The Photoemission Process
When an atom or molecule absorbs an X-ray photon, an electron can be ejected. The kinetic energy (KE) of the electron depends upon the photon energy (hν) and the binding energy (BE) of the electron (i.e., the energy required to remove the electron from the surface).
The photoemission process involved for XPS surface analysis. The discs represent electrons and the bars represent energy levels within the material being analyzed. The equation governing the process is: KE = hν - BE
By measuring the kinetic energy of the emitted electrons, it is possible to determine which elements are near a material’s surface, their chemical states and the binding energy of the electron. The binding energy depends upon a number of factors, including the following:
- The element from which the electron is emitted.
- The orbital from which the electron is ejected
- The chemical environment of the atom from which the electron was emitted.