无催化剂残留单壁碳纳米管的生长及其机理研究

Catalysts are indispensable for the growth of single-wall carbon nanotubes (SWCNTs) and are inevitably remained in the product as impurities, with potential risks for degrading the performance of SWCNT electronic devices. Post-purification methods have been effectively used to remove most of metallic catalysts, however, structural defects will be introduced during the liquid-phase treatment. In this project, we propose the direct growth of SWCNTs without any catalyst residues. By means of in-situ TEM technique, the thermodynamic properties and structural evolutions of Co/MgO catalysts will be studied at atomic scale, the precipitation from and dissolution into the solid solution of active nanoparticles under certain conditions are revealed. The effect of “reversible” metal catalyst in tuning the interfacial binding strength between catalyst-SWCNTs will be revealed during the whole growth periods of SWCNTs. After highly effective growth of the SWCNTs, they will be detached from the catalysts by weakening the interface binding at the later stage of growth. The driving force for the reversible process will be quantitatively calculated. On the above basis, SWCNTs without any catalyst residues will be produced by finely tuning the properties of catalysts and growth conditions by using chemical vapor deposition, which paves the way for the applications of SWCNT-based electronics.

单壁碳纳米管（简称碳管）的高效生长离不开金属催化剂，而产物中残留的催化剂严重影响碳管本征性能及广阔的应用前景。目前通过后处理纯化方法虽然能去除大部分颗粒，但引入新的缺陷造成碳管结构破坏和性能降低。针对以上问题，本项目提出一步生长-纯化制备高纯高质量碳管并研究相关机理。利用原位透射电子显微镜平台，通过直接在原子尺度上研究Co/MgO等催化剂体系在不同环境条件下的热力学性质和结构转变，揭示催化剂颗粒在基体上的可逆析出-溶入规律；揭示其对碳管不同生长阶段的碳管-催化剂界面结合的调控作用。通过弱化碳管-催化剂界面结合，实现生长后期碳管与催化剂的分离，进而建立可逆催化生长方法。实验与理论研究相结合，阐明催化剂颗粒可逆驱动力。在此基础上，优化催化剂的组分、结构及制备工艺，采用化学气相沉积法宏量可控生长无催化剂残留的碳管，为碳管基高性能电子器件的构建奠定材料基础。

单壁碳纳米管具有独特的一维中空管状结构及优异的物理化学性质，被认为是下一代纳电子器件的理想构筑材料。然而，由于实际制备的单壁碳纳米管中存在残留的金属催化剂、后处理分离引入的官能团等缺陷杂质，其实际性能远低于理论预测。因此，制备出高质量、无催化剂残留单壁碳纳米管是研究单壁碳纳米管本征性能，发挥其性能优势及推动相关应用进展的重要前提。针对这一挑战，本项目提出了一步生长-纯化制备高纯单壁碳纳米管的方法，利用了低压环境透射电镜技术和常压封闭环境透射电镜技术研究了Co/MgO催化剂相对载体的“可逆”析出-溶入过程和催化剂的热力学特性，揭示了催化剂-载体的界面调控规律以及单壁碳纳米管的生长终止机理，并且提出了基于活性可调的固溶体催化剂体系制备无催化剂残留碳纳米管的策略。基于此，系统研究了CVD宏量制备无催化剂残留单壁碳纳米管的影响因素，包括精细调控Co/MgO催化剂负载量、CVD参数等，建立了制备无催化剂残留单壁碳纳米管的方法，最终宏量制备了无催化剂残留单壁碳纳米管，为碳纳米管的性能研究及碳纳米管基高性能电子器件的构建奠定材料基础。