Nuclear magnetic resonance study of highly concentrated metallic and semiconducting single-walled carbon nanotubes

单壁碳纳米管（SWCNTs）可以是金属的或半导体的，这取决于它们的结构参数。到目前为止，已经对带有金属和半导体SWCNTs混合物束的样品进行了核磁共振（NMR）研究。在本研究中，我们成功地观察到了密度梯度超离心技术制备的金属和半导体swcnts束的不同的13C NMR谱。我们发现金属和半导体SWCNTs之间观察到的光谱存在显著差异。这可以通过Knight位移和电流位移对金属和半导体SWCNTs的不同贡献来解释。此外，我们还研究了包裹C60富勒烯的SWCNTs转化为双壁CNTs的机理。

Single-walled carbon nanotubes (SWCNTs) can be metallic or semiconducting, depending on their structural parameters. Up to now, nuclear magnetic resonance (NMR) studies have been performed on samples with bundles of mixtures of metallic and semiconducting SWCNTs. In this study, we have succeeded in observing the distinct 13C NMR spectra in the metallic and semiconducting SWCNT bundles prepared by density gradient ultracentrifugation technique. We found substantial differences in the observed spectra between the metallic and semiconducting SWCNTs. These were explained by difference contributions from Knight shift and current shift for metallic and semiconducting SWCNTs. Furthermore, we studied the mechanism for transformation of SWCNTs encapsulating C60 fullerene into double-walled CNTs.