Structure and reactivity of Cu-doped Au(111) surfaces

Abstract

The structure and surface chemistry of ultrathin metallic films of one metal on another are strongly influenced by factors such as lattice mismatch and the formation of near-surface alloys. New morphologies may result in modified chemical properties which in turn open up different routes for molecular adsorption, desorption and surface functionalization, with important consequences in several fields of application. The Cu/Au(111) system has received the attention of many studies, only a few however have been performed in ultra-high vacuum (UHV), using surface sensitive techniques. In this contribution, the room temperature deposition of copper onto the (22×√3)-Au(111) surface, from submonolayer to thick film, is investigated using scanning tunnelling microscopy (STM). The onset of copper adsorption is seen to occur preferentially at alternate herringbone elbows, with a preference for hcp sites. With increasing coverage, copper-rich islands exhibit a reconstructed surface reminiscent of the clean Au(111) herringbone reconstruction. Disordered, pseudo-ordered and ordered surface layers are observed upon annealing. Models for the initial adsorption/incorporation mechanism, formation of adlayers and evolution with increasing coverage and annealing are qualitatively discussed. Further, the reactivity of copper-doped Au(111) systems is considered towards the adsorption of organic molecules of interest in nanotechnology and their catalytic applications.