Time dependence and mechanism of Au nanostructure transformation during annealing

Abstract

Melting point of thin nanostructured materials decreases with decreasing particle size. This can influence thermal stability of thin films used in electronic applications and compromise their function. Therefore it is desirable to explore connection between metal film thickness and its thermal stability. Thin films of Au were sputtered for 10–300 s (2–60 nm thick layers). Post deposition annealing was carried out at 150–300°C for 15–180 min. Sheet electrical resistance measurements were employed to investigate electrical continuousness of the Au film. A significant leap in percolation threshold was found between samples annealed at 250°C and 300°C. This suggests that phase transition occurs during annealing, however, annealing for different times suggests the structural modification is a gradual and slow process, which is a sign of diffusion in a solid state. This was further supported by UV–Vis measurements which showed slow evolution of plasmon resonance peak. Convincing direct evidence of the surface morphology evolution was obtained by AFM microscopy.