Ultraviolet Photoemission Spectroscopy (UPS)

Ultra violet photoemission spectroscopy (UPS) is analogous to XPS but the excitation source is a helium discharge source.  Depending on the operating conditions of the source the photon energy can be optimised for He I = 21.22eV or He II = 40.8eV which is significantly lower energy than Al or Mg Kα used in XPS.  As with XPS the BE is related to the measured photoelectron KE by the simple equation; BE = hν - KE where hv is the photon (x-ray) energy.  The consequence of this lower photon energy is that only the low binding energy valence electrons may be excited using the He source.  A further consequence of the low photon energy is UPS is more surface sensitive than XPS and thus very sensitive to surface contamination.

UPS is very useful as a technique to determine the work function of the material being analysed and is finding increasing application in characterisation of organic and inorganic photovoltaics, organic LEDs.

The AXIS Supra and AXIS Nova may be configured with UPS.