The chemistry of simple alcohols, amino acids and nucleic acid bases on silicon substrates

Abstract

The interaction between organic molecules and silicon substrates has been investigated using several surface sensitive techniques. The studies of the competitive reactions between simple alcohols and water show that only isopropanol is able to passivate the surface and inhibit further adsorption of H2O. The reaction occurs through cleavage of OH bonds and the formation of Si-O linkages. At room temperature, the cleaved H atoms are kept at the surface through the formation of Si-H bonds. Unsaturated heterocyclic molecules like maleic anhydride react with the silicon surface through a 2+2-cycloaddition reaction and provide a well defined ordered template to achieve further film growth. Bifunctional molecules like glycine and 4-aminobenzoic acid react with the surface through the carboxylate group, leaving the amino group available for further film growth. Similarly to the alcohols, the reaction occurs through cleavage of OH bonds and formation of Si-O-C linkages. The presence of a surface modifier like Na, modifies the interaction of the carboxylate groups with the surface from unidentate to bidentate. This leads to the formation of an ordered layer with well-defined bonding sites. The study of the adsorption of uracil on Si(100)-2x1 showed that this molecule is able to form well ordered structures on the surface. The vibrational spectroscopy study indicated that only the enol tautomer of uracil is able to react with the surface.