Molecule oxygen-driven shaping of gold islands under thermal annealing

► We investigate the annealing of Au film in different thermal environments. ► The role played by O2 in the morphology evolution of Au film under annealing is generally ignored in literature. ► It is experimentally found that O2 drives the migration of Au atoms under thermal treatments. ► The shapes of Au islands formed by annealing are related with the interaction between O2 and the Au surface.