Formation of grain boundaries during diffusion between single crystal films of gold and palladium

Abstract

Single-crystal films of gold and palladium, in contact with one another and in parallel orientation, were prepared by evaporation onto hot rocksalt. The salt was dissolved and the films were heat treated to promote diffusion between them. Specimens at different stages in the diffusion process were examined by transmission electron microscopy. It was found that grain boundaries of one type were formed during diffusion and that a second type of boundary was formed after diffusion was complete. The boundaries that appeared during diffusion enclosed grains in which the difference between the lattice parameters of the upper and lower specimen surfaces was accommodated by lattice curvature. Outside the boundaries the variation in lattice parameter was accommodated by dislocations in edge orientation. The boundaries, that appeared after diffusion was complete, were the result of the rearrangement of isolated dislocations into walls. Some of the dislocations involved were formed during film growth; others were made by the climb of dislocations initially present to accommodate the difference between the lattice parameters of gold and palladium.