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22 pages, 4663 KiB

Open AccessFeature PaperArticle

Helical Nanostructures of Ferroelectric Liquid Crystals as Fast Phase Retarders for Spectral Information Extraction Devices: A Comparison with the Nematic Liquid Crystal Phase Retarders

by Marwan J. AbuLeil, Doron Pasha, Isaac August, Evgeny P. Pozhidaev, Vadim A. Barbashov, Timofey P. Tkachenko, Artemy V. Kuznetsov and Ibrahim Abdulhalim

Materials 2021, 14(19), 5540; https://doi.org/10.3390/ma14195540 - 24 Sep 2021

Cited by 9 | Viewed by 2955

Abstract

Extraction of spectral information using liquid crystal (LC) retarders has recently become a topic of great interest because of its importance for creating hyper- and multispectral images in a compact and inexpensive way. However, this method of hyperspectral imaging requires thick LC-layer retarders (50 µm–100 µm and above) to obtain spectral modulation signals for reliable signal reconstruction. This makes the device extremely slow in the case of nematic LCs (NLCs), since the response time of NLCs increases proportionally to the square of the LC-layer thickness, which excludes fast dynamic processes monitoring. In this paper, we explore two approaches for solving the speed problem: the first is based on the use of faster nanospiral ferroelectric liquid crystals as an alternative to NLCs, and the second is based on using a passive multiband filter and focuses on multispectral extraction rather than hyperspectral. A detailed comparative study of nematic and ferroelectric devices is presented. The study is carried out using a 9-spectral bands passive spectral filter, covering the visible and near-infrared ranges. We propose the concept of multispectral rather than hyperspectral extraction, where a small number of wavelengths are sufficient for specific applications. Full article

(This article belongs to the Special Issue New Advances in Modeling, Simulation and Analysis of Optical Materials)

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12 pages, 4217 KiB

Open AccessFeature PaperArticle

Au Nanospirals Transferred onto PDMS Film Exhibiting Circular Dichroism at Visible Wavelengths

by Gaku Furusawa and Tetsuo Kan

Micromachines 2020, 11(7), 641; https://doi.org/10.3390/mi11070641 - 29 Jun 2020

Cited by 5 | Viewed by 4303

Abstract

We propose a thin, single-layered circular dichroic filter with Au nanospiral structures on a polydimethylsiloxane (PDMS) thin film that has strong circular dichroism at visible wavelengths. Au nanospiral structures with a diameter of 70 nm were fabricated by cryogenic glancing angle deposition on a substrate with a nanodot array template patterned with the block copolymer PS-PDMS. The Au nanospiral structures were transferred onto a transparent and flexible PDMS thin film to fabricate a thin, single-layered circular dichroic filter. The filter had a very large circular dichroism peak of −830 mdeg at 630 nm. The results show that the Au nanospiral structures transferred onto PDMS thin film exhibit large circular dichroism at visible wavelengths. Full article

(This article belongs to the Special Issue Selected Papers from the 10th Symposium on Micro-Nano Science and Technology on Micromachines)

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10 pages, 2348 KiB

Open AccessArticle

Influence of InAlN Nanospiral Structures on the Behavior of Reflected Light Polarization

by Yu-Hung Kuo, Roger Magnusson, Elena Alexandra Serban, Per Sandström, Lars Hultman, Kenneth Järrendahl, Jens Birch and Ching-Lien Hsiao

Nanomaterials 2018, 8(3), 157; https://doi.org/10.3390/nano8030157 - 12 Mar 2018

Cited by 3 | Viewed by 4484

Abstract

The influence of structural configurations of indium aluminum nitride (InAlN) nanospirals, grown by reactive magnetron sputter epitaxy, on the transformation of light polarization are investigated in terms of varying structural chirality, growth temperatures, titanium nitride (TiN) seed (buffer) layer thickness, nanospiral thickness, and pitch. The handedness of reflected circularly polarized light in the ultraviolet–visible region corresponding to the chirality of nanospirals is demonstrated. A high degree of circular polarization (P_c) value of 0.75 is obtained from a sample consisting of 1.2 μm InAlN nanospirals grown at 650 °C. A film-like structure is formed at temperatures lower than 450 °C. At growth temperatures higher than 750 °C, less than 0.1 In-content is incorporated into the InAlN nanospirals. Both cases reveal very low P_c. A red shift of wavelength at P_c peak is found with increasing nanospiral pitch in the range of 200–300 nm. The P_c decreases to 0.37 for two-turn nanospirals with total length of 0.7 μm, attributed to insufficient constructive interference. A branch-like structure appears on the surface when the nanospirals are grown longer than 1.2 μm, which yields a low P_c around 0.5, caused by the excessive scattering of incident light. Full article

(This article belongs to the Special Issue Design and Development of Nanostructured Thin Films)

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