UV-light-driven immobilization of surface-functionalized oxide nanocrystals onto silicon

TiO2 nanorods (NRs) and gamma-Fe2O3 nanocrystals (NCs) passivated with unsaturated long-chain carboxylic acids, namely 10-undecylenic acid (10UDA) and oleic acid (OLEA), are covalently anchored to Si(100) at room temperature by UV-light-driven reaction of hydrogenated silicon with the carbon-carbon double bond (-C=C-) moieties of the capping surfactants. The high reactivity of vinyl groups towards Si provides a general tool for attaching particles of both materials via Si-C bonds. Interestingly, TiO2 NRs were efficiently attached to silicon even when capped by OLEA. This latter finding has been explained by a photocatalytic mechanism involving the primary role of hydroxyl radicals that can be generated upon bandgap, TiO2 photoexcitation with UV light. The increased oxide coverage achievable on Si opens access to further surface manipulation, as demonstrated by the possibility of depositing an additional film of An nanoparticles onto TiO2 via TiO2-catalyzed visible-light-driven reduction of aqueous AuCl4- ions. Extensive morphological and chemical characterization of the obtained NC-functionalized Si substrates is provided to support the effectiveness of proposed photochemical approaches.