Abstract
Diffusion coefficients are determined by coverage profile analysis of photoemission electron microscope (PEEM) images. The diffusion coefficients for carbon monoxide and oxygen on a Pt(110) single crystal surface were derived in the temperature range of 318 to 438 K for carbon monoxide and 606 to 668 K for oxygen. Carbon monoxide does not show a pronounced dependence of the diffusion coefficient on coverage but a significant dependence on the surface reconstruction. Anisotropy of diffusion is in the range of a factor of 2. In contrast, oxygen shows a very high anisotropy with diffusion occurring practically only parallel to the crystallographic [11̄0] direction and a strong coverage dependence. For an oxygen coverage less than 0.2 monolayer, the diffusion coefficient is higher by one order of magnitude than at high coverage. Activation energies for carbon monoxide diffusion are between 9 and 13 kcal/mol, while oxygen has an activation energy of 30 kcal/mol for low coverage and 40 kcal/mol for high coverage.
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