The epitaxial growth of cobalt on copper

Abstract

Single-crystal films of cobalt are grown by evaporation in ultra-high vacuum onto (001) copper substrates held at temperatures between 250°C and 350°C. It is found that the first misfit dislocations appear in the Cu-Co interface when the cobalt film is 13, Å thick. Although thicker films are no longer pseudomorphic, the mean strain in the cobalt is still much greater than the equilibrium value predicted by existing theory. A previously established mechanism for the generation of misfit dislocations is used to estimate the magnitude of this discrepancy between the theoretical and measured strains. It is suggested that the existence of large residual strains is inevitable in any film which initially grows as a continuous pseudomorphic layer.