Abstract-Iron-filled multi-walled carbon nanotubes for terahertz applications: effects of interfacial polarization, screening and anisotropy

Olga V. Sedelnikova, Evgeny Korovin, K. V. Dorozhkin, M. A. Kanygin, S. Arkhipov, Yury Shubin, Victor Zhuravlev, Valentin I. Suslyaev, Lyubov G Bulusheva, Alexander V Okotrub

http://iopscience.iop.org/article/10.1088/1361-6528/aaae43/pdf

Interface interactions in multicomponent nanoparticles can affect electromagnetic properties of an absorbing system. In this work, we investigate the electromagnetic response of multi-walled carbon nanotubes (MWCNTs) filled with iron-containing nanoparticles (ICNs) in the terahertz frequency range. MWCNTs with different iron content have been synthesized by aerosol-assisted catalytic chemical vapor deposition method from toluene containing a certain quantity of ferrocene used as a catalyst. According to the X-ray diffraction analysis, encapsulated ICNs were mainly in the form of iron carbide. Thin composite films were prepared from the iron-filled MWCNTs and polymethylmethacrylate (PMMA) by casting and stretching methods. The composites showed an enhanced permittivity and anisotropy in the transmittance spectra when iron content increased. This behavior was related to the mechanism based on electrical conductivity and polarization of ICNs and ICN/MWCNT interface. Since terahertz field penetrates inside MWCNTs, the filling of their cavities can be a way of varying the electromagnetic properties of MWCNT-containing composites.

Abstract-Terahertz emission from vertically aligned multi-wall carbon nanotubes and their composites by optical excitation

Shan Huang, Weilong Li.  Lipeng Zhu, Mi He, Zehan Yao, Yixuan Zhou, Xinlong Xu, Zhaoyu Ren,  Jinbo Bai,

https://www.sciencedirect.com/science/article/pii/S000862231830191X

Terahertz (THz) emission has been successfully observed from vertically aligned multi-wall carbon nanotube (VAMCNT) materials excited with polarized laser pulse in a reflection configuration. The effects of experimental parameters on THz generation are investigated systematically. The results indicate that the linear dependence of THz electric field on the pump power shows a typical second-order nonlinear optical effect and the transient photocurrent for generating THz waves is mainly originated from photon drag effect. By comparing with THz emission from polymer-coated VAMCNT composites, the detailed generation process of THz waves from VAMCNT materials is clarified: the free carriers in VAMCNT films could transport both along single nanotube and between the adjacent nanotubes, while free carriers in VAMCNT composite films transport mainly along the tube axis due to the isolated carrier transport between the adjacent nanotubes by the coated polymer. Thus, transient photocurrent for generating THz emission from VAMCNT composite films is only along the tube axis and its intensity depends on the component of the pump light electric field along the tube axis. In addition, THz emission from VAMCNT composites shows more regular response than that from pure VAMCNT films, which paves a way for stable performance of VAMCNT-based THz emitter.