Atomic-Beam Scattering from Epitaxially Grown Gold Films

Abstract

The spatial distribution of beams of He and Ar scattered by gold-target films was examined mass spectrometrically during and after the formation of these films by evaporative deposition. By controlling the target temperature during the deposition of the metal, varying degrees of crystallographic orientation and surface smoothness were obtained. The metallic deposition rate was maintained high as compared with the impingement rate of background gas particles, resulting in approximate clean-surface conditions during deposition. For rough polycrystalline films, only cosine scattering of He and Ar was observed. For smooth, well-oriented films, specular scattering of He was observed during deposition. In this latter case, a gradual time-dependent dispersion in He scattering was seen after deposition and is shown to result from the formation of adsorbed gas layers. For Ar scattered from a smooth gold film during deposition, a broad directed beam, displaced from the specular angle, is obtained, and very little dispersion occurs after deposition. This latter result is interpreted as being due to the greater interaction between Ar and gold, compared with that between He and gold, which masks the effects of adsorbed gases upon Ar scattering.