RESUMEN
We have synthesized two highly sensitive, room-temperature operating TeO2/SnO2 gas sensors with hierarchical nanowire structures. One is a brush-like nanostructure, from a two-step thermal vapor-transport route, and the other one is a TeO2/SnO2 bead-like nanostructure, from annealing of the former. The TeO2/SnO2 nanostructures exhibit a greatly enhanced room-temperature gas-sensing response compared to pristine TeO2 nanowires in the sequence: TeO2/SnO2 bead-like structure > brush-like structure > pristine TeO2 nanowire. The response of the TeO2/SnO2 bead-like structure is in a range of 10 to 20 against NO2 gas of ppm levels (3-100 ppm) at room temperature. This compares favorably to the response, smaller than 2, for the pristine TeO2 nanowires. Interestingly, the TeO2/SnO2 bead-like structure exhibits a typical n-type gas-sensing behavior, in contrast to the p-type behavior from the brush-like and the pristine TeO2 structures. Possible hybrid growth and sensing mechanisms are discussed.