SUPPRESSION OF CRYSTAL NUCLEATION IN AMORPHOUS LAYERS WITH SHARP CONCENTRATION GRADIENTS

Using simple thermodynamic arguements, it is shown that sharp concentration gradients occurring during diffusive mixing of multilayer composites facilitate amorphization by solid-state reaction by reducing or suppressing the driving force for crystallization Gac. As the concentration gradients diminish during diffusive layer growth, the driving force for crystalline phase formation is restored and the energetic barrier to their nucleation to the classical expression. This evolution yields a critical maximum amorphous-layer thickness as observed experimentally. © 1990 The American Physical Society.