derived from BaCO 3 . Small particle size has been shown to suppress a martensitic phase transition, and in this context microwave plasma synthesis appears rapid enough to prevent particle sintering and subsequent transition to the monoclinic phase. Prolonged exposure (1 h) to an O 2 or Ar plasma of either the orthorhombic or monoclinic phases did not result in a phase change as judged by powder XRD.In conclusion, we have used a simple microwave plasma reactor for reproducible bulk synthesis of several ternary niobate and titanate phases. MIP synthesis does not require direct interaction between a solid and microwave radiation and is, therefore, amenable to any solid-state reaction. Importantly, for some reactions the plasma can also be used to heat solids into a temperature regime where additional dielectric heating can occur, resulting in a local temperature much greater than the equilibrium MIP temperature. ExperimentalPrecursor oxides (Nb 2 O 5 , TiO 2 , and BaO 99.99 %) and carbonates (Li 2 CO 3 99.99 %, Na 2 CO 3 99.995 %, K 2 CO 3 99.995 %, CaCO 3 99.995+ %, BaCO 3 99.999 %, and PbCO 3 99.99+ %) were purchased from Aldrich and used as received. Plasma gases (Ar and O 2 ) were purchased from BOC. In a typical synthesis, a total mass of 2 g of precursors was ground in a drybox and pressed at 10 tonnes into a 13 mm pellet, and the pellet was transferred to the microwave apparatus via a desiccator. The pellet was placed in an alumina boat and exposed to a plasma at 13 mbar (1mbar = 10 2 Pa), 900 W, and a gas flow rate of 200 cm 3 min -1 for argon and 142 cm 3 min -1 for dioxygen. After microwave plasma irradiation, products were transferred directly into a drybox for storage. Products were characterized by powder X-ray diffraction (Philips 1800 diffractometer PH 03, with Cu Ka radiation (k = 1.54 Å) in reflection mode), scanning electron microscopy (FEI Sirion 200), and analytical transmission electron microscopy (FEI CM200 FEGTEM) that included electron energy loss spectroscopy (EELS). the synthesis of tubular nanomaterials has aroused worldwide interest -both in fundamental studies, and for their potential application in, for example, chemical sensors, and as catalysts and storage and/or release systems. [2][3][4][5] Zinc oxide (ZnO), a II-VI compound semiconductor, has many remarkable properties. The wide direct bandgap of ZnO (3.37 eV) and large exciton binding energy (∼ 60 meV at room temperature)

CdS quantum dots can be self-assembled on high surface area nanocrystalline TiO2 electrodes; spectroscopic and photoelectrochemical studies indicate that the size, and hence the absorption edge, of the CdS particles can be controlled; efficient photosensitization of the TiO2 electrode by the Q-particles has been achieved.

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ZnO nanorods (NRs) and nanotubes (NTs) have been synthesized by a hydrothermal method on Si substrates that had been precoated (by pulsed laser deposition (PLD)) with a thin ZnO film. High-resolution transmission electron microscopy and selected area electron diffraction analysis confirm that the NTs are ZnO single crystals and that their growth direction is along [0001] (the c-axis). Scanning electron microscopy points to the early-time formation of two classes of NRs on the PLD ZnO coating, one of which is longer and displays higher length/diameter aspect ratios than the other. The morphologies of NRs belonging to the first of these classes were seen to evolve with time, progressively tapering, and producing volcano-like surface structures that develop into NTs. In contrast, NRs belonging to the other (shorter) class retain their hexagonal cross-section and have flat tops. To explain these emergent structures and, in particular, the selective growth of ZnO NTs, we have undertaken a systematic investigation of the effects of different substrates (e.g., borosilicate glass, Pt-coated glass, and both bare and PLD ZnO-coated Si wafers) and of the reactive solution on the growth properties of ZnO NRs, NTs, and the ZnO nanopowders that precipitate from the reactive mixture. The experimental findings suggest the following ZnO NT growth mechanism. The PLD ZnO film consists of many nanocrystallites, with a preferred c-axis alignment. These serve to nucleate the hydrothermal growth of (c-axis aligned) NRs. The NRs are deduced to be Zn-polar, but can be either Zn-atom or O-atom terminated. It is proposed that the different surface terminations influence (by electrostatic interactions) the cation (Zn(2+) and ZnOH(+)) to anion (OH(-)) concentration ratio in the double layer at the growing polar surface. Zn-atom termination causes a reduction in the local Zn(2+)/OH(-) (and ZnOH(+)/OH(-)) ratios (i.e., the extent of solution supersaturation) relative to those in the bulk solution, thereby encouraging tapered NR growth and, as the zinc concentration falls further, the emergence of volcano-like structures on the polar surface, which seed the subsequent growth of ZnO NTs.

Self-assembled layers of Bi 2 S 3 nanoparticles have been used to sensitize nanocrystalline titanium dioxide, replacing the ruthenium dye used in conventional dye-sensitized solar cells. We report band-edge tuning of the bismuth sulfide quantum dot particles by adsorption of sulfide ions. In the absence of sulfide ions, only smaller Bi 2 S 3 particles with a large band gap inject electrons into the TiO 2 . Progressive addition of sulfide ions shifts the conduction band of the Bi 2 S 3 upward, so that larger nanoparticles begin to inject and the long wavelength component of the photocurrent response increases. The observation suggests that band-edge tuning may form a useful part of strategies designed to exploit semiconductor quantum dots as sensitizers.

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