Effect of annealing atmosphere on the thermal coarsening of nanoporous gold films

Abstract

The coarsening of nanoporous gold (NPG) is significantly influenced by surface adsorbates at elevated temperature. In this paper, the effect of annealing atmosphere on the thermal growth of the porous structure was investigated by scanning electron microscopy and X-ray photoelectron spectroscopy. The NPG films were annealed in oxidative (air), inert (Ar) and reductive (CO) atmospheres at 100–600°C for 2h, respectively. The experimental results indicate that the NPG films show the best stability in the reductive atmosphere and the worst thermal properties in oxidative air. The NPG films annealed in air exhibit a significant pore growth at 200°C and lose the porous structure at 300°C, while those annealed in CO gas at 600°C still remain the porous network. The thermal-induced coarsening of NPG films in air can be attributed to the desorption of O2 from the NPG surface above 200°C. In contrast, the stabilization of the NPG films in CO gas originates from the strong binding of CO with Au atoms to form a complex adsorption layer, which effectively inhibits the surface diffusion of Au atoms.