XPS o ESCA Photoemission Spectroscopies …rocca/Didattica/Laboratorio/pdf...Photoemission...

bull The physics of photoemission

bull How are photoemission spectra recorded sources and analyzers

bull Semi-quantitative analysis

bull Selected examples and measurements techniques

Photoemission Spectroscopies

XPS o ESCA UPS Threshold Spectroscopies (NEXAFS APS etchellip)

Spettroscopic tecniques

Electron out Photon out

Electron in HREELS

AES

Inv photoemission

SXAPS

Photon in XPS

UPS

EXAFS

IRAS

FTIR

SOLID

hn e-

SOLID

hn hn

SOLID

e-

hn

SOLID

e-

e-

The mean free path of electrons undergoing inelastic

scattering due to a material exhibits a minimum at

~100 eV Electron spectroscopies operating around this

energy are thus extremely surface sensitive

Single particle excitation

Plasmonic excitation

Photoemission Spectroscopy the ideal picture

Single Particle Scheme of Energy Levels

Ekin Eb

F

E f (N 1) Ekin Ei (N)

Many Particle Scheme Total Energies

Ekin = Final State Kinetic Energy = Work Function Eb

F(k) = Binding Energy of the k-th Initial State

Photoemission Spectroscopy Adiabatic vs Sudden Approximation

ADIABATIC approximation (ideal

case)

The process is slow and the

system (isolated atom or solid) has

the time needed to reach an

equilibrium state

SUDDEN approximation (more

realistic)

The photionization-photoemission

process is fast so that the final

state can have electrons in bound

excited states (shake-up) or in the

continuum of non bound states

(shake-off) This happens at

expenses of the kinetic energy

trasferred to the photoelectron

Photoemission Spectroscopy How real spectra look like Primary and Secondary Electrons

Photoemission Spectroscopy How single-particle and many-particle mechanisms are reflected in a photoemission spectrum

The adsorbed photon can cause

1 Direct excitation of a core electron

2 Direct excitation of a valence

electron

3 Auger process

4 Inelastic processes (plasmon

excitation and production of

secondary electrons)

The set of inelastic processes

determines the asymmetric shape of

XPS peaks (exhibiting a high binding

energy tail)

Photoemission Spectroscopy Photon Sources

Standard X-ray source

Standard monochromator

for X-ray source

Specs model

Ultra-violet photoemission spectroscopy

A Standard UV Discharge Lamp

Typical experimental setup

Hemispherical Analyzer of Electron Kinetic Energy with Entrance Optics Designed for Lateral Resolution

X rays

UV rays

The photoemission process is modelled by the

Three-Step Model of Photoemission in Solids bullPhoton Absorption - Photoionization

bullOptical Absorption Machinery bullSelection Rules

bullElectron Propagation within the Solid bullInelastic Mean Free Path [l(Ekin)]

bullElectron Escape from the Solid bullRefractive Effects at the Surface (for low Ekin electrons) bullCollection of photoemitted electrons

XPS as a core level spectroscopy

Quantitative chemical analysis of surfaces

How sensitive is it

Which is the mimimal detectable concentration of an element

How easily this techinique can be made quantitative

How reliable is it as a quantitative analysis technique

A key argument to answer such questions is provided by the

photoionization cross section of the different energetic levels of

different elements

bull One-particle approach

bull Electromagnetic Field-Matter Interaction

bull Semi-Classical Treatment of the Electromagnetic Field

bull Quantum Treatment of the Solid

H 1

2me

p e

cA

2

e V

p

A

V

H

Electron momentum

Vector potential

Scalar potential

Hamiltonian

Potential energy By appropriate treatment and care quantitative analysis of XPS

spectra can be performed with an accuracy of 5-10

Phoionization Cross Sections for Free Atoms vs Photon Energy

(Yeh and Lindau)

The Cooper mimimum in the

cross section is observed for

states having a node of the

radial wave function

When operating with a tunable X

ray source it can be of help to

measure at energies

corresponding to the Cooper

mimimum to suppress an intense

signal and to detect better the

photoemitted intensity from other

superimposed levels

Once the photon flux f is given the photoelectron current Ii of the (nl) orbital of the i-th atomic species is approximately given by

