Low Temperature Reoxidation Mechanism in Nanocrystalline TiO[sub 2−δ] Thin Films

Abstract

This paper deals with the reoxidation of nanocrystalline TiO2−δTiO2−δ thin films during exposure to ambient oxygen at relatively low temperatures. A phenomenological model is proposed to describe the reoxidation mechanism and its influence on the electrical conductance’s sensitivity to oxygen, taking into account both surface and bulk processes. Chemisorption of oxygen predominates during the first few minutes, followed by diffusion of oxygen into the film and recombination with oxygen vacancies. The model describes the kinetics of the change in the electrical conductance during the transition from the initial to the final equilibrium states. Logarithmic and modified parabolic laws are derived to describe the change in the conductance as a function of time during the first (surface-controlled) and second (bulk-controlled) stages of the reoxidation reaction, respectively. It is demonstrated that these expressions fit very well with experimental results from nanocrystalline TiO2−δTiO2−δ thin films during exposure to ambient oxygen at constant temperatures between 200 and 325°C. © 2001 The Electrochemical Society. All rights reserved.