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1258-Q04-14

Template-Assisted Growth of Tungsten Oxide Nanorods on Substrates and Their Electrochemical Properties Sun Hwa Park1,2, Jae Yong Song1,2, Hyun Min Park1,2and Hyunung Yu2 1 University of Science and Technology, Daejeon 305-333, Republic of Korea 2 Korea Research Institute of Standard and Science, Daejeon 305-340, Republic of Korea * To whom correspondence should be addressed: [email protected] ABSTRACT Tungsten oxide nanorods (TONs) with the diameters of 40 nm and the length of 130 nm have been synthesized on substrates using two step electrochemical anodizing processes. The TONs were vertically well-ordered on the substrates with the average interdistance of 100 nm. The TONs had amorphous structure and was mainly composed of W, Al, and O elements, of which the contents varied gradually along the nanorod length from the top surface to the bottom. The cyclic voltammograms (CVs) and galvanostatic charge-discharge analyses showed that TONs had the typical electrochemical pseudocapacitive features of rectangular CV hysteresis and symmetric charge-discharge behaviors, respectively. When the TONs were heat-treated at 600℃ in vacuum, they showed the maximum specific capacitance of 660 ㎌/cm2, which was higher, by an order of magnitude, than that (68 ㎌/cm2) of the TONs annealed at 300 ℃ in ambient atmosphere. INTRODUCTION In past decades, nanostructured semiconducting materials have attracted great attention due to their unusual physical properties, such as mechanical, electrical and optical properties, coming from the dimensional confinement effect [1]. Among them, tungsten oxides with amorphous or crystalline structures have been widely studied for the applications to electrochromic devices, electrochemical capacitors, and gas sensing devices [2-4]. The functional properties of tungsten oxides are affected by their morphologies, crystal structures and chemical compositions. Many researchers have investigated the nanostructured materials with high specific surface area for the applications to the anodic and cathodic electrodes of batteries and capacitors [5-7]. Recently, several researchers have synthesized the tungsten oxide nanowires using chemical vapor deposition, which were randomly grown on substrates [8, 9]. More recently, Mozalev et al. reported that TONs array with highly ordered structure can be vertically synthesized on substrate [10] and Huang et al. [3] showed that the amorphous tungsten oxides have good cycling performance as well as high volumetric capacitances [2]. In this study, we were motivated to study if the tungsten oxide nanorods, which were vertically well-ordered on substrates, could be used as an efficient pseudocapacitor. We have investigated the effects of heat treatment conditions on the electrochemical properties of the TONs. EXPERIMENT Thin film structures of Al(Nd)/W/Ti on Si substrates were in-situ deposited using a home-made sputtering deposition machine. The thicknesses of Al(Nd), W, and Ti films were controlled to be 200, 80, 20 nm, respectively, as shown in Fig.1(a). After d