4/9/2017

1

PHOTOELECTRON SPECTROSCOPY (XPS)

PRINCIPLES AND APPLICATIONS

Prof. Nizam M. El-Ashgar

٢

Photoelectron Spectroscopy XPS

• What is XPS?

• Aim of XPS Analysis.

• General Theory

• How can we identify elements and compounds?

• Instrumentation for XPS

• Examples of materials analysis with XPS

4/9/2017

2

٣

What is XPS?• X-ray Photoelectron Spectroscopy (XPS), also

known as Electron Spectroscopy for ChemicalAnalysis (ESCA) is a widely used technique toinvestigate the chemical composition ofsurfaces.

• Sample is illuminated with soft (1.5kV) X-rayradiation in an ultrahigh vacuum.

• The photoelectric effect leads to the productionof photoelectrons, the energy spectrum of whichcan be determined in a beta-ray spectrometer.

XX--rayray PhotoelectronPhotoelectron spectroscopy,spectroscopy, basedbased ononthethe photoelectricphotoelectric effect,effect,11,,22 waswas developeddeveloped ininthethe midmid--19601960’s’s byby KaiKai SiegbahnSiegbahn andand hishisresearchresearch groupgroup atat thethe UniversityUniversity ofof Uppsala,Uppsala,SwedenSweden..33

1. H. Hertz, Ann. Physik 31,983 (1887).

2. A. Einstein, Ann. Physik 17,132 (1905). 1921 Nobel Prize in Physics.

3. K. Siegbahn, Et. Al.,Nova Acta Regiae Soc.Sci., Ser. IV, Vol. 20 (1967). 1981 Nobel Prize in Physics.

4/9/2017

3

The Atom and the X-Ray

Core electrons

Valence electrons

X-RayFree electron

proton

neutron

electron

electron vacancy

The core electrons respond very well to the X-Ray energy

X-Rays on the Surface

Atoms layers

e- top layer

e- lower layer

with collisions

e- lower layer

but no collisionsX-Rays

Outer surface

Inner surface

4/9/2017

4

X-Rays on the Surface

• The X-Rays will penetrate to the core e- of theatoms in the sample.

• Some e-s are going to be released without anyproblem giving the Kinetic Energies (KE)characteristic of their elements.

• Other e-s will come from inner layers and collidewith other e-s of upper layers– These e- will be lower in lower energy.– They will contribute to the noise signal of the

spectrum.

X-Rays and the ElectronsX-RayElectron without collision

Electron with collision

The noise signalcomes from theelectrons that collidewith other electronsof different layers.The collisions causea decrease in energyof the electron and itno longer willcontribute to thecharacteristic energyof the element.

4/9/2017

5

٩

Aim of XPS Analysis• Identification of elements at surfaces (depth:

10 nm).• Identification of functional groups and redox

states.• Concentration and depth profiling.• Estimation of over layer thickness.• Comparison of bulk and surface composition.• Surface homogeneity/heterogeneity• Possible surface morphology of adlayers.

١٠

Physical Bases• Based upon photon in/electron out process.• Photon E (Einstein ): E= hνwhere: h - Planck constant ( 6.62 x 10 -34 J s ).

ν - frequency (Hz) of the radiation.• In XPS the photon is absorbed by an atom in a

molecule or solid, leading to ionization and theemission of a core (inner shell) electron.

• If the photon interacts with valence levels(ionization by lost of one of them) the technique isdifferent and called UPS, Ultraviolet photoelectronspectroscopy .

4/9/2017

6

Photoelectrıc effect

١٢

4/9/2017

7

١٣

Introduction to the Solid State

In solids, atomic and molecular energylevels broaden into bands that in principlecontain as many states as there areatoms/molecules in the solid.

١٤

Process of Photoionization

A + h ν A+ + e-

E(A) + h ν = E(A+ ) + E(e-)KE = h ν – [ E(A+ ) - E(A) ]• The difference in energy between the

ionized and neutral atoms, is generallycalled the binding energy (BE) of theelectron:

KE = h ν - BE

4/9/2017

8

nn XPSXPS spectralspectral lineslines areareidentifiedidentified byby thethe shellshellfromfrom whichwhich thethe electronelectronwaswas ejectedejected ((11s,s, 22s,s, 22p,p,etcetc..))..

nn TheThe ejectedejectedphotoelectronphotoelectron hashas kinetickineticenergyenergy::KEKE == hvhv –– BEBE -- φφ

nn FollowingFollowing thisthis process,process,thethe atomatom willwill releasereleaseenergyenergy byby thethe emissionemissionofof anan AugerAuger ElectronElectron..