Ii nl Cil Ekin f( ) nl ( )T Ekin

Where Ci Atomic Concentration of the i-th species l Escape Depth nl Orbital Cross Section T Instrumental Efficiency

Photoemission Spectroscopy semi-quantitative analysis

Once the efficiency of detection of an atomic species is calibrated via the sensitivity factors one gets

Ci

Ii

si

Ii

sii

Where Ci Atomic Concentration of the i-th species si Orbital Sensitivity Factor of the i-th species Ii Spectral Intensity Related to the i-th species

X-RAY Photoemission Spectroscopy

Elemental Sensitivity via Core Level Binding Energies

Chemical Environment Sensitivity via Core Level Chemical Shift

Quantitative Evaluation via Core Level Intensity Analysis amp Cross Section Evaluation

Access to Many Body Realm via Spectral Line Shape Analysis

XPS ndash A few examples Core Levels and Core level shift

Wide XPS spectrum of graphite (C)

The singlet C 1s line is characterized by

1) A finite width reflecting instrumental

resolution lifetime broadening and other

many-body effects

2) A specific binding energy which reflects the

specific atomic species (C) in a specific

chemical environment (core level shift)

C(1s) region

The vacuum level would be a reference to

determine precisely Eb e DEb It is however quite

sensitive to work function changes due to

modification of the surface For the sake of

simplicity the Fermi level is often used because

it is apparent from the XPS spectrum itself

SENSIBILITArsquo CHIMICA

j l sQuantum Numbers

j Total Angular Momentum

l Orbital Angular Momentum

s Spin Angular Momentum p-symmetry state l = 1

s = plusmn12

Degeneracy = |2j+1|

XPS Core Levels and Spin-Orbit Splitting

Si(100) oxidized in O2 The Si 2p line is characterized by the occurrence of 5 chemically distinct components which reflect different chemical states of the Si atoms at the interface

XPS ndash A few examples Core Levels and Core level shifts


Si 2p32 Core level shift with resect to bulk Si for

a) Films of different thickness grown on Si(100) b) Films ( 5 Aring ) grown on different surfaces


Photoemission Spectroscopy Surface Core Level Shifts

Surface sensitivity is achieved by exploiting the inelastic mean free path vs hn

Below threshold high chance to penetrate bulk photoelectrons dominate

At the mimimum of the penetration depth the sensitivity to surface photoelectrons is maximised

Background Subtraction in Core Level Photemission Spectra 1) The yellow areas correspond in principle to the primary photoelectrons 2) The case of Shirley base-line corresponds to the integral line of the pristine spectrum

Mechanisms Governing the Line-

width and Line-asymmetry in

Photoemission Spectroscopy

How the Instrumental Resolution can be determined by measuring the Fermi Edge of a Metallic Sample

Ag 4d-related manyfold Ag 5(sp)-related manyfold

Photoemission Spectroscopy Valence Band States

Any valence band spectrum brings altogether contributions related to differing atomic sites and orbital symmetry Thereby one has to properly design ad hoc experiments aiming at disentangling the various spectral components Cooper Minimum Photoemission and Resonant Photoemission are two examples of such ad hoc experiments

Pt 5d bonding

Pt 5d anti bonding

Pt 5d non-bonding

Cooper Minimum Photoemission Possible when one of the valence band orbital shows a Cooper minimum in the photoionization cross section

Cooper minimum in the Pt 5d cross section

The Pt 5d and Si 3p cross sections are comparable

A joint analysis of VB photoemission spectra taken at and off the Cooper minimum enables to disentangle the differing site- and orbital-specific

contributions

Valence band photoemission

Usually excitation sources with less than 150 eV are employed (UV lamp or synchrotron

radiation)

Ultimate resolution ~15 meV with a conventional UV lamp

Small integration in k so that it is possible to measure the photoemision signal from a specific

part of the Brillouin zone

The valence band spectrum is characterised much better than with X-rays

UPS information Measurement of the valence band states of a surface (ARUPS)

Investigation of bands and molecular orbitals of the adsorbates

Angle Resolved UPS

Mapping of the valence band states vs wavevector

The small integration window in

k allows to sample continuously

the entire Brillouin Zone by

measuring the band structure in

the energy allowed range

Volume and surface states can

be identified

a) By comparison with theoretical

predictions

b) By their different behaviour

following gas adsorption (which

obviously affects only the surface

states)

