XAS and XPS

KE (VB)
core
E VB

KE (core)
Evac EF
Edge
EF  Binding Energy (eV)

hv
BE = hv - KE - 
core Work function
1
 Photoelectron spectroscopy

• Photoelectron spectroscopy: photons (at a fixed

energy) in, electrons out technique - core and
valence electrons are ejected if the photon energy is
greater than the binding energy of the electrons.
Photoelectric effect, KE of electrons are studied.
• The kinetic energy (and sometimes the momentum)
of the photoelectrons are analysed (photoelectron
spectrum exhibits peaks which are chemically
sensitive)
• Information about the electronic structure (atomic
and molecular orbitals, and bands) of the
specimen can be obtained.
2
 Photoemission and X-ray Absorption

• XAS measures the absorption coefficient across

the threshold of the absorption edge of a core level
and the absorption coefficient is the sum of all
ionization channels.
• Photoemission measures the kinetic energy of the
photoelectrons ejected from all levels (binding
energy) accessible at a given photon energy.
(partial cross sections)
• They both are element and chemical specific since
they both monitor the change of the threshold of
core levels, which are element specific
3
 Photoelectron spectroscopy
• ESCA: Electron spectroscopy for chemical analysis
• XPS: X-ray photoelectron spectroscopy
• UPS: Ultraviolet photoelectron spectroscopy
• PES: Photoemission spectroscopy
KE
• Physical process:
photoelectric effect hv 
EF
(Einstein)
KE = hv – BE - 
BE
Kinetic energy
Work function
Binding energy
4
 What is PES/XPS measuring ?

• PES probes the electron energy states of matter

i) electrons with discrete energy – atomic orbital
ii) shallowly bound electrons – molecular
orbitals
iii) closely spaced energy states – energy bands
in solids
i) – Core level
ii) and iii) – Valence band

5
 What is in a peak in a PES/XPS spectrum
• Single particle approximation
The energy of the photoelectron is to a good
approximation independent of the movement of
the other electrons – yields a single peak (spin-
orbit doublets) in the PES spectrum.
• Manybody effects
The energy of the photoelectron depends on the
presence of other electrons which get excited
simultaneously yielding satellite peaks (shake-up,
shake-off, shake-down) or even the complete
disappearance of the single particle peak.

6
 Photoelectric effect
KE = hv – BE - 

KE hv
E vacuum level
Work function  EFermi level

BE

7
 Experimental considerations
• Let’s consider a metallic sample whose Fermi
level equalizes with the Fermi level of the
spectrometer upon contact at V = 0 Volt

EV
1 2
EF (sample) contact EF (spectrometer)
potential

EF (samp.) EF (spec.)

Ground, V = 0 volt
8
 Experimental consideration (cont’)
hemisphere
• KE is relative to the
Fermi level of the Ep
spectrometer at V =
0 volt
• KE is retarded to the
pass energy Ep of Electron lens
the electron energy
analyzer such that
Detector-channeltron
KE = Ep + VR or channel plate
Pass energy Spectrometer resolution,
Ep: 2, 5, 10, 20, 50, 100 V etc.
Retarding potential
Scanning V 9
 XPS peak notation: nlj

n: principle quantum #, n = 1,2,..

l: notation of orbital quantum #;
s for l = 0, p for l = 1, d for l =2
= hv –BE -
j: spin orbit coupling; j = l+s, l-s

2p6 + hv→ 2p5 + e 2p1 hole;

l = 1, s =1/2;
j: 2 possible values 2p3/2
j = l + s = 1 + 1/2 = 3/2
j = l - s = 1 - 1/2= 1/2 2p312
Multiplicity: 2j +1
I(2p3/2)/I(2p1/2)=4/2=2/1 1s
1s2 1s1 + e
What does an XPS spectrum of the core level and
Valence Band look like?
4f14 → 4f13 + e (4f1) n = 4, l = 3, s = 1/2; j = 7/2, 5/2

