【作者】 李峰；

【导师】 张彤；

【作者基本信息】 吉林大学 ， 微电子学与固体电子学， 2018， 博士

【摘要】 随着社会不断的发展与进步,化石燃料的开采和燃烧以及工业废气造成的大气污染越来越严重。气体传感器作为一种将气体的成份、浓度等信息转换成可以被人员、仪器仪表、计算机等利用的信息的装置,被广泛应用于有害气体进行实时检测,有利于人们对大气污染的治理。敏感材料是气体传感器领域的核心,对高性能的敏感材料的研究与开发,是提高气体传感器敏感特性的主要途径之一。本论文主要以研究核壳结构对半导体敏感材料气敏特性的影响为目标,立足于异质结中自由电子扩散方向与半导体电子功函数之间关系的设计,通过制备具有核壳结构的纳米纤维,研究纳米纤维的气敏特性与自由电子扩散方向之间的关系,深入研究了异质结、核壳结构对半导体敏感材料气敏特性提升的敏感机理,主要工作分如下四个部分:（1）SnO₂作为壳层材料,设计自由电子从内层向外层扩散的异质结,选择TiO₂作为核层材料,通过共轴静电纺丝法,制备了具有核壳结构的TiO₂-SnO₂纳米纤维,并以TiO₂、SnO₂单轴纳米纤维作为对照实验,重点对比了核壳结构纳米纤维与单轴纳米纤维气敏特性的差异,研究结果表明:当自由电子从内层向外层扩散,在壳层形成电子积累层时,可以提高核壳纳米纤维对待测气体的灵敏度如丙酮,并加快对丙酮的恢复速度。本章工作为研究核壳结构对气敏特性的影响做基础研究。（2）结合第一部分的研究工作,确定壳层材料为SnO₂,设计自由电子从外层向内层扩散的异质结,使得壳层为电子耗尽层,因此选择WO₃作为核层材料,制备了WO₃-SnO₂核壳纳米纤维。为了更深入的研究异质结在核壳结构中对气敏特性的影响,引入WO₃-SnO₂复合纳米纤维与WO₃、SnO₂单轴纳米纤维共同作为对照实验,通过对核壳纳米纤维和单轴纳米纤维气敏特性的全面测试与研究,发现当壳层为电子耗尽层时,核壳纳米纤维对待测气体的灵敏度仍有提高如乙醇,但是敏感材料对乙醇的响应恢复特性比SnO₂单轴纳米纤维的有所下降,尤其是恢复能力明显减弱。此外,核壳纳米纤维的气敏特性与壳层材料有着紧密的联系。通过本章的研究工作,证明自由电子在异质结中的扩散方向对核壳纳米纤维气敏特性的影响有着明显不同。（3）为了进一步研究核壳结构对纳米纤维气敏特性的影响,针对自由电子在异质结中的扩散方向的与半导体电子功函数之间的关系,设计了核壳材料互换的两种核壳纳米纤维,制备了In₂O₃-SnO₂核壳纳米纤维和SnO₂-In₂O₃核壳纳米纤维,通过对两种核壳纳米纤维气敏特性的测试并与In₂O₃、SnO₂单轴纳米纤维的气敏特性做对比,研究发现:无论自由电子的扩散方向如何,均会提升核壳纳米纤维对待测气体的灵敏度,证明了核壳结构是提升敏感材料的灵敏度的重要方法之一。然而,当自由电子从外层向内层扩散时,削弱了敏感材料的恢复特性,这是核壳结构带来的缺陷与弊端。至此,研究发现核壳结构中对气敏特性的影响有着一定的规律,当自由电子向壳层流动,在壳层形成电子积累层时,会加快其恢复速度;当自由电子向核层流动,在壳层形成电子耗尽层时,则会减慢其恢复速度。（4）针对因自由电子向核层扩散,在壳层形成电子耗尽层,大幅度削弱核壳纳米纤维对待测气体恢复速度这一缺陷,利用贵金属的催化活性,以SnO₂-In₂O₃核壳纳米纤维为研究主体,对In₂O₃壳层进行贵金属Au掺杂,制备SnO2-Au/In2O3核壳纳米纤维,并对掺杂量进行调控,筛选出最佳的掺杂比例的样品材料,对其进行气敏特性测试。测试结果表明:通过对壳层金属氧化物半导体进行贵金属掺杂,可以进一步提升其对目标气体的灵敏度和选择性,更重要的是,掺杂后的核壳纳米纤维对待测气体的恢复特性得到大幅度的提升,弥补了因自由电子的流动而导致核壳纳米纤维恢复速度慢的缺陷。本论文通过以上四部分的工作,系统地研究了核壳结构、自由电子在异质结中扩散的方向与金属氧化物半导体纳米纤维气敏特性的关系与规律,深入地研究了核壳纳米纤维的气敏敏感机理。更多还原

