Study on Growth Mechanism of Carbon Nanotubes Grown Using Self-Organized Catalyst Nanoclusters

碳纳米管的合成方法有化学气相沉积法、电弧放电法、激光汽化法等。目前已经提出了碳纳米管的生长机理。在提出的机理中，关键步骤是催化剂纳米颗粒的形成和液化。然而，碳纳米管的生长机制尚未完全阐明。在这个项目中，自组织的纳米催化剂被用作碳纳米管的成核种子，目的是研究碳纳米管的生长机制。众所周知，利用氢诱导的自组织可以很好地控制金属纳米颗粒的性质，如尺寸、形状、结晶度或晶体平面。值得特别提及的新发现如下。(1)利用自组织金属纳米颗粒催化剂，通过CVD方法成功合成了不同取向的碳纳米管。通过优化生长条件，证明了碳纳米管在基质上的横向或垂直生长。此外，还发现在CVD过程中辅助等离子体可以改善碳纳米管的垂直排列。(2)表征了不同取向生长的CNTs在衬底上的结构特性。基于对碳纳米管的TEM观察，提出了一种新的生长模型。在模型中，自组织催化剂纳米颗粒的形状显著影响CNTs的生长。研究了所得碳纳米管的场电子发射（FE）性能。结果表明，随机取向的CNTs表现出更好的FE性能，表明表面缺陷可能是CNTs上的发射位点。

Carbon nanotube (CNT) has been synthesized by chemical vapor deposition (CVD), arc discharge, laser vaporization and so on. So far the growth mechanism of the CNT has been proposed. In the proposed mechanism, the key steps are the formation and liquefaction of the catalyst nanoparticles. However, the growth mechanism of CNT has not been fully elucidated. In this project, self-organized catalyst nanoparticles are used as a nucleation seed of the CNT with the aim of investigating the growth mechanism of CNT. It is known that the properties of metal nanoparticles such as size, shape, crystallinity, or crystallographic plane are well-controlled using hydrogen-induced self-organization. The new findings worthy of special mention are as follows.(1) We successfully synthesized CNTs with different orientations using self-organized catalyst metal nanoparticles by CVD. By optimizing the growth conditions, lateral or vertical growth of the CNTs was demonstrated against the substrates. Moreover, it was found that assisting plasma during CVD improved the vertical alignment of the CNTs.(2) The structural properties of the grown CNTs with different orientations against the substrates were characterized. Based on the TEM observation for the CNTs, a new growth model was proposed. In the model, the shape of the self-organize catalyst nanoparticles considerably affects the growth of the CNTs. The field electron emission (FE) property for the obtained CNTs was also investigated. As a result, the randomly oriented CNTs exhibited better FE property, indicating the surface defect could be an emission site on the CNTs.