Comparative STM studies on island equilibrium shapes, shape fluctuations and island coalescence on Au(0 0 1) electrodes in chloric and sulfuric acid solutions

We present scanning tunneling microscopy data on the dynamics of monatomic high islands on gold electrodes in different electrolytes. From a statistical analysis of the island fluctuations around the equilibrium shape and from the investigation of the local perimeter curvature of the latter we determine the step line tension and the kink energy of gold islands on an Au(0 0 1) surface as a function of the electrode potential. We find that in chloric acid the step line tension is smaller than for Au(0 0 1) in sulfuric acid, however, the kink energy is much higher which leaves us with the puzzling result that island fluctuations are large, however, island edges are comparatively straight. Both energies show merely a weak dependence on the electrode potential in contrast to our previous findings in sulfuric acid. Furthermore, by analyzing the relaxation time of island coalescence events we determine the dominant mass transport on the Au(0 0 1) electrode to be terrace diffusion where the time limiting step of the migration process is the creation of transport species at the island edge rather than the hopping of species on the surface. This is in apparent contradiction to previous results from island decay studies where a diffusion limited terrace diffusion was found. All results can be explained if one assumes that the relevant mass transport species on Au(0 0 1) in chloride containing electrolytes are larger (linear) structure units rather than single adatoms. Possible candidates for these units are Au-Cl complexes.