  We calculate the Casimir force between slabs of finite thickness made of
intrinsic and doped silicon with different concentration of carriers and
compare the results to those obtained for gold slabs. We use the Drude and the
plasma models to describe the dielectric function for the carriers in doped Si.
We discuss the possibility of experimentally testing the appropriateness of
these models. We also investigate the influence of finite thickness on $VO_2$,
which has recently been proposed for Casimir effect measurements testing the
metal-insulator transition.
