Electrodeposition of Co and Ni/Au(111) ultrathin layers.: Part I:: nucleation and growth mechanisms from in situ STM

The growth mechanisms of Co and Ni/Au(1 1 1) ultrathin layers electrodeposited from dilute sulfate solutions are investigated using in situ STM and electrochemical measurements. Bulk cobalt deposition occurs for potentials 0.25 V negative of the Nernst potential E-Co(0) of the reaction Co2+ + 2e(-) --> Co, while bulk nickel may be deposited very close to E-Ni(0). Closer to the Nernst potential slow nucleation is driven by place exchange for both metals. Subsequent growth leads to ML-thick cobalt nanostructures confined onto hcp regions of reconstructed Au(1 1 1) surface, which only cover a small faction of the gold surface, and to a progressive needle growth of nickel until full surface coverage. At greater overpotentials both Co and Ni films grow epitaxially on Au(1 1 1) in a layer-by-layer fashion under appropriate conditions of polarization. The main difference concerns the first Co layer which is strained (4.4%) and biatomic whereas nickel growth starts with a relaxed monolayer. The mechanisms of deposition are discussed from a detailed analysis of STM images, atomic models of the interface are presented and a strain relief mechanism is discussed in light of dissolution experiments. (C) 2004 Elsevier B.V. All rights reserved.