Propane Gas Sensing Properties of SnO 2 and SnO 2 :Ag Thin Films Prepared by Sol-Gel Technique
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Propane Gas Sensing Properties of SnO2 and SnO2:Ag Thin Films Prepared by Sol-Gel Technique S. Tirado Guerra Escuela Superior de Física y Matemáticas del Instituto Politécnico Nacional, Apdo. Postal 75-544, México, D. F. 07300, México. Tel: + 52 55 5729 6000 55015; Fax: + 52 55 5729 6000 55015. E-mail: [email protected]; [email protected] ABSTRACT Both SnO2 and SnO2:Ag thin films were fabricated by the sol-gel process and dip-coating technique. SnCl4•5H2O was used as a precursor of tin to prepare a 0.2M solution with 2methoxyethanol and monoethanolamine as solvents. From AgNO3 a 0.012M solution in ethanol was prepared, from where the Ag was used as catalyst, which was incorporated superficially to SnO2 film grown on soda-lime substrate. Two series of samples (A and B) about 150 and 300 nm in thickness were prepared and studied. Several layers of Ag as catalyst on the surface of SnO2 films were applied. The films were characterized in structure (RXD), morphology (SEM and AFM) and EDX, electrical and optical properties (UV-vis). The sensing properties of films to the propane at, 0, 1, 5, 50, 100, 200, 300, 400 and 500 ppm gas concentrations were tested in sensors operating at 23, 100, 200 and 300ºC. Results for a selection of sensors are presented in this paper. Keywords: Sn, oxide, Ag, sensors, sol-gel.
INTRODUCTION Application of the SnO2 and the ZnO as gas sensors are given in the literature [1-29]. Physical techniques [4-6,12-13,16,25] and chemical [2,14], electro spray [8] and sol-gel [1,3,22] are used in the manufacture of sensors. Using sol-gel and dip-coating [22], and spray pyrolysis technique [14], gas sensors have been reported previously. In this work, SnO2 and SnO2:Ag thin films have been prepared by the sol-gel process and the dip-coating technique in a home-made equipment which is automatically controlled with a PC. Both, pure SnO2 as those deposited with 3, 5 and 10 layers of Ag, as catalyst, SnO2:Ag, thin films were characterized and tested as propane gas sensors. The range of 0, 1, 5, 50, 100, 200, 300, 400 and 500 ppm were used for the concentration of propane gas. The sensors were tested at operating temperatures of 23, 100, 200 and 300ºC. The response from selected sensors, are presented in this study. EXPERIMENTAL Thin films synthesis and characterization Thin SnO2 films have been prepared by the sol-gel process and by dip-coating procedure. The SnO2 and the surface modified with Ag (SnO2:Ag) thin films were obtained, and grown on sodalime substrates. From tin chloride [SnCl4 • 5H2O] (Merck) a 0.2M solution was prepared from 2-
Mater. Res. Soc. Symp. Proc. Vol. 1275 © Materials Research Society
methoxyethanol [CH3OCH2CH2OH] (Merck) and monoethanolamine [(CH2CH2OH) NH2] (Merck) solvents, following the procedure already reported [22]. Dissolving silver nitrate [AgNO3] in ethanol [CH3CH2OH] a 0.012M solution was prepared, which was used for surface layers depositions of Ag as catalyst. The procedure, for the films deposition to obtain samples with 150 (series A) and 300 nm (series B) in
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