碳纳米管形核机制及碳纳米管夹持金属原子链的透射电镜原位研究

IMR OpenIR

	碳纳米管形核机制及碳纳米管夹持金属原子链的透射电镜原位研究
	汤代明
学位类型	博士
导师	成会明 ; 刘畅
	2010
学位授予单位	中国科学院金属研究所
学位授予地点	北京
学位专业	材料学
关键词	碳纳米管形核机制金属原子链原位透射电子显微镜
摘要	"碳纳米管的生长机制、控制制备和实际应用是碳纳米管研究中相互制约、相互促进的三个重要研究方向。生长机制的深入理解是指导和实现控制制备的关键；控制制备是碳纳米管实际应用的物质基础，也为生长机制的理解提供实验证据和验证平台；根据特定结构和性质设计的实际应用是实现碳纳米管价值和保持碳纳米管研究领域活力的必然要求，同时也为控制制备提供指向。本文利用原位透射电镜技术在碳纳米管的生长机制研究和器件构建方面开展工作。在碳纳米管的生长机制方面，首先利用透射电镜原位研究了SiOx催化碳纳米管的形核生长行为。发现活性催化物质是氧化物，催化剂颗粒在碳纳米管形核和生长过程中保持固态非晶结构，碳原子通过表面扩散的路径供给，生长过程符合固体表面扩散生长机制。进一步对比研究了Fe和SiOx催化生长碳纳米管的过程。提出合适的颗粒尺度、适当的颗粒-碳层相互作用及必要的驱动力条件是碳纳米管生长的必要条件。传统碳纳米管生长机制（VLS）中催化裂解碳氢气体、出现催化剂液相颗粒、碳溶入-碳化物形成-碳析出过程不是碳纳米管生长不可或缺的条件。采用透射电镜原位研究了螺旋碳纤维在高密度直流电作用下的结构演变，发现在没有外加催化剂的条件下可实现双壁碳纳米管的生长。提出异质外延生长碳纳米管的新方法，以叠杯状氮化硼（BN）纳米纤维为种籽，制备出直径分布在石墨层间距（0.33 nm）整数倍的单壁碳纳米管，为碳纳米管的结构控制制备提供了新思路。在碳纳米管器件构建方面，针对碳纳米管具有纳米尺度和电子输运散射小的特点，设计并在透射电镜中原位制备了具有量子化电导性质的碳纳米管夹持金属原子链，实现了多种金属及合金原子链与碳纳米管的有效连接和集成，为金属原子链的装配提供了有效途径，并可望促进碳纳米管在纳电子和自旋器件中的应用。利用高分辨透射电子显微镜以及第一原理计算和模拟研究了Fe原子链的形成过程，发现沿（110）面的滑移和扭折是其形成过程中的重要机制。Fe原子链的表面由（110）和（100）面构成，异于面心立方金属倾向形成（111）构成的表面，归结于体心立方结构与面心立方结构在原子堆垛方式和表面性质的差异。利用第一原理计算方法研究了碳纳米管夹持Fe原子链的电子结构，发现二者形成牢固的共价键结合，Fe原子链保持其半金属特性，碳纳米管保持其金属性质。利用透射电子显微镜原位操纵平台测试了碳纳米管夹持Fe原子链的导电属性，发现其电导呈量子化，表明与碳纳米管结合以后，金属原子链仍保持其独特的物理性质。"
其他摘要	"Understanding of the growth mechanism, structure and property controllable synthesis and exploration practical applications are three important directions for current research of carbon nanotubes (CNTs). The deep understanding of growth mechanism is the key to controllable synthesis, while controllable synthesis could provide experimental evidence for the investigation of growth mechanism. Controllable synthesis is essential for practical applications, while practical applications could provide clear guidance for the synthesis. In this study, the growth mechanism of CNTs and CNT-clamped metal atomic chains (MACs) were investigated by in situ transmission electron microscopy (TEM). The catalytic growth process of CNTs from SiOx nanoparticles was investigated. And it was found that the growth seed is silicon oxide, rather than silicon carbide. During nucleation and growth process, the SiOx particles remain solid and amorphous, and carbon atoms are provided through a surface diffusion route, consistent with a solid surface diffusion growth mechanism. By comparing the nucleation of CNTs from traditional Fe catalyst and metal-free SiOx nanoparticles, a hypothesis for the growth of CNTs is proposed: the key factors for a catalyst to grow CNTs are suitable size, desired graphene layer-catalyst particle interaction, and suitable driving force. The catalytic decomposition ability for hydrocarbons, liquid catalyst zone, and carbon dissolution-saturation-precipitation process are not indispensable. It was found that under a high-density direct current, a carbon microcoil can be broken, and double-walled CNTs can be obtained without adding any hetero-catalysts. A hetero-epitaxial growth of CNTs is proposed and realized by using cup-stacked BN nanofibers as growth seeds. Due to the epitaxial growth mode, SWCNTs with diameters of integral multiples of the graphite (002) intra-layer distances are produced. This provides a novel route for the structure controlled growth of CNTs. A CNT-clamped metal atomic chain (MAC) structure is proposed to make use of the nanometer size, high conductivity and low electron scattering of CNTs by connecting CNTs with ultimately small MACs. The device is fabricated in situ inside a TEM by machining metal filled CNTs with electron beam irradiation and elongation. The formation process of CNT-clamped Fe ACs is explored by both in situ TEM observations and first-principles calculations. It was found that the slip and distortion along (110) is an important deformation mechanism for the formation of Fe AC. The surface is constituted with (110) and (100), which differs from the MACs of FCC metals. And the difference is attributed to the different surface energies for different crystalline structures. The interface structure and electronic properties were investigated by first principles calculations. Strong covalent interactions are found at the boundary of CNTs and MACs. For ferromagnetic metal Fe, the Fe AC remains half-metallic, while CNT is metallic. In addition, the electrical properties were measured in situ, and quantized conductance of the CNT-clamped Fe AC is demonstrated. Therefore, after the combination with CNT, MACs could keep their unique physical properties, and our proposed CNT-clamped MAC provides an effective method for the connection of MACs."
文献类型	学位论文
条目标识符	http://ir.imr.ac.cn/handle/321006/64179
专题	中国科学院金属研究所
推荐引用方式 GB/T 7714	汤代明. 碳纳米管形核机制及碳纳米管夹持金属原子链的透射电镜原位研究[D]. 北京. 中国科学院金属研究所,2010.