Au Cu

Cu component
Au
component
5% Au
in Cu

Chemical shift→ charge redistribution upon alloying 11

 Typical photon source for photoelectron
spectroscopy
XPS
• Al K1, K2 : 1486.3 eV, 1486.7 eV
• Mg K1, K2 : 1253.4 eV 1253.7 eV
UPS
• He (I) 21.2 eV
• He (II) 40.8 eV
Synchrotron radiation
• 5 -10000 eV
 XPS with tunable photon energy
• Surface sensitivity varies
with hv (hence e- KE)
e.g. Si surface core level
shifts
• The photoionization cross section (intensity)
changes as a function of photon energy.
Cross section with a Cooper minimum can
enhance element sensitivity: e.g. Cs on
Ru(0001)
13
 Probing matters with light
XPS
photon e ion (photon)
surface 0.1-1 nm
near surface nm-10 nm
Interface
Light-matter
bulk-like Interaction: soft x-ray 10-103 nm
Absorption
& Scattering
X-ray probes:
Electronic
properties hard x-ray
Morphology Structure
14
 Surface sensitivity in photoemission
Electron Escape Depth: Distance a photoelectron can travel
in a solid without losing its energy (chemical identity), 1/e

Recent measurements of
the electron escape
depth in comparison
with the universal escape
depth curve as known up
to now (shaded curve).
Measurements at ID32,
ESRF (European
Synchrotron Radiation
Facility (J. Zegenhagen)

Electron with 6400 eV KE

Can only be done with SR
15
Escape depth is sometimes known as Inelastic Mean Free Path (IMFP)
 Probing depth variation

Normal Glancing Glancing incident,

emission: emission: normal emission:
bulk sensitive surface sensitive surface sensitive

16
 Si 2p 3/2
Disappearance of surface state
Formation of hydride states
2p1/2
Surface atom
Si 2p 3/2

KE = (hv -99.5 – 4)eV

hv KE
surface sensitivity

108 4.5
115 11.5
130 26.5

Si XPS BE(2p3/2) ~ 99.5 eV

17
 Peak width and corehole lifetime
Lifetime of a core hole
The lifetime of the core hole contributes as a broadening to
the photoelectron peak. In the absence of any other
contributions the width at half maximum of the peak is related
to the lifetime according to the uncertainty principle

ΔE ·Δt  ħ/2

where ΔE and Δt are the uncertainty in energy and time in the

alternative expression; ħ = h/2, h is the Planck constant, h =
6.63 x10 –34 J s,
(1 eV = 1.6 x 10-19 J; 1 J = 6.24 x 10 18 eV )

18
 The linewidth (uncertainty in energy) is related to the
corehole lifetime (uncertainty in time)

 .   ħ/2

(eV) = (6.63 x 10 –34  6.24 x1018)/[2 x 3.1416  (sec)]2

= 1.43  10 –16/ (sec)
(eV) = 1.43  10 –16/  (sec)

Example: A femto sec. (10 -15 s) corehole lifetime ( typical)

will contribute to a lifetime broadening of 0.143 eV to the
PES peak. Other contributions come from instrumentation,
photon and electron analyzer (E = Ecore
2
+ Einstru
2
.)

19
 The differential cross section (intensity):
a semi-classical view
• The Hamiltonian of a bound electron, in an em field
radiation, A = |Ao|e ikr (photon) is
 
2 2
 (  r )
p e 2 e
H= + 2 A
+ V(r) - A.p
2m 2 mc mc

Hamiltonian for H'

a good
the unperturbed Hamiltonian system for the
photoelectric interaction Approx.

