I am working on the variation of current in low pressure across thin film, usually current increases at vacuum conditions because of desorption of surface adsorbed groups, but in case of my sample current decreases with vacuum. Can somebody help me with explaining this effect?
If, as you say, the surface and not the film bulk carries the conductivity, there may also be cases in which the adsorbed groups do not hinder but actually propagate the conduction, maybe in some sort of hopping mechanism scheme. Is it classical ohmic conduction or is it some sort of semiconductor conduction mechanism? If you have already analyzed your I-F-curves in that respect, it could help you understand what's happening.
the current (resistance) in p-type semiconductor which is capable to adsorb oxygen at defect sites or dangling points can decrease (increase) due to desorption of oxygen under vacuum. it depends on the nature of sample, type of doping, defects etc.
Anyway what type of sample are you measuring? at what pressure like UHV or rough vacuum?
could it just be the change in humidity? how do you purge the chamber after sample loading? N2 absorbs humidity, so you can use it to rule this mechanism.
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