I have obtained several potential maps by using the AM-KPFM mode of Bruker Dimension Icon. However, I am having difficulties in understanding the data. I would really appreciate if someone could help me out.

1. While trying to image a particular spot, once the potential data is in positive range but if I just withdraw and engage again at the same spot, at times the potential turns to negative side (and vice versa)

2. Owing to this random switching of potential data, I do not know how to caliberate the tip against HOPG.

3. Owing to the above reasons, if I dont wish to calculate the absolute work function, can I at least get some information based on the variation across local surface of my sample. Does lower surface potential (more -ve value when the potential is negative or less +ve value when potential is positive) translate to higher work function?

I am not applying any DC bias and only AC bias of 3500 mV to the tip. Let me know if any further details are required.