| New nanomaterials have been synthesized continuously due to the development of nanotechnology, which show a series of greatly different physical properties from their bulk counterparts, making so them to have a great potential application in the physics, chemistry, materials science, biology and life science, nanoelectronics and nanotechnology etc.. For example, tubular metal nanomaterials have their unique optical and electronic properties, making them to have extensive and potential applications in large scale integrate circuit, nanoelectronics, fiber optics and sensor areas. In addition, the new graphene-like materials, e.g., the single layer molybdenum disulfide (MoS2), tungsten disulfide (WS2) and hexagonal boron nitride (h-BN) etc, have the intrinsic direct band gap, overcoming the basic limitation of the semimetal graphene with a zero band gap, which makes them have promising applications in the nanoelectronic and nano-optoelectronic devices. Therefore, the nanomaterials have attracted so many experimental and theoretical researchers working in different scientific fields, becoming a very hot research topic in the related fields. This thesis is mainly focused on the confined growth of tubular metal nanostructures, and the electronic and magnetic properties of the two dimensional (2D) graphene-like materials, such as the h-BN and MoS2, embedded with the line defects. In Chapter1, we firstly introduce the development of nanotechnology and then the related backgrounds for the carbon nanotubes, tubular metal nanostructures and the2D graphene-like nanomaterials.In Chapter2, we have made a special introduction of the classical molecular dynamics (MD) method. We firstly give a simple description of its basic principles and then a detailed introduction of its several basic components, such as the interaction potentials, boundary conditions, simulation ensembles, controlling temperature and pressure, and some related numerical integration methods to solve dynamic equations of motion. Finally, we have briefly given an introduction to the famous MD simulation software package-LAMMPS, including its modification and extension, and some featured examples done by LAMMPS.In Chapter3, the growths of single-walled pure gold, silver and copper nanotubes and bimetallic gold-silver, gold-copper and silver-copper alloy nanotubes (NTs) and nanowires (NWs) in confined carbon nanotubes (CNTs) have been investigated by using the classical MD method. It is found that these three kinds of pure transition metal (Au, Ag and Cu) nanotubes and three kinds of single-walled Au-Ag, Au-Cu and Ag-Cu alloy NTs or NWs could be indeed formed in confined CNTs, whose geometric structures are mainly determined by CNT’s diameters, but less sensitive to the tube index of the outside CNTs. In addition, their fluid-solid phase transitions under confinement are also studied. Finally, the variations of their radial breathing mode (RBM) frequencies with their tube diameters and the alloy ratios have been obtained, which will be very helpful for identifying accurately their tube diameters and alloy ratio in the future experiments.In Chapter4, the electronic and magnetic properties of boron nitride nanoribbons (BNNRs) with a square-octagon line defect (LD-(4|8)), parallel to its edges, have been investigated by the first-principles calculations. It is found that the zigzag type LD-(4|8)-BNNR with boron terminated edges is an antiferromagnetic (AFM) insulator with an indirect bandgap, but that with nitrogen terminated edges has two degenerate ground states with the same energy, among which one is ferromagnetic (FM "++++") half-metallic and another is AFM "++--" metallic. In contrast, it is more interesting to find that the bared and fully-hydrogen terminated armchair edge LD-(4|8)-BNNRs with an unsymmetrical (4|8) line defect are all the nonmagnetic semiconductors with an indirect and direct gap, respectively, both of which show a characteristic three family oscillation behavior, depending only on the ribbon width of its narrower part, but not the whole BNNR’s width. Finally, the stabilities of a two dimensional h-BN sheet with the zigzag or armchair type LD-(4|8) in it are further confirmed, among which the one with the armchair type LD-(4|8) is much more stable than that with the zigzag type counterpart.In Chapter5, the electronic and magnetic properties of monolayer MoS2and its nanoribbon with one sulfur line defects (SV) or two staggered ones (DV), parallel to their armchair (AC) or zigzag (ZZ) direction, have been investigated systematically by the first-principles calculations. It is found that both the SV-or DV-embedded monolayer MoS2along its AC direction behave as insulators with a direct or an indirect band gap, which is much smaller than that of a perfect monolayer MoS2. However, it is more interesting to find that the out of plane deformations in the monolayer MoS2, embedded by the SV or DV along its ZZ direction will decrease the gap value seriously or even make the band gap nearly closed. Additionally, for the MoS2nanoribbons with the symmetric SV or DV, parallel to their AC or ZZ direction, the SV-or DV-embedded AC-type one is nonmagnetic semiconductor, but the SV-or DV-embedded ZZ-type one is magnetic metal with ferromagnetic coupling along the same edge, similar to that of pristine ones. Finally, the stability of the SV and DV in the monolayer MoS2has been studied, indicating that the SV along the AC direction in it is the most stable one, which could be possibly observed in the future experiment. |
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