| Gas sensors have great demand and application potential in medical diagnostics,environmental monitoring,public safety,automation,etc.Generally,chemical gas sensors have poor selectivity and are difficult to detect gases with low adsorption.Gas ionization sensors,based on the unique property of the ionization energy of gases,can be used to detect low-adsorption gases with fast response,fast recovery,and high sensitivity.Zn O nanomaterials have broad application prospects in gas ionization sensors due to their high oxidation resistance,good stability and excellent photoelectric properties.However,existing studies have shown that gas ionization sensors based on Zn O nanoelectrode tend to have a higher breakdown voltage,and how to improve the electric field enhancement effect of Zn O nanostructures is the key to reducing the breakdown voltage.In this paper,Zn O and Na-doped Zn O nanorod arrays were prepared by two-step hydrothermal method,and the effects of Na doping on the micromorphology,light absorption and photoluminescence properties of Zn O nanorods were studied.The nanorods were formed into nanoneedle structures by etching the samples with diluted HF acid solution,and the breakdown voltage of different gases was successfully measured.The influence of doping on the breakdown voltage was studied,and the stability of the sensor was repeated for many times.(1)Zn O and Na-doped Zn O nanorod arrays were prepared on nickel-plated silicon substrates by low-cost two-step hydrothermal method,and it was found that Na doping reduced the average diameter of the nanorods and increased the length-todiameter ratio.The best effect is achieved at a doping concentration of 7.5%,with an average diameter of 91 nm,and too high doping concentration will inhibit the refinement of the doping.Doped Zn O light absorption performance is enhanced,and the band gap is reduced.Ultraviolet emission is enhanced and green light emission is weakened.(2)The samples were etched with a diluted HF acid solution,and the nanorods form a nanoneedle tip with a minimum top diameter of about 20 nm.Based on the gas sensor made of the etched sample,the breakdown voltage of the three organic gases,acetone,isopropanol and isopropanol,is reduced to about 10 V,and the breakdown voltage of air is reduced to 132 V,showing the strong local electric field enhancement effect of the tip structure and the important influence of electrode shape on the breakdown voltage.(3)The influence of Na doping on gas breakdown voltage was studied,and it was found that air,nitrogen and argon reached the maximum reduction range of 75 V,97V and 68 V respectively when doped at 7.5% concentration,indicating that the refinement of doping improved the local electric field enhancement effect of Zn O nanostructures,and once again showed the importance of appropriate doping.However,Na-doped Zn O also showed insufficient stability defects after repeated tests,which may be greatly affected by the preparation process.(4)The electric field enhancement effect of nanotip was simulated by using COMSOL simulation software,and the decisive influence of the length-diameter ratio of the nanorod on the local electric field of the tip was found.The electric field of the tip remained unchanged when the length-diameter ratio was fixed,and the electric field of the tip increased with the increase of the length-diameter ratio.The shielding effect of nanorod array was simulated by doubling the nanorod spacing.When the spacing was maintained at 8 times the length of the nanorods,the array as a whole could obtain a better electric field enhancement effect. |
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