X-ray Photoelectron Spectroscopy (XPS)

X-ray Photoelectron X-ray Photoelectron Spectroscopy (XPS)Spectroscopy (XPS)

Center for Microanalysis of MaterialsCenter for Microanalysis of Materials

Frederick Seitz Materials Research Frederick Seitz Materials Research LaboratoryLaboratory

University of Illinois at Urbana-University of Illinois at Urbana-ChampaignChampaign

Surface AnalysisSurface AnalysisThe Study of the Outer-Most Layers of Materials (<100 The Study of the Outer-Most Layers of Materials (<100 ).).

Electron Electron SpectroscopiesSpectroscopies

XPS: X-ray XPS: X-ray Photoelectron Photoelectron SpectroscopySpectroscopy

AES: Auger Electron AES: Auger Electron SpectroscopySpectroscopy

EELS: Electron EELS: Electron Energy Loss Energy Loss SpectroscopySpectroscopy

Ion SpectroscopiesIon Spectroscopies

SIMS: Secondary Ion SIMS: Secondary Ion Mass SpectrometryMass Spectrometry

SNMS: Sputtered SNMS: Sputtered Neutral Mass Neutral Mass SpectrometrySpectrometry

ISS: Ion Scattering ISS: Ion Scattering SpectroscopySpectroscopy

Introduction to Introduction to X-ray Photoelectron X-ray Photoelectron Spectroscopy (XPS)Spectroscopy (XPS)

Introduction to X-ray Introduction to X-ray Photoelectron Spectroscopy Photoelectron Spectroscopy (XPS)(XPS)

What is XPS?- General What is XPS?- General TheoryTheory

How can we identify How can we identify elements and compounds?elements and compounds?

Instrumentation for XPSInstrumentation for XPS Examples of materials analysis Examples of materials analysis

with XPSwith XPS

What is XPS?What is XPS?

X-ray Photoelectron Spectroscopy X-ray Photoelectron Spectroscopy (XPS), also known as Electron Spectroscopy (XPS), also known as Electron Spectroscopy for Chemical Analysis (ESCA) is a widely for Chemical Analysis (ESCA) is a widely used technique to investigate the chemical used technique to investigate the chemical composition of surfaces.composition of surfaces.

What is XPS?What is XPS?

X-ray Photoelectron spectroscopy, X-ray Photoelectron spectroscopy, based on the photoelectric effect,based on the photoelectric effect,1,21,2 was was developed in the mid-1960’s by Kai developed in the mid-1960’s by Kai Siegbahn and his research group at the Siegbahn and his research group at the University of Uppsala, Sweden.University of Uppsala, Sweden.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.

X-ray Photoelectron X-ray Photoelectron SpectroscopySpectroscopySmall Area DetectionSmall Area Detection

X-ray BeamX-ray Beam

X-ray penetration X-ray penetration depth ~1depth ~1m.m.Electrons can be Electrons can be excited in this excited in this entire volume.entire volume.

X-ray excitation area ~1x1 cmX-ray excitation area ~1x1 cm22. Electrons . Electrons are emitted from this entire areaare emitted from this entire area

Electrons are extracted Electrons are extracted only from a narrow solid only from a narrow solid angle.angle.

1 mm1 mm22

10 nm10 nm

XPS spectral lines are XPS spectral lines are identified by the shell from identified by the shell from which the electron was which the electron was ejected (1s, 2s, 2p, etc.).ejected (1s, 2s, 2p, etc.).

The ejected photoelectron has The ejected photoelectron has kinetic energy:kinetic energy:

KE=hv-BE-KE=hv-BE- Following this process, the Following this process, the

atom will release energy by atom will release energy by the emission of an Auger the emission of an Auger Electron.Electron.

Conduction BandConduction Band

Valence BandValence Band

L2,L3L2,L3

L1L1

KK

FermiFermiLevelLevel

Free Free Electron Electron LevelLevel

Incident X-rayIncident X-rayEjected PhotoelectronEjected Photoelectron

1s1s

2s2s

2p2p

The Photoelectric ProcessThe Photoelectric Process

L electron falls to fill core level L electron falls to fill core level vacancy (step 1).vacancy (step 1).

