Function Application Of Defect States Nano-carbon Materials

Due to their unique structure and physical and chemical properties, the potential application research has been briskly undertaken since the discovery of carbon nanotube and Fullerene and becomes one of current research focus. The graphitelike structures of carbon nanotubes and Fullerenes limit their flexibility in their using of catalyst substrates and composition component because of their large chemical stability and infusibility. It is an urgent scientific problem how to decorate carbon nanotubes and Fullerenes effectively for their potential application. Decorating of carbon nanotubes and Fullerenes with defects enable them possess new physical and chemical properties and bring some new applications. This thesis deals with the electronic structure and their appilications of carbon nanotubes and Fullerenes with defects by using density functional theory based on the first-principles method. The goal of this thesis is aimed at proposing available appilication methods for carbon nanotubes and Fullerenes. The thesis is organized as follows:In Chapter one, the appilication, structure and electronic character of nano-carbon materials are introduced.In Chapter 2, we present the effects of radial strain on desorption of hydrogen from the surface of palladium-doped carbon nanotubes. Our calculations reveal that the chemisorbed H atoms can not be desorbed by only using radial deformation or catalyst and that the Pd-doped nanotube can reduce the height of hydrogen desorption barrier upon radial deformation. This may be due to the enhanced coupling between Pd and SWCNT or molecular hydrogen. The disturbed Pd HOMO orbital is essential for the enhanced Pd-SWCNT and Pd-H2 interaction. Calculated binding energies, several tenths of an eV, are well suited to reversible storage under standard conditions for molecular hydrogen. In addition, the amount of adsorbed hydrogen can be increased, while the height of hydrogen desorption barrier can also be reduced via using Pd.In Chapter 3, we show that water molecule can be dissociated on the surface of carbon nanotubes with charge and defect. Considering the existing of adsorbed carbon atoms and large electronegativity character, we select a model of carbon nanotube with C dopant and charge injection is used to depress the dissociation barrier height. It is shown that charged carbon nanotubes with C dopant are very effective to the dissociation of water molecules. A large number of charges are localized around the adsorbed carbon atom which is heaved on the surface of carbon nanotube. When water molecule approaches the adsorbed carbon atom, a number of charges transfer between carbon nanotubes and water molecule because of strong electrostatic interaction between delocalizedπelectron of carbon nanotube and water, which is the main mechanism of adsorption. Furthermore, the results display that the reactivity of C_SWCNT comes mainly from adsorbed carbon atom rather than the injection of charges and that desorption and the adsorption strength between functional groups and carbon nanotube can be controlled by the injection of charges. Calculations also indicate that only barriers of 0.167 eV between transition state and reactant must be offered for the dissociation of water molecule.In Chapter 4, we provide a dissociation method for water molecule on the molybdenum doped fullerene. Compared with same sized carbon nanotube, the reactivity of Fullerene is larger than that of carbon nanotube. Due to the strongest reactivity of C20 among Fullerenes, the interaction between C20 and water molecule is calculated and Mo atom is adopted in this work to enhance the interaction between C20 and H2O for its large reactivity and the strong interaction between Mo and fullerene. We demonstrate that C20 with Mo dopant are very effective to the dissociation of water molecule and that the interaction strength can be strengthened by injection of charges. In addition, frequency analysis indicates that the transition state is a true minimum, which has a single imaginary frequency, -309.3cm^-1.In Chapter 5, we present the calculations about charge and nearly free electron behavior induced by strain for the purpose of property tuning of carbon nanotubes. The electronic structure calculations between radial deformed carbon nanotubes and alkali metal, polar molecule and unpolar molecule exhibit that charge transfer between components and the change of charge flow direction determine the movement of nearly free electron bands. Moreover, there are no direct correspondences between the graphite interlayer distance 3.4 ? and charge transfer or the movement of nearly free electron band. Although the nearly free electron band can only downshift rapidly in energy relative to Fermi level by n- and p-type doping, the nearly free electron band of carbon nanotube can upshit rapidly in energy relative to Fermi level through radial deformation, which can expand the selectivity of material design. Finally, I summarize the thesis and propose the future works in Chapter 6.