Highly sensitive CO sensors based on cross-linked TiO2 hollow hemispheres

We report the fabrication of a highly sensitive gas sensor based on a network of nanostructured TiO2 hollow hemispheres (NTHH). O2 plasma etching induces cross-linking of hexagonal-close-packed polystyrene array, which is adopted as a template substrate for room-temperature deposition of TiO2 thin film. High-temperature calcination effectively removes polystyrene template beads and promotes crystallization of TiO2, finally producing cross-linked NTHH via nanobridges. The gas-sensing capability of a NTHH-based sensor is demonstrated using 1–500 ppm CO. Our sensor exhibits a very high response of 4220% change in resistance when exposed to 500 ppm CO at 250 °C, whereas a gas sensor based on a plain TiO2 film shows a 195% change. The high sensitivity of the NTHH-based sensor is attributed to the enhanced gas sensing performance of the narrow nanobridges between hollow hemispheres.