Hi there.
I'm using HOPG to calibrate tip. However, soon after cleaving, I usually observe a drift in the surface potential level as high as 100 mV. Sometimes it stabilizes, afterwards, but I can hardly believe that it is due to adsorption of moisture, since it is pretty slow (takes half an hour or so), I supposed that should be much faster (few seconds-tens of seconds?). Also, terraces with different contrast appear, usually darker (lower potential), at probably floating flakes.
Does anyone experience the same troubles? It seems to me that nobody cares and mentions in the papers, it sounds like freshly cleaved graphite is a universal standard, independent on the ambient conditions (eg humidity) and invariant over time :(
Marco, you're absolutely right! we also systematically observed a drift in the surface potential (SP) of HOPG measured with KPFM. I was also puzzled that no one has reported these changes over time or the different contrast for different flakes in a single sample under the same conditions.
So the two observations are: 1) time-evolution of the SP of HOPG, and 2) different contrast for different domains. I was hesitating to write a small letter about these observations but it seems it is important for the KPFM community. Specially, considering the use of HOPG as a reference sample for the evaluation of a tip's work function, for example, or that of an arbitrary sample. If you wish we could compare our results and possible explanations for these observations and report this in a joint paper.
yes, why not. We could try to investigate the effect, eg kinetics of change, at different relative humidities (eg 10, 30, 50%: I don't care about glove box conditions, these do not apply for most people and working setups) and temperature, again not far from real conditions: RT (say 20°C), 30, 40°C.
But I would like to learn first from a broader audience what they think and feel about that! Thank you for your answer and proposal. Bye
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