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28 pages, 13067 KiB

Open AccessReview

Tamm Plasmons: Properties, Applications, and Tuning with Help of Liquid Crystals

by Victor Yu. Reshetnyak, Igor P. Pinkevych, Michael E. McConney, Timothy J. Bunning and Dean R. Evans

Crystals 2025, 15(2), 138; https://doi.org/10.3390/cryst15020138 - 27 Jan 2025

Cited by 2 | Viewed by 1403

Abstract

This article provides a brief overview of the research on localized optical states called Tamm plasmons (TPs) and their potential applications, which have been extensively studied in recent decades. These states arise under the influence of incident light at the interface between a metal film and a medium with the properties of a Bragg mirror, or between two media with the properties of a Bragg mirror. The localization of the states in the interfacial region is a consequence of the negative dielectric constant of the metal and the presence of a photonic band gap of the Bragg reflector. Optically, TPs appear as resonant reflection dips or peaks in the transmission and absorption spectra in the region corresponding to the photonic band gap. The relative simplicity of creating a Tamm structure and the significant sensitivity of TPs to its parameters make them attractive for applications. The formation of broadband and tunable TP modes in hybrid structures containing, in particular, rugate filters and porous distributed Bragg reflectors are considered. Considerable attention is paid to TP designs that include liquid crystals, which allow for the remote tuning of the TP spectrum without the mechanical restructuring of the system. The application of TPs in sensors, thermal emitters, absorbers, laser generation, and the experimental capabilities of TP-liquid crystal devices are also discussed. Full article

(This article belongs to the Special Issue Liquid Crystal Research and Novel Applications in the 21st Century)

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16 pages, 4905 KiB

Open AccessArticle

Bare Eye Detection of Bacterial Enzymes of Pseudomonas aeruginosa with Polymer Modified Nanoporous Silicon Rugate Filters

by Qasim Alhusaini, Walter Sebastian Scheld, Zhiyuan Jia, Dipankar Das, Faria Afzal, Mareike Müller and Holger Schönherr

Biosensors 2022, 12(12), 1064; https://doi.org/10.3390/bios12121064 - 22 Nov 2022

Cited by 4 | Viewed by 2406

Abstract

The fabrication, characterization and application of a nanoporous Silicon Rugate Filter (pSiRF) loaded with an enzymatically degradable polymer is reported as a bare eye detection optical sensor for enzymes of pathogenic bacteria, which is devoid of any dyes. The nanopores of pSiRF were filled with poly(lactic acid) (PLA), which, upon enzymatic degradation, resulted in a change in the effective refractive index of the pSiRF film, leading to a readily discernible color change of the sensor. The shifts in the characteristic fringe patterns before and after the enzymatic reaction were analyzed quantitatively by Reflectometric Interference Spectroscopy (RIfS) to estimate the apparent kinetics and its dependence on enzyme concentration. A clear color change from green to blue was observed by the bare eye after PLA degradation by proteinase K. Moreover, the color change was further confirmed in measurements in bacterial suspensions of the pathogen Pseudomonas aeruginosa (PAO1) as well as in situ in the corresponding bacterial supernatants. This study highlights the potential of the approach in point of care bacteria detection. Full article

(This article belongs to the Special Issue Functional Nanomaterials for Biosensing)

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12 pages, 1021 KiB

Open AccessArticle

Influence of Rugate Filters on the Spectral Manifestation of Tamm Plasmon Polaritons

by Victor Yu. Reshetnyak, Igor P. Pinkevych, Timothy J. Bunning and Dean R. Evans

Materials 2021, 14(5), 1282; https://doi.org/10.3390/ma14051282 - 8 Mar 2021

Cited by 16 | Viewed by 2345

Abstract

This study theoretically investigated light reflection and transmission in a system composed of a thin metal layer (Ag) adjacent to a rugate filter (RF) having a harmonic refractive index profile. Narrow dips in reflectance and peaks in transmittance in the RF band gap were obtained due to the excitation of a Tamm plasmon polariton (TPP) at the Ag–RF interface. It is shown that the spectral position and magnitude of the TPP dips/peaks in the RF band gap depend on the harmonic profile parameters of the RF refractive index, the metal layer thickness, and the external medium refractive index. The obtained dependences for reflectance and transmittance allow selecting parameters of the system which can be optimized for various applications. Full article

