硅纳米线/氧化钒纳米棒复合材料的制备与气敏性能研究

Synthesis and gas-sensing properties of the silicon nanowires/vanadium oxide nanorods composite

采用纳米球光刻和金属辅助刻蚀法以p型单晶硅片制备了硅纳米线阵列,并以此作为基底,通过溅射不同时长的金属钒薄膜并进行热退火氧化处理,制备出硅纳米线/氧化钒纳米棒复合材料.采用扫描电子显微镜和X射线衍射仪表征了该复合材料的微观特性,结果表明该结构增大了材料的比表面积,有利于气体传感,并且镀膜时间对后续生长的氧化钒纳米棒形貌有明显影响.采用静态配气法在室温下测试了该复合材料对NO_2的气敏性能,气敏测试结果表明沉积钒膜的时间对复合材料的气敏性能影响较大.当选择合适的镀膜时间时,适量氧化钒纳米棒增加了材料表面积并形成大量pn结结构,相比纯硅纳米线对NO_2气体的灵敏度有明显提升,且在室温下表现出优良的选择性.同时,对气敏机理做了定性解释,认为硅纳米线与氧化钒纳米棒之间形成的pn结及能带结构在接触NO_2时的动态变化是其气敏响应提升的主要机制.

As air pollution is becoming more and more serious in recent years,gas-sensing devices have attracted intensive attention.In particular,NO_2 is one of the most toxic gases in the atmosphere,which tends to produce acid rain and photochemical smog.Thus,there is a strong demand of cheap,reliable and sensitive gas sensors targeting NO_2.Gas sensors fabricated on silicon substrates with room-temperature operation are very promising in power saving,integrated circuit processing and portable detectors.More important,the silicon nanowires（Si NWs）-based devices are compatible with very large scale integration processes and complementary metal oxide semiconductor technologies.In the present work,the novel nanocomposite structure of（Si NWs）/vanadium oxide（V_2O_5） nanorods for NO_2 detection is successfully synthesized.The Si NWs are fabricated by a combination of nanosphere lithography and metal-assisted chemical etching.Vanadium films are deposited on Si NWs by DC magnetron sputtering,and then V_2O_5 nanorods are synthesized with subsequent thermal annealing process for full oxidation in air.The morphology and crystal structure of product obtained are characterized by field-emission scanning electron microscopy and X-ray diffraction.The characterization results indicate that V_2O_5 nanorods are uniformly distributed on the surfaces of Si NWs.The increased specific surface area of Si NWs/V_2O_5 nanocomposite provides more adsorption sites and diffusion conduits for gas molecules.Therefore,the novel structure of the nanocomposite is conducive to gas-sensing.In addition,the sputtering time has an obvious influence on the morphology of vanadium oxide.With the increase of the sputtering time,the specific surface area and the number of p-n heterojunctions formed in the nanocomposite are both less than those of nanocomposite with appropriate sputtering time.The gas-sensing properties are examined by measuring the resistance change towards 0.5–4 ppm NO_2 gas at room temperature by the static volumetric method.Results show that the nanocomposite with shorter deposition time has better gas-sensing properties to low-concentration NO_2 gas than those of bare Si NWs and nanocomposite with longer deposition time.On the contrary,the responses of the nanocomposite to other high-concentration reducing gases are very low,indicating good selectivity.The enhancement in gas sensing properties may be attributed to the change in width of the space charge region,which is similar to the behavior of p-n junction under forward bias,in the high-density p-n heterojunction structure formed between Si NWs and V_2O_5 nanorods.In conclusion,these results demonstrate that the Si NWs/V_2O_5 nanocomposite has great potential for future NO_2 gas detection applications with low consumption and good performance.