Large-scale SnO2 nanoblades have been synthesized on a glass substrate covered with a 100-nm-thick SnO2 buffer layer in a controlled aqueous solution at temperatures below 100 degrees C. Typical widths of the nanoblades were about 100-300 nm and the lengths were up to 10 mu m, depending on the growth temperature. The thicknesses were about a few tens of nanometers. Transmission electron microscopy data, x-ray diffraction patterns, and x-ray photoelectron spectroscopy spectral analyses confirmed that the as-grown nanoblades had the phase structure of the rutile form of SnO2 growing along the [110] direction. No other impurities, such as elemental Sn and tin oxides, were detected. An intense blue luminescence centered at a wavelength of 445 nm with a full width at half maximum of 75 nm was observed in the as-grown SnO2 nanoblades, which is different from the yellow-red light emission observed in SnO2 nanostructures prepared by other methods. It is believed that the strong blue luminescence from the as-grown SnO2 nanoblades is attributed to oxygen-related defects that have been introduced during the growth process. (c) 2006 American Institute of Physics

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To elucidate the growth mechanism of In 2 O 3 nanotowers synthesized via a Au-catalyzed vapor transport process, the structural evolution of In 2 O 3 nanotowers was carefully examined during the synthesis process. It was found that Au catalysts only play a role at the initial stage, where they facilitate the formation of In 2 O 3 nanoparticles and nanorods. After the Au atoms are consumed by the formation of Au-In compound(s), the liquid In droplets will form on the tips of In 2 O 3 nanoparticles or nanorods, and the self-catalytic vapor-liquid-solid (VLS) growth mechanism will dominate the subsequent one-dimensional (1D) growth of In 2 O 3 nanopillars. Since the supply of In 2 O may not be sufficient for the continuous 1D growth, the lateral growth of In 2 O 3 nanopillars governed by the vapor-solid (VS) mechanism will occur. The periodical axial and continuous lateral growth leads to the formation of In 2 O 3 nanotowers with a truncated octahedron structure of 4-fold symmetry {111} accumulated planes along the [100] direction. The photoluminescence (PL) spectrum of In 2 O 3 nanotowers exhibited an intense green-yellow luminescence at the wavelength of 580 nm, which can be ascribed to the possible recombination of electrons on singly ionized oxygen vacancies and holes on the valence band or doubly ionized oxygen vacancies.

We have synthesized brushlike p-Te/n-SnO2 hierarchical heterostructures by a two-step thermal vapor transport process. The morphologies of the branched Te nanostructures can be manipulated by adjusting the source temperature or the argon flow rate. The growth of the branched Te nanotubes on the SnO2 nanowire backbones can be ascribed to the vapor-solid (VS) growth mechanism, in which the inherent anisotropic nature of Te lattice and/or dislocations lying along the Te nanotubes axis should play critical roles. When exposed to CO and NO2 gases at room temperature, Te/SnO2 hierarchical heterostructures changed the resistance in the same trend and exhibited much higher responses and faster response speeds than the Te nanotube counterparts. The enhancement in gas sensing performance can be ascribed to the higher specific surface areas and formations of numerous Te/Te or TeO2/TeO2 bridging point contacts and additional p-Te/n-SnO2 heterojunctions.

The h-WO3/a-WOx core/shell heterostructures combine the assets of the constituent phases and exhibit highly improved and balanced electrochromic properties.