一维宽禁带半导体气相沉积及气敏性研究

发布时间：2018-01-06 22:45

本文关键词：一维宽禁带半导体气相沉积及气敏性研究　出处：《河南大学》2016年博士论文　论文类型：学位论文

【摘要】：随着纳米科技的出现和纳米材料的发展,人们发现材料的性能不仅与材料的成分有关,而且与材料的微观结构和聚集状态密切相关,然而材料的微观结构与聚集状态又受制备方法和工艺的影响。因此,通过研究材料的制备过程、形成机理,调控材料的微观结构,从而改善材料的性能,对材料科学的发展具有重要的研究意义。宽禁带半导体材料既包括氮化镓(GaN)、碳化硅(SiC)、金刚石(C)、氮化铝(AlN)、氧化锌(ZnO)等无机半导体材料,还包括一些禁带宽度大于2.7 eV(室温条件下)的有机小分子半导体材料等。因为宽禁带半导体材料在气体传感器、光催化与太阳能电池、大功率光电器件等方面有着极为重要的应用,所以宽带隙半导体是最近研究热点之一。其中,纳米ZnO是一种Ⅱ-Ⅵ族直接带隙的宽禁带半导体材料,具有优越的光电性能和在气相条件下容易生成一维结构纳米材料等特点,在气敏、压电、传感、液晶显示器、太阳能电池、紫外发光器件以及催化等领域表现出潜在的应用前景,引起了研究人员的广泛关注。另外,有机半导体材料,尤其是共轭有机小分子材料由于其具有质轻、价廉和种类繁多等优点,低温条件下可通过实验过程与条件的控制,制备出具有不同形貌、不同性能的一维纳米材料,而且结构及性能可通过分子设计进行调控,这推动了低维分子、电子学领域快速发展。尤其是一维有机单晶微/纳米结构的材料,具有许多新颖的性质,在光电等领域具有重要的应用前景。本论文选取具有代表性的两种宽禁带半导体材料：无机镉掺杂ZnO和有机共轭小分子3,4,9,10-傒四甲酸二酐(PTCDA)为研究对象,采用可调控的气相沉积法,进行微／纳米结构的制备和气敏性能研究,并利用电泳法和光掩膜技术组装了单根微/纳米线器件,并研究了该器件的气敏性能。同时针对目前这两种材料在制备过程中存在的一些关键性问题,提出了有效的解决方案,并对样品制备中微观结构形态与气敏性能之间的关系进行了研究,实现了对材料结构和性能的有效控制。通过探索材料结构与性能之间的基本关系,为半导体微纳米材料的制备和应用提供了理论和实验依据。具体工作如下：一、采用物理气相沉积法(PVD),通过调控衬底的温度,在硅(Si)衬底上实现了有机共轭小分子PTCDA微米管通过自扭曲而转变形成双螺旋结构微米纤维。采用场发射扫描电子显微镜(FESEM)、透射电镜(TEM)及高分辨透射电子显微镜(HRTEM)、X-射线衍射(XRD)、紫外-可见光谱(UV-vis)仪器等对材料性能进行了表征。研究结果表明,PTCDA微米管在PVD过程中通过自扭曲而形成具有双螺旋结构的微米纤维,螺旋纤维直径大约为200纳米,长度约为几微米。通过一系列研究,我们推测微米纤维是在卷绕的多层微管从内向外分子层释放其内部的旋转应力的过程中,逐步扭曲,最终形成稳定的双螺旋结构,微管中相邻的分子层间改变的范德华作用和表面自由能是诱导螺旋结构形成的驱动力。这项工作为PTCDA微米管通过自扭曲形成双螺旋结构的形成提供了实验依据,同时为设计和构筑螺旋微米结构以及有序的一维有机小分子组装提供了新的合成途径。另外,我们进一步采用光掩膜技术组装了单根螺旋结构微米纤维器件,利用该器件研究了该螺旋纤维对乙醇的敏感特性。研究发现,该器件对较低浓度的乙醇(例如20 ppm)在室温下具有较高的灵敏度(4.85)和响应稳定性,尤其对5ppm的乙醇也表现出一定的敏感性,因此该螺旋纤维是一种有具潜在应用前景的气敏材料。二、采用气相沉积法,通过调控不同的制备温度生成了一系列具有不同镉(Cd)掺杂量的ZnO纳米线(0wt%、1.0 wt%、2wt%、3wt%和4 wt%),并通过XRD、SEM、 EDS、TEM、HRTEM、XPS和BET等测试手段对样品的形貌、结构及组成的元素价态进行了分析。实验结果发现,在600℃和镉掺杂的条件下,ZnO纳米线具有较好的有序结构和高的比表面积,随着反应温度进一步的增加,纳米结构缺陷明显增多,并且出现一定的团聚现象,这是因为温度升高,反应速度加快,产物生长速度增大,导致不利于控制材料的生长方向。在此基础上,我们探究了纳米线的生长机制,该生长过程符合气-固(VS:Vapor-Solid)生长机制,并且详细论述了该机制下纳米线的生长过程。另外,我们采用电泳法组装了单根纳米线器件,利用制备的纳米线器件,研究了不同Cd掺杂量的ZnO纳米线对还原性气体尤其是H2S气体的敏感特性,研究了不同Cd掺杂量与材料气敏性之间的关系规律。研究结果发现,当Cd掺杂量为3 wt%时,制备的纳米线对H2S气体有较高的灵敏度(410),是未掺杂ZnO纳米线灵敏度(150)的两倍多。当更高Cd掺杂量(4 wt%)时ZnO纳米线对H2S气体的响应值略有降低。这种纳米线器件对其他还原性气体也有一定的响应性。另外,我们进一步探讨了Cd掺杂ZnO纳米线的气敏机制,对H2S气体高的敏感性,主要归因气体分子在材料表面的吸附与脱附,引起材料表面结构及能带发生变化,势垒高度发生相应改变,导致载流子在纳米线表面的传输速度不同,宏观表现为纳米线的电阻发生变化,这一过程是化学吸附脱附与电子敏化作用协同作用的结果。
[Abstract]:With the development of nano technology and nano materials, people found that the material performance is not only related to the material composition, and microstructure and material and aggregation are closely related, however, the microstructure of the materials and the aggregation state by the preparation method and the effect of process. Therefore, the formation mechanism of the preparation process of materials the microstructure, material control, and improve the properties of materials, have important significance to the development of materials science. Both gallium nitride semiconductor material with wide band gap (GaN), silicon carbide (SiC), diamond (C), aluminum nitride (AlN), Zinc Oxide (ZnO) and other inorganic semiconductor materials, including some the band gap width is greater than 2.7 eV (room temperature) of small molecule organic semiconductor materials. Because of wide band gap semiconductor materials in gas sensors, photocatalysis and solar batteries, high-power