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Biomedical subjects

Chengchun Tang

Publications and source records attributed to Chengchun Tang.

At least 19 recordsLinked to original sources
PubMed2006

Unconventional zigzag indium phosphide single-crystalline and twinned nanowires.

Unconventional zigzag indium phosphide (InP) single-crystalline and twinned nanowires were produced via thermal evaporation of indium phosphide in the presence of zinc selenide. The structure and morphology of the as-synthesized products were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Studies found that two type of nanowires exist in the products, namely, the periodic-rhombus-decorated single-crystalline InP (type I) nanowires and jagged twinned InP (type II) nanowires. Both of them have preferential 111 growth directions. The optical properties were also investigated at room temperature, and they show that the nanowires display a strong emission at approximately 750 nm, which is quite different from that observed in all previous reports related to the InP nanostructures.

Journal Article↗
PubMed2006

Thermal conductivity of nanostructured boron nitride materials.

We have measured the thermal conductivity of bulky pellets made of various boron nitride (BN)-based nanomaterials, including spherical nanoparticles, perfectly structured, bamboo-like nanotubes, and collapsed nanotubes. The thermal conductivity strongly depends on the morphology of the BN nanomaterials, especially on the surface structure. Spherical BN particles have the lowest thermal conductivity while the collapsed BN nanotubes possess the best thermoconductive properties. A model was proposed to explain the experimental observations based on the heat percolation passage considerations.

Journal Article↗
PubMed2006

SnO2 nanoparticle-functionalized boron nitride nanotubes.

Boron nitride nanotubes (BNNTs) were synthesized by a carbon-free chemical vapor deposition method using boron and metal oxide as reactants. Then SnO(2) nanoparticles were functionalized on them via a simple wet chemistry method. Detailed transmission electron microscopy (TEM) observations reveal that SnO(2) nanoparticles may cover the tube surface or be encapsulated in tube channels. The lattice distances of both BNNT and SnO(2) have been changed due to the strong interactions between them. The band gap energy of SnO(2) particles is found enlarged due to the size effect and interaction with BNNTs.

Boron Compounds↗
PubMed2006

Self-organized hierarchical ZnS/SiO(2) nanowire heterostructures.

Novel hierarchical heterostructures formed by wrapping ZnS nanowires with highly dense SiO(2) nanowires were successfully synthesized by a vapor-liquid-solid process. The as-synthesized products were characterized using X-ray diffraction, scanning electron microscopy and transmission electron microscopy equipped with an energy-dispersive X-ray spectrometer. Studies indicate that a typical hierarchical ZnS/SiO(2) heterostructure consists of a single-crystalline ZnS nanowire (core) with diameter gradually decreasing from several hundred nanometers to 20 nm and adjacent amorphous SiO(2) nanowires (branches) with diameters of about 20 nm. A possible growth mechanism was also proposed for the growth of the hierarchical heterostructures.

Journal Article↗
PubMed2006

Systematic investigation of the formation of 1D alpha-Si(3)N(4) nanostructures by using a thermal-decomposition/nitridation process.

This article describes a simple thermal-decomposition/nitridation method for the large-scale synthesis of 1D alpha-Si(3)N(4) nanostructures, such as millimeter-scale microribbons, nanosaws, nanoribbons, and nanowires. These nanostructures are systematically investigated by checking the product deposited at different areas by using powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and electron energy loss spectroscopy. Studies show that all these nanostructures have a single-crystalline nature and predominantely grow along the [011] direction. These 1D nanostructures are formed by thermal decomposition, followed by the nitridation of SiO.

Journal Article↗
PubMed2006

Purification of boron nitride nanotubes through polymer wrapping.

An effective method was proposed to remove obstinate boron nitride phase impurities in boron nitride nanotubes (BNNTs). The method is based on strong interactions between BNNTs and a conjugated polymer wrapping them and significant weight and size difference between BNNTs and impurities. The as-grown samples and purified samples were compared through detailed characterization, using scanning electron microscopy, transmission electron microscopy, and Raman and Fourier transformed infrared spectroscopy. The results reveal that impurities are effectively removed and resultant BNNTs possess perfect crystallization.

Journal Article↗
PubMed2005

Immobilization of proteins on boron nitride nanotubes.

We report for the first time that proteins are immobilized on boron nitride nanotubes. It is found that there is a natural affinity of a protein to BNNT; this means that it can be immobilized on BNNT directly, without usage of an additional coupling reagent. For the most effective immobilization, noncovalently functionalized BNNTs should be used. The effect of immobilization was studied using high-resolution transmission electron microscopy and energy dispersion spectroscopy.

Boron Compounds↗
PubMed2005

Perfectly dissolved boron nitride nanotubes due to polymer wrapping.

