<i>In situ</i>x-ray-diffraction and -reflectivity studies of the Au(111)/electrolyte interface: Reconstruction and anion adsorption

Abstract

In situ x-ray-scattering studies of the Au(111) electrode surface have been carried out in NaF, NaCl, LiCl, CsCl, KCl, and NaBr solutions using grazing-incident-angle diffraction and reflectivity techniques. The top layer of gold atoms undergoes a reversible phase transition between the (1\ifmmode\times\else\texttimes\fi{}1) bulk termination and a (p\ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}3 ) uniaxial discommensuration (striped) phase on changing the electrode potential. Below the critical potential, in all solutions, p=23, which is identical to that obtained in vacuum. An ordered array of discommensuration kinks is not observed. Above the critical potential, 23p30. At sufficiently positive potentials, the surface forms an ideally terminated (111) surface. In the negative potential sweep, the reconstruction starts to reform at the critical potential. Analysis of the potential dependence of the scattered x-ray intensity with differing anions in NaF, NaCl, and NaBr solutions supports a unifying model that depends on the induced surface charge density. The transition to the (1\ifmmode\times\else\texttimes\fi{}1) phase is much faster than the formation of the reconstructed phase. Cycling the potential in the reconstructed region improves the reconstructed surface order. The adsorption of anions and ``surface water'' at the gold interface has been investigated using specular x-ray reflectivity.