Is it necessary to apply a negative bias voltage while analysing the sample using UPS ?
What is the need for applying bias voltage ?
I am new to UPS so please bare with these simple questions!
Thanks in advance.
Please have a look at the answers of a similar question:
https://www.researchgate.net/post/Can_anyone_help_me_with_photoelectron_spectroscopy
Please see also lower part of page 4 of :
http://vixra.org/pdf/1312.0171v1.pdf
...."To distinguish secondary electron cutoff from the low kinetic energy electron scattering, Negative bias voltages were put on the sample. Plural negative bias voltages (-8, -10, -12 V) were selected to check a charge on the sample surface."....
The bias is needed to get the secondary cut off rised to some eV kinetic energy. For measuring the valenceband you dont need the bias. The bias might change the properties of the first lens stage so be careful and watch the shape of the spectrum change with rising bias. In most cases you will get a lot of secondaries piling up at the cut off. Be aware for a good value for the work function you must have the sample in normal emission. This might be checked by the steepness of the cut off.
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