Volume and surface states can be identified a) By comparison with theoretical predictions b) By their different behaviour following gas adsorption (which obviously affects only the surface states)

Chemisorbed C6H6

Condensed C6H6

Gas-phase C6H6

UPS for the study of adsorbed molecules

The comparison of spectra for benzene chemisorbed

on Ni(111) and for benzene condensed on the

same surface (ie for physisorbed benzene not

chemically bound to the surface) shows

1 at least three structures corresponding to the

molecular orbitals

2 A shift of the p orbital toward more negative

energies for the chemisorbed phase indicating

that interaction with the surface involves mainly

this orbital

The assignment of peaks due to adsorbates are

made mainly by comparison with theoretical

predictions or with experimental data available

either for the gas phase or for adsorption on

previously studied surfaces

Threshold Spettroscopies

In XPS the energy of the impinging photons may be much higher than the photoionization

threshold When operating with tunable sources (synchrotron) the energy of the photons is

chosen in such a way to maximise the photionization cross section and the surface sensitivity

Alternatively it is possible to study core levels looking for their photionization threshold by a

source at tunable energy The overcoming of the threshold for photoionization will be detected

either by a decrease of the impining flux or more often by the emission of photons or of Auger

electrons associated with the filling of the vacancies produced by the impinging photon beam

There are several tecniques employing different detection techniques They are collectively

addressed as APS (Appearance Potential Spectroscopy)

The excitation source (50 eV to several KeV) can be provided either by photons or by electrons

In the former case a synchrotron light osurce is needed

NEXAFS (Near Edge X-ray Absorption Fine Structure) opp XANES (X-ray Absorption Near Edge Structure)

In the near edge region the excitation probability

depends on the density of available empty states

which may be strongly modulated below and at the

vacuum level

Biatomic molecule

Keeping in mind the relevant selection rules the

transition of an 1s electron to p and levels is

modulated by the photon energy

Working with tunable X ray sources (Synchrotron Radiation) one may chose the energy at which

surface sensitivity is maximised

Alternatively one may look at the threshold energy and look for the onset of photoemission or

AES signals Such technique is called APS (Appearance Potential Spectroscopies)

Fig 3 Schematic potential (bottom) and corresponding NEXAFS

K-shell spectrum (top) of a diatomic molecular (sub)group In

addition to Rydberg states and a continuum of empty states

similar to those expected for atoms unfilled molecular orbitals

are present which is reflected in the absorption spectrum

NEXAFS (Near Edge X-ray Adsorption Fine Structure) opp XANES (X-ray Adsorption Near Edge Structure)

The threshold energies depend on the material

2p levels in non metals

K-edge (1s2p)= 285 eV for C

400 eV for N

530 eV for O

685 eV for F


K-edge (1s3p)= 1830 eV for Si

2140 eV for P

2470 ev for S

2830 eV for Cl

L-edge (2p4s 3d) in the range 100-270 eV

3d metals LIIIII (2p 3d) lt1000 eV

K-egde (1s 4p) gt4500 eV

4d metals MIIIII (2p4d) lt1000 eV

K-edge (1s4p) gt4500 eV

Fig 1 Schematic molecular potentials (bottom) and K-edge

spectrum (top) of a diatomic molecule XY The K-edge features are

due to transitions from the ls core level of atom X to the following

partially filled or unfilled molecular orbitals p orbitals in the

bound state Rydberg states at energies just below the Fermi level

and resonances in the continuum state (From St6hr [1]

copyright Springer-Verlag)

h= incident photon energy

e m= charge and mass of electrons

(E)= energy density of the final state

Iltff|Ap|figt|=dipole matrix

(h+Ei-Ef)=delta function for the

conservation of energy

)()(14 2

2

2

22

fiifx EEhpAEhhc

e

m

h ff

p

X-ray absorption cross section

The matrix describes the dipolar interaction between the electron

(momentum p) and the electric field (vector potential A) The orientation

of the molecule determines the parity of initial state (generally a

symmetric s level) and final state Photoemission and hence X ray

absorption takes place only when the matrix element is even

Angular momentum conservation implies moreover Dl=plusmn1 between

initial and final state

Information about the molecular orientation

In the case of linearly polarized light the angular dependence of the matrix element of interest

assumes a simple form

For a 1s initial state and a directional final state orbital the matrix element

points in the direction of the final state orbital O and the transition intensity

becomes cos2

(with angle between the electric field vector e and the direction of the final state orbital)

