Grain boundary character distribution and texture evolution during surface energy-driven grain growth in nanocrystalline gold thin films

The evolution of grain boundary microstructure during annealing in sputtered gold thin films was investigated on the basis of FEG-SEM/EBSD/OIM analyses of nanocrystalline microstructure, in order to find a clue to the precise control of grain boundary microstructure for development of high performance polycrystalline thin films. Remarkably high fractions of coincidence site lattice (CSL) boundaries with specific sigma values such as sigma 1, sigma 3, sigma 7, sigma 13, sigma 19 and sigma 21 occurred in the gold thin film specimens on Pyrex glass substrate by annealing in air. The occurrence of higher fraction of these specific low-sigma boundaries is probably attributed to the evolution of a very sharp {111}-textures of different degrees which results from the preferential growth of {111}-oriented grains due to surface energy-driven grain growth. The fraction of low-sigma CSL boundaries increased with increasing area fraction of {111}-texture. The grain boundary character distribution in the gold thin film specimens was strongly affected by the annealing atmosphere and substrate materials. The sharpness of {111}-texture in the specimen annealed in low-vacuum was weaker than that in the specimen annealed in air, and an extraordinarily high fraction of sigma 3 CSL boundaries occurred. The grain growth of gold thin film specimens on SiO2 glass substrate was much slower than that of specimens on Pyrex glass substrate. The fraction of low-sigma CSL boundaries observed for the gold thin film specimens on SiO2 glass substrate was lower than that in the specimens on Pyrex glass substrate. The inverse cubic root sigma dependence of low-sigma CSL boundaries in the gold thin film specimens was discussed in connection with the process of the evolution of grain boundary microstructure.