A Review of the Terahertz Conductivity and Photoconductivity of Carbon Nanotubes and Heteronanotubes

Abstract

particular, at that stage, it was realized that single-walled carbon nanotubes (SWCNTs) shown in Figure 1a have a unique property that makes them different from other NTs: they are semiconducting or metallic depending on their chirality in comparison to graphene, a Dirac semimetal. This makes SWCNTs promising for both electronic and optoelectronic applications. [11] In the years following the work of Iijima, numerous different classes of 1D materials were reported. In 1992 and 1995, the discovery of WS 2 and MoS 2 NTs were reported. [4,6] In 1999, initial reports showed the feasibility of growing highly aligned arrays of TiO 2 NTs. [12] A number of groups reported progress in the synthesis of BN NTs. [5] The main difference between non-organic NTs (for example, MoS 2 , MoSe 2 , WS 2 , WSe 2 , etc.) and CNTs is that non-organic NTs are mostly semiconducting. Their mobility and transport properties have been widely investigated. [13][14][15] The family of 1D materials has grown appreciably. Each new NT demonstrated unique properties associated with their small dimensionality, thus being different from their 2D and 3D counterparts. In the same way as proposed for 2D materials, [16] NTs can be grown outside or inside of each other, like a Russian doll, forming 1D van der Waals (vdW) heterostructure (or so-called heteronanotube) (Figure 1d). In most of them, CNTs are used as a template for growth. For example, the first composite of CNTs wrapped by MoS 2 NTs (here and later in the text-C@ MoS 2 NT) was synthesized in 2006. [17] Later on, the charge transport properties were investigated in ref. [18]. Recently the optical, electrical and transport properties of atomically thin Terahertz (THz) spectroscopy is an ideal non-contact and non-destructive technique that probes the electrical conductivity of nanomaterials. This review presents the current status of research in the THz properties of quasi-1D materials, such as nanotubes (NTs) and NT heterostructures. Detailed descriptions of THz experimental methods (THz time-domain spectroscopy, optical pump-THz probe spectroscopy) and conductivity extraction methods are presented along with the physical models (Drude, plasmon, effective medium theories, etc.) supporting them. Optoelectronic applications, such as optical modulators, switches, and shielding devices, are discussed and illustrate a bright future for these materials.

Zigzag HgTe Nanowires Modify the Electron–Phonon Interaction in Chirality-Refined Single-Walled Carbon Nanotubes

“…The broad absorption maxima in the free-carrier absorption regime (below 3000 cm –1 ) result from the axial plasmon resonance of finite-length nanotubes. 4 , 33 − 35 The absorbance profiles for semiconducting and metallic SWCNTs are distinctly different. The semiconducting SWCNTs exhibited a narrower absorption peak centered at around 300 cm –1 , while the metallic tubes had a broader absorption peak around 1000 cm –1 .…”

Synthesis, Sorting, and Applications of Single-Chirality Single-Walled Carbon Nanotubes

“…Either one of these properties can be tuned to the desired value by changing the thickness of the CNT. In addition, it has been discovered that a number of factors, including the CNT length and diameter, electrical characteristics, chemical doping, purity, synthesis, and preparation procedures, have a significant impact on the resistance and, consequently, conductivity of a CNT network [ 158 , 159 ].…”

Nanotube Functionalization: Investigation, Methods and Demonstrated Applications

“…Unlike non-covalent functionalization, it changes the electronic structure, resulting in the irreversible loss of double bonds. These changes can affect conductivity properties and therefore, some applications [ 5 , 6 , 7 , 8 , 9 , 10 ].…”