Structural modification of Au-Co thin films induced by annealing in oxidizing atmosphere

The stability upon air-annealing of uncapped Au-Co thin films is investigated. The analysis focuses on the modifications of the crystalline fraction of the films produced by physical vapor deposition. The film with the highest Au concentration exhibits the strongest diffraction signal, corresponding to a Au-rich fcc AuxCo1−x solid solution alloy, with nanocrystals which have a rod-like shape. Air annealing induces a progressive de-alloying which is complete at 500 °C, as shown by X-ray Absorption Spectroscopy and X-ray diffraction. The film, that is directly exposed to the oxidizing atmosphere, undergoes a de-wetting process, likely triggered by Au. X-ray nanoimaging mapping enlightens the presence of interpenetrating sub-μm Au and Co3O4 domains. This peculiar annealed nanostructured system can have interesting applications in the field of catalysis. •The crystalline fraction of Au-Co co-sputtered alloy is stable for T < 200 °C.•Air annealing promote a decomposition of the crystalline Au-Co alloy at T > 250 °C.•Air annealing at 800 °C, leads to interpenetrating sub-μm Au and Co3O4 domains.