MICROFACETTING OF AU(110) ELECTRODES - AN OPTICAL 2ND-HARMONIC GENERATION STUDY

The formation and lifting of microfacetting at an Au(110) electrode su rface was studied by using in-situ optical Second-Harmonic Generation (SHG). In contrast to the unreconstructed (1 x 1) Au(110) surface whic h has a C-2v symmetry, the reconstructed surface exhibits a C-s symmet ry due to essentially (111)-oriented microfacets. Hence, it shows SHG- anisotropy patterns fundamentally different to those of a non-reconstr ucted surface. Apparently, the nonlinear susceptibility tenser contain s an additional threefold symmetry element. Its amplitude was determin ed using Fourier analysis of SHG-anisotropy curves and, thus, served a s a measure of microfacetting of the Au(110) surface. We observed that adsorption of an organic molecule, such as pyridine, has little effec t 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 expe riments gave time constants for the lifting of microfacetting in the r ange of 50 < tau(1/2) < 150 ms.