optoelectronic devices plays a very As an important application, so a wide band gap semiconductor is one of the hot research recently. Among them, the nano ZnO is a kind of wide band gap semiconductors VI direct bandgap, with excellent optoelectronic properties and under the condition of gas phase to form one-dimensional nanomaterials, etc., in gas sensor, piezoelectric sensor. Liquid crystal display, solar cell, UV light emitting devices and catalytic fields exhibit potential applications, attracted the attention of researchers. In addition, organic semiconductor materials, especially the conjugated organic small molecule material because of its lightweight, low cost and wide variety of advantages, under the condition of low temperature can control the experiment process and the conditions, prepared with different morphologies, one-dimensional nano materials with different properties, and the structure and properties can be controlled by molecular design, which promoted the rapid development of the field of low dimensional molecular electronics especially. The material is one dimensional organic single crystal micro / nano structure, with many novel properties, have important applications in optoelectronics and other fields. This paper selects two representative of wide band gap semiconductor materials: inorganic cadmium doped ZnO and organic conjugated molecules 3,4,9,10- Xi acid anhydride tetra two (PTCDA) as the research object. Deposition method using gas control, micro / nano structure preparation and gas sensing properties, and optical mask assembly of single micro / nano line devices using electrophoresis method, and studied the gas sensing properties of the device. Aiming at some key problems in the preparation process of the two materials at present, put forward an effective solution, and the relationship between sample preparation microstructure and gas sensing properties were studied, the effective control of the structure and properties of materials. Through the exploration of materials The basic relationship between the structure and properties of semiconductor micro nano materials, preparation and application provides a theoretical and experimental basis. The specific work is as follows: first, using physical vapor deposition (PVD), by controlling the temperature of the substrate, the silicon (Si) substrate to achieve organic conjugated molecules by PTCDA micro tube since the distortion and change form a double helix structure of micron fiber. By field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM), X- ray diffraction (XRD), UV Vis spectroscopy (UV-vis) on the properties of the materials were characterized by instruments. The results of the study show that PTCDA micron tube in the PVD process by self distortion is formed with the double helix structure of micron fibers, the spiral fiber diameter is about 200 nm, the length is about a few microns. Through a series of studies, we hypothesized that micro meters fiber is wound in multilayer microtubules Gradually distorted outward from the molecular layer release their internal stress in the process of rotation, and eventually formed a stable double helix structure, molecular layer between adjacent microtubules in