Noncontact Atomic Force Microscopy - Yale School of Engineering ...

Drude corrections to Casimir force calculations in liquids
Raul Esquivel-Sirvent 1
1 Instituto de Física, Universidad Nacioanl Autónoma de México, México D.F. 01000.
Mo-1050
The Casimir force for metals immersed in different fluids has been measured recently
[1,2,3]. The comparison with theory is based on the Lifshitz formula and the knowledge
of the dielectric function of the involved materials. In the case of the reported
experiments, Au is a common metal used in the force measurements. The data for the
dielectric function of Au can be obtained from tabulated data with a low frequency
interpolation using the Drude model. The data for the optical properties of Au are usually
measured in air or partial vacuum. However, changes in the Drude parameters of metals
when immersed in fluids have been reported in the literature. Gugger [4] using the
method of total attenuated internal reflection measured the dielectric function of Ag films
in contact with different liquids. The measurements showed a change in the dielectric
function of the Ag film depending on the index of refraction of the fluids. The same
conclusion was reached in the work of Chen [5] that by means of spectroscopic
ellipsometry measured the Drude parameters for Au and Ag films immersed in liquids,
confirming the change in the Drude parameters of the metals.
In this paper we examine the change in the Casimir force between two Au surfaces
immersed in different fluids and how the change in the Drude parameters affects the
Casimir force calculations. In particular, we show that variations of the order of 8% are
possible and observed discrepancies between theory and experiment can be explained
by this effect. The change of the Drude parameters of a metal immersed in a fluid are
described by a Bruggeman effective medium theory. Finally, we discuss the possible
applications of effective medium theories within the Lifshitz formalism.
[1] J. N. Munday and F. Capasso, Phys. Rev. A 75, 060102(R) (2007).
[2] J. N. Munday, F. Capasso, V. A. Parseguian and S. M. Bezrukov, Phys. Rev. A 78,
029906 (2008).
[3] P. J. van Zwol, G. Palasantzas and J. Th. M. De Hosson, Phys. Rev. B 79, 195428
(2009).
[4] H. Guger, M. Jurich and J. D. Swalen, Phys. Rev. B 30, 4189 (1984).
[5] L. Y. Chen and D. W. Lynch, Phys. Rev. B 36, 1425 (1987).
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