In situ STM study of thermal annealing of Au thin films: An investigation on decay of nanometer Au clusters and 2D islands

An in situ, ultrahigh vacuum scanning tunneling microscopy(UHV STM) study of thermal annealing of gold thin films is presented in this paper. The gold thin films was heated and annealed in the UHV chamber in the temperature range from room temperature to maximum of 300°C , while a consecutive STM imaging was performed on the surface of the gold films during the heating and annealing. The STM results showed that the surface corrugation changes became more apparent after the temperature increased above 100°C, whereas much smoothened surface and large Au(111)crystalline terraces(>200nm) formed at temperature of 160°C or above. Besides the surface morphology change, our images clearly revealed the melting of multilayer gold clusters and shrinking of monolayer gold islands in a nanometer scale. It was shown that the decay of the gold clusters and islands constitute the microscopic processes contributing to the thermal activated surface morphology change. A classical theory of mass flow kinetics was adopted in analyzing the decay processes. The results showed that surface diffusion is the dominate mechanism in the thermal annealing of the gold thin films. This study presents the first microscopic investigation of thermal annealing processes of metal thin films observed by in situ and real-time STM.