spectroscopic method X-ray photo-electron spectroscopy

1. NCE PHYSICAL CHEMISTRY UNIVERSITY OF PESHAWAR
2020
X-ray photoelectron
spectroscopy
Abdul sabur
abdul
[ T Y P E T H E C O M P A N Y A D D R E S S ]

2. Submitted to: Dr: farooq sab
Submitted by: abdul sabur
Assignment topic:
photoelectron spectroscopy(XPS)
Date: 7/o6/2020
Class :M.phil
Semester : 1
Institute : NCE physical chemistry
university of Peshawar
Submitted to: Dr: farooq sab
Submitted by: abdul sabur
Assignment topic: x-ray
photoelectron spectroscopy(XPS)
Date: 7/o6/2020
Class :M.phil
Semester : 1st
Institute : NCE physical chemistry
university of Peshawar
Submitted to: Dr: farooq sab
Submitted by: abdul sabur
ray
photoelectron spectroscopy(XPS)
Institute : NCE physical chemistry

4. Outlines:
 History of XPS
 Introduction of XPS
 Principle of XPS technique
 XP spectrophotometer
 Application of XPS
 Advantages and disadvantages of XPS
 Refrences.

5. History of XPS:
 Heinrich hertz observed emission of electrons in 1887.
 Einstein explained the photoelectric effect (in 19050) and got the Noble
prize in 1921.
 Rutherford recognized the kinetic energy of the emitted electron in 1914.
 Robinson and Young observed the line shift caused by chemical bonding
1930.
 Professor Kai Siegbahn recorded the first high resolution XPS spectrum of
sodium chloride in 1954, revealing the potential of XPS.
 First commercial XPS machine available in 1970.
 Kai Siegbahn got the Noble prize in Physics in 1981.

6. Introduction:
X-ray photoelectron spectroscopy was invented by kia Siegbahn in 1954,
received Nobel prize in 1981. XPS are also called electron spectroscopy for
chemical analysis (ESCA).it is used to determined elemental composition,
chemical formula, and chemical/electronic state of the element. XPS is based on
photoelectric effect. Photoelectric effect was originally observed by Hertz and later
Einstein works on the manifestation of the quantum nature of light.
Why XPS is also known as ESCA?
Because in contrast to UPS, and AES, the XPS provides not only the
information about the atomic
composition of a sample but also
the information about the structure
and oxidation state of the
compounds.
X-ray photoelectron
spectroscopy: He recognized
that when a light is incident on a
sample, an electron can absorb a
photon and escape from the
material with a maximum kinetic
energy Ek=hν-EB -eФ where ν
is the photon frequency, Ek is the
kinetic energy, h is the planks
constant, EB electron binding
energy and Ф spectrometer
work function, which gives the
minimum energy required to remove a delocalized electron from the surface of
the metal . The work function is a measure of the potential barrier at the surface
that prevents the valence electrons from escaping. Here we will show how the
photoelectric effect can be used to explore chemical composition and quantum
states of material surface.
The surface of sample has different chemical composition and physical
properties. When a beam of uv light or x-ray light ionizes the molecules or atoms.
The light ionizes the highest valence shell of atoms. If hv is larger, electrons may
be ejected also from deeper levels.
XPS statement:
When photons with the wavelength in the lower energy, X-ray region are
incident on the crystal surface then core electrons are knocked out of atoms.
Spectrum is obtained by measuring the characteristics of electrons that escape from
the surface. This electron spectroscopic method is called X-ray photoelectron

7. spectroscopy (XPS).
Surface analysis: this technique is very surface specific. Surfaces: (3
atomic layers) using xps and angle resolved xps. Ultra thin films: (3-30) atomic
layers using xps and angle resolved xps. thin films: (3-600) atomic layers
using xps in combination with sputter etching for profiling.
XPS is used to measure:
 elemental composition of the surface (top 1–10 nm usually)
 empirical formula of pure materials
 elements that contaminate a surface
 chemical or electronic state of each element in the surface
 uniformity of elemental composition
across the top surface (or line
 profiling or mapping)
 uniformity of elemental composition
as a function of ion beam etching (or depth
profiling)
Principle of XPS technique:
 Surface of the specimen is
irradiated by x-ray with the energy of hv.
A mono-energetic X-ray beam emits
photoelectrons from the surface of the
sample.
 Higher energy hv photons penetrate deeper into the sample surface, at
about a micrometer of the sample.
 The XPS spectrum contains information of top 10-100Ǻ of the sample.
 Ultrahigh vacuum environment to eliminate excessive suface
contamination.
 Cylindrical Mirror Analyzer (CMA) measures the KE of emitted
electrons.
 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.

