Electrochemical copper deposition on Au(100): a combined in situ STM and in situ surface X-ray diffraction study

The electrochemical deposition of copper onto Au(100) has been investigated using in situ scanning tunneling microscopy (STM) and in situ surface X-ra y scattering (SXS). Copper deposition from sulfuric acid solutions starts a t potentials positive of the reversible Nernst potential, where a pseudomor phic (1x1) copper monolayer forms. Negative of the Nernst potential, STM me asurements have revealed that bulk copper nucleates at the surface defects, step edges or island rims of the gold substrate. A bilayer of copper is fo rmed on top of the underlying copper monolayer and further growth proceeds in a layer-by-layer fashion. Atomic resolution STM images have shown that t he copper film has a pseudomorphic structure for films less than or equal t o 10 layers. Surface X-ray scattering measurements have confirmed the pseud omorphic arrangement and have provided a precise measure of the copper laye r spacing (1.45+/-0.02 Angstrom), in good agreement with the value obtained from the copper-copper step height in the STM measurements. This layer spa cing is much smaller than the value expected for fee copper. The combined s tructural analysis leads to the conclusion of a thermodynamically stable bc c-like structure. Both the X-ray and STM results suggest alloying at the co pper-gold interface. (C) 2000 Published by Elsevier Science B.V. All rights reserved.