| Chapter One is an introduction to m&barbelow;onolayer p&barbelow;rotected metal c&barbelow;lusters (MPCs) as species that, because of their small size, bridge the gap between bulk and molecular behavior. The method of and variations in their synthesis, as well as their general chemical and electrochemical properties, are presented, as are recent examples of their practical applications.; Chapter Two introduces a new 1-2 nm diameter organic-soluble silver MPC species protected by 4-tert-butylbenzyl mercaptan (BBT) ligands and synthesized using two different protocols. The BBT ligands impart crucial stability to the small silver cores that otherwise is extremely difficult to maintain. MPCs produced with a two-phase protocol exhibit quantized double layer (QDL) charging voltammetry and a strong surface plasmon resonance at 475 nm, whereas MPCs produced with a one-phase protocol show neither of these features. The difference is due to an oxide coating on the one-phase product, observed with XPS. Average stoichiometric formulae of Ag140BBT 53 and Ag225BBT75 are obtained, for the two most populous core sizes, from a combination of thermogravimetric, microscopic, mass spectral, and electrochemical data.; Chapter Three presents the assembly and characterization of dithiol-linked gold MPC network polymer films grown using protocols all based on ligand place-exchange chemistry but differing in growth time, growth cycles, and solution preparation. A study of the growth mechanism and the rate of growth is also presented. The electronic conductivities, electron transfer rate constants, and activation energy barriers were observed to change systematically depending on the chain lengths of both the linking (dithiol) and nonlinking (monolayer) ligands, implying electronic tunneling through both kinds of ligands.; Chapter Four presents the interaction of dithiol-linked gold MPC films of different thicknesses with various solvent vapors. Increases in film conductivity were observed upon the absorption of both polar and nonpolar vapors, implying that the changing of the distance between MPC cores is not the sole mechanism occurring in this process. Thinner (27 nm) films are seen to be better suited for the detection of low vapor concentrations, and these capabilities are examined with short pulses of vapor. Airbrushed gold MPC films are also described in terms of their sensing aspects and are observed to respond identically to differing vapor pressures, presumably due to the "on/off" tendencies of their electronic pathways upon absorption and desorption, respectively.; Chapter Five examines the electron transfer kinetics in solvent-wetted dithiol-linked gold MPC films in terms of electron diffusion coefficients (De) and times-of-flight (t max) determined using electronic charge and voltage pulses. Interdigitated array electrodes were used as generator-collector systems in a four-electrode setup, with a pulse generating a flow of electrons at the generator and traveling through the film in amounts of time dependent on the magnitude and duration of the pulse. Electron transfers were observed to be faster with poorly absorbed solvents, due to less film swelling, and were faster overall than those previously seen in various redox polymers and hydrogels. Film conductivities were irreversibly increased as a result of the pulses, due to doping of the films with electrons/holes. |
