x-ray photoelectron spectroscopy (xps) center for microanalysis of materials frederick seitz...
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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).
Conduction BandConduction Band
Valence BandValence Band
L2,L3L2,L3
L1L1
KK
FermiFermiLevelLevel
Free Free Electron Electron LevelLevel
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
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: 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
Where: Where: BEBE= Electron Binding Energy= Electron Binding Energy
KEKE= Electron Kinetic Energy= Electron Kinetic Energy
specspec= Spectrometer Work Function= Spectrometer Work Function
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.
Conduction BandConduction Band
Valence BandValence Band
FermiFermiLevelLevel
Free Free Electon Electon LevelLevel Conduction BandConduction Band
Valence BandValence 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
Electronic EffectsElectronic EffectsSpin-Orbit CouplingSpin-Orbit Coupling
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
Electronic EffectsElectronic EffectsSpin-Orbit CouplingSpin-Orbit Coupling
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
Conduction BandConduction Band
Valence BandValence Band
1s1s
2s2s
2p2p
Conduction BandConduction Band
Valence BandValence Band
L2,L3L2,L3
L1L1
KK
FermiFermiLevelLevel
Free Free Electron Electron LevelLevel
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