03-05-2012, 12:22 PM
X-Ray Photoelectron Spectroscopy (XPS)
x-ray photoelectron spectroscopy (xps).ppt (Size: 2.71 MB / Downloads: 307)
XPS Background
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 electrons from a surface when photons were impinged upon it
During the mid 1960’s Dr. Siegbahn and his research group developed the XPS technique.
In 1981, Dr. Siegbahn was awarded the Nobel Prize in Physics for the development of the XPS technique
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.
Binding Energy (BE)
The Binding Energy (BE) is characteristic of the core electrons for each element. The BE is determined by the attraction of the electrons to the nucleus. If an electron with energy x is pulled away from the nucleus, the attraction between the electron and the nucleus decreases and the BE decreases. Eventually, there will be a point when the electron will be free of the nucleus.
XPS Instrument
The instrument uses different pump systems to reach the goal of an Ultra High Vacuum (UHV) environment.
The Ultra High Vacuum environment will prevent contamination of the surface and aid an accurate analysis of the sample.