Optical and electronic properties of iodine and bromine doped chirality enriched (12,1) and (13,2) single-walled carbon nanotubes

 

Abozied, Asmaa M., A. Abouelsayed, A. F. Hassan, A. A. Ramadan, Emad A. Al-Ashkar, and Badawi Anis. "Optical and electronic properties of iodine and bromine doped chirality enriched (12, 1) and (13, 2) single-walled carbon nanotubes." Carbon (2021).

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for full paper see https://www.sciencedirect.com/science/article/abs/pii/S0008622321009477

Abstract

We present transmission measurements on chirality enriched semiconducting (12,1) and (13,2) single-walled carbon nanotubes (CE-s-SWCNTs) and CE-s-SWCNTs doped with iodine (I2@CE-s-SWCNTs) and bromine (Br2@CE-s-SWCNTs) in wide frequency range from 0.1 to 40 THz. The real part of the optical conductivity σreal(ω) was fitted using Drude-Lorentz model. The Drude (D) term in the CE-s-SWCNTs was attributed to the presence of metallic tubes traces in the sample. The D/scattering rate(γD) ratio was increased by a factor of 1.13 and 2.35 with iodine and bromine p-doping, respectively. This increase was compensated by large increase in D term leading to an increase in the optical conductivity at the DC limit (σDC), growing from 186 Ω−1cm−1 for the CE-s-SWCNTs to 203 and 426 Ω−1cm−1 for the I2@CE-s-SWCNTs and Br2@CE-s-SWCNTs, respectively. In addition, the plasmon peak was shifted to higher frequencies and gains more spectral weight with doping. The calculated optical parameters determine that iodine and bromine create acceptor levels above the top of the CE-s-SWCNTs valence band by 0.04 and 0.08 eV, respectively, shifting the Fermi level. The high σDC value of the Br2@CE-s-SWCNTs is due to the higher electronegativity of bromine which enables removal of more electrons from the valence band of CE-s-SWCNTs to bromine acceptor levels.

Passively Tunable Terahertz Filters Using Liquid Crystal Cells Coated with Metamaterials

Chiang, Wei-Fan, Yu-Yun Lu, Yin-Pei Chen, Xin-Yu Lin, Tsong-Shin Lim, Jih-Hsin Liu, Chia-Rong Lee, and Chia-Yi Huang. "Passively tunable terahertz filters using liquid crystal cells coated with metamaterials." Coatings 11, no. 4 (2021): 381.

for full paper see https://www.mdpi.com/2079-6412/11/4/381/pdf

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Abstract

Liquid crystal (LC) cells that are coated with metamaterials are fabricated in this work. The LC directors in the cells are aligned by rubbed polyimide layers, and make angles θ of 0◦ , 45◦ , and 90◦ with respect to the gaps of the split-ring resonators (SRRs) of the metamaterials. Experimental results display that the resonance frequencies of the metamaterials in these cells increase with an increase in θ, and the cells have a maximum frequency shifting region of 18 GHz. Simulated results reveal that the increase in the resonance frequencies arises from the birefringence of the LC, and the LC has a birefringence of 0.15 in the terahertz region. The resonance frequencies of the metamaterials are shifted by the rubbing directions of the polyimide layers, so the LC cells coated with the metamaterials are passively tunable terahertz filters. The passively tunable terahertz filters exhibit promising applications on terahertz communication, terahertz sensing, and terahertz imaging.


Experimental

.......Figure 2 displays the experimental terahertz spectra of three metamaterials that are coated with the PI layers. These spectra are obtained using a commercial terahertz spectrometer (TPS 3000, TeraView, Cambridge, UK) in transmission mode, and the chamber in the spectrometer is filled with nitrogen gas to prevent terahertz waves from absorbing moisture. The polarization of incident terahertz waves is set parallel to the x axis of Figure 1a. The PI-coated metamaterials have transmission peaks in their terahertz spectra due to the absorption of the electromagnetic resonance of the metamaterials. The transmission peaks are at an identical frequency of 0.588 THz, and the two PI-coated metamaterials .........

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A double layer FSS filter for sub-THz applications

 Ghavidel, A., M. Kokkonen, and S. Myllymäki. "A double layer FSS filter for sub-THz applications." Scientific Reports 11, no. 1 (2021): 1-8.

