Contact potential measurements with a local Kelvin probe

Abstract

The Kelvin probe technique can be used as a very accurate tool to measure contact potential differences (CPDs). However, the experimentally observed CPD dependence on the probe-sample distance, the so-called stray capacitance effect, is a parasitic effect not explained in the simple Kelvin probe theory. It can be especially disturbing when using a local Kelvin probe or Kelvin probe microscopy as it hinders quantitative use of CPD measurements. We show that this effect can be described without the expedient of stray capacitors by taking into account the electrostatic induction of metal objects located in the vicinity of the probe-sample system. This model leads to excellent agreement with the experimental variations in the apparent value of CPD with the probe-sample distance and allows us to recover the exact CPD value.