A medium energy ion scattering study of metal-on-metal epitaxy and surfactant-mediated growth for the Au on Cu(111) system

The growth of Au on Cu(111) single crystal substrate has been investigated both with and without Sb surfactant. Room temperature deposition of approximately 10 ml of Au onto Cu(111) gave a film with twinned fcc structure, a reasonable degree of crystallinity and clear indications of inter-diffusion at the interface. Annealing this layer to progressively higher temperatures encouraged the diffusion of the Au into the substrate, thus reducing the strain arising from the lattice mismatch between Au and Cu. For a 400°C anneal the Au had almost entirely dissolved into the Cu substrate, such that no apparent twinning could be observed. The use of pre-deposited Sb as a surfactant in the growth of the Au layer was investigated for two levels, 0.2 and 0.5 ml, since above 0.33 ml Sb induces a stacking fault into the top most layer of Cu(111). For the lower coverage, similar results were observed in terms of the degree of crystalline order, but there was some indication that the twinning effect was partially suppressed. This effect was not observed for the higher Sb coverage. The compositional information as a function of depth indicated that for both coverages, the Sb remained at the surface. However, it was also evident that for the lower Sb coverage somewhat greater inter-diffusion between the Au and Cu occurred and it is possible that it is this effect that is actually responsible for the apparent reduction in twinning. These results indicate little benefit in the use of Sb as a surfactant for the epitaxial growth of Au on Cu(111).