Terahertz spectra of multi-walled carbon nanotubes with different parameters

The terahertz time-domain spectroscopy (THz-TDS) was applied to investigate the characteristics of terahertz absorption spectra and refractivities of multi-walled carbon nanotubes (MWCNTs). Five types of MWCNTs with different tube diameters and lengths were studied. The experiment results show that, in the frequency range of 0.2 to 2.0 THz, no characteristic absorption of MWCNTs is found but the absorption strengths increase with the frequency, which can be fitted into lines with different slopes. Furthermore, the terahertz absorption strengths of MWCNTs are proportional to the tube diameters and lengths. However, the refractivities decrease exponentially with the increase of frequency. The tube diameter is an important factor affecting the refractivities, while the influence of tube length can be neglected.