Photo Electron Spectroscopy

X-Ray Photo Electron Spectroscopy
Auger Emission Spectroscopy
Electron Spectroscopy for Chemical Analysis (ESCA)

1. X-ray Photoelectron X-ray Photoelectron
Spectroscopy (XPS)Spectroscopy (XPS)
Dr.S.RADHADr.S.RADHA
Assistant Professor of ChemistryAssistant Professor of Chemistry
SaivaBhanuKshatriya CollegeSaivaBhanuKshatriya College
AruppukottaiAruppukottai

2. Surface AnalysisSurface Analysis
The Study of the Outer-Most Layers of Materials (<100 The Study of the Outer-Most Layers of Materials (<100 AA).).
Electron Electron
SpectroscopiesSpectroscopies
XPS: X-ray XPS: X-ray
Photoelectron Photoelectron
SpectroscopySpectroscopy
AES: Auger Electron AES: Auger Electron
SpectroscopySpectroscopy
EELS: Electron Energy EELS: Electron Energy
Loss SpectroscopyLoss Spectroscopy
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

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

4. 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.

5. What is XPS?What is XPS?
X-ray Photoelectron spectroscopy, X-ray Photoelectron spectroscopy,
based on the photoelectric effect, was based on the photoelectric effect, 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.

6. X-ray Photoelectron SpectroscopyX-ray Photoelectron Spectroscopy
Small Area DetectionSmall Area Detection
X-ray BeamX-ray Beam
X-ray penetration X-ray penetration
depth ~1depth ~1mmm.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 cm
22
. 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 mm
22
10 nm10 nm

7. 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-FF
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
FermiFermi
LevelLevel
Free Free
Electron Electron
LevelLevel
Incident X-rayIncident X-ray
Ejected PhotoelectronEjected Photoelectron
1s1s
2s2s
2p2p
The Photoelectric ProcessThe Photoelectric Process

8. 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
FermiFermi
LevelLevel
Free Free
Electron Electron
LevelLevel
Emitted Auger ElectronEmitted Auger Electron
1s1s
2s2s
2p2p
Auger Relation of Core HoleAuger Relation of Core Hole

9. XPS Energy ScaleXPS Energy Scale
The XPS instrument measures the The XPS instrument measures the
kinetic energy of all collected 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.

10. KEKE = hv - = hv - BEBE - - FF
specspec
Where: Where: BEBE= Electron Binding Energy= Electron Binding Energy
KEKE= Electron Kinetic Energy= Electron Kinetic Energy
FF
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 scale, If XPS spectra were presented on a kinetic energy scale,
one would need to know the X-ray source energy used to collect one would need to know the X-ray source energy used to collect
the data in order to compare the chemical states in the sample the data in order to compare the chemical states in the sample
with data collected using another source.with data collected using another source.
XPS Energy Scale- Kinetic energyXPS Energy Scale- Kinetic energy

11. XPS Energy Scale- Binding XPS Energy Scale- Binding
energyenergy
BEBE = hv - = hv - KEKE - - FF
specspec
Where: Where: BEBE= Electron Binding Energy= Electron Binding Energy
KEKE= Electron Kinetic Energy= Electron Kinetic Energy
FF
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 energy.on photon 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.

12. 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-E
ff)/kT] + 1)/kT] + 1
1.01.0
f(E)f(E)
00
0.50.5
EE
ff1. At T=0 K:1. At T=0 K:f(E)=1 for E<Ef(E)=1 for E<E
ff
f(E)=0 for E>Ef(E)=0 for E>E
ff
2. At kT<<E2. At kT<<E
ff (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=E
ff
T=0 KT=0 K
kT<<EkT<<E
ff
Fermi Level ReferencingFermi Level Referencing

13. 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

E
f
Fermi Edge of
TiN, room temperture
Binding energy (eV)
N
(
E
)
/
E

14. 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,
FF
specspec, to calculate BE(1s). , to calculate BE(1s).
EE
1s1s
SampleSample SpectrometerSpectrometer
ee
--
Free Electron EnergyFree Electron Energy
Fermi Level, EFermi Level, E
ff
Vacuum Level, EVacuum Level, E
vv
F
sample
KE(1s)
KE(1s)
F
spec
BE(1s)
Sample/Spectrometer Energy Level Sample/Spectrometer Energy Level
Diagram- Conducting SampleDiagram- Conducting Sample

