Tools for Nano Characterization:
X-Ray Spectroscopy
Prepared By: Organized By:
Anila Anwar Dr. Abu Bin Imran
Student No: 1018032716 Associate Professor
Dept. of Chemistry, BUET Dept. of Chemistry BUET
X-Ray Spectroscopy:
X-ray spectroscopy is a technique that detects and
measures photons, or particles of light, that have
wavelengths in the X-ray portion of the
electromagnetic spectrum.
Wavelength range of X-Ray 0.01 to 10 nanometer.
Energy range 100eV to 100keV.
Different types of X-Ray Spectroscopy
1. XRD (X-Ray Diffraction)
2. XPS (X-Ray Photon Spectroscopy)
3. XRF (X-Ray Fluorescence)
XPS
(X-Ray Photon Spectroscopy)
XPS is a surface sensitive spectroscopic technique to analyze the
structure of atoms and get information about electronic
structure.
XPS is also known as ESCA (Electron Spectroscopy for Chemical
Analysis) as in often use to investigate the chemical composition
of various materials.
It is based on photoelectric effect which was described by
Einstein in 1905.
Basic Principle of XPS
The Working principles of XPS is ejection of electron from the
surface of sample in UHV condition.
Elements present in sample can be identified on the basis of
kinetic energies and binding energies of their photo electrons.
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.
Theoretical Background:
Photoelectric Effect:
When an X-ray (with energy hν) 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.
Theoretical Background:
The ejected photoelectron has kinetic energy:
K. E = hv - B.E - Ø
KE → Kinetic Energy
hv → Energy of photon emitted by X-rays
Ø → Spectrometer work function
BE → Binding Energy
Theoretical Background:
No emission of photon if hν < Ø
No emission of photon from
levels with BE + Ø > hν
Increase in KE of photoelectron
cause decrease in BE.
Require monochromatic beam.
Each element has different value
of KE for core level electrons.
X-Ray Photon Spectrometer:
Setup of XP-Spectrometer:
Diagram of the Side View of XPS System
How Does XPS Technology Work?
A mono energetic x-ray beam Ultrahigh vacuum environment to
emits photoelectrons from the eliminate excessive surface
surface of the sample. contamination.
The X-Rays either of two energies: Cylindrical Mirror Analyzer (CMA)
Al Kα(1486.6eV) measures the KE of emitted
Mg Kα(1253.6 eV) electrons.
The x-ray photons penetrate about The spectrum plotted by the
a micrometer of the sample. computer from the analyzer signal.
The XPS spectrum contains The binding energies can be
information only about the top 10 - determined from the peak
100 Ǻ of the sample. positions and the elements present
in the sample identified.
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).
Analysis: 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
Analysis: 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.
Chemical Shift
In the figure Ti 2P
spectrum of a pure metal
titanium is compared
with Titanium di oxide.
A chemical shift of about
5eV between the
oxidation state and pure
metal state is observed.
Advantages and Limitations
Advantages Limitations
Non-destructive technique. Very expensive technique.
Surface Sensitive (10-100 Å). High vacuum is required.
Detection unit: ppt and some Slow processing.
conditions ppm.
Large area analysis is
Quantitative measurements are required.
obtained.
Provides information about
H and He can not be
chemical bonding. identified.
Elemental mapping. Data collection is slow 5 to
10 min.
Uses
XPS is used to measure: Applications in the industry:
Elemental composition of the Failure analysis
surface (top 1–12 nm usually). Polymer surface
Empirical formula of pure Corrosion
materials. Adhesion
Chemical or electronic state of Semiconductors
each element in the surface.
Dielectric materials
Uniformity of composition Thin film coatings
across the top surface.
References:
http://www.casaxps.com/help_manual/XPSInformation/XPSInstr.htm
http://www.lanl.gov/orgs/nmt/nmtdo/AQarchive/04summer/XPS.html
https://www.spectroscopynow.com/
https://en.wikipedia.org/wiki/X-ray_photoelectron_spectroscopy
