X-Ray Photoelectron Spectroscopy (XPS)
  Electron Spectroscopy for Chemical Analysis (ESCA)

     Description Samples are placed into a 10^-8 Torr vacuum chamber and irradiated with either non-monochromated Mg or Al X-rays, or monochromatic Al X-rays which cause the ejection of photoelectrons from the surface. The electron kinetic energies, as measured by a high resolution electron spectrometer, are used to calculate the binding energy of those electrons in the elements present in the surface of the material.  In many cases, this measurement leads to information about the valence state(s) or chemical bonding environment(s) of the elements thus detected. The actual depth of the analysis, typically less than the outer 10 nm of the sample, is determined by the escape depth of the photoelectrons and the angle of the sample plane relative to the spectrometer.