| Recently, with the advancing study of self-assembly nanostructure, the highly ordered nanoscale array structure materials (such as nanotubes, nanowires and nanocolumns) have attracted more and more scientists. Nanostructure arrays can be employed as the basic components of well-controlled microdevices owing to their properties which can be controlled by the external forces such as electrics,magnetics and optics. At present, the ordered nano-structure materials have been used in the fields of the magnetic recording,optoelectronic modules,sensors,neterogeneous catalysis and so on. Nanopillar arrays with the qualities of even size,controllable structure and directional integration have been regarded as the key elements in the fabrication of micro/nano channel, separation of long DNA molecules, selection cell patter and study of photonic crystals.The main work is described as following:Firstly, We applied density functional theory B3LYP/6-31G(d) to study the graphene quantum dots with the zigzag edges, the result showed that the different sizes of graphene quantum dots in the triplet have ferromagnetism is the ground state. On the one hand, the magnetic properties from the boundary carbon atom occupied protruding position, on the other hand from the carbon atom has unpaired electron. On the whole,, the energy gap of other structures decreases with the increasing of the number of benzene ring excepted for the structure of 6b, and the energy gap decreased significantly after the structure charged. In addition, using time-dependent density functional theory (TD-DFT), the excited states of the triangular structure consists of six carbon ring which have an energy gap is 3.83eV was calculated, and found that the 17th excited state have the greatest strength, the excited energy is 3.93eV, corresponding to the wavelength 315.8nm, close to experimental results.Secondly, Density functional theory investigations showed that the Li+ion is stabilized at the center of hexagonal carbon ring and the height of Li+ion at the energy minimum is 1.8A. In addition, the electronic densities of states (DOS) indicated that there are some charges transferred from the graphene surface to Li+ion, the potential barrier is 0.167eV when Li+ion diffusions through the point defect in graphene. We also found that there is a high potential barrier about 3.4 1eV for Li+ion through the point defect to the reverse side on the graphene surface, it is more difficult for Li+ion passing the carbon ring.Thirdly, The density functional theory (DFT) investigation show that graphene has changed from semi-metallic to semiconductor with the increasing number of doped boron atoms. Lithium and boron atoms acted as charge contributors and recipients, which attracted to each other. Further investigations show that, the potential barrier for lithium diffusion on boron doped graphene is higher than that of intrinsic graphene. The potential barrier is up to 0.22eV when six boron atoms doped (B6C26), which is the lowest potential barrier in all of the doped graphene. The potential barrier is dramatically affected by the surface structure of graphene.Finally, By studying the B/N/S/Si-doped graphene with zigzag edges we found that the structure of B/N doped graphene change is very small, and S/Si doping graphene surface uplift, C-C, C-S bond length far exceeds the C-C bond length. In all of the structure, the negative charge mainly located in the place of the carbon at the zigzag edges. In the B-doped structure, three adjacent carbon atoms neutral, with the three adjacent carbon atoms N positive charges compared with the B doped structures an order of magnitude. Adsorption energy results show that Li can be stable adsorbed on the structure of the four elements. However, due to B doping on the change of structure is very small, and are conducive to adsorption of Li atoms around the B, and HOMO, LUMO distribution, with high conductivity, so the most favorable doping is B. |
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