that are more polarizable are more Raman-active Examples ndash N2 (dinitrogen) symmetric stretch cause no change in dipole (IR-inactive) cause a change in the polarizability of the bond ndash as the bond gets longer it is more easily deformed (Raman -active)
ndash CO2 asymmetric stretch cause a change in dipole (IR-active) Polarizability change of one C=O bond lengthening is cancelled by the shortening of the other ndash no net polarizability (Raman-inactive) Some modes may be both IR and Raman-active others may be one or the other
19
Condition for raman spectroscopy
Raman spectra occurs as a result of oscillation of a dipole moment induced in a molecules by the oscillating electric field of an incident wave
As the induced dipole moment is directly proportional to the polarisability of the molecules the molecules must possess anisotropic polarisability which should change during molecular rotation or vibration for vibrational or rotational-vibrational raman spectra
Anisotropic polarisability depends upon the orientation of the molecules
In the presence of an electric field the electron cloud of an atom or molecules is distorted or polarised
20
Mutual Exclusion Principle
For molecules with a center of symmetry no IR active transitions are Raman active and vice versa
THORNSymmetric molecules IR-active vibrations are not Raman-active Raman-active vibrations are not IR-active
O = C = O O = C = O
Raman active Raman inactive IR inactive IR active
21
Raman Instrumentation
22
There are following component involves
1 Laser or source of light 2 Filter3 Sample holder 4 detector
23
The block design dispersive Raman scattering system
Radiation sources
Sample Wavelength
selector
Detector InGaAs or
Ge
RecorderDetector InGaAs or
Ge
RecorderDetector
InGaAs or Ge
Recorder
Block diagram
90
24
Flow diagram dispersive Raman scattering system
25
Schematic diagram dispersive raman scattering system
26
1 Laser or source of light
bull Lasers are generally the only source strong enough to scatter lots of light and lead to detectable raman scattering
bull Lasers operate using the principle of stimulated emission
bull Electronic population inversion is required to achieve gain via stimulated emission (before the fluorescence lifetime is reached)
bull Population inversion is achieved by ldquopumpingrdquo using lots of photons in a variety of laser gain media
27
List of Various laser source
SNo Laser wavelength01 NdYAG 1064nm
02 HeNe 633nm
03 Argon ion 488nm
04 GaAlAs diode 785nm
05 Co2 10600nm
06 Ti-Sapphire 800nm
28
A - HeNe laserbull Filled with 71 He amp Ne gas optimum output of 6328 Aring
bull High voltage excitation is preferred
B - NdYAG Systembull A typical laser system ndashthe neodymium-doped yttrium aluminum garnet or Nd+3
bull YAG is a cubic crystalline material
bull Crystal field splitting causes electronic energy level splitting
bull NdYAG laser are optically pumped using a flash tube or laser diodes
bull These are the one of the most common type of laser
bull It emits 1064 nm wavelength
29
2Filter bull It is therefore essential to have monochromatic radiations
bull For getting monochromatic radiations filters are used
bull They may be made of nickel oxide glass or quartz glass
bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator
30
3Sample holder bull For the study of raman effect the type of sample holder to be used
depends upon the intensity of sources the nature and availability of the sample
bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids
bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be
used for the study of raman spectra
bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy
31
4detectorbull Researchers traditionally used single points detectors such as
photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality
bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)
bull Sensitivity amp performance of modern CCD detectors are high
32
APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling
33
bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and
gypsum illustrating how Raman can be used for fast mineral ID
bull Gemstone and mineral identification
bull Fluid inclusions
bull Mineral and phase distribution in rock sections
bull Phase transitions
bull Mineral behavior under extreme conditions
34
Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance
35
Semiconductors
bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width
bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis
36
Life Sciences
bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level
bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure
37
Differences between IR and Raman methodsSNo Raman IR
01 It is due to the scattering of light by the vibrating molecules
It is the result of absorption of light by vibrating molecules
02 The vibration is Raman active if it causes a change in polarisability
Vibration is IR active if there is change in dipole moment
03 The molecule need not possess a permanent dipole moment
The vibration concerned should have a change in dipole moment due to that vibration
04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR
05 Sample preparation is not very elaborate it can be in any state
Sample preparation is elaborateGaseous samples can rarely be used
06 Gives an indication of covalent character in the molecule
Gives an indication of ionic character in the molecule
07 Cost of instrumentation is very high
Comparatively inexpensive
38
Advantages of Raman over IR
bull Water can be used as solvent bull Very suitable for biological samples in native state (because water
can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral
overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power
39
Advantages of IR over Ramanbull Simpler and cheaper instrumentation
bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio
bull Lower detection limit than (normal) Raman
bull Background fluorescence can overwhelm Raman
bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)
40
Several variations of Raman spectroscopy
1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal
bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)
bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977
bull A comprehensive theory of the effect was given by Lombardi and Birke
41
2 Resonance Raman spectroscopy The excitation wavelength is matched to an
electronic transition of the molecule or crystal so that vibrational modes associated with the excited electronic state are greatly enhanced This is useful for studying large molecules such as polypeptides which might show hundreds of bands in conventional Raman spectra It is also useful for associating normal modes with their observed frequency shifts
42
3 Surface-enhanced resonance Raman spectroscopy (SERRS) ndash A combination of SERS and resonance Raman spectroscopy that uses proximity to a surface to increase Raman intensity and excitation wavelength matched to the maximum absorbance of the molecule being analysed
4 Coherent anti-Stokes Raman spectroscopy (CARS) ndash
Two laser beams are used to generate a coherent anti-Stokes frequency beam which can be enhanced by resonance
43
5 Raman optical activity (ROA) ndash Measures vibrational optical activity by means of a small difference in the intensity of Raman scattering from chiral molecules in right- and left-circularly polarized incident light or equivalently a small circularly polarized component in the scattered light
6 Spatially offset Raman spectroscopy (SORS)
7 Spontaneous Raman spectroscopy (SRS) 8 Optical tweezers Raman spectroscopy (OTRS)
44
9 Angle-resolved Raman spectroscopy10 Inverse Raman spectroscopy11 Tip-enhanced Raman spectroscopy
(TERS) 12 Surface plasmon polariton enhanced
Raman scattering (SPPERS)13 Stand-off Remote Raman ndash 14 Fourier-transform Rama spectroscopyapplied
to photobiological systems
45
18
Condition for raman spectroscopyVibrational modes that are more polarizable are more Raman-active Examples ndash N2 (dinitrogen) symmetric stretch cause no change in dipole (IR-inactive) cause a change in the polarizability of the bond ndash as the bond gets longer it is more easily deformed (Raman -active)
ndash CO2 asymmetric stretch cause a change in dipole (IR-active) Polarizability change of one C=O bond lengthening is cancelled by the shortening of the other ndash no net polarizability (Raman-inactive) Some modes may be both IR and Raman-active others may be one or the other
19
Condition for raman spectroscopy
Raman spectra occurs as a result of oscillation of a dipole moment induced in a molecules by the oscillating electric field of an incident wave
As the induced dipole moment is directly proportional to the polarisability of the molecules the molecules must possess anisotropic polarisability which should change during molecular rotation or vibration for vibrational or rotational-vibrational raman spectra
Anisotropic polarisability depends upon the orientation of the molecules
In the presence of an electric field the electron cloud of an atom or molecules is distorted or polarised
20
Mutual Exclusion Principle
For molecules with a center of symmetry no IR active transitions are Raman active and vice versa
THORNSymmetric molecules IR-active vibrations are not Raman-active Raman-active vibrations are not IR-active
O = C = O O = C = O
Raman active Raman inactive IR inactive IR active
21
Raman Instrumentation
22
There are following component involves
1 Laser or source of light 2 Filter3 Sample holder 4 detector
23
The block design dispersive Raman scattering system
Radiation sources
Sample Wavelength
selector
Detector InGaAs or
Ge
RecorderDetector InGaAs or
Ge
RecorderDetector
InGaAs or Ge
Recorder
Block diagram
90
24
Flow diagram dispersive Raman scattering system
25
Schematic diagram dispersive raman scattering system
26
1 Laser or source of light
bull Lasers are generally the only source strong enough to scatter lots of light and lead to detectable raman scattering
bull Lasers operate using the principle of stimulated emission
bull Electronic population inversion is required to achieve gain via stimulated emission (before the fluorescence lifetime is reached)
bull Population inversion is achieved by ldquopumpingrdquo using lots of photons in a variety of laser gain media
27
List of Various laser source
SNo Laser wavelength01 NdYAG 1064nm
02 HeNe 633nm
03 Argon ion 488nm
04 GaAlAs diode 785nm
05 Co2 10600nm
06 Ti-Sapphire 800nm
28
A - HeNe laserbull Filled with 71 He amp Ne gas optimum output of 6328 Aring
bull High voltage excitation is preferred
B - NdYAG Systembull A typical laser system ndashthe neodymium-doped yttrium aluminum garnet or Nd+3
bull YAG is a cubic crystalline material
bull Crystal field splitting causes electronic energy level splitting
bull NdYAG laser are optically pumped using a flash tube or laser diodes
bull These are the one of the most common type of laser
bull It emits 1064 nm wavelength
29
2Filter bull It is therefore essential to have monochromatic radiations
bull For getting monochromatic radiations filters are used
bull They may be made of nickel oxide glass or quartz glass
bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator
30
3Sample holder bull For the study of raman effect the type of sample holder to be used
depends upon the intensity of sources the nature and availability of the sample
bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids
bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be
used for the study of raman spectra
bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy
31
4detectorbull Researchers traditionally used single points detectors such as
photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality
bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)
bull Sensitivity amp performance of modern CCD detectors are high
32
APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling
33
bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and
gypsum illustrating how Raman can be used for fast mineral ID
bull Gemstone and mineral identification
bull Fluid inclusions
bull Mineral and phase distribution in rock sections
bull Phase transitions
bull Mineral behavior under extreme conditions
34
Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance
35
Semiconductors
bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width
bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis
36
Life Sciences
bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level
bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure
37
Differences between IR and Raman methodsSNo Raman IR
01 It is due to the scattering of light by the vibrating molecules
It is the result of absorption of light by vibrating molecules
02 The vibration is Raman active if it causes a change in polarisability
Vibration is IR active if there is change in dipole moment
03 The molecule need not possess a permanent dipole moment
The vibration concerned should have a change in dipole moment due to that vibration
04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR
05 Sample preparation is not very elaborate it can be in any state
Sample preparation is elaborateGaseous samples can rarely be used
06 Gives an indication of covalent character in the molecule
Gives an indication of ionic character in the molecule
07 Cost of instrumentation is very high
Comparatively inexpensive
38
Advantages of Raman over IR
bull Water can be used as solvent bull Very suitable for biological samples in native state (because water
can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral
overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power
39
Advantages of IR over Ramanbull Simpler and cheaper instrumentation
bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio
bull Lower detection limit than (normal) Raman
bull Background fluorescence can overwhelm Raman
bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)
40
Several variations of Raman spectroscopy
1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal
bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)
bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977
bull A comprehensive theory of the effect was given by Lombardi and Birke
41
2 Resonance Raman spectroscopy The excitation wavelength is matched to an
electronic transition of the molecule or crystal so that vibrational modes associated with the excited electronic state are greatly enhanced This is useful for studying large molecules such as polypeptides which might show hundreds of bands in conventional Raman spectra It is also useful for associating normal modes with their observed frequency shifts
42
3 Surface-enhanced resonance Raman spectroscopy (SERRS) ndash A combination of SERS and resonance Raman spectroscopy that uses proximity to a surface to increase Raman intensity and excitation wavelength matched to the maximum absorbance of the molecule being analysed
4 Coherent anti-Stokes Raman spectroscopy (CARS) ndash
Two laser beams are used to generate a coherent anti-Stokes frequency beam which can be enhanced by resonance
43
5 Raman optical activity (ROA) ndash Measures vibrational optical activity by means of a small difference in the intensity of Raman scattering from chiral molecules in right- and left-circularly polarized incident light or equivalently a small circularly polarized component in the scattered light
