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The IUP Journal of Electrical and Electronics Engineering:
Simulation of Surface Sensing Behavior of Pt Doped SnO2 (110) with CO
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To study the sensing mechanism at atomic, geometrical and electronic structural levels, density functional theory (DFT) technique is useful. Based on ab initio, DFT calculations for CO gas sensing behavior on undoped and Pt doped SnO2 are done. After surface relaxation, optimum adsorption site is selected based on adsorption energy calculated for four different sites, O2C (bridging oxygen), Sn6c (6 fold Sn), Sn5c (5 fold Sn) and O3c (plane oxygen), and CO sensing behavior is observed on favorable site. For estimation of conductance, which is a measure of sensitivity of gas sensing system, analysis of related physical parameters like surface density of states (DOS) and Mulliken population analysis are done. Enhanced sensitivity is observed for Pt doped surface as compared to undoped ones, which is in agreement with the experimental results. Modeling and simulations help to optimize the sensor for any specific application, prior to fabrication. Conclusions help in designing the framework of SnO2-based CO gas sensor.

 
 

Gas sensors play a vital role in the areas of environmental monitoring, quality control in food and cosmetic industry, detecting toxic and combustible gases, etc. They employ polymers, metal oxide semiconductors, optical and mass sensing materials, etc. Metal oxide gas sensors are best because they are inexpensive, as compared to other sensing technologies, and have lightweight, quick response and better sensitivity, and are easy to fabricate and interface electronically (Barsan et al., 2001; Wetchakun et al., 2011; and George et al., 2010). Various metal oxides such as WO3, ZnO, CuO, Al2O3, TiO2, SnO2, Cr2O3, La2O3, GeO2, V2O3 and NiO are used to detect a large number of toxic gases like CO, H2S, CH4, O3, Cl2, H2, NoX, NH3, etc. (Korotcenkov, 2005; and Ihokura and Watson, 1994). CO is a colorless and odorless gas, making it undetectable. On exposure to CO, oxygen can no longer be absorbed in blood and vital organs stop working, resulting in loss of human life within minutes, which demands more research work on CO gas sensors (George et al., 2010). Over the past decades, tin oxide (SnO2)—an n-type semiconductor material—became attractive for its scientific and technological importance (Batzill and Diebold, 2005). Sensors based on pure SnO2 have poor sensitivity, selectivity and response, so their performance is enhanced by doping. In doping process, noble metals Pd, Pt, Cu, Ru, Au, etc. are added to semiconductor materials in a controlled manner which affects its electronic and optical properties resulting in improved performance (Zhu et al., 2009; Hübner et al., 2011; and Streetman and Banerjee, 2016). Among these, Pt doped SnO2 exhibits high sensitivity to CO (Morazzoni et al., 2001; Arienzo et al., 2010; and Barsan et al., 2012). Many experimental works based on Pt doped SnO2 have been done and involve a lot of time, money, materials and manpower (Morazzoni et al., 2001; Arienzo et al., 2010; and Hübner et al., 2011). Still electronic and geometrical characterizations of surface are very difficult to predict due to complexity in experimentation. To explore more about gas surface interactions, several studies are focused on size of grain, direction of grain growth, sensing surface area, etc. but failed to give reasonable explanation, therefore further knowledge at atomic level was felt (Zhou et al., 2012). In recent years, computational techniques have become powerful research tool for theoretical study at atomic level to model the physical and chemical properties of complex solids as complement to experimental work. Density Functional Theory (DFT) based on first principles or ab initio computations with plane waves and pseudopotentials is widely used to study the gas surface adsorption properties (Payne,1992; Zhu et al., 2009; Xue and Tang, 2009; Ming et al., 2011; Zhou et al., 2012; and Shasha et al., 2014). The main objective of this work is to investigate theoretically the sensitivity of system having CO adsorption on pure and Pt doped SnO2 surface based on DFT using slab model.

 
 
 

Electrical and Electronics Engineering Journal, SnO2, Density Functional Theory (DFT), CO gas sensing, Density Of States (DOS), Platinum, Doping, Adsorption energy, CASTEP.