Conduction BandConduction Band

Valence BandValence Band

LL22,L,L33LL11

KK

FermiFermi

LevelLevel

Free Free

Electron LevelElectron Level

Incident XIncident X--rayrayEjected PhotoelectronEjected Photoelectron

11ss

22ss22pp

The Photoelectric Process

١٦

4/9/2017

9

The BE is a direct measure of the energy required to justremove the electron concerned from its initial level to thevacuum level and the KE of the photoelectron is againgiven by :

KE = h ν - BENOTE - the binding energies (BE) of energy levels in

solids are conventionally measured with respect to theFermi-level of the solid, rather than the vacuum level.

This involves a small correction to the equation givenabove in order to account for the work function (φ) ofthe solid, but for the purposes of the discussion belowthis correction will be neglected.

١٧

Binding Energy (BE)vThe Binding Energy (BE) is characteristic of the core electrons for

each element.

vThe BE is determined by the attraction of the electrons to the nucleus.

vIf an electron with energy x is pulled away from the nucleus, theattraction between the electron and the nucleus decreases and theBE decreases.

vEventually, there will be a point when the electron will be free of thenucleus.

These electrons areattracted to the protonwith certain bindingenergy x

This is the point with 0 energyof attraction between theelectron and the nucleus. Atthis point the electron is freefrom the atom.0

x

p+

B.E.

4/9/2017

10

Why the Core Electrons?• An electron near the Fermi level is far from the nucleus,

moving in different directions all over the place, and will notcarry information about any single atom.– Fermi level is the highest energy level occupied by an

electron in a neutral solid at absolute 0 temperature.– Electron binding energy (BE) is calculated with respect to

the Fermi level.

• The core e-s are local close to the nucleus and have bindingenergies characteristic of their particular element.

• The core e-s have a higher probability of matching theenergies of AlKα and MgKα X rays.

Core e-

Valence e-

Atom

19

٢٠

XPS Spectra1- Characteristic binding energy associated with each

core atomic orbital i.e. each element will give rise to acharacteristic set of peaks in the photoelectronspectrum at kinetic energies determined by thephoton energy and the respective binding energies.

2- The presence of peaks at particular energiestherefore indicates the presence of a specific elementin the sample under study.

3- The intensity of the peaks is related to theconcentration of the element within the sampledregion. (quantitative analysis of the surfacecomposition).

4/9/2017

11

KE versus BE

E E E

KE can be plotteddepending on BE.

Each peak represents theamount of e-s at a certainenergy that ischaracteristic of someelement.

1000 eV 0 eV

BE increase from right to left

KE increase from left to right

Binding energy

# of

ele

ctro

ns

(eV)

KE = hv – BE - Ø

XPS Spectrum• The XPS peaks are sharp.

• In a XPS graph it is possible to see Augerelectron peaks.

• The Auger peaks are usually wider peaks in aXPS spectrum.

• Aluminum foil is used as an example on thenext slide.

4/9/2017

12

XPS Spectrum

O 1s

O because

of Mg source

CAl

Al

O 2s

O Auger

Identification of XPS Peaks

• The plot has characteristic peaks for eachelement found in the surface of the sample.

• There are tables with the KE and BE alreadyassigned to each element.

• After the spectrum is plotted you can look forthe designated value of the peak energy fromthe graph and find the element present on thesurface.

4/9/2017

13

X-rays vs. e- Beam

• X-Rays– Hit all sample area simultaneously permitting

data acquisition that will give an idea of theaverage composition of the whole surface.

• Electron Beam– It can be focused on a particular area of the

sample to determine the composition ofselected areas of the sample surface.

XPS Technology• Consider as non-

destructive.– because it produces

soft x-rays to inducephotoelectronemission from thesample surface

• Provide information aboutsurface layers or thin filmstructures

• Applications in theindustry:– Polymer surface– Catalyst– Corrosion– Adhesion– Semiconductors– Dielectric materials– Electronics packaging– Magnetic media– Thin film coatings

4/9/2017

14

How Does XPS Technology Work?• A monoenergetic x-ray beam emits photoelectrons from the from

the surface of the sample.

