SnO2 thin films were prepared by sol–gel spin-coating technique and different cooling rates were employed in annealing process. The influences of cooling rate and re-annealing on gas sensing characteristics of thin films were investigated, concluding slow cooling rate benefits gas sensing characteristics. The variation of oxygen vacancies density was found to be responsible for the conclusions. Thus, a model of oxygen vacancy distribution was proposed based on the formation and dynamics of vacancies. The diffusion equation was established on the basis of diffusion and exclusion of vacancies in cooling process and the steady state solution revealed a gradient distribution of oxygen vacancies, which exhibited a trend that vacancies accumulate near the surface. Combining the solution of distribution equation and Schottky model, the quantitative expressions of film resistance (R/R0) and response were formulated. The validity and limitation of the model were also considered.

Influences of Cooling Rate on Gas Sensitive Tin Oxide Thin Films and a Model of Gradient Distributed Oxygen Vacancies in SnO2 Crystallites. J.Liu, S.Gong, L.Quan, Z.Deng, H.Liu, D.Zhou: Sensors and Actuators B, 2010, 145[2], 657-66