REACTIVE DIFFUSION IN THIN-FILMS

Interdiffusions in thin films and in bulk specimens are not basically different, contrarily to a frequent statement. The kinetics of the whole process results from a number of elemental processes, i.e. diffusion of chemical species and point defects, chemical reactions at interfaces leading to the nucleation and growth of intermediate phases, point defect production and/or annihilation at interfaces, grain boundary diffusion,... The interplay of these various elemental processes, either in parallel or in series, makes the resulting story rather complicated, and very sensitive to the geometry of the specimen, the microstructure and the preparation of the material. The general features of the so-called "reactive diffusion" will be discussed in this article on the basis of simple arguments. Some rules - or eventually absence of rule - will be set forth, that should serve as guide lines for the people who have to tackle such problems.