Metal–oxide-layer-coated single-walled carbon nanotubes as a sensor for trace amounts of oxygen

We found that resistive sensors using a single-walled carbon nanotube thin film covered with a SrTiO3 or CeO2 thin layer exhibit excellent responses to trace amounts (?10?3 Pa) of oxygen. By analysis based on the Langmuir adsorption model, their responses were revealed to be due to O2 adsorption on the metal oxide layer, which involves two adsorption processes. They were assigned to identical adsorptions as superoxide species on the sites at separate locations on the metal oxide surface, i.e., at directly accessible flat areas and at recessed areas that are only accessible via thermally activated surface diffusion.