15. 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 E
chch will develop. will develop.
EE
1s1s
SampleSample SpectrometerSpectrometer
ee
--
Free Electron EnergyFree Electron Energy
BE(1s)
Fermi Level, EFermi Level, E
ff
Vacuum Level, EVacuum Level, E
vv
KE(1s)
F
spec
E
ch
Sample/Spectrometer Energy Sample/Spectrometer Energy
Level Diagram- Insulating Level Diagram- Insulating
SampleSample

16. Binding Energy DeterminationBinding 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
Electon Electon
LevelLevel
Conduction BandConduction Band
Valence BandValence Band
1s1s
2s2s
2p2p
Initial StateInitial State Final StateFinal State

17. 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
EE
B,KB,K @@ - -ee
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):
EE
BB = E = E
ff
N-1N-1
- E - E
ii
NN

18. Binding Energy Shifts Binding Energy Shifts
(Chemical Shifts)(Chemical Shifts)
Point Charge Model:Point Charge Model:
EE
ii = E = E
ii
00
+ kq + kq
ii + + SS q q
ii/r/r
ijij
EE
BB in atom i in given in atom i in given
refernce state refernce state
Weighted charge of iWeighted charge of iPotential at i due to Potential at i due to
surrounding charges surrounding charges

19. 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
BindingBinding
EnergyEnergy
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

20. Chemical Shifts- Chemical Shifts-
Electronegativity EffectsElectronegativity Effects
Functional
Group
Binding Energy
(eV)
hydrocarbon C-H, C -C 285.0
amine C-N 286.0
alcohol, etherC-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

21. Electronic EffectsElectronic Effects
Spin-Orbit CouplingSpin-Orbit Coupling
2 8 4 2 8 0 2 7 62 8 82 9 0
B i n d i n g E n e r g y ( e V )
C 1 s
O r b i t a l = s


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

22. Electronic EffectsElectronic Effects
Spin-Orbit CouplingSpin-Orbit Coupling
9 6 5 9 5 5 9 4 5 9 3 5 9 2 5
1 9 . 8
B i n d i n g E n e r g y ( e V )
C u 2 p
2 p1 / 2
2 p
3 / 2
P e a k A r e a 1 : 2
O r b i t a l = p


l s = 1 / 2 , 3 / 2

l = 1
s=+ / -1 / 2

23. Electronic EffectsElectronic Effects
Spin-Orbit CouplingSpin-Orbit Coupling
3 7 03 7 43 7 8 3 6 6 3 6 2
6 . 0
B i n d i n g E n e r g y ( e V )
P e a k A r e a 2 : 3
A g 3 d
3 d3 / 2
3 d
5 / 2
O r b i t a l = d

l s = 3 / 2 , 5 / 2

l = 2
s = + / - 1 / 2

24. Electronic EffectsElectronic Effects
Spin-OrbitCouplingSpin-OrbitCoupling
3 . 6 5
8 79 1 8 3 7 9
B i n d i n g E n e r g y ( e V )
P e a k A r e a 3 : 4
A u 4 f
4 f
5 / 2
4 f
7 / 2
O r b i t a l = f
l = 3
s = + / - 1 / 2
l s = 5 / 2 , 7 / 2

25. Electronic Effects- Spin-Orbit CouplingElectronic Effects- Spin-Orbit Coupling
Ti MetalTi Metal Ti OxideTi Oxide

26. 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)

27. Comparison of SensitivitiesComparison of Sensitivities
A T O M I C N U M B E R
2 0 4 0 6 0 8 0 1 0 0
5 E 1 3
5 E 1 6
5 E 1 9
H N e C o Z n Z r S n N d Y b H g T h
1 %
1 p p m
1 p p b
0
R B S
A E S a n d X P S
S IM S
P I X EP IX E

28. Instrumentation for X-ray Instrumentation for X-ray
Photoelectron Photoelectron
SpectroscopySpectroscopy

29. 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.

30. 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 Vacuum
1010
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
PressurePressure
TorrTorr
Why UHV for Surface Analysis?Why UHV for Surface Analysis?

