【作者】 魏燕；

【导师】 胡慧芳；

【作者基本信息】 湖南大学 ， 凝聚态物理， 2010， 硕士

【摘要】 碳纳米管因其独特的结构和奇异的电学性能在下一代纳米电子和光电子器件中具有广阔的应用前景。近年来,电子在碳纳米管中的输运行为成为人们研究的重点,关于输运的理论研究大多是针对非手性碳纳米管,而实验表明碳纳米管的生长更倾向于手性碳纳米管,很多电子输运实验也都是在碳管手性未知的情况下进行的。因此,手性碳纳米管输运性质的模拟对基于碳纳米管的分子器件研究显得尤为重要。本文采用基于第一性原理的密度泛函理论并结合非平衡格林函数方法,对单壁手性碳纳米管中存在的硼、氮原子取代掺杂、空位缺陷体系进行了系统的研究,获得了一些有意义的结论。这对基于单壁碳管的电子器件的实际制备和开发具有重要的理论指导意义。对不同的掺杂浓度和掺杂分布位型的氮原子取代掺杂的情况,我们进行了系统的研究。对于金属型(6,3)管,氮原子掺杂显著改变了碳管的电子结构,使体系的电子输运明显降低。在一定条件下,将使其发生金属型向半导体型的转变。对于半导体型(8,4)管,由于其管径较大,氮原子掺杂对其影响相对较小。在偏压较小时,其输运性能有所提高。某些情况下,由于出现较大的能隙而使电子无法跃迁。对不同的掺杂分布位型进行的模拟计算表明,硼、氮原子共掺使金属型手性碳纳米管的的输运性能大大降低,电流-电压曲线呈非线性变化。手性碳管的输运性能随着原胞内硼、氮原子间距的变化而发生显著改变。在杂质原子浓度不,变的、情况下,最近邻杂质原子在距离3个碳原子时,对掺杂管在小偏压下的电子输运性能是不利的。硼、氮原子共掺杂不能明显改变碳管的整流性。本文也模拟计算了手性碳管中掺氮和空位复合缺陷以及这两者的复合情况。对于半导体型(4,2)管,单个氮原子、空位缺陷以及这两者的复合结构都不能改变碳管的半导体特性,但是在一定程度上使得半导体型(4,2)管的输运性能有所提高,偏压较大时电流明显增加。氮原子掺杂体系的导通电压相对于理想管有所降低,单个空位缺陷结构具有很好的整流性。利用缺陷来调制碳纳米管的性能是很有应用价值的一个方法,所以进一步深入和广泛研究碳纳米管的缺陷性能及其器件的研制是非常重要的课题。更多还原

【Abstract】 Carbon nanotubes (CNTs) have unique electronics and optical properties which destine them to play a major role in the next generation of nanoscale electronic and optoelectronic devices. In particular, electronic transport properties of single-wall carbon nanotubes (SWCNTs) have attracted considerable experimantial and theoretical interest. Previous theoretical work has focused on the understanding of transport in achiral of zigzag (n,0), armchair (n,n). However, control of the nanotube fabrication process is still a challenge. Electronic transport experiments are often performed on tubes of unknown chirality. A recent study has show that nanotube growth slightly favors chiral CNTs. Thus, a complete picture of electron transport in CNTs requires an understanding of transport in chiral CNTs.Using the first principles density functional theory combined with noequilibrium green function technology, the paper systematically explores substitutive doping, vacancy defect in single-walled carbon nanotubes, and gets some helpful results. It is significant for the practical preparation and development of the nanotubes-based photoelectric devices.We have investigated the systems with different concentration and different distribution. It is show that the electronic structures of the chiral (6,3)carbon nanotubes with doping of nitrogen atoms are changed obviously and the transport properties are reduced. Under certain conditions the metallic single-walled carbon nanotubes convert into semiconductor. Because of large diameter, doping of nitrogen atoms make a little impact on the chiral (8,4)CNTs. The transport properties of the system are improved when the bias is small. In some cases, the doping is unfavorable to the transport properties owning to widen band gap.The simulations of the systems with different distribution show that the transport properties of the metallic nanotube are reduced obviously by co-doping of boron/nitrogen atoms. The currents-voltage curves present nonlinear variation. The transport properties change significantly with the positions of impurity atoms in the structure. When the bias is small, the transport properties of the doping nanotube which the interval is three carbons bwteen the impurity atoms are disadvantageous. The boron/nitrogen co-doping only slightly modify the rectification ratio of the nanotube. We also studied the systems with the nitrogen doping、vacancy and the compound defects composed of nitrogen and vacancy. The characteristics of the chiral (4,2) carbon nanotube can’t be changed by single nitrogen atom doping、single vacancy and the compound defects composed of nitrogen doping and vacancy. but the transport properties are improved to some extent. The currents increase significantly when the bias voltage is high. The on-state voltage of the systems with nitrogen doping go down. The structure of single vacancy possesses good rectification ratio.It is one of the most promiseful methods for application to modulate the properties of nanotubes by impurity doping and defects. So that it is an important subject to investigate the properties and the device fabrication of defective nanotubes more deeply and comprehensively.更多还原