We report for the first time that boron nitride nanotubes (BNNTs) may be dissolved in organic solvents by wrapping them with a polymer. Transmission electron microscopy and cathodoluminescence studies indicate the strong pi-pi interactions between BNNTs and the polymer. A band gap ranging from 5.2 to 5.5 eV was documented for the BNNTs independent of their geometrical characteristics by using ultraviolet-visible absorption experiments on composite films and thin BNNT films prepared from solutions.

Journal Article↗
PubMed2005

Double-helix structure in multiwall boron nitride nanotubes.

A new nanotube structural form is reported that resembles a double helix in multiwall boron nitride nanotubes (MW-BNNT) grown by a carbon-free chemical-vapor-deposition process as documented by evidence obtained by transmission electron diffraction and microscopy. The double-helix structure is found in MW-BNNTs exhibiting the same chirality in its different walls. The MW-BNNTs deviate from the structure of ideal nested coaxial cylindrical tubes. Most significantly, bright- and dark-field electron imaging reveals regular zigzag dark and bright spots on the side walls of the nanotubes. The repeating distance between the bright, or dark, spots is related to the chiral angle of the nanotube. Electron diffraction patterns recorded from individual nanotubes show additional diffraction spots belonging to the 201 zone axes, which are not allowed in a perfectly cylindrical nanotube. These additional diffraction spots become asymmetrical as smaller sections of the nanotube are probed. A series of diffraction patterns recorded along the tube axis showed that the imperfections giving rise to these spots move in a regular fashion around the circumference of the tube. It is shown that all experimental evidence supports the structure model of two helices; one is polygonal in cross section and highly crystalline and the other is circular and less ordered. It is further suggested that the double-helix structure is a result of stronger wall-wall interactions associated with the ionic bonding in boron nitride.

Journal Article↗
PubMed2005

Needlelike bicrystalline GaN nanowires with excellent field emission properties.

Large-yield and crystalline GaN nanowires have been synthesized on a Si substrate via a simple thermal evaporation process. The majority of the GaN nanowires has bicrystalline structures with a needlelike shape, a triangular prism morphology, and a uniform diameter of approximately 100 nm. Field-emission measurements show that the bicrystalline GaN nanowires with sharp tips have a lower turn-on field of approximately 7.5 V/microm and are good candidates for low-cost and large-area electron emitters. It is believed that the excellent filed emission property is attributed to the bicrystalline structure defects and sharp tips.

Journal Article↗
PubMed2005

Fluorination and electrical conductivity of BN nanotubes.

Fluorination of BN nanotubes has been performed using a catalytic growth method, which leads to the appearance of markedly curved fluorine-doped BN sheets and converts originally insulating BN nanotubes to semiconductors, as confirmed by the comparative electron transport four-probe measurements on doped and undoped individual BN nanotubes.

Journal Article↗
PubMed2005

Synthesis of SiC nanowires with in-situ deposition of carbon coating.

SiC nanowires are effective reinforcement materials in ceramic matrix composites. A compliant coating such as carbon on nanowires is necessary in order to moderate the nanowire/matrix interfacial bounding for taking the most advantages of SiC nanowires. SiC nanowires with an in-situ deposition of carbon shell coating were fabricated by a novel chemical vapor growth process. Highresolution transmission electron microscopy examinations showed that the nanowires consisted of a single crystal beta-SiC core with an amorphous carbon shell 2-5 nm in thickness. The nanowires were straight with a length generally over 10 microm and a diameter 15-150 nm. The growth direction of the core SiC nanowires is (111). A simple three-step growth model for SiC nanowires was proposed based on a vapor-solid growth mechanism. Because the carbon-coated nanowires were grown directly on continuous Tyranno-SA SiC fibers, in-situ application of the present technique on the fabrication of SiC nanowire-reinforced SiC/SiC composites is expected.

Carbon↗
PubMed2002

Catalyzed collapse and enhanced hydrogen storage of BN nanotubes.

The novel morphology of BN nanotubes with a collapsed structure has been discovered by a metal-catalyzed treatment. The collapse causes the dramatic enlargement of a specific surface area of BN nanotubes and remarkably enhances the hydrogen storage capacity of BN nanotubes.

Journal Article↗
PubMed2002

Large-scale synthesis and structure of boron nitride sub-micron spherical particles.

A novel method, combining chemical vapor deposition and pyrolysis of trimethoxyborane under ammonia atmosphere, has been developed to synthesize spherical boron nitride particles with a uniform diameter distribution from 50 to 400 nm; chemical composition and high-resolution transmission electron microscopy analyses indicate that the sub-micron boron nitride particles exhibit a slightly distorted arrangement of the shell layers.

Journal Article↗