Abstract-Efficient terahertz anti-reflection properties of metallic anti-dot structures

Kumar Neeraj, Samiran Choudhury, Debanjan Polley, Rakhi Acharya, Jaivardhan Sinha, Anjan Barman, and Rajib Kumar Mitra

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-42-9-1764

We report the use of micrometer-sized copper (Cu) anti-dot structures as a novel terahertz (THz) anti-reflection coating (ARC) material and their superior performance over conventionally used metallic (Cu) thin films. Cu anti-dot structures of two different thicknesses (7 and 10 nm) with varying anti-dot diameters (100, 200, and 300 μm, inter-anti-dot separation fixed at 100 μm) are deposited on silicon substrates by RF magnetron sputtering and e-beam evaporation. The anti-reflection performance of these samples is studied in the frequency range of 0.3–2.2 THz. While continuous metallic (Cu) thin film minimizes the Fabry–Perot (FP) peak, it also suppresses the primary transmission peak, reducing the advantage due to the former effect. On the contrary, the anti-dot arrays reduce both the absolute amplitude of the FP peak and the amplitude ratio (AR) of the FP peak to the primary peak, making them a superior material for ARC applications. The AR can be further manipulated by varying the anti-dot size. A universal conductivity phase-matching condition, which is a prerequisite for the disappearance of the FP peak, is observed in these samples. The enhanced anti-reflection performance promotes these anti-dot structures as an efficient terahertz ARC material.

© 2017 Optical Society of America

Abstract-Terahertz conductivity engineering in surface decorated carbon nanotube films by gold nanoparticles

Debanjan Polley, Animesh Patra, Anjan Barman, and Rajib Kumar Mitra

https://www.osapublishing.org/ao/abstract.cfm?uri=ao-56-4-1107

We report the controllable conductivity of single-walled carbon nanotubes (SWNTs) and multiwalled carbon nanotubes with their surface walls decorated by gold nanoparticles (Au NPs) with varying concentration in terahertz (THz) frequency range. Colloidal Au NPs of nominal diameter ∼15  nm$\sim 15\mathrm{nm}$ are synthesized by the reduction of gold chloride solution using tri-sodium citrate. A simple chemical route is followed to attach Au NPs on the surfaces of both types of carbon nanotubes (CNTs). The attachment of Au NPs on the sidewalls of CNTs is confirmed by UV-visible spectroscopy and scanning electron microscope images. THz spectroscopic measurements are carried out at room temperature in transmission geometry in the frequency range of 0.3–2.0 THz. It is found that the THz conductivity of the surface decorated SWNT composites can either be increased or decreased by ±15%$\pm 15\%$ than that of the as-prepared SWNT composites by carefully choosing the Au NP concentration. The conductivity variation is qualitatively explained in terms of carrier trapping potential for low Au NP density, and alternative carrier conduction pathways at higher Au NP density and analyzed with the help of a modified universal dielectric relaxation model.

© 2017 Optical Society of America

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Abstract-Controllable terahertz conductivity in single walled carbon nanotube/polymer composites

Debanjan Polley¹, Anjan Barman^1,a) and Rajib Kumar Mitra2,a)
http://scitation.aip.org/content/aip/journal/jap/117/2/10.1063/1.4905958?TRACK=RSS
1 Department of Condensed Matter Physics and Material Sciences, S. N. Bose National Centre for Basic Sciences, Block JD, Sector III, Salt Lake, Kolkata 700098, India
2 Department of Chemical, Biological and Macromolecular Sciences, S. N. Bose National Centre for Basic Sciences, Block JD, Sector III, Salt Lake, Kolkata 700098, India
a) Electronic addresses: abarman@bose.res.in and rajib@bose.res.in.
J. Appl. Phys. 117, 023115 (2015); http://dx.doi.org/10.1063/1.4905958

Terahertz (THz) conductivity of single walled carbon nanotube (SWNT)/poly-vinyl alcohol (PVA)composites has been studied in the frequency window of 0.3–2.0 THz. SWNT/PVA compositefilms with a constant thickness of 300 ± 20 μm are grown by dispersing required amount ofSWNT in PVA solution via a slow drying process at room temperature under ambient condition. THz time domain spectroscopic measurements have been performed in transmission geometry at room temperature under N2 atmosphere and THz conductivity spectra have been extracted from the time domain data. It is found that conductivity of these samples can be efficiently tuned by changing the length of the SWNTs and also the SWNT weight fraction. For the highest weight fraction at a frequency of 1.5 THz, longer SWNT sample (average length ∼ 15 μm) showed 80% increased conductivity than its shorter counterpart (average length ∼ 2 μm) of the same diameter (1–2 nm). Shielding effectiveness of the samples has also been engineered by simply changing the effective length of SWNT inclusion in the polymer matrix. A modified Universal Dynamic Response model is applied to analyze the conductivity spectra of the samples.