• The penetration of the x-ray photons about a micrometer of thesample

• The XPS spectrum contains information only about the top 10 -100 Ǻ of the sample.

• Ultrahigh vacuum environment to eliminate excessive surfacecontamination.

• Cylindrical Mirror Analyzer (CMA) or hemispherical sector analyzer (HSA) measure the KE of emitted e-s.

• The spectrum plotted by the computer from the analyzer signal.

• The binding energies can be determined from the peak positionsand the elements present in the sample identified.

Instrumentation:COMPONENTS OF XPS

vA source of X-raysvAn ultra high vacuum (UHV) vAn electron energy analyzervmagnetic field shieldingvAn electron detector systemvA set of stage manipulators

4/9/2017

15

٢٩

The basic requirements:• A source of fixed-energy radiation (an x-ray

source).

• An electron energy analyzer (which can dispersethe emitted electrons according to their kineticenergy, and thereby measure the flux of emittedelectrons of a particular energy).

• A high vacuum environment (to enable theemitted photoelectrons to be analyzed withoutinterference from gas phase collisions).

XPS Instrument

X-Ray Source

Ion Source

SIMS Analyzer

Sample introduction

Chamber

Secondary ion mass spectrometry (SIMS)

4/9/2017

16

٣١

X-ray Photoelectron Spectrometer

Diagram of the Side View of XPS SystemX-Ray source

Ion source

Axial Electron Gun

Detector

CMA

sample

SIMS Analyzer

Sample introduction Chamber

Sample Holder

Ion PumpRoughing Pump Slits

4/9/2017

17

Schematic Diagram of XPS

٣٣

Energy of Light

Wavelength

(λ)106µm 103µm 1 µm 10-3µm 10-6µm

Energy

(E)

Bro

ad-c

ast

Shor

t wav

e ra

dio

X-ra

y

1 MeV1 KeV1 eV10-3eV10-6eV

4/9/2017

18

X-Ray Sources• Irradiate the sample surface, hitting the core electrons

(e-) of the atoms.• The X-Rays penetrate the sample to a depth on the

order of a micrometer.• Useful e- signal is obtained only from a depth of around

10 to 100 Å on the surface.• Normally, the sample will be radiated with photons of a

single energy (MgKα or AlKα).• This is known as a monoenergetic X-Ray beam.• The X-Ray source produces photons with certain

energies:– MgKα photon with an energy: hν = 1253.6 eV– AlKα photon with an energy :h ν = 1486.6 eV

The emitted photoelectrons will therefore have kineticenergies in the range of ca. 0 - 1250 eV or 0 - 1480 eV

X-ray Source Requirements• 1. High X-ray flux at sample• 2. Narrow X-ray line width• 3. Multiple-anode capability• 4. Ability to move the X-ray source (X-Y)

and retract it (Z)• 5. Long anode and filament lifetime

٣٦

4/9/2017

19

The X-ray source for XPS:• In contrast to the electron source, the X-ray

source energy depends on the choice of theanode material, resulting in the availability of anumber of discrete energies rather than acontinuous variation of the energy, as exists forelectron and ion guns.

• The photon energy must be sufficiently high toexcite intense photoelectron peaks from allelements of the periodic table.

• For XPS analysis, it is very important toconsider the energy resolution of the primary X-rays.

٣٧

X-ray tubeEarly x-ray source

Standard lab X-ray source is byvery high energy ebeam hitting theanode.

4/9/2017

20

X-ray spectrum from x-ray tube

Characteristic lines from the X ray fluorescence process (XRF) and a broad background (Bremsstrahlung), which is strongly depends on the energy of the electron

Monochromatic X-ray

1. Narrow peak width2. Reduced background3. No satellite & Ghost

peaks

Goal to achieve

SampleSample

XX--ray Anoderay Anode

Energy Energy

AnalyzerAnalyzer Quartz Quartz

Crystal DisperserCrystal Disperseree--

Rowland CircleRowland Circle

nλ=2dsinθ

For quartz (1010)surface, d=0.42 nm and78.5 degree for Al Kα0.93 nm

4/9/2017

21

Synchrotron RadiationThe synchrotron storage ring is a tubular vacuum chamber made to:

Hold an electron beam travelling through it at nearly the speed of light.Maintain the high energy of the electron beam. As the accelerating electronscircle the ring at relativistic velocities, they give off intense beams of lightincluding x-rays. By using a monochromator the light will beMonochromatic.

