An electron diffraction study of alloying and diffusion in epitaxial growth

The growth of vapour deposited face-centred cubic metals on (111) silver and copper substrates has been investigated in ultra-high vacuum conditions using low and high energy electron diffraction and electron spectroscopy. Extensive diffusion and possible alloying during the epitaxial growth of nickel on copper were observed, in contrast to earlier work claiming pseudomorphism in this system. The results have been shown to be consistent with published diffusion rates, and possible explanations for the disagreement with the earlier work have been put forward. Thin epitaxial films of nickel and copper in thermodynamic equilibrium on silver were found to consist of islands, and silver formed flat layers on nickel and copper, in accordance with surface energy considerations. Metastable, fairly continuous epitaxial films of nickel and -copper were grown on silver, the annealing of which produced phenomena tending to reduce the surface free energy, i.e. thin films drew up into islands and thick films became coated with a thin layer of silver. The _rates at which these processes occurred have been shown to be in broad agreement with published grain-boundary and surface diffusion data. To alloying of silver with either nickel or copper was observed. Preliminary investigations showed that lead formed a √3 x √3 submonolayer structure on (ill) silver, and that thicker layers were misoriented by a small angle. The contraction of an epitaxial lead layer (a few 1 thick) by -.510 on (ill) copper was also observed. The analysis of diffraction patterns from thin epitaxial monolayer type structures of one metal on another suggested that multiple diffraction is the primary origin of satellite diffraction features. Lattice spacing measurements from the same patterns showed that under certain conditions, thin lead layers were constrained to fit a copper substrate in an integral ratio of lattice distances at the interface, and that a similar matching may have occurred for thin silver layers on nickel and corner.