BENSON ET AL. VOL. 6 ’ NO. 1 ’ 118 –125 ’ 2012 www.acsnano.org 118 December 13, 2011 C 2011 American Chemical Society Chemical Vapor Deposition of Aluminum Nanowires on Metal Substrates for Electrical Energy Storage Applications James Benson, † Sofiane Boukhalfa, † Alexandre Magasinski, † Alexander Kvit, ‡ and Gleb Yushin †, * † School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, United States and, ‡ Materials Science Center & Materials Science Department, University of Wisconsin, Madison, Wisconsin 53706, United States P otential use of metal nanowires (NWs) is rapidly growing. Earlier studies of metal NWs were largely motivated by fundamental studies of the effects of con- strained dimensions on electrical and ther- mal conductivities in one-dimensional (1D) conductors 13 and magnetic properties of transition metals. 46 The size-dependent breakdowns of superconductivity in small diameter NWs draw a particular interest in the past decade. 13 Other important potential applications include sensors, 7 ultra-high-density magnetic recording and spintronics, 8 interconnects, 9 transparent current collectors (charge collectors) for touch screens and organic solar cells, 10 catalysis, 11,12 fuel cells, 12 active anodes for Li-ion batteries, 13,14 hydrogen storage, 15 current collectors for Li-ion batteries, 16,17 supercapacitors, 18,19 and capacitors. 20 Currently, conductive carbon nanotubes (CNTs) mass-produced by chemical vapor deposition (CVD) are explored in some of the discussed above applications. However, the CNT structure suffers from the lack of surface sites available for the formation of chemical bonds with the deposited functional layers (such as metal oxide coatings). 1620 While surface oxidation of multiwalled CNTs allows for the formation of defects and carboxylic surface groups on their outer walls, the concentration of the functional groups on a CNT surface is sig- nificantly smaller than what is available on the metal surfaces. As a result, the quality of a CNT/metal oxide interface is generally in- ferior to that of a metal/metal oxide one. 21 More importantly, due to the low concentra- tion of free electrons in the CNT, the dc electrical conductivity of the CNT is orders of magnitude smaller than that of Cu, Al, Au, or Ag. Therefore, for most applications re- quiring high surface area conductors 9,1620 with low resistance and high concentration of bonding cites on their surface, NWs of low- cost lightweight highly conductive metals (such as Al) may provide superior perfor- mance than CNTs. The most common route for synthesis of metal NWs is electrodeposition. 17,16,17 The use of porous alumna templates attached to the conductive substrate surface has be- come a routine approach for the growth of aligned NWs. 13,16,17 The slow deposition rate and the need of tubular templates, how- ever, prevent large-scale commercial synthe- sis of metal NWs using electrodeposition approaches. Several promising wet chemistry approaches have also been explored for * Address correspondence to yushin@gatech.edu. Received for review August 5, 2011 and accepted December 13, 2011. Published online 10.1021/nn202979y ABSTRACT Metal nanowires show promise in a broad range of applications, but many synthesis techniques require complex methodologies. We have developed a method for depositing patterned aluminum nanowires (Al NWs) onto Cu, Ni, and stainless steel substrates using low- pressure decomposition of trimethylamine alane complex. The NWs exhibited an average diameter in the range from 45 to 85 nm, were crystalline, and did not contain a detectable amount of carbon impurities. Atomic layer deposition of 50 nm of vanadium oxide on the surface of Al NW allows fabrication of supercapacitor electrodes with volumetric capacitance in excess of 1400 F 3 cc 3 , which exceeds the capacitance of traditional activated carbon supercapacitor electrodes by more than an order of magnitude. KEYWORDS: nanowires . chemical vapor deposition . double layer capacitors . supercapacitors . organic electrolytes ARTICLE