Key properties of synchrotron radiation:high intensity

tunability in wide range

near-coherenceمتماسكة

polarized.

pulsed

well collimated NUS has such a source in Singapore!

Sample charging effectsThe light for XPS always charges surface positively (shifting ofspectrum to higher binding energy) and leads to general instability(spectral noise).For the metal sample, which can be grounded and the charges canbe quickly gone.However, for insulator, this effects are serious and need to betreated.

C 1s shifts due to the charging

For XPS (even For XPS (even AES) never forget AES) never forget ground the ground the sample !!!sample !!!

4/9/2017

22

Inhomogeneous Surface ChargingCharging can even change the line shape due to InhomogeneousSurface Charging, which have different positive voltage on thesurface.

In a lot of cases,there is onlyspectral shift due tocharging, which canbe determined bycomparison withknown elementalXPS lines, forexample C 1s.

Vacuum System

• The instrument usesdifferent pump systemsto reach the goal of anUltra High Vacuum(UHV) environment.

• The Ultra High Vacuumenvironment willprevent contaminationof the surface and aidan accurate analysis ofthe sample.

University of Texas at El Paso, Physics Department

Side view of the Phi 560 XPS/AES/SIMS UHV System

4/9/2017

23

٤٥

UHV for Surface Analysis? Why

XPS AnalyzerAnalyzer Requirements1. Precision energy measurement across a

wide energy range2. High-energy resolution capability3. Ability to define the analysis area and, if

possible, to change it4. High dynamic range and low noise

detector

٤٦

4/9/2017

24

Instrumentation (analyzers)

Analyzer:

Most essential part of any electron spectroscopy,its characteristic are: energy range, energyresolution, sensitivity and acceptance angle.

Normally its functions involve: retarding اعاقة ofthe incoming electron, selection of the electronswith right kinetic energy (pass energy), detectingof the electrons (channeltron)

Detection of electron energy (Analyzers)

• Mainly two types of detectors are used in AES and XPSsystems: The cylindrical mirror analyser (CMA) and thehemispherical sector analyzer (HSA).

• In the past, the CMA was preferred for AES systems merely forgeometrical reasons and for its high analyzer transmissionfunction, and the HSA analyzer for XPS for its superior energyresolution.

• More and more, however, depending on the constructor and onthe requirements of the customer, the HSA detector is alsoused in AES systems.

• A multifunctional AES-XPS system is evidently operated byonly one electron detector, and mostly a HSA type is chosen.

• Yet, it is important to mention that not all of the requirementsimposed by the type of analysis coincide for XPS and AES .

٤٨

4/9/2017

25

The hemispherical sector analyzers (HSA• All constructors use HSA detectors for electron dispersion

analysis in XPS.• A typical configuration is shown in Fig. bellow.• The HSA is designed to have a constant and as high as

possible energy resolution for the detection ofphotoelectrons.

• The best energy resolution in XPS is 0.4 eV,corresponding to the line width of the monochromator.

• In order to reduce the size of the analyzer, it is standardpractice to retard the kinetic energies of thephotoelectrons either to a user-selected analyzer energy,called pass energy, or by a user-selected ratio.

٤٩

Mode of fixed analyzer transmission mode (FAT)• Also known as the constant analyzer energy mode (CAE).• In this mode of operation, which is applied for the detection of

photoelectrons, a constant voltage is applied across the hemispheresallowing electrons of a particular energy to pass between them.

• The most important characteristic in this case is a constant energyresolution in the spectrum as a function of the energy, in contrast tothe CMA analyser where a relative energy resolution is obtained.

• The electrons are emitted from the specimen and transferred to thefocal point of the analyzer by the lens assembly.

• At this point they are retarded electrostatically before entering theanalyzer itself.

• Those electrons with energies matching the pass energy of theanalyser are transmitted, detected and counted by the electrondetector.

