Low temperature reoxidation mechanism in nanocrystalline TiO2-delta thin films

This paper deals with the reoxidation of nanocrystalline TiO2-delta thin fi lms during exposure to ambient oxygen at relatively low temperatures. A phe nomenological model is proposed to describe the reoxidation mechanism and i ts influence on the electrical conductance's sensitivity to oxygen, taking into account both surface and bulk processes. Chemisorption of oxygen predo minates during the first few minutes, followed by diffusion of oxygen into the film and recombination with oxygen vacancies. The model describes the k inetics of the Change in the electrical conductance during th transition fr om the initial to the final equilibrium states. Logarithmic and modified pa rabolic laws are derived to describe the change in the conductance as a fun ction of time during the first (surface-controlled) and second (bulk-contro lled) stages of the reoxidation reaction, respectively. It is demonstrated that these expressions fit very well with experimental results from nanocry stalline TiO2-delta thin Elms during exposure to ambient oxygen at constant temperatures between 200 and 325 degreesC. (C) 2001 The Electrochemical So ciety. [DOI: 10.1149/1.1379952] All rights reserved.