Spin Hall Conductance of the Two Dimensional Hole Gas in a Perpendicular Magnetic Field

The charge and spin Hall conductance of the two-dimensional hole gas within the Luttinger model with and without inversion symmetry breaking terms in a perpendicular magnetic field are studied, and two key phenomena are predicted. The sign of the spin Hall conductance is modulated periodically by the external magnetic field, which means a possible application in the future. Furthermore, a resonant spin Hall conductance in the two-dimensional hole gas with a certain hole density at a typical magnetic field is indicated, which implies a likely way to firmly establish the intrinsic spin Hall effect. The charge Hall conductance is unaffected by the spin-orbit coupling.Comment: accepted for publication in Phys. Rev. B; 6 pages, 4 figure

Final Report

The premise of this project was that coordination chemistry could be used to devise new kinds of microporous materials and that these materials could exhibit nanoscale porosity and selective chemical separation capabilities. Our initial materials focus was on aggregates of discrete hollow molecules, especially molecular squares. Subsequently our focus turned largely toward permanently microporous metal-organic frameworks (MOFs). Our approach emphasized coupling predictive & explanative computational modeling to materials design, synthesis, and property characterization

Mechanism for zirconium oxide atomic layer deposition using bis(methylcyclopentadienyl)methoxymethyl zirconium

The mechanism for zirconium oxide atomic layer deposition using bis(methylcyclopentadienyl)methoxymethyl zirconium and H(2)O was examined using ab initio calculations of hydrolysis energies to predict the order of ligand loss. These predictions were tested using in situ mass spectrometric measurements which revealed that the methyl ligand, and 65% of the methylcyclopentadienyl ligands are lost during the zirconium precursor adsorption. The remaining 35% of the methylcyclopentadienyl ligands and the methoxy ligand are lost during the subsequent H(2)O exposure. These measurements agree very well with the predictions, demonstrating that thermodynamic calculations are a simple and accurate predictor for the reactivities of these compounds. (c) 2007 American Institute of Physics. (DOI: 10.1063/1.2824814

Glass-Encapsulated Light Harvesters: More Efficient Dye-Sensitized Solar Cells by Deposition of Self-Aligned, Conformal, and Self-Limited Silica Layers

A major loss mechanism in dye-sensitized solar cells (DSCs) is recombination at the $TiO_2$/electrolyte interface. Here we report a method to reduce greatly this loss mechanism. We deposit insulating and transparent silica $(SiO_2)$ onto the open areas of a nanoparticulate $TiO_2$ surface while avoiding any deposition of $SiO_2$ over or under the organic dye molecules. The $SiO_2$ coating covers the highly convoluted surface of the $TiO_2$ conformally and with a uniform thickness throughout the thousands of layers of nanoparticles. DSCs incorporating these selective and self-aligned $SiO_2$ layers achieved a 36% increase in relative efficiency versus control uncoated cells.Chemistry and Chemical Biolog

Atomic layer deposition of Pt@CsH_2PO_4 for the cathodes of solid acid fuel cells

Atomic layer deposition (ALD) has been used to apply continuous Pt films on powders of the solid acid CsH_2PO_4 (CDP), in turn, used in the preparation of cathodes in solid acid fuel cells (SAFCs). The film deposition was carried out at 150 °C using trimethyl(methylcyclopentadienyl)platinum (MeCpPtMe_3) as the Pt source and ozone as the reactant for ligand removal. Chemical analysis showed a Pt growth rate of 0.09 ± 0.01 wt%/cycle subsequent to an initial nucleation delay of 84 ± 20 cycles. Electron microscopy revealed the contiguous nature of the films prepared using 200 or more cycles. The cathode overpotential (0.48 ± 0.02 V at a current density of 200 mA/cm^2) was independent of Pt deposition amount beyond the minimum required to achieve these continuous films. The cell electrochemical characteristics were moreover extremely stable with time, with the cathode overpotentials increasing by no more than 10 mV over a 100 h period of measurement. Thus, ALD holds promise as an effective tool in the preparation of SAFC cathodes with high activity and excellent stability

Video in Survey Interviews: Effects on Data Quality and Respondent Experience

This study investigates the extent to which video technologies - now ubiquitous - might be useful for survey measurement. We compare respondents' performance and experience (n = 1,067) in live video-mediated interviews, a web survey in which prerecorded interview­ers read questions, and a conventional (textual) web survey. Compared to web survey re­spondents, those interviewed via live video were less likely to select the same response for all statements in a battery (non-differentiation) and reported higher satisfaction with their experience but provided more rounded numerical (presumably less thoughtful) answers and selected answers that were less sensitive (more socially desirable). This suggests the presence of a live interviewer, even if mediated, can keep respondents motivated and con­scientious but may introduce time pressure - a likely reason for increased rounding - and social presence - a likely reason for more socially desirable responding. Respondents "in­terviewed" by a prerecorded interviewer, rounded fewer numerical answers and responded more candidly than did those in the other modes, but engaged in non-differentiation more than did live video respondents, suggesting there are advantages and disadvantages for both video modes. Both live and prerecorded video seem potentially viable for use in pro­duction surveys and may be especially valuable when in-person interviews are not feasible