Interpretation of atomic force microscope (AFM) signals from surface charge on insulators

摘要

The surface of an insulator can accumulate charge by a variety of means. There is a need for good experimental procedures to measure these surface charge densities. The most promising new method is to use an atomic force microscope (AFM). Resolutions of the order of 100 nm have been reported (Stern et al [1], Guethner et al [2], Uchihashi et al [3], while 10 nm has been claimed (Cahur [4]). The vastly improved resolution compared with the previous methods, coupled with use in the ambient atmosphere, mean that this method will become widely used. The observed signals show a spatial spreading and a temporal decay. In this paper we show how these measurements can be related to the physical mechanisms causing charge motion on the surface and within the bulk of the sample.