Patterned Micro/ Nanowires by Electroplate and Lift Lithography on Reusable Ultrananocrystalline Diamond Template
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Patterned Micro/ Nanowires by Electroplate and Lift Lithography on Reusable Ultrananocrystalline Diamond Template Jeffrey Machovec,1 Lori A. Lepak,1 Anirudha V. Sumant,2 Ralu Divan,2 C. Suzanne Miller,2 Daniel Rosenmann,2 and Michael P. Zach*1 1 Chemistry Department, UW-Stevens Point, Stevens Point, WI 54481 2 Center for Nanoscale Materials, Argonne National Laboratory, Argonne, IL 60439 ABSTRACT Patterned micro- and nanowires composed of Iron Oxide (FexOy) were electrochemically deposited from an ionic liquid solution of choline chloride (ChCl) and urea, using ultrananocrystalline diamond (UNCD) TM templates originally developed for Electroplate and Lift (E&L) Lithography. The wires were electroplated under varying rigor of anhydrous and inert atmosphere techniques, at voltages of either -2V or -5V vs. an Al/Al(III) reference electrode. The morphology of the deposited FexOy wires was studied by scanning electron microscopy (SEM), while their oxygen content was evaluated using energy dispersive spectroscopy (EDS). By using sublimed grade reagents and minimizing exposure to atmospheric water vapor and oxygen, the oxygen content of the electroplated wires decreased from 15 at% to 5 at%. INTRODUCTION Iron and its oxides are inexpensive materials, which hold great promise for many potential nanowire applications. Metallic iron may serve as a catalytic substrate for the growth of other advanced electronic materials such as graphene and carbon nanotubes [1]. Iron wires encapsulated by carbon nanotubes possess, in essence, a surface chemical passivation which preserves their magnetic properties, making them useful for applications as diverse as tissuespecific drug delivery and probe tips for magnetic force microscopy (MFM) [2]. Iron oxide wires have been studied for use in gas sensing, photocatalysis, solar cells, and lithium ion intercalation in batteries [3]. Iron oxide nanoparticles are also known to nucleate diamond growth [4]. Diamond-coated iron oxide microwires may be of particular interest for use as electrodes in biological applications. Diamond is an almost perfect biocompatible coating, which does not excite an inflammatory response either in vitro or in vivo.[5] Such electrodes could be used to either measure or electrically stimulate individual living cells. However, a major challenge in the synthesis of iron nanowires is that they oxidize rapidly, particularly in an aqueous environment. Fortunately, many potential iron-containing synthetic precursors are soluble in nonaqueous solvents known as ionic liquids. Ionic liquids are organic salts, typically with melting points near or even below 100 °C. Since they are made entirely of ions, ionic liquids are generally good solvents for both water-stable and water-reactive metals, and are highly electrically conductive. In addition, most ionic liquids are thermally stable up to their temperature of combustion (typically ~ 200 oC), and electrochemically stable across a wider range of applied voltages than water. These properties make ionic liquids outstanding electrol
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