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Cs adsorbs on Ag(lll) to form layers of relatively low atomic density; unlike the other alkalis, it does not significantly penetrate the Ag lattice. Multilayer growth proceeds by the Frank-van der Merwe mechanism, but oxygen chemisorption followed by heating drastically perturbs the structure of the alkali film; bare Ag sites are created, and there is evidence for the formation of higher oxides of Cs. The desorption properties of the system suggest that oxygen can induce the formation of a "surface alloy". The behavior of such cesiated surfaces in the selective and total oxidation of ethylene was investigated by two different approaches. The results are in good agreement in that they indicate that, in a certain coverage regime, Cs enhances both the total activity and the selectivity for ethylene oxide formation. This can be rationalized in terms of the effect of the alkali in respectively promoting and moderating certain aspects of the primary and secondary chemistry. Detailed molecular mechanisms are suggested.

Carbonaceous deposits produced on Ru-capped multilayer mirrors under extreme ultraviolet (EUV) irradiation in the presence of adventitious gaseous hydrocarbons are a major obstacle to process implementation of EUV lithography, the key to fabrication of next generation semiconductor chips. The technical problem has been simulated by examining graphitic film growth on Ru(0001) under low-energy electron irradiation in the presence of 1-butene, C5-C8 linear alkanes, and toluene. We show that this provides a practical and reliable means of simulating the photon-induced chemistry and of distinguishing between benign and harmful species. Linear alkanes up to n-heptane are relatively benign, whereas n-octane and toluene are much more harmful, giving rise to rapid growth of graphitic films of a thickness sufficient to seriously impair mirror reflectivity. 1-Butene exhibits behavior in between these extremes. These properties may be understood in terms of the surface residence lifetimes of the various adsorbates on graphitic surfaces.