6 Spatially offset Raman spectroscopy (SORS)
7 Spontaneous Raman spectroscopy (SRS) 8 Optical tweezers Raman spectroscopy (OTRS)
44
9 Angle-resolved Raman spectroscopy10 Inverse Raman spectroscopy11 Tip-enhanced Raman spectroscopy
(TERS) 12 Surface plasmon polariton enhanced
Raman scattering (SPPERS)13 Stand-off Remote Raman ndash 14 Fourier-transform Rama spectroscopyapplied
to photobiological systems
45
19
Condition for raman spectroscopy
Raman spectra occurs as a result of oscillation of a dipole moment induced in a molecules by the oscillating electric field of an incident wave
As the induced dipole moment is directly proportional to the polarisability of the molecules the molecules must possess anisotropic polarisability which should change during molecular rotation or vibration for vibrational or rotational-vibrational raman spectra
Anisotropic polarisability depends upon the orientation of the molecules
In the presence of an electric field the electron cloud of an atom or molecules is distorted or polarised
20
Mutual Exclusion Principle
For molecules with a center of symmetry no IR active transitions are Raman active and vice versa
THORNSymmetric molecules IR-active vibrations are not Raman-active Raman-active vibrations are not IR-active
O = C = O O = C = O
Raman active Raman inactive IR inactive IR active
21
Raman Instrumentation
22
There are following component involves
1 Laser or source of light 2 Filter3 Sample holder 4 detector
23
The block design dispersive Raman scattering system
Radiation sources
Sample Wavelength
selector
Detector InGaAs or
Ge
RecorderDetector InGaAs or
Ge
RecorderDetector
InGaAs or Ge
Recorder
Block diagram
90
24
Flow diagram dispersive Raman scattering system
25
Schematic diagram dispersive raman scattering system
26
1 Laser or source of light
bull Lasers are generally the only source strong enough to scatter lots of light and lead to detectable raman scattering
bull Lasers operate using the principle of stimulated emission
bull Electronic population inversion is required to achieve gain via stimulated emission (before the fluorescence lifetime is reached)
bull Population inversion is achieved by ldquopumpingrdquo using lots of photons in a variety of laser gain media
27
List of Various laser source
SNo Laser wavelength01 NdYAG 1064nm
02 HeNe 633nm
03 Argon ion 488nm
04 GaAlAs diode 785nm
05 Co2 10600nm
06 Ti-Sapphire 800nm
28
A - HeNe laserbull Filled with 71 He amp Ne gas optimum output of 6328 Aring
bull High voltage excitation is preferred
B - NdYAG Systembull A typical laser system ndashthe neodymium-doped yttrium aluminum garnet or Nd+3
bull YAG is a cubic crystalline material
bull Crystal field splitting causes electronic energy level splitting
bull NdYAG laser are optically pumped using a flash tube or laser diodes
bull These are the one of the most common type of laser
bull It emits 1064 nm wavelength
29
2Filter bull It is therefore essential to have monochromatic radiations
bull For getting monochromatic radiations filters are used
bull They may be made of nickel oxide glass or quartz glass
bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator
30
3Sample holder bull For the study of raman effect the type of sample holder to be used
depends upon the intensity of sources the nature and availability of the sample
bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids
bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be
used for the study of raman spectra
bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy
31
4detectorbull Researchers traditionally used single points detectors such as
photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality
bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)
bull Sensitivity amp performance of modern CCD detectors are high
32
APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling
33
bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and
gypsum illustrating how Raman can be used for fast mineral ID
bull Gemstone and mineral identification
bull Fluid inclusions
bull Mineral and phase distribution in rock sections
bull Phase transitions
bull Mineral behavior under extreme conditions
34
Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance
35
Semiconductors
bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width
bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis
36
Life Sciences
bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level
bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure
37
Differences between IR and Raman methodsSNo Raman IR
01 It is due to the scattering of light by the vibrating molecules
It is the result of absorption of light by vibrating molecules
02 The vibration is Raman active if it causes a change in polarisability
Vibration is IR active if there is change in dipole moment
03 The molecule need not possess a permanent dipole moment
The vibration concerned should have a change in dipole moment due to that vibration
04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR
05 Sample preparation is not very elaborate it can be in any state
Sample preparation is elaborateGaseous samples can rarely be used
06 Gives an indication of covalent character in the molecule
Gives an indication of ionic character in the molecule
07 Cost of instrumentation is very high
Comparatively inexpensive
38
Advantages of Raman over IR
bull Water can be used as solvent bull Very suitable for biological samples in native state (because water
can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral
overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power
39
Advantages of IR over Ramanbull Simpler and cheaper instrumentation
bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio
bull Lower detection limit than (normal) Raman
bull Background fluorescence can overwhelm Raman
bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)
40
Several variations of Raman spectroscopy
1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal
bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)
bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977
bull A comprehensive theory of the effect was given by Lombardi and Birke
41
2 Resonance Raman spectroscopy The excitation wavelength is matched to an
electronic transition of the molecule or crystal so that vibrational modes associated with the excited electronic state are greatly enhanced This is useful for studying large molecules such as polypeptides which might show hundreds of bands in conventional Raman spectra It is also useful for associating normal modes with their observed frequency shifts
42
3 Surface-enhanced resonance Raman spectroscopy (SERRS) ndash A combination of SERS and resonance Raman spectroscopy that uses proximity to a surface to increase Raman intensity and excitation wavelength matched to the maximum absorbance of the molecule being analysed
4 Coherent anti-Stokes Raman spectroscopy (CARS) ndash
Two laser beams are used to generate a coherent anti-Stokes frequency beam which can be enhanced by resonance
43
5 Raman optical activity (ROA) ndash Measures vibrational optical activity by means of a small difference in the intensity of Raman scattering from chiral molecules in right- and left-circularly polarized incident light or equivalently a small circularly polarized component in the scattered light
6 Spatially offset Raman spectroscopy (SORS)
7 Spontaneous Raman spectroscopy (SRS) 8 Optical tweezers Raman spectroscopy (OTRS)
44
9 Angle-resolved Raman spectroscopy10 Inverse Raman spectroscopy11 Tip-enhanced Raman spectroscopy
(TERS) 12 Surface plasmon polariton enhanced
Raman scattering (SPPERS)13 Stand-off Remote Raman ndash 14 Fourier-transform Rama spectroscopyapplied
to photobiological systems
45
20
Mutual Exclusion Principle
For molecules with a center of symmetry no IR active transitions are Raman active and vice versa
THORNSymmetric molecules IR-active vibrations are not Raman-active Raman-active vibrations are not IR-active
O = C = O O = C = O
Raman active Raman inactive IR inactive IR active
21
Raman Instrumentation
22
There are following component involves
1 Laser or source of light 2 Filter3 Sample holder 4 detector
23
The block design dispersive Raman scattering system
Radiation sources
Sample Wavelength
selector
Detector InGaAs or
Ge
RecorderDetector InGaAs or
Ge
RecorderDetector
InGaAs or Ge
Recorder
Block diagram
90
24
Flow diagram dispersive Raman scattering system
25
Schematic diagram dispersive raman scattering system
26
1 Laser or source of light
bull Lasers are generally the only source strong enough to scatter lots of light and lead to detectable raman scattering
bull Lasers operate using the principle of stimulated emission
bull Electronic population inversion is required to achieve gain via stimulated emission (before the fluorescence lifetime is reached)
bull Population inversion is achieved by ldquopumpingrdquo using lots of photons in a variety of laser gain media
27
List of Various laser source
SNo Laser wavelength01 NdYAG 1064nm
02 HeNe 633nm
03 Argon ion 488nm
04 GaAlAs diode 785nm
05 Co2 10600nm
06 Ti-Sapphire 800nm
28
A - HeNe laserbull Filled with 71 He amp Ne gas optimum output of 6328 Aring
bull High voltage excitation is preferred
B - NdYAG Systembull A typical laser system ndashthe neodymium-doped yttrium aluminum garnet or Nd+3
bull YAG is a cubic crystalline material
bull Crystal field splitting causes electronic energy level splitting
bull NdYAG laser are optically pumped using a flash tube or laser diodes
bull These are the one of the most common type of laser
bull It emits 1064 nm wavelength
29
2Filter bull It is therefore essential to have monochromatic radiations
bull For getting monochromatic radiations filters are used
bull They may be made of nickel oxide glass or quartz glass
bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator
30
3Sample holder bull For the study of raman effect the type of sample holder to be used
depends upon the intensity of sources the nature and availability of the sample
bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids
bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be
used for the study of raman spectra
bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy
31
4detectorbull Researchers traditionally used single points detectors such as
photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality
bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)
bull Sensitivity amp performance of modern CCD detectors are high
32
APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling
33
bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and
gypsum illustrating how Raman can be used for fast mineral ID
bull Gemstone and mineral identification
bull Fluid inclusions
bull Mineral and phase distribution in rock sections
bull Phase transitions
bull Mineral behavior under extreme conditions
34
Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance
35
Semiconductors
bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width
bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis
36
Life Sciences
bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level
bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure
37
Differences between IR and Raman methodsSNo Raman IR
01 It is due to the scattering of light by the vibrating molecules
It is the result of absorption of light by vibrating molecules
02 The vibration is Raman active if it causes a change in polarisability
Vibration is IR active if there is change in dipole moment
03 The molecule need not possess a permanent dipole moment
The vibration concerned should have a change in dipole moment due to that vibration
04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR
05 Sample preparation is not very elaborate it can be in any state
Sample preparation is elaborateGaseous samples can rarely be used
06 Gives an indication of covalent character in the molecule
Gives an indication of ionic character in the molecule
07 Cost of instrumentation is very high
Comparatively inexpensive
38
Advantages of Raman over IR
bull Water can be used as solvent bull Very suitable for biological samples in native state (because water
can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral
overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power
39
Advantages of IR over Ramanbull Simpler and cheaper instrumentation
bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio
bull Lower detection limit than (normal) Raman
bull Background fluorescence can overwhelm Raman
bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)
40
Several variations of Raman spectroscopy
1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal
bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)
bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977
bull A comprehensive theory of the effect was given by Lombardi and Birke
41
2 Resonance Raman spectroscopy The excitation wavelength is matched to an
electronic transition of the molecule or crystal so that vibrational modes associated with the excited electronic state are greatly enhanced This is useful for studying large molecules such as polypeptides which might show hundreds of bands in conventional Raman spectra It is also useful for associating normal modes with their observed frequency shifts
42
3 Surface-enhanced resonance Raman spectroscopy (SERRS) ndash A combination of SERS and resonance Raman spectroscopy that uses proximity to a surface to increase Raman intensity and excitation wavelength matched to the maximum absorbance of the molecule being analysed
4 Coherent anti-Stokes Raman spectroscopy (CARS) ndash
Two laser beams are used to generate a coherent anti-Stokes frequency beam which can be enhanced by resonance
43
5 Raman optical activity (ROA) ndash Measures vibrational optical activity by means of a small difference in the intensity of Raman scattering from chiral molecules in right- and left-circularly polarized incident light or equivalently a small circularly polarized component in the scattered light
6 Spatially offset Raman spectroscopy (SORS)
7 Spontaneous Raman spectroscopy (SRS) 8 Optical tweezers Raman spectroscopy (OTRS)
44
9 Angle-resolved Raman spectroscopy10 Inverse Raman spectroscopy11 Tip-enhanced Raman spectroscopy
(TERS) 12 Surface plasmon polariton enhanced
Raman scattering (SPPERS)13 Stand-off Remote Raman ndash 14 Fourier-transform Rama spectroscopyapplied
to photobiological systems
45
21
Raman Instrumentation
22
There are following component involves
1 Laser or source of light 2 Filter3 Sample holder 4 detector
23
The block design dispersive Raman scattering system
Radiation sources
Sample Wavelength
selector
Detector InGaAs or
Ge
RecorderDetector InGaAs or
Ge
RecorderDetector
InGaAs or Ge
Recorder
Block diagram
90
24
Flow diagram dispersive Raman scattering system
25
Schematic diagram dispersive raman scattering system
26
1 Laser or source of light
bull Lasers are generally the only source strong enough to scatter lots of light and lead to detectable raman scattering
bull Lasers operate using the principle of stimulated emission
bull Electronic population inversion is required to achieve gain via stimulated emission (before the fluorescence lifetime is reached)
bull Population inversion is achieved by ldquopumpingrdquo using lots of photons in a variety of laser gain media
27
List of Various laser source