Therefore the intensity of a resonance is largest when e lies along the direction of the final

state molecular orbital and vanishes when e is perpendicular to it

2

if pe ff

if p ff

Schematic representation of the origin of the angular

dependence of NEXAFS resonances for a p-bonded

diatomic molecule adsorbed with its molecular axis

normal to the surface As a result of the different

overlap between the electric field vector and the

direction of the final state orbitals the p -resonance is

maximized at normal incidence (left) while the -

resonance is maximized at grazing incidence (right)

Experimental detection of X-ray absorption

The absorption of a photon

implies the excitation of an

electron from a core level to the

valence state This excited state

will decay either by AES or by

photoluminescence and be

detected

Energy liberated in the de-excitation process

Fluorescence (f) Auger electron (a)

f+ a=1

Fluorescence

- Photon-in Photon-out technique no UHV required

- The penetration depth of photons vs electrons allows to distinguish between

bulk and surface processes

- It is insensitive to charging problems

But hellip measuring thresholds in the soft X-Ray region may be complicated

When the x-ray photon energy resonantly connects a core level with a narrow final state in a solid such as an exciton readily identifiable characteristic peaks will appear in the spectrum These narrow characteristic spectral peaks give the NEXAFS technique A lot of its analytical power is illustrated by the B 1s π exciton shown below


In NEXAFS the final state of the photoelectron may be a bound state such as an exciton Measuring fluorescent photons or Auger electrons allows to tune the sensitivity of the technique The signal corresponds to the sum over all possible final states of the photoelectrons meaning that what NEXAFS measures is the total joint density of states of the initial core level with all final states which are consistent with the conservation rules

The great power of NEXAFS derives from its elemental specificity Because the various elements have different core level energies NEXAFS permits extraction of the signal from a surface monolayer or even a single buried layer in the presence of a huge background signal


K-edge of O in 50 Aring NiO(100)Ni(100)

Comparing fluorecence and electron yield

The peak positions and the relative intensities of the O K-edge features are identical in the two measurements The NEXAFS features labeled A B and C are assigned to the one-electron transition to the 3eg 3a1g and 4t1u orbitals respectively The peaks labeled B and C are related to multielectron configuration interactions

Flourescence

Electron yield

Comparing fluorecence and electron yield the information you can get

NEXAFS The fluorescence yield remains unchanged after annealing to 800 K while the electron yield decreases Oxygen remains near the surface region (mean free path of the O K-edge photons 2000 Aring) The thickness of the O containing region is larger than the electron escape depth (10-15 Aring at 500 eV)

NiONi(100) Preparation at 300 K followed by annealing to T=800 K

NiO clusters + c(2times2) O chemisorbed phase the O signal decreases in AES or XPS

Such decrease can originate either because of the formation of thicker NiO(100) clusters or by diffusion of oxygen deep into the metal bulk Which one of the two

NEXAFS characterization of Molecules

NEXAFS spectra differ significantly even

for rather similar molecular structures so

that they can be used as a fingerprint of

each polymer In many cases enough is

known about how chemical structure and

X-ray absorption spectral features are

related to allow one to identify unknown

species from measured NEXAFS spectra

Individual spectral features particularly the

low energy p features are often sufficient

for qualitative identification in reasonably

well characterized systems and they can

serve as useful energies for selective

chemical contrast in X-ray microscopy

POLYMERS K-edge for C

Photoelectron Diffraction Basic Principles c(2x2)SNi(100)

Photoelectron Diffraction Basic Principles Condition of Constructive Interference

Chemically-Shifted P 2p Components of PFx Fragments Chemisorbed at the Ni (111) Surface

Photoelectron Diffraction Experiment vs Simulation PF3Ni(111)

