Editing X-ray photoelectron spectroscopy (section)

==Basic physics==
[[Image:XPS PHYSICS.png|thumb|350px|XPS physics - the photoelectric effect''.'']]
Because the energy of an X-ray with particular wavelength is known (for Al K<sub>α</sub> X-rays, ''E''<sub>photon</sub> = 1486.7 eV), and because the emitted electrons' kinetic energies are measured, the [[electron binding energy]] of each of the emitted electrons can be determined by using the [[photoelectric effect]] equation,

:<math>E_\text{binding} = E_\text{photon} - \left(E_\text{kinetic} + \phi\right)</math>,

where ''E''<sub>binding</sub> is the binding energy of the electron measured relative to the chemical potential, ''E''<sub>photon</sub> is the energy of the X-ray photons being used, ''E''<sub>kinetic</sub> is the kinetic energy of the electron as measured by the instrument and <math> \phi </math> is a [[work function]]-like term for the specific surface of the material, which in real measurements includes a small correction by the instrument's work function because of the [[Volta potential|contact potential]]. This equation is essentially a [[conservation of energy]] equation. The work function-like term <math> \phi </math> can be thought of as an adjustable instrumental correction factor that accounts for the few eV of kinetic energy given up by the photoelectron as it gets emitted from the bulk and absorbed by the detector. It is a constant that rarely needs to be adjusted in practice.