SnO2-core/ZnO-shell nanowires were synthesized using a two-step process: the synthesis of SnO2 nanowires by the thermal evaporation of Sn powders followed by the atomic layer deposition of ZnO. The room temperature NO2 gas sensing properties of the nanowires under ultraviolet (UV) illumination were examined. The cores and shells of the nanowires were primitive tetragonal-structured single crystal SnO2 and wurtzite-structured single crystal ZnO, respectively. The responses of multiple networked SnO2 nanowire sensors were increased 2-3-fold at NO2 concentrations ranging from 1 to 5 ppm by encapsulating the nanowires with ZnO. The SnO2-core/ZnO-shell nanowire sensors showed a remarkably enhanced response under UV illumination. The sensing mechanism of the core/shell nanowires under UV illumination is also discussed.
Submicron-sized monodispersed TiO 2 spheres (SPs) with high porosity were synthesized by a controlled hydrolysis of titanium tetraisopropoxide (TTIP) and subsequent hydrothermal treatment at 230 C. By adjusting the ratio of TTIP to water (the r-factor) in the hydrolysis reaction, the diameters of SPs were selectively controlled to 260, 350, 450, 560, 800, and 980 nm. The prepared SPs in the pure anatase phase were highly porous structures with crystallite sizes of $15 nm and surface areas of 101-121 m 2 g À1 . The synthesized nanoporous SPs in different sizes were then applied as the lightscattering layer (LSL) of dye-sensitized solar cells (DSCs) for efficient utilization of solar spectrum, and the size-dependent light-scattering effects of those SPs were systematically investigated. The 450 nm sized SP (SP450) provided the highest light-scattering efficiency among those in the 260-800 nm range. Relatively higher efficiency is caused by the characteristic light-scattering effect based on its unique diameter and also by the photonic reflection effect originating from its size-uniformity and long-range ordering. As a result the photovoltaic conversion efficiency (h) of DSC was improved from 6.92 to 9.04% with introducing the nanoporous SP450 as LSL.
We have prepared Al2O3 films by the atomic layer deposition technique using trimethylaluminum as the precursor for aluminum and O3, instead of commonly used H2O, as an oxidant. We show that even without any postdeposition annealing or any preventive layer between the Al2O3 film and Si substrate to suppress the formation of metallic clusters, the Al2O3 films prepared using O3 have significantly less amount of defect states like Al–Al and OH bonds compared with those prepared by H2O. The films show device quality leakage characteristics, with Al2O3 film prepared with O3 showing a leakage current density one or two orders lower and a smaller flatband voltage shift than that of Al2O3 film prepared with H2O, demonstrating improved interface characteristics. The former also shows a very low wet etch rate.
For the first time, a single crystalline FeTiO 3 nanodisc in the ilmenite phase has been synthesized by a hydrothermal reaction at 220 °C. The prepared FeTiO 3 was a hexagonal disk-like structure with an average diameter of ∼400 nm and a thickness of ∼70 nm, while its hexagonal face was oriented in (001) plane and grown to (110) direction. The heterojunction structure was formed between the as-prepared FeTiO 3 nanodisc and Degussa P25 with an average particle size of ∼25 nm by employing maleic acid as an organic linker. The prepared FeTiO 3 /TiO 2 coupled at a nanoscale demonstrated greatly enhanced photocatalytic activity in removing 2-propanol and evolving CO 2 in gas phase under visible light irradiation (λ g 420 nm). Its degradation constant (k) in removing 2-propanol was ∼25 times that of Degussa P25, which suggests that its catalytic efficiency is comparable to that of a typical N-doped TiO 2 . The remarkable photocatalytic activity of FeTiO 3 / TiO 2 could be explained by the intersemiconductor hole-transfer mechanism caused by the unique relative band positions of these two semiconductors.
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