Beijing National Laboratory for Molecular Science, Key Laboratory for the Physics and Chemistry of Nanodevices, State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China.
Institute of Textiles and Clothing, Hong Kong Polytechnic University, Kowloon, Hong Kong, China.
Nature. 2014 Jun 26;510(7506):522-4. doi: 10.1038/nature13434.
Carbon nanotubes have many material properties that make them attractive for applications. In the context of nanoelectronics, interest has focused on single-walled carbon nanotubes (SWNTs) because slight changes in tube diameter and wrapping angle, defined by the chirality indices (n, m), will shift their electrical conductivity from one characteristic of a metallic state to one characteristic of a semiconducting state, and will also change the bandgap. However, this structure-function relationship can be fully exploited only with structurally pure SWNTs. Solution-based separation methods yield tubes within a narrow structure range, but the ultimate goal of producing just one type of SWNT by controlling its structure during growth has proved to be a considerable challenge over the last two decades. Such efforts aim to optimize the composition or shape of the catalyst particles that are used in the chemical vapour deposition synthesis process to decompose the carbon feedstock and influence SWNT nucleation and growth. This approach resulted in the highest reported proportion, 55 per cent, of single-chirality SWNTs in an as-grown sample. Here we show that SWNTs of a single chirality, (12, 6), can be produced directly with an abundance higher than 92 per cent when using tungsten-based bimetallic alloy nanocrystals as catalysts. These, unlike other catalysts used so far, have such high melting points that they maintain their crystalline structure during the chemical vapour deposition process. This feature seems crucial because experiment and simulation both suggest that the highly selective growth of (12, 6) SWNTs is the result of a good structural match between the carbon atom arrangement around the nanotube circumference and the arrangement of the catalytically active atoms in one of the planes of the nanocrystal catalyst. We anticipate that using high-melting-point alloy nanocrystals with optimized structures as catalysts paves the way for total chirality control in SWNT growth and will thus promote the development of SWNT applications.
碳纳米管具有许多材料特性，使其在应用中具有吸引力。在纳米电子学领域，人们对单壁碳纳米管（SWNTs）感兴趣，因为管直径和缠绕角的微小变化（由手性指数（n，m）定义）将使它们的电导率从金属态的一个特性转变为半导体态的一个特性，并将改变带隙。然而，只有结构纯净的 SWNTs 才能充分利用这种结构-功能关系。基于溶液的分离方法可以得到结构范围较窄的管，但在过去二十年中，通过在生长过程中控制其结构来生产仅一种类型的 SWNT 的最终目标被证明是一个相当大的挑战。这些努力旨在优化催化剂颗粒的组成或形状，这些催化剂颗粒用于化学气相沉积合成过程中分解碳原料并影响 SWNT 成核和生长。这种方法导致在生长样品中报告的最高比例为 55%的单一手性 SWNTs。在这里，我们表明，当使用基于钨的双金属合金纳米晶体作为催化剂时，可以直接生产单一手性的 SWNTs，其丰度高于 92%。与迄今为止使用的其他催化剂不同，这些催化剂具有如此高的熔点，以至于它们在化学气相沉积过程中保持其晶体结构。这一特性似乎至关重要，因为实验和模拟都表明，（12，6）SWNTs 的高度选择性生长是由于纳米管圆周周围的碳原子排列与纳米晶体催化剂的一个平面中的催化活性原子的排列之间的良好结构匹配的结果。我们预计，使用具有优化结构的高熔点合金纳米晶体作为催化剂将为 SWNT 生长中的总手性控制铺平道路，并将促进 SWNT 应用的发展。
