Abstract

The salient features of an automatic ellipsometer suitable for studying the nucleation and growth of zinc sulfide films in ultrahigh vacuum are described. The instrument is operated automatically in a selfnulling classical mode by means of two Faraday cells driven by currents with both ac and dc components. Sensitive measurements of the dc components in the null condition provide values of two functions δψ = ψ − ψ₀ and δΔ = Δ − Δ₀, where ψ₀ and Δ₀ are the initial values of the usual ellipsometric functions ψ and Δ for the uncoated glass substrate surface. The refractive index and thickness of the growing films are deduced from a plot of [δψ, (δΔ)²]. A point P on the [δψ, (δΔ)²] curve represents a film of thickness d and refractive index n, where n is obtained from the slope of OP and d from its length. The ellipsometric functions and optical parameters of the growing film are related to structural parameters via the Volmer-Weber model for film growth on amorphous substrates. Such growth proceeds around islands or nuclei; and in the simplest form of the model, the nuclei are assumed to be spherical and their surface number density fixed ab initio.

© 1989 Optical Society of America