How does photoionization eject electrons in X-ray photoelectron spectroscopy?

In X-ray photoelectron spectroscopy (XPS), photoionization is the primary process used to eject electrons from a material. When an atom in a sample is irradiated with X-rays, it absorbs an incident photon, which causes the ejection of an electron.1

This process is represented by the equation $m+h\nu \to m^{+*}+e^{-}$, where $m$ is an atom in the material, $h\nu$ is the energy of the incident photon, and $e^{-}$ is the ejected electron. The resulting electron possesses a discrete kinetic energy, which is measured by the spectrometer. This kinetic energy is essentially the difference between the energy of the incident photon and the binding energy of the electron. By measuring these energies, researchers can infer details about the chemical species and the atomic structure of the surface, as the amount of energy required to eject an electron depends on the specific environment and arrangement of the atoms.12