A () is the vector potential corresponding to the

e-m field (photon).
20
 The differential cross section is

d → →
= 4   h |< f | A p | i > |
2 2

d
2
 = e is the fine structureconstant
c

: solid angle; h: photon energy

d
=> photoelectron peak intensity
d

21
Angular dependence of the photoemission process:
The Yang’s Theorem [C.N. Yang, Phys. Rev. 74, 764
(1948)]
d → →
= 4   h |< f | A p | i > |
2 2

d

The differential 
cross section
illustrated for
polarized and
unpolarized light.

22
 For linear polarized radiation
d     
= [1 +  P2 (cos )] =  1
 2+ (3 cos 2
 - 1) 
d  4 4

: asymmetric parameter

varies from -1 to 2;
P2(cos) = 2(3cos2-1),
: angle between light and angle of
detection

Experimentally, angular average means that the analyzer has to

collect as large a solid angle as possible! In most solid experiments
the angular dependence is neglected. Fortunately for random
samples (powder, polycrystalline) this is usually o.k. (not always
valid for single crystals).
23
 For unpolarized light
d  
= [1 - P2 (cos )]
d  4 2

has an angular 
d dependence except when
d P2(cos) = 0 or  = 54.73o
(magic angle).

Exercise: Show that the magic angle is indeed

54.730. Gas phase experiments are often
conducted at this angle
24
 Binding energy and Koopmans theorem
(what is BE really measuring? details)
If the kinetic energy of the photoelectron is large, then
the photon electron, can be assumed to leave the system
faster than the rest of the electrons in the system can
respond to the core-hole (Sudden Approximation).
K.E.>>0 eV
In a free atom (gas phase), Koopmans theorem is
equivalent to the following expression Ev KE = 0

BE = - i BE
i
Binding Energy one electron energy of level i
A +ve value Hatree-Fock approximation
25
Rigorously speaking, BE is the difference in the total
energy between the initial and the final state!
BE = Efexact(N-1) - Eiexact(N)
BE = EfHF(N-1) + EfC - [Ei HF (N) + EiC] EHF
BE = [Ef HF(N-1) -EiHF(N)] + (Ef C- EiC) EC Eexact

The first term is the one electron energy - i and the second term
is the difference in Correlation energy, C, and is always positive.
If the atom is allowed to relax (response of all the electrons to the
core), we have to include
the Relaxation energy, R (always –ve)

A realistic description of the binding energy is

BE = -i + C + R
26
In solids such as metal or semiconductor, the BE
can be described as

BE +  = - i + C + R
i: one electron energy, determined by chemical
environment, no correlation, - ve
BE: binding energy ref. to the Fermi level, + ve
: work function (minimum energy to remove an e-
from Fermi level to vacuum), + ve
C: difference in correlation energy (EfC- EiC), + ve
Note: correlation energy EC (-ve) increases in
magnitude as the number of electrons increases
R: Relaxation, it is associated with the final state, it
is always -ve
27
Transport of photoelectron from bulk to vacuum solids:
the three step model

Step 1. Photoexcitation of an electron from a bound state

(core or valence) of an atom in the solid to an energetic
state in the solid.

Step 2. The energetic

electron migrates to the
surface, in the process, the
electron undergoes inelastic
and elastic scattering.

Step 3. The electron escapes Free atom Solid

into the vacuum 28
Theoretical photoionization cross-sections of elements
Yeh and Lindau, At. Data & Nucl. Data 32, 1 (1985)
There are photon energy dependent cross-section
minima associated with some atomic orbitals in the
vicinity above an absorption threshold. There are called
Cooper minimum and are associated with the initial
state wavefunction () which has a node in r.
Cooper minimum is widely used in the optimization of
adsorbate vs. substrate signals.

s that do not have a node in r: 1s, 2p, 3d, 4f etc.

s that have a node (changes sign) in r: 2s, 3p, 4p, 4d,
5d, etc.
29
 Graphical illustration of Cooper minimum
0 node
R2p (r) d wave

1 node
Ne (2p)

Wavefunction
p r d

R3p (r)
Ar
Ar (3p)
(3p) d wave

Kr (4p)

d wave
R4p (r)

E - Eo

2 nodes
r 30
 Valence band using variable photon energies
a. The interaction of d electrons in Au-Cu alloys:
The figs. below show the valence band spectra of a Au-Cu alloy.

