In 2 O 3 nanowire mat devices as high performance NO 2 gas sensors
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In2O3 nanowire mat devices as high performance NO2 gas sensors Daihua Zhang, Zuqin Liu, and Chongwu Zhou Department of Electrical Engineering - Electrophysics University of Southern California Los Angeles, California 90089, U. S. A ABSTRACT A high sensitive and reliable In2O3 nanowire mat devices are fabricated. Detection of NO2 gas down to ppb levels was achieved. This represents orders-of-magnitude improvement over previously reported metal oxide film or nanowire/nanobelt sensors. Furthermore, this simple device shows certain selectivity to NO2 with other common chemicals such as NH3, O2, CO and H2 around. INTRODUCTION Chemical sensing based on various nanostructures [1-11] has attracted enormous attention, as this is widely perceived as one of the most promising areas for nanotechnology to generate significant impact. Among the chemicals studied, NO2 is one of the most dangerous air pollutants, which plays a major role in the formation of ozone and acid rain; Continued or frequent exposure to NO2 concentrations higher than the air quality standard (53 ppb) may cause increased incidence of acute respiratory illness in children [12]. The detection and measurement of NO2 gas are thus of great importance in both environmental protection and human health. Solid-state sensors for NO2 detection have been under development based on both conventional metal oxide thin films and one-dimensional nanostructures, however, with various limitations. For instance, most existing metal oxide thin-film sensors work at elevated temperatures with sensing limitations around 1 ppm or even higher [13-17]. Nanowires or nanobelts made of metal oxides can deliver better performance because of their enhanced surface-to-volume ratios, and SnO2 nanobelts have been demonstrated to detect 3 ppm NO2 at room temperature [5]. In addition, by operating SnO2 nanobelt sensors at 400 oC, detection down to 0.5 ppm NO2 has been successfully achieved [7]. These represent significant advance in the field of solid-state chemical sensing; however, the detection limit does not satisfy the requirement of 53 ppb NO2 set by the US Environmental Control Agency. On the other hand, carbon nanotube mat samples have been reported to reliably detect NO2 down to 1 ppb or less, with the aid of functional polymer coating to enhance the sticking coefficient [3]. In this paper we report the detection of NO2 down to ppb levels with metal oxide nanowire transistors. Multiple In2O3 nanowire devices operating at room temperature and without the help of functional polymer coating. This represents orders-of-magnitude improvement over previously reported metal oxide film or nanowire/nanobelt sensors, and rivals the performance of the best nanotube chemical sensors. Sensors based on multiple In2O3 nanowires displayed numerous advantages in terms of great reliability, high sensitivity down to 5 ppb, and simplicity in fabrication. Furthermore, selective detection of NO2 among other common chemicals has been observed with multiple-nanowire sensors without the extra step of po
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