复合缺陷对低维纳米材料电子输运性能的调控及器件设计

发布时间：2019-05-23 08:27

【摘要】：近年来,随着纳米材料的迅速发展,分子器件的研究已经引起了实验设计和理论预测的极大关注。随着电子器件尺寸的缩小和微电子技术的快速发展,分子器件将会替代微电子器件成为当今世界引领科学技术的主导力量。众所周知,各种新型的纳米材料是设计分子器件的基元。低维纳米材料在力学、电学、光学以及热学等方面,尤其是电子输运性能方面的优越性能,使其在电子器件发展过程中发挥了重要的作用。纳米材料在实际生产和制备的过程中,不可避免地会引入缺陷和杂质,影响其材料的力学、电学、光学以及电子输运等特性,这使得含有缺陷和杂质的低维纳米结构的科学研究更加有意义。本文采用密度泛函理论结合非平衡格林函数的第一性原理方法,系统地研究了几种复合缺陷对低维纳米材料电子输运性能的调控效应及器件设计。涉及的研究对象包含:碳纳米管(CNTs)、石墨烯纳米带(GNRs)和硅烯纳米带(Si NRs)等。主要研究内容如下:研究了含氮空位复合缺陷的螺旋手性单壁碳纳米管(SWCNTs)的电子输运性能。计算结果表明在手性SWCNTs中空位和氮原子组成的类嘧啶复合缺陷的引入有效地提高了体系的电子输运性能,并观察到明显的负微分电阻效应和强烈的整流效应。进一步的研究发现,复合掺杂体系输运透射系数在偏压窗口内的变化是产生整流效应的根本原因。研究了含羧化缺陷复合体的手性(8,4)碳纳米管和含羧化硼缺陷复合体的手性(6,3)碳纳米管的电子结构及输运性能。结果表明,(i)对于(8,4)SWCNTs体系,无论是本征缺陷还是含羧基的复合缺陷均在费米能级附近产生了缺陷态。其中,本征缺陷的缺陷态所导致的电子局域化效应阻碍了碳纳米管的电子传导能力,而羧基对本征缺陷的氧化作用却有效地增强了SWCNTs的传输电导。进一步对含羧基缺陷复合体的SWCNTs器件电子输运性能的研究,表明偏压作用下缺陷复合体降低了SWCNTs的电子传导,且器件出现了显著的负微分电阻效应。当且仅当羧基吸附单空位缺陷时,体系出现了强烈的整流效应,这为高性能分子整流器的研究提供了有价值的参考。(ii)对于(6,3)SWCNTs体系,含羧化硼空位复合结构与其他复合缺陷结构相比更加的稳定。其中,羧化硼空位复合缺陷增强了(6,3)SWCNTs的电子传导能力,而羧化硼掺杂和羧化硼SW复合缺陷却阻碍了体系的电子输运通道。进一步研究证实了该现象完全归因于羧基与硼缺陷复合体分子轨道之间的相互耦合作用。这些特殊的现象表明含羧化缺陷复合体碳纳米管在器件研究方面存在潜在的应用价值。研究了硅/氮复合掺杂体(sinx)对扶手椅型石墨烯纳米带(agnrs)的电子结构及输运性能的影响。其中,通过在相邻原子格点嵌入si和n原子而构成sinx复合掺杂体。结果表明sinx复合掺杂体使得agnrs体系在费米能级附近产生杂质态,且掺杂能带随着n原子浓度的增加而向下移动并与费米能级相交。进一步的研究表明杂质能级和施主能级是分离的,并且均受到杂质的微扰作用。在sinx复合掺杂agnrs体系中观察到明显的负微分电阻效应,且该效应随着n浓度的增加而减弱。这说明低n浓度的sinx复合掺杂能够有效的调节扶手椅型石墨烯纳米带的电子传导特性。研究了类相邻磷原子掺杂a格点(aa-p2)对扶手椅型硅烯纳米带(asinrs)的电子结构和输运性能的影响。结果表明,随着aa-p2杂质位置从纳米带中心到边缘掺杂的过程中asinrs发生了半导体性和金属性之间的转化。这完全归因于杂质磷(p)原子与硅(si)原子pz轨道之间的相互耦合。各掺杂体系在低偏压下均出现了对称的负微分电阻效应。然而,随着aa-p2掺杂体从中心到边缘的过程中,负微分电阻效应的对称性逐渐降低。更加有趣的是当且仅当aa-p2位于边缘对角掺杂位置时,体系出现了强烈的整流效应。其次,基于稳定的aa-p2对角掺杂asinrs结构,研究了连接非对称电极的aa-p2掺杂asinrs器件的电子输运性能,其中左电极为理想硅烯纳米带,右电极为aa-p2掺杂硅烯纳米带。结果表明器件的电子输运性能强烈地依赖于纳米带的宽度和aa-p2的掺杂位置。在器件中观察到了强烈的整流行为,且器件的整流效应可以通过改变纳米带的宽度和aa-p2杂质位置得以有效地调控。进一步的研究表明,左右电极能带的匹配区域和对应分子轨道与电子能带之间的耦合作用是产生整流效应的根本原因。研究了氟(f)原子和羟基(-oh)官能团边缘终端对两个正三角石墨烯纳米片(tgns)顶点相接的分子器件的电子输运及整流性能的影响。计算结果表明f原子和-oh官能团对左边tgns(ltgns)的边缘修饰使得分子器件展现出不同强度和方向的整流行为。原子或官能团对ltgns边缘修饰位置的不同使分子器件出现完全相反的整流方向。而边缘修饰原子或官能团的化学活性直接影响了分子器件的整流强度。进一步的研究表明电荷在相互连接的左右电极与左右tgns截面处的移动所产生的肖特基势垒是影响整流行为的根本原因。这对基于边缘管能化tgns分子整流器的了解和发展是重要的。其次,研究了铝(al)原子和磷(p)原子顶点掺杂正三角硅烯纳米片(tsins)分子结器件的整流行为。结果表明不同构型的顶点掺杂显著地影响了器件的整流性能。其中,al-si、al-p掺杂器件表现正向整流行为,且al-p体系的整流比更大。相反地,Si-P掺杂体系却表现反向整流行为。这表明左右TSi Ns在顶点的不同掺杂构型能够有效地调控分子结器件的整流效应,为分子整流器的设计提供有利条件。
[Abstract]:In recent years, with the rapid development of the nano-materials, the research of molecular devices has given great attention to the experimental design and the theoretical prediction. With the reduction of the size of the electronic device and the rapid development of the micro-electronic technology, the molecular device will replace the microelectronic device to become the leading force of the world's leading science and technology. As is well known, a variety of new nanomaterials are the primitives of the design of molecular devices. The advantage of the low-dimensional nano-material in the aspects of mechanics, electricity, optics and heat, especially the electron transport property, can play an important role in the development of the electronic device. In the process of the actual production and preparation of the nano-materials, the defects and the impurities are inevitably introduced, and the mechanical, electrical, optical and electron transport properties of the materials are affected, which makes the scientific research of the low-dimensional nanostructures containing defects and impurities more meaningful. In this paper, the control effect of several composite defects on the electron transport performance of low-dimensional nano-materials and the device design are systematically studied by using the first principle method of density functional theory and