• The retarding field potential is then ramped, and so the electrons arecounted as function of energy.٥٠

4/9/2017

26

Improving Sensitivity of HSA• To improve the sensitivity of the HSA, the electron

detection is done by a multichannel detectorsystem.

• Depending on the type of system, the number ofelectron multipliers may go up to 16.

• This parallel electron detection is especiallyuseful when a monochromator is used due to theloss of intensity of the primary X-rays.

٥١

٥٢

4/9/2017

27

Sample Preparation & Surface Damage in XPS1. Any Sample that is vacuum stable can be analyzed

by XPS.2. Sample containing volatile components can be

cooled to low temp. to avoid devolatilization3. Normally, Solid materials, such as metals ceramics

& polymer, are fairly stable under X-ray irradiationand damage caused by X-ray is minimal during atypical XPS experiment

4. Films, plaques الواح or powders can be mounted ona sample holder with a double-sided sticky tape

الصق شریط of low volatility first and then examined asbulk samples.

٥٣

5. Certain Polymer & Biological samples wouldundergo some chemical changes under prolongedX-ray exposures in an XPS experiment.

Examples are: PTFE, PVC, PVA, especially., whenthe materials are in thin films.

6. To minimize the damage, the exposure timeshould be as short as possible, and the samplesare cooled to low temperatures.

7. The causes for the XPS induced damage include:secondary electrons generated at X-ray source &impinging on the polymer or biological samplesurface.

٥٤

4/9/2017

28

XPS Instrument

The XPS is controlled byusing a computer system.

The computer system willcontrol the X-Ray typeand prepare theinstrument for analysis.

University of Texas at El Paso, Physics Department

Front view of the Phi 560 XPS/AES/SIMS UHV System and the computer system that controls the XPS.

٥٦

Where do Binding Energy Shifts Come From? Or element or compound identification.

4/9/2017

29

٥٧

Elemental Shifts

Elemental Shifts

4/9/2017

30

Binding Energy Determination

The photoelectron’s binding energy will be based on the element’s final-state configuration.

Conduction BandConduction Band

Valence BandValence Band

FermiFermi

LevelLevel

Free Free

ElectonElecton

LevelLevel Conduction BandConduction Band

Valence BandValence Band

11ss

22ss

22pp

Initial StateInitial State Final StateFinal State

٦٠

Electronic EffectSpin-Orbit Splitting or Spin-Orbit Coupling• Some electronic levels (most obviously 3p and 3d ) give

rise to a closely spaced doublet, Which appear whenspectra expanded.

• Permitted J values = L ± S• Coupling between L: The Angular Q.N., S: Unpaired

Spin• The lowest energy final state is the one with maximum J• The relative intensities of the two peaks reflects the

degeneracies of the final states (gJ = 2J + 1),• 2D 5/2: gJ = 2x{5/2}+1 = 6 (lower B.E)• 2D 3/2: gJ = 2x{3/2}+1 = 4 (higher B.E)• These two values determines the probability of transition

to such a state during photoionization.

4/9/2017

31

٦١

٦٢

4/9/2017

32

٦٣

s-Orbital

٦٤

p-Orbital

4/9/2017

33

٦٥

d-Orbital

٦٦

f-Orbital

4/9/2017

34

٦٧

Chemical ShiftsThe exact binding energy of an electron depends notonly upon the level from which photoemission isoccurring, but also upon :

1) The formal oxidation state of the atom.2) The local chemical and physical environment.

Changes in either (1) or (2) give rise to small shifts in thepeak positions in the spectrum - so-called chemical shifts .

Atoms of a higher positive oxidation state exhibit ahigher binding energy due to the extra coulombicinteraction between the photo-emitted electron and theion core.

• The shifts are typically a few to 10 eV or more, andtherefore detectors with a high energy resolution are used.

• To subtract chemical information , it is imperative todetermine peak positions as accurately as possible.

• The line of interest is preferentially evoked by ایضاح meansof a monochromatic X-ray source, and recorded with thehighest possible energy resolution.

• When dealing with small chemical shifts, overlapping peaksmay anyway occur in the spectra.

• Peak deconvolution التداخل فك and peak fitting tools areavailable in the commercial data handling systems.٦٨

4/9/2017

35

• The capability to distinguish between different chemical statesis the main characteristic of XPS.

• Due to this, another acronym is in use for this technique: ESCA,which stands for ‘Electron Spectroscopy for Chemical Analysis’.

