X-ray photoelectron spectroscopy (XPS) is a surface-sensitive quantitative spectroscopic technique that measures the elemental composition at the parts per thousand range,
empirical formula,
chemical state and
electronic state of the elements that exist within a material. XPS
spectra are obtained by irradiating a material with a beam of
X-rays while simultaneously measuring the
kinetic energy and number of
electrons that escape from the top 0 to 10
nm of the material being analyzed. XPS requires high vacuum (
P ~ 10
-8 milli
bar) or
ultra-high vacuum (UHV;
P < 10
-9 millibar) conditions, although a current area of development is ambient-pressure XPS, in which samples are analyzed at pressures of a few tens of millibar.