the non-equilibrium Green's function. The research objects involved include carbon nanotubes (CNTs), graphene nanoribbons (GNRs), and graphene nanobelt (Si NRs), and the like. The main contents of the study are as follows: The electron transport properties of spiral chiral single-walled carbon nanotubes (SWCNTs) with compound defects of nitrogen-containing vacancies are studied. The results of the calculation show that the introduction of the compound defect of the class-like compound composed of the vacancy and the nitrogen atom in the hand SWCNTs effectively improves the electron transport performance of the system, and the obvious negative differential resistance effect and the strong rectification effect are observed. Further studies have found that the variation of the transport coefficient of the composite doping system within the bias window is the root cause of the rectification effect. The electron structure and transport properties of the chiral (8,4) carbon nanotubes and the chiral (6,3) carbon nanotubes containing the encapsulated boron-deficient complex were studied. The results show that (i) for the (8,4) SWCNTs system, the defect state is generated near the Fermi level, whether the intrinsic defect or the compound defect containing the metal matrix. In which the electron local effect caused by the defect state of the intrinsic defect can hinder the electron conduction ability of the carbon nano tube, and the oxidation of the intrinsic defect to the intrinsic defect effectively enhances the transmission conductance of the SWCNTs. In this paper, the electron transport performance of the SWCNTs (SWCNTs) device with the matrix-based defect complex is further studied, which shows that the defect complex under the bias effect reduces the electronic conduction of the SWCNTs, and the device has a significant negative differential resistance effect. The system has a strong rectifying effect when and only when the single-vacancy defect of the high-performance molecular rectifier is defective, which provides valuable reference for the research of the high-performance molecular rectifier. (ii) For the (6,3) SWCNTs system, the encapsulated boron-vacancy composite structure is more stable than other composite defect structures. In this paper, the electron-conduction ability of (6,3) SWCNTs is enhanced by the compound defect of the encapsulated boron vacancy, and the combined defects of the encapsulated boron and the encapsulated boron SW have hindered the electron transport channel of the system. Further studies have confirmed that the phenomenon is completely attributable to the mutual coupling between the base and the molecular orbital of the boron-deficient complex. These special phenomena indicate the potential application value of the carbon nanotubes with the encapsulated defect complex in the research of the device. The effect of sinx on the electronic structure and transport properties of an armchair-type graphene nanobelt was studied. In which a sinx composite dopant is formed by embedding si and n atoms at an adjacent atomic lattice point. The results show that the sinx composite doped body causes the agrs system to generate the impurity state near the Fermi level, and the doping energy band moves down with the increase of the n-atom concentration and intersects the Fermi level. Further studies show that the impurity level and the donor energy level are separated and are all subject to the perturbation of the impurities. A significant negative differential resistance effect is observed in the sinx composite dopant system and the effect is reduced as the n concentration increases. This indicates that the low-n-concentration sinx