KLL Auger electron emitted to KLL Auger electron emitted to conserve energy released in conserve energy released in step 1.step 1.

The kinetic energy of the The kinetic energy of the emitted Auger electron is: emitted Auger electron is:

KE=E(K)-E(L2)-E(L3).KE=E(K)-E(L2)-E(L3).



L2,L3L2,L3

L1L1

KK



Emitted Auger ElectronEmitted Auger Electron

1s1s

2s2s

2p2p

Auger Relation of Core HoleAuger Relation of Core Hole

XPS Energy ScaleXPS Energy Scale

The XPS instrument measures The XPS instrument measures the kinetic energy of all collected the kinetic energy of all collected electrons. The electron signal includes electrons. The electron signal includes contributions from both photoelectron contributions from both photoelectron and Auger electron lines.and Auger electron lines.

KEKE = hv - = hv - BEBE - - specspec

Where: Where: BEBE= Electron Binding Energy= Electron Binding Energy

KEKE= Electron Kinetic Energy= Electron Kinetic Energy

specspec= Spectrometer Work Function= Spectrometer Work Function

Photoelectron line energies: Photoelectron line energies: DependentDependent on photon energy.on photon energy.

Auger electron line energies: Auger electron line energies: Not DependentNot Dependent on photon energy.on photon energy.

If XPS spectra were presented on a kinetic energy If XPS spectra were presented on a kinetic energy scale, one would need to know the X-ray source energy used to scale, one would need to know the X-ray source energy used to collect the data in order to compare the chemical states in the collect the data in order to compare the chemical states in the sample with data collected using another source.sample with data collected using another source.

XPS Energy Scale- Kinetic energyXPS Energy Scale- Kinetic energy

XPS Energy Scale- Binding XPS Energy Scale- Binding energyenergy

BEBE = hv - = hv - KEKE - - specspec




Photoelectron line energies: Photoelectron line energies: Not DependentNot Dependent on photon on photon energy.energy.

Auger electron line energies: Auger electron line energies: DependentDependent on photon on photon energy.energy.

The binding energy scale was derived to make uniform The binding energy scale was derived to make uniform comparisons of chemical states straight forward.comparisons of chemical states straight forward.

Free electrons (those giving rise to conductivity) find Free electrons (those giving rise to conductivity) find an equal potential which is constant throughout the material.an equal potential which is constant throughout the material.

Fermi-Dirac Statistics:Fermi-Dirac Statistics:

f(E) = 1f(E) = 1 exp[(E-Eexp[(E-Eff)/kT] + 1)/kT] + 1

1.01.0f(E)f(E)

00

0.50.5

EEff1. At T=0 K:1. At T=0 K: f(E)=1 for E<Ef(E)=1 for E<Eff

f(E)=0 for E>Ef(E)=0 for E>Eff

2. At kT<<E2. At kT<<Eff (at room temperature kT=0.025 eV) (at room temperature kT=0.025 eV)

f(E)=0.5 for E=Ef(E)=0.5 for E=Eff

T=0 KT=0 KkT<<EkT<<Eff

Fermi Level ReferencingFermi Level Referencing

Fermi Level ReferencingFermi Level Referencing

1.0 0.8 0.6 0.4 0.2 0.0 -0.2 -0.4 -0.6 -0.8 -1.0

Ef

Fermi Edge of

TiN, room temperture

Binding energy (eV)

N(E

)/E

hv

Because the Fermi levels of the sample and spectrometer are Because the Fermi levels of the sample and spectrometer are aligned, we only need to know the spectrometer work function, aligned, we only need to know the spectrometer work function, specspec, to calculate BE(1s). , to calculate BE(1s).

