2. Introduction
• XPS is also known as ESCA (Electron Spectroscopy for Chemical Analysis).
• Useful to find chemical composition, chemical state and electronic
configuration of material.
• Reveal information about thin film structures and surface layer.
• XPS is based on Einstein's idea about photoelectric effect which was
presented in 1905.
• Very simple and widely used technique and data obtain from it is analyzed
easily.
3. Principle
The working principle of XPS is ejection of electron from the surface of sample in
UHV condition when it is expose to the soft x-rays.
Elements present in sample can be identified on the basis of kinetic energies and
binding energies of their photoelectrons.
Intensities of photoelectron provide information about concentration of element in a
sample.
The electrons emitted from atoms near the sample surface (10-100 Angstroms) can
escape the sample surface. This depth is about twenty atomic layers.
4. Photoelectric effect
1 s 2 s 2 p
K
L
Photoemission
1 s 2 s 2 p
K
L
Relaxation
1 s 2 s 2 p
K
L
Auger Electron Emission
or
X-ray Fluorescence
• When an X-ray (with energy hv) ejects out an electron (by energy B.E). The
ejected electron is called photoelectron and this effect is called photoelectric
effect.
• The atom will release energy by the emission of an Auger Electron
5. The ejected photoelectron has kinetic energy:
K.E=hv-B.E- Ø
KE Kinetic Energy (which is measured by spectrometer of XPS)
hv Energy of photon emitted by X-rays
Ø Spectrometer work function. Few eV. calculated by calibration.
BE Binding Energy
6. • No emission of photon if h
ν< Ø
• No emission of photon from levels with BE + Ø > h
ν
• Increase in KE oh photoelectron cause decrease ki
BE.
• Photoemission intensity is represented by α
.
• Require monochromatic beam.
•
• Each element has different value of KE for core level
electrons.
E V
Kinetic
Energy
Binding
Energy
φ
Photoelectron
Valence
band
Core
levels
Photon
Ef
Core hole
7. Instrumentation
Components
A source of X-rays
An electron detector system
A set of stage manipulators
X-Ray Source
An ultra high vacuum (UHV)
Ion Source
An electron energy analyzer
CMA Analyzer
Magnetic field shielding
Sample introduction
Chamber
8. Schematic Diagram
5 4 . 7
X-ray
Source
Electron
Optics
Hemispherical Energy Analyzer
Position Sensitive
Detector (PSD)
Magnetic Shield
Outer Sphere
Inner Sphere
Sample
Computer
System
Analyzer Control
Multi-Channel Plate
Electron Multiplier
Lenses for Energy
Adjustment
(Retardation)
Lenses for Analysis
Area Definition
Resistive Anode
Encoder
Position Computer
Position Address
Converter
9. Instrumentation
X-ray Source
Monochromatic Al Kα: hv=1486.6 eV and Mg Kα: h
ν= 1253.6 eV
🠶An Ultra High Vacuum (UHV) chamber
(Pressure < 10-9 Torr)
🠶Hemispherical Analyzer
It contain positive charge on inner plate of hemisphere to attract electron and
negative charge on outer plate to repel electron which help to move electron in an
orbit.
Only electrons of certain voltage can allow to pass through plates due to potential
difference
🠶 Data Collection System
(Detector, Analyzer Control and Computer System)
http://www.seallabs.com/how-xps-works.html
cylindrical mirror analyzer
can also be use
10. Sample preparation
Sample preparation is not require usually. We just mount the sample and place it
for analysis
Removal of Volatile Material with the help of pumping or by washing with a
solvent like ethanol.
Removal of Nonvolatile Organic Contaminants by freshly distilled solvents.
Surface Etching (surface contaminants can remove by ion sputtering and other
erosion techniques).
Abrasion cause roughen the surface by grinding up to 600 grade paper. It
increase intensity of signal as compare to smooth surface.
11. XPS peak Elemental Shift
• XPS peak is plotted between No. of electrons (CPS) and B.E.
• Electron-nucleus attraction helps us identify the elements.
• Each element and orbital has different binding energy for each electron
present in it.
