多壁碳纳米管薄膜在THz波段的传输与偏振特性

利用化学气相沉积法制备了三种类型多个超有序排列的多壁碳纳米管薄膜样品，通过太赫兹时域光谱技术，获取相位和振幅信息，详细研究了薄膜在太赫兹波段的传输特性。结果表明:超有序多壁碳纳米管薄膜在纳米管轴向方向与垂直于轴向方向表现出明显的光、电各向异性特性；测试的介电常数实部为负，虚部为正，证实了制备的薄膜具有金属性；薄膜具有的各向异性为研究其偏振特性提供了直接证据，随着薄膜厚度的增加，偏振度和消光比增加，其9 m厚的自由薄膜度可以获得99%的偏振度。研究结果对开展超有序多壁碳纳米管薄膜在太赫兹偏振器、调制器与光开关等领域的研究有重要指导意义。

Transmission and polarization properties of multi-walled carbon nanotubes film in terahertz waveband

Carbon nanotubes film has attracted significant attention and has the potential application in photo-electrical devices because of its outstanding electrical, optical and mechanical properties in the wide frequency range from microwave to visible light. The active and passive terahertz devices are progressing at a rapid rate. The highly quality carbon nanotubes film offers an alternative to generation, detection, and polarization of terahertz wave. The vertically aligned multi-walled carbon nanotubes film was grown by low pressure chemical vapor deposition. The drawing method was employed to fabricate the super-aligned carbon nanotubes film. The transmission and polarization properties of the carbon nanotubes film (three kinds of film:one is carbon nanotubes film with gratings on Si substrate; another is carbon nanotubes film without gratings on Si substrate, and last is a freestanding carbon nanotubes film) had been investigated by terahertz time-domain spectroscopy. The results show that the anisotropic properties of the complex refraction index and permittivity of carbon nanotubes film were observed. The transmittance in the case of the terahertz polarization perpendicular to the axis of carbon nanotubes is more than that of the terahertz polarization parallel to the axis of carbon nanotubes. The degree of polarization and extinction ratio of film increases with increasing film thickness. The degree of polarization is up to 99% and keeps constant for 9 m-thick multi-walled carbon nanotubes film. This research provides basic knowledge useful for emerging applications of multi-walled carbon nanotubes in optoelectronics and plasmonics in the technologically important terahertz frequency range.