Measurement and compensation of electrostatic forces between conducting surfaces at distances in the micrometer range by means of PTB's nanonewton force facility

The measurement and compensation of electrostatic forces between conducting surfaces play a major role in various experiments, including measurements of the Newtonian constant of gravitation, measurements of the Casimir force, precision tests of general relativity in space, searches for hypothetical forces (fifth forces), gravity on elementary particles, heating in ion traps, and the physics of Rydberg atoms [1, 2]. Although the actual value of the contact potential was not of direct interest, it was necessary to eliminate it accurately in these experiments in order to avoid residual electrostatic forces that may limit the accuracy and precision of such experiments. We demonstrate how PTB's nanonewton force facility [3, 4] can be used to accurately determine and compensate for the contact potential difference. To measure the contact potential difference as well as the distance between a force sensor and a measured object, a new three-voltage method was developed. A new method of adjusting the parallelism of the plates is also presented. The methods and the results of measuring the contact potential difference and the distance in vacuum are presented for a so-called plane-plane geometry and a ball-plane geometry. Measurements of the temporal and spatial variations of the contact potential difference were performed. Measurements were carried out at distances in the micrometer range between the metallic surfaces. A significant dependence of the contact potential difference on the distance between the conducting surfaces and on the time was found.