Department of Chemistry, Research Group PLASMANT, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk, Antwerp, Belgium.
Department of Electronic Engineering, Tohoku University, 6-6-05 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan.
Nanoscale. 2017 Jan 26;9(4):1653-1661. doi: 10.1039/c6nr08005g.
Unlocking the enormous technological potential of carbon nanotubes strongly depends on our ability to specifically produce metallic or semiconducting tubes. While selective etching of both has already been demonstrated, the underlying reasons, however, remain elusive as yet. We here present computational and experimental evidence on the operative mechanisms at the atomic scale. We demonstrate that during the adsorption of H atoms and their coalescence, the adsorbed ortho hydrogen pairs on single-walled carbon nanotubes induce higher shear stresses than axial stresses, leading to the elongation of HC-CH bonds as a function of their alignment with the tube chirality vector, which we denote as the γ-angle. As a result, the C-C cleavage occurs more rapidly in nanotubes containing ortho H-pairs with a small γ-angle. This phenomenon can explain the selective etching of small-diameter semiconductor nanotubes with a similar curvature. Both theoretical and experimental results strongly indicate the important role of the γ-angle in the selective etching mechanisms of carbon nanotubes, in addition to the nanotube curvature and metallicity effects and lead us to clearly understand the onset of selective synthesis/removal of CNT-based materials.
解锁碳纳米管巨大的技术潜力强烈依赖于我们特异性生产金属或半导体管的能力。虽然已经证明了这两种材料的选择性刻蚀，但其中的根本原因迄今仍难以捉摸。我们在这里提供了原子尺度上操作机制的计算和实验证据。我们证明，在 H 原子的吸附和它们的聚合并合期间，单壁碳纳米管上吸附的邻位氢对会产生比轴向应力更高的剪切应力，从而导致 HC-CH 键的伸长，这取决于它们与管手性矢量的对齐，我们将其表示为 γ 角。因此，C-C 键的断裂在含有小 γ 角的邻位 H 对的纳米管中更快发生。这一现象可以解释具有相似曲率的小直径半导体纳米管的选择性刻蚀。理论和实验结果都强烈表明，γ 角在碳纳米管的选择性刻蚀机制中除了纳米管曲率和金属性的影响之外，还起着重要作用，并使我们能够清楚地理解基于 CNT 材料的选择性合成/去除的开始。