Theoretical Simulations Best Fit

Experiment



Experiment

Photoelectron Diffraction Experiment vs Simulation PFNi(111)


Experiment

2 photon photo emission 2PPE

For negative delays only the probe laser is in action Electrons are then promoted from bulk band to the n=1 and 2 image potential states by the 2PPE mechanism and pumped from there by a third photon The electrons in the surface Shockley state are photoemitted by the same 2PPE mechanism ending up at halfway between the n=1 and n=2 photoemission energies At time 0 the pump laser enters in action The n=0 state is then rapidly depleted of electrons (vanishing of the n=0 signal) Such electrons are promoted to the states n=1 and n=2 (increasing photoemission from such states induced by the probe laser) At positive delays the probe laser probes the surviving electron density ins taes n=1 and 2 The Xe layer decouples the image potential states from the Cu surface so that the lifetime of electrons in the image states becomes longer

Spettroscopic tecniques

Electron out Photon out

Electron in HREELS

AES

Inv photoemission

SXAPS

Photon in XPS

UPS

EXAFS

IRAS

FTIR

SOLID

hn e-

SOLID

hn hn

SOLID

e-

hn

SOLID

e-

e-

The mean free path of electrons undergoing inelastic

scattering due to a material exhibits a minimum at

~100 eV Electron spectroscopies operating around this

energy are thus extremely surface sensitive

Single particle excitation

Plasmonic excitation



Ekin Eb

F







case)




equilibrium state


realistic)














electron

3 Auger process







energy tail)




for X-ray source

Specs model





X rays

UV rays








How sensitive is it






different elements





H 1

2me

p e

cA

2

e V

p

A

V

H

Electron momentum

Vector potential

Scalar potential

Hamiltonian




(Yeh and Lindau)







measure at energies





superimposed levels






Ci

Ii

si

Ii

sii












many-body effects




C(1s) region












s = plusmn12

Degeneracy = |2j+1|




















Pt 5d bonding

Pt 5d anti bonding

Pt 5d non-bonding





contributions



radiation)







Angle Resolved UPS








be identified


predictions




states)


Chemisorbed C6H6

Condensed C6H6

Gas-phase C6H6







molecular orbitals




this orbital






















vacuum level

Biatomic molecule

















400 eV for N

530 eV for O

685 eV for F



2140 eV for P

2470 ev for S

2830 eV for Cl



















)()(14 2

2

2

22

fiifx EEhpAEhhc

e

m

h ff

p














becomes cos2




2

if pe ff

if p ff
















detected



f+ a=1

Fluorescence














Flourescence

Electron yield



























Experiment



Experiment



Experiment





Ekin Eb

F







case)




equilibrium state


realistic)














electron

3 Auger process







energy tail)




for X-ray source

Specs model





X rays

UV rays








How sensitive is it






different elements





H 1

2me

p e

cA

2

e V

p

A

V

H

Electron momentum

Vector potential

Scalar potential

Hamiltonian




(Yeh and Lindau)







measure at energies





superimposed levels






Ci

Ii

si

Ii

sii












many-body effects




C(1s) region












s = plusmn12

Degeneracy = |2j+1|




















Pt 5d bonding

Pt 5d anti bonding

Pt 5d non-bonding





contributions



radiation)







Angle Resolved UPS








be identified


predictions




states)


Chemisorbed C6H6

Condensed C6H6

Gas-phase C6H6







molecular orbitals




this orbital






















vacuum level

Biatomic molecule

















400 eV for N

530 eV for O

685 eV for F



2140 eV for P

2470 ev for S

2830 eV for Cl



















)()(14 2

2

2

22

fiifx EEhpAEhhc

e

m

h ff

p














becomes cos2




2

if pe ff

if p ff
















detected



f+ a=1

Fluorescence














Flourescence

Electron yield



























Experiment



Experiment



Experiment





case)




equilibrium state


realistic)














electron

3 Auger process







energy tail)




for X-ray source

Specs model





X rays

UV rays








How sensitive is it






different elements





H 1

2me

p e

cA

2

e V

p

A

V

H

Electron momentum

Vector potential

Scalar potential

Hamiltonian




(Yeh and Lindau)







measure at energies





superimposed levels






Ci

Ii

si

Ii

sii












many-body effects




C(1s) region












s = plusmn12

Degeneracy = |2j+1|




















Pt 5d bonding

Pt 5d anti bonding

Pt 5d non-bonding





contributions



radiation)







