In the context of studying the feasibility of photocatalytically self-cleaning windows and windshields, clear, abrasion resistant, photocatalytic films of TiO2 were formed on soda lime glass and on fused quartz by a sol-gel process. The rate of photooxidation of contaminant deposits was estimated by measuring the rate of decrease in the integrated IR absorbance associated with the C-H stretching vibrations of a thin solution-cast film of stearic acid under 365 nm (2.4 mW/cm2) or 254 nm (0.8 mW/cm2) irradiation. Approximately 3 X 1 0 " * stearic acid molecules were stripped per 365 nm photon in either front-or back-illuminated soda lime glass, and 6 X 10"* molecules when the films were coated on fused quartz. For thin TiO2 films on fused quartz, the rate of photooxidation, normalized by the number of photons absorbed per unit area, was independent of the wavelength. In contrast, for films on soda lime glass, the rate of photooxidation, when similarly normalized, was higher for the less penetrating wavelength. The reduced photoactivity on glass at the deeply penetrating wavelength (365 nm), as well as the greater photoefficiency on quartz than on glass, are attributed to diffusion of sodium oxide from the glass into the inner glass-contacting zone of the T1O2 layer.

The thermal conductivity of wurtzite and zinc blende indium arsenide nanowires was measured using a microfabricated device, with the crystal structure of each sample controlled during growth and determined by transmission electron microscopy. Nanowires of both phases showed a reduction of the thermal conductivity by a factor of 2 or more compared to values reported for zinc blende indium arsenide bulk crystals within the measured temperature range. Theoretical models were developed to analyze the measurement results and determine the effect of phase on phonon transport. Branch-specific phonon dispersion data within the discretized first Brillouin zone were calculated from first principles and used in numerical models of volumetric heat capacity and thermal conductivity. The combined results of the experimental and theoretical studies suggest that wurtzite indium arsenide possesses similar volumetric heat capacity, weighted average group velocity, weighted average phonon-phonon scattering mean free path, and anharmonic scattering-limited thermal conductivity as the zinc blende phase. Hence, we attribute the differing thermal conductivity values observed in the indium arsenide nanowires of different phases to differences in the surface scattering mean free paths between the nanowire samples.

The surface of LiCoO 2 cathodes was modified with Al 2 O 3 , TiO 2 , and ZrO 2 by a chemical processing procedure followed by heat treatment at 300°C in air for 4 h. The surface-modified LiCoO 2 samples show much better capacity retention at both 25 and 60°C than the unmodified LiCoO 2 cathode to higher cutoff charge voltages of as high as 4.7 V vs. lithium. For example, Al 2 O 3 -modified LiCoO 2 shows approximately 180 mAh/g at 4.5 to 3.2 V with a capacity fade of only 8% in 100 cycles, compared to 32% for the unmodified LiCoO 2 . Transmission electron microscopic studies reveal that the guest materials are present as loose oxides ( Al 2 O 3 and ZrO 2 ) or as monolayers ( TiO 2 ) on the surface of LiCoO 2 particles. The improved capacity retention and the higher reversible capacity (180 mAh/g) of the surface-modified LiCoO 2 compared to the unmodified LiCoO 2 (140 mAh/g) could be due to a suppression of the chemical and structural instabilities of the charged Li 1 − x CoO 2 cathodes and/or reduction of interparticle stresses and strains. © 2003 The Electrochemical Society. All rights reserved.

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We report a study of the effect of the growth base pressure on the thermoelectric (TE) properties of indium antimonide (InSb) nanowires (NWs) synthesized using a vapour-liquid-solid method at different base pressures varying from ambient to high vacuum.A suspended device was used to characterize the TE properties of the NWs, which are zinc-blende structure with 1 1 0 growth direction based on transmission electron microscopy (TEM) characterization of the same NWs assembled on the suspended device. The obtained Seebeck coefficient is negative, with the magnitude being smaller than the literature bulk values and increasing with decreasing growth base pressure. These results are attributed to the loss of In from the source materials due to oxidation by residual oxygen in the growth environment and the consequent formation of Sb-doped NWs. The electron mobility and lattice thermal conductivity in the NWs are lower than the corresponding bulk values because of both surface scattering and stronger dopant scattering in the Sb-doped NWs. Based on these findings, it is suggested that growth from In-rich source materials can be used to achieve composition stoichiometry in the NWs so as to increase the Seebeck coefficient and TE figure of merit.