金属氧化物半导体表面态的调控设计及气敏性能的研究
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摘要
在城市化进程不断加速、机动车保有量持续增加、能源消耗量快速增长的今天，传感器作为信息获取的器件或系统，已经成为现代科技的重要支柱之一。敏感材料是气体传感器的核心，大力发展和开发敏感材料是提高气体传感器性能的战略途径之一。近年来，纳米科技的发展为敏感材料的研究和材料微观结构的设计注入了新的元素，也提供了驱动力和创新的源泉。对敏感材料结构的物化性、电学性质进行分析，重点研究尺寸、相成分和结构对材料物化特性的影响，对获得新型的敏感材料并拓展其在化学传感领域的应用具有非常重要的意义。另外，纳米材料表面的调控与气体传感器宏观特性的内在关系的分析突破了常规的机理研究，为发展高性能敏感器件拓展了无限空间。本论文主要围绕金属氧化物半导体传感器在气体检测中存在的问题，从提高材料的识别功能、转换功能和利用效率入手，利用水热合成法制备种类丰富、形态各异的氧化物半导体敏感材料，通过调节反应条件对多种半导体氧化物敏感材料进行表面、界面和相成分的调控，来增强气体传感器的灵敏度、选择性、响应恢复速度和稳定性等。主要内容如下：
(1)利用水热合成技术制备了实心SnO2和ZnO纳米球，解决了无规则纳米粒子由于范德华力作用团聚的问题，增大了比表面积，根据粒子的尺寸效应，初步分析了实心纳米材料的气体敏感特性，阐述了实心结构和无规则纳米粒子敏感特性机理。
(2)将中空结构纳米材料应用在气体传感器上，深入研究疏松壳层和中空结构对待测气体分子传输的作用，增加了待测气体分子在敏感体表面的吸附量；提高了待测气体分子在敏感体内部的传输速率，使敏感元件的响应恢复时间大幅度的缩短。
(3)通过添加表面活性剂和改变其种类来调控组成结构单元的维数，获得由不同维数的纳米结构单元所构成的分等级结构。然后通过高温煅烧的方法除去吸附在材料表面的表面活性剂，制得表面疏松及多孔的分等级结构。探索表面疏松程度对气敏特性的影响。
(4)首次将具有核壳结构的纳米材料应用在气体传感器上，揭示了金属氧化物半导体材料表（界）面状态对化学敏感特性的调制作用，发现气体传感器性能高度依赖材料微观结构，并建立了金属氧化物半导体气体敏感机理的模型；
(5)利用分等级材料、中空材料和核壳材料的表面修饰等新的手段调制材料与待测气体之间的相互作用，同时可对纳米材料的化学修饰或改性可实现其性能裁剪，改善其表面结构，增强其在纳米材料基体中的分散特性及其与基体之间的界面结合作用。从而提高气体传感器的检测精度、选择性和稳定性；此外结合化学和电子敏感机制，初步建立了理论模型。为纳米电子器件的深入研究提供了基础；
(6)发展一种新型抗环境湿度由p型半导体和n型半导体组成的复合敏感材料，将这种复合异质材料应用在气体传感器上，利用p型半导体在一维纳米材料上的生长减小p型半导体纳米粒子的聚集，将这些纳米粒子集中修饰在纳米纤维的外围，增强其与水分子之间的相互作用，从而消除湿度对敏感性能的影响，提高传感器的检测精度和稳定性。
本论文的开展不仅为气体传感器提供新型纳米材料、微纳加工方法和技术，而且还在基础研究层面，深入理解纳米尺度下敏感材料的结构、相成分与敏感功能的关系，明晰微纳结构的增强机制，为气体传感器的研究与开发提供新理念。丰富了金属氧化物半导体气体传感器的敏感机理，为气体传感器的研究提供新理论、新方法和新技术。
With the acceleration of urbanization, the increase of vehicle population and therapid growth of energy consumption, gas sensor technology as devices or systemsaccess to information has already become one of the important pillars of moderntechnology. In practice, chemical sensors have played important roles in militaryengineering, industrial, environmental protection, human life, medical and so on.Sensing material is a core part of the gas sensor, and the design and development ofnovel and efficient synthetic strategies for nanomaterials are playing an importantrole in the enhanced sensing performance of gas sensor. In recent years,development of nanotechnology not only injects new elements for research ofsensing materials and design of sensing materials microstructures but it alsoprovides the motivation and innovation. Metal oxide semiconductor nanomaterialsexhibit the wide application prospects in gas sensor field. For example, hollownanostructure-based sensor exhibits fast response and recovery time,heterostructures-based sensor could enhance the selectivity to target gases and so on.The analysis of the relationship between structure and performance of sensingmaterials and the effect research of the size, component and structure to sensingperformance of sensing materials are of great significance and practical engineeringvalue. Moreover, the analysis of the intrinsic relationship between the surfaceregulation of sensing materials and macroscopic properties of gas sensor break theconventional mechanism for the development of new sensitive devices and expandthe application space. In the project, we have comprehensively investigated the problem of the sensor based on metal oxide semiconductor nanomaterials. It is ofgreat importance to regulate and control the surface structure of semiconductingmetal oxides and explore the relationship between the component, morphology andsensing performances, which are also the research topic of the modification of thegas-sensing properties (such as response, response/recovery time, selectivity andstability) of sensing materials. The main research contents in this thesis aresummarized as follows:
(1) Solid SnO2and ZnO nanospheres have been prepared by using a simplehydrothemal method. The gas sensing preformances of the as-prepared solid SnO2and ZnO nanospheres were researched according to the “size effect” discussed inchapter one.
