Gas Sensing Properties of Tin Oxide Powder Synthesized in the Presence of Surfactants
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Gas Sensing Properties of Tin Oxide Powder Synthesized in the Presence of Surfactants Kiran Jain, A.K.Srivastava1, R.K.Saxena1 and K.Ramesh2 Electronic Materials Division, 1Materials Characterization Division National Physical Laboratory, New Delhi-110012, India 2 Department of Physics, Indian Institute of Sciences, Banglore, India ABSTRACT Nanocrystalline tin oxide powder was prepared using a solution precipitation technique after adding the surfactant sodium bis (2-ethylhexyl) sulfosuccinate (AOT). Powders were characterized using X-ray diffraction (XRD), surface area (BET) and transmission electron microscopy (TEM). The gas sensitivity for surfactant added powders increased for liquid petroleum gas (LPG) as well as compressed natural gas (CNG), due to the decreased particle size and the increased surface area. The LPG gas sensitivity increased several times using phosphorus treated surfactant AOT. INTRODUCTION In recent years, a great deal of research efforts were directed towards the development of low cost gas sensing devices, particularly for inflammable / toxic gas detection. Metal oxide semiconductors offer cost-effective devices suitable for mass production in a variety of applications ranging from industrial, medical, domestic, automotive, and environmental applications, etc. SnO2 shows high sensitivity to many reducing gases, such as H2, CO, and alcohol, and is widely investigated. The principle on which the metal oxide semiconductor devices operate is the change in resistance on exposure to various gases. The resistance change is caused by a loss or gain of surface electrons as a result of adsorbed oxygen reacting with the target gas. If the oxide is an n-type, there is either a donation (reducing gas) or subtraction (oxidation gas) of an electron from the conduction band. The result is that in an n-type material, resistance increases in the presence of oxidizing gases and decreases in the presence of reducing gases. The converse is true for p-type oxides. Grain-size reduction and gas-diffusion control are some of the important factors for improving the gas-sensing properties. Xu et al [1] studied the effect of particle size of SnO2 and proposed that for particle sizes smaller than the Debye length, the grain size can be reduced, inducing the inverse dependence of particle size and gas sensitivity. The surface area of a semiconductor oxide increases as the grain size decreases. Higher surface area means that more surface active sites are available to react with the target gas molecules resulting in higher sensitivity of the sensor. The use of nanoparticles, nanobelts and nanowires is widely investigated for gas sensing applications, since they can offer high surface areas and unique structural features that are expected to promote the sensitivity of the oxide materials to the gaseous components as well as affecting the temperature dependence of sensitivity. Mesoporous materials were investigated by various researchers for gas sensor applications since the grain size reduction as well as faster ga
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