CO Sensor based on Thin Film of ZnO Nanoparticles
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CO Sensor based on Thin Film of ZnO Nanoparticles Carlos Aquino López1, Guillermo Carbajal-Franco1, Fernanda Márquez Quintana1 and Alejandro Ávila Garcia2 1
Division of Graduate Studies and Research, Instituto Tecnológico de Toluca, TecNM-SEP, Avenida Tecnológico, s/n, Colonia Agrícola Buenavista, Metepec, 52149, México. 2 Departamento de Ingeniería Eléctrica, Sección de Electrónica del Estado Sólido, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Av. Instituto Politécnico Nacional, No. 2508, Cd. de México, 07360, Mexico. ABSTRACT In this research, zinc chloride has been used as precursor and zinc oxide nanostructures have been synthesized by Sol-Gel process, using deionized water and 2-propanol as solvents in order to evaluate their influence on the final materials and their properties. Thin films of synthesized samples were deposited on glass substrates by the dipping method. The structure and morphology of crystals were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) respectively. The electrical response of the samples to CO was investigated at different operating temperatures and sensitivity curves are presented for samples synthesized in water and 2-propanol (IsOH) solvents. The SEM analysis revealed that ZnO thin films have yielded to different morphologies depending on the solvent, and material was found on the nonimmersed side of the substrate attributable to migration during the dip-coating process. XRD analysis shows that the samples present the ZnO wurtzite structure. In EDS analysis it was found the presence of chlorine on the sample, opening the possibility the presence of zinc oxychloride. INTRODUCTION Several semiconducting metal oxides such as ZnO, have attracted the attention of numerous researchers interested in gas sensors, due to their surface properties suitable for gas detection. The gas sensing mechanism is based on several gas/semiconductor interactions including reduction/oxidation processes of the semiconductor and adsorption of the chemical species directly into the semiconductor surface [1-3]. The effect of these surface phenomena generates a significant change in electrical resistance (increase or decrease under exposure to oxidizing or reducing gases respectively, based on an n-type semiconductor metallic oxide). This resistance variation can be measured and used to detect chemical species in the ambient. Numerous authors have shown the advantage of reducing the metal oxide grain size down to the nanometric scale in order to improve the sensing properties [4, 5]. The interaction of gaseous species with metallic oxide nanoparticles may give rise to high and fast responses in term of changes in the electrical properties of the sensing materials [6]. In past decades, Zinc oxide has been intensely studied owing to his good stability and gas sensing properties to a wide range of gases like CO, NO2 [7], methane[8] and acetone [9]. Recently, substantial efforts have been devoted to synthesize ZnO-nanostructured materials in
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