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  Sci. Lett. J. 2015, 4: 126  
  Review Article Free Article
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Gas sensing mechanism of metal oxides: The role of ambient atmosphere, type of semiconductor and gases - A review  
  Prabakaran Shankar, John Bosco Balaguru Rayappan  
School of Electrical & Electronics Engineering (SEEE) & Centre for Nanotechnology & Advanced Biomaterials (CeNTAB) SASTRA University, Thanjavur – 613 401, India
  Metal oxide thin films have emerged as a promising choice in the gas sensor industry. Several key parameters such as physical and chemical characteristics of the metal oxides, synthesis techniques used, nature of gases, type of atmosphere and the operating temperature collectively influence the sensor properties. The chemiresistive property change in the conductivity associated with adsorption and desorption of gas molecules on the metal oxide surface, is the principle of sensing mechanism. However, owing to the multitude of factors involved, understanding the interaction mechanism behind the sensing property remains a challenge. In this review, the chemical kinetics of reduction-oxidation (REDOX) reactions occurring at the metal oxide surface during its interaction with various gases in dry and wet atmospheres have been analysed. Along with, the sensing characteristics of the metal oxide materials toward the detection of toxic gases, the various determining factors of sensing behaviour of metal oxides and the role of gas molecules have been discussed. For this study, the most toxic, combustible and hazardous gases such as CO, CO2, NO2, SO2, NH3, H2S and C2H5OH have been considered as target gases while, ZnO, SnO2, In2O3, WO3 and CuO, NiO represent n-type and p-type semiconductors respectively to study the influence of base materials.  
  Metal oxide gas sensor; REDOX reactions; Temperature; Nanostructures; Thin films  
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