31. X-ray Photoelectron X-ray Photoelectron
SpectrometerSpectrometer

32. X-ray Photoelectron SpectrometerX-ray Photoelectron Spectrometer
5 4 . 7
X-rayX-ray
SourceSource
ElectronElectron
OpticsOptics
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
MultiplierMultiplier
Resistive 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

33. XPS at the ‘Magic Angle’XPS at the ‘Magic Angle’
Orbital Angular Symmetry FactorOrbital Angular Symmetry Factor
LL
AA ( (gg) = 1 + ) = 1 + bb
AA (3sin (3sin
22
gg/2 - 1)/2/2 - 1)/2
where: where: gg = source-detector angle = source-detector angle
bb = 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’
LL
AA = 1 = 1

34. 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
EE
11 EE
22 EE
33 EE
11 EE
22 EE
33 EE
11 EE
22 EE
33

35. 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 memory
EE
11 EE
22 EE
33 EE
11 EE
22 EE
33 EE
11 EE
22 EE
33 EE
11 EE
22 EE
33 EE
11 EE
22 EE
33
Step 1Step 1 2 2 3 3 4 4 5 5
Step 1Step 1 2 2 3 3 4 4 5 5

36. 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
FermiFermi
LevelLevel
Free Free
Electron Electron
LevelLevel
1s1s
2s2s
2p2p
Secondary Secondary
electronelectron
Incident Incident
electronelectron
X-ray X-ray
PhotonPhoton

37. Relative Probabilities of Relaxation of a K Relative Probabilities of Relaxation of a K
Shell Core HoleShell Core Hole
5
B N e P C a M n Z n B r Z r
1 0 1 5 2 0 2 5 3 0 3 5 4 0 A t o m i c N u m b e r
E l e m e n t a l S y m b o l
0
0 . 2
0 . 4
0 . 6
0 . 8
1 . 0
P
r
o
b
a
b
i
l
i
t
y
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

38. 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

39. 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
--

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

41. XPS Analysis of Pigment from Mummy XPS Analysis of Pigment from Mummy
ArtworkArtwork
150 145 140 135 130
Binding Energy (eV)Binding Energy (eV)
PbO
2
Pb
3
O
4
500 400 300 200 100 0
Binding Energy (eV)Binding Energy (eV)
O
PbPb
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 Pb
33OO
44
rather than Ferather than Fe
22OO
33
Egyptian Mummy Egyptian Mummy
2nd Century AD2nd Century AD
World Heritage MuseumWorld Heritage Museum
University of IllinoisUniversity of Illinois

42. 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
Binding energy (eV)
N
(
E
)
/
E

43. Analysis of Materials for Solar Energy Collection Analysis of Materials for Solar Energy Collection
by XPS Depth Profiling-by XPS Depth Profiling-
The amorphous-SiC/SnOThe amorphous-SiC/SnO
22 Interface Interface
The profile indicates a reduction of the SnOThe profile indicates a reduction of the SnO
22
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- SnO
22
p-type a-SiCp-type a-SiC
a-Sia-Si
Solar EnergySolar Energy
SnOSnO
22
SnSn
Depth
500 496 492 488 484 480
Binding Energy, eV
Data courtesy A. Nurrudin and J. Abelson, University of Illinois

44. Angle-resolved XPSAngle-resolved XPS
q =15° q = 90°
More Surface More Surface
SensitiveSensitive
Less Surface Less Surface
SensitiveSensitive
Information depth = dsinInformation depth = dsinqq
d = Escape depth ~ 3 d = Escape depth ~ 3 ll
q q = Emission angle relative to surface= Emission angle relative to surface
l l == Inelastic Mean Free PathInelastic Mean Free Path
q
q

45. Angle-resolved XPS Analysis of Self-Angle-resolved XPS Analysis of Self-
Assembling MonolayersAssembling Monolayers
Angle Resolved XPS Can Angle Resolved XPS Can
DetermineDetermine
Over-layer ThicknessOver-layer Thickness
Over-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 0
0 . 1
0 . 2
0 . 3
0 . 4
0 . 5
0 . 6
C ( W )
C ( A u )
A u
S i W O
1 2 4 0 d
E l e c t r o n E m i s s i o n A n g l e , d e g r e e s
E x p t . D a t a
M o d e l