Abstract
This work presents the simulated and measured performance of single- and double-layer frequency selective surface filters for operation at sub-THz frequencies (250 GHz center frequency). They were composed of concentric square loops with a split as a unit cell resonator on top of a low dielectric permittivity, low thickness material (RT5880). Both a single layer filter and a cascaded two layer filter with varied distances were investigated. The simulated bandwidth for the cascaded filter was 27 GHz and 16 GHz and 9 GHz bandwidth measured with a THz-TDS and microwave system.

for full paper see https://www.nature.com/articles/s41598-021-99256-2

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Measurement using THz time-domain spectroscopy

A TeraPulse system (TeraPulse 4000, TeraView UK,  Fig. 7a, was used to measure the FSS filter’s impact on time-delay and transmittance and the results are shown in Fig. 7b,c. The single layer FSS filter was placed between two mirrors and the thickness of the FSS created a time-delay (around 0.1 picosecond) and reduced the amplitude to 0.9 compared to the reference signal amplitude (12.5). With a second layer, the time-delay increased to 0.5 ps and reduced the transmittance amplitude to 0.43. It was observed that each layer reduced the transmitted wave amplitude by around 30%. The bandwidth was measured to be ~ 12 GHz with one layer and ~ 16 GHz with two layers at 95% transmittance level.

Figure 7

(a) TeraPulse 4000 Spectroscopy system for measuring FSS filter, measured and normalized (b) measured pulse response of electric field amplitude where the refence signal was measured without the FSS layer and (c) measured signal transmittance of single- and double-layer unit cell.

Terahertz spectroscopic analysis of non-radiated and radiated synthetic and natural polymer/GO nanocomposites

Mohamed, F., R. A. Zaghlool, and W. El Hotaby. "Terahertz spectroscopic analysis of non-radiated and radiated synthetic and natural polymer/GO nanocomposites." Journal of Molecular Structure (2021): 131659.

Abstract

Absorption coefficient, refractive index, and dielectric parameters of two sets of polymers: synthetic polymers (poly acrylamide, and poly vinyl alcohol), and natural polymers (chitosan, and cellulose acetate) have been investigated using Terahertz time-domain spectroscopy THz-TDS in the frequency range of 0.3 THz - 3.0 THz. It is found that these parameters are significantly boosted by the presence of graphene oxide (GO) as a filler. The influence of electron beam radiation of a dose of 50 kGy on the absorption coefficient, and refractive index is also investigated. An observable decrease in these parameters is illustrated in the un-doped and doped membranes upon irradiation. By this study, we shed light on how the THz-TDS is able to identify any variant change in the structure due to incorporation of GO or as an influence of electron beam radiation.

… atmosphere. 2.2.4. THz time- domain spectroscopy (THz-TDS). The terahertz spectrometer in the frequency range of 0.3 THz and 3 THz (10 cm −1 -100 cm −1 ), TPS spectra 3000 system, TeraView Ltd England, was used. To … 

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Study of Thin hBN /WS2 Films by Terahertz Time Domain Spectroscopy

 Oparin, E. N., M. O. Zhukova, V. G. Bulgakova, S. A. Pozdnyakova, and A. N. Tcypkin. "Study of Thin hBN/WS2 Films by Terahertz Time-Domain Spectroscopy."

Abstract 

Estimates of the linear optical properties of promising material for the THz modulators manufacture, i. e., thin films of the mixture of tungsten disulfide and boron nitride with hexagonal lattice on polyethylene terephthalate (PET) substrate in the broadband terahertz frequency range are presented in this paper. In the range from 0.5 to 2.5 THz the films showed high transparency exceeding 90%. The calculated refractive index value 1.75 exceeded the ones for TPX and PET – materials used in the manufacture of THz optics.

for full paper see https://www.photonics.su/files/article_pdf/8/article_8237_682.pdf

..........The studies were carried out using a laboratory setup of THz time-domain spectroscopy of TeraPulse 4000 manufactured by TeraView, shown in Fig. 1. In this system, a photoconductive antenna illuminated by the radiation of a femtosecond (fs) fiber laser is used......

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