Gas Sensors using Laterally-aligned Metal Oxide Nanowire prepared by Electro-hydrodynamic Nanowire Printing

Abstract

They are various air pollutants in many urban environments. This has propelled a significant research on the development of sensors that can detect various gases. Gas sensors with high-sensitivity and selectivity will play a key role in industrial processes, environmental toxins and pollutants monitoring. Especially, metal oxide gas sensors have been widely used and investigated in the detection of gases. Because they have many advantages in the field of gas sensing under atmospheric conditions such as their low cost, flexibility in production, simplicity of their use and large number of detectable gases. In this work, gas sensors based on various metal oxide nanowires (MONW) such as ZnO, SnO2, In2O3 and WO3 were studied. Polyvinylpyrrolidone/metal oxide precursors were prepared by using sol-gel processing and Electrohydrodynamic nozzle Nanowire Printing (ENP) method. After calcinations of the above precursor wires, MONWs could be successfully obtained. By using these methods, we can not only synthesize porous MONWs with high surface to volume ratio but also print large-area MONWs array directly on device substrates in a precisely controlled manner. Nanwires were characterized by optical microscopy (OM), scanning electron microscopy (SEM), thin film X-ray diffraction (XRD) and transmission electron microscopy (TEM).The sensing performances of the synthetic nanowires s are investigated by various gases such as nitrogen dioxide vapor (NO2), ethanol vapor (C2H5OH), ammonia gas (NH3) and acetone (CH3COCH3) in air. Especially, ZnO wires showed good sensitivity and selectivity to nitrogen dioxide vapor. At 300℃, the ZnO wire gas sensor was up to 20 times more responsive to nitrogen dioxide vapor than ethanol vapor. Also, ZnO sensor exhibited a very high response of 10847% change in resistance when exposed to 5 ppm NO2, whereas a gas sensor based on a plain ZnO film shows a 115% change. Other MONWs (SnO2, In2O3 and WO3) showed high sensitivity to nitrogen dioxide vapor and ethanol vapor, as well. This result suggests that high surface to volume ratio of one dimensional nanostructure and porous structure by Electro-hydrodynamic nozzle Nanowire Printing (ENP) method provide a good opportunity to dramatically increase their sensing properties.