单壁碳纳米管中空位缺陷的曲率效应

发布时间：2018-04-22 20:18

本文选题：密度泛函理论 + 缺陷曲率　；参考：《内蒙古科技大学》2015年硕士论文

【摘要】：完美的碳纳米管具有良好的电子、机械与结构性能。然而，实际中不可避免地引入各种缺陷结构，，如吸附质吸附、SW(stone—wales)拓扑缺陷、原子空位缺陷。在这些结构缺失中，原子结构缺失是最多产和重要的结构缺陷，碳纳米管中空位的产生对其机械、物理化学性质有极其重要的影响。因此，针对碳纳米管原子结构缺陷的问题研究是深入了解其结构和物理化学性能及解决其在实际应用的根本问题之一。本论文采用密度泛函方法系统地研究了(5,5)椅型管和(n,0)(n=6～10)锯齿型管单到八空位缺陷(V1～V8)的空位形成能、产物结构、空位结构的稳定性随空位原子数的变化规律及其它们随(n,0)管中n的变化规律，且主要结果如下， (1)基于曾提出的方向曲率理论推导了缺陷曲率，并将其应用于椅型与锯齿型单壁碳纳米管的V1～V8空位形成能预测。对一种Vn，空位形成能随着缺陷曲率的增大而总体呈现减小趋势，且对椅型碳纳米管，原子容易沿着锯齿形链去除；对锯齿型碳纳米管，原子容易沿着椅形链去除。此外，产物中缺陷区的局域结构影响空位形成能的大小； (2)不管是椅型还是锯齿型管，每一种Vn中的最小空位形成能随空位原子数n值的增大呈奇偶振荡规律，且具有偶数个原子空位的形成能小，奇数个原子空位对应的形成能大； (3)为了探讨Vn缺陷的稳定性，考虑了两种解离过程，即Vn→Vn1+V1和2Vn→Vn1+Vn+1，且分别对应第一和第二解离能。计算结果表明，Vn缺陷中的n为偶数时对应的第一和第二解离均大于Vn-1和Vn+1的，即，V2, V4和V6缺陷较稳定； (4)对(n,0)锯齿型单壁碳纳米管，每一种Vn中的最小空位形成能管径的增大整体呈现增大趋势，且当(n,0)管中的n值为3的倍数时，由于其能隙最小，这个最小空位形成能比预期值要小。
[Abstract]:The perfect carbon nanotubes have excellent electronic, mechanical and structural properties. However, it is inevitable to introduce a variety of defect structures, such as adsorbent adsorbent SWS stone-wales topological defect and atomic vacancy defect. Among these structural deletions, atomic structure deletion is the most productive and important structural defect. The generation of vacancies in carbon nanotubes (CNTs) has an extremely important effect on the mechanical, physical and chemical properties of CNTs. Therefore, it is one of the fundamental problems to understand the structure and physicochemical properties of carbon nanotubes (CNTs) and to solve their practical applications. In this paper, the vacancy formation energy and product structure of the zigzag tube with single to eight vacancy defects (V1 / V8) have been systematically studied by using the density functional method (DFT). The stability of the vacancy structure varies with the number of vacancy atoms and the variation of n with the number of vacancies in the tube. The main results are as follows. 1) based on the previously proposed directional curvature theory, the defect curvature is derived and applied to predict the V1~V8 vacancy formation energy of chair and sawtooth single-walled carbon nanotubes. For one type of Vns, the vacancy formation energy decreases with the increase of defect curvature, and for chair carbon nanotubes, atoms are easily removed along the sawtooth chain, and for sawtooth carbon nanotubes, atoms are easily removed along the chair chain. In addition, the local structure of the defect region in the product affects the size of the vacancy formation energy. (2) for both chair and sawtooth tubes, the minimum vacancy formation energy of each type of V _ n oscillates with the increase of the number of vacancy atoms n, and the formation energy of even number of atomic vacancies is small, and the formation energy of odd number of atomic vacancies is large; In order to study the stability of Vn defects, two kinds of dissociation processes are considered, that is, VN Vn1 V1 and 2Vn Vn1 VN1, which correspond to the first and second dissociation energies, respectively. The results show that the first and second dissociation of the V _ n defect is larger than that of Vn-1 and V _ n _ 1 when n is even number, that is, the defects of V _ 2, V _ 4 and V _ 6 are more stable. (4) for zigzag single-walled carbon nanotubes, the minimum vacancy formation energy tube diameter in each type of V _ n shows an increasing trend as a whole, and when the n value in the zigzag _ 0) tube is a multiple of 3, the energy gap is the smallest. This minimum vacancy formation energy is smaller than expected.
【学位授予单位】：内蒙古科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB383.1;O613.71

【参考文献】