Chemical reactivity and surface chemistry of porous silicon

Abstract

The chemical reactions of porous Si, involving formation of Si-O, Si-C, Si-N, or Si-metal surface bonds, is reviewed. The reactivity of as-formed porous Si is dominated by the chemistries of silicon-hydrogen (Si-H) and silicon-silicon (Si-Si) bonds, which are strong reducing agents. Depending on the oxidant, various surface species can be generated in oxidation-reduction reactions of porous Si: in particular metal nanoparticles, silicon oxides, or silicon-carbon species. The oxidation chemistry of porous Si, involving air, water, chemical oxidants, or electrochemical oxidation is discussed. The aqueous stability of these various silicon oxides is quite dependent on the means by which a particular oxide is formed. Si-C bond forming reactions including hydrosilylation, hydrocarbonization, carbonization, and reductive electrochemical grafting, and the chemical method used to confirm Si-C bond formation are presented. Because much interest in the chemistry of porous Si is focused on the generation of functional nanostructures to graft molecules such as drugs, proteins, targeting agents, or biological receptor molecules to porous Si surfaces, the review emphasizes the covalent chemistry of Si-O and Si-C surface species for the attachment of functional species (particularly biomolecules) to porous Si.