Software Package Performs Molecular Dynamics Simulation with Over 5 Billion Particles
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Au, Ag, and Pt Nanowires Produced in Mesoporous Silica Metal nanowires with tunable diameters below 10 nm have been intensively studied because they provide an excellent platform for investigation of the fundamental physics of nanowires and have potential applications in electro-optic chip devices. Professor Galen D. Stucky, postdoctoral associate Ji Man Kim, and graduate student Yong-Jin Han at the Department of Chemistry and Biochemistry at the University of California—Santa Barbara have introduced a method for the synthesis of such nanowires. The researchers produced Au, Ag, and Pt nanowires by reduction of the corresponding metal salts loaded into the pores of the mesoporous silicate template SBA-15. SBA-15 is characterized by large surface area; variable pore diameter (4–30 nm); a well-ordered, hexagonal array of pores; and long-range order. The resulting nanowires were 7 nm in diameter and 50 nm–1 µm in length. Free nanowires produced by dissolution of the template had an average length of 0.5 µm and retained the 7 nm diameter. 6
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As reported in the August issue of Chemistry of Materials, SBA-15 with 7 nm diameter pores was loaded with precursors by immersion in an appropriate aqueous salt solution followed by drying and treatment with methylene chloride to force the outer surface bound precursors into the channels of the SBA-15. The loaded template was then dried in a vacuum oven, and the Au, Ag, and Pt salts reduced under continuous hydrogen flow at 393, 623, and 593 K, respectively. The SBA-15 was dissolved with HF/H2O/ethanol to obtain free nanowires. Longer nanowires can be obtained by varying the degree of template loading and the annealing temperature. Thicker nanowires can be prepared by using SBA-15 with a larger pore diameter. The researchers said that x-ray diffraction studies of the metal/SBA-15 samples demonstrate the formation of reduced metals with a 2D hexagonal structure and excellent textural uniformity. The pres-
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of Electrochemical and Solid-State Letters by collaborators at National Chiao-Tung University and National Nano Device Labs, Taiwan, and University of Illinois at Urbana-Champaign. This metal-oxide dielectric was formed using direct oxidation of sputtered Co/Ti films. Samples were fabricated on p-type (100)oriented silicon wafers. First, an ultrathin, ~10 Å-buffered layer of either Si-N or Si3N4 was formed to improve the interfacial quality. The former was created by growing a nitrided oxide on silicon, while the latter by NH3-nitridization. Afterwards, the 50-Å Ti and Co films were deposited using the sputtering method, then direct thermal oxidation was conducted at 700 or 800°C in diluted O2 gas, and annealed in N2 gas ambient. Finally, a gate electrode of aluminum film was deposited on the wafer by a thermal coater. X-ray diffraction analysis shows that NH3-nitridization can suppress the diffusion of the metal, resulting in a pure CoTiO3 phase, as also exhibited by transmission electron microscope cross-sectional analysis. The effective dielectric constant of Co
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