SNo Laser wavelength01 NdYAG 1064nm
02 HeNe 633nm
03 Argon ion 488nm
04 GaAlAs diode 785nm
05 Co2 10600nm
06 Ti-Sapphire 800nm
28
A - HeNe laserbull Filled with 71 He amp Ne gas optimum output of 6328 Aring
bull High voltage excitation is preferred
B - NdYAG Systembull A typical laser system ndashthe neodymium-doped yttrium aluminum garnet or Nd+3
bull YAG is a cubic crystalline material
bull Crystal field splitting causes electronic energy level splitting
bull NdYAG laser are optically pumped using a flash tube or laser diodes
bull These are the one of the most common type of laser
bull It emits 1064 nm wavelength
29
2Filter bull It is therefore essential to have monochromatic radiations
bull For getting monochromatic radiations filters are used
bull They may be made of nickel oxide glass or quartz glass
bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator
30
3Sample holder bull For the study of raman effect the type of sample holder to be used
depends upon the intensity of sources the nature and availability of the sample
bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids
bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be
used for the study of raman spectra
bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy
31
4detectorbull Researchers traditionally used single points detectors such as
photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality
bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)
bull Sensitivity amp performance of modern CCD detectors are high
32
APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling
33
bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and
gypsum illustrating how Raman can be used for fast mineral ID
bull Gemstone and mineral identification
bull Fluid inclusions
bull Mineral and phase distribution in rock sections
bull Phase transitions
bull Mineral behavior under extreme conditions
34
Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance
35
Semiconductors
bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width
bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis
36
Life Sciences
bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level
bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure
37
Differences between IR and Raman methodsSNo Raman IR
01 It is due to the scattering of light by the vibrating molecules
It is the result of absorption of light by vibrating molecules
02 The vibration is Raman active if it causes a change in polarisability
Vibration is IR active if there is change in dipole moment
03 The molecule need not possess a permanent dipole moment
The vibration concerned should have a change in dipole moment due to that vibration
04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR
05 Sample preparation is not very elaborate it can be in any state
Sample preparation is elaborateGaseous samples can rarely be used
06 Gives an indication of covalent character in the molecule
Gives an indication of ionic character in the molecule
07 Cost of instrumentation is very high
Comparatively inexpensive
38
Advantages of Raman over IR
bull Water can be used as solvent bull Very suitable for biological samples in native state (because water
can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral
overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power
39
Advantages of IR over Ramanbull Simpler and cheaper instrumentation
bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio
bull Lower detection limit than (normal) Raman
bull Background fluorescence can overwhelm Raman
bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)
40
Several variations of Raman spectroscopy
1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal
bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)
bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977
bull A comprehensive theory of the effect was given by Lombardi and Birke
41
2 Resonance Raman spectroscopy The excitation wavelength is matched to an
electronic transition of the molecule or crystal so that vibrational modes associated with the excited electronic state are greatly enhanced This is useful for studying large molecules such as polypeptides which might show hundreds of bands in conventional Raman spectra It is also useful for associating normal modes with their observed frequency shifts
42
3 Surface-enhanced resonance Raman spectroscopy (SERRS) ndash A combination of SERS and resonance Raman spectroscopy that uses proximity to a surface to increase Raman intensity and excitation wavelength matched to the maximum absorbance of the molecule being analysed
4 Coherent anti-Stokes Raman spectroscopy (CARS) ndash
Two laser beams are used to generate a coherent anti-Stokes frequency beam which can be enhanced by resonance
43
5 Raman optical activity (ROA) ndash Measures vibrational optical activity by means of a small difference in the intensity of Raman scattering from chiral molecules in right- and left-circularly polarized incident light or equivalently a small circularly polarized component in the scattered light
6 Spatially offset Raman spectroscopy (SORS)
7 Spontaneous Raman spectroscopy (SRS) 8 Optical tweezers Raman spectroscopy (OTRS)
44
9 Angle-resolved Raman spectroscopy10 Inverse Raman spectroscopy11 Tip-enhanced Raman spectroscopy
(TERS) 12 Surface plasmon polariton enhanced
Raman scattering (SPPERS)13 Stand-off Remote Raman ndash 14 Fourier-transform Rama spectroscopyapplied
to photobiological systems
45
22
There are following component involves
1 Laser or source of light 2 Filter3 Sample holder 4 detector
23
The block design dispersive Raman scattering system
Radiation sources
Sample Wavelength
selector
Detector InGaAs or
Ge
RecorderDetector InGaAs or
Ge
RecorderDetector
InGaAs or Ge
Recorder
Block diagram
90
24
Flow diagram dispersive Raman scattering system
25
Schematic diagram dispersive raman scattering system
26
1 Laser or source of light
bull Lasers are generally the only source strong enough to scatter lots of light and lead to detectable raman scattering
bull Lasers operate using the principle of stimulated emission
bull Electronic population inversion is required to achieve gain via stimulated emission (before the fluorescence lifetime is reached)
bull Population inversion is achieved by ldquopumpingrdquo using lots of photons in a variety of laser gain media
27
List of Various laser source
SNo Laser wavelength01 NdYAG 1064nm
02 HeNe 633nm
03 Argon ion 488nm
04 GaAlAs diode 785nm
05 Co2 10600nm
06 Ti-Sapphire 800nm
28
A - HeNe laserbull Filled with 71 He amp Ne gas optimum output of 6328 Aring
bull High voltage excitation is preferred
B - NdYAG Systembull A typical laser system ndashthe neodymium-doped yttrium aluminum garnet or Nd+3
bull YAG is a cubic crystalline material
bull Crystal field splitting causes electronic energy level splitting
bull NdYAG laser are optically pumped using a flash tube or laser diodes
bull These are the one of the most common type of laser
bull It emits 1064 nm wavelength
29
2Filter bull It is therefore essential to have monochromatic radiations
bull For getting monochromatic radiations filters are used
bull They may be made of nickel oxide glass or quartz glass
bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator
30
3Sample holder bull For the study of raman effect the type of sample holder to be used
depends upon the intensity of sources the nature and availability of the sample
bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids
bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be
used for the study of raman spectra
bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy
31
4detectorbull Researchers traditionally used single points detectors such as
photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality
bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)
bull Sensitivity amp performance of modern CCD detectors are high
32
APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling
33
bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and
gypsum illustrating how Raman can be used for fast mineral ID
bull Gemstone and mineral identification
bull Fluid inclusions
bull Mineral and phase distribution in rock sections
bull Phase transitions
bull Mineral behavior under extreme conditions
34
Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance
35
Semiconductors
bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width
bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis
36
Life Sciences
bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level
bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure
37
Differences between IR and Raman methodsSNo Raman IR
01 It is due to the scattering of light by the vibrating molecules
It is the result of absorption of light by vibrating molecules
02 The vibration is Raman active if it causes a change in polarisability
Vibration is IR active if there is change in dipole moment
03 The molecule need not possess a permanent dipole moment
The vibration concerned should have a change in dipole moment due to that vibration
04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR
05 Sample preparation is not very elaborate it can be in any state
Sample preparation is elaborateGaseous samples can rarely be used
06 Gives an indication of covalent character in the molecule
Gives an indication of ionic character in the molecule
07 Cost of instrumentation is very high
Comparatively inexpensive
38
Advantages of Raman over IR
bull Water can be used as solvent bull Very suitable for biological samples in native state (because water
can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral
overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power
39
Advantages of IR over Ramanbull Simpler and cheaper instrumentation
bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio
bull Lower detection limit than (normal) Raman
bull Background fluorescence can overwhelm Raman
bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)
40
Several variations of Raman spectroscopy
1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal
bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)
bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977
bull A comprehensive theory of the effect was given by Lombardi and Birke
41
2 Resonance Raman spectroscopy The excitation wavelength is matched to an
electronic transition of the molecule or crystal so that vibrational modes associated with the excited electronic state are greatly enhanced This is useful for studying large molecules such as polypeptides which might show hundreds of bands in conventional Raman spectra It is also useful for associating normal modes with their observed frequency shifts
42
3 Surface-enhanced resonance Raman spectroscopy (SERRS) ndash A combination of SERS and resonance Raman spectroscopy that uses proximity to a surface to increase Raman intensity and excitation wavelength matched to the maximum absorbance of the molecule being analysed
4 Coherent anti-Stokes Raman spectroscopy (CARS) ndash
Two laser beams are used to generate a coherent anti-Stokes frequency beam which can be enhanced by resonance
43
5 Raman optical activity (ROA) ndash Measures vibrational optical activity by means of a small difference in the intensity of Raman scattering from chiral molecules in right- and left-circularly polarized incident light or equivalently a small circularly polarized component in the scattered light
6 Spatially offset Raman spectroscopy (SORS)
7 Spontaneous Raman spectroscopy (SRS) 8 Optical tweezers Raman spectroscopy (OTRS)
44
9 Angle-resolved Raman spectroscopy10 Inverse Raman spectroscopy11 Tip-enhanced Raman spectroscopy
(TERS) 12 Surface plasmon polariton enhanced
Raman scattering (SPPERS)13 Stand-off Remote Raman ndash 14 Fourier-transform Rama spectroscopyapplied
to photobiological systems
45
23
The block design dispersive Raman scattering system
Radiation sources
Sample Wavelength
selector
Detector InGaAs or
Ge
RecorderDetector InGaAs or
Ge
RecorderDetector
InGaAs or Ge
Recorder
Block diagram
90
24
Flow diagram dispersive Raman scattering system
25
Schematic diagram dispersive raman scattering system
26
1 Laser or source of light
bull Lasers are generally the only source strong enough to scatter lots of light and lead to detectable raman scattering
bull Lasers operate using the principle of stimulated emission
bull Electronic population inversion is required to achieve gain via stimulated emission (before the fluorescence lifetime is reached)
bull Population inversion is achieved by ldquopumpingrdquo using lots of photons in a variety of laser gain media
27
List of Various laser source
SNo Laser wavelength01 NdYAG 1064nm
02 HeNe 633nm
03 Argon ion 488nm
04 GaAlAs diode 785nm
05 Co2 10600nm
06 Ti-Sapphire 800nm
28
A - HeNe laserbull Filled with 71 He amp Ne gas optimum output of 6328 Aring
bull High voltage excitation is preferred
B - NdYAG Systembull A typical laser system ndashthe neodymium-doped yttrium aluminum garnet or Nd+3
bull YAG is a cubic crystalline material
bull Crystal field splitting causes electronic energy level splitting
bull NdYAG laser are optically pumped using a flash tube or laser diodes
bull These are the one of the most common type of laser
bull It emits 1064 nm wavelength
29
2Filter bull It is therefore essential to have monochromatic radiations
bull For getting monochromatic radiations filters are used
bull They may be made of nickel oxide glass or quartz glass
bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator
30
3Sample holder bull For the study of raman effect the type of sample holder to be used
depends upon the intensity of sources the nature and availability of the sample
bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids
bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be
used for the study of raman spectra
bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy
31
4detectorbull Researchers traditionally used single points detectors such as
photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality
bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)
bull Sensitivity amp performance of modern CCD detectors are high
32
APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling
33
bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and
gypsum illustrating how Raman can be used for fast mineral ID
bull Gemstone and mineral identification
bull Fluid inclusions
bull Mineral and phase distribution in rock sections
bull Phase transitions
bull Mineral behavior under extreme conditions
34
Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance
35
Semiconductors
bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width
bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis
36
Life Sciences
bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level
bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure
37
Differences between IR and Raman methodsSNo Raman IR
01 It is due to the scattering of light by the vibrating molecules
It is the result of absorption of light by vibrating molecules
02 The vibration is Raman active if it causes a change in polarisability
Vibration is IR active if there is change in dipole moment
03 The molecule need not possess a permanent dipole moment
The vibration concerned should have a change in dipole moment due to that vibration
04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR
05 Sample preparation is not very elaborate it can be in any state
Sample preparation is elaborateGaseous samples can rarely be used
06 Gives an indication of covalent character in the molecule
Gives an indication of ionic character in the molecule
07 Cost of instrumentation is very high
Comparatively inexpensive
38
Advantages of Raman over IR
bull Water can be used as solvent bull Very suitable for biological samples in native state (because water
can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral
overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power
39
Advantages of IR over Ramanbull Simpler and cheaper instrumentation
bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio
bull Lower detection limit than (normal) Raman
bull Background fluorescence can overwhelm Raman
bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)
40
Several variations of Raman spectroscopy
1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal
bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)
bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977
bull A comprehensive theory of the effect was given by Lombardi and Birke
41
2 Resonance Raman spectroscopy The excitation wavelength is matched to an
electronic transition of the molecule or crystal so that vibrational modes associated with the excited electronic state are greatly enhanced This is useful for studying large molecules such as polypeptides which might show hundreds of bands in conventional Raman spectra It is also useful for associating normal modes with their observed frequency shifts
42
3 Surface-enhanced resonance Raman spectroscopy (SERRS) ndash A combination of SERS and resonance Raman spectroscopy that uses proximity to a surface to increase Raman intensity and excitation wavelength matched to the maximum absorbance of the molecule being analysed
4 Coherent anti-Stokes Raman spectroscopy (CARS) ndash
Two laser beams are used to generate a coherent anti-Stokes frequency beam which can be enhanced by resonance
43
5 Raman optical activity (ROA) ndash Measures vibrational optical activity by means of a small difference in the intensity of Raman scattering from chiral molecules in right- and left-circularly polarized incident light or equivalently a small circularly polarized component in the scattered light
6 Spatially offset Raman spectroscopy (SORS)
7 Spontaneous Raman spectroscopy (SRS) 8 Optical tweezers Raman spectroscopy (OTRS)
44
9 Angle-resolved Raman spectroscopy10 Inverse Raman spectroscopy11 Tip-enhanced Raman spectroscopy
(TERS) 12 Surface plasmon polariton enhanced
Raman scattering (SPPERS)13 Stand-off Remote Raman ndash 14 Fourier-transform Rama spectroscopyapplied
to photobiological systems
45
24
Flow diagram dispersive Raman scattering system
25
Schematic diagram dispersive raman scattering system
26
1 Laser or source of light
bull Lasers are generally the only source strong enough to scatter lots of light and lead to detectable raman scattering
bull Lasers operate using the principle of stimulated emission
bull Electronic population inversion is required to achieve gain via stimulated emission (before the fluorescence lifetime is reached)
bull Population inversion is achieved by ldquopumpingrdquo using lots of photons in a variety of laser gain media
27
List of Various laser source
SNo Laser wavelength01 NdYAG 1064nm
02 HeNe 633nm
03 Argon ion 488nm
04 GaAlAs diode 785nm
05 Co2 10600nm
06 Ti-Sapphire 800nm
28
A - HeNe laserbull Filled with 71 He amp Ne gas optimum output of 6328 Aring
bull High voltage excitation is preferred
B - NdYAG Systembull A typical laser system ndashthe neodymium-doped yttrium aluminum garnet or Nd+3
bull YAG is a cubic crystalline material
bull Crystal field splitting causes electronic energy level splitting
bull NdYAG laser are optically pumped using a flash tube or laser diodes
bull These are the one of the most common type of laser
bull It emits 1064 nm wavelength
29
2Filter bull It is therefore essential to have monochromatic radiations
bull For getting monochromatic radiations filters are used
bull They may be made of nickel oxide glass or quartz glass
bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator
30
3Sample holder bull For the study of raman effect the type of sample holder to be used
depends upon the intensity of sources the nature and availability of the sample
bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids
bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be
used for the study of raman spectra
bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy
31
4detectorbull Researchers traditionally used single points detectors such as
photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality
bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)
bull Sensitivity amp performance of modern CCD detectors are high
32
APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling
33
bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and
gypsum illustrating how Raman can be used for fast mineral ID
bull Gemstone and mineral identification
bull Fluid inclusions
bull Mineral and phase distribution in rock sections
bull Phase transitions
bull Mineral behavior under extreme conditions
34
Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance
35
Semiconductors
bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width
bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis
36
Life Sciences
bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level
bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure
37
Differences between IR and Raman methodsSNo Raman IR
01 It is due to the scattering of light by the vibrating molecules
It is the result of absorption of light by vibrating molecules
02 The vibration is Raman active if it causes a change in polarisability
Vibration is IR active if there is change in dipole moment
03 The molecule need not possess a permanent dipole moment
The vibration concerned should have a change in dipole moment due to that vibration
04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR
05 Sample preparation is not very elaborate it can be in any state
Sample preparation is elaborateGaseous samples can rarely be used
06 Gives an indication of covalent character in the molecule
Gives an indication of ionic character in the molecule
07 Cost of instrumentation is very high
Comparatively inexpensive
38
Advantages of Raman over IR
bull Water can be used as solvent bull Very suitable for biological samples in native state (because water
can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral
overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power
39
Advantages of IR over Ramanbull Simpler and cheaper instrumentation
bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio
bull Lower detection limit than (normal) Raman
bull Background fluorescence can overwhelm Raman
bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)
40
Several variations of Raman spectroscopy
1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal
bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)
bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977
bull A comprehensive theory of the effect was given by Lombardi and Birke
41
2 Resonance Raman spectroscopy The excitation wavelength is matched to an
electronic transition of the molecule or crystal so that vibrational modes associated with the excited electronic state are greatly enhanced This is useful for studying large molecules such as polypeptides which might show hundreds of bands in conventional Raman spectra It is also useful for associating normal modes with their observed frequency shifts
42
3 Surface-enhanced resonance Raman spectroscopy (SERRS) ndash A combination of SERS and resonance Raman spectroscopy that uses proximity to a surface to increase Raman intensity and excitation wavelength matched to the maximum absorbance of the molecule being analysed
4 Coherent anti-Stokes Raman spectroscopy (CARS) ndash
Two laser beams are used to generate a coherent anti-Stokes frequency beam which can be enhanced by resonance
43
5 Raman optical activity (ROA) ndash Measures vibrational optical activity by means of a small difference in the intensity of Raman scattering from chiral molecules in right- and left-circularly polarized incident light or equivalently a small circularly polarized component in the scattered light
6 Spatially offset Raman spectroscopy (SORS)
7 Spontaneous Raman spectroscopy (SRS) 8 Optical tweezers Raman spectroscopy (OTRS)
44
9 Angle-resolved Raman spectroscopy10 Inverse Raman spectroscopy11 Tip-enhanced Raman spectroscopy
(TERS) 12 Surface plasmon polariton enhanced
Raman scattering (SPPERS)13 Stand-off Remote Raman ndash 14 Fourier-transform Rama spectroscopyapplied
to photobiological systems
45
25
Schematic diagram dispersive raman scattering system
26
1 Laser or source of light
bull Lasers are generally the only source strong enough to scatter lots of light and lead to detectable raman scattering
bull Lasers operate using the principle of stimulated emission
bull Electronic population inversion is required to achieve gain via stimulated emission (before the fluorescence lifetime is reached)
bull Population inversion is achieved by ldquopumpingrdquo using lots of photons in a variety of laser gain media
27
List of Various laser source
SNo Laser wavelength01 NdYAG 1064nm
02 HeNe 633nm
03 Argon ion 488nm
04 GaAlAs diode 785nm
05 Co2 10600nm
06 Ti-Sapphire 800nm
28
A - HeNe laserbull Filled with 71 He amp Ne gas optimum output of 6328 Aring
bull High voltage excitation is preferred
B - NdYAG Systembull A typical laser system ndashthe neodymium-doped yttrium aluminum garnet or Nd+3
bull YAG is a cubic crystalline material
bull Crystal field splitting causes electronic energy level splitting
bull NdYAG laser are optically pumped using a flash tube or laser diodes
bull These are the one of the most common type of laser
bull It emits 1064 nm wavelength
29
2Filter bull It is therefore essential to have monochromatic radiations
bull For getting monochromatic radiations filters are used
bull They may be made of nickel oxide glass or quartz glass
bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator
30
3Sample holder bull For the study of raman effect the type of sample holder to be used
depends upon the intensity of sources the nature and availability of the sample
bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids
bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be
used for the study of raman spectra
bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy
31
4detectorbull Researchers traditionally used single points detectors such as
photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality
bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)
bull Sensitivity amp performance of modern CCD detectors are high
32
APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling
33
bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and
gypsum illustrating how Raman can be used for fast mineral ID
bull Gemstone and mineral identification
bull Fluid inclusions
bull Mineral and phase distribution in rock sections
bull Phase transitions
bull Mineral behavior under extreme conditions
34
Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance
35
Semiconductors
bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width
bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis
36
Life Sciences
bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level
bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure
37
Differences between IR and Raman methodsSNo Raman IR
01 It is due to the scattering of light by the vibrating molecules
It is the result of absorption of light by vibrating molecules
02 The vibration is Raman active if it causes a change in polarisability
Vibration is IR active if there is change in dipole moment
03 The molecule need not possess a permanent dipole moment
The vibration concerned should have a change in dipole moment due to that vibration
04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR
05 Sample preparation is not very elaborate it can be in any state
Sample preparation is elaborateGaseous samples can rarely be used
06 Gives an indication of covalent character in the molecule
Gives an indication of ionic character in the molecule
07 Cost of instrumentation is very high
Comparatively inexpensive
38
Advantages of Raman over IR
bull Water can be used as solvent bull Very suitable for biological samples in native state (because water
can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral
overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power
39
Advantages of IR over Ramanbull Simpler and cheaper instrumentation
bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio
bull Lower detection limit than (normal) Raman
bull Background fluorescence can overwhelm Raman
bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)
40
Several variations of Raman spectroscopy
1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal
bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)
bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977
bull A comprehensive theory of the effect was given by Lombardi and Birke
41
2 Resonance Raman spectroscopy The excitation wavelength is matched to an
electronic transition of the molecule or crystal so that vibrational modes associated with the excited electronic state are greatly enhanced This is useful for studying large molecules such as polypeptides which might show hundreds of bands in conventional Raman spectra It is also useful for associating normal modes with their observed frequency shifts
42
3 Surface-enhanced resonance Raman spectroscopy (SERRS) ndash A combination of SERS and resonance Raman spectroscopy that uses proximity to a surface to increase Raman intensity and excitation wavelength matched to the maximum absorbance of the molecule being analysed
4 Coherent anti-Stokes Raman spectroscopy (CARS) ndash
Two laser beams are used to generate a coherent anti-Stokes frequency beam which can be enhanced by resonance
43
5 Raman optical activity (ROA) ndash Measures vibrational optical activity by means of a small difference in the intensity of Raman scattering from chiral molecules in right- and left-circularly polarized incident light or equivalently a small circularly polarized component in the scattered light
6 Spatially offset Raman spectroscopy (SORS)
7 Spontaneous Raman spectroscopy (SRS) 8 Optical tweezers Raman spectroscopy (OTRS)
44
9 Angle-resolved Raman spectroscopy10 Inverse Raman spectroscopy11 Tip-enhanced Raman spectroscopy
(TERS) 12 Surface plasmon polariton enhanced
Raman scattering (SPPERS)13 Stand-off Remote Raman ndash 14 Fourier-transform Rama spectroscopyapplied
to photobiological systems
45
26
1 Laser or source of light
bull Lasers are generally the only source strong enough to scatter lots of light and lead to detectable raman scattering
bull Lasers operate using the principle of stimulated emission
bull Electronic population inversion is required to achieve gain via stimulated emission (before the fluorescence lifetime is reached)
bull Population inversion is achieved by ldquopumpingrdquo using lots of photons in a variety of laser gain media
27
List of Various laser source
SNo Laser wavelength01 NdYAG 1064nm
02 HeNe 633nm
03 Argon ion 488nm
