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.

Single-crystalline In(OH)(3) nanocubes were synthesized in a simple aqueous solution, without using a surfactant, at a temperature as low as 90 degrees C. To elucidate the growth mechanism, the structural evolution of In(OH)(3) nanocubes during the synthesis process were carefully examined. The experimental results showed that the formation of the In(OH)(3) nanocubes is primarily guided by the oriented attachment mechanism, following a zero-dimensional (0D) -> one-dimensional (1D) -> three-dimensional (3D) mode. The 0D In(OH)(3) nanoparticles will first assemble to form 1D nanorods, then the nanorods will orientedly attach to form 3D nanorod bundles and finally the In(OH)(3) nanorod bundles will fuse into strip-like or square nanocubes. Small strip-like or square nanocubes can further orientedly attach and fuse into big single-crystalline strip-like or square nanocubes. However, the growth of strip-like and square nanocubes may also occur based on the Ostwald ripening. The cathodoluminescence (CL) spectra at room temperature of the as-synthesized In(OH)(3) nanocubes exhibited a weak ultraviolet luminescence at 350 nm (3.54 eV) and a strong blue luminescence at 450 nm (2.75 eV), which can be attributed to the hydroxy ion defects generated by the incomplete reaction of the In(3+) ions with OH(-) radicals during the synthesis process

Brush-like hierarchical In 2 O 3 nanostructures on SnO 2 nanowires have been synthesized by a two-step thermal vapor transport process. To elucidate the growth mechanism, the structural evolution of hierarchical In 2 O 3 nanostructures during the synthesis process was carefully examined. The experimental results showed that a self-catalytic vapor-liquid-solid (VLS) growth mechanism was responsible for the growth of hierarchical In 2 O 3 nanostructures. Compared with the film counterparts, the hierarchical In 2 O 3 nanostructures exhibited a higher sensitivity to low-concentration CO, which can be attributed to more active centers on the surface obtained from the enhanced oxygen vacancy defects and formation of bridging point contacts in the random network between the two electrodes.

Single crystalline Sb-additivated SnO2 nanorods, beaklike nanorods, and nanoribbons were synthesized by an in situ catalyst-assisted thermal evaporation process on single-crystal Si substrates. As the Sb:Sn weight ratios were increased, the morphologies of Sb-additivated SnO2 nanostructures would progressively transform from nanorods to beaklike nanorods and to the mixture of nanowires and nanoribbons. The SnO2 nanorods grow along the [0 (2) over bar0] direction and with lateral facets defining a square column consisting of {100} and {001} planes. The Sb-additivated SnO2 beaklike nanorods initially grow along the [0 (1) over tilde(1) over bar] direction and then switch to the [03 (1) over tilde] direction to form the beak, while the nanoribbons grow along the [110] direction. The Sb atoms were found to uniformly distribute over the whole Sb-additivated SnO2 nanostructures and that it would not affect the single crystallinity of SnO2 nanostructures. The photoluminescence spectra of the nonadditivated and Sb-additivated SnO2 nanostructures exhibited multipeaks with peak positions centered at 403, 453, 485, 557, and 622 nm. When Sb atoms were additivated into SnO2 nanostructures, the luminescence intensities would significantly decrease and photoluminescence at 557 and 622 nm would almost disappear. These can be explained by the replacements of the six- and fivefold coordinated Sn atoms on low-index facets by five- and fourfold coordinated Sb atoms, respectively, leading to the cancellation of 100 degrees tin coordinated on-plane oxygen bridging vacancies and 130 degrees tin coordinated in-plane oxygen vacancies. (c) 2009 American Institute of Physics. [DOI: 10.1063/1.3068487