EE1s1s

SampleSample SpectrometerSpectrometer

ee--

Free Electron EnergyFree Electron Energy

Fermi Level, EFermi Level, Eff

Vacuum Level, EVacuum Level, Evv

sample

KE(1s) KE(1s)

spec

BE(1s)

Sample/Spectrometer Energy Sample/Spectrometer Energy Level Diagram- Conducting Level Diagram- Conducting SampleSample

hv

A relative build-up of electrons at the spectrometer A relative build-up of electrons at the spectrometer raises the Fermi level of the spectrometer relative to the raises the Fermi level of the spectrometer relative to the sample. A potential Esample. A potential Echch will develop. will develop.

EE1s1s

SampleSample SpectrometerSpectrometer

ee--

Free Electron EnergyFree Electron Energy

BE(1s)

Fermi Level, EFermi Level, Eff

Vacuum Level, EVacuum Level, Evv

KE(1s)

spec

Ech

Sample/Spectrometer Energy Sample/Spectrometer Energy Level Diagram- Insulating Level Diagram- Insulating SampleSample

Binding Energy Binding Energy ReferencingReferencing

BEBE = hv - = hv - KEKE - - specspec- E- Echch




EEchch= Surface Charge Energy= Surface Charge Energy

EEchch can be determined by electrically calibrating the can be determined by electrically calibrating the

instrument to a spectral feature.instrument to a spectral feature.

C1s at 285.0 eVC1s at 285.0 eV

Au4fAu4f7/2 7/2 at 84.0 eVat 84.0 eV

Where do Binding Energy Shifts Where do Binding Energy Shifts Come From?Come From?-or How Can We Identify Elements and Compounds?-or How Can We Identify Elements and Compounds?

Electron-electron Electron-electron repulsionrepulsion

Electron-nucleus Electron-nucleus attractionattraction

ElectronElectron

NucleusNucleus

BindingBindingEnergyEnergy

Pure ElementPure Element

Electron-Electron-Nucleus Nucleus SeparationSeparation

Fermi LevelFermi Level

Look for changes here Look for changes here by observing electron by observing electron binding energiesbinding energies

Elemental Elemental ShiftsShifts

Binding Energy (eV)

Element 2p3/2 3p

Fe 707 53 654

Co 778 60 718

Ni 853 67 786

Cu 933 75 858

Zn 1022 89 933

Electron-nucleus attraction helps us identify theelements

Elemental ShiftsElemental Shifts

Binding Energy Binding Energy DeterminationDetermination

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




Free Free Electon Electon LevelLevel Conduction BandConduction Band


1s1s

2s2s

2p2p

Initial StateInitial State Final StateFinal State

The Sudden ApproximationThe Sudden Approximation

Assumes the remaining orbitals (often called the passive orbitals) are Assumes the remaining orbitals (often called the passive orbitals) are the same in the final state as they were in the initial state (also called the same in the final state as they were in the initial state (also called the the frozen-orbital approximationfrozen-orbital approximation). Under this assumption, the XPS ). Under this assumption, the XPS experiment measures the negative Hartree-Fock orbital energy:experiment measures the negative Hartree-Fock orbital energy:

Koopman’s Binding EnergyKoopman’s Binding Energy

EEB,KB,K - -B,KB,K

Actual binding energy will represent the readjustment of the N-1 Actual binding energy will represent the readjustment of the N-1 charges to minimize energy (relaxation):charges to minimize energy (relaxation):

EEBB = E = Eff N-1N-1 - E - Eii NN

Binding Energy Shifts Binding Energy Shifts (Chemical Shifts)(Chemical Shifts)

Point Charge Model:Point Charge Model:

EEii = E = Eii00 + kq + kqii + + q qii/r/rijij

EEBB in atom i in given in atom i in given

refernce state refernce state Weighted charge of iWeighted charge of i Potential at i due to Potential at i due to

surrounding charges surrounding charges

Carbon-Oxygen BondCarbon-Oxygen Bond

Valence LevelValence Level C 2pC 2p

Core LevelCore Level C 1sC 1s

Carbon NucleusCarbon Nucleus

Oxygen AtomOxygen Atom

C 1s C 1s BindingBindingEnergyEnergy

Electron-oxygen Electron-oxygen atom attractionatom attraction(Oxygen Electro-(Oxygen Electro-negativity)negativity)

