Despite their technological importance for nanoscale technologies, the initial stages of reaction at interfaces (and their dependence on experimental conditions) are still poorly understood. In this article we analyze the initial stages of solid state reaction (SSR) in Al/Pt multilayers (period: 54 nm, overall composition: Al4Pt) and compare the results to those recently obtained by high temperature sequential deposition (HTSD). These two methods differ in several aspects, the most important being the state of reacting Pt (solid in SSR, vapor in HTSD) and its flux (limited in HTSD by the deposition rate). The chemical driving force for the Al/Pt reaction are thus different. We have shown that: (i) The first reaction product observed during SSR or HTSD is the same: namely, a metastable amorphous Al2Pt phase (a-Al2Pt): (ii) This amorphous phase grows in a layer by layer mode. Its growth is diffusion controlled during SSR and stops when all the available Pt is consumed. In the case of HTSD the layer growth is limited by the Pt evaporation rate and diffusion only controls the "critical" thickness that the amorphous layer can reach, (iii) The Al diffusion coefficients in a-Al2Pt deduced from the a-Al2Pt growth rate (SSR) or "critical" thickness (HTSD), using the Nernst-Einstein equation in order to take into account the difference in the chemical driving forces, are similar.
ASJC Scopus subject areas
- Physics and Astronomy(all)