Modeling for Sensing Behavior of SnO2-CuO Nanostructures toward H2S Gas

Boroun, Zhoubin | 2017

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 49269 (48)
  4. University: Sharif University of Technology
  5. Department: Institute for Nanoscience and Nanotechnology
  6. Advisor(s): Ghorbani, Mohammad; Moosavi, Ali; Mohammadpour, Raheleh
  7. Abstract:
  8. H2S is a toxic and corrosive gas which is detrimental for both human’s health and some of important industries such as oil and gas. Based on different experimental research among various systems, resistive sensors fabricated from SnO2-CuO nanostructures have promising performance toward detection of this gas. High sensitivity and selectivity, response time of order of seconds, recovery times of order of tens of seconds and determining concentration of H2S gas below ppm level are advantages of this system. Unfortunately due to lack of a theoretical model, current experimental researches are excessively based on “trial and error” methodology. In this research some of the basic questions which are important in design such as effect of H2S gas concentration on response, origin of working temperature, origin of optimum CuO thickness, effect of surface coverage on response, and effect of morphology on response were theoretically answered and also new approaches toward fabrication of H2S gas sensor based on SnO2-CuO nanostructures were also proposed. Poisson, Laplace and continuity equations were solved utilizing finite difference method to compute electrical resistances in air and gas and ultimately response of the sensor. In the beginning, relation between electrical conductivity of covellite (CuxS) and H2S gas concentration was obtained using materials thermodynamics and physical metallurgy. Model explains why SnO2-CuO system can determine concentration of H2S gas from sub-ppm levels to hundred ones. Also theoretical response-concentration curve of bilayer system matches the experimental curve relatively well in term of behavior. Afterwards origins of working temperature and optimum CuO thickness were explained by considering Schottky interaction between SnO2 and CuS in bilayer system. Results showed that existence of both working temperature and optimum CuO thickness is the outcome of competition between Schottky barrier and ohmic resistivity of metallic covellite. Then by considering macroscopic aspects of oxygen adsorption, it was proved that in air, partially covered system has lager electrical resistance than completely covered system. In presence of H2S gas it was demonstrated that due to reduction of Schottky barrier, partially covered system has lower electrical resistance than completely covered system. Finally response of the sensor was computed for three systems including mono nano-wire, two nano-wires and two nano-spheres and it was shown that among different morphologies, under equivalent conditions, two nano-spheres system has the highest response value due to largest relative electrical resistance in air
  9. Keywords:
  10. Gas Sensor ; Hydrogen Sulfide Sensor ; Tin Dioxide-Copper Monoxide ; Theoretical Modeling ; Covellite ; Schottky Interaction

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