composite doping can effectively adjust the electron-conducting properties of the armchair-type graphene nanobelt. The effect of a lattice point (aa-p2) on the electron structure and transport properties of an armchair-type silicon-ene nanobelt was studied. The results show that the conversion between the semiconductor and the metallic property occurs in the process of doping the aa-p2 impurity from the center of the nanobelt to the edge. This is due entirely to the mutual coupling between the impurity phosphorus (p) atom and the silicon (si) atom pz track. Each doping system has a symmetric negative differential resistance effect under a low bias voltage. However, with the process of the aa-p2 dopant from the center to the edge, the symmetry of the negative differential resistance effect is gradually reduced. More interesting is that the system has a strong rectifying effect when and only when aa-p2 is in the edge diagonally-doped position. Secondly, based on the stable aa-p2, the electron transport performance of the aa-p2-doped asinth device is studied. The left electrode is an ideal graphene nanobelt, and the right electrode is aa-p2-doped graphene nanobelt. The results show that the electron transport property of the device is strongly dependent on the width of the nanobelt and the doping position of aa-p2. A strong rectifying behavior is observed in the device, and the rectifying effect of the device can be effectively regulated by changing the width of the nanobelt and the aa-p2 impurity position. Further studies have shown that the coupling between the matching region of the left and right electrode bands and the corresponding molecular orbital and the electron energy band is the root cause of the rectification effect. The effects of the edge termination of fluorine (f) and hydroxyl (-oh) functional groups on the electron transport and rectification of two n-triangular graphene nanosheets (tgns) were studied. The results show that the edge modification of the left tgns (ltgns) by the f-atom and-oh functional group makes the molecular device exhibit the rectification behavior of different strength and direction. The difference of the atom or functional group to the ltgns edge modification position causes the molecular device to appear in a completely opposite direction of rectification. While the chemical activity of the edge-modified atoms or functional groups directly affects the rectification strength of the molecular device. Further studies have shown that the Schottky barrier produced by the movement of the charge between the left and right electrodes connected to one another and the left and right tgns cross-section is the root cause of the effect of the rectification. This is important for the understanding and development of the edge-tube-enabled tgns molecular rectifier. In this paper, the rectification behavior of the (al) atom and the phosphorus (p) atom vertex-doped n-triangular silicon nano-sheet (tsins)-junction device is studied. The results show that vertex doping in different configurations significantly affects the rectifying performance of the device. In which, the al-si and al-p-doped devices show forward rectification behavior, and the rectifying ratio of the al-p system is larger. In contrast, the Si-P doping system exhibits a reverse rectification behavior. This indicates that the different doping configurations of the left and right TSi Ns can effectively control the rectifying effect of the molecular junction device and provide favorable conditions for the design of the molecular rectifier.
【学位授予单位】：湖南大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TB383.1

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