二氧化钒纳米线的制备和导电特性与相变调控

发布时间：2018-03-23 14:03

本文选题：VO_2纳米线　切入点：金属-绝缘体相变　出处：《哈尔滨工业大学》2017年博士论文

【摘要】：凝聚态物理和材料科学中,二氧化钒(VO_2)是最典型的具有金属-绝缘体相变(metal-insulator transition,MIT)特性的过渡金属氧化物。由于VO_2特殊的d电子轨道结构而产生的电子强关联效应,使其显示出十分丰富的物理和化学性质。研究发现具有MIT相变特性的二氧化钒包含两种不同的同质异形结构,分别是VO_2(A)和VO_2(M)。并且,低维纳米VO_2(A)和VO_2(M)的相变仍然非常显著,基于低维纳米二氧化钒优异的相变性能,可以被广泛的应用于传感器、光电开关、电阻开关、Mott场效应管和微纳动力驱动等领域。当下低维纳米VO_2(A)和VO_2(M)的研究尚处于初始阶段,尤其是一维纳米二氧化钒的研究,其导电特性、M-R畴结构形成、演变和稳定机制以及相变调控机理仍不清晰。基于此,本论文利用水热合成和化学气相沉积(CVD)技术分别制备了表面形貌光滑、单晶结构的VO_2(A)和VO_2(M)纳米线,通过自主搭建的热-电微探针测试平台系统研究了二氧化钒相变过程的导电特性,揭示了M-R畴结构演变规律,探索了基底失配应变对相变的调控机制,为相关微纳器件研发奠定理论和实验基础。主要研究内容和结果如下:研究了VO_2(A)和VO_2(M)纳米线的制备工艺,讨论了合成条件对纳米线形貌、结构及生长效率的影响。研究分析表明,在水热合成VO_2(A)纳米线中表面活性剂PEG-6000可以有效地促进前驱体五氧化二钒向B相二氧化钒的转变,避免了中间相V_3O_7?H_2O和V_6O_(13)的产生,使得合成VO_2(A)纳米线的速度加快,反应温度降低;在化学气相沉积技术制备VO_2(M)纳米线中,使用熔点较低的V2O5粉末作反应源,将纳米线的合成温度降低到1133K,合成时间缩短至2h以内。另外,实验发现使用未抛光的石英基底可以得到大量自由状态(free-standing)的VO_2(M)纳米线。研究了不同尺寸VO_2(A)纳米线相变过程中的导电特性,通过第一性原理计算得到VO_2(A)的能带结构和带隙宽度,揭示了尺寸效应对VO_2(A)相变的影响规律。第一性原理计算得到VO_2(A)高温相时的禁带宽度为0.75eV,低温相时1.12eV。实验发现宽度在微米级的VO_2(A)纳米线的相变伴随有一个多数量级的电阻突变,相变温度为444K。随着纳米线宽度的减小,其相变越来越迟缓,统计结果表明VO_2(A)纳米线相变温度与其宽度的倒数成正比。然而,当VO_2(A)纳米线尺寸降为72nm时,固有的一阶结构相变完全消失,转变为高阶连续相变。TEM的形貌和结构测试分析发现VO_2(A)纳米线的表面非常粗糙,表面与内部结构有很大差异。研究分析表明VO_2(A)纳米线的表面粗糙指数与纳米线宽度的倒数也成正比。这说明尺寸越小的纳米线,其表面效应越显著,而VO_2(A)纳米线表面的异相成核在相变过程中扮演重要角色,因此VO_2(A)纳米线表面效应是导致尺寸效应的直接原因。同时,这也告诉我们在应用相变材料时务必考虑其尺寸效应的影响。通过对电滞回线、电阻突变率和相变温度的对比分析,系统研究了失配应变对VO_2(M)纳米线M-R畴结构演变、形成和稳定的影响规律,讨论了VO_2(M)纳米线在失配应变作用下的导电特性。研究结果表明随着温度的变化VO_2(M)纳米线的M-R畴结构成周期性变化。与自由状态的VO_2(M)纳米线相比,失配应变作用下的VO_2(M)纳米线相变温度升高,相变滞后宽度增加,并在相变前表现出M1与M2的相互转换。另外,受到基底失配应变力的作用,VO_2(M)纳米线表现出多级相变特性,这可以被应用在快速多位存储领域。探索了电压调控VO_2(M)纳米线相变的方法。通过加载合适的电压使“镶嵌”在SiO_2基底中的VO_2(M)纳米线在绝缘相M和金属相R之间相互转换,其阻值突变达到3个数量级,循环次数超过100次,基于这一性能可以将其开发为快速存储器件。同时,这也进一步说明可以通过对二氧化钒纳米线形貌、结构以及生长方式的控制来调控其金属-绝缘体相变。本论文中对VO_2(A)和VO_2(M)纳米线制备、导电特性、尺寸效应和相变调控的系统研究,揭示了一维纳米二氧化钒基本的相变性质,提出了相变调控的方法,为一维纳米相变二氧化钒的应用和相关微纳器件的研发奠定基础。
[Abstract]:Condensed matter physics and material science, two vanadium oxide (VO_2) is the most typical metal insulator transition (metal-insulator transition, MIT) transition metal oxide properties. The electron strong correlation effect due to VO_2 special d electronic configuration, which shows the physical and chemical properties are very rich. The study found that two of vanadium oxide with MIT transformation characteristics include two kinds of paramorph structure different, are VO_2 (A) and VO_2 (M). Moreover, the low dimensional nano VO_2 (A) and VO_2 (M) phase transition is very significant, phase change properties of low vanadium oxide based on Vinami two excellent, can be widely used in sensor, photoelectric switch, switch resistor, Mott FET and micro power driven fields. The low dimensional nano VO_2 (A) and VO_2 (M) research is still at the initial stage, especially on a Wiener two meters of vanadium oxide, the conductive properties of M The formation of -R domain structure, evolution and stability mechanism and the transformation mechanism is still not clear. Based on this, this paper using the hydrothermal synthesis and chemical vapor deposition (CVD) was prepared with smooth surface morphology were single crystal structure technology, VO_2 (A) and VO_2 (M) nanowires, the conductive properties of vanadium phase change process two the study of oxidation of self built thermo electric micro probe test platform system through the evolvement of M-R domain structure, explores the base mismatch strain regulation mechanism on the phase transformation, lay a theoretical and experimental basis for related micro nano devices. The main research contents and results are as follows: VO_2 (A) and VO_2 (M) preparation of nanowires, discussed the synthesis conditions on the morphology of the nanowires, affect the structure and growth efficiency. Research shows that in the hydrothermal synthesis of VO_2 (A) PEG-6000 surfactant nanowires can effectively promote the five of two vanadium precursor to B The two phase transition of vanadium oxide, to avoid the middle phase of V_3O_7? H_2O and V_6O_ (13) which makes the synthesis of