Initial formation and growth of an amorphous phase in Al-Pt thin films andmultilayers: Role of diffusion

Despite their technological importance for nanoscale technologies, the init ial stages of reaction at interfaces (and their dependence on experimental conditions) are still poorly understood. In this article we analyze the ini tial stages of solid state reaction (SSR) in Al/Pt multilayers (period: 54 nm, overall composition: Al4Pt) and compare the results to those recently o btained 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 depos ition rate). The chemical driving force for the Al/Pt reaction are thus dif ferent. We have shown that: (i) The first reaction product observed during SSR or HTSD is the same: namely, a metastable amorphous Al(2)pt phase (a-Al (2)pt): (ii) This amorphous phase grows in a layer by layer mode. Its growt h 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 evapor ation rate and diffusion only controls the "critical" thickness that the am orphous layer can reach. (iii) The Al diffusion coefficients in a -Al(2)pt deduced from the a-Al2Pt growth rate (SSR) or "critical" thickness (HTSD), using the Nernst-Einstein equation in order to take into account the differ ence in the chemical driving forces, are similar. (C) 2001 American Institu te of Physics.