The Kelvin probe is a non-contact, non-destructive vibrating capacitor device used to measure the work function (wf) of conducting materials or surface potential (sp) of semiconductor or insulating surfaces. The wf of a surface is typically defined by the topmost 1 - 3 layers of atoms or molecules, so the Kelvin probe is one of the most sensitive surface analysis techniques available. KP Technology systems offer a very high wf resolution of 1 - 3 meV, currently the highest achieved by any commercial device.
The Kelvin probe does not actually touch the surface; rather an electrical contact is made to another part of the sample or sample holder. The probe tip is typically 0.2 - 2.0 mm away from the sample and it measures the 'traditional work function', i.e. that found in literature tables. Other techniques, using very sharp tips some 10's of nanometers away from the sample, measure very reduced and distorted work functions due to the close separation of tip and sample.