  We consider the fluctuation-induced (Casimir) pressure in peptide films
deposited on GaAs, Ge, and ZnS substrates which are either in dielectric or
metallic state. Calculations of the Casimir pressure are performed in the
framework of fundamental Lifshitz theory employing the frequency-dependent
dielectric permittivities of all involved materials. The electric conductivity
of semiconductor substrates is taken into account within the experimentally and
thermodynamically consistent approach. According to our results, the Casimir
pressure in peptide films deposited on dielectric-type semiconductor substrates
vanishes for some definite film thickness, is repulsive for thinner and
attractive for thicker films. The dependence of this effect on the fraction of
water in the film and on the static dielectric permittivity of semiconductor
substrate is determined. For the metallic-type semiconductor substrates, the
Casimir pressure in peptide coatings is shown to be always repulsive. Possible
applications of these results to the problem of stability of thin coatings in
microdevices are discussed.
