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