Ultraviolet Photoelectron Spectroscopy (UPS)

Ultraviolet Photoelectron Spectroscopy (UPS) utilises the same principles as XPS, however ionising radiation at energies of 10s of eV are used to induce the photoelectric effect, as opposed to photons of greater than 1keV that are used in XPS.  Ultraviolet (UV) photons are produced using a helium gas discharge lamp with photons emitted having energies of  21.2eV (He I) and 40.8eV (He II). These lower energies means only the outermost electronic shells can be probed with UPS with high surface sensitivity but poor spatial resolution.

The UPS capability on the Monash X-ray Platform can be used for valence band acquisition as well as work function measurements in conjunction with a sample bias stage. The workfunction is the difference between the Fermi level and Vacuum level, or the energy required to extract an electron from the surface of a solid. As a surface property, the workfunction is strongly influenced by variation in composition or structure at the surface.