MODERN CONCEPTS IN SURFACE SCIENCE AND HETEROGENEOUS CATALYSIS

Surface science studies using small-area single crystals and a combination of electron, ion, photon, and molecular beam scattering techniques have been exploring surface properties on the molecular level. Many new phenomena were discovered that could be used to recast the models or concepts we employ to describe surfaces. The surface structure exhibits relaxation, reconstruction, and the presence of steps and kinks on the atomic scale. Chemisorption causes adsorbate-induced restructuring of surfaces, and the substrate has a significant influence on the growth mode of the deposited material (epitaxy). The surface chemical bond is clusterlike, thermal activation is needed for chemical bond breaking, and rough, more open surfaces are markedly more reactive than flat surfaces with close atomic packing. The adsorbate-adsorbate interaction that may be repulsive or attractive induces weakening of the adsorbate-substrate bond and ordering in the surface monolayer. Surface dynamics studies reveal low potential energy barriers for the diffusion of molecules along the surface (two-dimensional phase approximation) and rapid energy transfer between incident gas and surface atoms. Catalyzed surface reactions may be surface structure sensitive or structure insensitive and coadsorbed "promoter" atoms act by altering the structure and/or the bonding of adsorbed molecules. © 1990 American Chemical Society.