利用同調兆赫光譜研究巴克紙的光電特性

Abstract

Buckypaper is a thin carbon sheet made from carbon nanotubes (CNTs), which are connected by the van der Waals force. Since buckypaper is a macroscopic aggregate of CNTs, the material properties of individual CNT can be suppressed and the macroscopic properties of buckypapers may be due to the ensemble averaging over a large number of tubes. The conventional electrical property characterization methods such as two-point method cannot be used for individual or ensemble of nanostructures. In this thesis, the terahertz time-domain spectroscopy (THz-TDS), which is an optical and non-contact method, was utilized to elucidate the complex THz conductivity and dielectric responses of buckypapers. The frequency dependent THz conductivities of a series of buckypapers were analyzed by using the Drude, Drude-Smith, and Drude-Lorentz models. Despite its high conductivity, the frequency dependence of THz conductivity cannot be described by the simple Drude model. The excellent fitting to the experimental data was obtained by the Drude-Smith model, which includes the effect of backscattering while free carriers moving across solid concentric CNT layers. The backscattering factor c for our buckypapers is ~-0.74 and this is very close to the theoretical value for a single conductor in 3D space. With the Drude-Lorentz model which is derived from plasmon resonance, the resonance frequency is estimated to be ~3 – 3.5 THz, which also shows the excellent agreement with those of single-walled CNTs or multi-walled CNTs.

Buckypaper is a thin carbon sheet made from carbon nanotubes (CNTs), which are connected by the van der Waals force. Since buckypaper is a macroscopic aggregate of CNTs, the material properties of individual CNT can be suppressed and the macroscopic properties of buckypapers may be due to the ensemble averaging over a large number of tubes. The conventional electrical property characterization methods such as two-point method cannot be used for individual or ensemble of nanostructures. In this thesis, the terahertz time-domain spectroscopy (THz-TDS), which is an optical and non-contact method, was utilized to elucidate the complex THz conductivity and dielectric responses of buckypapers. The frequency dependent THz conductivities of a series of buckypapers were analyzed by using the Drude, Drude-Smith, and Drude-Lorentz models. Despite its high conductivity, the frequency dependence of THz conductivity cannot be described by the simple Drude model. The excellent fitting to the experimental data was obtained by the Drude-Smith model, which includes the effect of backscattering while free carriers moving across solid concentric CNT layers. The backscattering factor c for our buckypapers is ~-0.74 and this is very close to the theoretical value for a single conductor in 3D space. With the Drude-Lorentz model which is derived from plasmon resonance, the resonance frequency is estimated to be ~3 – 3.5 THz, which also shows the excellent agreement with those of single-walled CNTs or multi-walled CNTs.