8. XP SPECTROMETERS:
COMPONENTS OF XPS:
 A source of X-rays
 An ultra high vacuum (UHV)
 An electron energy analyzer
 magnetic field shielding
 An electron detector system
 A set of stage manipulators

9. XPS INSTURMENT:XPS INSTURMENT:

10. X-ray Photoelectron Spectrometer:
Ultra-High Vacuum System
 Allows longer photoelectron
path length
 Ultra-high vacuum keeps
surfaces clean, Preventing the
contaminations to produce X
ray signal
 Pressure < 10-8 Torr
 Vacuum pumps
 Roughing Pump
 Turbo Pump
 Ion Pump
ray Photoelectron Spectrometer:
High Vacuum System:
Allows longer photoelectron
high vacuum keeps
Preventing the
contaminations to produce X-

11. X-ray source:
 A heated filament (cathode) emits electrons which are accelerated towards a
solid anode (water cooled) over a potential of the order of 5-20 kv.
 Holes are in the inner levels of the anode atoms by the electron
bombardment and are then radioactively filled by transition from higher-
lying levels.
 Dual Anode X-ray source
 Mg Kα radiation: hν = 1253.6 eV
 Al Kα radiation: hν = 1486.6 eV
 Monochromatic using quartz crystal
Electron analyzer:
 Lens system to collect photoelectrons
 Hemispherical in shape
with very high
electrostatic field is
applied to analyser.
 Pressure maintained
inside analyzer is 10-5
torr.
 Analyzer to filter electron
energies
 Detector to count
electrons
Ion gun:
 Single electron pass
through multiplier tube it
gets converted into number of electrons or pulses of electron (106
to
108
electrons)
 Sample cleaning
 Depth profiling
 Ar+
is the most widely used ion

12. Application of XPS/ESCA:
 Identification of active site.
 Determination of surface contamination on semiconductors.
 Study of oxide layers on metal.
 Analysis of dust on the sample.
 Determination of oxidation state.
 All the elements of periodic table can be determined or identified except
hydrogen and helium as they do not emit inner core electron.
Advantages of XPS:
 It is surface sensitive technique.
 Wide range of solid surface sample can be identified.
 Relatively non-destructive.
Disadvantages of XPS:
 It is very expensive.
 Slow and poor resolution power.
 Required high vacuum.

13. Refrences:
 Surface Analysis, The Principal Techniques Edited by John C. Vickerman,
John Wiley &Sons (1997).
 Handbook X-ray and ultraviolet photoelectron spectroscopy, Briggs, Heyden
&Son Ltd (1977).
 Solid State Chemistry: Techniques, A. K. Cheetham and Peter Day, Oxford
Science Publication (1987).
 Practical Surface Analysis by D. Briggs and M. P. Seah.
 H. Hertz, "Ueber den Einfluss des ultravioletten Lichtes auf die electrische
Entladung" , Annalen der Physik 31, p983(1887).
 A. Einstein, Concerning an Heuristic Point of View Toward the Emission
and Transformation of Light, Annalen der Physik 17, p132 (1905)
 F. Reinert , S. Hüfner, Photoemission spectroscopy—from early days
to recent applications, Universität Würzburg, Universität des Saarlandes,
New Journal of Physics 7 , p5(2005)
 N. Winograd, S.W. Gaarenstroom, X-ray Photoelectron Spectroscopy,
Department of chemistry, The Pennsylvania State University University,
University Park, Pennsylvania, Physical methods in modern chemical
analisys , vol 2, p128-152,(1980)
 J.F. Watts, X-ray photoelectron spectroscopy, Surface science techniques,
p12 Loughborough University of Technology, Leicesterhier, Pergamon, UK,
(1994)
 F.Schwable , Quantum mechanics, p289Springer-Verlag, Berlin, (1993)
 G.Kladnik, Elecronic structures and charge transfer at nanostructures an
hybrid interfaces , dissertation p17-21, Universitiy of Ljubljana, Faculty of
mathematics and physics, Ljubljana (2012)
 S. Hüfner, Photoelectron Spectroscopy, Springer-Verlag, Berlin Heidelberg,
3rd edition, p39-51 (2003)
 J. Vohs, Introduction to X-Ray Photo-Electron Spectroscopy (XPS),
University of Pennsylvania, (2006), found at:www.pire-
ecci.ucsb.edu/pire-ecci-old/.../papers/vohs1.pdf (21.03 2015)