04 GaAlAs diode 785nm
05 Co2 10600nm
06 Ti-Sapphire 800nm
28
A - HeNe laserbull Filled with 71 He amp Ne gas optimum output of 6328 Aring
bull High voltage excitation is preferred
B - NdYAG Systembull A typical laser system ndashthe neodymium-doped yttrium aluminum garnet or Nd+3
bull YAG is a cubic crystalline material
bull Crystal field splitting causes electronic energy level splitting
bull NdYAG laser are optically pumped using a flash tube or laser diodes
bull These are the one of the most common type of laser
bull It emits 1064 nm wavelength
29
2Filter bull It is therefore essential to have monochromatic radiations
bull For getting monochromatic radiations filters are used
bull They may be made of nickel oxide glass or quartz glass
bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator
30
3Sample holder bull For the study of raman effect the type of sample holder to be used
depends upon the intensity of sources the nature and availability of the sample
bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids
bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be
used for the study of raman spectra
bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy
31
4detectorbull Researchers traditionally used single points detectors such as
photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality
bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)
bull Sensitivity amp performance of modern CCD detectors are high
32
APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling
33
bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and
gypsum illustrating how Raman can be used for fast mineral ID
bull Gemstone and mineral identification
bull Fluid inclusions
bull Mineral and phase distribution in rock sections
bull Phase transitions
bull Mineral behavior under extreme conditions
34
Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance
35
Semiconductors
bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width
bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis
36
Life Sciences
bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level
bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure
37
Differences between IR and Raman methodsSNo Raman IR
01 It is due to the scattering of light by the vibrating molecules
It is the result of absorption of light by vibrating molecules
02 The vibration is Raman active if it causes a change in polarisability
Vibration is IR active if there is change in dipole moment
03 The molecule need not possess a permanent dipole moment
The vibration concerned should have a change in dipole moment due to that vibration
04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR
05 Sample preparation is not very elaborate it can be in any state
Sample preparation is elaborateGaseous samples can rarely be used
06 Gives an indication of covalent character in the molecule
Gives an indication of ionic character in the molecule
07 Cost of instrumentation is very high
Comparatively inexpensive
38
Advantages of Raman over IR
bull Water can be used as solvent bull Very suitable for biological samples in native state (because water
can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral
overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power
39
Advantages of IR over Ramanbull Simpler and cheaper instrumentation
bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio
bull Lower detection limit than (normal) Raman
bull Background fluorescence can overwhelm Raman
bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)
40
Several variations of Raman spectroscopy
1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal
bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)
bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977
bull A comprehensive theory of the effect was given by Lombardi and Birke
41
2 Resonance Raman spectroscopy The excitation wavelength is matched to an
electronic transition of the molecule or crystal so that vibrational modes associated with the excited electronic state are greatly enhanced This is useful for studying large molecules such as polypeptides which might show hundreds of bands in conventional Raman spectra It is also useful for associating normal modes with their observed frequency shifts
42
3 Surface-enhanced resonance Raman spectroscopy (SERRS) ndash A combination of SERS and resonance Raman spectroscopy that uses proximity to a surface to increase Raman intensity and excitation wavelength matched to the maximum absorbance of the molecule being analysed
4 Coherent anti-Stokes Raman spectroscopy (CARS) ndash
Two laser beams are used to generate a coherent anti-Stokes frequency beam which can be enhanced by resonance
43
5 Raman optical activity (ROA) ndash Measures vibrational optical activity by means of a small difference in the intensity of Raman scattering from chiral molecules in right- and left-circularly polarized incident light or equivalently a small circularly polarized component in the scattered light
6 Spatially offset Raman spectroscopy (SORS)
7 Spontaneous Raman spectroscopy (SRS) 8 Optical tweezers Raman spectroscopy (OTRS)
44
9 Angle-resolved Raman spectroscopy10 Inverse Raman spectroscopy11 Tip-enhanced Raman spectroscopy
(TERS) 12 Surface plasmon polariton enhanced
Raman scattering (SPPERS)13 Stand-off Remote Raman ndash 14 Fourier-transform Rama spectroscopyapplied
to photobiological systems
45
27
List of Various laser source
SNo Laser wavelength01 NdYAG 1064nm
02 HeNe 633nm
03 Argon ion 488nm
04 GaAlAs diode 785nm
05 Co2 10600nm
06 Ti-Sapphire 800nm
28
A - HeNe laserbull Filled with 71 He amp Ne gas optimum output of 6328 Aring
bull High voltage excitation is preferred
B - NdYAG Systembull A typical laser system ndashthe neodymium-doped yttrium aluminum garnet or Nd+3
bull YAG is a cubic crystalline material
bull Crystal field splitting causes electronic energy level splitting
bull NdYAG laser are optically pumped using a flash tube or laser diodes
bull These are the one of the most common type of laser
bull It emits 1064 nm wavelength
29
2Filter bull It is therefore essential to have monochromatic radiations
bull For getting monochromatic radiations filters are used
bull They may be made of nickel oxide glass or quartz glass
bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator
30
3Sample holder bull For the study of raman effect the type of sample holder to be used
depends upon the intensity of sources the nature and availability of the sample
bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids
bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be
used for the study of raman spectra
bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy
31
4detectorbull Researchers traditionally used single points detectors such as
photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality
bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)
bull Sensitivity amp performance of modern CCD detectors are high
32
APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling
33
bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and
gypsum illustrating how Raman can be used for fast mineral ID
bull Gemstone and mineral identification
bull Fluid inclusions
bull Mineral and phase distribution in rock sections
bull Phase transitions
bull Mineral behavior under extreme conditions
34
Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance
35
Semiconductors
bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width
bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis
36
Life Sciences
bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level
bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure
37
Differences between IR and Raman methodsSNo Raman IR
01 It is due to the scattering of light by the vibrating molecules
It is the result of absorption of light by vibrating molecules
02 The vibration is Raman active if it causes a change in polarisability
Vibration is IR active if there is change in dipole moment
03 The molecule need not possess a permanent dipole moment
The vibration concerned should have a change in dipole moment due to that vibration
04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR
05 Sample preparation is not very elaborate it can be in any state
Sample preparation is elaborateGaseous samples can rarely be used
06 Gives an indication of covalent character in the molecule
Gives an indication of ionic character in the molecule
07 Cost of instrumentation is very high
Comparatively inexpensive
38
Advantages of Raman over IR
bull Water can be used as solvent bull Very suitable for biological samples in native state (because water
can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral
overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power
39
Advantages of IR over Ramanbull Simpler and cheaper instrumentation
bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio
bull Lower detection limit than (normal) Raman
bull Background fluorescence can overwhelm Raman
bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)
40
Several variations of Raman spectroscopy
1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal
bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)
bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977
bull A comprehensive theory of the effect was given by Lombardi and Birke
41
2 Resonance Raman spectroscopy The excitation wavelength is matched to an
electronic transition of the molecule or crystal so that vibrational modes associated with the excited electronic state are greatly enhanced This is useful for studying large molecules such as polypeptides which might show hundreds of bands in conventional Raman spectra It is also useful for associating normal modes with their observed frequency shifts
42
3 Surface-enhanced resonance Raman spectroscopy (SERRS) ndash A combination of SERS and resonance Raman spectroscopy that uses proximity to a surface to increase Raman intensity and excitation wavelength matched to the maximum absorbance of the molecule being analysed
4 Coherent anti-Stokes Raman spectroscopy (CARS) ndash
Two laser beams are used to generate a coherent anti-Stokes frequency beam which can be enhanced by resonance
43
5 Raman optical activity (ROA) ndash Measures vibrational optical activity by means of a small difference in the intensity of Raman scattering from chiral molecules in right- and left-circularly polarized incident light or equivalently a small circularly polarized component in the scattered light
6 Spatially offset Raman spectroscopy (SORS)
7 Spontaneous Raman spectroscopy (SRS) 8 Optical tweezers Raman spectroscopy (OTRS)
44
9 Angle-resolved Raman spectroscopy10 Inverse Raman spectroscopy11 Tip-enhanced Raman spectroscopy
(TERS) 12 Surface plasmon polariton enhanced
Raman scattering (SPPERS)13 Stand-off Remote Raman ndash 14 Fourier-transform Rama spectroscopyapplied
to photobiological systems
45
28
A - HeNe laserbull Filled with 71 He amp Ne gas optimum output of 6328 Aring
bull High voltage excitation is preferred
B - NdYAG Systembull A typical laser system ndashthe neodymium-doped yttrium aluminum garnet or Nd+3
bull YAG is a cubic crystalline material
bull Crystal field splitting causes electronic energy level splitting
bull NdYAG laser are optically pumped using a flash tube or laser diodes
bull These are the one of the most common type of laser
bull It emits 1064 nm wavelength
29
2Filter bull It is therefore essential to have monochromatic radiations
bull For getting monochromatic radiations filters are used
bull They may be made of nickel oxide glass or quartz glass
bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator
30
3Sample holder bull For the study of raman effect the type of sample holder to be used
depends upon the intensity of sources the nature and availability of the sample
bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids
bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be
used for the study of raman spectra
bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy
31
4detectorbull Researchers traditionally used single points detectors such as
photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality
bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)
bull Sensitivity amp performance of modern CCD detectors are high
32
APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling
33
bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and
gypsum illustrating how Raman can be used for fast mineral ID
bull Gemstone and mineral identification
bull Fluid inclusions
bull Mineral and phase distribution in rock sections
bull Phase transitions
bull Mineral behavior under extreme conditions
34
Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance
35
Semiconductors
bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width
bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis
36
Life Sciences
bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level
bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure
37
Differences between IR and Raman methodsSNo Raman IR
01 It is due to the scattering of light by the vibrating molecules
It is the result of absorption of light by vibrating molecules
02 The vibration is Raman active if it causes a change in polarisability
Vibration is IR active if there is change in dipole moment
03 The molecule need not possess a permanent dipole moment
The vibration concerned should have a change in dipole moment due to that vibration
04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR
05 Sample preparation is not very elaborate it can be in any state
Sample preparation is elaborateGaseous samples can rarely be used
06 Gives an indication of covalent character in the molecule
Gives an indication of ionic character in the molecule
07 Cost of instrumentation is very high
Comparatively inexpensive
38
Advantages of Raman over IR
bull Water can be used as solvent bull Very suitable for biological samples in native state (because water
can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral
overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power
39
Advantages of IR over Ramanbull Simpler and cheaper instrumentation
bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio
bull Lower detection limit than (normal) Raman
bull Background fluorescence can overwhelm Raman
bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)
40
Several variations of Raman spectroscopy
1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal
bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)
bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977
bull A comprehensive theory of the effect was given by Lombardi and Birke
41
2 Resonance Raman spectroscopy The excitation wavelength is matched to an
electronic transition of the molecule or crystal so that vibrational modes associated with the excited electronic state are greatly enhanced This is useful for studying large molecules such as polypeptides which might show hundreds of bands in conventional Raman spectra It is also useful for associating normal modes with their observed frequency shifts
42
3 Surface-enhanced resonance Raman spectroscopy (SERRS) ndash A combination of SERS and resonance Raman spectroscopy that uses proximity to a surface to increase Raman intensity and excitation wavelength matched to the maximum absorbance of the molecule being analysed
4 Coherent anti-Stokes Raman spectroscopy (CARS) ndash