Since Au 5d and Cu
3d have different
cross sections, one
can reveal the Cu and
Au character of the
valence electrons by
changing the photon 60 eV
160 eV
energy. Au 5d has a Cu 3d Au 5d
Cooper minimum at
160 eV

60 eV 160 eV
31
 Cu 3d: No
Cooper minimum

160 eV
60 eV

2 orders of
magnitude

Au 5d: Cooper
minimum
Au signal is suppressed at 160 eV
32
b. Cross section optimization and electron escape
depth considerations: layer-resolved spectroscopy:
Cs on Ru (001)

by selecting an appropriate photon energy, one can

reveal the identity of many different adsorption
states with very high sensitivity.

Cs on Ru(001) is an example in that we can select a

good photon energy at which the Cs 4d cross
section is high and the Ru 4d cross section is
minimized (Cooper minimum)

33
 Photoionization Cross Section of Cs and Ru
10 1 Yeh & Lindau At. Data & Nucl. Data, 32 (1(1985)

Cooper minimum: minimum in the cross section

associated with initial radial wavefunction that
Cross-section (Mb)

has a note in r, e.g. 2s, 3p, 4d etc.

10 0

Cs 3d cross-section is
103 larger than Ru 4d
10 -1

Cs 4d
10 -2

Ru 4d

0 200 400 600 800 1000

Photon Energy (eV)
34
 Photoemission: Examples
Surface core-level shifts (SCS) = BEs –BEb:
Observation: in metals, the core level BE of
the surface atom is shifted relative to that of
the bulk (surface atom has reduced
coordination)
i) SCS is + ve when the d band is less than
half filled (e.g. Ta)
ii) SCS is –ve when d band is more than half
filled (e.g. Au)
iii)SCS is also dependent on the surface
structure 35
 4f SCS from W and Ta
bcc (110)
s s
b b

bcc (100)
s
s
KE ~ minimum

Wertheim et al. Phys. Rev. B 30, 4343(1984)

Increasing BE
6s1 5d4 6s1 5d5

36
 Interpretation of SCS- the band model
Realignment of the surface and bulk Fermi levels
[Citrin and Wertheim PRB 27, 3176 (1983)]

d band more than half filled

Shaded area
contains the
same # of d
electrons

• Surface d band always narrows, d count remains the same

• Surface and bulk Fermi level must equalize 37
 SCS in metals based on the Band model

• Noble metal, SCS = -ve

• Transition metal with dn n > 5, SCS = -ve
• Transition metal with dn n < 5, SCS = +ve
• Experimentally, the trend is generally valid
• Alkali and alkaline earth metals are more
difficult to predict.
 Interpretation of SCS: the JM model
Thermodynamic (JM) model: Born-Haber cycle, equivalent
core [Johnasson & Martensson, PRB,21, 4427(1980)]

It is generally Core hole

with a
recognized that screening
electron,
the surface neutral atom

cohesion energy Screening

a
is approx.80% energy

that of bulk

SCS(BEs-b) = [EZ+1coh,b –Ezcoh,b]- [EZ+1coh,s –Ezcoh,s]

e.g. : if Z = Na, Z+1 = Mg; etc.

