Reducing detrimental electrostatic effects in precision Casimir force measurements using argon ion bombardment and UV light

In precision Casimir force measurements between two neutral and grounded surfaces, the role and effect of electrostatic forces have to be fully understood in vacuum. The two Au coated surfaces can be contaminated with adsorbates leading to potential electrostatic patches. We have used 500 eV Ar ion bombardment of the surfaces and UV cleaning to remove the adsorbates prior to Casimir force measurements. The measurements were performed by means of dynamic atomic force microscopy operated in frequency shift mode. The force was measured between an Au coated hollow glass sphere attached to a Si cantilever and an Au coated silicon plate. To improve the sensitivity of the cantilever by reducing its spring constant, it was etched using concentrated KOH solution prior to attachment of the sphere. The residual potential difference between the Au sphere and the plate was reduced using Ar ion bombardment and UV light and checked to be independent of the sphere-plate separation. The measured Casimir force has been compared to theoretical prediction of the Lifshitz theory. For the distance ranges measured the experimental data are consistent with the electric permittivity of Au using the lossless plasma model behavior at zero frequency and tabulated optical data at all other frequencies.