| Summary: | 碩士 === 國立中興大學 === 材料科學與工程學系所 === 105 === In this study, single-crystalline In2O3 nanoneedles and nanotowers with [100] growth direction were fabricated via vapor transport method. We investigated the effect of morphology (including shape and size of the nanostructure) on NO2 gas-sensing properties over an optimal working temperature 100 oC and an NO2 concentration range from 10 to 30 ppm. The widths at the bottom of In2O¬3 nanoneedles and nanotowers were found in a range between 540~1480 nm and 340~1000 nm, while the total lengths were ranged between 3.1~23.8 μm and 1.6~10.6 μm, respectively. The sensitivity of In2O3 nanoneedles with an aspect ratio of 11.5 was 61.6 for 30 ppm NO2, then the response time and recovery time were 115 s and 257 s, respectively. Moreover, the sensitivity of In2O3 nanotowers with an aspect ratio 10.4 was 67.5, then the response time and recovery time were 123 s and 220 s, respectively. An appropriate aspect ratio was favorable to expand the charge depletion layer on the surface layer of nanowires when was brought in contact with the oxidative NO2 gas. In addition, an appropriate aspect ratio could also reduce the number of nanowire junctions between the electrodes of sensing device so that it decreased the electrical resistance in air so that electrons can transport more efficiently. Therefore, the aspect ratio of nanostructures is critically important to the gas-sensing property of semiconducting nanowires gas sensors.
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