Embossed TiO2 thin films with high surface areas are achieved using soft-templates composed of monolayer polystyrene beads. The form of links between the beads in the templates is controlled by varying the O2 plasma etching time on the templates, resulting in various templates with close-linked, nano-linked, and isolated beads. Room-temperature deposition of TiO2 on the plasma-treated templates and calcination at 550℃ result in embossed films with tailored links between anatase TiO2 hollow hemispheres. Although all the embossed films have similar surface areas, the sensitivity of films with nano-linked TiO2 hollow hemispheres to 500 ppm CO and ethanol gases are much higher than that of films with close-linked and isolated hollow hemispheres, and the detection limits of them are as low as 0.6 ppm for CO and 0.1 ppm for ethanol. The strong correlation of sensitivity with the form of links between hollow hemispheres reveals the critical role of potential barriers formed at the links. The facile, large-scale, and on-chip fabrication of embossed TiO2 films with nano-linked hollow hemispheres on Si substrate and the high sensitivity without the aid of additives give us a sustainable competitive advantage over various methods for the fabrication of highly sensitive TiO2-based sensors.

Multifunctional structures with two kinds of materials have been intensively investigated in order to improve their electrical characteristic with two functions simultaneously. However, the research regarding of multifunctional ceramic sensor is still in a preliminary stage and how to integrate them with low-cost and high-yield mass production process remains a challenge issue. In this study, we fabricated the multifunctional ceramic sensor composed of temperature and gas sensors. Moreover, we investigated the CO sensing properties of three dimensional nanostuctured Nb2O5 thin film gas sensors fabricated with silica (SiO2) nanosphere (Ø= 750 nm). Compared to plain films, the nanostructured films show enhanced gas sensing of greater sensitivity and a faster response. This result reveals that significantly increased sensitivity is an increase in the effective surface area for the adsorption of gas molecules.