Surface structures of Au and Rh deposited on O-pre-adsorbed Cu(110)

We have studied the structures of Au and Rh deposited on (2 × 1)O-Cu(110) and c(6 × 2)O-Cu(110) surfaces with varied surface probe techniques and modeling based on density functional theory. On either (2 × 1)O-Cu(110) or c(6 × 2)O-Cu(110) surface, the deposited Au nucleated into fractal two-dimensional islands and grew further into thin films via a layer-by-layer fashion. Both the (2 × 1) and c(6 × 2) ordered structures persisted notably despite the grown Au thin films, not only as the Au atoms were stacked according to the O-Cu(110) lattice but also as both O and Cu_a (referring to the added Cu alternating with O at the O-Cu(110) surfaces) remained at the surface and formed Cu_a-O-Au structures to promote the surface stability. In contrast, the Rh on the O-Cu(110) surfaces formed round, structurally ordered three-dimensional nanoclusters, at the expense of the (2 × 1) and c(6 × 2) structures. The Rh clusters grew preferentially in an fcc phase and (110) orientation, as the (110) facet matched better, structurally, with either (2 × 1)O-Cu(110) or Cu(110) surfaces. The disparate structuring of Au and Rh on O-Cu(110) surfaces was controlled by both lattice and energetic effects; in particular, the bond strengths in the order of Rh-Rh > Rh-O > Au-O > Au-Au at the surfaces predominated. The formation of the surface Cu_a-O-Au structure, instead of the pure Au multilayers, arose from the stronger Au-O and enhanced Cu_a-O bonds in the Cu_a-O-Au structure.