Angular dependent anisotropic terahertz response of vertically aligned multi-walled carbon nanotube arrays with spatial dispersion

Abstract

Spatial dispersion effect of aligned carbon nanotubes (CNTs) in the terahertz (THz) region has significance for both theoretical and applied consideration due to the unique intrinsically anisotropic physical properties of CNTs. Herein, we report the angular dependent reflection of p-polarized THz wave from vertically aligned multi-walled CNT arrays in both experiment and theory. The spectra indicate that the reflection depends on the film thickness of vertically aligned CNTs, the incident angle, and the frequency. The calculation model is based on the spatial dispersion effect of aligned CNTs and performed with effective impedance method and the Maxwell-Garnett approximation. The results fit well with the experiment when the thickness of CNT film is thin, which reveals a coherent superposition mechanism of the CNT surface reflection and CNTs/Si interface reflection. For thick CNT films, the CNTs/Si interface response determines the reflection at small incident angles, while the CNTs surface effect dominates at large incident angles. This work investigates the spatial dispersion effect of vertically aligned CNT arrays in the THz region, and paves a way for potential anisotropic THz applications based on CNTs with oblique incidence requirements.

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

“…Enhancement of alignment of nanotubes in the polymer matrix may be a key point for improvement the electromagnetic performance of CNT-based composites. At 1 THz, reflection anisotropy coefficient for vertically aligned CNTs varied from 3 to 8 depending on the array thickness [58]. For single-walled CNT network, THz transmission anisotropy could be enhanced by stretching [59].…”

Dielectric properties of vertically aligned multi-walled carbon nanotubes in the terahertz and mid-infrared range

“…For the complex refractive index ñ of the CNT, we considered several conductivity models, used previously for conducting CNT and other nanostructures [13][14][15]24]. These included the standard Drude model…”

“…Another approach previously employed to fit the THz properties for multi-wall CNT in this range is to assume a Lorentzian function σ L (ω), either alone [15] or in addition to a standard Drude model [14,16,25]. A global fit of our data with the Drude-Lorentzian (DL) model produces a similar (but slightly worse) fit quality compared to the DS model (figure 2(g)), despite the additional degrees of freedom in the model, with a broad Lorentzian peak at ν 0L = 3.0 THz (outside the measured spectral range, with Γ L /2π = 4 THz), while ν p reduces to 1.3 THz with significantly larger uncertainty compared to the DS fits (see figures 2(e) and (f)).…”

“…While the THz-mid-infrared conductivity response of (aligned) single-wall (SW) CNT films has been studied in detail [7][8][9][10][11][12], such studies for the case of VACNT are relatively few [13][14][15], and to our knowledge, restricted to low frequencies (i.e. in the conventional THz range below ∼3 THz), which motivated the experiments extending into the IR spectral range presented below.…”

Giant angular dependence of electromagnetic induced transparency in THz metamaterials

“…Similar to the angle-resolved photoemission spectroscopy, the angle-resolved optical spectroscopy can also be used to obtain many novel physical information, such as chirality [12], photonic band [13], and spatial dispersion [14]. Angular resolved spectroscopy can also be used to find a new plasmonic mode under oblique incidence such as sub-radiant plasmons [15].…”