MONOCRYSTALLINE GOLD-AQUEOUS INTERFACES AS A MODEL EXPERIMENTAL LINK BETWEEN MACROSCOPIC ELECTROCHEMISTRY AND IN-SITU ELECTROCHEMICAL SURFACE SCIENCE

Comparisons are undertaken between some voltammetric and ac impedance responses of ordered monocrystalline gold electrodes in the presence of adsorbed anions, and the electrode potential-dependent atomic structures and surface phase transitions sensed by in situ scanning tunneling microscopy (STM). Emphasis is placed on facilitating such links between macroscopic and microscopic double-layer phenomena by acquiring individual and/or temporal sequences of so-called ''potentiodynamic'' STM images (PDSTM) during potential sweeps or steps. Two types of double-layer phenomena are considered. The first involves the formation and removal of reconstruction on low-index gold surfaces, chiefly in iodide electrolytes. The marked influence of anion adsorption on the real-space dynamics as well as the thermodynamics of potential-induced reconstruction are discussed in terms of surface bonding and electronic factors. The detailed information on local variations in reconstructed atomic patterns discernable by STM is also briefly described, along with the virtues of PDSTM for unraveling the atomic-level transport mechanisms associated with the potential-induced formation and removal of reconstruction. The other type of phenomenon considered is the formation of ordered anionic adlayers at higher potentials, and the nature of phase transitions that are thereby involved, specifically for iodide, bromide, and sulfate adsorption. The overall synergetic value of coupled electrochemical and probe microscopic measurements for enhancing our atomic-level understanding of double-layer phenomena is pointed out, along with the unique value of ordered gold surfaces for this endeavor.