| 摘要 | 碳纳米管，尤其是双壁碳纳米管，作为一种新型一维纳米材料，由于它独特的结构、机械、化学、电子、光学等性能及其极具发展潜力的各种应用，近十年来引起了世界各国科学家的广泛关注。由于目前在双壁碳纳米管研究中，多以制备、性能和应用为主，对于其原子结构方面的研究很有限，而碳管的许多性质都直接与其原子结构有关，所以准确地确定双壁碳纳米管的原子结构是使其获得实际应用的关键步骤。本文利用高分辨电子显微术及电子衍射研究观察了由甲酸镍二水合物作为催化剂前驱体，多壁管为原料，采用氢电弧放电法制得的双壁碳纳米管样品。
首先，分析研究了样品中不同管壁数目碳纳米管的分布、单壁及双壁碳管直径分布。发现样品中单壁和双壁碳管占主要地位，单壁管的直径主要分布在1.33-2.67 nm之间，双壁管的内径主要分布在1.67-3.67 nm之间，外径主要分布在2.33-4.33 nm之间。从而得知，通过本文所使用的方法制备出的双壁碳纳米管样品具有较高的结构稳定性，但其纯度不高。
其次，精确测定了三个非相公度型双壁碳纳米管的螺旋指数，分别为[(28, 3) (29, 17)]，[(19, 8) (29, 6)]及[(23, 15) (28, 22)]，其电学性能分别为[半导体性，金属性]，[半导体性，半导体性]及[半导体性，金属性]，衍射图呈2mm对称。
最后，利用原位高分辨电子显微术观察了在不同条件下碳纳米管的电子辐照效应。结果表明，由于间隙原子沿内层管道移动，碳管的最内层管壁最先发生断裂，并且在电子辐照作用下，碳管的形变速度会减缓并易依附于大块物质。在相同的辐照条件下，管壁数目越多碳管越稳定。当管壁数目相同时，直径小的管比直径大的管稳定。高加速电压及高束流密度加速碳管的变形。 |
| 其他摘要 | Carbon nanotubes (CNTs), especially double-walled carbon nanotubes (DWNTs), as a one-dimensional nanoscale material, have attracted intense attention due to their unique structural, mechanical, chemical, electronic, optical properties and promising applications recently. Because it is focused on the preparations, properties and applications, there has not been much literature on the atomic structure analysis in the study of DWNTs. Whereas, many properties of carbon nanotubes are directly influenced by their atomic structure. It is therefore a vital step to determine the atomic structure of DWNTs accurately. In this thesis, we have investigated the DWNTs synthesized from multi-walled carbon nanotubes (MWNTs) by the hydrogen arc discharge technique using nickel formate dihydrate as a catalyst precursor by transmission electron microscopy and electron diffraction.
Firstly, the diameter distribution of 270 DWNTs, the diameter distribution of 241 single-walled carbon nanotubes (SWNTs), and the distribution of 602 carbon nanotubes selected randomly with different number of shells in a carbon nanotube sample were examined. It was found that the SWNTs and DWNTs are dominant in the specimen. The diameter of the SWNTs ranged from 1.33 to 2.67 nm. The inner tube diameter and the outer tube diameter of the DWNTs ranged from 1.67 to 3.67 nm and 2.33 to 4.33 nm, respectively. The as-synthesized DWNT samples have a high structural stability, but are not of high purity.
Secondly, the chiral indices of three incommensurate DWNTs were determined using electron diffraction: they are [(28, 3) (29, 17)], [(19, 8) (29, 6)] and [(23, 15) (28, 22)], respectively. Their respective metallicity is [semiconducting, metallic], [semiconducting, semiconducting], and [semiconducting, metallic]. The electron diffraction patterns have 2mm symmetry and the scattering intensity distribution on each layer line can be described by a single Bessel function .
Thirdly, the electron irradiation effects in both SWNTs and DWNTs under 200 kV and 300 kV were examined to reveal the structural collapses of the nanotubes. It was observed that the innermost shell of a CNT would break first and the deformation was slowed down after several minutes’ irradiation. Under the same irradiation conditions, the CNTs showed a higher stability when they have more shells, smaller tube diameter, or at lower acceleration voltage and lower beam current density. |
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