ZnO基传感器的气敏和湿敏特性研究
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摘要
自从1962年发现ZnO材料的电导率会随环境气氛发生变化以来，有关ZnO基气、湿敏传感器的研究就一直受到人们的关注。近年来，随着纳米科技与相关制备工艺的快速发展，ZnO基敏感材料的制备技术已臻成熟，如何提高传感器的敏感性能成为研究的重点。本文从纳米ZnO的结构与形貌控制、掺杂、复合和修饰出发，制备了几种ZnO基材料体系，并通过制作传感器原型器件，对其相应的湿度或气体敏感性能研究，分析了相关的敏感机理。论文取得了以下主要研究结果：
1、多孔片层ZnO球的制备及其气敏性能研究
采用水热法制备了多孔片层ZnO球并对其形貌和结构进行了表征。通过制作电阻型原型器件，研究了其对乙醇气体的敏感性能。结果表明，该气敏元件的最佳工作温度为280oC。在此温度下，元件对2ppm乙醇的灵敏度达到2.8，响应和恢复时间分别为10和15s，且在2-500ppm乙醇气体浓度范围内的响应曲线具有很好的线性度。与目前商业ZnO粉末气敏元件相比，基于多孔片层ZnO球的气体传感器优势在于其具有更低的工作温度和更高的灵敏度。
2、Zn掺杂SnO2多孔空心球的制备及其气敏性能研究
以碳球为模板，采用直接沉淀法制备Zn掺杂SnO2多孔空心球，并对其形貌和结构进行了表征。通过制作电阻型原型器件，研究了其对乙醇气体的敏感性能。结果表明，在240oC的工作温度下，该气敏元件对乙醇的响应值最大。对于2ppm、5ppm、10ppm、50ppm、100ppm、200ppm、300ppm和500ppm的乙醇气体，其响应值分别为：2.8、4.6、4.9、16、27.4、48.8、71.9和100，其响应和恢复时间分别为29和16s。与具有相同结构特征的纯ZnO或SnO2多孔空心球相比，Zn掺杂SnO2多孔空心球气敏元件在灵敏度与稳定性表现出较大的优势。
3、Zn2SnO4纳米结构的制备及其气敏性能研究
采用水热制备Zn2SnO4纳米结构并对其形貌和结构进行了表征。研究表明，通过改变水热液的pH值，可以对其形貌及晶体生长取向进行调控。在材料制备过程中，当反应溶液的pH值由9到11再到13时，Zn2SnO4的形貌由单一的纳米颗粒转变为纳米颗粒-纳米棒并存，最终转变为纳米棒；Zn2SnO4生长的择优取向从（311）转变为（331），材料的比表面积也随之增大。结果表明，pH为13时制备的样品对乙醇气体具有最好的敏感性能。在300oC的工作温度下，该敏感元件对100ppm乙醇的响应值达到30.7，响应和恢复时间分别为10和9s。同时，该元件被放置15周，响应值随时间几乎没有变化，表现出很好的测量稳定性。
4、ZnO/Si-NPA的制备与湿敏性能研究
以硅纳米孔柱阵列（Si-NPA）为衬底，采用溶胶-凝胶法结合旋涂技术制备了ZnO/Si-NPA，并对其形貌和结构特征进行了表征。研究表明，旋涂于Si-NPA衬底上的ZnO纳米晶粒大致呈球状，平均粒径为~5.87nm；ZnO/Si-NPA保持了良好的柱状阵列结构。通过制作电容型原型器件，对其湿敏性能进行了研究。结果表明，当湿敏元件暴露于33%、54%、75%、95%相对湿度环境中时，其灵敏度分别达到~124.5%、536.2%、2035.4%和5522%，元件的响应和恢复时间分别为65s和48s。放置15周后，该元件的电容值变化相对较大，稳定性有待进一步提高。
5、PVP修饰ZnO/Si-NPA的制备与湿敏性能研究
采用溶胶-凝胶法制备了PVP修饰的ZnO纳米颗粒。光吸收谱测试表明，随着PVP添加量的增大，ZnO的吸收边先发生蓝移。当Zn2+/PVP摩尔比达到5:3时，蓝移最大；此时PVP修饰ZnO纳米颗粒呈球形，分散性好且粒径分布均匀，平均粒径为3.52nm。继续增大PVP的添加量，其吸收边将发生红移。对不同剂量PVP修饰ZnO纳米颗粒/Si-NPA的湿敏特性进行研究发现，随着PVP的添加量的增大，PVP修饰ZnO/Si-NPA的灵敏度逐渐增加，但与此同时湿滞也逐渐增大。当Zn2+/PVP摩尔比为5：3时，元件的湿敏性能最佳。此时，当PVP修饰ZnO/Si-NPA湿敏元件暴露于33%、54%、75%、95%的相对湿度环境中时，器件的灵敏度分别达到~80.9%、571%、10334%和1127198%。该元件的响应和恢复时间分别为16s和8s。放置15周后，该元件的电容值随时间变化很小，具有很好的稳定性。
Since the year of1962, when the conductance of ZnO was found to change withthe appearance of ethanol, study on ZnO gas and humidity sensor has come to be thehot topic. With the development of nanotechnology and production, preparation ofZnO sensing materials has become perfect, and most of the attentions have beenfocused on how to improve the sensing properties. In this paper, we studied the gasand humidity sensing properties of sensors based on ZnO. The effect of morphologyand structure, dopping, materials composite, and modifying on the sensing propertieswas investigated. The main conclueds were as follows:
1. Studies on preparation and gas sensing properties of porous flake ZnO spheres
We prepared ZnO spheres composed of porous flake by hydrothermal methodcombined with heat treatment, and their morphology and structure were characterized.Resistance-type gas sensor based on porous flake ZnO spheres was prepared and itsethanol gas sensing property was studied. It is found the sensor desmontrated obviousresponse to2ppm ethanol with the corresponding response of2.8at the optimumoperation temperature of280oC, and the response and recovery time of10and15s.The sensor showed good linearity with the concentration of ethanol in the range of2~500ppm. The sensos based on porous ZnO spheres showed improved ethanolresponse on working temperature and sensitivity compared to that based oncomemerical ZnO powders.
2. Studies on preparation and gas sensing properties of Zn-doped SnO2poroushollow microspheres.