Angle Resolved UPS








be identified


predictions




states)


Chemisorbed C6H6

Condensed C6H6

Gas-phase C6H6







molecular orbitals




this orbital






















vacuum level

Biatomic molecule

















400 eV for N

530 eV for O

685 eV for F



2140 eV for P

2470 ev for S

2830 eV for Cl



















)()(14 2

2

2

22

fiifx EEhpAEhhc

e

m

h ff

p














becomes cos2




2

if pe ff

if p ff
















detected



f+ a=1

Fluorescence














Flourescence

Electron yield



























Experiment



Experiment



Experiment








electron

3 Auger process







energy tail)




for X-ray source

Specs model





X rays

UV rays








How sensitive is it






different elements





H 1

2me

p e

cA

2

e V

p

A

V

H

Electron momentum

Vector potential

Scalar potential

Hamiltonian




(Yeh and Lindau)







measure at energies





superimposed levels






Ci

Ii

si

Ii

sii












many-body effects




C(1s) region












s = plusmn12

Degeneracy = |2j+1|




















Pt 5d bonding

Pt 5d anti bonding

Pt 5d non-bonding





contributions



radiation)







Angle Resolved UPS








be identified


predictions




states)


Chemisorbed C6H6

Condensed C6H6

Gas-phase C6H6







molecular orbitals




this orbital






















vacuum level

Biatomic molecule

















400 eV for N

530 eV for O

685 eV for F



2140 eV for P

2470 ev for S

2830 eV for Cl



















)()(14 2

2

2

22

fiifx EEhpAEhhc

e

m

h ff

p














becomes cos2




2

if pe ff

if p ff
















detected



f+ a=1

Fluorescence














Flourescence

Electron yield



























Experiment



Experiment



Experiment






for X-ray source

Specs model





X rays

UV rays








How sensitive is it






different elements





H 1

2me

p e

cA

2

e V

p

A

V

H

Electron momentum

Vector potential

Scalar potential

Hamiltonian




(Yeh and Lindau)







measure at energies





superimposed levels






Ci

Ii

si

Ii

sii












many-body effects




C(1s) region












s = plusmn12

Degeneracy = |2j+1|




















Pt 5d bonding

Pt 5d anti bonding

Pt 5d non-bonding





contributions



radiation)







Angle Resolved UPS








be identified


predictions




states)


Chemisorbed C6H6

Condensed C6H6

Gas-phase C6H6







molecular orbitals




this orbital






















vacuum level

Biatomic molecule

















400 eV for N

530 eV for O

685 eV for F



2140 eV for P

2470 ev for S

2830 eV for Cl



















)()(14 2

2

2

22

fiifx EEhpAEhhc

e

m

h ff

p














becomes cos2




2

if pe ff

if p ff
















detected



f+ a=1

Fluorescence














Flourescence

Electron yield



























Experiment



Experiment



Experiment







X rays

UV rays








How sensitive is it






different elements





H 1

2me

p e

cA

2

e V

p

A

V

H

Electron momentum

Vector potential

Scalar potential

Hamiltonian




(Yeh and Lindau)







measure at energies





superimposed levels






Ci

Ii

si

Ii

sii












many-body effects




C(1s) region












s = plusmn12

Degeneracy = |2j+1|




















Pt 5d bonding

Pt 5d anti bonding

Pt 5d non-bonding





contributions



radiation)







Angle Resolved UPS








be identified


predictions




states)


Chemisorbed C6H6

Condensed C6H6

Gas-phase C6H6







molecular orbitals




this orbital






















vacuum level

Biatomic molecule

















400 eV for N

530 eV for O

685 eV for F



2140 eV for P

2470 ev for S

2830 eV for Cl



















)()(14 2

2

2

22

fiifx EEhpAEhhc

e

m

h ff

p














becomes cos2




2

if pe ff

if p ff
















detected



f+ a=1

Fluorescence














Flourescence

Electron yield



























Experiment



Experiment



Experiment










How sensitive is it






different elements





H 1

2me

p e

cA

2

e V

p

A

V

H

Electron momentum

Vector potential

Scalar potential

Hamiltonian




(Yeh and Lindau)







measure at energies





superimposed levels






Ci

Ii

si

Ii

sii












many-body effects




C(1s) region












s = plusmn12

Degeneracy = |2j+1|




















Pt 5d bonding

Pt 5d anti bonding

Pt 5d non-bonding





contributions



radiation)







