Arrayed ZnO Nanorods Fabrication on ZnO Film by Self-catalyst Growth Method in Aqueous Solution
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Arrayed ZnO Nanorods Fabrication on ZnO Film by Self-catalyst Growth Method in Aqueous Solution E. K.C. Pradeep1, X. Li1, T. Kawaharamura1, D.Wang2, A. Hatta1, C. Li1* 1
Institute for Nanotechnology, Kochi University of Technology, Kami city, Kochi 782-8502, JAPAN 2 Department of Environmental Science and Engineering, Kochi University of Technology, Kami city, Kochi 782-8502, JAPAN ABSTRACT ZnO nanorods were grown up from as-deposited ZnO film on which the zinc self-catalysts generated by a novel reducing method. Well aligned ZnO nanorods with a uniform high aspect ratio were grown up on multi-annealed samples. The length of nanorods depended significantly on the reaction time in the hydrothermal synthesis. INTRODUCTION ZnO has received a very high attention from different research groups around the world, owing to its chemical, physical, and electrical properties. ZnO is an amphoteric material having a direct wide band gap (3.37 eV), and high exciton binding energy (60 meV), and it can be prepared with a good crystallinity [1,2]. Recently, ZnO nanostructures including nanorods, and nanowires have been widely experimented to be used in dye sensitized solar cells [3], ZnO-polymer hybrid LEDs [4], photo catalysts [5] and piezoelectric generators [6]. Various physical and chemical methods have been used to fabricate one-dimensional arrays of ZnO nanostructures [7-10]. Some of physical methods, such as, chemical vapor deposition [11], pulsed laser deposition [12] and molecular beam epitaxy [13] are less attractive, comparing to chemical methods [8], due to the requirement of high temperature and vacuum processes. Electrodeposition and hydrothermal synthesis are low cost ecofriendly chemical fabrication methods [9,14]. However, the application of electrodeposition method is limited to conductive substrates. Therefore, the hydrothermal synthesis has become one of most popular synthetic methods for one-dimensional ZnO nanostructure fabrication [15]. Most of hydrothermal synthesis methods for ZnO nanostructure fabrication require catalyst assistance [16]. Transition metals are commonly used as catalysts [17,18], and those catalytic seeds contaminate nanostructures [19]. Up to date, there are a few reports for growingwell arrayed ZnO nanostructures with a catalyst free or self-catalyst growth method. In this work, a novel self-catalyst growth hydrothermal method for arrayed ZnO nanorod fabrication is demonstrated. The obtained nanorods were fabricated on a transparent conductive oxide glass substrate are expected to be used as the photo-anodes of dye sensitized solar cells (DSSCs) in future experiments. EXPERIMENTAL DETAILS Double layered ZnO films (150nm/25nm) were deposited on Indium-Tin-Oxide (ITO) glass substrates using a conventional 13.56 MHz radio frequency (RF) magnetron sputtering
system. The RF power of the system was 180 W. A 4-inch ZnO (99.999%) ceramic target was located on a cathode 60 mm distance from a substrate stage. The sputtering chamber was evacuated up to about 6×10−5 Pa with the aid of a turbo molec
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