|
ULTRAVIOLET
PHOTOELECTRON SPECTROSCOPY (UPS)
The spectroscopy is similar
to the XPS technique. Heilum light (He(I) or He(II) lines) are
used as excitation source instead of the X-ray gun in the XPS.
As a result, effective excitation of the valence state electrons
occurs. Our He lamp
is installed on the ULTRA spectrometer and all sample requirements
and analyzer parameters are similar to that of the ULTRA instrument.
For UPS we use one detector only (#3 or #5), pass energy of
5 eV, bias -10 or -15 volts.
The technique provides detailed
data for the occupancy of the states in the valence band and
near Fermi edge. The work function can be calculated using the
equiation
Work Function = hv-(Ecut-off - Ef)
where hv = 21.21 eV for He(I), Ef is the Fermi energy (BE scale)
and Ecut-off is the secondary electron cut-off (BE scale) (i.e.
Ecut-off - Ef is the absolute difference between the two values).
A pdf file showing how to calculate Ef and Ecut-off from a
UPS spectrum can be found here.
|
