Yağmur Celasun,Görkem Erdoğan.Fatma Sırkıntı

Department Of Chemical Engineering

Hacettepe University

12/04/2012

INTRODUCTION TO X-RAY PHOTOELECTRONS SPECTROSCOPY

What is XPS? General Theory

How can we identify elements and compounds?

What is the instrumentation of XPS?

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

1.In 1887, Henriech Rudolf Hertz,photoelectric effect1.In 1887, Henriech Rudolf Hertz,photoelectric effect

2.In 1907, Innes the first XPS spectrum2.In 1907, Innes the first XPS spectrum

3.Kai Siegbahn(Uppsala) with Hewlett Packard (USA) 3.Kai Siegbahn(Uppsala) with Hewlett Packard (USA)

produceproduce the first commertial monochromatic XPSthe first commertial monochromatic XPS

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

Following this process, the atom will Following this process, the atom will release energy by the emission of an release energy by the emission of an Auger Electron.Auger Electron.

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

What elements and the quantity elements of the sample surface(1-12nm)

What contamination in the surface or the bulk of the sample

Empirical formula of a material The chemical state identification of the elements in the

sample The binding energy of electronic states The thickness of different materials The density of electronic state

A source of X-raysAn ultra high vacuum (UHV) An electron energy analyzer magnetic field shieldingAn electron detector systemA set of stage manipulators

X-Ray Source

Ion Source

SIMS Analyzer

Sample introductionChamber

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

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

SecondaSecondary ry 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

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

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

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

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

A monoenergetic x-ray beam emits photoelectrons from the from the surface of the sample.

The x-ray photons The penetration about a micrometer of the sample

The XPS spectrum contains information only about the top 10 - 100 Ǻ of the sample.

Ultrahigh vacuum environment to eliminate excessive surface contamination.

Cylindrical Mirror Analyzer (CMA) measures the KE of emitted e-s.

The spectrum plotted by the computer from the analyzer signal.

The binding energies can be determined from the peak positions and the elements present in the sample identified.

XPS is routinely used to analyze inorganic compounds,metals,semiconductors,polymers, ceramics,etc.

Organic chemicals are not routinely analyzed by XPS because they are readily degraded by either the energy of the X-rays or the heat from non-monochromatic X-ray sources

XPS detects all elements with (Z) >3. It cannot detect H (Z = 1) or He (Z = 2) because the diameter of these orbitals is so small, reducing the catch probability to almost zero

Dedection unit: ppt and some conditions ppm

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

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

XPS devices is also named ESCA(Electron Spectroscopy Chemical Analysis)It works base on the photoelectron effect .

XPS is primarly used for chemical analysis as determining thicknesses and emprical formulas of different elements and,binding energies,densities of electronic states.

XPS is used from starting Li(A>=3) because of smaller orbital’s radius and analysis of organic compounds cannot be done with XPS because of degredation with radiation.

XPS is used also determination of others like; metals,ceramics,semiconductors,papers,etc.

Siegbahn, K.; Edvarson, K. I. Al (1956). "β-Ray spectroscopy in the precision range of 1 : 1e6". Nuclear Physics

Turner, D. W.; Jobory, M. I. Al (1962). "Determination of Ionization Potentials by Photoelectron Energy Measurement".

journals.tubitak.gov.tr nanohub.org srdata.nist.gov www.eaglabs.com

www.files.chem.vt.edu Bio interface.org www.spectroscopynow.com www.surfaceanalysis.org www.csma.ltd.uk