XPS requires high vacuum (residual gas pressure p ~ 10 −6 Pa) or ultra-high vacuum (p < 10 −7 Pa) conditions, although a current area of development is ambient-pressure XPS, in which samples are analyzed at pressures of a few tens of millibar. Chemical states are inferred from the measurement of the kinetic energy and the number of the ejected electrons. XPS belongs to the family of photoemission spectroscopies in which electron population spectra are obtained by irradiating a material with a beam of X-rays. It is often applied to study chemical processes in the materials in their as-received state or after cleavage, scraping, exposure to heat, reactive gasses or solutions, ultraviolet light, or during ion implantation. The technique can be used in line profiling of the elemental composition across the surface, or in depth profiling when paired with ion-beam etching. XPS is a powerful measurement technique because it not only shows what elements are present, but also what other elements they are bonded to. X-ray photoelectron spectroscopy ( XPS) is a surface-sensitive quantitative spectroscopic technique based on the photoelectric effect that can identify the elements that exist within a material (elemental composition) or are covering its surface, as well as their chemical state, and the overall electronic structure and density of the electronic states in the material.

Basic components of a monochromatic XPS system.

Xps peak area ratio