Growth of epitaxial layers of Co and CoO on Au(111)

The growth of epitaxial Co and CoO layers on Au(111) is studied at temperatures between 300 and 600 K by means of scanning tunneling microscopy. The layers were prepared by Co deposition in ultrahigh vacuum and in an O atmosphere, respectively. The Co and CoO layers display characteristic misfit-induced moire-like superstructures which yield information on the layer structure. Clean Co grows with its own lattice simultaneously releasing the compression of the underlying Au(111) top layer. Growth of CoO layers starts by the formation of a pseudomorphic Co base layer of monatomic height. Subsequently, a CoO(111) layer is developed. At 300 K growth temperature a large density of islands and defects is observed. Growth of CoO at higher temperatures ameliorates the layer quality. The CoO surface shows a (1 x 1) structure, indicating its stabilization by OH- termination. The compression of the underlying Au(111) top layer is preserved during CoO layer formation. Hence the effective misfit between the CoO layer and the Au(111) substrate is larger than expected from the bulk data, which may explain the relatively poor quality of the CoO film.