Grain coarsening and gas bubbles in annealed gold films

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Abstract
The annealing behaviour of thin (300–400 Å) vacuum-evaporated gold films has been studied by transmission electron microscopy. Films evaporated at room temperature are found to be composed of small grains a few hundred Å across, some of which grow on annealing by high-angle boundary migration, the extent to which this occurs depending on the residual gas pressure during evaporation in the range studied, 2 × 10−-4 –2 × 10−-6 torr. One reason for this dependence appears to be the presence of small bubbles of insoluble gas ≤50 Å in diameter, which as seen within the grains in numbers related to evaporation gas pressure and which are also observed to impede the motion of grain boundaries by a pinning effect. The mechanism by which the bubbles come to be within the grains is deduced to be that of detachment of pockets of included gas from mobile grain boundaries in the early stages of annealing.