A Marker Technique to Identify Diffusing Elements During Initial Reactions Using Ion-Scattering Spectroscopy

A variation of classical marker techniques has been combined with low-energy ion scattering spectroscopy (ISS) to study the diffusion of species during the initial formation of several reacted monolayers, allowing the study of thinner layers than standard marker techniques allow. Results are presented for the reaction of oxygen with GaAs under 248 nm laser illumination and at 400-degrees-C, as well as for the well-studied case of Ni oxidation at room temperature. We discuss the criteria for choosing an appropriate marker element, and the limitations on the information that can be obtained with this method. The results show that inward oxygen diffusion can be distinguished from outward metal diffusion as the reaction proceeds. This information is crucial for developing an understanding of reaction mechanisms in thin films.