IN-SITU X-RAY-SCATTERING STUDY OF THE AU(001) RECONSTRUCTION IN ALKALINE AND ACIDIC ELECTROLYTES

X-ray scattering from the solid/liquid interface of a Au(001) single crystal in 0.1 M potassium hydroxide and 0.1 M perchloric acid electrolytes has been measured. In both solutions the Au surface reconstruction consists of an incommensurate-hexagonal monolayer with a structure similar to the clean annealed vacuum surface at room temperature. In KOH electrolyte the reconstruction is aligned along the (110] direction, unlike the vacuum and perchloric acid interfaces, where the reconstruction is rotated +/-(05-0.8)-degrees from the [110] direction. In KOH solution the reconstruction forms rapidly at electrode potentials below -0.25 V (versus the saturated calomel electrode) and is lifted in a narrow potential region (40 mV) above -0.10 V, very close to the estimated potential of zero charge (PZC) for the reconstructed surface. In perchloric acid solution the reconstruction forms much more slowly at potentials just below the PZC of the unreconstructed surface, and is stable up to approximately 0.30 V, which is just positive of the PZC. In KOH solution the stability of the reconstruction is controlled primarily by the interaction of the surface with hydroxyl anions. The controlling mechanism in perchloric acid is unclear.