• The orbit which are closer to nucleus has high binding energy but low K.E
Elemental Shifts
Binding Energy (eV)
Element 2p3/2 3p
Fe 707 53 654
Co 778 60 718
Ni 853 67 786
Cu 933 75 858
Zn 1022 89 933
12. Chemical Shift
• It occur due to electronegativity difference and bonding of atoms.
• Higher positive oxidation state has high BE due to interaction between emitted
electrons and nucleus.
• Differentiate between different oxidation state and chemical environment is
major use of XPS.
Functional Binding Energy
Group (eV)
hydrocarbon C-H, C-C 285.0
amine C-N 286.0
alcohol, ether C-O-H, C-O-C 286.5
Cl bound to C C-Cl 286.5
F bound to C C-F 287.8
carbonyl C=O 288.0
Polyethylene Terephthalate (PET).
13. XPS Peak - Electronic effect
🠶 The binding energy of core electron not
only depends on the energy shell level
they occupy but also on
n principle quantum number
l orbital angular quantum number
s spin angular quantum number
j total angular quantum number
(j=l+s)
For orbital p
orbital angular quantum number l = 1
Spin angular quantum number s = ± 𝟏/𝟐
total angular quantum number j =𝟏/𝟐, 𝟑/𝟐
Electronic shift
effect also known as
multiplet splitting
14. Surface and bulk investigations of organ metal pipe degradation
Samples of degraded organ pipe are obtain from the Sicily island where aging of
metal alloys are influenced by environment.
These samples are investigated by XPS, EDX and XRD.
Tin and lead are cheap metals, shiny appearance and ductile in nature so use in
organ pipes.
Formation of tin oxide blisters, tin chloride phases and formation of lead nitrate
salts are the types of degradation observe during analysis.
XPS was recorded In order to determine the oxidation states of elements and
their surface atomic concentration were performed on PHI 5600 system using
Al Kα Source.
Binding energies were calculated with respect to C 1s which is ionize at 285 eV.
Because it is generally accepted to be independent of chemical state of the
sample which is under investigation.
15. a
b
The colour of tin is light grey but in several places circular white areas can be
observed. Because of the degradation on the edges of the mouth and it makes
metal brittle.
XPS analysis clearly shows the presence of nitrogen and chlorine in the samples
taken from zone completely degraded.
The XPS atomic concentration of sample a and b contain Sn 34,84%, Cl 35,11%
and O 30,05% respectively .
16. By Antonio Bovelaccia, Enrico Cilibertob, Enrico Grecob, Ezio Viscusob in 2012
www.sciencedirect.com
17. Advantages and Disadvantages
Advantages
Non-destructive technique.
Surface Sensitive (10-100 Å).
Detection unit: ppt and some
conditions ppm.
Quantitative measurements are
obtained.
Provides information about chemical
bonding.
Elemental mapping.
Limitations
Very expensive technique.
High vacuum is required.
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.
Poor lateral resolution.
18. XPS is used to measure:
Elemental composition of the
surface (top 1–12 nm usually).
Empirical formula of pure materials.
Chemical or electronic state of each
element in the surface.
Uniformity of composition across
the top surface (line profiling).
Uniformity of elemental composition
as a function of ion beam etching
(depth profiling).
Applications in the industry:
Failure analysis
Polymer surface
Corrosion
Adhesion
Semiconductors
Dielectric materials
Thin film coatings
Uses
XPSPEAK 4.1, FitXPS, CasaXPS and
Spectral Data Processor (SDP) V3.0
are the softwares use for XPS analysis
19. References
• http://www.seallabs.com/how-xps-works.html
• http://www.chem.qmul.ac.uk/surfaces/scc/scat5_3.htm
• http://ssrl.slac.stanford.edu/nilssongroup/corelevel.html
• http://goliath.emt.inrs.ca/surfsci/arxps/fundamentalscss.html
• http://www.casaxps.com/help_manual/XPSInformation/XPSInstr.htm
• http://www.lanl.gov/orgs/nmt/nmtdo/AQarchive/04summer/XPS.html
• X-Ray Photoelectron Spectroscopy (XPS) by David Echevarría Torres
• X-RAY PHOTOELECTRON SPECTROSCOPY (XPS) by Yağmur Celasun,Görkem
Erdoğan.Fatma Sırkınti
