Benjamin Messer

Nanowire Ultraviolet Photodetectors and Optical Switches

no attention has been given to the photoconducting properties of nanowires despite the exciting possibilities for use in optoelectronic circuits. Here, we show the possibility of creating highly sensitive nanowire switches by exploring the photoconducting properties of individual semiconductor nanowires. The conductivity of the ZnO nanowires is extremely sensitive to ultraviolet light exposure. The light-induced conductivity increase allows us to reversibly switch the nanowires between “OFF” and “ON” states, an optical gating phenomenon analogous to the commonly used electrical gating. [2,3,10]

Patterning Porous Oxides within Microchannel Networks

A continuing challenge for materials chemists and engineers is the ability to create multifunctional composite structures with well-defined superimposed structural order from nanometer to micrometer length scales. Materials with three-dimensional structures ordered over multiple length scales can be prepared by carrying out colloidal crystallization and inorganic/organic cooperative self-assembly within microchannel networks. The resulting materials show hierarchical ordering over several discrete and tunable length scales ranging from several nanometers to micrometers. These patterned porous materials hold promise for use as advanced catalysts, sensors, low-k dielectrics, optoelectronic and integrated photonic crystal devices.

A theoretical study of ROX (R=H, CH3; X=F, Cl, Br) enthalpies of formation, ionization potentials and fluoride affinities

Abstract We report the results of a systematic Gaussian2 ab initio study of the ROX (R=H, CH 3 ; X=F, Cl, Br) series. The calculated standard enthalpies of formation (Δ H f 298K ) provide the following estimates for the previously undetermined R=CH 3 series; Δ H f =−94.9, −74.0, and −57.0 kJ mol −1 for X=F, Cl, and Br, respectively. The calculated ionization potentials (IP) provide an estimate of 10.24 eV for the previously undetermined IP of CH 3 OBr. The first determination of fluoride affinities for ROX species are presented and are shown to depend strongly on the orientation of the F − +ROX complex and on the identity of the halogen substituent.

Computational and experimental studies of chemical ionization mass spectrometric detection techniques for atmospherically relevant peroxides

Abstract We report the results of computational and experimental studies concerning the chemical ionization mass spectrometric detection of hydrogen peroxide (HOOH) and methyl hydroperoxide (CH 3 OOH). GAUSSIAN2 (G2) electronic structure calculations are used to predict structures, natural charges of the atoms and energies for the neutral species, as well as for the cation, anion, and the proton and fluoride adduct species. These calculations are used to predict ion–molecule reaction thermodynamics as a guide to the experimental development of chemical ionization mass spectrometric detection methods. Both HOOH and CH 3 OOH are predicted to react exothermically with O 2 + and F − to yield the cationic and fluoride adduct species, respectively. In addition, CH 3 OOH is predicted to react exothermically with H 3 O + to yield the proton adduct species. The feasibility of F − chemical ionization mass spectrometric detection of peroxides was experimentally explored through kinetic studies. The fluoride adduct formation reactions for both HOOH and CH 3 OOH were found to proceed at or near collision-limited rates.