Atomic force microscopy is an important tool in the research of surface topography and property, not only utilized in thin film, but also single crystal surface. Thermoelectric materials can generate electricity from waste heat, so it is environmental friendly. SnSe is a promising thermoelectric material with record-breaking figure of merit 2.6 at 923K, thus being widely used in prospect. However, the self-hole-doping mechanism in SnSe is still absent. Here we use AFM to study two kinds of defects in SnSe: SnSe2 micro domain and point dislocation. Then we provide an explanation for its self-hole-doping mechanism and electronic structure. This webinar consists of two parts: (1)Theory and operation of Kelvin probe force microscopy (2) Investigation of thermoelectric material SnSe using AFM.