Solid state charge transfer in nanoparticle solids

Charge transfer in quantum dots is important to both the fundamental science and its application in nanosized electronic devices. This thesis is primarily focused on electrochemical and spectroscopic investigations of the solid-state charge transfer properties of organized assemblies of metal and semiconductor quantum dots.;In metal nanoparticles, the key motivation arises from our recent observation that upon deliberate control of the particle structure, interparticle interactions and temperature, lateral single electron transfer (SET) across a particle monolayer can be achieved at ambient temperature. Experimentally, the Langmuir-Blodgett (LB) method was used to deposit highly ordered monolayer films of monodisperse alkanethiolate-protected gold nanoparticles at varied interparticle separations onto an interdigitated arrays (IDA) electrode.;The above techniques were extrapolated to metal nanoparticles with unsaturated capping ligands in which the effects of core size on the solid state conductivity of arenethiolate gold nanoparticle monolayer were investigated. Interestingly, it was found that the conductivity was maximum for the configuration when the aromatic rings from adjacent nanoparticle solids were stacked over each other.;For semiconductor quantum dots (QDs), my work is focused on the ensemble electronic conductivity within the context of photochemical and photophysical manipulation. These studies suggest that chemical environment plays an important role in the determination of the chemical stability and electronic conductivity of CdSe QD thin films.;For silicon nanoparticles, the solid state electrochemistry of the monolayer of the silicon nanoparticles was investigated. It was found that the photoconductivity increased with increasing photon energy in photoirradiation whereas the enhancement diminished gradually with increasing temperature, as a consequence of the combined effects of enhanced radiative and nonradiative recombination rate and increasing contribution from thermally activated interparticle charge transfer.;Janus particles were prepared by ligand exchange reactions of a Langmuir monolayer of hydrophobic alkanethiolate - passivated gold nanoparticles at relatively high surface pressures with hydrophilic thiol derivatives injected into the water subphase. The ligand intercalation between adjacent particles led to impeded interfacial mobility of the particles. Consequently, ligand place-exchange reactions were limited only to the side of the particles facing the water phase, leading to the formation of amphiphilic nanoparticles which exhibited hydrophobic characters on one side and hydrophilic on the other, analogous to the dual-face Roman god, Janus. The unique amphiphilic characters of the Janus particles were confirmed by a variety of experimental measurements, including contact angle measurements, FTIR, UV visible, and NMR spectroscopies. Interestingly, the Janus particles might be dispersed in water, forming micelle-like aggregates, as revealed in dynamic light scattering and AFM measurements.