Embossed TiO₂ thin films with tailored links between hollow hemispheres: Synthesis and gas-sensing properties

Embossed TiO₂ thin films with high surface areas were achieved using soft templates composed ofmonolayer polystyrene beads.The structure of links between beads in the templates could be controlled by varying O2 plasma etching time, resulting in a variety of templates with close-linked, nanolinked, or isolated beads. Room-temperature deposition of TiO₂ on the plasma-treated templates and calcination at 550 °C resulted in embossed films with tailored links between anatase TiO₂ hollow hemispheres. Although all embossed TiO₂ films displayed a similar increase in the surface-to-volume ratio compared with a plain TiO₂ thin film, the response of embossed TiO₂ films with nanolinked hollow hemispheres to CO or ethanol gases was much higher than the response of films with close-linked or isolated hollow hemispheres. The strong correlation between gas sensitivity and the structure of links between the TiO₂ hollow hemispheres revealed the critical importance of tailoring links between individual oxide nanostructures for enhancing gas-sensing properties of the ensemble of the individual nanostructures. The facile and large-scale synthesis of embossed TiO₂ films with nanolinked hollow hemispheres on Si substrates and the high sensitivity that is achieved without the aid of additives provide a sustainable competitive advantage over other methods for fabricating highly sensitive metal oxide gas sensors.