THE EFFECT OF SURFACE RECONSTRUCTION ON THE CAPACITANCE OF AU(100) SURFACES

The effect of reconstruction of the Au(100) surface on the double-layer capacity was measured using standard ac methods combined with UHV surface preparation and ex situ structure analysis. The (5 x 20) reconstruction present on the UHV-prepared surface was found to be stable in dilute HClO4 over a wide range of electrode potential. In dilute H2SO4, the (5 x 20) reconstruction was lifted at potentials near the pzc by specific adsorption of HSO4- even when the anion was present at very low concentrations, eg 10(-5) M. In 0.01 M HClO4, the reconstruction was lifted only at potentials 0.2 V positive of the pzc, and was restored when the potential was made ca 0.1 V negative of the pzc for the (1 x 1) surface, ie the (5 x 20) reversible (1 x 1) transformation was quasi-reversible in dilute HClO4. Atomic scale roughness, eg steps, appeared to lower the stability of the (5 x 20) structure. The capacity curve for the (5 x 20) reconstructed surface was dramatically different from that of the (1 x 1) surface, with a negative shift in the pzc of ca 0.2 V following the transformation (5 x 20) --> (1 x 1), and a decrease in the capacitance of 20-25%, approximately equal to the change in atomic density of the surface. The vacuum work functions (PHI) of the emersed (5 x 20) and (1 x 1) surfaces were measured using photoemission spectroscopy, and found to be 5.30 +/- 0.05, and 5.05 +/- 0.05 eV, respectively, which gives a DELTA-PHI consistent with the relative values of the pzcs. Our results were consistent in every respect with the previous findings of Kolb and co-workers on the effect of reconstruction on the double-layer capacity of Au(100) surfaces.