Water react dissociatively on the Si(001)-2x1 surface, preserving the dimerization. Monohydrides and silanols are present on the surface, together with a low (10-2 ML) surface concentration of isolated dangling bonds, whose electronic structure is identical to those found on the H-terminated surface.1 Therefore by analogy the case of the H terminated surface, radical chain reactions (via H jumps) between isolated dangling bonds and pi bonded molecules are expected.2 However (i) radical reactions via OH jumps, together with direct reactions with (ii) silanols and (iii) monohydrides must be envisaged. We present here a study of the chemical reactivity of the water-covered Si(001) surface exposed to alkenes, carboxylic acids and aldehydes, using synchrotron x-ray photoemission and scanning tunneling microscopy in combination. While, alkenes likely react via a radical mechanism (H jump), carboxylic acid grafting consumes surface OH and an ester is formed. The reaction of aldehydes is discussed in terms of the formation of (hemi-)acetals or of ethers. Compared with classic organic reactions (esterification,acetal formation) which are slow/reversible, the grafting of aldehydes/carboxylic acids is efficient on the water-covered Si(001)-2x1. This class of high selectivity reactions is a interesting option for the grafting of organic molecules on Si(001), especially for polyfunctional molecules, which generally adopt multiple bonding configurations on the clean Si(001) surface.References:(1) J.-J. Gallet, F. Bournel, F. Rochet, U. Ko�hler, S. Kubsky, M.G. Silly, F. Sirotti, and D. Pierucci, J. Phys. Chem. C, 2011, 115 (15), pp 7686�7693(2) Lopinski, G. P.; Wayner, D. D. M.; Wolkow, R. A. Nature 2000, 406, 48� 51

Surface chemistry of water-covered Si(001)-2[times]1: Silicon radical vs. silanol reactivity

245th National Meeting (2013)

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