The Kelvin probe works with a non-destructive, contactless measuring principle and serves for the local determination of the contact potential difference between the vibrating measuring tip and the sample (in most cases metallic). The contact potentialdifference is based on the different work functions of the two metals or, in the case of non-metallic samples, on the surface potential. As a surface-sensitive method, the Kelvin probe reacts to adsorption process and to changes in the redox state, which is why it is an interesting method for many applications.
SKP surface scan of a steel sample loaded with hydrogen:
measured contact potential difference (CPD)
topography from automatic height correction