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.
RESUMEN
We have synthesized brushlike p-Te/n-SnO2 hierarchical heterostructures by a two-step thermal vapor transport process. The morphologies of the branched Te nanostructures can be manipulated by adjusting the source temperature or the argon flow rate. The growth of the branched Te nanotubes on the SnO2 nanowire backbones can be ascribed to the vapor-solid (VS) growth mechanism, in which the inherent anisotropic nature of Te lattice and/or dislocations lying along the Te nanotubes axis should play critical roles. When exposed to CO and NO2 gases at room temperature, Te/SnO2 hierarchical heterostructures changed the resistance in the same trend and exhibited much higher responses and faster response speeds than the Te nanotube counterparts. The enhancement in gas sensing performance can be ascribed to the higher specific surface areas and formations of numerous Te/Te or TeO2/TeO2 bridging point contacts and additional p-Te/n-SnO2 heterojunctions.