Functional group selectivity in adsorption of 4-aminobenzoic acid on cleanand Na modified Si(100)-2 x 1 surfaces

The adsorption of 4-aminobenzoic acid on the clean and Na modified Si(1 0 0 )-2 x 1 surfaces has been studied by high-resolution electron energy loss s pectroscopy (HREELS) and near edge X-ray absorption fine structure. HREELS indicates that adsorption of 4-aminobenzoic acid on Na/Si(1 0 0)-2 x 1 occu rs through cleavage of the OH bond in the carboxylic group. The 4-aminobenz oate species are bonded through the formation of a delocalized bond between the deprotonated carboxylate group and the adsorbed Na atom, leading to sp ecies in a bidentate coordination. At room temperature, 4-aminobenzoate sat uration is reached at a coverage of one 4-aminobenzoate species per Na or S i dimer. At this coverage, the molecules are tilted in the polar direction by 61 +/- 5 degrees to the surface plane. In contrast, we observe monodenta te 4-aminobenzoate species following the exposure of Si(1 0 0)2 x 1 to 4-am inobenzoic acid. (C) 2001 Elsevier Science B.V. All rights reserved.