Otsuka Keigo, Ishimaru Ryoya, Kobayashi Akari, Inoue Taiki, Xiang Rong, Chiashi Shohei, Kato Yuichiro K, Maruyama Shigeo
Department of Mechanical Engineering, The University of Tokyo, Tokyo 113-8656, Japan.
Nanoscale Quantum Photonics Laboratory, RIKEN Cluster for Pioneering Research, Saitama 351-0198, Japan.
ACS Nano. 2022 Apr 26;16(4):5627-5635. doi: 10.1021/acsnano.1c10569. Epub 2022 Mar 22.
Single-walled carbon nanotubes have been a candidate for outperforming silicon in ultrascaled transistors, but the realization of nanotube-based integrated circuits requires dense arrays of purely semiconducting species. In order to directly grow such nanotube arrays on wafers, control over kinetics and thermodynamics in tube-catalyst systems plays a key role, and further progress requires a comprehensive understanding of seemingly contradictory reports on the growth kinetics. Here, we propose a universal kinetic model that decomposes the growth rates of nanotubes into the adsorption and removal of carbon atoms on the catalysts, and we provide its quantitative verification by ethanol-based isotope labeling experiments. While the removal of carbon from catalysts dominates the growth kinetics under a low supply of precursors, resulting in chirality-independent growth rates, our kinetic model and experiments demonstrate that chiral angle-dependent growth rates emerge when sufficient amounts of carbon and etching agents are cosupplied. The kinetic maps, as a product of generalizing the model, include five types of kinetic selectivity that emerge depending on the absolute quantities of gases with opposing effects. Our findings not only resolve discrepancies existing in the literature but also offer rational strategies to control the chirality, length, and density of nanotube arrays for practical applications.
单壁碳纳米管一直是超大规模晶体管中性能优于硅的候选材料，但基于纳米管的集成电路的实现需要纯半导体物种的密集阵列。为了在晶圆上直接生长这种纳米管阵列，管 - 催化剂系统中动力学和热力学的控制起着关键作用，而进一步的进展需要全面理解关于生长动力学的看似矛盾的报道。在这里，我们提出了一个通用动力学模型，该模型将纳米管的生长速率分解为催化剂上碳原子的吸附和去除，并通过基于乙醇的同位素标记实验提供了定量验证。在前体供应不足的情况下，催化剂上碳的去除主导生长动力学，导致与手性无关的生长速率，而我们的动力学模型和实验表明，当同时供应足够量的碳和蚀刻剂时，会出现与手性角相关的生长速率。作为模型推广的产物，动力学图谱包括五种类型的动力学选择性，它们根据具有相反作用的气体的绝对量而出现。我们的发现不仅解决了文献中存在的差异，还为实际应用中控制纳米管阵列的手性、长度和密度提供了合理策略。
