Magnetoresistance and Differential Conductance in Multiwalled Carbon Nanotubes
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Soluble CdS and CdSe Nanorods Synthesized Some potential practical applications of semiconductor nanorods—for example, optoelectronic light-emitting diodes for nanowires—require the fabrication of nanorods with precisely specified aspect ratios (length/diameter). However, no method has been reported so far for the synthesis of colloidal semiconductor rods with a narrow distribution of aspect ratios. Researchers at National Taiwan Normal University have synthesized water-soluble crystalline nanorods of CdS and CdSe by using micellar templating in which the shapes of the templates are controlled by the addition of cyclohexane to a micelle suspension. As reported in the July 2000 issue of Chemistry of Materials, the micelle suspensions were formed by the dissolution of CTAB (CH3(CH2)15N(CH3)3Br) in deionized water. Metal and chalcogenide precursors (CdCl2, Na2S, or Na2Se) were then added to form two precursor suspensions. The researchers added various amounts of cyclohexane (0–0.1% by volume) to these suspensions, followed by sonication. They slowly added the chalcogenide suspensions to the metal suspensions, and the resulting mixture was sonicated and centrifuged to separate out the suspended product. Transmission electron micrographs
Review Articles The April 21 issue of Science features the following review articles on Correlated Electron Systems: Y. Tokura and N. Nagaosa, “Orbital Physics in Transition-Metal Oxides”; J. Orenstein and A.J. Millis, “Advances in the Physics of High-Temperature Superconductivity”; S. Sachdev, “Quantum Criticality: Competing Ground States in Low Dimensions”; and P.W. Anderson, “Sources of Quantum Protection in High-T c Superconductivity.” The July issue of Reviews of Modern Physics contains the following review articles: J.J. Rehr and R.C. Albers, “Theoretical Approaches to X-ray Absorption Fine Structure”; H. Feldmeier and J. Schnack, “Molecular Dynamics for Fermions”; S. Hofmann and G. Münzenberg, “The Discovery of the Heaviest Elements”; J.E. Sonier, J.H. Brewer, and R.F. Kiefl, “muSR Studies of the Vortex State in Type II Superconductors”; J.-L. Viovy, “Electrophoresis of DNA and Other Polyelectrolytes: Physical Mechanisms.”
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showed that the reaction products consist of crystalline nanorods as well as spherical and irregularly shaped nanocrystalline materials. The TEM images revealed CdSe and CdS samples with the mean aspect ratios of ~6. A high-resolution TEM image of the CdS nanorods showed an average diameter of ~9 nm. Although further work is needed, the results suggest that rod aspect ratio increases with increasing amounts of added cyclohexane. HRTEM images indicated that CdS and CdSe nanocrystals have wurtzite and zincblende structures, respectively. Selectedarea dispersive x-ray studies of the CdS nanocrystals showed a Cd:S ratio of 1:1. The addition of cyclohexane is thought to affect the shapes of the micelles and, therefore, the nanocrystals that form inside them. While the exact role of the hydrocarbon is not known, according to the researchers, one possibility is t
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