Zn-doped SnO2porous hollow microspheres have been prepared by a directprecipitation methoed combined with heat treatment, using colloidal carbon sphere astemplate, and their morphology and structure were characterized. Resistance-type gassensor based on Zn-doped SnO2porous hollow microspheres was prepared and itsethanol gas sensing property was studied. It is found the sensor has a good selectivityto ethanol at the optimum working temperature of240oC. The response of the sensor to ethanol with the concentration of2,5,10,50,100,200,300and500ppm was2.8,4.6,16,27.4,48.8,71.9and100, respectively. The response and recovery time was29and16s, respectively. Compared to the single ZnO and SnO2with the samenanostructure, Zn-doped SnO2porous hollow microspheres sensor exhibitedimproved ethanol gas sensing properties on sensitivity and stability.
3. Studies on preparation and gas sensing properties of Zn2SnO4nanostructure.
Ternary material Zn2SnO4were prepared by hydrothermal method combinedwith heat treat, and their morphology and structure were characterized. It is found wecan regulate the morphology and preferential orientation of Zn2SnO4by the pH value.The morphology of Zn2SnO4nanostructure changed from single nanoparticles to bothnanoparticles and nanorods, the preferential orientation varied from (311) to (311),and the special surface area increased when the pH value of the solution changedfrom9to13. Zn2SnO4sensor prepared at the pH of13exhibited the best gas sensingproperties. At the working temperature of300oC, the sensor response to100ppmethanol was30.7, the response and recovery time was10and9s, respectively, andthe stability was good after aging for15weeks.
4. Studies on preparation and humidity sensing properties of ZnO/Si-NPA.
ZnO/Si-NPA was prepared by sol-gel method combined with dipping, usingSi-NPA as the template and substrate, and their morphology and structure werecharacterized. It is found the morphology of ZnO nnaoparticles on Si-NPA wasapproximately sphere-like, with the size of5.87nm, and the ZnO/Si-NPA keep thepillar arrays. Studies on humidity sensing properties of ZnO/Si-NPA sensor found thatwhen the ZnO/Si-NPA humidity sensor was exposed in33%,54%,75%,95%RH, thesensitivity was124.5%,536.2%,2035.4%and5522%, respectively. The response andrecovery time was65and48s, respectively. After aging for15weeks, the variation ofcapacitance was relatively large, and we should improve it in further studies.
5. Studies on preparation and humidity sensing properties of PVP modifiedZnO/Si-NPA.
PVP modified ZnO nanoparticles was prepared by sol-gel method. Theabsorption edge of ZnO exhibited blue shift with the increment of PVP. And that exhibited red shift with the increment of PVP when the mole ratio of Zn2+/PVP wassmaller than5:3. When the mole ratio of Zn2+/PVP was5:3, PVP modified ZnO wassphere-like, with good dispersion and uniform size of5.87nm. Studies on humiditysensing properties of PVP modified ZnO found that the sensitivity and hysteresis ofPVP modified ZnO/Si-NPA sensor increased with the increment of PVP. Humiditysensor with the mole ratio of Zn2+/PVP of5:3, exhibited the best sensing properties.When the sensor was exposed in33%,54%,75%,95%RH, the sensitivity was80.9%,571%,10334%and1127198%, respectively. The response and recovery time was16and8s, respectively. After aging for15weeks, the variation of capacitance was slight,and the sensor exhibited good stability.
