Effect of low-temperature oxidation and heat treatment under vacuum on the Al–Be interdiffusion process

Abstract

The oxidation of the Be/Al and Al/Be bilayer thin film systems deposited by magnetron sputtering have been studied by photoelectron spectroscopy and transmission electron microscopy. Both systems are oxidized according to the Cabrera–Mott model in the air. A Be/BeO/Al/Al₂O₃ structure is formed, with aluminium represented as localized nanocrystals. The thickness of the beryllium in the Al/Be system and the formed beryllium oxide is not enough to prevent the diffusion of aluminium ions under the influence of the Mott potential, and as a result, the surface layer is a mixture of beryllium and aluminium oxides. The effect of oxidation processes on the intermixing of non-interacting metals in a bilayer nanostructure has been shown for the first time. Annealing of the Be/Al bilayer leads to beryllium diffusion to the surface and the reduction of aluminium oxide, which leads to the destruction of the bilayer structure. In the Al/Be system in the range up to 200 °C, additional beryllium oxide is formed with increasing temperature, and the rest of the metallic beryllium diffuses into the aluminium layer. Based on studies, we conclude that multilayer Al/Be nanostructures have potentially low thermal stability, which requires the use of barrier layer techniques to limit interdiffusion.