I'm measuring 250 micrometer thick film of exfoliated graphite. With zero applied current I get 22 mV tensions (it's still going up 0.01 mV/sec) and even negative tensions (it has gone to -8 mV) in Forward mode with a similar sample. What the hell is happening? Someone?
You should be more specific about the details of your experiment (the nature, set-up, temperature dependence, etc.). For now, on the basis of the information you provide I am inclined to think about what has been termed as pseudo-Hall effect. For details, you may wish to consult the following recent paper by Qamar et al. (J. Phys. Conf. Ser. 829, 012004 (2017)):
https://doi.org/10.1088/1742-6596/829/1/012004
https://doi.org/10.1088/1742-6596/829/1/012004
Thank you Behnam. I'll read the paper. There is no more details to provide about the sample unless how it was fabricated. I didn't make any other characterizations, only measures the resistance with the multimeter ( 5-10 ohm). The sample was measured at room temperature and the substrate below is aluminum foil. Someone told me there was a conversion factor associated with conductive substrates when doing 4 probe measurements, but the equipment does not mention this factor at all, only the thickness correction factor. I tried with a ITO (Indium-Tin Oxide) Sample and I didn't have this problem (the substrate was glass). I can't use glass as a substrate in this case because of it's application.
You are welcome Maria. What I mostly wanted to know was the geometry of the system you are doing measurements on. For now, I hope the reference I cited above will prove helpful.
As for the conducting substrate, it affects the screening, via the image potential*) (since the reflectivity of a metal is a function of the frequency, the strength of this potential is dependent on the frequency of the applied signal, but I suppose that your measurements are DC ones).
*) Consult, for instance, the contents of the attached page.
https://www.uni-marburg.de/fb13/researchgroups/of/dynamics/impot.html?language_sync=1
Behnam. Thank you again. It turns out the explanation was much more simple than that: the 4 probes were not in a good contact with the sample...that needs to be in a thicker substrate to have sufficient hight. Ridiculous I know. But now the measurements are stable.
You are welcome Maria. Good to know that you have solved your problem.
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