The Evaluation of Surface Diffusion Coefficients of Gold and Platinum Atoms at Electrochemical Interfaces from Combined STM-SEM Imaging and Electrochemical Techniques

A simple method is presented for measuring the surface diffusion coefficients of Au and Pt atoms at electrodispersed electrodes of the same metals in contact with 0.5M H2SO4. The technique isbased upon the time dependence of the surface roughness factor of electrodispersed metal overlayers. The method requires amodel for the surface roughness of the metal structure. The model is deduced from microscopic measurements by a STM integrated into a conventional SEM micro-scope. This allows the relationship between the roughness factor and the area of the surface structure to be obtained. For Au and Pt in contact with an electrolyte solution, the values of our diffusion coefficients are higher than those reported in vacuum at the same temperature. The evaluation of surface diffusion coefficients from par-ticle coalescence processes is widely used in solid-state physics. Usually the methods involve the estimation of the time dependence of crystal size by microscopy (1), optical diffraction (2), or ion scattering (3), and the use of the theory developed first by Mullins (4) and extended in re-cent years by several authors (5, 6)