IOP PUBLISHING NANOTECHNOLOGY Nanotechnology 22 (2011) 295503 (11pp) doi:10.1088/0957-4484/22/29/295503 Highly selective GaN-nanowire/TiO 2 - nanocluster hybrid sensors for detection of benzene and related environment pollutants Geetha S Aluri 1,2 , Abhishek Motayed 1,3,5 , Albert V Davydov 1 , Vladimir P Oleshko 1 , Kris A Bertness 4 , Norman A Sanford 4 and Mulpuri V Rao 2 1 Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA 2 Department of Electrical and Computer Engineering, George Mason University, Fairfax, VA 22030, USA 3 Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, MD 20742, USA 4 Physical Measurement Laboratory, National Institute of Standards and Technology, Boulder, CO 80305, USA E-mail: amotayed@nist.gov Received 13 April 2011, in final form 25 May 2011 Published 15 June 2011 Online at stacks.iop.org/Nano/22/295503 Abstract Nanowire–nanocluster hybrid chemical sensors were realized by functionalizing gallium nitride (GaN) nanowires (NWs) with titanium dioxide (TiO 2 ) nanoclusters for selectively sensing benzene and other related aromatic compounds. Hybrid sensor devices were developed by fabricating two-terminal devices using individual GaN NWs followed by the deposition of TiO 2 nanoclusters using RF magnetron sputtering. The sensor fabrication process employed standard microfabrication techniques. X-ray diffraction and high-resolution analytical transmission electron microscopy using energy-dispersive x-ray and electron energy-loss spectroscopies confirmed the presence of the anatase phase in TiO 2 clusters after post-deposition anneal at 700 ◦ C. A change of current was observed for these hybrid sensors when exposed to the vapors of aromatic compounds (benzene, toluene, ethylbenzene, xylene and chlorobenzene mixed with air) under UV excitation, while they had no response to non-aromatic organic compounds such as methanol, ethanol, isopropanol, chloroform, acetone and 1,3-hexadiene. The sensitivity range for the noted aromatic compounds except chlorobenzene were from 1% down to 50 parts per billion (ppb) at room temperature. By combining the enhanced catalytic properties of the TiO 2 nanoclusters with the sensitive transduction capability of the nanowires, an ultra-sensitive and selective chemical sensing architecture is demonstrated. We have proposed a mechanism that could qualitatively explain the observed sensing behavior. (Some figures in this article are in colour only in the electronic version) 1. Introduction Detection of chemical species in air such as industrial pollutants, poisonous gases, chemical fumes and volatile 5 Author to whom any correspondence should be addressed. organic compounds (VOCs) is vital for the health and safety of communities around the world [1]. Due to their small size, ease of deployment and low-power operation, solid-state thin film sensors are often favored over analytical techniques like optical and mass spectroscopy, and gas chromatography when it comes to real-time environmental monitoring [2–4]. 0957-4484/11/295503+11$33.00 © 2011 IOP Publishing Ltd Printed in the UK & the USA 1