Microfacetting of Au(110) electrodes: An optical second-harmonic generation study

Abstract

The formation and lifting of microfacetting at an Au(110) electrode surface was studied by using in-situ optical Second-Harmonic Generation (SHG). In contrast to the unreconstructed (1×1) Au(110) surface which has aC _2v symmetry, the reconstructed surface exhibits aC _s symmetry due to essentially (111)-oriented microfacets. Hence, it shows SHG-anisotropy patterns fundamentally different to those of a non-reconstructed surface. Apparently, the nonlinear susceptibility tensor contains an additional threefold symmetry element. Its amplitude was determined using Fourier analysis of SHG-anisotropy curves and, thus, served as a measure of microfacetting of the Au(110) surface. We observed that adsorption of an organic molecule, such as pyridine, has little effect on the electrode-surface crystallography. In contrast, adsorption of bromide ions results in the lifting of microfacetting as indicated by the disappearence of the threefold symmetry term. Potential-step experiments gave time constants for the lifting of microfacetting in the range of < τ_1/2<150 ms.