1、多孔片层ZnO球的制备及其气敏性能研究
采用水热法制备了多孔片层ZnO球并对其形貌和结构进行了表征。通过制作电阻型原型器件，研究了其对乙醇气体的敏感性能。结果表明，该气敏元件的最佳工作温度为280oC。在此温度下，元件对2ppm乙醇的灵敏度达到2.8，响应和恢复时间分别为10和15s，且在2-500ppm乙醇气体浓度范围内的响应曲线具有很好的线性度。与目前商业ZnO粉末气敏元件相比，基于多孔片层ZnO球的气体传感器优势在于其具有更低的工作温度和更高的灵敏度。
2、Zn掺杂SnO2多孔空心球的制备及其气敏性能研究
以碳球为模板，采用直接沉淀法制备Zn掺杂SnO2多孔空心球，并对其形貌和结构进行了表征。通过制作电阻型原型器件，研究了其对乙醇气体的敏感性能。结果表明，在240oC的工作温度下，该气敏元件对乙醇的响应值最大。对于2ppm、5ppm、10ppm、50ppm、100ppm、200ppm、300ppm和500ppm的乙醇气体，其响应值分别为：2.8、4.6、4.9、16、27.4、48.8、71.9和100，其响应和恢复时间分别为29和16s。与具有相同结构特征的纯ZnO或SnO2多孔空心球相比，Zn掺杂SnO2多孔空心球气敏元件在灵敏度与稳定性表现出较大的优势。
3、Zn2SnO4纳米结构的制备及其气敏性能研究
采用水热制备Zn2SnO4纳米结构并对其形貌和结构进行了表征。研究表明，通过改变水热液的pH值，可以对其形貌及晶体生长取向进行调控。在材料制备过程中，当反应溶液的pH值由9到11再到13时，Zn2SnO4的形貌由单一的纳米颗粒转变为纳米颗粒-纳米棒并存，最终转变为纳米棒；Zn2SnO4生长的择优取向从（311）转变为（331），材料的比表面积也随之增大。结果表明，pH为13时制备的样品对乙醇气体具有最好的敏感性能。在300oC的工作温度下，该敏感元件对100ppm乙醇的响应值达到30.7，响应和恢复时间分别为10和9s。同时，该元件被放置15周，响应值随时间几乎没有变化，表现出很好的测量稳定性。
4、ZnO/Si-NPA的制备与湿敏性能研究
以硅纳米孔柱阵列（Si-NPA）为衬底，采用溶胶-凝胶法结合旋涂技术制备了ZnO/Si-NPA，并对其形貌和结构特征进行了表征。研究表明，旋涂于Si-NPA衬底上的ZnO纳米晶粒大致呈球状，平均粒径为~5.87nm；ZnO/Si-NPA保持了良好的柱状阵列结构。通过制作电容型原型器件，对其湿敏性能进行了研究。结果表明，当湿敏元件暴露于33%、54%、75%、95%相对湿度环境中时，其灵敏度分别达到~124.5%、536.2%、2035.4%和5522%，元件的响应和恢复时间分别为65s和48s。放置15周后，该元件的电容值变化相对较大，稳定性有待进一步提高。
5、PVP修饰ZnO/Si-NPA的制备与湿敏性能研究
采用溶胶-凝胶法制备了PVP修饰的ZnO纳米颗粒。光吸收谱测试表明，随着PVP添加量的增大，ZnO的吸收边先发生蓝移。当Zn2+/PVP摩尔比达到5:3时，蓝移最大；此时PVP修饰ZnO纳米颗粒呈球形，分散性好且粒径分布均匀，平均粒径为3.52nm。继续增大PVP的添加量，其吸收边将发生红移。对不同剂量PVP修饰ZnO纳米颗粒/Si-NPA的湿敏特性进行研究发现，随着PVP的添加量的增大，PVP修饰ZnO/Si-NPA的灵敏度逐渐增加，但与此同时湿滞也逐渐增大。当Zn2+/PVP摩尔比为5：3时，元件的湿敏性能最佳。此时，当PVP修饰ZnO/Si-NPA湿敏元件暴露于33%、54%、75%、95%的相对湿度环境中时，器件的灵敏度分别达到~80.9%、571%、10334%和1127198%。该元件的响应和恢复时间分别为16s和8s。放置15周后，该元件的电容值随时间变化很小，具有很好的稳定性。
Since the year of1962, when the conductance of ZnO was found to change withthe appearance of ethanol, study on ZnO gas and humidity sensor has come to be thehot topic. With the development of nanotechnology and production, preparation ofZnO sensing materials has become perfect, and most of the attentions have beenfocused on how to improve the sensing properties. In this paper, we studied the gasand humidity sensing properties of sensors based on ZnO. The effect of morphologyand structure, dopping, materials composite, and modifying on the sensing propertieswas investigated. The main conclueds were as follows:
1. Studies on preparation and gas sensing properties of porous flake ZnO spheres
We prepared ZnO spheres composed of porous flake by hydrothermal methodcombined with heat treatment, and their morphology and structure were characterized.Resistance-type gas sensor based on porous flake ZnO spheres was prepared and itsethanol gas sensing property was studied. It is found the sensor desmontrated obviousresponse to2ppm ethanol with the corresponding response of2.8at the optimumoperation temperature of280oC, and the response and recovery time of10and15s.The sensor showed good linearity with the concentration of ethanol in the range of2~500ppm. The sensos based on porous ZnO spheres showed improved ethanolresponse on working temperature and sensitivity compared to that based oncomemerical ZnO powders.