Electron-nucleus Electron-nucleus attraction (Loss of attraction (Loss of Electronic Screening)Electronic Screening)

Shift to higher Shift to higher binding energybinding energy

Chemical Shifts- Chemical Shifts- Electronegativity EffectsElectronegativity Effects

Chemical Shifts- Chemical Shifts- Electronegativity EffectsElectronegativity Effects

FunctionalGroup

Binding Energy(eV)

hydrocarbon C-H, C -C 285.0

amine C-N 286.0

alcohol, ether C-O-H, C -O-C 286.5

Cl bound to C C-Cl 286.5

F bound to C C-F 287.8

carbonyl C=O 288.0

Electronic EffectsElectronic EffectsSpin-Orbit CouplingSpin-Orbit Coupling

284 280 276288290Binding Energy (eV)

C 1s

O rb ita l= s

l= 0 s= + /-1 /2 ls= 1 /2


965 955 945 935 925

19.8

Binding E nergy (eV)

Cu 2p

2p1/2

2p3/2

Peak Area 1 : 2

O rb ita l= p ls= 1 /2 ,3 /2

l= 1s= + /-1 /2


370374378 366 362

6.0

Binding E nergy (eV)

Peak Area 2 : 3

Ag 3d

3d3/2

3d5/2

O rb ita l= d

ls= 3 /2 ,5 /2

l= 2 s= + /-1 /2

Electronic EffectsElectronic EffectsSpin-OrbitCouplingSpin-OrbitCoupling

3.65

8791 83 79

Binding Energy (eV)

Peak Area 3 : 4

Au 4f

4f5/2

4f7/2

O rb ita l= f l= 3 s= + /-1 /2 ls= 5 /2 ,7 /2

Electronic Effects- Spin-Orbit CouplingElectronic Effects- Spin-Orbit Coupling

Ti MetalTi Metal Ti OxideTi Oxide

Final State Effects-Final State Effects-Shake-up/ Shake-offShake-up/ Shake-off

Monopole transition: Only the principle Monopole transition: Only the principle quantum number changes. Spin and quantum number changes. Spin and angular momentum cannot change.angular momentum cannot change.

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

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

Results from energy made available in the relaxation of the final Results from energy made available in the relaxation of the final state configuration (due to a loss of the screening effect of the state configuration (due to a loss of the screening effect of the

core level electron which underwent photoemission).core level electron which underwent photoemission). L(2p) -> Cu(3d)L(2p) -> Cu(3d)

Final State Effects- Final State Effects- Shake-up/ Shake-offShake-up/ Shake-off

Ni MetalNi Metal Ni OxideNi Oxide

Final State Effects- Multiplet Final State Effects- Multiplet SplittingSplitting

Following photoelectron emission, the Following photoelectron emission, the remaining unpaired electron may remaining unpaired electron may couple with other unpaired couple with other unpaired electrons in the atom, resulting in electrons in the atom, resulting in an ion with several possible final an ion with several possible final state configurations with as many state configurations with as many different energies. This produces different energies. This produces a line which is split a line which is split asymmetrically into several asymmetrically into several components.components.

Electron Scattering Electron Scattering EffectsEffects Energy Loss Peaks Energy Loss Peaks

Photoelectrons travelling through the Photoelectrons travelling through the solid can interact with other electrons in solid can interact with other electrons in the material. These interactions can result the material. These interactions can result in the photoelectron exciting an electronic in the photoelectron exciting an electronic transition, thus losing some of its energy transition, thus losing some of its energy (inelastic scattering).(inelastic scattering).

eph + esolid e*ph + e**solid

Electron Scattering EffectsElectron Scattering EffectsPlasmon Loss PeakPlasmon Loss Peak

a

A=15.3 eV

a a a

Al 2s

M e ta l

Electron Scattering EffectsElectron Scattering EffectsPlasmon Loss PeakPlasmon Loss Peak