 The JM Model, cont’
This model makes use of the Born-Harber cycle (equivalent core
approximation, Z* = Z+1) and experimentally derived energies.
Relevant parameters:
(1) Cohesive energy, Ezcoh = energy required to remove an atom
(atomic # Z) from the solid, a positive value.
(2) The binding energy of an atom with atomic number Z, BEaz
(3) The screening energy S gained by an electron from the lattice to
screening the atom Z with a core hole, Z*.
Note: Z* is an atom with a core hole and a neutralized charge from
the surrounding, Z* is neutral locally.
(4) The cohesion energy of the atom Z*, EZ*coh. (note: equivalent-
core implied)
(5) The heat of solution of dissolving Z* atom in the Z host, EZ*sol

40
 Alignment of energy levels in metals,
semiconductors and molecules:
Fermi level, F : the highest occupied electronic level (analogous to
HOMO in molecules
Vacuum level Evac: electrons with zero kinetic energy
Intrinsic semiconductor: no doping
p-type : doped with e- acceptor, e.g. Si doped with B.
n-type : doped with e- donors, e.g. Si doped with N, P
Valence band: occupied densities of states below the Fermi level
Conduction band: unoccupied densities of states above the Fermi
level
Densities of States (DOS): In a solid, the atom orbital in the valence
region overlaps to form energy bands. The occupancy of the energy
levels within the band per unit energy (energy distribution of the
electrons) is the densities of states.
41
Band gap: The energy separation between the top of
the valence band and the bottom of the conduction band
Direct band gap: The top and bottom of the valence
band and conduction band respectively have the same k
(lattice vector) value; e.g. GaAs
Indirect band gap: The top and bottom of the valence
band and conduction band respectively do not have the
same k (lattice vector) value; e.g. Si, Ge
Contact potential: when materials of different work
functions are in contact, there exits a potential
difference between them.
Fermi level pinning and band banding: when metals
and semiconductors are in contact, the Fermi level
equalizes. 42
 Binding energy shifts in
semiconductors:

For semiconductor such as Si and Ge or InP and GaAs,

there exist a band-gap between the valence band and the
conduction band.
For intrinsic semiconductor (undoped), the Fermi level
is in the mid-point of the band gap,
For p-type or n-type Si for example, the Fermi level
moves towards, the top of the conduction band and the
bottom of the valence band, respectively, resulting in
large Fermi level shift, hence a large shift in the
observed energy.
43
 Metals and semiconductors
Electron distribution

Metal Semiconductor (Si)

conduction band

Fermi level
band gap
EF

valence band

sp-band d-band intrinsic n-doped p-doped

Mg, Al Ni, Cu Si, Ge N, P B 44
doped doped
Metals and semiconductor contacts

Schottky
barrier

45
Matching of energy levels at interface upon contact

46
47
 The p - n junction
When p type
and n type
semiconductor
are in contact, : contact potential
the Fermi level
equalizes

At equilibrium,
there is a charge
depletion in the
region of the
interface

48
 The BE of the Si 2p level is
a constant with respect to
the mid point of the band
gap in pure Si. All the shift
in doped silicon is given
rise by Fermi level shifts
Heavily doped n and p type Si moves the
Fermi level toward CB and VB respectively

Ref. Himpsel et.al. Proc.of the

Enrico Fermi School on
"Photoemission and absorption
spectroscopy of solids and
interfaces with Synchrotron
Radiation". ed. by M Campagna
and R. Rosei, North Holland
(Amsterdam 1990).
49
 SCS in semiconductors overlayers
2p3/2,1/2
Native oxide

Remove
the 2p1/2
component

MBE grown

F.J. Himpsel et al. Phys. Rev. B 38 (1988)

50
Photoemission: Layer-resolved spectroscopy
KE = 40 – BE -  = ~ 20 eV
s b s
i

b
i

Surf. Sci. Lett. 210, L185 (1989)

51
Cs overlayers/Ru: application of the Cooper minimum

10 1 hv = 105 eV

By selecting the photon energy at the

Cross-section (Mb)

