In SituScanning-Tunneling-Microscope Observation of Roughening, Annealing, and Dissolution of Gold (111) in an Electrochemical Cell

Abstract

We report in situ scanning tunneling microscopy at atomic-layer resolution of the topographic changes accompanying electrochemical reactions. In dilute perchloric acid, Au(l 11) terraces roughen during the electrochemical formation and reduction of more than a monolayer of gold oxide, but anneal in minutes at moderate potential. Trace chloride enhances step motion, prevents the observation of roughening, and promotes the dissolution of gold during oxidation and rereduction. These observations illustrate the role adsorbates have in determining the surface mobility of substrate atoms.PACS numbers: 61.16.Di, 66.30.Lw, 81.60.Bn, 82.45.+ZThe microscopic details underlying important interfacial electrochemical processes such as electron transfer, plating, passivation, and corrosion are traditionally inferred from in situ measurements of macroscopic quantities: charge, potential, concentrations, surface tension, etc. Recently, various groups have demonstrated the feasibility of using ex situ electron spectroscopies, microscopies, and diffraction techniques 1 " 5 and in situ techniques such as glancing angle x-ray absorption and diffraction 6 " 8 and infrared reflection-absorption spectroscopy 9 to obtain structural information about the electrochemical interface at the atomic level. Scanning tunneling microscopy (STM) could offer a microscopic, realspace view of the electrochemical interface to complement these other tools. 10 One immediate target for investigation with the STM is the growth, dissolution, or rearrangement of crystalline surfaces due to electrochemical reactions. A prototypical example of electrochemically induced change at a crystalline surface is the electrochemical oxidation and rereduction of gold. 11 " 16 Recently, Wiechers et al. have demonstrated resolution of monatomic gold layers at the interface of Au(lll) and aqueous solutions while controlling the electrochemical potential of the gold surface. 17 Here, we report the first in situ STM observations with atomic-layer resolution of the consequences of an electrochemical surface reaction: the roughening, annealing, and dissolution accompanying the oxidation and rereduction of the Au(lll) surface.Gold (111) films on mica were prepared by evaporation of gold onto mica at 225 °C as reported earlier. 18 The samples were clamped to the base plate of a Nanoscope I STM (Digital Electronics) with a Teflon ring, which also formed the electrochemical cell. The counter electrode was a Pt wire, and the reference electrode was an Ag wire in an AgClC>4 solution separated from the cell by a length of Teflon tubing. All electrochemical potentials are reported with respect to the normal hydrogen electrode (NHE). HCIO4 was Ultra grade (Hopkin and Williams Co.), HC1 was reagent grade, water was from a Milli-Q purification train (Millipore Corp.), and oxygen was not removed from the cell. The sample potential was controlled relative to the reference electrode by driving the potential of the counter electrode, and the tip-tosample bias was fixed at -10 mV.The tunnelin...

Dynamics of Metastable Nanoscale Island Growth and Dissolution at Electrochemical Interfaces by Time-Resolved Scanning Tunneling Microscopy

“…It is distinct from "electrochemical annealing" that, on the contrary, results in the disappearance of islands due to anion-enhanced mobility. 25 The concept of "voltammetric annealing" may offer an explanation for the observed decrease transition rate from Au(100)-(1 × 1) to Au(100)-(hex) with the length of time at which the Au(100)-(1 × 1) surface was held at positive potentials. 26 Holding the surface at a positive potential results in "voltammetric annealing" of the island structures that characterize the Au(100)-(1 × 1) phase and that are one of the major sources of atoms needed to make the higher density Au(100)-(hex) reconstructed phase.…”

Potential-Induced Structural Change in a Self-Assembled Monolayer of 4-Methylbenzenethiol on Au(111)

“…21 The chemisorption of adsorbates on metal surfaces can lead to a weakening of bonding between surface metal atoms or the bonding between surface and bulk metal atoms, resulting in higher metal adatom mobility. 29,30 The surface morphology of thiol modified gold can be influenced by the nature and dynamic behavior of thiolate-Au complexes. For example, the lower binding energy of sulfur to Au for arenethiols, compared with alkanethiols, can lead to less mobility of arenethiolate-Au complexes in the SAMs.…”

Surface-plasmon voltammetry using a gold grating

“…Hamelin et al 1 Additionally, several techniques have been used in combination with cyclicvoltammetry to gain further information regarding these processes including scanningtunneling microscopy (STM), [14][15][16][17][18] atomic-force microscopy (AFM), 19 the quartz crystal microblance (QCM), [20][21][22] reflectance studies, 23 ellipsometry [24][25][26][27] and surface-plasmon resonance (SPR) studies. [28][29][30][31][32][33][34][35][36][37][38] It is SPR-electrochemistry, which has now been recognised as a new and powerful tool for exploring not just electrochemistry but also bioelectrochemistry [37][38][39][40] that is of interest in this work.…”