Humidity sensor based on heterogeneous CoTiO3/TiO2 film with vertically aligned nanocrystalline structure

Vertically aligned nanocrystalline films with heterojunctions have attracted much attention as gas sensors because they provide high efficient transport pathways for carriers and large surface area with high activity for adsorption. In this work, a heterogeneous CoTiO3/TiO2 film is prepared by radio frequency sputtering TiO2 on prefabricated CoTiO3 film with a post annealing process. The vertically aligned nanocrystalline surface is achieved by atom inter diffusion and growth competition of the two phases. The obtained CoTiO3/TiO2 film shows nano-columnar arrays structure with dominant (104) orientation. As a humidity sensor, the film shows ultra-high response with fast response/recovery and good stability. The response value reaches 157.23 to 95% relative humidity, which is 38 times that of the pristine CoTiO3 film. Such excellent sensing performance is attributed to the corporation of vertically aligned nanocrystalline surface, advanced hydrophilicity and uniformly distributed heterojunctions.