【作者】 王春；

【导师】 郑伟涛；

【作者基本信息】 吉林大学 ， 材料物理与化学， 2009， 博士

【摘要】 近年来随着纳米科学技术的发展,特别是随着纳米金刚石、富勒烯、碳纳米管、以及石墨烯片等纳米结构的不断被发现,碳素纳米材料科学研究得到了广泛的关注,并取得了巨大的进步。同时,随着计算方法和计算机技术的飞速方展,计算材料学在材料研究中已经占有越来越重要的地位。而密度泛函方法已经成为计算材料学领域中最重要的理论方法。在本论文中,我们利用第一原理密度泛函理论等理论手段,针对目前倍受关注的几种碳素纳米材料(纳米金刚石、碳纳米管以及石墨烯片)的性能进行了理论模拟,这对设计和制备碳纳米材料有一定的理论指导意义。计算纳米金刚石的结果表明粒子的尺寸影响纳米粒子的结构、稳定性以及电子结构。计算场发射性能表明,发射电流主要是来自表面的氢原子位置,同时发射的最大电流并非是来自最高占据态轨道,而是能量更低的轨道。电子密度是限制纳米金刚石场发射性能的主要因素。计算氮掺杂碳纳米管的场发射性能表明,氮原子引入的“耦合电子态”对场发射有重要的贡献。同时,外加电场的不同也会影响氮原子对场发射性能增强效果。计算石墨烯纳米结构的结果表明,石墨烯纳米带的力学性能与其边界的原子形貌有关。不同应变下纳米带输运性质的变化说明这种材料可以用于应力测量器件。计算三角形石墨烯片的电子结构表明,氮掺杂会改变三角片的电子结构以及自旋。本论文的计算结果解释了实验观测到的现象,同时为合成和设计新型纳米器件提供了新的途径和方法。更多还原

【Abstract】 With the rapid development of nanoscience and nanotechnology, especially with the discovery of nanodiamond, carbon nanotube, fulleren and graphene, carbon related nanostructures have attracted much interest. Meanwhile, with the rapid development of computational methods and computer technology, computational materials science has become more and more important in modern materials reseach. Density functional theory (DFT) has become one of the most important methods in computational materials science. In this dissertation, we calculate various properties of three kinds of carbon related nanometer-sized materials, i.e. nanodiamond, carbon nanotube and graphene, which have been widely studied using DFT. This work will be helpful in designing and synthezing carbon based nanometer-sized devices.In Chapter 1, we give a brief introduction to the structures, properties, applications and syntheses of these three kinds of carbon-related materials. Furthermore, some unresolved issues in the study of these three kinds of materials and the objective of this dissertation are given.In Chapter 2, firstly, we introduce the basic concepts and progress of the theoretical method used in this work in detail, including first-principles calculations and density functional theory. We also describe the basic principles of the simulation package DMol3, which is used in this work. Then we give a brief introduction of the basic concepts of semi-empirical tight-binding (TB) model as well as the formula of TB potentials for carbon. At the end of this chapter, we briefly introduce the method of calculating the field emission current and transport properties of nanometer-sized materials.In Chapter 3, the size dependent effect as well as the field emission properties of nanodiamonds with the sizes smaller than 1.5 nm are studied using first-principles DFT method, and the electronic properties for larger nanodiamonds are explored using tight-binding method. Our calculations reveal that many properties, such as structure, stability, electronic properties and so on, for nanodiamond show a size dependent effect. Calculations on the field emission properties reveal that the emission current of nanodiamond mainly comes from the surface hydrogen atoms. Furthermore, the largest emission current comes from the lower occupied orbital rather than the highest occupied molecular orbital. Electron density is the bottleneck limiting the field emission properties for nanodiamond.In Chapter 4, we perform first-principles DFT calculations to investigate the field emission properties of N-doped CNTs. Using DFT, the emission current of N-doped CNTs are calculated, which reveals that the "couple states" in N-doped CNT play an important role in the field emission properties. On the other hand, the strength of applied electric field influences the field emission properties of N-doped CNT.In Chapter 5, we carry out first-principles DFT calculations to investigate the mechanical properties of one-dimension graphene nanoribbon and the electronic structure of zero-dimension triangular shaped graphene sheet. We calculate stress-strain response and the change of the electronic structure during tensile deformation of graphene nanoribbons, and the calculated results reveal that mechanical properties are related to the edge configurations of graphene nanoribbon. The change in the electronic structure as well as the transport properties indicates that graphene nanoribbon can be used as a strain sensor. Calculation on the triangular shaped graphene reveals that N-doping can modulate both the electronic properties and total spin of the triangle graphene.In conclusion, we perform first-principles DFT calculations on the properties of nanodiamond, carbon nanotube and graphene, and the calculated results can be used to explain the experimental observations and provide a potential method in synthesizing and designing new nanometer-sized devices.更多还原