O 1s21 eV

x4In su la tin g

M a teria l

Quantitative Analysis by XPSQuantitative Analysis by XPS

For a Homogeneous sample:For a Homogeneous sample:I = NI = NDJLDJLATAT

where: N = atoms/cmwhere: N = atoms/cm33

= photoelectric cross-section, cm= photoelectric cross-section, cm22

D = detector efficiencyD = detector efficiencyJ = X-ray flux, photon/cmJ = X-ray flux, photon/cm22-sec-sec

L = orbital symmetry factorL = orbital symmetry factor = inelastic electron mean-free path, cm= inelastic electron mean-free path, cm

A = analysis area, cmA = analysis area, cm22

T = analyzer transmission efficiencyT = analyzer transmission efficiency

Quantitative Analysis by XPSQuantitative Analysis by XPS

N = I/N = I/DJLDJLATAT

Let denominator = elemental sensitivity factor, SLet denominator = elemental sensitivity factor, S

N = I / SN = I / S

Can describe Relative Concentration of observed elements as a Can describe Relative Concentration of observed elements as a number fraction by:number fraction by:

CCxx = N = Nx x / / NNii

CCxx = I = Ixx/S/Sxx / / IIii/S/Sii

The values of S are based on empirical data.The values of S are based on empirical data.

Relative Sensitivities of the Relative Sensitivities of the ElementsElements

0

2

4

6

8

10

12

Elemental Symbol

Re

lativ

e S

ens

itivi

ty

Li

Be

B

C

N

O

F

Ne

Na

M

Al

Si

P

S

Cl

Ar

K

Ca

Sc

Ti

V

Cr

M

Fe

Co

Ni

Cu

Zn

G

G

As

Se

Br

Kr

Rb

Sr

Y

Zr

Nb

M

Tc

Ru

Rh

Pd

Ag

Cd

In

Sn

Sb

Te

I

Xe

Cs

Ba

La

Ce

Pr

Nd

P

S

Eu

G

Tb

Dy

Ho

Er

T

Yb

Lu

Hf

Ta

W

Re

Os

Ir

Pt

Au

Hg

Tl

Pb

Bi

1s

2p

3d

4d

4f

XPS of Copper-Nickel alloyXPS of Copper-Nickel alloy

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

20

40

60

80

100

120

Th

ou

san

ds

B inding Energy (eV)

N(E

)/E

PeakArea

M ct-eV/sec

Rel.Sens.

A tom icConc

%

Ni 2.65 4.044 49Cu 3.65 5.321 51

Cu 2p

Cu 3p

Ni 2p

Ni 3p

Ni LM M Ni

LM M Ni LM M

CuLM M

CuLM M

CuLM M

Comparison of SensitivitiesComparison of Sensitivities

ATOMIC NUMBER

20 40 60 80 1005E13

5E16

5E19

H Ne Co Zn Zr Sn Nd Yb Hg Th

1%

1ppm

1ppb0

RBS

AES a nd XPS

SIM S

PIXEPIXE

Instrumentation for X-Instrumentation for X-ray Photoelectron ray Photoelectron SpectroscopySpectroscopy

Introduction to X-ray Introduction to X-ray Photoelectron Spectroscopy Photoelectron Spectroscopy (XPS)(XPS)

What is XPS?- General TheoryWhat is XPS?- General Theory How can we identify elements and How can we identify elements and

compounds?compounds? Instrumentation for XPSInstrumentation for XPS Examples of materials analysis with Examples of materials analysis with

XPSXPS

Instrumentation for XPSInstrumentation for XPS

Surface analysis by XPS requires Surface analysis by XPS requires irradiating a solid in an Ultra-high Vacuum irradiating a solid in an Ultra-high Vacuum (UHV) chamber with monoenergetic soft X-(UHV) chamber with monoenergetic soft X-rays and analyzing the energies of the rays and analyzing the energies of the emitted electrons.emitted electrons.

Remove adsorbed gases from Remove adsorbed gases from the sample.the sample.

Eliminate adsorption of Eliminate adsorption of contaminants on the sample. contaminants on the sample.

Prevent arcing and high voltage Prevent arcing and high voltage breakdown.breakdown.

Increase the mean free path for Increase the mean free path for electrons, ions and photons.electrons, ions and photons.

