Casimir force calculations near the insulator-conductor transition in gold thin films

We present theoretical calculations of the Casimir force for Au thin films near the insulator-conductor transition that has been observed experimentally. The dielectric function of the Au thin films is described by the Drude-Smith model. The parameters needed to model the dielectric function such as the relaxation time, plasma frequency and the backscattering constant depend on the thickness of the film. The Casimir force decreases as the film thickness decreases until it reaches a minimum after which the force increases again. The minimum of the force coincides with the critical film thickness where a percolation conductor-insulator occurs.Comment: 5 figures, 1 tabl

Reduction of the Casimir force using aerogels

By using silicon oxide based aerogels we show numerically that the Casimir force can be reduced several orders of magnitude, making its effect negligible in nanodevices. This decrease in the Casimir force is also present even when the aerogels are deposited on metallic substrates. To calculate the Casimir force we model the dielectric function of silicon oxide aerogels using an effective medium dielectric function such as the Clausius-Mossotti approximation. The results show that both the porosity of the aerogel and its thickness can be use as control parameters to reduce the magnitude of the Casimir force.Comment: to appear J. Appl. Phy

Variations of the Lifshitz-van der Waals force between metals immersed in liquids

We present a theoretical calculation of the Lifshitz-van der Waals force between two metallic slabs embedded in a fluid, taking into account the change of the Drude parameters of the metals when in contact with liquids of different index of refraction. For the three liquids considered in this work, water, $CCl_3F$ and $CBr_3F$ the change in the Drude parameters of the metal imply a difference of up to 15% in the determination of the force at short separations. These variations in the force is bigger for liquids with a higher index of refraction.Comment: 2 figures, 1 tabl

Van der Waals torque induced by external magnetic fields

We present a method for inducing and controlling van der Waals torques between two parallel slabs using a constant magnetic field. The torque is calculated using the Barash theory of dispersive torques. In III-IV semiconductors such as $InSb$, the effect of an external magnetic field is to induce an optical anisotropy, in an otherwise isotropic material, that will in turn induce a torque. The calculations of the torque are done in the Voigt configuration, with the magnetic field parallel to the surface of the slabs. As a case study we consider a slab made of calcite and a second slab made of $InSb$. In the absence of magnetic field there is no torque. As the magnetic field increases, the optical anisotropy of $InSb$ increases and the torque becomes different from zero, increasing with the magnetic field. The resulting torque is of the same order of magnitude as that calculated using permanent anisotropic materials when the magnetic fields is close to 1 T.Comment: to appear in Journal of Applied Physic