Fan Dehua and surface free energy change is the driving force to induce the formation of the spiral structure. This work formed by self distortion provides the experimental basis for the formation of double the helical structure of PTCDA microtubes, and provides a new synthetic route for the design and construction of spiral micrometer structure and one-dimensional organic small molecule ordered assembly. In addition, we use a photomask technology assembly of single helical structure of micron fiber devices, study the sensitive characteristics of the helical fibers to ethanol by using the device. The study found that the ethanol device for low concentration (e.g. 20 ppm) with high sensitivity at room temperature (4.85) and response stability, especially for 5ppm ethanol also showed some The sensitivity of the spiral fiber is a kind of gas sensitive material has potential application prospect. Two, using vapor deposition method by controlling different preparation temperature generated with a series of different cadmium (Cd) doped ZnO nanowires (0wt% 1, wt%, 2wt%, 3wt% and 4 wt%) and, through XRD, SEM, EDS, TEM, HRTEM, XPS and morphology of the samples BET test methods, element valence structure and composition were analyzed. The experimental results showed that at 600 DEG C and CD doping conditions, ZnO nanowires have better ordered structure and high specific surface area. With the further increase of reaction temperature, nano structure defects increased significantly, and the emergence of agglomeration phenomenon, this is because the temperature increases, the reaction speed, product growth rate increase, which is harmful to the growth direction of control materials. On this basis, we explore the growth mechanism of the nanowires, the Long process with gas - solid (VS:Vapor-Solid) growth mechanism, and discussed the mechanism of nanowire growth process. In addition, we use electrophoresis assembled nanowire devices, the preparation of nanowire devices, ZnO nanowires were studied with different Cd doping amount is especially sensitive to the characteristics of H2S gas reductive gas, study the relationship between gas sensitivity with different Cd doping materials. The results of the study showed that when the doping amount of Cd is 3 wt%, the sensitivity of the prepared nanowires have higher H2S gas (410), is not doped ZnO nanowires sensitivity (150) more than two times. When the higher Cd content (4 wt%) response of ZnO nanowires of H2S gas decreased slightly. The nanowire device also has a certain response to other reducing gas. In addition, we further discuss the gas sensing mechanism of Cd doped ZnO nanowires, high sensitivity to H2S gas Emotional, mainly attributed to gas molecules adsorbed on surface and desorption, caused by the material surface structure and band change, change the corresponding height barrier, resulting in the transmission speed of carrier surface nanowires of different resistance nanowires shows macroscopic changes, this process is the interaction of chemical adsorption desorption and electron the result of sensitization.

【学位授予单位】：河南大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TN304.055

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