Impedance of a thin film in the presence of spatial dispersion and the problem of additional boundary conditions

Publisher Website
Google Scholar
Abstract
We have calculated the surface impedance of a thin, spatially dispersive, dielectric film deposited on a metal substrate for two commonly used forms of the additional boundary conditions (ABC's) at the film-vacuum and film-substrate interfaces. The reflectivity has been calculated from the surface impedance for frequencies in the vicinity of the resonance frequency of the film, and numerical results are presented for the case of a ZnSe film on an Al substrate. The results for very thin films show not only quantitative but also qualitative differences between the predictions of the two ABC's that should enable a choice to be made between them on the basis of experimental reflectivity data. An approximate analytic expression for the reflectivity is obtained in the limit of very small film thicknesses, and its range of validity determined.