(Figure Presented) Promising building blocks: High-density radially-oriented amorphous silica nanowires standing on a single-crystal Si nanocore were synthesized by simple thermal evaporation of silicon with tin as catalyst. The growth process (see schematic picture) appears to involve concurrent vapor-liquid-solid and oxide-assisted growth mechanisms. Scanning electron micrographs corresponding to 1 and 2 are also shown. © 2005 Wiley-VCH Verlag GmbH & Co. KGaA.
Hui Wang 张晓宏 Meng Zhou Shaomin Wu Shikang 师文生 李述汤
Angewandte Chemie - International Edition
2005
The metal-ligand complex 1 ([Mg (L)]) (or 2 ([Ca (L)] )) was demonstrated to selectively bind HSO (or HPO) over other anions by using UV-vis absorption and fluorescence spectroscopy. The studied complex exhibits the remarkable color change and fluorescence quenching upon introducing HSO (or HPO) anion in acetonitrile. Both the mechanism and structure of the secondary complex of complex 1 with anion were proposed on the basis of theoretical computation.
Zhou Li Li Sun Hao Li Huaping Hui Wang 张晓宏 Wu Shikang 李述汤
Organic Letters
2004
Wong T. C. Li Ruiqin Zhang 李述汤
Applied Physics Letters
2004
The Si-H bond energies and wet oxidation of SiH (x = 1-3) configurations on silicon cluster surfaces have been studied by ab initio calculations It is found that the Si-H bond energy is simply determined by its local configuration and is about 75.2 to ∼76.3 kcal/mol for silicon monohydride, 77.9 to ∼78 9 kcal/mol for silicon dihydride, and 80.9 to ∼81.6 kcal/mol for silicon trihydride. The evaporation energies of a hydrogen molecule from the dihydride and trihydride configurations are found to be slightly higher than the calculated bond energies However, when a water molecule reacts with them, the reaction energy barriers are found to be generally smaller than 500 kcal/mol, much less than these bond energies. The calculated reaction barriers and heats do not show clear relationships with the bond energies. Rather, the results show that the reaction at SiH is the most unfavorable one whereas the most easy reaction may take place at the Si-Si dimer on a (2 × 1) reconstructed Si(001)-like configuration, Our results indicate that the degradation of hydrogenated silicon nanostructures or bulk silicon surfaces might be significantly determined by the possibility of reaction with water molecules, a hydrogenated surface covered by dihydride configurations being the most inert case.
Ruiqin Zhang Lu W. C. Zhao 李述汤
Journal of Physical Chemistry B
2004
Semimetal nanostructures in semiconductor matrices of tetrahedral carbon (ta-C) films induced by ion beam implantation at high doses have been studied. The structural analysis shows that originally abundant sp carbon atomic bonding of ta-C is gradually converted to a graphitic phase during the course of ion bombardment. Growing and clustering the sp bonded carbon component in the ta-C films by ion implantation is indicated by Raman spectral analysis, but the examination of the films evolved on an atomic scale shows the formation of structures with the higher degree of order. The graphitic basal planes are formed preferably in the perpendicular direction to the film surface. The critical rearrangement is observed at 0.24 displacements per atom when the onset of the transformation occurs. Unlike amorphisation of crystal structure by ion bombardment, here the initially amorphous phase with short ordered sp bonding is nanostructured to the higher degree of an ordered structure using proper ion energies and doses. The structural rearrangement gives rise to the change in resistivity, which can vary from original 10 to 10 Ω cm at the highest doses used. The transformation process is associated with the change from interband to intraband absorption due to overlapping conduction and valence bands, which is the indicative of transforming a semiconducting material to a semimetallic nanocomposite material. The material evolved becomes electrically conductive while it retains considerable amount of sp bonding and high hardness being above 15 GPa. © 2003 Elsevier B.V. All rights reserved.
Luk W. Y. Kutsay Bello I. Yeshayahu Lifshitz Lam Christopher Wai-Kei Meng 李述汤
Diamond and Related Materials
2004
Yanquan Feng Ruiqin Zhang 李述汤
Journal of Applied Physics
2004
Sandip Dhara Nair Li Wong T. C. Ruiqin Zhang 李述汤
Applied Physics Letters
2004
We report a soft x-ray excited optical luminescence (XEOL) and x-ray emission spectroscopy (XES) study of silicon nanowires (SiNW) with excitations at the silicon K and L edge, respectively. It is found that the XEOL of SiNW exhibits several luminescence bands at ∼460, ∼530, and ∼630 nm. These luminescence bands are broad and are sensitive to the Si 1s excitation channel (Si versus SiO whiteline). These chemical- and morphology-dependent luminescences are attributable to the emission from the encapsulating silicon oxide, the quantum-confined silicon crystallites of various sizes embedded in the oxide layer, and the silicon-silicon oxide interface. XES clearly shows the presence of a relatively thick oxide layer encapsulating the silicon nanowire and the densities of states tailing across the Fermi level. The implications of these findings to the electronic and optical properties of silicon nanowires are discussed.
Tsunkong Sham Naftel Kim P. S. Grace Sammynaiken Yuanhong Tang Coulthard Alexander Moewes John Freeland Yongfeng Hu 李述汤
Physical Review B - Condensed Matter and Materials Physics
2004
Baumer Andrea Martin Stutzmann Brandt Frederick wing fai Au 李述汤
Applied Physics Letters
2004
We demonstrate the bulk synthesis of single crystalline Cu-doped ZnO nanowires using (CuI + ZnI) powders at 600°C. These mass nanowires are characterized through x-ray diffraction, scanning electron microscopy, energy dispersive x-ray spectroscopy, transmission electron microscopy (TEM), selected area electron diffraction, and high-resolution TEM; they have uniform diameters of about 65 nm and are several tens of microns in length. The growth of ZnCuO nanowires is suggested for self-catalyzed vapour-liquid-solid. In particular, the PL spectra of these nanowires show emission peaks that strongly shift to long wavelength with increasing Cu, and the doping quantity is found to be responsible for the different characteristics; the PL mechanism is explained in detail.
Zhou Shaomin 张晓宏 Meng Zou Kai Fan Xia Wu Shikang 李述汤
Nanotechnology
2004