Functional group selectivity in adsorption of 4-aminobenzoic acid on clean and Na modified Si(1 0 0)-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 spectroscopy (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 occurs through cleavage of the OH bond in the carboxylic group. The 4-aminobenzoate species are bonded through the formation of a delocalized bond between the deprotonated carboxylate group and the adsorbed Na atom, leading to species in a bidentate coordination. At room temperature, 4-aminobenzoate saturation is reached at a coverage of one 4-aminobenzoate species per Na or Si dimer. At this coverage, the molecules are tilted in the polar direction by 61 +/- 5 degrees to the surface plane. In contrast, we observe monodentate 4-aminobenzoate species following the exposure of Si(1 0 0)2 x 1 to 4-aminobenzoic acid. (C) 2001 Elsevier Science B.V. All rights reserved.