On electrostatic and Casimir force measurements between conducting surfaces in a sphere-plane configuration

TL;DR

This study measures electrostatic and Casimir forces between conducting surfaces in a sphere-plane setup, revealing anomalies in electrostatic calibration and providing evidence for short-range Casimir-Lifshitz forces after correction.

Contribution

It introduces a method to account for electrostatic anomalies and demonstrates the presence of Casimir-Lifshitz forces in the 35 nm to 1 micrometer range.

Findings

Electrostatic calibration exponents are smaller than ideal predictions.

The bias potential varies with sphere-plane distance.

Evidence of Casimir-Lifshitz forces at short distances after electrostatic correction.

Abstract

We report on measurements of forces acting between two conducting surfaces in a spherical-plane configuration in the 35 nm-1 micrometer separation range. The measurements are obtained by performing electrostatic calibrations followed by a residual analysis after subtracting the electrostatic-dependent component. We find in all runs optimal fitting of the calibrations for exponents smaller than the one predicted by electrostatics for an ideal sphere-plane geometry. We also find that the external bias potential necessary to minimize the electrostatic contribution depends on the sphere-plane distance. In spite of these anomalies, by implementing a parametrixation-dependent subtraction of the electrostatic contribution we have found evidence for short-distance attractive forces of magnitude comparable to the expected Casimir-Lifshitz force. We finally discuss the relevance of our findings in the more general context of Casimir-Lifshitz force measurements, with particular regard to the critical issues of the electrical and geometrical characterization of the involved surfaces.