【作者】 郭朝晖；

【导师】 颜晓红；

【作者基本信息】 南京航空航天大学 ， 凝聚态物理， 2008， 博士

【摘要】 独特的结构及优异的物理化学性质使碳纳米管、富勒烯在众多领域具有广泛的潜在应用,成为纳米材料科学研究的热点课题之一。碳纳米管、富勒烯的类石墨结构具有极高的化学稳定性和不溶性,这极大地限制了它们作为化学反应载体、复合材料组分的可操作性。如何对碳纳米管、富勒烯进行有效的功能修饰,是当前碳纳米管、富勒烯研究和应用领域中亟待解决的一个科学问题。对碳纳米管、富勒烯进行缺陷修饰,将可能赋予其全新的物理和化学性质,进而为碳纳米管、富勒烯的应用开辟新的途径。本论文以碳纳米管、富勒烯为研究对象,采用第一性原理方法计算了缺态碳纳米结构的电子性质及其应用。其目的在于为拓展碳纳米管、富勒烯的功能应用提出合理的手段。本文共分为六章,具体安排如下:第一章是引言,分析了碳纳米材料的结构特征和电子结构,并对碳纳米材料的功能应用做了一个简单介绍。第二章,分析了径向应变调制作用下的碳纳米管表面氢的脱附。我们发现,只加径向应变或者催化元素都不足以将化学吸附的氢原子脱离碳纳米管。而径向变形的Pd掺杂纳米管能有效的降低氢的脱附势垒。这可能是由于Pd与单壁碳纳米管（SWCNT）或Pd与氢分子之间的作用被加强的缘故。而Pd最高占据分子轨道（HOMO）的改变是Pd-SWCNT与Pd-H2相互作用加强的关键。计算显示, Pd与氢分子之间的结合能（十分之几电子伏特）很适合在标准条件下氢的可逆储存。储氢时,Pd可以促进氢的吸附量,在氢释放的时候,径向变形的Pd掺杂纳米管又能有效的降低氢的脱附势垒。因此加径向变形且掺杂Pd不仅可以促进纳米管对氢的吸附,又可以降低氢的脱附势垒。第三章,讨论了缺陷态碳纳米管表面水分子的分解。基于碳纳米管外表面可能存在C杂质和碳纳米管具有大的电负性的特点,我们采用含C吸附原子的碳纳米管模型,并在其中注入电荷来降低水的分裂势垒。结果证明带电的、有缺陷的碳纳米管能使水分子有效分解。由于局部结构的突起,C吸附原子处会积累比其它位置多得多的电荷。当水分子接近这一位置时,水分子与碳纳米管之间发生大的电荷转移,导致碳纳米管离域π电子与水分子之间存在强的静电相互作用,这是吸附产生的最主要机制。计算还发现C_SWCNT的化学活性主要来源于碳吸附原子而不是注入的电荷。被吸附官能团的吸附强度及其脱附可由注入的电荷量来控制。计算得到了反应中真实的过渡态结构,并通过过渡态搜索计算找到了过渡态与反应物之间的能量势垒仅仅为0.167 eV。第四章,计算了钼掺杂富勒烯表面水分子的分解。与同尺寸的碳纳米管相比富勒烯的活性更强, C 20是活性最强的富勒烯。本章研究了C 20与水之间的吸附,并通过掺入活性很强的钼元素来加强C 20与水之间的相互作用。结果表明Mo掺杂的C₂₀能有效分解水分子。而水与C₂₀之间的相互作用强度能通过注入电荷得到加强。另外,对得到的稳定结构的频率分析发现,过渡态具有唯一的虚频-309.3cm^-1,表明找到的过渡态是一个真正的过渡态结构。第五章,研究了应变诱导的电荷、近自由电子态（NFE）行为,并着眼于碳纳米管体系性质的调制。通过径向变形碳纳米管及其与碱金属、极性分子、非极性分子相作用体系的电子结构的计算发现,体系分子间电荷的转移或者电荷流向的改变决定体系近自由电子态、费米能级的移动。另外,我们还发现3.4 （A|°）这一表征石墨层间相互作用的特征量与电荷转移方向、近自由电子态移动并无必然的关联作用。尽管n型、p型掺杂只能让近自由电子态相对于费米能级往下移,径向应变能使碳纳米管的近自由电子态相对于费米能级往上移。这极大的扩大了人们对材料设计的选择性。第六章,本文的总结及对未来工作的展望。更多还原

【Abstract】 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.更多还原