Thin-film reactions

Thin-film geometries, where at least one of the reactants is in the form of a thin film, are particularly useful for studying the earliest stages of solid-state reactions in oxides. In the present work, a thin-film approach has been developed to study the earliest stages of reactions in two model oxide systems. The first being NiO/Al2O3, where the NiO is an epitactic film on various orientations of single-crystal Al2O3. In this case, both interfacial-reaction and diffusion control of the kinetics have been observed and correlated with the interfacial structure. In the second, a thin-film approach has also allowed reaction kinetics in the system Fe2O3/MgO to be measured. In this case, the Fe2O3 is an epitactic film on an (001)-oriented MgO single crystal. In contrast with the NiO/Al2O3 system only diffusion control of the kinetics was observed. The results of fine-scale 'marker' experiments in both of the above systems will also be discussed. © by R. Oldenbourg Verlag, München 1998.