ABSTRACTEfforts to produce stable, derivatized porous silicon have yielded a number of chemical methods capable of functionalizing this interesting material with organic monolayers. Hydride-terminated porous silicon substrates react with alkenes and alkynes in the presence of dilute triphenylcarbenium salt solutions to respectively produce alkyl- and alkenyl-functionalized materials. Characterization by transmission FTIR and solid-state NMR suggests the formation of highly stable silicon-carbon bonds to yield covalently bound organic moieties. Porous silicon passivated in this fashion exhibits a greater resistance than that of the native material to chemical degradation, indicating that the organic functionalities may serve to sterically shield the nanocrystallites from nucleophiles. Hydrosilylation is proposed to proceed via hydride abstraction from the substrate followed by electrophilic attack by the subsequent species upon the alkene/alkyne, a mechanism previously hypothesized for the formation of stabilized β-silyl carbocations. The reaction is tolerant of a variety of substrate functional groups and native porous silicon surfaces but depends markedly upon the identity of the salt counteranion, among other solution parameters.
Preparation and Nanopatterning of Organic Monolayers Anchored Covalently to Silicon Surfaces.