X-ray reflectivity was used to track the diffusion of Au into Si(001) substrates, with time, at room temperature. It was observed that the diffusion of Au into Si substrates depended strongly upon the initial pre-treatment conditions of the Si surface. In particular, there was very little diffusion in the case of the untreated Si surface, while a Si surface pre-treated with HF seemed to be prone to strong diffusion, and a surface further pre-treated with Br exhibited intermediate diffusion. Such different diffusion and apparent non-Fickian time-dependence of the diffusion could be quantitatively explained by the Fickian diffusion of Au through changing unblocked interfacial layer. The growth of the blocking (oxide) layer with time essentially prevented further diffusion through those areas, and the growth of that layer was directly related to the surface stability due to the surface pre-treatment and/or passivation conditions, which gave control over the formation of diffusion-induced Au-Si nanolayers of differing widths and compositions. The morphology and evolution of the top surface, mapped using atomic force microscopy and scanning electron microscopy, further helped to verify and understand such differences.

Interfacial Role in Room-Temperature Diffusion of Au into Si Substrates. J.K.Bal, S.Hazra: Physical Review B, 2007, 75[50], 205411