A physicochemical mechanism of chemical gas sensors using an AC analysis

Abstract

Electrical modeling of the chemical gas sensors was successfully applied to TiO₂ nanofiber gas sensors by developing an equivalent circuit model where the junction capacitance as well as the resistance can be separated from the comparable stray capacitance. The Schottky junction impedance exhibited a characteristic skewed arc described by a Cole–Davidson function, and the variation of the fit and derived parameters with temperature, bias, and NO₂ gas concentration indicated definitely a physicochemical sensing mechanism based on the Pt|TiO₂ Schottky junctions against the conventional supposition of the enhanced sensitivity in nanostructured gas sensors with high grain boundary/surface area. Analysis on a model Pt|TiO₂|Pt structure also confirmed the characteristic impedance response of TiO₂ nanofiber sensors.