【Abstract】 With the continuous development and progress of society,people’s demand for energy is increasing.The exploitation and combustion of fossil fuels and the air pollution caused by industrial waste are also more and more serious.In the face of the severe pollution situation and the people’s desire for the healthy atmosphere,it is imminent to control the air pollution and reduce the emission of harmful gases.The gas sensor device as a component of the gas concentration and other information can be converted into the use of personnel,instrumentation,computers and other information,is widely used in real-time detection of harmful gases,is conducive to the people of atmospheric pollution control and self protection.Sensitive material is the core of the field of gas sensors.The research and development of sensitive materials for high performance is one of the main ways to improve the sensitive characteristics of gas sensors.In recent years,the vigorous development of nanotechnology has opened up new ideas and directions for the research and exploration of sensitive materials,and has also provided a powerful driving force for the development and innovation of gas sensors.This paper mainly studies the core-shell structure on the gas sensing properties of semiconductor sensitive materials for influence,design based on free electron diffusion between semiconductor heterostructure and reactive direction function,through the preparation of nano fibers with core-shell structure,the relationship between the gas sensing properties and free electron diffusion direction of nano fiber the in-depth study of the sensitive mechanism of heterojunction,the core-shell structure of semiconductor material sensitive gas sensing properties of ascension,the main work is as follows:（1）In this work,a core-shell heterostructure nanowires（NWs）have been synthesized via a coaxial electrospinning approach.SnO₂ and TiO₂ were chosen as the samples for the synthesis of the core-shell NWs.A comparative gas sensing study among the TiO₂/SnO₂ core-shell NWs,the SnO₂ NWs and the TiO₂ NWs were performed to demonstrate the excellent gas sensing properties.The sensors based on the TiO₂/SnO₂ core-shell NWs exhibited excellent sensing properties[quick response to acetone（2 s）,high response to acetone（13.7）and good selectivity]at 280 ^oC operating temperature.The enhanced sensing properties relies on the changes of adsorbed oxygen species and electron depletion layer on the surface,because the electrons flow to the surface resulting from differences in the work functions.（2）In this work,core-shell WO₃-SnO₂（CS-WS）nanofibers（NFs）have been successfully synthesized via a coaxial electrospinning approach.The structure and morphology characteristics of the resultant products were investigated by X-ray diffraction（XRD）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,and X-ray photoelectron spectra（XPS）.To investigate the sensing mechanism of the CS-WS NFs,sensors based on SnO₂ NFs,WO₃ NFs,and SnO₂-WO₃ composite NFs were fabricated respectively,and their gas sensing properties were investigated by using CO,ethanol,toluene,acetone,and ammonia as the test gas.The enhanced ethanol sensing properties of CS-WS NFs compared with those of SnO₂ NFs were closely associated with the CS structure and its derivative effect.The approach proposed in this study may contribute to the realization of more sensitive metal oxide semiconductor（MOS）core-shell heterostructure sensors.（3）In this work,two types of core-shell heterostructure NFs,In₂O₃-SnO₂ core-shell NFs and SnO₂-In₂O₃ core-shell NFs were synthesized by a coaxial electrospinning method.To demonstrate the potential applications,gas sensors based on above two core-shell NFs were fabricated and their gas sensing characteristics were investigated by using TMA as the target gas.In order to explain the sensing behaviors,the SnO₂pristine NFs and In₂O₃ pristine NFs were also synthesized respectively by electrospinning and their gas sensing behaviors were investigated.The sensing mechanism could be illustrated by the differences of the gas sensing properties of the core-shell NFs and the pristine NFs.（4）SnO₂/Au-doped In₂O₃ core-shell（CS）nanofibers（NFs）were designed and synthesized through a facile coaxial electrospinning method.To investigate its potential application,commercial gas sensor was fabricated and its gas sensing properties were tested.The SnO₂/Au-doped In₂O₃ CS NFs sensor showed enhanced acetone gas sensing properties compared to the Au-doped In₂O₃ single NFs sensor counterpart.The SnO₂/Au-doped In₂O₃ CS NFs sensor exhibited a high response at300 ^oC,whereas Au-doped In₂O₃ NFs sensor showed a relative low response at 300^oC.Furthermore,the former sensors also showed a fast response speed and a good selectivity to acetone.In addition,the underlying mechanism for the enhanced acetone sensing properties of SnO₂/Au-doped In₂O₃ CS NFs sensor could be attributed to the catalytic activity of Au and the CS structure.The approach and results proposed in this study may contribute to the realization of more sensitive CS structure NFs sensors.Based on the above four parts,the relationship between the core shell structure and the direction of free electrons in the heterojunction and the gas sensing properties of metal oxide semiconductor nanofibers has been systematically studied.The gas sensing mechanism of core shell nanofibers has been deeply studied.更多还原