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Effects of Doping and Defects on Electronic Structure and Optical Properties of Carbon Nanotubes

Author: ZhangLiJuan
Tutor: HuHuiFang
School: Hunan University
Course: Condensed Matter Physics
Keywords: single-walled carbon nanotube doping Stone-Wales defects electronic structure optical properties
CLC: TB383.1
Type: Master's thesis
Year: 2009
Downloads: 292
Quote: 1
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Abstract


Single-walled carbon nanotubes, as a novel one-dimensional material, have been become a focus of physical, chemical, material and biological fields, due to their unique structures and electronic properties since their discovery by Iijima in 1991. Many people have studied the structural defects and their effect on the transport properties of carbon nanotubes, but the study on the electronic structure and optical properties in a variety of defects is very little. Therefore, the research of the electronic structure and optical properties on the complex defects is particularly important.Using the first principles density functional theory, the paper systematically explores the complex defects systems, including substitutive doping, Stone-Wales (SW) defects and boron/nitrogen co-doping. Some helpful results are significant for the practical preparation and development of the nanotubes-based photoelectric devices.The paper also takes into account both Stone-Wales defects and nitrogen substitutive doping effect of the electronic structure and optical properties. SW defects decrease the degeneracy substantially in semiconducting (8, 0) nanotube, and the complex defects change the electronic structure remarkably. The complex defects of the system weaken light absorption and reflection and red-shift observed in the low-energy, and produces characteristic peak of impurities. In addition, the nitrogen atoms and vacancy defects have a significant impact on the optical properties, which makes absorption, reflecting increase in peak and move to the far-infrared regions.We also studied the electronic structure and optical properties on different chiral metallic carbon nanotubes of boron/nitrogen co-doping. The results showed that the electronic structure of carbon nanotube evolves from metallic to semiconducting as a result of boron/nitrogen co-doping. This complex defects have also an obvious influence on optical properties, that is absorption decreased and red-shift in the low-energy after boron/nitrogen co-doping. In addition, for chiral metallic carbon nanotubes, optical anisotropy is extremely obvious, absorption peak intensity is much larger than the other absorption peaks in the E = 10.25eV.Taking boron-doped as an example, we investigate the effection of the electronic structure and optical properties in B-Doped single-walled carbon nanotubes for formaldehyde (HCHO) adsorption. The calculated results show that the charge transfers is more significant, indicating that the B-doped SWCNT is sensitive to HCHO. Peak of absorption and reflection spectra increase and peak of value decrease and occurs blue shift in the lower energy region, there was a distinct peak in HCHO adsorption on B-doped carbon nanotubes at the energy of E=17.2eVIt 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 doped nanotubes more deeply and comprehensively.

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