In situ STM imaging of spontaneously deposited ruthenium on Au(111)

Abstract

Spontaneous deposition of ruthenium on Au(1 1 1) surfaces from 1.0 mM RuCl3 + 0.5 M H2SO4 (or 0.1 M HClO4) solutions was investigated by in situ STM and cyclic voltammetry, focusing on the morphology of the resulting submonolayer Ru modified surfaces. STM results show a pronounced step decoration, indicating that the steps are active sites for the nucleation of Ru monolayer islands, while a random distribution of Ru nuclei is observed on terraces. During deposition, the open circuit potential rapidly increases from 0.38 to above 0.72 V vs. (Ag/AgCl). Experiments with different deposition times show that deposition from sulfuric acid solution saturates after 3 min deposition, the island size reaches its saturation value of 2.8 nm after 1 min. Significantly higher deposition activities and saturation coverages are found for deposition from perchlorate solution and for deposition on highly stepped surfaces/surface areas, indicative of a pronounced anion effect and reflecting the higher activity of steps for Ru deposition, respectively. In both cases, in particular for deposition in perchlorate solution, islands grow to multilayer heights and assume hexagonal shapes. Finally it is shown that multiple deposition can be utilized to reach higher coverages, attaining step saturation also in sulfuric acid solution. The Ru modified Au(1 1 1) electrode was found to be inert for hydrogen adsorption, and the electrochemical results indicate that the ruthenium islands inhibit long-range ordering of the sulfate adlayer on the substrate.