Precision Casimir Force Measurements After In Situ Argon-Ion Beam Bombardment: Studying the Role of Electrostatic Patches

The Casimir effect was first predicted by Hendrik Casimir in 1948. It was described as an attractive force between two neutral, parallel conducting plates placing in a vacuum. It is explained by the quantum field theory using the zero-point oscillations of quantized electromagnetic fields with the presence of boundaries. As a macroscopic phenomenon arises from the zero-point energy, it plays an important role in both fundamental physics and, micro- and nano-technology. The development of precision Casimir force measurements since 1997 allows a quantitative comparison between experiment and theory. Specifically, the comparison results help us to investigate the thermal Casimir effect and set constraints on the hypothetical non-Newtonian gravity.In this work, we study the residual force induced by electrostatic patches in precision Casimir force measurements. We find that the residual force can be eliminated even prior to Ar ion cleaning. Compensation could be achieved only if the residual potential for the two grounded surfaces did not vary with distance within the experimental error. This however happens for a small fraction of the measurements. For most surfaces the residual potential changed as a function of distance due to the electrostatic patches. The optimal Ar ion cleaning was found to be 500 V beam voltage, 80% focus voltage, 10 uA anode current, 2x10^{-5} torr Argon pressure and 15 cm gun-sample separation. After 100 minutes Ar ion cleaning the residual potential decreased to 1.3 +/- 1.2 mV. For cleaned surfaces the residual potential did not change as a function of distance allowing compensation of the electrostatic force. The Casimir force for cleaned surfaces matches the Lifshitz theory for Au where the energy loss from free electron scattering with zero point photons in the metal has been neglected