Hexagonal-arranged ZnO Nanowire Arrays by Using Au Nanohole Membranes as Fabrication Template
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Hexagonal-arranged ZnO Nanowire Arrays by Using Au Nanohole Membranes as Fabrication Template H. J. Fan, W. Lee, K. Nielsch, and M. Zacharias Max Planck Institute of Microstructure Physics, Weinberg 2, 06120 Halle, Germany A. Dadgar and A. Krost Institute of Experimental Physics, Otto-von-Guericke-University, postbox 2410, 39016 Magdeburg, Germany ABSTRACT A new template method for large-scale fabrication of hexagonally patterned and vertically aligned ZnO nanowires is demonstrated. The process involves a novel type of metal membrane, a gold catalyst template produced using the membrane as deposition mask, and the catalyst-guided growth of ZnO nanowires. The metal membranes, composed of hexagonal nanohole arrays, are electrochemically replicated from ordered porous alumina. The ZnO nanowires obtained have a uniform alignment perpendicular to the GaN surface and a distribution according to the pattern defined by the nanohole membrane. Such periodically arranged ZnO nanowires have potential applications as sensor arrays and piezoelectric transducers. INTRODUCTION ZnO-based one-dimensional (1-D) nanoscale materials, as important functional oxide nanostructures, have received increasing attention over the past few years due to their potential applications in optoelectronic switches, high-efficiency photonic devices, near-UV lasers, and assembling complex three-dimensional nanoscale systems [1]. Most of these applications can be advanced if the alignment, distribution and aspect ratio of the 1-D nanostructures can be controlled during the growth process. For this purpose, a straightforward approach is to create patterned metal nanoparticles, which are used as catalyst templates for the subsequent guided growth of nanowires [2]. In the past few years, a number of approaches have been used to obtain patterned metal catalysts for successful fabrication of ZnO nanowires arrays. They include direct deposition through masks such as grids and monolayer arrays of microspheres [3-5], electron beam [6] and imprint lithography [7], and more recently, soft-photolithographic etching route [8]. In the present letter, a new template method for growth of perfect arranged arrays of ZnO nanowires is demonstrated. The catalyst gold templates are produced using a novel type of metal nanohole membranes as deposition masks. Our fabrication approach could reinforce the feasibility of creating nanoscale-patterned 1-D nanomaterials for applications such as sensor arrays, field electron emitter arrays, and vertical field-effect transistors [9]. For the particular case of the present work on ZnO nanowires, we use highly-doped GaN epilayers as substrates. GaN and ZnO have a similar fundamental bandgap energy (~3.4 eV), the same wurtzite crystal symmetry, and a low misfit of the lattice constant (1.9%). This makes GaN a good candidate for both epitaxial growth [5,10] and device applications of ZnO nanowires.
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EXPERIMENTAL DETAILS The fabrication procedure involves 5 steps, as schematically demonstrated in Figure 1. First, monodo
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