Optical Hydrogen Sensing Properties Of ZnO:Cd Nanorod Array

Hydrogen,as one of the most prominent of efficient and pollution-free energy,will be widely used in various fields such as hydrogenation processes,petroleum transformation,soldering,cryogenic cooling,chemical substances production,rocket engines,etc.However,Hydrogen's flammable and combustible characters make it easy to explode if the hydrogen concentration exceeds the critical point.Any leakage during the storage and transportation of hydrogen can lead to severe consequences.Hence,the most important is the room temperature hydrogen gas sensor development.Many researches focus on nanostructured ZnO or doped ZnO based H2 sensors.In most of those studies,ZnO have been doped with noble metals such as palladium(Pd)and platinum(Pt)to enhance the performance of sensor.the one-dimensional ZnO nanomaterials also have good hydrogen-sensitive properties,but they are mostly resistive gas sensors,and it's working temperature above 150 ?.Our laboratory preliminary study found that one-dimensional ZnO:Cd nanomaterials not only have good stability,but also the working temperature can be reduced to 80?.The aim of this study is to improve the material and device structure on the basis of previous research,and to explore the realization of non-energized optical hydrogen sensor at room temperature.In this work,ZnO nanorod arrays were prepared by two-step method.A 50 nm thick ZnO seed layer was deposited by R.F.magnetron sputtering at the top of the substrate.Using the hydrothermal method,we let the quasi-continuous ZnO:Cd nanorods array grow on the ZnO seed layer..By controlling Cd-doping content and the growth time of the material adjust the diameter and length of the nanorods.The doping concentrations of Cd were 0%,2%,4%,6% and the growth time was 0.5h,1h,2h,3h respectively.The crystal structure,surface morphology and transmission spectra were analyzed by XRD,SEM and spectrophotometer respectively.The Zn O:Cd nanorod arrays with different Cd concentration and different growth time were prepared into optical gas sensor(micro-size 18mm×18mm×4mm)composed of micro-air chamber,the optical hydrogen sensitivity was tested and analyzed.The XRD and SEM analysis showed that the Zn O:Cd nanomaterials with different doping concentrations for 2 hours were oriented nanorods,the 2% Cd-doped ZnO:Cd nanorod array has the smallest size,the largest surface area,and the largest gap between the nanorod arrays.In the study,it was found that the nanorods increased linearly with the growth time,but the nanorod diameter changed little with the growth time by changing the growth time of ZnO:Cd-2 nanorods.The results show that the growth of ZnO nanorods can be inhibited by controlling the doping concentration of Cd.All the films have good optical properties as their transmittances are all above 60% when the wavelength is between 450 nm to 800 nm.In addition,the transmittance increase after Cd-doping and the Zn O:Cd-2 film shows the highest transmittance.the hydrogen sensitive sensor was based on Zn O: Cd nanorod array,the optical sensitivity of 500 ppm hydrogen was tested for different dopant devices.The results showed that the ZnO:Cd-2 based sensor presented the greatest change of transmittance,which is to say that this sensor were most sensitive to H2.Then,the response recovery curve of ZnO:Cd-2 sensor was tested by introducing 500 ppm H2 at a working wavelength of 480 nm.After calculating the sensitivity,the sensitivity,response time and recovery time were above 60%,17 s and 15 s,indicating that it has good optical hydrogen sensitivity.Further reducing the test gas concentration,the sensor can effectively detect the minimum concentration of hydrogen 100 ppm,the sensitivity of 20%,the response time of 16 s.Finally,we discuss the mechanism of optical gas sensitivity.All operations are carried out at room temperature,the sensitivity has improved in the compared with the previous study,the practical application provides a practical way.