A comparative chemisorption study of acrylic, vinyl acetic, fumaric, maleic and tartaric acid on Si(100)2x1 by Van der Waals corrected DFT

The comparative chemisorption of multifunctional carboxylic acids on Si(100)2x1 has been investigated by van der Waals corrected DFT. Several configurations with one or more functional groups involved in the binding process were considered for acrylic, vinyl acetic, maleic, fumaric and tartaric acid both in meso and in chiral form. In general, the dissociative adsorption is more favourable than the molecular one. The comparison between uni- and bidentate configurations indicates that the latter is the more favourable for all except for vinyl acetic acid, for which the unidentate on top adsorption is preferred. C=C [2+2] cycloadditions are less stable when a second carboxylic group is present and in general are less favourable than Si-O linkages. Adsorption through hydroxyl groups is on average slightly less stable than through carboxylic groups. The most stable configuration is obtained with the adsorption through two carboxylic groups bridging two dimers along a line, by meso tartaric and maleic acid. The simultaneous binding through three functional groups decrease the adsorption energy, whereas the linkage through four functional groups makes the adsorbate unstable. Molecular adsorption such as C=O [2+2] cycloadditions and hydroxyl dative bonds have small adsorption energies.