X-ray photoelectron spectroscopy (XPS) is a surface-sensitive technique that uses X-rays to eject electrons from the surface of a material. An XPS instrument measures the kinetic energy of the ejected electrons to identify the elements present and analyze the chemical and electronic states of the surface. XPS can analyze the top 10-100 angstroms of a material in an ultra-high vacuum environment. The technique works by measuring the binding energy of electrons ejected from a material by X-ray photons, each element has characteristic binding energies that can be used for identification and analysis of oxidation states or impurities in the surface.

1. X-Ray Photoelectron Spectroscopy (XPS)
Presented By :Presented By :
Mr. Sanjeet Kumar Paswan
Research Scholar
Department of Nanoscience & Technology
Central University of Jharkhand , Ranchi-835205

2. OUTLINE
 XPS Background
 The Photoelectric process
 X-Rays
 XPS Instrument
 How Does XPS Technology Work ?
 Analysıs of XPS
 The Atom and the X-Ray The Atom and the X-Ray
 X-Rays on the Surface
 Interpreting XPS Spectrum: Background
 Identification of XPS Peaks
 Advantages and Disadvantages
 XPS Technology
 References

3.  X-ray photoelectron spectroscopy (XPS) or Electron spectroscopy
for chemical analysis (ESCA) is a surface sensitive spectroscopic
technique widely used in materials science to investigate the
molecular surface stress , chemical composition of surfaces and their
electronic properties.
 XPS technique is based on Einstein’s idea about the photoelectric
effect, developed around 1905.
The concept of photons was used to describe the ejection of
XPS Background
The concept of photons was used to describe the ejection of
electrons from a surface when photons were impinged upon it.
In 1960, Dr. Siegbahn and his research group, developed the XPS
technique and produce the first commercial monochromatic XPS and
in 1981, Dr. Seighbahn won the noble prize.
 ESCA is based on the Photoelectron effect.
Electros knock away from the surface with definite hν shown in next slide
Fig.

4. Conduction BandConduction Band
Valence BandValence Band
FermiFermi
LevelLevel
FreeFree
ElectronElectron
LevelLevel
Incident XIncident X--rayray
Ejected PhotoelectronEjected Photoelectron
The Photoelectric process
L2,L3L2,L3
L1L1
KK1s1s
2s2s
2p2p
 Following this process, the atom willFollowing this process, the atom will
release energy by the emission of anrelease energy by the emission of an
Auger Electron.Auger Electron.
Fig: Photoelectric effect
K.E = Ephoton – Ebinding + φ
Incoming X-ray and if it has some
energy and it ll observed by an atom
then initial electron ll ejected this
phenomena is known as Photoelectric
effect. Because energy of the X-ray
with the particular λ is known ejected
Photoelectron has K.E be calculated.
Φ is Work function

5. Conduction BandConduction Band
Valence BandValence Band
FermiFermi
LevelLevel
FreeFree
ElectronElectron
LevelLevel
Emitted Auger ElectronEmitted Auger Electron
Auger Relation of Core Hole
 Sample bombardment by electrons and
core electrons removed.
 Electron from a higher energy level fall
into the vacancy and after that release of
energy.
 Measured energy and defined samples.
 L electron falls to fill core level vacancy
L2,L3L2,L3
L1L1
KK1s1s
2s2s
2p2p
 L electron falls to fill core level vacancy
(step1).
 KLL Auger electron emitted to conserve
energy released in step1.

6. Binding Energy (BE)
 The Binding Energy (BE) is characteristic of the core electrons for each element.
0
x
p+
B.E.
This is the point with 0 energy of
attraction between the electron and
the nucleus. At this point the
electron is free from the atom.
These electrons are attracted to the
proton with certain binding energy xp+ proton with certain binding energy x
B.E=Ehv-K.E-Ø
 K.E is Kinetic Energy (measure in the XPS spectrometer).
 hv is photon energy from the X-Ray source (controlled).
 Ø is spectrometer work function. It is a few eV, it gets more complicated because
the materials in the instrument will affect it. Found by calibration.
 B.E is the unknown variable.
 The equation will calculate the energy needed to get an e- out from the surface of
the solid and Knowing KE, hv and Ø the BE can be calculated.

7. X-Rays
 Irradiate the sample surface, hitting the core electrons (e-) of the atoms.
 The X-Rays penetrate the sample to a depth on the order of a micrometer.
 Useful e- signal is obtained only from a depth of around 10 to 100 Å on the
surface.
The X-Ray source produces photons with certain energies:
 MgK photon with an energy of 1253.6 eV
 AlK photon with an energy of 1486.6 eV
 Normally, the sample will be radiated with photons of a single energy (MgK
or AlK). This is known as a monoenergetic X-Ray beam.or AlK). This is known as a monoenergetic X-Ray beam.
Why the Core Electrons ?
 An electron near the Fermi level is far from the nucleus, moving in different
directions all over the place, and will not carry information about any single atom.
 The core e-s are local close to the nucleus and have binding energies characteristic
of their particular element.
 The core e-s have a higher probability of matching the energies of AlK and MgK.
Core e-
Valence e-
Atom

8. XPS Instrument
X-Ray Source
Ion Source
SIMS Analyzer
Sample introduction
Chamber
 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
 Essential Components
 Sample : Usually 1 cm2
 X-ray Source : Al is 1486.6 eV and Mg is 1256.6 eV.
 Electron Energy Analyzer
 Detector : Electron multiplier.
 Electronics, Computer.

