Mechanism of the sensitivity enhancement in TiO₂hollow-hemisphere gas sensors

We investigate the mechanism of the sensitivity enhancement in TiO₂ hollow-hemisphere gas sensors. Using monolayer close-packed polystyrene microspheres as a sacrificial template, a TiO₂ thin film based on a network of ordered hollow hemispheres is formed by room-temperature sputtering deposition and subsequent calcination at 550°C. A thin film gas sensor based on the TiO₂ hollow hemispheres exhibits a 225% change in its resistance when exposed to 50 ppm CO at 250°C, whereas a gas sensor based on a flat TiO₂ film shows an 85% change. Numerical analysis reveals that the enhancement of the gas sensitivity in the hollow-hemisphere gas sensor is simply the result of an increase in the effective surface area for the adsorption of gas molecules.