| Summary: | 碩士 === 國立中興大學 === 材料科學與工程學系所 === 106 === This research examines in detail the effect of ambient humidity to room-temperature gas-sensing property of needle-like In2O3 and NiO/In2O3 nanostructures. The semiconducting n-type In2O3 nanoneedles were synthesized by vapor-transport method and were decorated with p-type NiO nanoparticles on the surface by chemical wet deposition followed by heat treatment. The aspect ratio of In2O3 nanoneedles was kept at 6.0 deliberately, and the diameter of NiO particles was about 20 nm. Comparing the pristine and the NiO-decorated In2O3, it was found that the electrical resistance of In2O3 increased upon exposure to oxidizing NO2 gas at room temperature under 17% relative humidity (dry air). The greatest sensitivity of the In2O3 nanostructure was 140.9. However, the electrical resistance of the pristine In2O3 nanosensors decreased with the presence of NO2 gas at room temperature when relative humidity of the ambient was increased to a range of 40 to 80% (wet air) and the sensitivity plummeted to 2.2, indicating a strong humidity-dependent gas-sensing behavior at room temperature. By using pH paper tests, it was believed that the In2O3 resistance decrease was caused by detection toward reducing nitrogen monoxide (MO) at the wet-air atmosphere. In contrast, electrical resistance of the NiO/In2O3 nanosensors was increased when exposed to NO2 over a broad range of relative humidity(17-80%), and the sensitivity was slightly increased from 2.7 to 6.1 with the relative humidity, as expected for n-type semiconductor in the presence of oxidizing gases. This result was referred to the anti-humidity of NiO/In2O3 heterostructure. In addition, both of the pristine and NiO/In2O3 nanosensors were examined against H2S gas at room temperature. Over a humidity range from 11 to 80%, the sensitivity of In2O3 against 6 ppm H2S decreased to 1.04 from 2, whilst, the sensitivity of NiO/In2O3 decreased to 1.07 from 1.35. The findings demonstrate that the NiO/In2O3 heterostructure nanoneedles are beneficial in terms of the reduced dependence on humidity for room-temperature gas-sensing.
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