Scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED) have been used to examine the structure of ordered adlayers of Ca on TiO 2 (110)-1×1 formed by metal vapor deposition. A comparison is made with structures formed by segregation of Ca from the bulk, with similar structures being found for the two preparation methods below a monolayer coverage. At low coverages, rows of width ∼0.6-0.9 nm develop in the [11 h0] and [001] azimuths. At coverages equivalent to a single calcium layer, a c(6×2) overlayer is formed. At coverages above a single layer, a disordered structure develops and a LEED pattern with ( -0.1 2 1 0 ) symmetry is observed.

Scanning tunneling microscopy and core level photoelectron spectroscopy measurements have been used to investigate the morphology of ZnO(0001 macro)-O, and its reactivity with carbon monoxide and carbon dioxide, as a function of surface preparation. Real space images of the surface indicate that increasing the substrate anneal temperature during preparation significantly reduces the surface step density. Surface defect concentration is also monitored by employing formic acid as a chemical probe, which is shown to adsorb dissociatively (HCOOH --> [HCOO](-) + H(+)) only on zinc cations at step edges. Carbon 1s X-ray photoelectron spectra show that carbon monoxide and carbon dioxide both react to form surface carbonate species. Spectra, recorded both as a function of surface preparation and following coadsorption, demonstrate that the carbonate formed from either reactant molecule is located at oxygen vacancies at step edges, evidencing the significant role that defects can play in the surface chemistry of ZnO(0001 macro)-O.

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