Response characteristics of a highly sensitive gas sensor using a titanium oxide nanotube film decorated with platinum nanoparticles

Titanium oxide nanotube thin films formed by anodic oxidation of titanium metal exhibit high reactivity towards various gases at high temperatures. To date, various types of gas sensors using titanium oxide nanotube films have been proposed. Previously, we proposed a microscale gas sensor with titanium oxide nanotube thin films fabricated by local anodization of titanium microelectrodes. In this study, to improve the response characteristics of titanium oxide nanotube-based microscale gas sensors, we decorated titanium oxide nanotube films with catalytic noble metals of platinum nanoparticles using atomic layer deposition technique. We confirmed that due to Pt decoration the sensitivity was significantly improved for hydrogen and carbon monoxide gases. The detection limit of hydrogen gas was found to be in the sub-ppm range. The response characteristics of hydrogen and carbon monoxide gases were analyzed in detail based on the Langmuir adsorption model. It was found that when the concentration of gas increased, the adsorption mode changed from adsorption on the top surface of the film to that on the inner wall of the titanium oxide nanotubes. We also show that the trace amounts of carbon monoxide gas in a mixed gas containing oxygen and nitrogen can be detected.