Underpotential deposition of Cu on Au(111) from neutral chloride containing electrolyte

The structure of a chloride terminated copper monolayer electrodeposited onto Au(111) from a CuSO4/KCl electrolyte was investigated ex situ by three complementary experimental techniques (scanning tunneling microscopy (STM), photoelectron spectroscopy (PES), X-ray standing wave (XSW) excitation) and density functional theory (DFT) calculations. STM at atomic resolution reveals a stable, highly ordered layer which exhibits a Moire structure and is described by a (5 x 5) unit cell. The XSW/PES data yield a well-defined position of the Cu layer and the value of 2.16 angstrom above the topmost Au layer suggests that the atoms are adsorbed in threefold hollow sites. The chloride exhibits some distribution around a distance of 3.77 angstrom in agreement with the observed Moire pattern due to a higher order commensurate lattice. This structure, a high order commensurate Cl overlayer on top of a commensurate (1 x 1) Cu layer with Cu at threefold hollow sites, is corroborated by the DFT calculations.