Mapping of Surface Potentials by Electrons on a Helium Film

A novel way to investigate perturbations of the electrostatic potential across a sample surface is presented, aiming at application in 2D contact phenomena. The idea is to deposit surface state electrons (SSE) on a thin layer of liquid helium covering the surface of a solid state sample. The density of the SSE adjusts to screen perturbations of the electrostatic potential across the sample. As a result, the helium layer thickness varies due to the variation of the electrostatic pressure, thus providing a map. This map may be read interferometrically by a technique already employed for the investigation of multi-electron dimples on helium. We realized this mapping for a structured metal electrode as a test sample to investigate the resolution of the method.