A study of the electromagnetic-fluctuation-induced forces on thin metallic films

Using the plasma model for the metal dielectric function we have calculated the electromagnetic-fluctuation-induced forces on a free standing metallic film in vacuum as a function of the film size and the plasma frequency. The force for unit area is attractive and for a given film thickness it shows an intensity maximum at a specific plasma value, which cannot be predicted on the basis of a non-retarded description of the electromagnetic interaction. If the film is deposited on a substrate or interacts with a plate, both the sign and the value of the force are modified. It is shown that the force can change the sign from attraction to repulsion upon changing the substrate plasma frequency. A detailed comparison between the force on the film boundaries and the force between film and substrate indicates that, for 50–100 nm thick films, they are comparable when film–substrate distance is of the order of the film thickness.