Two laser beams are used to generate a coherent anti-Stokes frequency beam which can be enhanced by resonance
43
5 Raman optical activity (ROA) ndash Measures vibrational optical activity by means of a small difference in the intensity of Raman scattering from chiral molecules in right- and left-circularly polarized incident light or equivalently a small circularly polarized component in the scattered light
6 Spatially offset Raman spectroscopy (SORS)
7 Spontaneous Raman spectroscopy (SRS) 8 Optical tweezers Raman spectroscopy (OTRS)
44
9 Angle-resolved Raman spectroscopy10 Inverse Raman spectroscopy11 Tip-enhanced Raman spectroscopy
(TERS) 12 Surface plasmon polariton enhanced
Raman scattering (SPPERS)13 Stand-off Remote Raman ndash 14 Fourier-transform Rama spectroscopyapplied
to photobiological systems
45
29
2Filter bull It is therefore essential to have monochromatic radiations
bull For getting monochromatic radiations filters are used
bull They may be made of nickel oxide glass or quartz glass
bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator
30
3Sample holder bull For the study of raman effect the type of sample holder to be used
depends upon the intensity of sources the nature and availability of the sample
bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids
bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be
used for the study of raman spectra
bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy
31
4detectorbull Researchers traditionally used single points detectors such as
photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality
bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)
bull Sensitivity amp performance of modern CCD detectors are high
32
APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling
33
bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and
gypsum illustrating how Raman can be used for fast mineral ID
bull Gemstone and mineral identification
bull Fluid inclusions
bull Mineral and phase distribution in rock sections
bull Phase transitions
bull Mineral behavior under extreme conditions
34
Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance
35
Semiconductors
bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width
bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis
36
Life Sciences
bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level
bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure
37
Differences between IR and Raman methodsSNo Raman IR
01 It is due to the scattering of light by the vibrating molecules
It is the result of absorption of light by vibrating molecules
02 The vibration is Raman active if it causes a change in polarisability
Vibration is IR active if there is change in dipole moment
03 The molecule need not possess a permanent dipole moment
The vibration concerned should have a change in dipole moment due to that vibration
04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR
05 Sample preparation is not very elaborate it can be in any state
Sample preparation is elaborateGaseous samples can rarely be used
06 Gives an indication of covalent character in the molecule
Gives an indication of ionic character in the molecule
07 Cost of instrumentation is very high
Comparatively inexpensive
38
Advantages of Raman over IR
bull Water can be used as solvent bull Very suitable for biological samples in native state (because water
can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral
overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power
39
Advantages of IR over Ramanbull Simpler and cheaper instrumentation
bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio
bull Lower detection limit than (normal) Raman
bull Background fluorescence can overwhelm Raman
bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)
40
Several variations of Raman spectroscopy
1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal
bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)
bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977
bull A comprehensive theory of the effect was given by Lombardi and Birke
41
2 Resonance Raman spectroscopy The excitation wavelength is matched to an
electronic transition of the molecule or crystal so that vibrational modes associated with the excited electronic state are greatly enhanced This is useful for studying large molecules such as polypeptides which might show hundreds of bands in conventional Raman spectra It is also useful for associating normal modes with their observed frequency shifts
42
3 Surface-enhanced resonance Raman spectroscopy (SERRS) ndash A combination of SERS and resonance Raman spectroscopy that uses proximity to a surface to increase Raman intensity and excitation wavelength matched to the maximum absorbance of the molecule being analysed
4 Coherent anti-Stokes Raman spectroscopy (CARS) ndash
Two laser beams are used to generate a coherent anti-Stokes frequency beam which can be enhanced by resonance
43
5 Raman optical activity (ROA) ndash Measures vibrational optical activity by means of a small difference in the intensity of Raman scattering from chiral molecules in right- and left-circularly polarized incident light or equivalently a small circularly polarized component in the scattered light
6 Spatially offset Raman spectroscopy (SORS)
7 Spontaneous Raman spectroscopy (SRS) 8 Optical tweezers Raman spectroscopy (OTRS)
44
9 Angle-resolved Raman spectroscopy10 Inverse Raman spectroscopy11 Tip-enhanced Raman spectroscopy
(TERS) 12 Surface plasmon polariton enhanced
Raman scattering (SPPERS)13 Stand-off Remote Raman ndash 14 Fourier-transform Rama spectroscopyapplied
to photobiological systems
45
30
3Sample holder bull For the study of raman effect the type of sample holder to be used
depends upon the intensity of sources the nature and availability of the sample
bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids
bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be
used for the study of raman spectra
bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy
31
4detectorbull Researchers traditionally used single points detectors such as
photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality
bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)
bull Sensitivity amp performance of modern CCD detectors are high
32
APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling
33
bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and
gypsum illustrating how Raman can be used for fast mineral ID
bull Gemstone and mineral identification
bull Fluid inclusions
bull Mineral and phase distribution in rock sections
bull Phase transitions
bull Mineral behavior under extreme conditions
34
Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance
35
Semiconductors
bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width
bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis
36
Life Sciences
bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level
bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure
37
Differences between IR and Raman methodsSNo Raman IR
01 It is due to the scattering of light by the vibrating molecules
It is the result of absorption of light by vibrating molecules
02 The vibration is Raman active if it causes a change in polarisability
Vibration is IR active if there is change in dipole moment
03 The molecule need not possess a permanent dipole moment
The vibration concerned should have a change in dipole moment due to that vibration
04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR
05 Sample preparation is not very elaborate it can be in any state
Sample preparation is elaborateGaseous samples can rarely be used
06 Gives an indication of covalent character in the molecule
Gives an indication of ionic character in the molecule
07 Cost of instrumentation is very high
Comparatively inexpensive
38
Advantages of Raman over IR
bull Water can be used as solvent bull Very suitable for biological samples in native state (because water
can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral
overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power
39
Advantages of IR over Ramanbull Simpler and cheaper instrumentation
bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio
bull Lower detection limit than (normal) Raman
bull Background fluorescence can overwhelm Raman
bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)
40
Several variations of Raman spectroscopy
1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal
bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)
bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977
bull A comprehensive theory of the effect was given by Lombardi and Birke
41
2 Resonance Raman spectroscopy The excitation wavelength is matched to an
electronic transition of the molecule or crystal so that vibrational modes associated with the excited electronic state are greatly enhanced This is useful for studying large molecules such as polypeptides which might show hundreds of bands in conventional Raman spectra It is also useful for associating normal modes with their observed frequency shifts
42
3 Surface-enhanced resonance Raman spectroscopy (SERRS) ndash A combination of SERS and resonance Raman spectroscopy that uses proximity to a surface to increase Raman intensity and excitation wavelength matched to the maximum absorbance of the molecule being analysed
4 Coherent anti-Stokes Raman spectroscopy (CARS) ndash
Two laser beams are used to generate a coherent anti-Stokes frequency beam which can be enhanced by resonance
43
5 Raman optical activity (ROA) ndash Measures vibrational optical activity by means of a small difference in the intensity of Raman scattering from chiral molecules in right- and left-circularly polarized incident light or equivalently a small circularly polarized component in the scattered light
6 Spatially offset Raman spectroscopy (SORS)
7 Spontaneous Raman spectroscopy (SRS) 8 Optical tweezers Raman spectroscopy (OTRS)
44
9 Angle-resolved Raman spectroscopy10 Inverse Raman spectroscopy11 Tip-enhanced Raman spectroscopy
(TERS) 12 Surface plasmon polariton enhanced
Raman scattering (SPPERS)13 Stand-off Remote Raman ndash 14 Fourier-transform Rama spectroscopyapplied
to photobiological systems
45
31
4detectorbull Researchers traditionally used single points detectors such as
photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality
bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)
bull Sensitivity amp performance of modern CCD detectors are high
32
APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling
33
bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and
gypsum illustrating how Raman can be used for fast mineral ID
bull Gemstone and mineral identification
bull Fluid inclusions
bull Mineral and phase distribution in rock sections
bull Phase transitions
bull Mineral behavior under extreme conditions
34
Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance
35
Semiconductors
bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width
bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis
36
Life Sciences
bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level
bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure
37
Differences between IR and Raman methodsSNo Raman IR
01 It is due to the scattering of light by the vibrating molecules
It is the result of absorption of light by vibrating molecules
02 The vibration is Raman active if it causes a change in polarisability
Vibration is IR active if there is change in dipole moment
03 The molecule need not possess a permanent dipole moment
The vibration concerned should have a change in dipole moment due to that vibration
04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR
05 Sample preparation is not very elaborate it can be in any state
Sample preparation is elaborateGaseous samples can rarely be used
06 Gives an indication of covalent character in the molecule
Gives an indication of ionic character in the molecule
07 Cost of instrumentation is very high
Comparatively inexpensive
38
Advantages of Raman over IR
bull Water can be used as solvent bull Very suitable for biological samples in native state (because water
can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral
overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power
39
Advantages of IR over Ramanbull Simpler and cheaper instrumentation
bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio
bull Lower detection limit than (normal) Raman
bull Background fluorescence can overwhelm Raman
bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)
40
Several variations of Raman spectroscopy
1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal
bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)
bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977
bull A comprehensive theory of the effect was given by Lombardi and Birke
41
2 Resonance Raman spectroscopy The excitation wavelength is matched to an
electronic transition of the molecule or crystal so that vibrational modes associated with the excited electronic state are greatly enhanced This is useful for studying large molecules such as polypeptides which might show hundreds of bands in conventional Raman spectra It is also useful for associating normal modes with their observed frequency shifts
42
3 Surface-enhanced resonance Raman spectroscopy (SERRS) ndash A combination of SERS and resonance Raman spectroscopy that uses proximity to a surface to increase Raman intensity and excitation wavelength matched to the maximum absorbance of the molecule being analysed
4 Coherent anti-Stokes Raman spectroscopy (CARS) ndash
Two laser beams are used to generate a coherent anti-Stokes frequency beam which can be enhanced by resonance
43
5 Raman optical activity (ROA) ndash Measures vibrational optical activity by means of a small difference in the intensity of Raman scattering from chiral molecules in right- and left-circularly polarized incident light or equivalently a small circularly polarized component in the scattered light
6 Spatially offset Raman spectroscopy (SORS)
7 Spontaneous Raman spectroscopy (SRS) 8 Optical tweezers Raman spectroscopy (OTRS)
44
9 Angle-resolved Raman spectroscopy10 Inverse Raman spectroscopy11 Tip-enhanced Raman spectroscopy
(TERS) 12 Surface plasmon polariton enhanced
Raman scattering (SPPERS)13 Stand-off Remote Raman ndash 14 Fourier-transform Rama spectroscopyapplied
to photobiological systems
45
32
APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling
33
bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and
gypsum illustrating how Raman can be used for fast mineral ID
bull Gemstone and mineral identification
bull Fluid inclusions
bull Mineral and phase distribution in rock sections
bull Phase transitions
bull Mineral behavior under extreme conditions
34
Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance
35
Semiconductors
bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width
bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis
36
Life Sciences
bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level
bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure
37
Differences between IR and Raman methodsSNo Raman IR
01 It is due to the scattering of light by the vibrating molecules
It is the result of absorption of light by vibrating molecules