Cooper minimum of the Ru 4d cross section

10 0

We can enhance the Cs 4d signal by three

orders of magnitude
Cs atom
10 -1

Cs 4d
Ru
10 -2

Ru 4d

0 200 400 600 800 1000

Photon Energy (eV)
52
 Enhanced Cs 4d photoemission

0.0008 ML
p(2x2) 0.0075 ML
(3x3)R30o 0.02 ML

bilayer 0.046 ML

Thin
multilayer 0.078 ML

0.17 ML
Thick
multilayer
0.28 ML

Surf. Sci. Lett. 241, L16 (1991) KE = 105 – BE -  = ~ 78 eV 53

 Cs 5p photoemission of Cs/Ru(0001):
Implications to charge transfer and decay dynamics
submono
bilayer I S

bilayer II B
I multilayer

II S
B

54
Two-dimension alloying

1ML Cu/Au/Ru

as-deposited
annealed 600K
1ML Au/Cu/Ru
as-deposited
annealed 600K
Sum:1ML Cu/Ru +
1ML Au/Ru
Kuhn et al. Phys. Rev. B 45, 3703(1992)
55
 Electronic structure of Ag and Au
overlayers & 2D- alloying on Ru(0001)

TDS of Ag/Ru VB of Ag/Ru VB of Ag/Ru

A. Bzowski et al. PRB 51,9979 (1995); PRB 59, 13379 (1999).

56
 Photoemission: Fine structures and
beyond the single particle approximation

• Manybody lineshape in metallic materials

• Shake-up and shake-off
• Exchange splitting
• Vibrational/thermal broadening
• Crystal field splitting
• Plasmons
• Complete absence of a single particle peak
(total break down of single particle approximation)

57
 Normal XPS line shape
 = E2 + E I2

The observed peak is normally fitted to a Voigt function which

is a convolution of Gaussian and Lorenztian

http://www.casaxps.com/help_manual/line_shapes.htm
58
Core hole life time and widths (radiative, X-ray and Auger)

high z
Total
low z

Auger

fluorescence

59
 Manybody (Doniac Sunjic) line shape
Metals with a high densities of states at the Fermi level often
exhibit an asymmetric line shape in the core level peak due to
manybody effect – I.e. that the itinerant electrons gets excited
simultaneously into the unoccupied band states.

(typically 0-0.5)

60
 Metallic systems with high densities of states at the Fermi level,
The core level exhibits a skew shape at higher BE

4f Au d band

EF

Pt d band

Wertheim Phys. Rev. B 25, 1987(1982)

EF
Doniach & Sunjic, J. Phys. C 3, 285(1970).

61
Shake-up and shake-off
processes
They occur in atoms, molecules
as well as solids.
Shake-up satellites arises from
simultaneous excitation of a
valence electron to an unoccupied
orbital. It is common and intense
for compounds where the orbitals Neon satellite spectrum

involved are in close proximity of

each other.
Shake-off are similar excitations
to the continuum. Similarly for
molecules
62
 Satellites in Metal carbonyls

E.W. Plummer, et.al. Phys. Rev. B18, 1673 (1978) 63

shake-up satellites in first row transition metal compounds
where the metal has partially filled d orbitals and ligand to metal
charge transfer can occur. Cu2O and CuO are good examples. As
the atom approaches a d10 configuration (no more d orbital is
available to accommodate the electron), the satellite disappears

Cu(II), d9

Cu(I), d10

G.A. Vernon et al. Inorg. Chem.15, 278 (1976) Wallband et al. J. Chem. Phys.69, 5405 (1975)

Note: Satellites can also be observed in metals; they are often weaker. The
most famous one is the 6 eV satellite in Ni. These states are often dealt with as
64
completely screened and unscreened states
Satellite involving empty d orbitals

65
The 6 eV satellite of Ni

66
 Vibrational splitting/broadening in gas phase

Frank-Condon transitions populate more than one vibrational

state of the final state of the excited molecule. The best example
is CH4(g) C 1s , first resolved in 1973 by Siegbahn et.al. It was
not until more recently, more vibrational structures were resolved.

67
The vibrational structure from Si 2p3/2,1/2 of SH4
(shown below) can be seen more clearly as the
resolution improves through the years: J.D. Bozek
et.al. Phys. Rev. Lett. 65, 2757(1990).

