The technique is based on the photoelectric effect, discovered by Hertz in 1887, where the emission of electrons from a material occurs under photon irradiation. While early XPS experiments showed promise it was not until much later that the true power of the technique would be revealed. In the 1950s, Kai Siegbahn (Uppsala University, Sweden), using a high resolution spectrometer and a Cu Kα X-ray source, for the first time resolved the sharp peak at the high kinetic “edge” seen by previous studies. This enabled, for the first time, accurate determination of photoelectron kinetic energies and thus core level binding energies. In 1981 Siegbahn was awarded the Nobel Prize for Physics for this pioneering work.
When an X-ray of known energy (hν), generally, with laboratory-based equipment either Al Kα at 1486.7eV or Mg Kα at 1253.6eV, interacts with an atom, a photoelectron can be emitted via the photoelectric effect (Figure 1). The emitted electron’s kinetic energy (Ek) can be measured and the atomic core level binding energy (Eb) relative to the Fermi level (EF) of the sample can be determined using the following equation:
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