Interfacial Reactions between Oxide Films and Refractory Metal Substrates

The interfacial reactions between oxide thin films and refractory metal substrates [NiO/Mo(100), MgO/Mo(100), and Al 2 O 3 /Ta(110)] have been investigated with temperature-programmed reaction, X-ray photoelectron spectroscopy, and ion scattering spectroscopy. The thermal stabilities of the oxide films are considerably less than the corresponding bulk oxides. NiO films react with a Mo substrate between 900 and 1100 K to form molybdenum oxides and metallic nickel, the latter being encapsulated by the molybdenum oxides. Above 1200 K, both metallic nickel and molybdenum oxides are evolved from the surface, the molybdenum oxides desorbing as MoO 3 . The reaction between MgO films and a Mo substrate occurs at a higher temperature (>1300 K) than that found for NiO. The products of the reaction (Mg and MoO 3 ) evolve immediately upon formation; however, both magnesia and molybdenum oxides are found within the topmost surface layer upon quenching the interfacial reaction. Upon reaction of alumina with Ta(110), aluminum desorbs at >1400 K with the product oxygen diffusing into the tantalum substrate.