【作者】 张华；

【导师】 陈小华；

【作者基本信息】 湖南大学 ， 材料物理与化学， 2006， 硕士

【摘要】 碳纳米管具有十分优异的物理、化学性能,使其具有巨大的应用前景。但由于实验制备的碳纳米管初产品中含有大量的杂质,因此在对碳纳米管进行实验研究或应用之前通常都需要对碳纳米管进行表面纯化改性,这些化学或物理的方法在提纯了碳纳米管的同时,也会将一些官能团比如羧基和羟基接枝到碳纳米管上;另一方面,在对碳纳米管进行应用的时候,比如制备碳纳米管复合材料、纳米器件和纳米生物学应用中,经常人为地将一些官能团接枝到碳纳米管上,通过这样的表面修饰来改变碳纳米管的表面性能,以实现某些特定的功能化。但是,目前实验和理论上对接枝官能团后碳纳米管本身性能的变化的研究很少,而这些性能上的变化对于碳纳米管的应用来说是至关重要的。因此,我们从理论上讨论接枝官能团对碳纳米管本身电学性能的影响。我们以局域密度泛函理论为基础,采用第一原理方法,利用DMol3、CASTEP软件进行理论模拟研究。建立了对(5,5)、(9,0)和(8,0)型有限长碳纳米管接枝羧基和羟基官能团的原子模型,通过计算其电子分布和态密度的变化,讨论羧基和羟基官能团对碳纳米管电子结构和电子输运特性的影响。计算结果表明,接枝官能团的碳纳米管,其电子结构明显改变,其费米能级上的电子态密度下降;最高占据轨道上的非定域程度减弱,致使电子输运性能呈下降趋势。通过比较两种官能团对碳纳米管的影响发现,虽然接枝羧基或羟基官能团后碳纳米管的电子输运性能都有下降趋势,但下降的程度不一样。接枝羟基官能团使碳纳米管的电子输运能力降低的幅度较接枝羟基时更大;金属型碳纳米管在接枝官能团后电子密度降低的幅度要大于半导体型碳纳米管。另外,我们还尝试性地研究了掺杂对碳纳米管电学性能的影响。我们利用原子替换的方法建立氟掺杂的碳纳米管模型。计算发现,掺氟后三种碳纳米管的费米能的绝对值都降低了,费米能级上的态密度却增大了,说明氟掺杂后的碳纳米管比纯碳纳米管更有利于场发射。三种不同结构的碳纳米管在费米能的增幅上有些差异,带宽减小的程度也是不同的,一端封闭的碳纳米管在F掺杂后费米能的增幅最大,说明在制备场发射电极时选择一端封闭的碳纳米管更加有利。更多还原

【Abstract】 The super high strength, ductility, nanometer scale and large aspect ratio of carbon nanotubes (CNTs) make it an ideal reinforcement additive for composites. Also, the good electrical conductivity, high thermal conductivity, good thermal and chemical stability of CNTs could make the composites versatile. Surface decoration by grafting carboxyl & hydroxyl groups on CNTs are often applied to achieve special functionality in the preparation of CNTs composite, Nano-device and Nano-biology area. In this paper, we have studied the effect of grafted groups on electrical properties of CNTs, which is theoretically of great importance.Based on the density-functional theory and the first-principle method, the electronic distribution and the density of states of the armchair (5,5) and zigzag (8,0) and (9,0) single-walled carbon nanotubes grafted by carboxyl or hydroxyl are calculated. A geometry optimization of SCNTs is performed by using BLYP function in DMol3 program, then, the variations of electronic distribution and DOS are calculated by adopting the DMol3 and CASTEP program. It has been found that the electronic structure of the grafted SCNTs changes significantly, namely, the electron density of states near Fermi level, the delocalized degree of the highest occupied molecular orbital, and accordingly the transport properties of SCNTs decreased as the number of hydroxyl functional groups grafted increased.Although the transportation ablity of SCNT decreases no matter what groups (carboxyl or hydroxyl) are grafted on its surface, the decreased scope is different. The effect on the density of state of hydroxyl is stonger than that of carboxyl, and the density of state for armchair CNT decreases faster than zigzag CNT by the grafted functional group.The investigation of the fluorine doping effect on electrical performance of CNTs has been conducted. Results indicate that the absolute value of Fermi energy decreases for three kinds of CNTs doped with fluorine in the the form of replacement, which is beneficial for field emission. Difference in extent of the Fermi energy and decrease of band-gap energy for three kinds of CNTs show that CNT with one end open is favorable for the preparation of field emission electrode.更多还原