(2) For structure of sensing materials, we will propose that the hollow SnO2andZnO nanospheres as sensing material used in gas sensor, and indepth studiedconfinement effects of the loose structure to gas transmission. This structureimproves the speed of the gas go inner and outer surfaces of sensing material, sodecreased the response and recovery time of the sensor.
(3) By adding the surfactant composition to regulate the dimension of thestructural unit obtained hierarchical SnO2and ZnO nanostructure with differentstructure unit. The hierarchical SnO2and ZnO nanostructure were obtained by asimple hydrolysis method with subsequent calcination process. It is of greatimportance to regulate and control the surface structure of semiconducting metaloxides and explore the relationship between the loose degree, size, morphology andgas-sensing properties,
(4) The core-shell SnO2and ZnO nanostructures with hollow and multiple-shellarchitectures have been successfully synthesized and the first time used in gas sensor.The gas sensing results show the surface state of metal oxide semiconductornanomaterials have moderating effect on sensing performance. We find that thestructure dependence of the gas-sensing characteristics in metal oxidesemiconductor nanomaterials-based sensors, one of the greatest factors in gas-sensorapplications, is managed by various structures. Moreover, we established gas sensing mechanism model for of a metal oxide semiconductor.
(5) The surface modification by hierarchical, hollow and core-shell (SnO2andZnO) nanostructure materials would concol the interfaceaction between sensingmaterials and target gases, and enhace the the dispersibility of nanomaterials and theinterfacial bonding with the nanostructure. The structure and content of thesurface-modified compounds would be regulated to balance the dispersingcharacteristic and conductivity of the composite membrane. The enhancement of thedetection precision, selectivity and stablity in gas sensor would be realized, Abovereseach results will provide a scientific basis for devoloping high-quality highhumidity sensing materials and gas sensors.
(6) We will develop a new strategy to produce humidity-independent chemicalsensors by combining readily gas-accessible hierarchical sensing layers (n-typesemiconductor nanomaterials) and catalytic surface additives (p-type semiconductornanomaterials). The modified1D nanofibers would be used as the conductivefiller.The loading of p-type Co3O4into n-type1D TiO2nanofibers enhanced thesensing performance remarkably. Moreover, the humidity dependence of all of thesensing characteristics, including the detection precision, selectivity and stablity,was almost removed by the p-type Co3O4nanomaterials loading.
In conclusion, in this paper, we have systemically studied the relationshipbetween the composite materials structure/size and the gas sensing properties of thesensors, and in-depth know the sensing mechanism of metal oxide semiconductornanomaterials-based sensor, which establishes the foundation for devolopinghigh-quality high performance sensing materials and gas sensors.
(1)利用水热合成技术制备了实心SnO2和ZnO纳米球，解决了无规则纳米粒子由于范德华力作用团聚的问题，增大了比表面积，根据粒子的尺寸效应，初步分析了实心纳米材料的气体敏感特性，阐述了实心结构和无规则纳米粒子敏感特性机理。
(2)将中空结构纳米材料应用在气体传感器上，深入研究疏松壳层和中空结构对待测气体分子传输的作用，增加了待测气体分子在敏感体表面的吸附量；提高了待测气体分子在敏感体内部的传输速率，使敏感元件的响应恢复时间大幅度的缩短。
(3)通过添加表面活性剂和改变其种类来调控组成结构单元的维数，获得由不同维数的纳米结构单元所构成的分等级结构。然后通过高温煅烧的方法除去吸附在材料表面的表面活性剂，制得表面疏松及多孔的分等级结构。探索表面疏松程度对气敏特性的影响。
(4)首次将具有核壳结构的纳米材料应用在气体传感器上，揭示了金属氧化物半导体材料表（界）面状态对化学敏感特性的调制作用，发现气体传感器性能高度依赖材料微观结构，并建立了金属氧化物半导体气体敏感机理的模型；
(5)利用分等级材料、中空材料和核壳材料的表面修饰等新的手段调制材料与待测气体之间的相互作用，同时可对纳米材料的化学修饰或改性可实现其性能裁剪，改善其表面结构，增强其在纳米材料基体中的分散特性及其与基体之间的界面结合作用。从而提高气体传感器的检测精度、选择性和稳定性；此外结合化学和电子敏感机制，初步建立了理论模型。为纳米电子器件的深入研究提供了基础；
(6)发展一种新型抗环境湿度由p型半导体和n型半导体组成的复合敏感材料，将这种复合异质材料应用在气体传感器上，利用p型半导体在一维纳米材料上的生长减小p型半导体纳米粒子的聚集，将这些纳米粒子集中修饰在纳米纤维的外围，增强其与水分子之间的相互作用，从而消除湿度对敏感性能的影响，提高传感器的检测精度和稳定性。
本论文的开展不仅为气体传感器提供新型纳米材料、微纳加工方法和技术，而且还在基础研究层面，深入理解纳米尺度下敏感材料的结构、相成分与敏感功能的关系，明晰微纳结构的增强机制，为气体传感器的研究与开发提供新理念。丰富了金属氧化物半导体气体传感器的敏感机理，为气体传感器的研究提供新理论、新方法和新技术。
With the acceleration of urbanization, the increase of vehicle population and therapid growth of energy consumption, gas sensor technology as devices or systemsaccess to information has already become one of the important pillars of moderntechnology. In practice, chemical sensors have played important roles in militaryengineering, industrial, environmental protection, human life, medical and so on.Sensing material is a core part of the gas sensor, and the design and development ofnovel and efficient synthetic strategies for nanomaterials are playing an importantrole in the enhanced sensing performance of gas sensor. In recent years,development of nanotechnology not only injects new elements for research ofsensing materials and design of sensing materials