02 The vibration is Raman active if it causes a change in polarisability
Vibration is IR active if there is change in dipole moment
03 The molecule need not possess a permanent dipole moment
The vibration concerned should have a change in dipole moment due to that vibration
04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR
05 Sample preparation is not very elaborate it can be in any state
Sample preparation is elaborateGaseous samples can rarely be used
06 Gives an indication of covalent character in the molecule
Gives an indication of ionic character in the molecule
07 Cost of instrumentation is very high
Comparatively inexpensive
38
Advantages of Raman over IR
bull Water can be used as solvent bull Very suitable for biological samples in native state (because water
can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral
overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power
39
Advantages of IR over Ramanbull Simpler and cheaper instrumentation
bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio
bull Lower detection limit than (normal) Raman
bull Background fluorescence can overwhelm Raman
bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)
40
Several variations of Raman spectroscopy
1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal
bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)
bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977
bull A comprehensive theory of the effect was given by Lombardi and Birke
41
2 Resonance Raman spectroscopy The excitation wavelength is matched to an
electronic transition of the molecule or crystal so that vibrational modes associated with the excited electronic state are greatly enhanced This is useful for studying large molecules such as polypeptides which might show hundreds of bands in conventional Raman spectra It is also useful for associating normal modes with their observed frequency shifts
42
3 Surface-enhanced resonance Raman spectroscopy (SERRS) ndash A combination of SERS and resonance Raman spectroscopy that uses proximity to a surface to increase Raman intensity and excitation wavelength matched to the maximum absorbance of the molecule being analysed
4 Coherent anti-Stokes Raman spectroscopy (CARS) ndash
Two laser beams are used to generate a coherent anti-Stokes frequency beam which can be enhanced by resonance
43
5 Raman optical activity (ROA) ndash Measures vibrational optical activity by means of a small difference in the intensity of Raman scattering from chiral molecules in right- and left-circularly polarized incident light or equivalently a small circularly polarized component in the scattered light
6 Spatially offset Raman spectroscopy (SORS)
7 Spontaneous Raman spectroscopy (SRS) 8 Optical tweezers Raman spectroscopy (OTRS)
44
9 Angle-resolved Raman spectroscopy10 Inverse Raman spectroscopy11 Tip-enhanced Raman spectroscopy
(TERS) 12 Surface plasmon polariton enhanced
Raman scattering (SPPERS)13 Stand-off Remote Raman ndash 14 Fourier-transform Rama spectroscopyapplied
to photobiological systems
45
33
bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and
gypsum illustrating how Raman can be used for fast mineral ID
bull Gemstone and mineral identification
bull Fluid inclusions
bull Mineral and phase distribution in rock sections
bull Phase transitions
bull Mineral behavior under extreme conditions
34
Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance
35
Semiconductors
bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width
bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis
36
Life Sciences
bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level
bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure
37
Differences between IR and Raman methodsSNo Raman IR
01 It is due to the scattering of light by the vibrating molecules
It is the result of absorption of light by vibrating molecules
02 The vibration is Raman active if it causes a change in polarisability
Vibration is IR active if there is change in dipole moment
03 The molecule need not possess a permanent dipole moment
The vibration concerned should have a change in dipole moment due to that vibration
04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR
05 Sample preparation is not very elaborate it can be in any state
Sample preparation is elaborateGaseous samples can rarely be used
06 Gives an indication of covalent character in the molecule
Gives an indication of ionic character in the molecule
07 Cost of instrumentation is very high
Comparatively inexpensive
38
Advantages of Raman over IR
bull Water can be used as solvent bull Very suitable for biological samples in native state (because water
can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral
overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power
39
Advantages of IR over Ramanbull Simpler and cheaper instrumentation
bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio
bull Lower detection limit than (normal) Raman
bull Background fluorescence can overwhelm Raman
bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)
40
Several variations of Raman spectroscopy
1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal
bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)
bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977
bull A comprehensive theory of the effect was given by Lombardi and Birke
41
2 Resonance Raman spectroscopy The excitation wavelength is matched to an
electronic transition of the molecule or crystal so that vibrational modes associated with the excited electronic state are greatly enhanced This is useful for studying large molecules such as polypeptides which might show hundreds of bands in conventional Raman spectra It is also useful for associating normal modes with their observed frequency shifts
42
3 Surface-enhanced resonance Raman spectroscopy (SERRS) ndash A combination of SERS and resonance Raman spectroscopy that uses proximity to a surface to increase Raman intensity and excitation wavelength matched to the maximum absorbance of the molecule being analysed
4 Coherent anti-Stokes Raman spectroscopy (CARS) ndash
Two laser beams are used to generate a coherent anti-Stokes frequency beam which can be enhanced by resonance
43
5 Raman optical activity (ROA) ndash Measures vibrational optical activity by means of a small difference in the intensity of Raman scattering from chiral molecules in right- and left-circularly polarized incident light or equivalently a small circularly polarized component in the scattered light
6 Spatially offset Raman spectroscopy (SORS)
7 Spontaneous Raman spectroscopy (SRS) 8 Optical tweezers Raman spectroscopy (OTRS)
44
9 Angle-resolved Raman spectroscopy10 Inverse Raman spectroscopy11 Tip-enhanced Raman spectroscopy
(TERS) 12 Surface plasmon polariton enhanced
Raman scattering (SPPERS)13 Stand-off Remote Raman ndash 14 Fourier-transform Rama spectroscopyapplied
to photobiological systems
45
34
Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance
35
Semiconductors
bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width
bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis
36
Life Sciences
bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level
bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure
37
Differences between IR and Raman methodsSNo Raman IR
01 It is due to the scattering of light by the vibrating molecules
It is the result of absorption of light by vibrating molecules
02 The vibration is Raman active if it causes a change in polarisability
Vibration is IR active if there is change in dipole moment
03 The molecule need not possess a permanent dipole moment
The vibration concerned should have a change in dipole moment due to that vibration
04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR
05 Sample preparation is not very elaborate it can be in any state
Sample preparation is elaborateGaseous samples can rarely be used
06 Gives an indication of covalent character in the molecule
Gives an indication of ionic character in the molecule
07 Cost of instrumentation is very high
Comparatively inexpensive
38
Advantages of Raman over IR
bull Water can be used as solvent bull Very suitable for biological samples in native state (because water
can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral
overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power
39
Advantages of IR over Ramanbull Simpler and cheaper instrumentation
bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio
bull Lower detection limit than (normal) Raman
bull Background fluorescence can overwhelm Raman
bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)
40
Several variations of Raman spectroscopy
1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal
bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)
bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977
bull A comprehensive theory of the effect was given by Lombardi and Birke
41
2 Resonance Raman spectroscopy The excitation wavelength is matched to an
electronic transition of the molecule or crystal so that vibrational modes associated with the excited electronic state are greatly enhanced This is useful for studying large molecules such as polypeptides which might show hundreds of bands in conventional Raman spectra It is also useful for associating normal modes with their observed frequency shifts
42
3 Surface-enhanced resonance Raman spectroscopy (SERRS) ndash A combination of SERS and resonance Raman spectroscopy that uses proximity to a surface to increase Raman intensity and excitation wavelength matched to the maximum absorbance of the molecule being analysed
4 Coherent anti-Stokes Raman spectroscopy (CARS) ndash
Two laser beams are used to generate a coherent anti-Stokes frequency beam which can be enhanced by resonance
43
5 Raman optical activity (ROA) ndash Measures vibrational optical activity by means of a small difference in the intensity of Raman scattering from chiral molecules in right- and left-circularly polarized incident light or equivalently a small circularly polarized component in the scattered light
6 Spatially offset Raman spectroscopy (SORS)
7 Spontaneous Raman spectroscopy (SRS) 8 Optical tweezers Raman spectroscopy (OTRS)
44
9 Angle-resolved Raman spectroscopy10 Inverse Raman spectroscopy11 Tip-enhanced Raman spectroscopy
(TERS) 12 Surface plasmon polariton enhanced
Raman scattering (SPPERS)13 Stand-off Remote Raman ndash 14 Fourier-transform Rama spectroscopyapplied
to photobiological systems
45
35
Semiconductors
bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width
bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis
36
Life Sciences
bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level
bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure
37
Differences between IR and Raman methodsSNo Raman IR
01 It is due to the scattering of light by the vibrating molecules
It is the result of absorption of light by vibrating molecules
02 The vibration is Raman active if it causes a change in polarisability
Vibration is IR active if there is change in dipole moment
03 The molecule need not possess a permanent dipole moment
The vibration concerned should have a change in dipole moment due to that vibration
04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR
05 Sample preparation is not very elaborate it can be in any state
Sample preparation is elaborateGaseous samples can rarely be used
06 Gives an indication of covalent character in the molecule
Gives an indication of ionic character in the molecule
07 Cost of instrumentation is very high
Comparatively inexpensive
38
Advantages of Raman over IR
bull Water can be used as solvent bull Very suitable for biological samples in native state (because water
can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral
overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power
39
Advantages of IR over Ramanbull Simpler and cheaper instrumentation
bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio
bull Lower detection limit than (normal) Raman
bull Background fluorescence can overwhelm Raman
bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)
40
Several variations of Raman spectroscopy
1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal
bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)
bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977
bull A comprehensive theory of the effect was given by Lombardi and Birke
41
2 Resonance Raman spectroscopy The excitation wavelength is matched to an
electronic transition of the molecule or crystal so that vibrational modes associated with the excited electronic state are greatly enhanced This is useful for studying large molecules such as polypeptides which might show hundreds of bands in conventional Raman spectra It is also useful for associating normal modes with their observed frequency shifts
42
3 Surface-enhanced resonance Raman spectroscopy (SERRS) ndash A combination of SERS and resonance Raman spectroscopy that uses proximity to a surface to increase Raman intensity and excitation wavelength matched to the maximum absorbance of the molecule being analysed
4 Coherent anti-Stokes Raman spectroscopy (CARS) ndash
Two laser beams are used to generate a coherent anti-Stokes frequency beam which can be enhanced by resonance
43
5 Raman optical activity (ROA) ndash Measures vibrational optical activity by means of a small difference in the intensity of Raman scattering from chiral molecules in right- and left-circularly polarized incident light or equivalently a small circularly polarized component in the scattered light
6 Spatially offset Raman spectroscopy (SORS)
7 Spontaneous Raman spectroscopy (SRS) 8 Optical tweezers Raman spectroscopy (OTRS)
44
9 Angle-resolved Raman spectroscopy10 Inverse Raman spectroscopy11 Tip-enhanced Raman spectroscopy
(TERS) 12 Surface plasmon polariton enhanced
Raman scattering (SPPERS)13 Stand-off Remote Raman ndash 14 Fourier-transform Rama spectroscopyapplied
to photobiological systems
45
36
Life Sciences
bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level
bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure
37
Differences between IR and Raman methodsSNo Raman IR
01 It is due to the scattering of light by the vibrating molecules
It is the result of absorption of light by vibrating molecules
02 The vibration is Raman active if it causes a change in polarisability
Vibration is IR active if there is change in dipole moment
03 The molecule need not possess a permanent dipole moment
The vibration concerned should have a change in dipole moment due to that vibration
04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR
05 Sample preparation is not very elaborate it can be in any state
Sample preparation is elaborateGaseous samples can rarely be used
06 Gives an indication of covalent character in the molecule
Gives an indication of ionic character in the molecule
07 Cost of instrumentation is very high
Comparatively inexpensive
38
Advantages of Raman over IR
bull Water can be used as solvent bull Very suitable for biological samples in native state (because water
can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral
overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power
39
Advantages of IR over Ramanbull Simpler and cheaper instrumentation
bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio
