Synthesis of Magnetic Self-Assembled Nickel-Rich Oxide Nanowires Using a Novel Electrochemical Process
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Synthesis of Magnetic Self-Assembled Nickel-Rich Oxide Nanowires using a Novel Electrochemical Process Yash V. Bhargava1, Shawn A. Thorne1, Todd S. Mintz1, Tzipi Cohen Hyams1, Velimir Radmilovic2, Yuri Suzuki1, Thomas M. Devine1 1
Department of Materials Science and Engineering, 210 Hearst Memorial Mining Building, University of California, Berkeley, Berkeley, California 94720 2 National Center for Electron Microscopy, Lawrence Berkeley National Laboratory 1 Cyclotron Road, Berkeley, California 94720 Abstract We present a novel self-assembly nanowire synthesis technique capable of producing nickelrich oxide nanowires of lengths up to 20µm and diameters as small as 5nm. The method was discovered while examining the oxidation of Alloy 600 (nickel- 15.5a/o Cr, 8a/o Fe) in a pressurized water reactor environment. The nanowires have been grown on substrates of Alloy 600 and other nickel-chromium substrates exposed to oxidizing conditions in 1500psi pressurized water with 2ppm lithium and 1200ppm boron at temperatures ranging from 238oC to 288oC. Oxidizing conditions can be controlled in one of two ways: by controlling the aqueous solution’s dissolved oxygen concentration, or by use of a potentiostat. Compositional studies performed via energy dispersive spectroscopy (EDS) using a transmission electron microscope (TEM) indicate the content of the nanowires grown on Alloy 600 to be 49a/o oxygen, 47a/o Ni, and 4a/o Fe. Preliminary TEM analysis has revealed the nanowires to be single crystalline with an aspect ratio up to 1000:1. The nickel-rich oxide nanowires are particularly exciting because of their functional properties. The oxide composition of the nanowires gives them an inherent resistance to electrochemically aggressive environments, such as ones found in the body or many other aqueous solutions, in contrast to simple metal nanowires, which are susceptible to corrosion in such environments. Most importantly, analysis with a superconducting quantum interference device (SQUID) magnetometer indicates that the nickel-rich oxide nanowires are ferromagnetic with a coercivity of approximately 85Oe and a remnant field of 0.032emu/g at 300K. Introduction With the set of properties they have to offer, nanowires present an exciting opportunity at the forefront of miniaturization and development of new devices. Nanowires also offer means of investigating the effects of dimensionality on electrical, magnetic, and transport properties of materials [1]. Recently, nanowires have been utilized as chemical and biological sensors [2-4], nanolasers [5], and as interconnects in integrated circuits [6]. Magnetic nanowires are particularly important because magnetic behavior can be significantly altered at the nanoscale dimensions due to increased importance of the size of the grain, domain wall width, and exchange length [7]. To date nanowires of different materials have been fabricated using techniques such as vapor phase transport processes, chemical vapor deposition, laser ablation, and solution and template-based methods [8-
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