Quantitative Measurements of Adsorbate-Adsorbate Interactions at Solid-Liquid Interfaces

The interactions between adsorbates at a solid-liquid interface were studied by video-rate STM for the case of sulfur on Cu(100) electrode surfaces in HCl solution. Quantitative data were obtained by analyzing the Sad dimer dynamics within the surrounding c(2 x 2)-Cl adlattice as well as the adsorbate configurations. The interactions are repulsive for S-ad separated by one or two lattice spacings and attractive at a separation of root 2 with energies comparable to adsorbates at the solid-vacuum interface. The S-ad diffusion barriers are significantly reduced in the vicinity of a neighboring adsorbate.