microstructures but it alsoprovides the motivation and innovation. Metal oxide semiconductor nanomaterialsexhibit the wide application prospects in gas sensor field. For example, hollownanostructure-based sensor exhibits fast response and recovery time,heterostructures-based sensor could enhance the selectivity to target gases and so on.The analysis of the relationship between structure and performance of sensingmaterials and the effect research of the size, component and structure to sensingperformance of sensing materials are of great significance and practical engineeringvalue. Moreover, the analysis of the intrinsic relationship between the surfaceregulation of sensing materials and macroscopic properties of gas sensor break theconventional mechanism for the development of new sensitive devices and expandthe application space. In the project, we have comprehensively investigated the problem of the sensor based on metal oxide semiconductor nanomaterials. It is ofgreat importance to regulate and control the surface structure of semiconductingmetal oxides and explore the relationship between the component, morphology andsensing performances, which are also the research topic of the modification of thegas-sensing properties (such as response, response/recovery time, selectivity andstability) of sensing materials. The main research contents in this thesis aresummarized as follows:
(1) Solid SnO2and ZnO nanospheres have been prepared by using a simplehydrothemal method. The gas sensing preformances of the as-prepared solid SnO2and ZnO nanospheres were researched according to the “size effect” discussed inchapter one.
(2) For structure of sensing materials, we will propose that the hollow SnO2andZnO nanospheres as sensing material used in gas sensor, and indepth studiedconfinement effects of the loose structure to gas transmission. This structureimproves the speed of the gas go inner and outer surfaces of sensing material, sodecreased the response and recovery time of the sensor.
(3) By adding the surfactant composition to regulate the dimension of thestructural unit obtained hierarchical SnO2and ZnO nanostructure with differentstructure unit. The hierarchical SnO2and ZnO nanostructure were obtained by asimple hydrolysis method with subsequent calcination process. It is of greatimportance to regulate and control the surface structure of semiconducting metaloxides and explore the relationship between the loose degree, size, morphology andgas-sensing properties,
(4) The core-shell SnO2and ZnO nanostructures with hollow and multiple-shellarchitectures have been successfully synthesized and the first time used in gas sensor.The gas sensing results show the surface state of metal oxide semiconductornanomaterials have moderating effect on sensing performance. We find that thestructure dependence of the gas-sensing characteristics in metal oxidesemiconductor nanomaterials-based sensors, one of the greatest factors in gas-sensorapplications, is managed by various structures. Moreover, we established gas sensing mechanism model for of a metal oxide semiconductor.
(5) The surface modification by hierarchical, hollow and core-shell (SnO2andZnO) nanostructure materials would concol the interfaceaction between sensingmaterials and target gases, and enhace the the dispersibility of nanomaterials and theinterfacial bonding with the nanostructure. The structure and content of thesurface-modified compounds would be regulated to balance the dispersingcharacteristic and conductivity of the composite membrane. The enhancement of thedetection precision, selectivity and stablity in gas sensor would be realized, Abovereseach results will provide a scientific basis for devoloping high-quality highhumidity sensing materials and gas sensors.
(6) We will develop a new strategy to produce humidity-independent chemicalsensors by combining readily gas-accessible hierarchical sensing layers (n-typesemiconductor nanomaterials) and catalytic surface additives (p-type semiconductornanomaterials). The modified1D nanofibers would be used as the conductivefiller.The loading of p-type Co3O4into n-type1D TiO2nanofibers enhanced thesensing performance remarkably. Moreover, the humidity dependence of all of thesensing characteristics, including the detection precision, selectivity and stablity,was almost removed by the p-type Co3O4nanomaterials loading.
In conclusion, in this paper, we have systemically studied the relationshipbetween the composite materials structure/size and the gas sensing properties of thesensors, and in-depth know the sensing mechanism of metal oxide semiconductornanomaterials-based sensor, which establishes the foundation for devolopinghigh-quality high performance sensing materials and gas sensors.
引文
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