Research Article 1(2)210-214 Advanced Materials Proceedings Copyright © 2016 VBRI Press 210 Catalyst assisted vapor phase transport growth and characterization of ZnO nanowires Shrisha B V 1 , Shashidhara Bhat 1 , Parvathy Venu M 1 , Dushyant Kushavah 2 , K Gopalakrishna Naik 1 1 Department of studies in Physics, Mangalore University, Mangalagangotri, Mangalore, 574199, India 2 Centre for Research in Nanotechnology & Science, IIT Bombay, Powai, Mumbai, 400076, India * Corresponding author, E-mail: gopal_mng@yahoo.com; Tel: (+91) 9945301454 Received: 31 March 2016, Revised: 02 September 2016 and Accepted: 03 September 2016 DOI: 10.5185/amp.2016/218 www.vbripress.com/amp Abstract Zinc Oxide (ZnO) nanowires (NWs) were grown on p-silicon (p-Si) substrates coated with around 10 nm thick metal films of Au, Al and Cu using vapor phase transport growth method. The effect of these metal catalysts and the substrate temperatures on the morphologies of ZnO NWs were studied using field emission scanning electron microscopy (FESEM). The growth of ZnO NWs with high aspect ratio was observed at substrate temperatures above 600 o C. The structural and optical properties of the as grown ZnO NWs were characterized using X-ray diffraction (XRD) and photoluminescence spectroscopy (PL) techniques, respectively. XRD study revealed that, the grown samples possess hexagonal wurtzite structure with (002) preferential orientation. The metal droplets were observed at the tips of ZnO NWs when Au was used as catalyst, but not in the case of Al and Cu. The PL spectra exhibited two peaks, one in the UV region and the other in the visible region. The low-cost Al and Cu metal catalyst assisted growth of metal contamination-free ZnO NWs may be suitable for the device applications. Copyright © 2016 VBRI Press. Keywords: ZnO, nanowires, metal catalyst, two zone furnace, vapor phase transport growth. Introduction The nanosize material structures have attracted great interest because of their unique physical and chemical properties. Various kinds of nanostructures such as nanorods, nanowires, nanobelts, nanotubes, nanowalls, nanohelixes, and nanorings of various semiconductor materials have been synthesized [1]. Among them, the one-dimensional nanostructures such as nanowires have attracted great attention for their potential applications in nanoscale electronic and optoelectronic devices [2]. Among various semiconductor materials, ZnO NWs are considered as the most promising one because of their band gaps coinciding with the UV region of the electromagnetic spectrum and also ZnO possesses large exciton energy (60 meV) that could lead to lasing action based on exciton recombination at room temperature [3]. ZnO NWs have been synthesized by different growth techniques such as vapor phase transport growth method (VPT), RF magnetron sputtering, molecular beam epitaxy (MBE), pulsed laser deposition (PLD), laser-assisted catalytic growth, solution phase methods, chemical vapor deposition (CVD), and metal organic chemical vapor deposition (MOCVD) [4]. Among the different growth methods, vapor phase transport growth method is a simple and low-cost technique used for the growth of high quality ZnO NWs [5]. The growth of ZnO NWs is proposed to takes place under any one of the following mechanisms: (1) vapor-liquid-solid (VLS), (2) vapor-solid (VS) process, and (3) vapor-solid- solid (VSS) process [6]. In VLS process, a metal liquid droplet serves as a preferential site for absorbing the vapor reactant. NW growth begins when the droplet is supersaturated with the source material, and growth continues as long as the droplet remains in the liquid state and vapor is supplied. The appearance of the metal droplets on the tips of the NWs is considered as the characteristic feature of VLS growth process [7]. The VS mechanism is generally used to describe catalyst-free growth of ZnO NWs. The VS mechanism results in the growth of nanostructures with variety of morphologies [8]. In VSS mechanism, the metal catalyst in the solid state acts as preferential site to initiate and guide the growth of one dimensional NWs [9]. The ZnO NW growth using vapor phase transport process is achieved by coating a thin film of metal catalysts such as Au, Sn, Al, Ag, Pt, Pd, Cu, Ni and Fe on the substrates [10]. Au is found to be most commonly