VO_2 (A) nanowires speed, reaction temperature decreased; preparation technology of VO_2 in chemical vapor deposition (M) nanowires, using V2O5 powder with low melting point as a reaction the source, will reduce the synthesis temperature of nanowires to 1133K, synthesis time is shortened to less than 2H. In addition, the experiment found that the use of quartz substrate polishing can have a lot of free state (free-standing) VO_2 (M) nanowires. Effects of different size VO_2 (A) conductive properties of nanowires during phase transition, VO_2 by first principle calculation (A) band structure and band gap width, reveal the size effect of VO_2 (A) effect of phase transition. The first principle calculation of VO_2 (A) band width is 0.75eV when the high temperature phase, low temperature phase 1.12eV. experiments found that the width at the micron level VO_2 (A) na The phase transition is accompanied by resistance wire one magnitude mutation, the phase transition temperature is 444K. with the decrease of the nanowire width, the phase change more and more slow, statistical results show that the VO_2 (A) proportional to the reciprocal of the nanowires and its phase transition temperature width. However, when VO_2 (A) nanowires size reduced to 72nm, a order phase transition inherent completely disappeared, found VO_2 into the morphology and structure of the test of high order continuous phase transition analysis of.TEM (A) nanowires surface is very rough, there is a great difference between the surface and internal structure. The analysis shows that VO_2 (A) inverse surface roughness index and nanowire width is proportional. This shows that the smaller size of the nanowires, the surface effect is more obvious, and the VO_2 (A) nanowires surface nucleation plays an important role in the transformation process, so the VO_2 (A) surface effect of nanometer line is a direct cause of size effect at the same time, This also tells us to consider the impact of the size effect in the application of phase change materials. Through the comparative analysis of the hysteresis loop, the resistance mutation rate and phase transition temperature, the misfit strain of VO_2 (M) system to study the evolution of M-R nanowires of domain structure, influence the formation and stability of VO_2 (M), is discussed. The conductive properties of nanowires in the misfit strain under the action. The results show that with the temperature change of VO_2 (M) M-R domain structure of nanowires into periodic changes. With the free state of VO_2 (M) nanowires compared to the misfit strain under the action of VO_2 (M) phase transition temperature of nanowires increases, hysteresis the increase of the width, and show the conversion between M1 and M2 in the phase transformation. In addition, by substrate misfit strain force, VO_2 (M) nanowires exhibit multi phase transition properties, which can be applied in many fields. To explore the rapid storage voltage regulation of VO_2 (M) nanowires phase transition The appropriate voltage loading method. The "mosaic" in the basement of SiO_2 VO_2 (M) conversion between R nanowires in the insulating phase of M and metal, the resistance mutation of up to 3 orders of magnitude more than 100 times the number of cycles, the performance can be developed as a fast memory device based on. At the same time, it also said that through the morphology of two vanadium oxide nanowires, structure and control methods to control the growth of metal insulator transition. In this paper VO_2 (A) and VO_2 (M) conductive properties of nanowires, system research, size effect and transformation regulation, reveals the phase transition properties of one-dimensional two basic nano vanadium oxide, and puts forward the method of phase control, lay the foundation for development of application of one-dimensional nano phase change two vanadium oxide and related micro nano devices.

【学位授予单位】：哈尔滨工业大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TB383.1;TQ135.11

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