Degree of VacuumDegree of Vacuum1010

1010

1010

1010

1010

22

-1-1

-4-4

-8-8

-11-11

Low VacuumLow Vacuum

Medium VacuumMedium Vacuum

High VacuumHigh Vacuum

Ultra-High VacuumUltra-High Vacuum

PressurePressureTorrTorr

Why UHV for Surface Why UHV for Surface Analysis?Analysis?

X-ray Photoelectron X-ray Photoelectron SpectrometerSpectrometer

X-ray Photoelectron X-ray Photoelectron SpectrometerSpectrometer

5 4 . 7

X-rayX-raySourceSource

ElectronElectronOpticsOptics

Hemispherical Energy AnalyzerHemispherical Energy Analyzer

Position Sensitive Position Sensitive Detector (PSD)Detector (PSD)

Magnetic ShieldShieldOuter SphereOuter Sphere

Inner SphereInner Sphere

SampleSample

Computer Computer SystemSystem

Analyzer ControlAnalyzer Control

Multi-Channel Multi-Channel Plate Electron Plate Electron MultiplierMultiplierResistive Anode Resistive Anode EncoderEncoder

Lenses for Energy Lenses for Energy Adjustment Adjustment (Retardation)(Retardation)

Lenses for Analysis Lenses for Analysis Area DefinitionArea Definition

Position ComputerPosition Computer

Position Address Position Address ConverterConverter

XPS at the ‘Magic Angle’XPS at the ‘Magic Angle’

Orbital Angular Symmetry FactorOrbital Angular Symmetry Factor

LLAA ( () = 1 + ) = 1 + AA (3sin (3sin22/2 - 1)/2/2 - 1)/2

where: where: = source-detector angle = source-detector angle = constant for a given sub-shell and X-ray photon= constant for a given sub-shell and X-ray photon

At 54.7º the ‘magic angle’At 54.7º the ‘magic angle’

LLAA = 1 = 1

Electron DetectionElectron Detection Single Channel DetectorSingle Channel Detector

Electron distribution on analyzer detection planeElectron distribution on analyzer detection plane

Counts in spectral memoryCounts in spectral memory

Step 1Step 1 2 2 33

Step 1Step 1 22 33

EE11 EE22 EE33 EE11 EE22 EE33 EE11 EE22 EE33

Electron DetectionElectron Detection Multi-channel Position Sensitive Detector (PSD)Multi-channel Position Sensitive Detector (PSD)

Electron distribution on analyzer detection planeElectron distribution on analyzer detection plane

Counts in spectral memoryCounts in spectral memoryEE11 EE22 EE33 EE11 EE22 EE33 EE11 EE22 EE33 EE11 EE22 EE33 EE11 EE22 EE33

Step 1Step 1 2 2 3 3 4 4 5 5

Step 1Step 1 2 2 3 3 4 4 5 5

X-ray GenerationX-ray Generation



1s1s

2s2s

2p2p



L2,L3L2,L3

L1L1

KK



1s1s

2s2s

2p2p

Secondary Secondary electronelectron

Incident Incident electronelectron

X-ray X-ray PhotonPhoton

Relative Probabilities of Relaxation of a K Relative Probabilities of Relaxation of a K Shell Core HoleShell Core Hole

5

B Ne P Ca M n Zn Br Zr

10 15 20 25 30 35 40 Atom ic Num ber

E lem ental S ym bol

0

0.2

0.4

0.6

0.8

1.0

Pro

bab

ility

Note: The light Note: The light elements have a elements have a low cross section low cross section for X-ray emission.for X-ray emission.