68
 Vibrational broadening in solids
Vibrational broadening in solids are primarily due to phonon
broadening and it is more difficult to observe quantitatively. In
general, the broadening at temperature T is treated with a
Gaussian width el-phon, where

el-phon2 = ( C/QD )[1+ [8T/3QD]2 ]1/2

where QD is the Debye temperature and C is a parameter

which depends on the electronic structure of the solid. Its
contribution to the total Gaussian width may be expressed as

tG2 = instr2 + inh2 + 8CT/3QD2 [1 + 1/2[3QD/8T]2 + ....]

QD = hvo/k e.g Au 165 oK, Ge 366o K etc.

Zero point energy Boltzmann constant (kT =0.0256 eV at 298K) 69
The Gaussian width can be extracted if the core hole lifetime,
instrument resolution and homogeneous broadening are known.
From temperature dependent measurement one can extract
parameters for the lattice dynamics of the system. This kind of
study has been carried out for a number of alkali metal overlayers.

70
D.M. Riffe et.al. Phys. Rev. Lett. 67, 117(1991).
 Crystal field splitting
The final state in a non-cubic environment is subjected to a crystal
field which splits the core level. The Hamiltonian in a linear
molecule, is H = C20 [3Lz2 - L(L + 1)]. For d electrons, H = C20
[3Lz2 - 6], operating on dz2; dxy,dyz; and dx2-y2, dxy; one gets, E0 = -
6C02; E1 = -3C02 ; and E2 = + 6 C02.. When the 4d and 3d core of Cd
and Zn respectively, ionizes, the final state is subjected to the same
kind of crystal field.

71
 Crystal field splitting

See Bancroft et.al. J. Chem. Phys. 67, 4891(1977) and 72

Inorg.Chem.5, 89(1986)
 Characteristic energy loss (plasmon)
In free-electron like metal such as alkali, alkaline and main group metals,
one often observes Plasmon loss peaks (collective oscillation of itinerant
electron in the metal). This process is primarily extra atomic. Both bulk
and surface plasmon can be seen. Surface Plasmon can often be quenched
by oxygen or any compound that quenches the free-electron-like property
of the electrons in the surface. The plasmon frequency wp in rad sec-1, can
be calculated using

wp =(4ne2/m)1/2

Where n is the
density of the
electron; n, number
of electrons per
cm3, m mass of the
electron 73
 Multiplet (exchange) splitting
When there are unpaired electrons in the valence band, there
exist exchange interaction between the core hole and the
unpaired spins. This is illustrated with the spectra of the
paramagnetic O2 and NO.
O 1s N 1s

*

O1s

74
Multiplet splitting & dn

Splitting 
# unpaired electrons

75
Multiplet splitting of L→M satellites

76
Complete breakdown of the single-particle formalism
When the single particle state couples with Coster Kronig states it
sometimes happens that the single particle state is totally wiped out.
It is quite common that the 4p level of some elements exhibits this
phenomenon due to 4p, 4d2av ("_ " denotes a core hole) interaction.
Lanthanides and actinides provide some of the examples.

77
 Single particle Manybody final
final state: 4p3/2 + state: 4d2 + CK
photoelectron Auger
continuum

N shell

4d5/2,3/2

4p3/2

4s
78
 Resonant Photoemission
hv A Intensity of B across
B the Ni M3,2 edge
hv = 69 eV

EF
Ni 3d band
hv(res.)
= 69 eV
Ni 3p

79
 XPS endstation at SXRMB (CLS)
Ep =100 eV
E ~ 0.38 eV
@ 3010 eV

mono
Au 4f

Si 1s Si

SiO2

80
Bulk sensitivity: SiO2 thin film on SiC wafer
SiC SiO2
Si 1s 10 nm SiO2
SiC
wafer

SiC
SiO2
Si 1s 5 nm SiO2
SiC
wafer

81