ELECTRON-DIFFRACTION AND PHOTOEMISSION-STUDIES OF CLEAN AND WATER-COVERED SI(5,5,12) AND SI(112) SURFACES

The structure of silicon surfaces in the orientation range (113)-(5,5, 12)-(337)-(112) has been investigated using high resolution LEED and p hotoemission both on a spherical and on flat samples. We find that Si( 5,5,12) [5.3 degrees from (113) and 0.7 degrees from (937)] is the onl y stable orientation between (113) and (111) and confirm the result of Baski et al. [Science 269, 1556 (1995)] that it has a 2 x 1 superstru cture with a very large unit cell of 7.68 x 53.5 Angstrom(2). Adsorpti on measurements of water on Si(5,5,12) yield a mobile precursor kineti cs with two kinds of regions saturating at 0.25 and 0.15 ML which are related to adsorption on different sites. Using these results, a modif ied structure model is proposed. Surfaces between (113) and (5,5,12) s eparate into facets of these two orientations; between (5,5,12) and (1 12), they separate into (5,5,12) and (111) facets. (337) facets in thi s range may be considered as defective (5,5,12) facets.