bull Lower detection limit than (normal) Raman
bull Background fluorescence can overwhelm Raman
bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)
40
Several variations of Raman spectroscopy
1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal
bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)
bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977
bull A comprehensive theory of the effect was given by Lombardi and Birke
41
2 Resonance Raman spectroscopy The excitation wavelength is matched to an
electronic transition of the molecule or crystal so that vibrational modes associated with the excited electronic state are greatly enhanced This is useful for studying large molecules such as polypeptides which might show hundreds of bands in conventional Raman spectra It is also useful for associating normal modes with their observed frequency shifts
42
3 Surface-enhanced resonance Raman spectroscopy (SERRS) ndash A combination of SERS and resonance Raman spectroscopy that uses proximity to a surface to increase Raman intensity and excitation wavelength matched to the maximum absorbance of the molecule being analysed
4 Coherent anti-Stokes Raman spectroscopy (CARS) ndash
Two laser beams are used to generate a coherent anti-Stokes frequency beam which can be enhanced by resonance
43
5 Raman optical activity (ROA) ndash Measures vibrational optical activity by means of a small difference in the intensity of Raman scattering from chiral molecules in right- and left-circularly polarized incident light or equivalently a small circularly polarized component in the scattered light
6 Spatially offset Raman spectroscopy (SORS)
7 Spontaneous Raman spectroscopy (SRS) 8 Optical tweezers Raman spectroscopy (OTRS)
44
9 Angle-resolved Raman spectroscopy10 Inverse Raman spectroscopy11 Tip-enhanced Raman spectroscopy
(TERS) 12 Surface plasmon polariton enhanced
Raman scattering (SPPERS)13 Stand-off Remote Raman ndash 14 Fourier-transform Rama spectroscopyapplied
to photobiological systems
45
37
Differences between IR and Raman methodsSNo Raman IR
01 It is due to the scattering of light by the vibrating molecules
It is the result of absorption of light by vibrating molecules
02 The vibration is Raman active if it causes a change in polarisability
Vibration is IR active if there is change in dipole moment
03 The molecule need not possess a permanent dipole moment
The vibration concerned should have a change in dipole moment due to that vibration
04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR
05 Sample preparation is not very elaborate it can be in any state
Sample preparation is elaborateGaseous samples can rarely be used
06 Gives an indication of covalent character in the molecule
Gives an indication of ionic character in the molecule
07 Cost of instrumentation is very high
Comparatively inexpensive
38
Advantages of Raman over IR
bull Water can be used as solvent bull Very suitable for biological samples in native state (because water
can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral
overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power
39
Advantages of IR over Ramanbull Simpler and cheaper instrumentation
bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio
bull Lower detection limit than (normal) Raman
bull Background fluorescence can overwhelm Raman
bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)
40
Several variations of Raman spectroscopy
1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal
bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)
bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977
bull A comprehensive theory of the effect was given by Lombardi and Birke
41
2 Resonance Raman spectroscopy The excitation wavelength is matched to an
electronic transition of the molecule or crystal so that vibrational modes associated with the excited electronic state are greatly enhanced This is useful for studying large molecules such as polypeptides which might show hundreds of bands in conventional Raman spectra It is also useful for associating normal modes with their observed frequency shifts
42
3 Surface-enhanced resonance Raman spectroscopy (SERRS) ndash A combination of SERS and resonance Raman spectroscopy that uses proximity to a surface to increase Raman intensity and excitation wavelength matched to the maximum absorbance of the molecule being analysed
4 Coherent anti-Stokes Raman spectroscopy (CARS) ndash
Two laser beams are used to generate a coherent anti-Stokes frequency beam which can be enhanced by resonance
43
5 Raman optical activity (ROA) ndash Measures vibrational optical activity by means of a small difference in the intensity of Raman scattering from chiral molecules in right- and left-circularly polarized incident light or equivalently a small circularly polarized component in the scattered light
6 Spatially offset Raman spectroscopy (SORS)
7 Spontaneous Raman spectroscopy (SRS) 8 Optical tweezers Raman spectroscopy (OTRS)
44
9 Angle-resolved Raman spectroscopy10 Inverse Raman spectroscopy11 Tip-enhanced Raman spectroscopy
(TERS) 12 Surface plasmon polariton enhanced
Raman scattering (SPPERS)13 Stand-off Remote Raman ndash 14 Fourier-transform Rama spectroscopyapplied
to photobiological systems
45
38
Advantages of Raman over IR
bull Water can be used as solvent bull Very suitable for biological samples in native state (because water
can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral
overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power
39
Advantages of IR over Ramanbull Simpler and cheaper instrumentation
bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio
bull Lower detection limit than (normal) Raman
bull Background fluorescence can overwhelm Raman
bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)
40
Several variations of Raman spectroscopy
1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal
bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)
bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977
bull A comprehensive theory of the effect was given by Lombardi and Birke
41
2 Resonance Raman spectroscopy The excitation wavelength is matched to an
electronic transition of the molecule or crystal so that vibrational modes associated with the excited electronic state are greatly enhanced This is useful for studying large molecules such as polypeptides which might show hundreds of bands in conventional Raman spectra It is also useful for associating normal modes with their observed frequency shifts
42
3 Surface-enhanced resonance Raman spectroscopy (SERRS) ndash A combination of SERS and resonance Raman spectroscopy that uses proximity to a surface to increase Raman intensity and excitation wavelength matched to the maximum absorbance of the molecule being analysed
4 Coherent anti-Stokes Raman spectroscopy (CARS) ndash
Two laser beams are used to generate a coherent anti-Stokes frequency beam which can be enhanced by resonance
43
5 Raman optical activity (ROA) ndash Measures vibrational optical activity by means of a small difference in the intensity of Raman scattering from chiral molecules in right- and left-circularly polarized incident light or equivalently a small circularly polarized component in the scattered light
6 Spatially offset Raman spectroscopy (SORS)
7 Spontaneous Raman spectroscopy (SRS) 8 Optical tweezers Raman spectroscopy (OTRS)
44
9 Angle-resolved Raman spectroscopy10 Inverse Raman spectroscopy11 Tip-enhanced Raman spectroscopy
(TERS) 12 Surface plasmon polariton enhanced
Raman scattering (SPPERS)13 Stand-off Remote Raman ndash 14 Fourier-transform Rama spectroscopyapplied
to photobiological systems
45
39
Advantages of IR over Ramanbull Simpler and cheaper instrumentation
bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio
bull Lower detection limit than (normal) Raman
bull Background fluorescence can overwhelm Raman
bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)
40
Several variations of Raman spectroscopy
1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal
bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)
bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977
bull A comprehensive theory of the effect was given by Lombardi and Birke
41
2 Resonance Raman spectroscopy The excitation wavelength is matched to an
electronic transition of the molecule or crystal so that vibrational modes associated with the excited electronic state are greatly enhanced This is useful for studying large molecules such as polypeptides which might show hundreds of bands in conventional Raman spectra It is also useful for associating normal modes with their observed frequency shifts
42
3 Surface-enhanced resonance Raman spectroscopy (SERRS) ndash A combination of SERS and resonance Raman spectroscopy that uses proximity to a surface to increase Raman intensity and excitation wavelength matched to the maximum absorbance of the molecule being analysed
4 Coherent anti-Stokes Raman spectroscopy (CARS) ndash
Two laser beams are used to generate a coherent anti-Stokes frequency beam which can be enhanced by resonance
43
5 Raman optical activity (ROA) ndash Measures vibrational optical activity by means of a small difference in the intensity of Raman scattering from chiral molecules in right- and left-circularly polarized incident light or equivalently a small circularly polarized component in the scattered light
6 Spatially offset Raman spectroscopy (SORS)
7 Spontaneous Raman spectroscopy (SRS) 8 Optical tweezers Raman spectroscopy (OTRS)
44
9 Angle-resolved Raman spectroscopy10 Inverse Raman spectroscopy11 Tip-enhanced Raman spectroscopy
(TERS) 12 Surface plasmon polariton enhanced
Raman scattering (SPPERS)13 Stand-off Remote Raman ndash 14 Fourier-transform Rama spectroscopyapplied
to photobiological systems
45
40
Several variations of Raman spectroscopy
1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal
bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)
bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977
bull A comprehensive theory of the effect was given by Lombardi and Birke
41
2 Resonance Raman spectroscopy The excitation wavelength is matched to an
electronic transition of the molecule or crystal so that vibrational modes associated with the excited electronic state are greatly enhanced This is useful for studying large molecules such as polypeptides which might show hundreds of bands in conventional Raman spectra It is also useful for associating normal modes with their observed frequency shifts
42
3 Surface-enhanced resonance Raman spectroscopy (SERRS) ndash A combination of SERS and resonance Raman spectroscopy that uses proximity to a surface to increase Raman intensity and excitation wavelength matched to the maximum absorbance of the molecule being analysed
4 Coherent anti-Stokes Raman spectroscopy (CARS) ndash
Two laser beams are used to generate a coherent anti-Stokes frequency beam which can be enhanced by resonance
43
5 Raman optical activity (ROA) ndash Measures vibrational optical activity by means of a small difference in the intensity of Raman scattering from chiral molecules in right- and left-circularly polarized incident light or equivalently a small circularly polarized component in the scattered light
6 Spatially offset Raman spectroscopy (SORS)
7 Spontaneous Raman spectroscopy (SRS) 8 Optical tweezers Raman spectroscopy (OTRS)
44
9 Angle-resolved Raman spectroscopy10 Inverse Raman spectroscopy11 Tip-enhanced Raman spectroscopy
(TERS) 12 Surface plasmon polariton enhanced
Raman scattering (SPPERS)13 Stand-off Remote Raman ndash 14 Fourier-transform Rama spectroscopyapplied
to photobiological systems
45
41
2 Resonance Raman spectroscopy The excitation wavelength is matched to an
electronic transition of the molecule or crystal so that vibrational modes associated with the excited electronic state are greatly enhanced This is useful for studying large molecules such as polypeptides which might show hundreds of bands in conventional Raman spectra It is also useful for associating normal modes with their observed frequency shifts
42
3 Surface-enhanced resonance Raman spectroscopy (SERRS) ndash A combination of SERS and resonance Raman spectroscopy that uses proximity to a surface to increase Raman intensity and excitation wavelength matched to the maximum absorbance of the molecule being analysed
4 Coherent anti-Stokes Raman spectroscopy (CARS) ndash
Two laser beams are used to generate a coherent anti-Stokes frequency beam which can be enhanced by resonance
43
5 Raman optical activity (ROA) ndash Measures vibrational optical activity by means of a small difference in the intensity of Raman scattering from chiral molecules in right- and left-circularly polarized incident light or equivalently a small circularly polarized component in the scattered light
6 Spatially offset Raman spectroscopy (SORS)
7 Spontaneous Raman spectroscopy (SRS) 8 Optical tweezers Raman spectroscopy (OTRS)
44
9 Angle-resolved Raman spectroscopy10 Inverse Raman spectroscopy11 Tip-enhanced Raman spectroscopy
(TERS) 12 Surface plasmon polariton enhanced
Raman scattering (SPPERS)13 Stand-off Remote Raman ndash 14 Fourier-transform Rama spectroscopyapplied
to photobiological systems
45
42
3 Surface-enhanced resonance Raman spectroscopy (SERRS) ndash A combination of SERS and resonance Raman spectroscopy that uses proximity to a surface to increase Raman intensity and excitation wavelength matched to the maximum absorbance of the molecule being analysed
4 Coherent anti-Stokes Raman spectroscopy (CARS) ndash
Two laser beams are used to generate a coherent anti-Stokes frequency beam which can be enhanced by resonance
43
5 Raman optical activity (ROA) ndash Measures vibrational optical activity by means of a small difference in the intensity of Raman scattering from chiral molecules in right- and left-circularly polarized incident light or equivalently a small circularly polarized component in the scattered light
6 Spatially offset Raman spectroscopy (SORS)
7 Spontaneous Raman spectroscopy (SRS) 8 Optical tweezers Raman spectroscopy (OTRS)
44
9 Angle-resolved Raman spectroscopy10 Inverse Raman spectroscopy11 Tip-enhanced Raman spectroscopy
(TERS) 12 Surface plasmon polariton enhanced
Raman scattering (SPPERS)13 Stand-off Remote Raman ndash 14 Fourier-transform Rama spectroscopyapplied
to photobiological systems
45
43
5 Raman optical activity (ROA) ndash Measures vibrational optical activity by means of a small difference in the intensity of Raman scattering from chiral molecules in right- and left-circularly polarized incident light or equivalently a small circularly polarized component in the scattered light
6 Spatially offset Raman spectroscopy (SORS)
7 Spontaneous Raman spectroscopy (SRS) 8 Optical tweezers Raman spectroscopy (OTRS)
44
9 Angle-resolved Raman spectroscopy10 Inverse Raman spectroscopy11 Tip-enhanced Raman spectroscopy
(TERS) 12 Surface plasmon polariton enhanced
Raman scattering (SPPERS)13 Stand-off Remote Raman ndash 14 Fourier-transform Rama spectroscopyapplied
to photobiological systems
45
44
9 Angle-resolved Raman spectroscopy10 Inverse Raman spectroscopy11 Tip-enhanced Raman spectroscopy
(TERS) 12 Surface plasmon polariton enhanced
Raman scattering (SPPERS)13 Stand-off Remote Raman ndash 14 Fourier-transform Rama spectroscopyapplied
to photobiological systems
45
45