Angle Resolved UPS








be identified


predictions




states)


Chemisorbed C6H6

Condensed C6H6

Gas-phase C6H6







molecular orbitals




this orbital






















vacuum level

Biatomic molecule

















400 eV for N

530 eV for O

685 eV for F



2140 eV for P

2470 ev for S

2830 eV for Cl



















)()(14 2

2

2

22

fiifx EEhpAEhhc

e

m

h ff

p














becomes cos2




2

if pe ff

if p ff
















detected



f+ a=1

Fluorescence














Flourescence

Electron yield



























Experiment



Experiment



Experiment




(Yeh and Lindau)







measure at energies





superimposed levels






Ci

Ii

si

Ii

sii












many-body effects




C(1s) region












s = plusmn12

Degeneracy = |2j+1|




















Pt 5d bonding

Pt 5d anti bonding

Pt 5d non-bonding





contributions



radiation)







Angle Resolved UPS








be identified


predictions




states)


Chemisorbed C6H6

Condensed C6H6

Gas-phase C6H6







molecular orbitals




this orbital






















vacuum level

Biatomic molecule

















400 eV for N

530 eV for O

685 eV for F



2140 eV for P

2470 ev for S

2830 eV for Cl



















)()(14 2

2

2

22

fiifx EEhpAEhhc

e

m

h ff

p














becomes cos2




2

if pe ff

if p ff
















detected



f+ a=1

Fluorescence














Flourescence

Electron yield



























Experiment



Experiment



Experiment








Ci

Ii

si

Ii

sii












many-body effects




C(1s) region












s = plusmn12

Degeneracy = |2j+1|




















Pt 5d bonding

Pt 5d anti bonding

Pt 5d non-bonding





contributions



radiation)







Angle Resolved UPS








be identified


predictions




states)


Chemisorbed C6H6

Condensed C6H6

Gas-phase C6H6







molecular orbitals




this orbital






















vacuum level

Biatomic molecule

















400 eV for N

530 eV for O

685 eV for F



2140 eV for P

2470 ev for S

2830 eV for Cl



















)()(14 2

2

2

22

fiifx EEhpAEhhc

e

m

h ff

p














becomes cos2




2

if pe ff

if p ff
















detected



f+ a=1

Fluorescence














Flourescence

Electron yield



























Experiment



Experiment



Experiment













many-body effects




C(1s) region












s = plusmn12

Degeneracy = |2j+1|




















Pt 5d bonding

Pt 5d anti bonding

Pt 5d non-bonding





contributions



radiation)







Angle Resolved UPS








be identified


predictions




states)


Chemisorbed C6H6

Condensed C6H6

Gas-phase C6H6







molecular orbitals




this orbital






















vacuum level

Biatomic molecule

















400 eV for N

530 eV for O

685 eV for F



2140 eV for P

2470 ev for S

2830 eV for Cl



















)()(14 2

2

2

22

fiifx EEhpAEhhc

e

m

h ff

p














becomes cos2




2

if pe ff

if p ff
















detected



f+ a=1

Fluorescence














Flourescence

Electron yield



























Experiment



Experiment



Experiment







s = plusmn12

Degeneracy = |2j+1|




















Pt 5d bonding

Pt 5d anti bonding

Pt 5d non-bonding





contributions



radiation)







Angle Resolved UPS








be identified


predictions




states)


Chemisorbed C6H6

Condensed C6H6

Gas-phase C6H6







molecular orbitals




this orbital






















vacuum level

Biatomic molecule

















400 eV for N

530 eV for O

685 eV for F



2140 eV for P

2470 ev for S

2830 eV for Cl



















)()(14 2

2

2

22

fiifx EEhpAEhhc

e

m

h ff

p














becomes cos2




2

if pe ff

if p ff
















detected



f+ a=1

Fluorescence














Flourescence

Electron yield



























Experiment



Experiment



Experiment





















Pt 5d bonding

Pt 5d anti bonding

Pt 5d non-bonding





contributions



radiation)







