Biomedical subjects

Z F Ren

Publications and source records attributed to Z F Ren.

11 recordsLinked to original sources

PubMed2006

Shape control of single crystalline bismuth nanostructures.

A synthesis approach for shape control of single crystalline Bi nanostructures has been developed. By controlling the molar ratio of PVP and Bi in a polyol process, Bi nanocubes with an edge length of approximately 60-80 nm, triangular nanoplates with an edge length of 200-500 nm, and nanospheres with an average diameter of 75 nm have been successfully synthesized. In the same synthetic process, Bi nanobelts with lengths of up to 80 microm and widths of up to 0.6 microm were synthesized in large quantities by introducing a trace amount of Fe3+ species into the reaction system. These single crystalline nanostructure Bi materials are expected to find potential applications in a variety of areas including high efficiency thermoelectric devices.

Journal Article↗

PubMed2006

Kink formation and motion in carbon nanotubes at high temperatures.

We report that kink motion is a universal plastic deformation mode in all carbon nanotubes when being tensile loaded at high temperatures. The kink motion, observed inside a high-resolution transmission electron microscope, is reminiscent of dislocation motion in crystalline materials: namely, it dissociates and multiplies. The kinks are nucleated from vacancy creation and aggregation, and propagate in either a longitudinal or a spiral path along the nanotube walls. The kink motion is related to dislocation glide and climb influenced by external stress and high temperatures in carbon nanotubes.

Journal Article↗

PubMed2006

Superplastic carbon nanotubes.

The theoretical maximum tensile strain--that is, elongation--of a single-walled carbon nanotube is almost 20%, but in practice only 6% is achieved. Here we show that, at high temperatures, individual single-walled carbon nanotubes can undergo superplastic deformation, becoming nearly 280% longer and 15 times narrower before breaking. This superplastic deformation is the result of the nucleation and motion of kinks in the structure, and could prove useful in helping to strengthen and toughen ceramics and other nanocomposites at high temperatures.

Journal Article↗

PubMed2006

Real-time observation of tubule formation from amorphous carbon nanowires under high-bias Joule heating.

The tubule formation process from amorphous carbon nanowires under high-bias-caused Joule heating was observed in real time in a high-resolution transmission electron microscope. The crystallization of the amorphous carbon nanowires occurred in two distinct ways: the formation of tubular graphitic basal planes parallel to the nanowire axis on the surface and the formation of nano-onions in the interior of the nanowire. The tubule formation mechanism is a process of solid-state atom diffusion at high temperatures. Energetically, the tubule formation is caused by the exceptionally low surface energy of the (0002) plane of graphite. Higher input power to the amorphous nanowires generally leads to improved graphitization and, in turn, to increased conductance. The results suggest that nanotube formation in the arc-discharge growth process may involve the formation and crystallization of amorphous carbon.

Computer Systems↗

PubMed2006

Broadband ZnO single-nanowire light-emitting diode.

We present a novel technique for reliable electrical injection into single semiconductor nanowires for light-emitting diodes and lasers. The method makes use of a high-resolution negative electron-beam resist and direct electron-beam patterning for the precise fabrication of a metallic top contact along the length of the nanowire, while a planar substrate is used as a bottom contact. It can be applied to any nanowire structure with an arbitrary cross section. We demonstrate this technique by constructing the first zinc oxide single-nanowire light-emitting diode. The device exhibits broad sub-bandgap emission at room temperature.

Electrochemistry↗

PubMed2006

Shape evolution of lead telluride and selenide nanostructures under different hydrothermal synthesis conditions.

Face-open nanoboxes of lead telluride and selenide have been synthesized by a simple hydrothermal method. Nano- and microcrystals of various morphologies, including microflowers, semi-microflowers, cubic nanoparticles, etc., have also been observed at different synthesis conditions. Temperature, time, and concentrations of various reactants play a major role in controlling the morphology and shape evolution of the product. This simple synthesis technique for the growth of various nano- and microstructures opens a new route to prepare hierarchical structures of a variety of binary semiconducting materials in a large quantity. A possible growth mechanism of such nano- and microstructures has been proposed.

Crystallization↗

PubMed2006

High throughput growth of zinc oxide nanowires from zinc powder with the assistance of sodium chloride.

Sodium chloride (NaCl) was found to be very helpful in producing single crystal zinc oxide (ZnO) nanowires in gram quantities. The growth involves heating the mixture of zinc powder and NaCl to 600-700 degrees C in flowing gases of oxygen and argon. A conversion efficiency of 70-80% (Zn to ZnO) was achieved when NaCl was used, and 5-10% without NaCl. The NaCl was completely removed by soaking and rinsing the mixture in water a few times. Photoluminescence spectra using excitation of 325 nm showed a very strong emission only in the visible frequency range, indicating that the surface states dominate the emission.

