Shidan Yu

Synthesis of High-Density Nanocavities inside TiO2−B Nanoribbons and Their Enhanced Electrochemical Lithium Storage Properties

Single crystalline TiO2-B nanoribbons with high-density nanocavities were successfully synthesized via a simple hydrothermal route. The as-prepared TiO2-B nanoribbons exhibited a large Brunauer, Emmett, and Teller (BET) surface area of about 305 m(2)/g because of the high-density nanocavities inside the thin nanoribbons. Electrochemical measurements indicated that the TiO2-B nanoribbons with dense nanocavities showed discharge specific capacity higher than those of TiO2-B nanotubes and nanowires. It was found that the dense nanocavities have an important influence on the electrochemical lithium intercalation properties.

Synthesis of ZnS nanocrystals with controllable structure and morphology and their photoluminescence property

The controllable synthesis of ZnS nanocrystals with desirable morphology and correlative structure has been carried out via the solvothermal method by simply changing the molar ratio of the reactants. The hexagonal-shaped ZnS nanosheets with a zinc-blende structure were synthesized in one step for the first time. ZnS nanorods with wurtzite structure and large ratio of length to diameter were also fabricated. We found that phase transformation is easily induced and there is a strong correlation between the morphology and structure of the ZnS nanocrystals by changing the ratio of the reactants. The photoluminescence spectra of the ZnS nanosheets and nanorods exhibit different emission bands. ZnS nanosheets show a strong emission at 534 nm while the nanorods have two emissions located at 520 and 578 nm.

Synthesis and high pressure induced amorphization of C60 nanosheets

C60 nanosheets with thicknesses in the nanometer range were synthesized by a simple method. Compared to bulk C60, the lattice of the nanosheets is expanded by about 0.4%. In situ Raman spectroscopy and energy-dispersive x-ray diffraction under high pressures have been employed to study the structure of the nanosheets. The studies indicate that the bulk modulus of the C60 nanosheets is significantly larger than that of bulk C60. The C60 cages in nanosheets can persist at pressures over 30GPa, 3GPa higher than for bulk C60. These results suggest that C60 crystals in even small size will be a potential candidate of superhard materials.

Rotational dynamics of confined C60 from near-infrared Raman studies under high pressure.

Peapods present a model system for studying the properties of dimensionally constrained crystal structures, whose dynamical properties are very important. We have recently studied the rotational dynamics of C60 molecules confined inside single walled carbon nanotube (SWNT) by analyzing the intermediate frequency mode lattice vibrations using near-infrared Raman spectroscopy. The rotation of C60 was tuned to a known state by applying high pressure, at which condition C60 first forms dimers at low pressure and then forms a single-chain, nonrotating, polymer structure at high pressure. In the latter state the molecules form chains with a 2-fold symmetry. We propose that the C60 molecules in SWNT exhibit an unusual type of ratcheted rotation due to the interaction between C60 and SWNT in the “hexagon orientation,” and the characteristic vibrations of ratcheted rotation becomes more obvious with decreasing temperature.

Solvothermal synthesis of ZnS nanorods and their pressure modulated photoluminescence spectra

ZnS nanorods in a wurtzite structure with an average diameter of 10 nm were synthesized via a solvothermal method. In situ photoluminescence and Raman spectra measurements on the ZnS nanorods under high pressure were carried out using a diamond anvil cell. The disappearance of the photoluminescence (PL) band and longitudinal-optical (LO) phonon mode indicates that the ZnS nanorods transform to the rock salt phase near 16.7 GPa. A visible change in the pressure dependence of the full width at half magnitude for the PL band and LO phonon was found near 9 GPa, indicating that a phase transition of the ZnS nanorods from the wurtzite phase to the zinc blende phase probably occurs. High pressure can obviously modulate the PL band of the ZnS nanorods-it shifts to a long wavelength band with increasing high pressure.

Photoluminescence properties of high-pressure-polymerized C60 nanorods in the orthorhombic and tetragonal phases

C60 nanorods in two polymeric phases have been synthesized under different high pressure and high temperature conditions. Orthorhombic and tetragonal phases have been identified from Raman spectra. The rod shape can be kept under quasihydrostatic pressure. The photoluminescence intensity of the polymeric C60 nanorods has been greatly enhanced compared with that of pristine C60 nanorods. The main fluorescence band shifted from 730nm in the unpolymeric phase to 748nm and near infrared 780nm in the orthorhombic and tetragonal phases, respectively. The enhanced photoluminescence with tunable frequency for different polymeric C60 nanorods suggests potential applications in luminescent nanomaterials.

AB INITIO STUDY OF NITROGEN-DOPED CARBON NANOTUBES

Calculations have been made for carbon nanotubes containing substitutional nitrogen impurity atoms using ab initio density functional theory. It is found that the distribution of N atoms depends upon the chirality and diameter of the tube. When two nitrogen atoms are introduced into the (5, 5), (6, 6) and (7, 4) tubes, nitrogen atoms prefer to be adjacent to each other along the circumference, while they tend to be far from each other in other carbon nanotubes. As more nitrogen atoms are incorporated, they prefer to be localized, leading to the broken N–N bond and the interstice is formed in the thin tubes. However, for thick tubes, nitrogen atoms tend to distribute uniformly. It is the finding in this work that the high radial stress plays an important role in nitrogen atom distribution for the thin tubes. For thin N-doped tubes, the major contribution to the structural stabilization comes from the radial stress release after the N–N bond is broken.

Comparative study of pressure-induced polymerization of C60 nanorods and single crystals

In this paper, we report a comparative study of pressure-induced polymerization in C60 nanorods and bulk single crystals, treated simultaneously under various pressures and temperatures in the same ...