Reducing detrimental electrostatic effects in Casimir-force measurements and Casimir-force-based microdevices

Abstract

It is well known that residual electrostatic forces create significant difficulties to precise measurements of the Casimir force and to wide use of Casimir-operated microdevices. We experimentally demonstrate that with the help of Ar-ion cleaning of the surfaces it is possible to make electrostatic effects negligibly small as compared to the Casimir interaction. Our experimental setup consists of the dynamic atomic force microscope supplemented with an Ar-ion gun and argon reservoir. The residual potential difference between the Au-coated surfaces of a sphere and a plate was measured both before and after the in situ Ar-ion cleaning. It is shown that this cleaning decreases the magnitude of the residual potential by up to an order of magnitude and makes it almost independent on separation. The gradient of the Casimir force was measured using ordinary samples subjected to the Ar-ion cleaning. The obtained results are shown to be in good agreement with both previous precision measurements using the specially selected samples and with theoretical predictions of the Lifshitz theory. The conclusion is made that the suggested method of in situ Ar-ion cleaning is effective in reducing the electrostatic effects and therefore is a great resource for experiments on measuring the Casimir interaction and for Casimir-operated microdevices. * Umar.Mohideen@ucr.edu

Precision measurements of the gradient of the Casimir force between ultraclean metallic surfaces at larger separations

“…1 is a rectangular cantilever. As compared to previous experiments [12][13][14][15]17], the precision of force measurements here was improved by increasing the sensitivity of the cantilever through a decrease of its spring constant. The cantilever spring constant is given by [62]…”

“…The experimental setup was placed inside a stainless steel vacuum chamber consisting of a mechanical scroll pump and a turbo pump connected in series to achieve a pressure down to 10 −9 Torr ≈ 1.3 × 10 −7 Pa, and an ion pump for further reduction (see Refs. [12,17] for details). During the force measurements only the ion pump was used in order to reduce the background mechanical noise to a minimum.…”

“…The Casimir puzzle consists in the fact that theoretical predictions of the Lifshitz theory for metallic test bodies obtained with inclusion of the relaxation properties of conduction electrons are excluded by the measurement data of all precise experiments at short separations [8][9][10][11][12][13][14][15][16][17]. The dielectric response of metals used in computations is found from the optical data extrapolated down to zero frequency by means of the Drude model, where the relaxation parameter γ describes the energy losses of conduction electrons.…”

“…The dielectric response of metals used in computations is found from the optical data extrapolated down to zero frequency by means of the Drude model, where the relaxation parameter γ describes the energy losses of conduction electrons. It is puzzling also that if one puts γ equal to zero (as if there were no energy losses at low frequencies) the Lifshitz theory comes to good agreement with the measurement data of the same experiments [8][9][10][11][12][13][14][15][16][17] (recall that all of them have been performed at separations below 750 nm between the interacting bodies). This means that the dissipationless plasma model, which is in fact applicable only at high frequencies in the region of infrared optics, works well for some reasons even at low frequencies characteristic of the normal skin effect.…”

Casimir force, causality, and the Gurzhi model

“…Surprisingly, in a number of experiments performed by two different groups [11][12][13][14][15][16][17][18][19][20][21] it was found that the measurement results exclude theoretical predictions of the Lifshitz theory obtained using an extrapolation of the optical data by means of the Drude model. The same results turned out to be in agreement with theory if the optical data reflecting the role of core (bound) electrons are extrapolated down to zero frequency by the free-electron plasma model [11][12][13][14][15][16][17][18][19][20][21]. An important role in these comparisons is played by the contribution of the zero-frequency term of the Lifshitz formula which depends heavily on the extrapolation used.…”