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). O ₂ 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.