Surface diffusion of H on Pt(111) surface has been studied systematically by a linear optical diffraction technique. The coverage-dependent diffusion coefficients on flat Pt(111) surface were measured over a wide H coverage range from 0.1 to 0.8ML. These results were analyzed within the framework of the lattice gas model using the quasi-chemical approximation, indicating that H-H repulsive interaction can significantly affect the energy of saddle points as well as that at the adsorption sites. Step effects on surface diffusion of hydrogen on stepped Pt(111) have been studied over a temperature range from 90K to 150K. Diffusion anisotropy on stepped Pt(111) surfaces has been observed: the unexpected enhanced diffusion perpendicular to steps cannot be explained within the lattice gas mode...[ Read more ]

Surface diffusion of H on Pt(111) surface has been studied systematically by a linear optical diffraction technique. The coverage-dependent diffusion coefficients on flat Pt(111) surface were measured over a wide H coverage range from 0.1 to 0.8ML. These results were analyzed within the framework of the lattice gas model using the quasi-chemical approximation, indicating that H-H repulsive interaction can significantly affect the energy of saddle points as well as that at the adsorption sites. Step effects on surface diffusion of hydrogen on stepped Pt(111) have been studied over a temperature range from 90K to 150K. Diffusion anisotropy on stepped Pt(111) surfaces has been observed: the unexpected enhanced diffusion perpendicular to steps cannot be explained within the lattice gas model on stepped substrates, manifesting a non-local and directional step effect. A nearly temperature independent diffusion coefficient of H on flat Pt(111) surfaces at low temperature regime was observed, marking diffusion of H atoms by quantum tunnelling. The almost constant quantum diffusion coefficient below the temperature of 95K is ~2x10^-11 cm²/s, consistent with the theoretical prediction of 6x10^-10 cm²/s. The strong isotope effects on quantum diffusion at low temperature were explained within the theoretical prediction and the simple WKB approximation.