Molecular interactions with photoluminescent porous silicon and the effects of chemical modifications of the silicon surface

This thesis explores photoluminescence, photochemical and chemical properties of porous silicon. First, a procedure for generating photoluminescent colloidal suspensions of silicon is described. Silicon, electrochemically etched to form porous silicon, can be ultrasonically dispersed into solvents forming a suspension of fine silicon particles that luminesce. TEM analyses show the silicon particles have irregular shapes, with diameters ranging from many microns to nanometers. Luminescent composite polystyrene/silicon films can also be made.; Next the photoluminescence response of porous silicon exposed to aqueous surfactant solutions is described. Porous silicon samples are exposed to acidic sodium dodecylsulfonate solutions, and the photoluminescence intensity is monitored. The sample photoluminescence decays to nearly zero over time. Removal of the surfactant from the porous silicon is not straight forward and is also described. The use of cationic surfactants resulted in surface oxidation, in addition to photoluminescence quenching, leading us to believe electron or hole transfer reactions are possible with porous silicon.; To explore this possibility, porous silicon is investigated as an initiator for radical polymerization reactions. The surface radicals and photogenerated e{dollar}-{dollar}/h+ pairs in porous silicon can initiate polymerization reactions. Porous silicon wafers are placed in monomer solutions and are left in the dark or excited by light. Methyl methacrylate polymerizes in the absence of light, presumably via silicon-based radical initiator sites. The N-vinylcarbazole polymerizes to a small extent in the dark and to a much greater extent when the porous silicon surface is illuminated with white light. Acrylonitrile and styrene showed very little to no polymerization either in the dark or under illumination.; Last, the chemistry of the material itself is investigated. Several methods for modifying the surface termination and hence the photoluminescence quenching sensitivity of porous silicon are presented. The preparation of deuterated porous silicon is described. Bromine, oxide, ether, and silyl ether terminated surfaces are prepared by reactions of both the hydrogen and deuterium terminated porous silicon surfaces. Mechanisms for the derivatizations are presented and the quenching characteristics of the derivatized surfaces are discussed.