大管径金属性单壁碳纳米管的可控生长及其导电行为研究

Selective Growth of semiconducting or metallic single-walled carbon nanotubes has always been a considerable challenge subject. Thoroughly understanding of the mechanism of selective growth and realizing the technology breakthrough of their control synthesis and applications will led to transformational influence on many fields such as nanoelectronics, new materials and so on. Due to their unique one-dimensional structure, metallic single-walled carbon-nanotubes (SWCNT) integrate excellent mechanical, electrical and thermal performances, which make them a very promising candidate for next-generation interconnects instead of copper wires for integrated circuits. It has long been a hot fundamental and technical topic that how to realize controlled growth of SWCNTs, continuous preparation and effective assembly of them, as well as the preserving of outstanding performances of individual nanotube in their bulk objects. Focusing on floating growth method, we will systematically investigate the nucleation process and structure control of catalysts in the floating catalytic system, and their effects on the growth and aggregative properties of the CNTs in gas phase. By designing the catalyst, adjusting the atmosphere and optimizing process parameters, we will obtain large-diameter and metallic SWCNTs with specific structure. Besides, we will thoroughly understand the principles of selective growth of CNTs and built the structure correlations between the catalysts and the corresponding nanotubes. We will further investigate the conductive behaviour on different scales of such carbon nanotubes based on their structure composition and post-processing. A new strategy will be developed to fabricate the highly conductive and strong current-carrying capacity CNT fibres, which will promote the application of CNTs in interconnects and high-ampacity power cables.

选择性生长单一导电属性的单壁碳纳米管一直是极具挑战性的课题，对其生长机理、可控制备方法与应用的认知深化与技术突破将对微纳电子器件、新材料等领域产生变革性的技术发展。金属性单壁碳纳米管凭借其独特的一维纳米结构而具有优异的力、电、热等性能，有望取代铜导线而成为下一代集成电路中的互连材料。如何实现碳纳米管的控制生长、连续制备和聚集组装，并在宏观体中保持其优异的特性是一直高度关注的热点问题。本项目拟以浮动生长技术为基础，系统研究催化剂在浮动催化体系中成核过程和构型调控以及对气相中碳纳米管生长与聚集行为的影响。通过催化剂的设计、气氛调节和生长条件优化，实现特定结构的大管径金属性单壁碳纳米管可控制备。深入认识碳纳米管选择性生长机理，构建催化剂与特定碳管之间结构的关联性，并探索不同尺度下碳纳米管自身结构及后处理对其导电行为的调制关系。发展高导电和高电流承载的大管径金属性碳纳米管制备技术，进一步开拓碳纳米管在互联材料和大载流导线等方面的应用。

相比于传统的金属导体，碳纳米管以其独特的一维纳米结构特性，具有密度低、力学性能高、电导率高、载流大等特性，有望实现对传统金属导体的部分取代。碳纳米管纤维等宏观组装体的导电性能一方面决定于碳纳米管的结构，如壁数、直径、导电类型、长度等，另一方面决定于碳纳米管的组装结构，如取向性、堆积密度、界面作用等。在本项目工作中，通过对浮动催化CVD过程中碳源进样方式、碳源组成、催化剂成分、催化剂成核生长条件、碳管生长等条件的有效调控，实现了直径范围1.4-5nm、壁数可控的单壁与少壁碳纳米管的制备。进一步地，通过对进样系统的改进，以及对催化剂成核条件、碳管生长组装条件等的控制，实现了高取向、高性能碳纳米管纤维原丝的均匀连续制备，原丝纤维比强度达3.1N/tex，电导率达7E5S/m。在制备高性能碳管纤维原丝的基础上，项目组通过氯磺酸辅助牵伸及辊压致密化后处理对纤维进行力电性能增强，优化牵伸条件、凝固条件及热退火条件，使碳管纤维的取向度、致密度均获得较大提升，使碳管纤维强度达到7.6GPa，电导率达到6E6S/m，载流达到1E5A/cm2。项目组还通过掺杂或与导电增强物质复合的方法进行碳纳米管纤维的电学性能增强，并分析纤维内的电子输运行为。采用石墨烯的氯磺酸溶液对碳管纤维进行连续牵伸复合处理，制备高结晶度石墨烯电学增强的碳纳米管复合纤维，有效提升了碳管纤维的电导率。采用气态溴对碳纳米管纤维进行p型掺杂，纤维电导率提升到6倍以上。采用连续电沉积方法获得碳纳米管-镍-铜复合纤维，优化沉积电流、时间、原纤维孔隙率等参数，改善金属晶粒尺寸及碳纳米管-金属间界面特性，使金属复合碳管纤维电导率提升至2.74E7S/m，载流达到1E6A/cm2。高强度、高导电、大载流碳纳米管纤维的连续制备，为其在轻质大载流功能导线方面的应用奠定了坚实的材料基础。