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1、湘潭大学 博士学位论文 新型碳纳米体系的结构与热稳定性 姓名：张凯旺 申请学位级别：博士 专业：凝聚态物理 指导教师：钟建新 20080301 摘 要 本文采用分子动力学模拟方法，研究了碳纳米管和 graphene 团簇的熔化和预熔 化性质，探讨了缺陷对碳纳米管热稳定性的影响，分析了碳纳米管、graphene 与金 属、半导体复合体系的结构及其热稳定性，发现了一些新颖的纳米复合体系。 研究了碳纳米管和 graphene 团簇的熔化和预熔化性质，探讨了缺陷对碳纳米管 热稳定性的影响。 使用Lindemann判据得到(5,5)碳纳米管的熔化温度为4800K左右。 研究表明，碳纳米管的熔化总是从缺陷
2、处开始，缺陷会大大降低碳纳米管的熔化温 度，含有缺陷的单壁碳纳米管的预熔化温度为 2600K 左右。Stone-Wales 缺陷是引 起碳纳米管预熔化的主要因素。Graphene 团簇的熔化总是从边缘开始的。Graphene 团簇熔化有着与纳米颗粒熔化相比而反常的纳米尺寸与熔化温度依赖关系，小尺寸 graphene 团簇的熔化温度比大尺寸的更高。 研究了碳纳米管与金属、半导体复合体系的结构及其热稳定性，发现了一些新 颖的复合纳米体系。研究发现，碳纳米管内填充的 Au 纳米线为壳层螺旋结构。碳纳 米管内壳层螺旋 Au 纳米线表现出非常好的热稳定性，其稳定温度高于块体 Au 晶体 的熔化温度。Si
3、 原子层在碳纳米管表面为三维结构的纳米颗粒，小 Si 纳米颗粒可以 稳定地附着在碳纳米管表面，随 Si 纳米颗粒原子数的增大分别呈类似帐篷状、笼状 和球状结构。尺寸大于碳纳米管半径的大 Si 纳米颗粒为无定形结构。Au 原子在碳 纳米管表面为三维结构的岛状纳米颗粒，随着 Au 原子数的增加会发生由无序结构 到有序面心立方结构的转变。 研究了 graphene 与金属、半导体复合体系的结构及其热稳定性，发现了一些新 颖的纳米复合体系。研究发现，半导体 Si 原子与 graphene 条带相互作用，Si 原子 会吸附到 graphene 条带的边缘，形成新颖的单原子链或纳米颗粒，而金属 Pt 原子
4、 与 graphene 团簇相互作用，Pt 原子会聚集到 graphene 团簇表面并使 graphene 团 簇卷曲， 生成新颖纳米复合体系。 Si 原子吸附到锯齿型 graphene 条带边缘， 在 2000K 至 2800K 之间，且 Si 原子数等于带边不饱和碳原子数时，带边形成较为完整的 Si 单原子链结构。 三角形 graphene 团簇和 Pt 纳米颗粒复合， 室温弛豫可能形成稳固的 碳纳米锥包裹 Pt 纳米颗粒类似花束状结构。 条形初始 Pt 纳米颗粒与长方形 graphene 团簇复合体系，graphene 团簇会卷起条形 Pt 纳米颗粒，形成碳纳米管包覆壳层螺旋 Pt 纳米
5、线的管线结构。 关键词：碳纳米管；Graphene；分子动力学模拟；纳米复合体系；热稳定性 I Abstract Using molecular dynamics simulation techniques, we have studied melting and premelting of single-walled carbon nanotubes (SWNTs) and graphene clusters as well as the effects of defects on melting of carbon nanotubes. We have also studied the s
6、tructures and thermal stability of composite nanomaterials combining carbon nanostructures with metal and semiconductor nanostructures and found a number of novel nano-systems with unique structural properties. Using the Lindemann parameter, we show that the melting temperature of perfect SWNTs is a
7、round 4800K. We further show that Stone-Wales defects in a SWNT significantly reduce the melting temperature of atoms around the defects, and premelting occurs in the regions close to the defects with premelting temperatures of 2600K for the StoneWales defects and 3200K for the cavity defects. The S
8、WNTs with Si impurity defects are thermally stable up to 3800K. Our results reveal that the melting temperature of graphene clusters depends on the diameter of the graphene cluster with smaller size corresponding to higher melting temperatures. Melting of a graphene cluster always starts from its ed
9、ges. The structure and thermal stability of gold nanowires encapsulated in SWCNTs have been studied. Our results show that a gold nanowire encapsulated in a SWCNT has a cylindrical shape and a helical shell structure. These helical shell nanowires are thermally stable at temperatures much higher tha
10、n the melting temperature of its bulk counterpart and are different from the gold nanowires formed in a free space without the nanotube confinement. We have also studied the formation of silicon and gold nanoparticles on surfaces of SWNTs. We found that, Si or Au atoms on surface of a carbon nanotub
11、e prefer to form a three-dimensional nanoparticle rather than a thin film covering the nanotube As nanoparticles size increases, small Si nanoparticles undergoe structural transitions from a tent-like structure to a cage-like structure and further to a spherical compact structureLarge Si nanoparticl
12、es elongate along the axial direction of the nanotube and have amorphous network structures of SiSmall gold nanoparticles have disordered structures while larger gold particles have the face centered cubic structure of crystalline bulk gold We have studied formation processes of silicon nanostructur
13、es on edges of graphene ribbons. We found that, Si atoms in a gas state can be absorbed on the edges of zigzag graphene ribbons, forming different types of silicon nanostructures under different temperatures, namely, amorphous clusters, chain structures, and defective chain structures. For the graph
14、ene ribbons with armchair edges, existence of multiple adsorption sites does not allow growth of chain-like Si nanostructures. Formation and structures of platinum nanoparticles on surfaces of graphene clusters have been studied We found that placing a platinum nanoparticle on surfaces of graphene c
15、lusters with different shapes results in different composite structuresA triangle graphene cluster forms a cone structure with the Pt nanoparticle inside the cone. A rectangle graphene cluster evolves into a tube structure with a Pt nanowire encapsulated in the tube Key Words: Carbon Nanotubes; Grap
16、hene; Molecular Dynamics Simulation; Nanocomposite; Thermal Stability II 湘潭大学湘潭大学 学位论文原创性声明学位论文原创性声明 本人郑重声明：所呈交的论文是本人在导师的指导下独立进行研究所取 得的研究成果。除了文中特别加以标注引用的内容外，本论文不包含任何其 他个人或集体已经发表或撰写的成果作品。对本文的研究做出重要贡献的个 人和集体，均已在文中以明确方式标明。本人完全意识到本声明的法律后果 由本人承担。 作者签名： 日期： 年 月 日 学位论文版权使用授权书学位论文版权使用授权书 本学位论文作者完全了解学校有关保留、使用学位论文的规定，同意学 校保留并向国家有关部门或机构送交论文的复印件和电子版，允许论文被查 阅和借阅。本人授权湘潭大学可以将本学位论文的全部或部分内容编入有关 数据库进行检索，可以采用影印、缩印或扫描等复制手段保存和汇编本学位 论文。 涉密论文按学校规定处理。 作者签名： 日期： 年 月 日
