Charge Transfer across Nanocrystalline Metal Oxide/DNA Interfaces Enables DNA Recognition
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gen atoms—mathematical entities that assign the surface atoms the same reactivity as that of a real nanoparticle in suspension. The positions of the interior atoms were calculated with the valence force field method, which models the strength, elasticity, and direction of bonds among atoms. Then LDA was used to determine the charge “motifs” around a number of representative atoms, including the surface pseudohydrogens. Through charge patching, the calculation is extended to include the entire nanostructure. In a final step, a “folded spectrum” method that Wang developed 10 years ago is used to determine the material’s electronic states near the bandgap, including the highest energy state of the valence band and the lowest energy state of the conduction band (see Figure 1b). Mapping the ways different compounds are assembled into different structures reveals the structures’ optical and electronic properties. Wang said, “The charge-patching method allows us to model thousandatom structures with ab initio accuracy in about one hour.”
uniform diameters were grown on the substrate after several hours of reaction for substrate temperatures between 850–1050°C. The diameter of the nanowires is in the rang0e of 30–150 nm and the length is 1–10 µm. The researchers said that the dimensions of the nanowires can be manipulated by growth time, substrate temperature, and BI3/H3BO3 vapor concentration. Each nanowire usually has a Pt/Pd nanoparticle attached to its end, suggesting a vapor–liquid–solid growth mechanism. Electrical transport measurement on a single nanowire indicates that the Mg2B2O5 is a semiconductor at room temperature, and its bandgap is 5.44 eV, according to theoretical calculation. Based on the high purity and controllable growth of Mg2B2O5 nanowires this experiment demonstrates, the researchers said, “Metal borate nanowires can be synthesized by introducing boron and boron oxide sources to a metal oxide substrate coated with a thin film of some catalyst.“ SHIMING WU
High Purity and Controllable Growth of Mg2B2O5 Nanowires Accomplished by CVD
Plasma-sprayed yttria-stabilized zirconia (YSZ) is commonly used as a thermal barrier coating. It produces coatings with a microstructure containing high porosity and microcracks that will have an effect on the mechanical behavior of the material. As reported in the May issue of the Journal of the American Ceramic Society (p. 960), J.P. Levin, G.R. Dickinson, and R.W. Trice at Purdue University observed in situ the microstructure evolution of a plasmasprayed YSZ stand-alone tube under incremental compressive load while simultaneously viewing it in a scanning electron microscope (SEM). They found that cracks oriented parallel to the loading direction have opened, while cracks oriented perpendicular to the applied stress have partially closed. They also observed that new cracks nucleated and then propagated parallel to the direction of the applied load. Previous observations indicated that plasma spraying forms a microstructure dominated by lamellae with significant poros
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