9. X-ray Photoelectron Spectrometer
ElectronElectron
OpticsOptics
Hemispherical Energy AnalyzerHemispherical Energy Analyzer
Magnetic ShieldShieldOuter SphereOuter Sphere
Inner SphereInner Sphere
ComputerComputer
SystemSystem
Analyzer ControlAnalyzer Control
MultiMulti--Channel PlateChannel Plate
Electron MultiplierElectron Multiplier
Lenses for EnergyLenses for Energy
AdjustmentAdjustment
5 4 . 7
XX--rayray
SourceSource
OpticsOptics
Position SensitivePosition Sensitive
Detector (PSD)Detector (PSD)
SampleSample
Electron MultiplierElectron Multiplier
Resistive AnodeResistive Anode
EncoderEncoder
AdjustmentAdjustment
(Retardation)(Retardation)
Lenses for AnalysisLenses for Analysis
Area DefinitionArea Definition
Position ComputerPosition Computer
Position AddressPosition Address
ConverterConverter

10. How Does XPS Technology Work ?
 A monoenergetic x-ray beam
emits photoelectrons 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 presentpositions and the elements present
in the sample identified.
Which materials are analazıed?
 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.

11. ANALYSIS OF XPS
 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.
The Atom and the X-Ray
Valence electrons
X-Ray
Free electron
Core electrons
Valence electrons
proton
neutron
electron
electron vacancy
The core electrons respond
very well to the X-Ray
energy

12. X-Rays on the Surface
e- top layer
e- lower layer
with collisions
e- lower layer
but no collisions
X-Rays
Outer surface
Inner surface
Atoms layers
 The surface contains the atom and molecules on the exterior of an object that can
interact with energy, atom and molecules outside of that objects.

13.  The X-Rays will penetrate to the core e- of the atoms in the sample.
 Some e-s are going to be released without any problem giving the Kinetic
Energies (KE) characteristic of their elements.
 Other e-s will come from inner layers and collide with other e-s of upper
layers
 These e- will be lower in lower energy.
 They will contribute to the noise signal of the spectrum.
X-Rays on the Surface

14. KE versus BE
KE can be plotted depending on
BE
Each peak represents the amount
of e-s at a certain energy that is
characteristic of some element.
#ofelectrons
E E E
1000 eV 0 eV
BE increase from right to left
KE increase from left to right
Binding energy
(eV)

15. Interpreting XPS Spectrum: Background
• The X-Ray will hit the e-s in the bulk
(inner e- layers) of the sample
• e- will collide with other e- from top
layers, decreasing its energy to
contribute to the noise, at lower kinetic
energy than the peak .
• The background noise increases with
BE because the SUM of all noise is
taken from the beginning of the
analysis.
#ofelectrons
N2
N3
N4
N = noise
Binding energy
#ofelectrons
N1
N2
Ntot= N1 + N2 + N3 + N4
• The XPS peaks are sharp.
• In a XPS graph it is possible to see Auger electron peaks.
• The Auger peaks are usually wider peaks in a XPS spectrum.
XPS Spectrum

16. Identification of XPS Peaks
 The plot has characteristic peaks for each element found in the surface of the sample.
 There are tables with the KE and BE already assigned to each element.
 After the spectrum is plotted we can look for the designated value of the peak energy
from the graph and find the element present on the surface.
 Electronic Effect: Auger lines, Chemical shifts, X-ray satellites, X-ray “Ghost” and
Energy loss lines.

17. Advantages and Disadvantages
Advantages Disadvantages
 Relatively Non-destructive technique.
 Surface Sensitive (10-100Å).
 Wide range of solids.
 Quantitative measurements are
obtained.
 Provides information about chemical
bonding.
 Elemental mapping.
 Limitations.
 Very expensive technique.
High vacuum is required (UHV).
 Slow processing (1/2 to 8
hours/sample).
 Large area analysis is required.
 H and He can not be identified.
 Data collection is slow 5 to 10 min. Elemental mapping.  Data collection is slow 5 to 10 min.
 Poor spatial resolution.
XPS Technology
 Consider as non-destructive.
 Provide information about surface
layers or thin film structures
Applications in the industry:
Surface contamination, Tribological effects,
Polymer surface, Catalyst, Corrosion,
Adhesion, Semiconductors, Dielectric
materials, Electronics packaging, Magnetic
media, Thin film coatings and Depth
Profiling (Ar+ Sputtering)

18. [1] Siegbahn, K.; Edvarson, K. I. Al (1956). "β-Ray spectroscopy in the
precision range of 1 : 1e6". Nuclear Physics
[2] Turner, D. W.; Jobory, M. I. Al (1962). "Determination of Ionization
Potentials by Photoelectron Energy Measurement".
[3] journals.tubitak.gov.tr
[4] nanohub.org
[5] srdata.nist.gov
[6] www.eaglabs.com and www.files.chem.vt.edu
References
[6] www.eaglabs.com and www.files.chem.vt.edu
[7] Bio interface.org
[8] www.spectroscopynow.com
[9] www.surfaceanalysis.org
[10] www.csma.ltd.uk

19. Thank You