Crystallization↗

PubMed2005

Synthesis of multiwalled carbon nanotubes through a modified Wolff-Kishner reduction process.

We report the synthesis of highly crystallized multiwalled carbon nanotubes through a modified Wolff-Kishner reduction process at a low temperature of 180 degrees C without adding the conventional catalysts of Fe/Co/Ni into the reaction vessel. The as-synthesized carbon nanotubes are about 10-40 nm in diameter and several tens of micrometers in length. The experimental results indicate that a high concentration of NaOH is essential to the formation of carbon nanotubes. This technique opens a new route for the synthesis of CNTs and other carbon nanostructured materials.

Journal Article↗

PubMed2005

High-yield synthesis of single-crystalline antimony telluride hexagonal nanoplates using a solvothermal approach.

We report a high-yield synthesis of single-crystal hexagonal Sb2Te3 nanoplates using a solvothermal approach. The experimental results show that the concentration of capping agent CTAB played a key role in the formation of nanoplates. This new nanostructure may provide opportunity for the exploration of novel thermoelectric properties and have potential applications in thermoelectric nanodevices.

Alloys↗

PubMed2005

Atomic-scale imaging of wall-by-wall breakdown and concurrent transport measurements in multiwall carbon nanotubes.

We report the atomic-scale imaging with concurrent transport measurements of the breakdown of individual multiwall carbon nanotubes inside a transmission electron microscope equipped with a piezomanipulator. We found unexpectedly three distinct breakdown sequences: namely, from the outermost wall inward, from the innermost wall outward, and alternatively between the innermost and the outmost walls. Remarkably, a significant amount of current drop was observed when an innermost wall is broken, proving unambiguously that every wall is conducting. Moreover, the breakdown of each wall in any sequence initiates in the middle of the nanotube, not at the contact, proving that the transport is not ballistic.

Journal Article↗

PubMedDate not supplied

Loss of heterozygosity and its correlation with clinical outcome and Epstein-Barr virus infection in nasopharyngeal carcinoma.

Sixty-one human nasopharyngeal carcinomas (NPC) were examined by allelotype analysis for the purposes of detecting potential association between loss of heterozygosity (LOH), clinicopathological parameters and Epstein-Barr virus (EBV) infection. LOH was performed using 257 polymorphic markers on 22 chromosomes. High frequency LOH (> or = 60%) was observed on 12 chromosome arms including 1p, 2p, 2q, 3p, 3q, 5q, 9p. 9q, 11q, 13q, 14q and 17q, with the highest LOH frequency of 91% on 3p. Seventy-three loci presented LOH frequency > or = 30%; most of these loci clustered on 1p36 p34, 2p25-p24, 3p14-p21, 3p24-p26, 5q11-q14, 5q31-q33, 9p21-p23, 9q33-q34, 11q23-q25, 13q12 q14, 13q31-q33, 14q13-q11, 14q32 and 19q13. On 1p36-p34, 2p25-p24, 5q13-q11, 5q31-q33 and 19q13 are reported for the first time. LOH was correlated with specific clinicopathological parameters including tumor T-stage, N-stage, TNM-stage, tumor differentiation and serum antibody titers of IgA against virus capsid antigens (VCA) and early antigen (EA) of EBV in NPC (LOH frequency > or = 30%). Significantly high LOH frequency was observed on 9p21 (56%) and 19q13 (50%) in NPC with stage T3+T4, while significantly higher LOH frequency was observed on 12p11 (65%) in NPC with stage T1 + T2. Significantly higher LOHfrequency on 19q13 was also observed in NPC with advanced TNM-stage (III+IV). High fractional allelic loss (FAL) value and high antibody titers of EBV IgA/VCA and/or IgA/EA were significantly correlated with T3 + T4-stage, distant lymph node metastasis and advanced TNM-stage of NPC. We also found that NPC patients with high titers of IgA/VCA and IgA/EA showed high LOH frequency on 16q (48%) and 19q13 (48%). These results suggest that LOH on 9p21, l6q and 19q13 may be responsible for the aggressiveness and progression of NPC; there may be an interaction between allelic loss and EBV infection in the etiology of NPC. High frequency of LOH on 4q21 and 14q11-q12 were alsofound to be correlated with WHO type III NPC histopathology, suggesting that LOH on these regions may cause poor NPC differentiation. Our data also may be useful for the development of a NPC molecular staging system, a system which may augment the use of clinical pathological features in the diagnosis and prognosis of this disease.

Adult↗