An alternative method to measure charge distributions: The scanning Kelvin probe

The scanning Kelvin probe is a non-contact measurement technique which permits the determination of potential distributions on the surface of insulators or work function differences in conductive materials. Any potential difference between the tip of an oscillating needle and the underlying surface results in influenced charges in the tip which cause an ac current. This current can be adjusted to zero by variation of the dc potential of the tip. Then the tip has the same potential as the surface and the surface potential is determined. In this way the potential distribution in ion-conducting polymers (polyethylene oxide) is measured. The voltage applied between two electrodes causes a strongly nonlinear potential distribution in the samples. Simultaneously the dc currents in the samples are detected.