ATOMIC-FORCE MICROSCOPY IMAGING OF TIO2 SURFACES ACTIVE FOR C-C BOND FORMATION REACTIONS IN ULTRAHIGH-VACUUM
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TiO 2 (001) single crystal surfaces active for a variety of different chemistries were examined using atomic force microscopy (AFM). C-C bond forming reactions previously identified on these surfaces include carboxylic acid ketonization, aldol condensation, reductive carbonyl coupling, and alkyne cyclotrimerization. The surfaces were prepared in ultrahigh vacuum (UHV) and examined by AFM in air. Surfaces examined included the {011}-faceted surface, {114}-faceted surface, and argon-ion-bombarded surfaces, as well as the mechanically polished singlecrystal surface prior to treatment in UHV. The one unifying feature of all the images was their extreme flatness. Root-mean-square roughnesses were routinely less than 10 in 500 500 nm scans. These same scans showed the surfaces to have surface areas exceeding that of an ideal flat surface by no more than 1.2%. Images of the polished surface revealed a variety of surface features, including polishing scratches and particle-like features. The argon-ion-bombarded surface and the faceted surfaces were composed of large flat plateaus ranging in size from 21 to 75 nm. The size of the plateaus was essentially the same for the ion bombarded surface and the {011}-faceted surface. The {114}-faceted surfaced exhibited slightly smaller plateau regions than the other surfaces. The images indicate that argon-ion bombardment, while disordering the surface and causing significant composition changes, does not lead to observable morphological changes on this scale. The relative uniformity of the surfaces examined is consistent with the selectivity of carbon-carbon bond-forming reactions that have been shown to take place on these surfaces. The images also reveal how the surface topography on the scale of the plateau structures observed is only slightly changed during the transformation of the surface unit cell structure from the {011}- to the {114}-faceted surface. 1994, American Chemical Society. All rights reserved.
