【摘要】：近年來,隨著納米材料的迅速發(fā)展,分子器件的研究已經(jīng)引起了實驗設計和理論預測的極大關注。隨著電子器件尺寸的縮小和微電子技術的快速發(fā)展,分子器件將會替代微電子器件成為當今世界引領科學技術的主導力量。眾所周知,各種新型的納米材料是設計分子器件的基元。低維納米材料在力學、電學、光學以及熱學等方面,尤其是電子輸運性能方面的優(yōu)越性能,使其在電子器件發(fā)展過程中發(fā)揮了重要的作用。納米材料在實際生產(chǎn)和制備的過程中,不可避免地會引入缺陷和雜質(zhì),影響其材料的力學、電學、光學以及電子輸運等特性,這使得含有缺陷和雜質(zhì)的低維納米結(jié)構(gòu)的科學研究更加有意義。本文采用密度泛函理論結(jié)合非平衡格林函數(shù)的第一性原理方法,系統(tǒng)地研究了幾種復合缺陷對低維納米材料電子輸運性能的調(diào)控效應及器件設計。涉及的研究對象包含:碳納米管(CNTs)、石墨烯納米帶(GNRs)和硅烯納米帶(Si NRs)等。主要研究內(nèi)容如下:研究了含氮空位復合缺陷的螺旋手性單壁碳納米管(SWCNTs)的電子輸運性能。計算結(jié)果表明在手性SWCNTs中空位和氮原子組成的類嘧啶復合缺陷的引入有效地提高了體系的電子輸運性能,并觀察到明顯的負微分電阻效應和強烈的整流效應。進一步的研究發(fā)現(xiàn),復合摻雜體系輸運透射系數(shù)在偏壓窗口內(nèi)的變化是產(chǎn)生整流效應的根本原因。研究了含羧化缺陷復合體的手性(8,4)碳納米管和含羧化硼缺陷復合體的手性(6,3)碳納米管的電子結(jié)構(gòu)及輸運性能。結(jié)果表明,(i)對于(8,4)SWCNTs體系,無論是本征缺陷還是含羧基的復合缺陷均在費米能級附近產(chǎn)生了缺陷態(tài)。其中,本征缺陷的缺陷態(tài)所導致的電子局域化效應阻礙了碳納米管的電子傳導能力,而羧基對本征缺陷的氧化作用卻有效地增強了SWCNTs的傳輸電導。進一步對含羧基缺陷復合體的SWCNTs器件電子輸運性能的研究,表明偏壓作用下缺陷復合體降低了SWCNTs的電子傳導,且器件出現(xiàn)了顯著的負微分電阻效應。當且僅當羧基吸附單空位缺陷時,體系出現(xiàn)了強烈的整流效應,這為高性能分子整流器的研究提供了有價值的參考。(ii)對于(6,3)SWCNTs體系,含羧化硼空位復合結(jié)構(gòu)與其他復合缺陷結(jié)構(gòu)相比更加的穩(wěn)定。其中,羧化硼空位復合缺陷增強了(6,3)SWCNTs的電子傳導能力,而羧化硼摻雜和羧化硼SW復合缺陷卻阻礙了體系的電子輸運通道。進一步研究證實了該現(xiàn)象完全歸因于羧基與硼缺陷復合體分子軌道之間的相互耦合作用。這些特殊的現(xiàn)象表明含羧化缺陷復合體碳納米管在器件研究方面存在潛在的應用價值。研究了硅/氮復合摻雜體(sinx)對扶手椅型石墨烯納米帶(agnrs)的電子結(jié)構(gòu)及輸運性能的影響。其中,通過在相鄰原子格點嵌入si和n原子而構(gòu)成sinx復合摻雜體。結(jié)果表明sinx復合摻雜體使得agnrs體系在費米能級附近產(chǎn)生雜質(zhì)態(tài),且摻雜能帶隨著n原子濃度的增加而向下移動并與費米能級相交。進一步的研究表明雜質(zhì)能級和施主能級是分離的,并且均受到雜質(zhì)的微擾作用。在sinx復合摻雜agnrs體系中觀察到明顯的負微分電阻效應,且該效應隨著n濃度的增加而減弱。這說明低n濃度的sinx復合摻雜能夠有效的調(diào)節(jié)扶手椅型石墨烯納米帶的電子傳導特性。研究了類相鄰磷原子摻雜a格點(aa-p2)對扶手椅型硅烯納米帶(asinrs)的電子結(jié)構(gòu)和輸運性能的影響。結(jié)果表明,隨著aa-p2雜質(zhì)位置從納米帶中心到邊緣摻雜的過程中asinrs發(fā)生了半導體性和金屬性之間的轉(zhuǎn)化。這完全歸因于雜質(zhì)磷(p)原子與硅(si)原子pz軌道之間的相互耦合。各摻雜體系在低偏壓下均出現(xiàn)了對稱的負微分電阻效應。然而,隨著aa-p2摻雜體從中心到邊緣的過程中,負微分電阻效應的對稱性逐漸降低。更加有趣的是當且僅當aa-p2位于邊緣對角摻雜位置時,體系出現(xiàn)了強烈的整流效應。其次,基于穩(wěn)定的aa-p2對角摻雜asinrs結(jié)構(gòu),研究了連接非對稱電極的aa-p2摻雜asinrs器件的電子輸運性能,其中左電極為理想硅烯納米帶,右電極為aa-p2摻雜硅烯納米帶。結(jié)果表明器件的電子輸運性能強烈地依賴于納米帶的寬度和aa-p2的摻雜位置。在器件中觀察到了強烈的整流行為,且器件的整流效應可以通過改變納米帶的寬度和aa-p2雜質(zhì)位置得以有效地調(diào)控。進一步的研究表明,左右電極能帶的匹配區(qū)域和對應分子軌道與電子能帶之間的耦合作用是產(chǎn)生整流效應的根本原因。研究了氟(f)原子和羥基(-oh)官能團邊緣終端對兩個正三角石墨烯納米片(tgns)頂點相接的分子器件的電子輸運及整流性能的影響。計算結(jié)果表明f原子和-oh官能團對左邊tgns(ltgns)的邊緣修飾使得分子器件展現(xiàn)出不同強度和方向的整流行為。原子或官能團對ltgns邊緣修飾位置的不同使分子器件出現(xiàn)完全相反的整流方向。而邊緣修飾原子或官能團的化學活性直接影響了分子器件的整流強度。進一步的研究表明電荷在相互連接的左右電極與左右tgns截面處的移動所產(chǎn)生的肖特基勢壘是影響整流行為的根本原因。這對基于邊緣管能化tgns分子整流器的了解和發(fā)展是重要的。其次,研究了鋁(al)原子和磷(p)原子頂點摻雜正三角硅烯納米片(tsins)分子結(jié)器件的整流行為。結(jié)果表明不同構(gòu)型的頂點摻雜顯著地影響了器件的整流性能。其中,al-si、al-p摻雜器件表現(xiàn)正向整流行為,且al-p體系的整流比更大。相反地,Si-P摻雜體系卻表現(xiàn)反向整流行為。這表明左右TSi Ns在頂點的不同摻雜構(gòu)型能夠有效地調(diào)控分子結(jié)器件的整流效應,為分子整流器的設計提供有利條件。
[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.
【學位授予單位】：湖南大學
【學位級別】：博士
【學位授予年份】：2015
【分類號】：TB383.1

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