Intersubband plasmon excited in heavily doped carbon nanotubes by the external electromagnetic field in the near-infrared range is known to be sensitive to both the nanotube diameter and Fermi level shift. This work provides experimental results on the intersubband plasmon frequency measured as a function of gating voltage in single-walled carbon nanotube (SWCNT) thin films. We have explored SWCNTs with three mean diameters of 1.0, 1.4, and 2.0 nm being electrochemically gated in the ionic liquid. It is demonstrated that the plasmon frequency could be tuned in the range from 0.8 to 1.5 eV while the Fermi level was shifted up to 1.2 eV by using the electrochemical gating. Indeed, we have observed the theoretically predicted intersubband plasmon and discussed the influence of tubes bundling on the plasmon frequency shift with respect to the theoretical prediction for isolated SWCNTs. The increase of the bundle size red-shifts the plasmon frequency similar to the increase of the nanotube diameter.

中文翻译：

---

电化学门控碳纳米管薄膜中的子带间等离子观察

已知通过在近红外范围内的外部电磁场在重掺杂碳纳米管中激发的子带间等离子体激元对纳米管直径和费米能级位移均敏感。这项工作提供了关于在单壁碳纳米管（SWCNT）薄膜中测得的作为门控电压的函数的子带间等离激元频率的实验结果。我们已经研究了在离子液体中电化学门控的1.0、1.4和2.0 nm三种平均直径的SWCNT。结果表明，通过使用电化学门控，可将等离激元频率调节在0.8至1.5 eV的范围内，而费米能级则可升至1.2 eV。确实，我们已经观察到理论上预测的子带间等离激元，并讨论了管束对等离激元频移的影响。束尺寸的增加使等离子体激元频率红移，类似于纳米管直径的增加。