Journal of Materials Science and Engineering A 6 (3-4) (2016) 51-56 doi: 10.17265/2161-6213/2016.3-4.002 Hydrogen Gas Sensor Based on ZnO Nanoroads Grown on Si by Thermal Evaporation Hind Ibraheem Abdulgafour 1 , Hassan Hadi Darwoysh 1, 2 and Faez Mohamad Hassan 2* 1. Departement of Physics, Ministry of Science and Technology, Baghdad, AlKerrada 10069, Iraq 2. Department of Physics, College of Education, Al-Mustansiriya University, Baghdad, New Baghdad 10062, Iraq Abstract: High-quality ZnO (Zinc oxide) nanorods grown on Si substrate have been synthesized for hydrogen gas sensor application through a low-cost catalyst-free process by thermal evaporation at 800 º C. The morphological, structural and optical properties of the ZnO nanorods have been examined. In this study, Pd/ZnO/Pd MSM (Metal-semiconductor-metal) gas sensor has been fabricated based on the ZnO nanorods. The absence of a seed layer and the coalescence of ZnO nanorods were the key factors responsible for the high sensitivity of the gas sensor at room temperature. The sensitivity of ZnO nanorods is measured at different concentrations from 25 ppm to 150 ppm of H 2 gas at room temperature. The highest response of the ZnO/Si sensor was 110% in the presence of 500 ppm of H 2 . This high sensitivity can be attributed to the high surface-area- to-volume ratio of the nanorods between the Pd contacts of the MSM configuration. Key words: ZnO, nanostructures, thermal evaporation, gas sensor. 1. Introduction Leaked hydrogen fuel could have small negative effects on atmosphere. Using hydrogen as an energy carrier can help reduce air pollution and GHG (Greenhouse gas) emissions associated with fossil fuels. However, if used on a large-scale, it is important that hydrogen does not leak significantly into the atmosphere as it might have some negative environmental effects, such as increasing the lifetime of methane, increasing climate effects and causing some depletion of the ozone layer [1]. In recent years, low-dimensional systems have attracted tremendous interest in nanosensor applications due to their gas sensitivity, UV (Ultraviolet) photoresponse, and optical transparency in the visible region, among other features [2, 3]. In particular, quasi-one dimensional nanowires or nanorods are promising low-cost material for high-speed UV photoconductive nanoscale detectors and gas sensors [4-6]. In the past decade, research on wide band gap semiconductors * Corresponding author: Faez Mohamad Hassan, Ph.D., research fileds: solid state physics and nanotechnology. has focused on ZnO (zinc oxide) due to its excellent properties as a semiconductor. Its high electron mobility, high thermal conductivity, good transparency, wide and direct band gap (3.37 eV), large exciton binding energy and ease of fabrication into micro- and nanostructures make ZnO suitable for a wide range of applications in optoelectronics, transparent electronics, lasing and sensing [7, 8]. Nanorods are some of the most common forms of ZnO that possess several excellent properties, such as high sensitivity to adsorbed oxygen on the surface, excellent electric transport, high photo-sensitivity, optical wave-guiding, and large surface area-to-volume ratio [9]. Compared with the bulk materials used in gas sensors, such as thin films, nanorods have greater gas sensitivity and selectivity and lower operating temperatures [10, 11]. Room-temperature hydrogen gas sensors have received a great deal of interest for use in several applications because of the extremely low power consumption, ability to be used safely in flammable environments, and long lifetime [12-14]. For gas sensing applications, ZnO is one of the promising D DAVID PUBLISHING