Angle Resolved UPS








be identified


predictions




states)


Chemisorbed C6H6

Condensed C6H6

Gas-phase C6H6







molecular orbitals




this orbital






















vacuum level

Biatomic molecule

















400 eV for N

530 eV for O

685 eV for F



2140 eV for P

2470 ev for S

2830 eV for Cl



















)()(14 2

2

2

22

fiifx EEhpAEhhc

e

m

h ff

p














becomes cos2




2

if pe ff

if p ff
















detected



f+ a=1

Fluorescence














Flourescence

Electron yield



























Experiment



Experiment



Experiment





radiation)







Angle Resolved UPS








be identified


predictions




states)


Chemisorbed C6H6

Condensed C6H6

Gas-phase C6H6







molecular orbitals




this orbital






















vacuum level

Biatomic molecule

















400 eV for N

530 eV for O

685 eV for F



2140 eV for P

2470 ev for S

2830 eV for Cl



















)()(14 2

2

2

22

fiifx EEhpAEhhc

e

m

h ff

p














becomes cos2




2

if pe ff

if p ff
















detected



f+ a=1

Fluorescence














Flourescence

Electron yield



























Experiment



Experiment



Experiment



Angle Resolved UPS








be identified


predictions




states)


Chemisorbed C6H6

Condensed C6H6

Gas-phase C6H6







molecular orbitals




this orbital






















vacuum level

Biatomic molecule

















400 eV for N

530 eV for O

685 eV for F



2140 eV for P

2470 ev for S

2830 eV for Cl



















)()(14 2

2

2

22

fiifx EEhpAEhhc

e

m

h ff

p














becomes cos2




2

if pe ff

if p ff
















detected



f+ a=1

Fluorescence














Flourescence

Electron yield



























Experiment



Experiment



Experiment




Chemisorbed C6H6

Condensed C6H6

Gas-phase C6H6







molecular orbitals




this orbital






















vacuum level

Biatomic molecule

















400 eV for N

530 eV for O

685 eV for F



2140 eV for P

2470 ev for S

2830 eV for Cl



















)()(14 2

2

2

22

fiifx EEhpAEhhc

e

m

h ff

p














becomes cos2




2

if pe ff

if p ff
















detected



f+ a=1

Fluorescence














Flourescence

Electron yield



























Experiment



Experiment



Experiment



















vacuum level

Biatomic molecule

















400 eV for N

530 eV for O

685 eV for F



2140 eV for P

2470 ev for S

2830 eV for Cl



















)()(14 2

2

2

22

fiifx EEhpAEhhc

e

m

h ff

p














becomes cos2




2

if pe ff

if p ff
















detected



f+ a=1

Fluorescence














Flourescence

Electron yield



























Experiment



Experiment



Experiment







400 eV for N

530 eV for O

685 eV for F



2140 eV for P

2470 ev for S

2830 eV for Cl



















)()(14 2

2

2

22

fiifx EEhpAEhhc

e

m

h ff

p














becomes cos2




2

if pe ff

if p ff
















detected



f+ a=1

Fluorescence














Flourescence

Electron yield



























Experiment



Experiment



Experiment









)()(14 2

2

2

22

fiifx EEhpAEhhc

e

m

h ff

p














becomes cos2




2

if pe ff

if p ff
















detected



f+ a=1

Fluorescence














Flourescence

Electron yield



























Experiment



Experiment



Experiment








becomes cos2




2

if pe ff

if p ff
















detected



f+ a=1

Fluorescence














Flourescence

Electron yield



























Experiment



Experiment



Experiment










detected



f+ a=1

Fluorescence














Flourescence

Electron yield



























Experiment



Experiment



Experiment











Flourescence

Electron yield



























Experiment



Experiment



Experiment
























Experiment



Experiment



Experiment





Experiment



Experiment





Experiment



XPS o ESCA Photoemission Spectroscopies …rocca/Didattica/Laboratorio/pdf...Photoemission...

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