Photoelectrons are generated by illuminating the samples to be investigated with X-Rays. The emitted photoelectrons are collected and analyzed with respect to their intensity and energy distribution. The chemical sensitivity of this measurement technique is given by the element-specific distribution of binding energies of the electronic core levels leading to characteristic energy spectra. The presented X-Ray Photoemission Spectra is taken from a clean Cu crystal as well as ultra thin Fe (~2 mono layers) and Ni (9 mono layers) films on the same Cu crystal featuring separated peaks which belong to individual elements. XPS is - due to the short mean free path (1-4nm) of the excited photoelectrons - rather surface sensitive, as can be recognized by the reduction of the Cu peaks in the spectra in the case of ~11 atomic layers of Fe and Ni on top of the Cu substrate. XPS is highly sensitive to metals.
The dimension of the samples to be investigated should be from 2 by 1 mm to maximum of about 2 inch or 51mm.