First-principles Investigation On The Properties Of Nanodiamond, Carbon Nanotube And Graphene

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.