٦٩

FWHM: fullwidth at halfmax. Int.

٧٠

4/9/2017

36

٧١

Chemical Shifts-Electronegativity Effects

Why Chemical Shift In AES, the situation is less promising

Ø Firstly, most AES lines are by nature broader than XPSlines.

Ø Secondly, the Auger transition involves three electrons andthe overall chemical shift is influenced by the three energylevels concerned.

• In general, similar shifts of a few eV as for XPS are to beexpected, especially when core electrons are involved in thetransition.

• Since in AES-specific equipment, detectors with lowerenergy resolution are used.

• It is clear that chemical shifts in AES are not often measuredaccurately.

• Moreover, peaks corresponding to transitions with valenceelectrons are broad and poorly defined, which makes theassignment of chemical shifts nearly impossible.

٧٢

4/9/2017

37

As the samples shown before, binding energies of Al3+ is higherthan the metal atom, in the meanwhile, the binding energy ofO atom (more positive charge) is higher than the O2- ion.

The chemicalshifts due to thevariation of thedistribution of thecharges at theatom site is themain reason forthe other name ofXPS:

ESCA (Electron Spectroscopy for Chemical Analysis)

٧٤

Chemical Shifts- Electronegativity Effects

4/9/2017

38

Electronic Effects- Spin-Orbit CouplingTi MetalTi Metal Ti OxideTi Oxide

٧٦

C1s envelope has been resolved into five components of polystyrene surface exposed to an oxygen plasma.

4/9/2017

39

Final State Effects-Shake-up/ Shake-off

• Monopole transition: Only the principle quantumnumber changes. Spin and angular momentumcannot change.

• Shake-up: Relaxation energy used to exciteelectrons in valence levels to bound states(monopole excitation).

• Shake-off: Relaxation energy used to exciteelectrons in valence levels to unbound states(monopole ionization).

ResultsResults fromfrom energyenergy mademade availableavailable inin thethe relaxationrelaxation ofof thethefinalfinal statestate configurationconfiguration (due(due toto aa lossloss ofof thethe screeningscreening effecteffect ofofthethe corecore levellevel electronelectron whichwhich underwentunderwent photoemission)photoemission)..

78

4/9/2017

40

٧٩

Ni MetalNi Metal Ni OxideNi Oxide

Shake-up and shake-offPhotoemission process canleave the ions in the groundstate (main peak) and alsopossibly in an excited sate(shake-up/shake-offsatellites), the latter makesthe KE of photoelectron less:higher BE.

- excitation of electron tobound state shake-upsatellite.

- excitation of electron tounbound (continuum)state shake-off satellite.

- excitation of hole stateshake-down satellite - rare.

4/9/2017

41

vThe shown is XPSspectra for Cu 2pphotoemission atdifferent chemical states.

vThe shake-up Lines doesnot exist in Cu metal, andis unique for CuO AndCuSO4

Energy loss lines

eph + esolid e*ph + e**solidPhotoelectrons travelling through the solid can interact with other electronsin the material. These interactions can result in the photoelectron exciting anelectronic transition, thus losing some of its energy (inelastic scattering).Most common are due to interband or plasmons (bulk or surface).

Surface plasmon

(bulk plasmon)

4/9/2017

42

The plasmon loss satellites are rarely sharp in insulators but veryprominent in the metals.

The main peak is normally observed at higher binding energy withseveral lines with the same energy intervals and reduced intensity, andthe interval can be not only single one due to different origins: bulk orsurface plasmons, bulk one is more prominent and interval larger (21/2

factor of the surface one).

O 1s21 eV

x4Insulating

Material

Electron Scattering EffectsPlasmon Loss Peak

Final State Effects- Multiplet Splitting

Following photoelectronemission, the remainingunpaired electron maycouple with other unpairedelectrons in the atom,resulting in an ion withseveral possible final stateconfigurations with asmany different energies.This produces a line whichis split asymmetrically intoseveral components.

