In situ scanning tunneling microscopy topography changes of gold (111) in aqueous sulfuric acid produced by electrochemical surface oxidation and reduction and relaxation phenomena

M.A. PASQUALE; F.J. RODRÍGUEZ NIETO; A.J. ARVIA

SURFACE REVIEW AND LETTERS

World Scientific Publishing Company

Lugar: Singapore; Año: 2008 vol. 15 p. 847 - 865

0218-625X

The electrochemical formation and reduction of O-layers on gold (111) films in 1 M sulphuric acid are investigated utilising in situ scanning tunnelling microscopy and different potentiodynamic routines. The interpretation of surface dynamics is made considering the anodic and cathodic reaction pathways recently proposed complemented with concurrent relaxation phenomena occurring after gold(111) lattice mild disruption (one gold deep) and moderate disruption (several gold atoms deep). The dynamics of both oxidized and reduced gold topography depends on the potentiodynamic routine utilised to form OH/O surface species. The surface topography resulting from a mild oxidative disruption is dominated by quasi-2D holes and hillocks of the order of 5 nm, involving about 500-600 gold atoms each, and their coalescence. A cooperative turnover process at the O-layer, in which the anion ad-layer plays a key role, determines the oxidised surface topography. The electrochemical reduction of O-layers results in gold clusters, their features depending on the applied potential routine. A moderate oxidative disruption produces surface topography of hillocks and holes several gold atoms high and deep, respectively. The subsequent reduction leads to a spinodal gold pattern. Concurrent coalescence appears to be the result of an Ostwald ripening that involves the surface diffusion of both gold atoms and clusters. These processes lead to an increase in surface roughness and an incipient gold faceting. The dynamics of different gold sample topographies can be qualitatively explained employing the arguments from colloidal science theory. For 1.1 V ³  E  @  Epzc weak electrostatic repulsions favour gold atom/cluster coalescence, whereas, for E < Epzc the electrostatic repulsions among gold surfaces stabilise small clusters over the substrate producing string-like patterns.