对含有拓扑缺陷碳纳米管电学性能的研究

【作者】 张丽芳；

【导师】 胡慧芳；

【作者基本信息】 中南大学 ， 凝聚态物理， 2004， 硕士

【摘要】 碳纳米管是在1991年日本S．Iijima首次发现的。作为一种新的准一维纳米材料，由于其独特的结构和奇特的物理，化学和力学特性以及潜在的应用前景，尤其是利用它的电学性能在研制和开发纳米器件中发挥重要的作用，十几年来倍受人们的关注，因此成为国际纳米材料研究领域的前沿课题。通过大量的实验发现，在制备碳纳米管的过程中会有拓扑缺陷(5／7)产生，从而可形成各种‘结’，本文旨在研究含有拓扑缺陷对碳纳米管的电学性能。 本文首先在紧束缚模型的基础上，利用扩展的Su-Schriffer-Heeger(SSH)模型，在实空间研究了在完整的“zigzag”碳纳米管中引入不同分布不同排列的五边形-七边形拓扑缺陷对(5／7)所形成的各种‘结’的电学性能。计算了在碳纳米管中分别引入5／7，5／6／7，5／6／6／7拓扑缺陷所构成的(9，0)-(8，0)，(9，0)-(7，0)和(9，0)-(6，0)三种系统和沿周长方向并排引入两个五边形-七边形拓扑缺陷对所形成(9，0)-(9，0)，(8，0)-(8，0)系统的电子结构和电子态密度。在此基础上，计入系统的库仑相互作用，并对电子关联相互作用采用了Hartree—Fork自洽场近似下，研究了电子关联对碳纳米管电学性能的影响。另外，在波矢空间，我们计算了在考虑次近邻电子跃迁作用下，理想锯齿型碳纳米管(9，0)和(10，0)电子结构及电子态密度。 研究表明，这些五边形和七边形拓扑缺陷不仅改变碳管的直径，支配费米能级附近的电学行为，而且随着拓扑缺陷在碳管中分布和排列方式的不同，碳管电学性能也明显不同。因此，可以研制出基于这些‘结’的不同的电子器件基元。电子-电子相互作用使得能带结构整体向能量高的方向移动，随着电子-电子相互作用强度U、V的增大，能带宽度逐渐拓宽，而能隙的变化大小取决于u、V的取值范围；另外，计入U、V使得电荷密度发生了重新分布，而且在缺陷及其周围格点上出现了束缚电荷；费米能级向能量升高的方向移动，并且在新的费米能级点出现了电子局域态。最后，在波矢空间，研究了次近邻电子跃迁对理想锯齿型碳纳米管(9，0)和(10，0)电子结构影响，结果表明，次近邻电子跃迁使得总的能带宽度加宽，但是各能带的简并度不变，特别是金属型碳管(9，0)出现了能隙；根据参数t的不同，碳管(9，0)和(10，0)的能隙呈现不同的变化趋势。这些现象说明，拓扑缺陷，电子-电子相互作中南大学硕士学位论文摘要用，次近邻电子跃迁对碳纳米管的电学性能具有重要的作用。更多还原

【Abstract】 As a new one-dimension nanomaterial ,Carbon nanotube have attracted great attention since their discoveries in 1991.The sensitivity of their electronic property to their geometry makes nanotube useful in many potential application., especially in nanoelecteonic devices. In this paper, we mainly study the electronic property of carbon nanotube which contain topological defects, pentagon-heptagon pairs(5/7).In this paper, using the extended Su-Schriffer-Heeger(SSH) model, we investigate the features of energetics and electronic properties of various ’junctions’ which are achieved by introducing different arrange and distribution of topological defects, pentagon-heptagon pairs(5/7) , in the perfect hexagonal network of the zigzag carbon nanotubes configuration in the real space. We calculate the electronic structure and the densities of states of three system,(9,0)-(8,0),(9,0)-(7,0)and (9,0)-(6,0), and other two system (9,0)-(9,0) and (8,0)-(8,0) . On this base , considering electron-electron correlation, furthermore we investigate the effects of electron-electron correlation on electrical properties of carbon nanotube. In addition, containing next-nearest-neighboring hopping interactions, we study the energy band and density of states of zigzag carbon nanotube, (9,0),(10,0), in reciprocal space .The result show that these topological defects are not only responsible for a change in nanotube diameter, but also for the electronic behavior in the vicinity to Fermi level .The effect of different arrangement of pentagon-heptagon pairs on the properties of carbon nanotube is remarkable. In addition, electron-electron interaction make the whole energy band move to the direction of high energy , with the increase of Coulomb interaction, the energy is broader gradually ,while the variation of energy gap depends mainly on U and V; Coulomb interaction V causes the inhomogeneous distribution of charge density, Fermi energy shift to high energy position and new Localized states appears. Finally, we study the effects of next-nearest-neighboring hopping interactions on the electronic properties of zigzag carbon nanotubes,(9,0)and (10,0), in reciprocal space. It is found that thedegeneracy is invariable and each level shifts up and down which lead to the whole band width broadening, especially ,for (9,0),the energy gap appears, and the gap of (9,0)and(10,0) change according to t .This facts imply that topological defects ,electron-electron interactions, and next-nearest-neighboring hopping interactions would play an important role in the electronic properties of carbon nanotube.更多还原