4/9/2017

43

Relative Sensitivities of the Elements

0

2

4

6

8

10

12

Elemental Symbol

Rel

ativ

e S

ensi

tivity

LiBe

BC

NO

FNe

NaM

AlSi

PS

ClAr

KCa

ScTi

VCr

MFe

CoNi

CuZn

GG

AsSe

BrKrRb

SrY

ZrNb

MTc

RuRh

PdAg

CdIn

SnSb

TeIXe

CsBa

LaCe

PrNd

PSEu

GTb

DyHo

ErTYb

LuHfTa

WRe

OsIrPt

AuHg

TlPb

Bi

1s

2p

3d

4d

4f

XPS of Copper-Nickel alloy

-1100 -900 -700 -500 -300 -1000

20

40

60

80

100

120

Tho

usan

ds

Binding Energy (eV)

N(E

)/E

PeakArea

Mct-eV/sec

Rel.Sens.

AtomicConc

%Ni 2.65 4.044 49Cu 3.65 5.321 51

Cu 2p

Cu 3p

Ni 2p

Ni 3p

Ni LMM Ni

LMM Ni LMM

CuLMM

CuLMM

CuLMM

4/9/2017

44

٨٧

Applications of X-ray Photoelectron

Spectroscopy (XPS)

vXPS is routinely used to analyze inorganic compounds,metals, semiconductors, polymers, ceramics, etc.

vOrganic chemicals are not routinely analyzed by XPSbecause they are readily degraded by either the energyof the X-rays or the heat from non-monochromatic X-ray sources.

Which Materials Analyzed

4/9/2017

45

ANALYSIS OF XPS

vXPS detects all elements with (Z) >3. It cannotdetect H (Z = 1) or He (Z = 2) because thediameter of these orbitals is so small, reducingthe catch probability to almost zero

vDedection unit: ppt and some conditions ppm.

For example: determination of alumınum oxide thickness wıth xps

4/9/2017

46

٩١

XPS Analysis of Pigment from Mummy Artwork

٩٢

Analysis Carbon Fiber- Polymer Composite Material by XPS

4/9/2017

47

٩٣

Analysis of Materials for Solar Energy Collection by XPS Depth Profiling-The amorphous SiC/SnO /SnO2 Interface

٩٤Electron Spectroscopy for Chemical Analysis (ESCA)

4/9/2017

48

٩٥

a) The C1s spectrum (resolved into component peaks) for thehardsegment polyurethane;

٩٦

(b) the O1s spectrum for the hard-segment polyurethane

4/9/2017

49

٩٧(c ) the N1s spectrum for the hard-segment polyurethane

٩٨

X-rays will penetrate deeply into asample, and stimulate electron

emission throughout thespecimen.

Only those electrons emitted fromthe surface zone that havesuffered no energy loss willcontribute to the photoemissionpeak.

Electrons emitted from the surfacezone that have lost some energydue to inelastic interactions willcontribute to the scatteringbackground.

4/9/2017

50

٩٩

ESCA spectra are convolutions of the information fromeach depth within the sampling depth.

١٠٠

4/9/2017

51

١٠١

Hydroxy groups and ethers on a surface cannot bedistinguished based upon ESCA chemical shifts. If the surfaceis reacted with trifluoroacetic anhydride, only hydroxyl groupswill pick up F. The size of the F peak in the ESCA spectrumwill be proportional to the number of reacted hydroxyl groups

١٠٢

Case study of XPS

Compositional Analysis of Surfaces:

Case I: Analysis of surface treatment of a piston.

Coating Material: Fluorocarbon

4/9/2017

52

١٠٣

Polysiloxane Immobilized Ligand System

O

O

O

Si

CH2

CH2 C2H5

C2H5

H2N(CH2)2NH2

O

O

O

Si

CH2

CH2 NH2

NH2

C2H5OH

N

C

O

O

O

O

+

C

O

O

NH

NH

-

C

C

N

Reflux/Toluene

١٠٤

4/9/2017

53

١٠٥

١٠٦

XPS Results

NOSiCElementSystem

N1sO1sSi2pC1sCore-linePrecursor

399.5532102285

2.8541.41738.8%Composition

N1sO1sSi2pC1sCore-lineProduct

399.5532102285

9.628.719.342.4%Composition

4/9/2017

54

١٠٧

Conclusion• XPS is a powerful technique for

characterizing solid surfaces.• All types of inorganic soids can be analyzed.• Elemental (except H, He) and chemical

analyses within a depth of 10 nm.• Quantitative technique.• Extremely useful for surface treatment of

materials.