Probe diameter and probe–specimen distance dependence in the lateral resolution of a scanning Kelvin probe

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Abstract
The ability of a scanning Kelvin probe (SKP) to resolve lateral differences in specimen surface potential is investigated by two routes. First, electrostatic calculations are used to obtain analytical expressions for the maximum lateral resolution attainable by a “point probe” of negligible physical dimensions, as a function of probe–specimen distance. Second, lateral resolution is measured experimentally by scanning plane-ended cylindrical probes of varying diameters at varying heights across a linear edge, delimiting two electrically continuous coplanar areas of dissimilar metal. Finally the two approaches are combined to obtain a semiempirical relationship between probe diameter, probe–specimen distance, and lateral resolution for plane-ended cylindrical probes. An expression is also developed for the minimum error to be expected in a surface potential measurement when this is associated with a specimen feature exhibiting a diameter comparable with the probe–specimen distance.