Gas Sensing Mechanism Of ZnO Nanowires

ZnO as a wide band semiconductor material has a high activation energy of the particles. This material has an important application on gas sensing performance. Pure ZnO nanowires and different metal elements doped ZnO nanowires have been prepared by our group. Gas sensors are made by ZnO nanowires to test its gas sensing properties.Ag, Ni, Al doped with different weitht ratio (1wt%,3 wt%,5 wt%) of ZnO nanowires prepared by heat evaporation method. The sensing properties (ethanol gas, methane, carbon monoxide, ammonia) of gas sensors made by different products were tested using static gas distribution. The sensing mechanism of the metal-doped ZnO nanowires was studied and the results were achieved as the followings:1. The gas sensing properties of 1wt% Ag doped ZnO nanowires have been improved the highest among the above three metal elements compared with that of pure ZnO. The ethanol gas sensitive properties of Ag-doped ZnO nanowires are the best. The sequence of gas sensing is methane, ammonia and carbon monoxide.2. Gas sensitive properties of 3wt% Ni doped ZnO nanowires has higher ethanol sensing performance than the pure nanowires of ZnO. The gas sensing properties of Ni-doped ZnO nanowire to the other three gases was little. The operating temperature of Ni doped was declined in the environment of ethanol and ammonia.3. The improvement of gas sensing performance of Al doped ZnO nanowires to the four target gas was all not obvious. While, the Al doped ZnO nanowires still win the highest sensing performance in the environment ethanol vapor and the carbon monoxide, ammonia and methane followed.4. Using the barrier theory, Ag,Ni,Al dopant would be filled into the ZnO grains, which reduce the grain boundary barrier and increase the conductivity. These metals had high affinity to target gas, which could speed up the reaction between the gas and oxygenions. Consequently, it improved gas sensing properties of ZnO nanowires. 5. Combining with band theory, the band gap of Ag doped ZnO become the narrowest. The band gap of Ni doped ZnO is narrower than the product of Al doped ZnO. The wider of the band gap is the more difficult electron excited to the conduction band. In contration, the narrower of band gap is the easier electron excited to the conduction band. Thus, at the same working temperature, electrons was excite more easily with the narrower band gap and better conductivity. As the result, excellent gas sensitivity is performed.