Casimir Forces between ThermallyActivated Nanocomposites
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Casimir Forces between ThermallyActivated Nanocomposites Raúl Esquivel-Sirvent, Carlos Villarreal, and Cecilia Noguez Instituto de Física, Universidad Nacional Autónoma de México, Circuito de la Investigación Científica, Ciudad Universitaria, México, DF, 04510, México. ABSTRACT We present a theoretical study of the modification of Casimir forces between nanocomposite slabs that exhibit a metal-dielectric transition. In particular, we consider slabs made of VO2 precipitates in sapphire, whose effective dielectric function is calculated within a mean field approximation. The results for the Casimir force as a function of the separation of the slabs, show that at a fixed separation the magnitude of the force changes as temperature increases from 300 K to 355 K. The possible applications of these results to Casimir devices is discussed.
INTRODUCTION In 1948 Casimir [1] showed that two parallel plates separated by a distance a and made of a perfect conductor will attract each other with a force per unit area given by F =−
π 2 hc 240a 4
.
(1)
This force is attributed to the quantum vacuum fluctuations of the electromagnetic field. Indeed, Casimir forces appear whenever the mode distribution of a fluctuating field is modified by the presence of boundaries [2]. Although Casimir forces are small (0.13 dynes for 1 mm2 plates separated by one micron) they have been measured through a series of ingenious experiments. Lamoreaux [3] reported an agreement with theory at the level of 5% using an electromechanical system based on a torsion balance. More recent experiments performed by Mohideen with atomic force microscopes achieved precisions close to 1% [4]. In another experiment, a micromachined torsional device was employed to measure the Casimir attraction between a plate and a spherical metallic surface [5]. The original formulation of Casimir was for perfect conductors motivating Lifshitz to propose in 1956 a theory for vacuum forces between semi-infinite dielectric media [6]. The corresponding theory for finite dielectric systems has been developed in last few years [7]. With the advent of novel experimental techniques associated to the development of micro electromechanical systems (MEMS), and instruments such as the atomic force microcope (AFM) different proposals related with the technological uses of the Casimir forces have been investigated. For example, the deflection of a thin microfabricated rectangular strip due to Casimir forces was calculated by Serry et al. [8]. According to their results, the strength of these forces is high enough as to buckle the strip and limit the operation of MEMS. Maclay [9] has also suggested to build MEMS devices in order to study the properties and energy balance of MEMS when static or vibrating membranes are V3.3.1
placed on the top of open rectangular cavities. The proposed experimental configuration consists of an array of open rectangular metallic cavities. A top plate suspended by micromecanical springs may be used to measure the sign and magnitude of the Casimir interaction
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