In Situ Surface Microscopy STM and AFM

It should be emphasized that the STM technique is only applicable for a conductive surface or electrode. Accordingly, problems may arise if an insulating oxide layer is 

It should be emphasized that the STM technique is only applicable for a conductive surface or electrode. Accordingly, problems may arise if an insirlating oxide layer is formed on a semiconductor surface. This problem is avoided by applying atomic force microscopy (AFM). In this case, the mass attraction and repulsion between a tip and a sample is measured, which is independent of the conductivity of insirlating layers at the surface of a given sample. In order to have sufficient sensitivity, the tip vibrates at a given resonance frequency and the change of this frequency is taken as a measure of the distance between the tip and the sample [27]. 

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