Ni electrochemical epitaxy on unreconstructed Au(111): An in-situ STM study

Gold (111) is a widely used substrate in vacuum and in electrolytes for studying the initial stages of metal growth. Its surface reconstruction is unavoidable using common preparation procedures in vacuum and this affects the growth mechanism of metal overlayers. In the electrochemical environment, the same surface reconstruction is obtained at potentials negative of the Au(111) potential of zero charge, whereas above this potential the surface structure is (1 × 1). In this paper we present a preparation procedure which allows blocking the Au step edges by Pd islands, inhibiting the formation of the Au(111) reconstruction and yielding the unreconstructed Au(111) surface (1 × 1) at any electrochemical potential. Using in-situ scanning tunnelling microscopy, we compare the Ni/Au(111) electrochemical epitaxy on reconstructed and on unreconstructed Au(111). Observations show that performing Ni growth on the (1 × 1) surface drastically improves the long-range order of the (8 × 8) moiré pattern created by the lattice mismatch between the Au substrate and Ni adlayer. Detailed characterizations of the moiré structure and of its electrochemical dependence provide new insights into the relative energy landscape of the multiple adsorption sites of the Ni atoms within the (8 × 8) unit cell. The possibility of stabilizing a Au(111)-1 × 1 surface opens up new perspectives for studying metal growth and molecular organisation.