Surface Dynamics of Lead Adsorbates at the Cu(100)-Electrolyte Interface

Direct quantitative studies of the dynamic behavior of individual cationic adsorbates at an electrochemical interface have been performed for Pb on Cu(100) electrode surfaces in Cl-containing electrolyte. Using in situ high-speed scanning tunneling microscopy, the motion of the Pb adsorbates on the c(2 x 2)-Cl covered Cu surface was monitored and analyzed by statistical models. Contrary to Pb on Cu(100) under ultrahigh vacuum conditions, the tracer diffusion of isolated adsorbates can be described by simple activated hopping between neighboring sites within the c(2 x 2) lattice, with an activation energy that increases linearly by 03 eV/V with potential. This surprising behavior, which is opposite in sign to that expected for a cation and similar to that for adsorbed sulfide at this interface, suggests a decisive influence of the surrounding Cl coadsorbates on the Pb diffusion. Furthermore, attractive interactions of similar to 20 meV were found between Pb adsorbates on nearest and next-nearest neighbor sites of the c(2 x 2) lattice. The effective diffusion barriers are increased, in the vicinity of neighboring Pb, resulting in a mutual stabilization of the adsorbates.