In Situ Soldering Attaches Nanotubes to Electrodes
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RESEARCH/RESEARCHERS Template-Grown Ni-Cu Nanowires Show High Magnetization and Enhanced Coercivities Magnetic nanoparticles and their potential applications have received increasing attention in recent years. Nanoscale particles of ferromagnetic elements are the size of single magnetic domains and exhibit high coercivities relative to the bulk metals, making them candidates for use in memory devices. However, current methods of assembling ordered arrays of nanoparticles for inclusion in devices are not cost-effective. As reported in the February 11 issue of Chemistry of Materials, a group of researchers at the Chinese Academy of Sciences has prepared an ordered array of Ni-Cu composite nanowires by using a facile template-based method. The nanowires exhibit the same desirable properties as arrays of simple nanoparticles. Yu-Guo Guo and co-workers used anodic aluminum oxide (AAO) membranes with well-defined arrays of columnar pores as templates for nanowire growth. The templates were immersed in
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a solution of copper sulfate and nickel sulfate, and the plating potential was pulsed in order to fill the pores with alternating layers of Ni and Cu. The AAO membrane was then dissolved, leaving behind an ordered array of nanowires, as confirmed by transmission electron microscopy. Magnetic force microscopy revealed that each Ni segment behaved as a single magnetic domain, and that the magnetization direction was the same for all segments in the wire. The coercivity for an array of nanowires was found by superconducting quantum-interference device measurements to be ~490 Oe, compared with 0.7 Oe for bulk Ni. The researchers said that the saturation magnetization was comparable to that of the bulk metal. Arrays of magnetic nanowires had previously been grown within AAO membranes, but the single-domain structure seen in nanoparticles was lost, and the coercivity was accordingly much lower. The researchers concluded that alternating segments of ferromagnetic Ni with nonferromagnetic Cu within the nanowire preserves
TheJanuary January2003 2003issue issueof ofReviews ReviewsofofModern ModernPhysics Physics75 75(1) (1)(partial (partialissue) issue)contains contains The the following following review review articles: articles: W.G. W.G. van van der der Wiel, Wiel, S. S. De De Franceschi, Franceschi, J.M. J.M. Elzerman, Elzerman, the T. Fujisawa, Fujisawa, S. S. Tarucha, Tarucha, and and L.P. L.P. Kouwenhoven, Kouwenhoven, “Electron “Electron Transport Transport through through T. Double Quantum Quantum Dots,” Dots,” p. p. 1; 1; and and J.R. J.R. Banavar Banavar and and A. A. Maritan, Maritan, “Colloquium: “Colloquium: Double GeometricalApproach Approachto toProtein ProteinFolding: Folding:A ATube TubePicture,” Picture,”p. p.23. 23. Geometrical The Journal Journal ofof Applied Applied Physics Physics 93 93 (2) (2) (2003) (2003) contains contains D.G. D.G. Cahill, Cahill, W.K. W.K. Ford, Ford, K.E. K.E. The Goodson, G.D. G.D. Mahan, Mahan, A. A. Majumdar, Majumdar, H.J. H.J. Maris, Maris, R. R. Mer
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