Selective hydrogen detection with TiO2 nanofilm via the porous-alumina-assisted anodizing of titanium layers

Nanostructured metal oxides grown via porous-alumina (PA)-assisted anodization of sputtered refractory metals are of increasing interest as active layers for gas microsensors. Although nanostructured titanium oxide is particularly attractive, PA-assisted anodic formation of titanium oxide nanostructures remains a challenge because of their chemical instability caused by substantially mixing titania with alumina during film growth. Here we advance the approach and employ a unique combination of electrical and electrolytic conditions to achieve the PA-assisted formation of a stable amorphous TiO₂ nanofilm on dielectric substrates, followed by high-temperature annealing to attain crystallization and enhance semiconductor properties of the film. A laboratory-scale microsensor employing the TiO₂ nanofilm as active layer shows good sensitivity and selectivity to hydrogen against ethanol and carbon monoxide, which is in demand for proton-exchange fuel-cell applications.