2. Studies on preparation and gas sensing properties of Zn-doped SnO2poroushollow microspheres.
Zn-doped SnO2porous hollow microspheres have been prepared by a directprecipitation methoed combined with heat treatment, using colloidal carbon sphere astemplate, and their morphology and structure were characterized. Resistance-type gassensor based on Zn-doped SnO2porous hollow microspheres was prepared and itsethanol gas sensing property was studied. It is found the sensor has a good selectivityto ethanol at the optimum working temperature of240oC. The response of the sensor to ethanol with the concentration of2,5,10,50,100,200,300and500ppm was2.8,4.6,16,27.4,48.8,71.9and100, respectively. The response and recovery time was29and16s, respectively. Compared to the single ZnO and SnO2with the samenanostructure, Zn-doped SnO2porous hollow microspheres sensor exhibitedimproved ethanol gas sensing properties on sensitivity and stability.
3. Studies on preparation and gas sensing properties of Zn2SnO4nanostructure.
Ternary material Zn2SnO4were prepared by hydrothermal method combinedwith heat treat, and their morphology and structure were characterized. It is found wecan regulate the morphology and preferential orientation of Zn2SnO4by the pH value.The morphology of Zn2SnO4nanostructure changed from single nanoparticles to bothnanoparticles and nanorods, the preferential orientation varied from (311) to (311),and the special surface area increased when the pH value of the solution changedfrom9to13. Zn2SnO4sensor prepared at the pH of13exhibited the best gas sensingproperties. At the working temperature of300oC, the sensor response to100ppmethanol was30.7, the response and recovery time was10and9s, respectively, andthe stability was good after aging for15weeks.
4. Studies on preparation and humidity sensing properties of ZnO/Si-NPA.
ZnO/Si-NPA was prepared by sol-gel method combined with dipping, usingSi-NPA as the template and substrate, and their morphology and structure werecharacterized. It is found the morphology of ZnO nnaoparticles on Si-NPA wasapproximately sphere-like, with the size of5.87nm, and the ZnO/Si-NPA keep thepillar arrays. Studies on humidity sensing properties of ZnO/Si-NPA sensor found thatwhen the ZnO/Si-NPA humidity sensor was exposed in33%,54%,75%,95%RH, thesensitivity was124.5%,536.2%,2035.4%and5522%, respectively. The response andrecovery time was65and48s, respectively. After aging for15weeks, the variation ofcapacitance was relatively large, and we should improve it in further studies.
5. Studies on preparation and humidity sensing properties of PVP modifiedZnO/Si-NPA.
PVP modified ZnO nanoparticles was prepared by sol-gel method. Theabsorption edge of ZnO exhibited blue shift with the increment of PVP. And that exhibited red shift with the increment of PVP when the mole ratio of Zn2+/PVP wassmaller than5:3. When the mole ratio of Zn2+/PVP was5:3, PVP modified ZnO wassphere-like, with good dispersion and uniform size of5.87nm. Studies on humiditysensing properties of PVP modified ZnO found that the sensitivity and hysteresis ofPVP modified ZnO/Si-NPA sensor increased with the increment of PVP. Humiditysensor with the mole ratio of Zn2+/PVP of5:3, exhibited the best sensing properties.When the sensor was exposed in33%,54%,75%,95%RH, the sensitivity was80.9%,571%,10334%and1127198%, respectively. The response and recovery time was16and8s, respectively. After aging for15weeks, the variation of capacitance was slight,and the sensor exhibited good stability.
引文
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