Auger Electron Auger Electron EmissionEmission

X-ray Photon X-ray Photon EmissionEmission

Schematic of Dual Anode X-ray SourceSchematic of Dual Anode X-ray Source

AnodeAnode

FenceFence

Anode 1Anode 1 Anode 2Anode 2

Filament 1Filament 1 Filament 2Filament 2

FenceFence

Cooling WaterCooling Water

Cooling WaterCooling Water

Water OutletWater Outlet

Water InletWater Inlet

Anode AssemblyAnode Assembly

Filament 1Filament 1

Anode 1Anode 1

FenceFence

Filament 2Filament 2

Anode 2Anode 2

Schematic of X-ray MonochromatorSchematic of X-ray Monochromator

SampleSample

X-ray AnodeX-ray Anode

Energy Energy AnalyzerAnalyzer Quartz Quartz

Crystal DisperserCrystal Disperser

Rowland CircleRowland Circle

ee--

Applications of Applications of X-ray Photoelectron X-ray Photoelectron Spectroscopy (XPS)Spectroscopy (XPS)

XPS Analysis of Pigment from Mummy XPS Analysis of Pigment from Mummy ArtworkArtwork

150 145 140 135 130

Binding Energy (eV)Binding Energy (eV)

PbO2

Pb3O4

500 400 300 200 100 0Binding Energy (eV)Binding Energy (eV)

O

Pb Pb

Pb

N

Ca

C

Na

Cl

XPS analysis showed XPS analysis showed that the pigment used that the pigment used on the mummy on the mummy wrapping was Pbwrapping was Pb33OO44

rather than Ferather than Fe22OO33

Egyptian Mummy Egyptian Mummy 2nd Century AD2nd Century ADWorld Heritage MuseumWorld Heritage MuseumUniversity of IllinoisUniversity of Illinois

Analysis of Carbon Fiber- Polymer Analysis of Carbon Fiber- Polymer Composite Material by XPSComposite Material by XPS

Woven carbon Woven carbon fiber compositefiber composite

XPS analysis identifies the functional XPS analysis identifies the functional groups present on composite surface. groups present on composite surface. Chemical nature of fiber-polymer Chemical nature of fiber-polymer interface will influence its properties.interface will influence its properties.

-C-C--C-C-

-C-O-C-O

-C=O-C=O

-300 -295 -290 -285 -280

B inding energy (eV )

N(E

)/E

Analysis of Materials for Solar Energy Analysis of Materials for Solar Energy Collection by XPS Depth Profiling-Collection by XPS Depth Profiling- The amorphous-SiC/SnOThe amorphous-SiC/SnO22 Interface Interface

The profile indicates a reduction of the SnOThe profile indicates a reduction of the SnO22

occurred at the interface during deposition. occurred at the interface during deposition. Such a reduction would effect the collector’s Such a reduction would effect the collector’s efficiency.efficiency.

Photo-voltaic CollectorPhoto-voltaic Collector

Conductive Oxide- SnOConductive Oxide- SnO22

p-type a-SiCp-type a-SiC

a-Sia-Si

Solar EnergySolar Energy

SnOSnO22

SnSn

Depth500 496 492 488 484 480

Binding Energy, eV

Data courtesy A. Nurrudin and J. Abelson, University of Illinois

Angle-resolved XPSAngle-resolved XPS

=15° = 90°

More Surface More Surface SensitiveSensitive

Less Surface Less Surface SensitiveSensitive

Information depth = dsinInformation depth = dsind = Escape depth ~ 3 d = Escape depth ~ 3 = Emission angle relative to surface= Emission angle relative to surface==Inelastic Mean Free PathInelastic Mean Free Path

Angle-resolved XPS Analysis of Angle-resolved XPS Analysis of Self-Assembling MonolayersSelf-Assembling Monolayers

Angle Resolved XPS Can Angle Resolved XPS Can DetermineDetermineOver-layer ThicknessOver-layer ThicknessOver-layer CoverageOver-layer Coverage

Data courtesy L. Ge, R. Haasch and A. Gewirth, University of IllinoisData courtesy L. Ge, R. Haasch and A. Gewirth, University of Illinois

0 2 0 4 0 6 0 8 0 1 0 00 . 1

0 . 2

0 . 3

0 . 4

0 . 5

0 . 6

C (W )

C (A u)

A u

S iW O12 40 d

E lectron E m iss ion A ng le , degrees

Expt. Data

M odel

Documents

X-ray Photoelectron Spectroscopy (XPS)