(This article belongs to the Special Issue Soft Photonic Crystals and Metamaterials)

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11 pages, 2931 KiB

Open AccessArticle

A Novel Chemical Gas Vapor Sensor Based on Photoluminescence Enhancement of Rugate Porous Silicon Filters

by Zicheng Zhou and Honglae Sohn

Sensors 2020, 20(9), 2722; https://doi.org/10.3390/s20092722 - 10 May 2020

Cited by 4 | Viewed by 3504

Abstract

In this study, an innovative rugate filter configuration porous silicon (PSi) with enhanced photoluminescence intensity was fabricated. The fabricated PSi exhibited dual optical properties with both sharp optical reflectivity and sharp photoluminescence (PL), and it was developed for use in organic vapor sensing. When the wavelength of the resonance peak from the rugate PSi filters is engineered to overlap with the emission band of the PL from the PSi quantum dots, the PL intensity is amplified, thus reducing the full width at half maximum (FWHM) of the PL band from 154 nm to 22 nm. The rugate PSi filters samples were fabricated by electrochemical etching of highly doped n-type silicon under illumination. The etching solution consisted of a 1:1 volume mixture of 48% hydrofluoric acid and absolute ethanol and photoluminescent rugate PSi filter was fabricated by etching while using a periodic sinusoidal wave current with 10 cycles. The obtained samples were characterized by scanning electron microscopy (SEM), and both reflection redshift and PL quenching were measured under exposure to organic vapors. The reflection redshift and PL quenching were both affected by the vapor pressure and dipole moment of the organic species. Full article

(This article belongs to the Special Issue Fabrication, Modeling and Integration of a Silicon Technology Based Sensor)

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29 pages, 1973 KiB

Open AccessReview

Nanostructural Engineering of Nanoporous Anodic Alumina for Biosensing Applications

by Josep Ferré-Borrull, Josep Pallarès, Gerard Macías and Lluis F. Marsal

Materials 2014, 7(7), 5225-5253; https://doi.org/10.3390/ma7075225 - 18 Jul 2014

Cited by 55 | Viewed by 9408

Abstract

Modifying the diameter of the pores in nanoporous anodic alumina opens new possibilities in the application of this material. In this work, we review the different nanoengineering methods by classifying them into two kinds: in situ and ex situ. Ex situ methods imply the interruption of the anodization process and the addition of intermediate steps, while in situ methods aim at realizing the in-depth pore modulation by continuous changes in the anodization conditions. Ex situ methods permit a greater versatility in the pore geometry, while in situ methods are simpler and adequate for repeated cycles. As an example of ex situ methods, we analyze the effect of changing drastically one of the anodization parameters (anodization voltage, electrolyte composition or concentration). We also introduce in situ methods to obtain distributed Bragg reflectors or rugate filters in nanoporous anodic alumina with cyclic anodization voltage or current. This nanopore engineering permits us to propose new applications in the field of biosensing: using the unique reflectance or photoluminescence properties of the material to obtain photonic barcodes, applying a gold-coated double-layer nanoporous alumina to design a self-referencing protein sensor or giving a proof-of-concept of the refractive index sensing capabilities of nanoporous rugate filters. Full article

(This article belongs to the Special Issue Advanced Nanomaterials for Biosensors)

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23 pages, 2318 KiB

Open AccessReview

Spectrally-Selective Photonic Structures for PV Applications

by Marius Peters, Jan Christoph Goldschmidt, Philipp Löper, Bernhard Groß, Johannes Üpping, Frank Dimroth, Ralf B. Wehrspohn and Benedikt Bläsi

Energies 2010, 3(2), 171-193; https://doi.org/10.3390/en3020171 - 27 Jan 2010

Cited by 67 | Viewed by 15332

Abstract

We review several examples of how spectrally-selective photonic structures may be used to improve solar cell systems. Firstly, we introduce different spectrally-selective structures that are based on interference effects. Examples shown include Rugate filter, edge filter and 3D photonic crystals such as artificial opals. In the second part, we discuss several examples of photovoltaic (PV) concepts that utilize spectral selectivity such as fluorescence collectors, upconversion systems, spectrum splitting concepts and the intermediate reflector concept. The potential of spectrally selective filters in the context of solar cells is discussed. Full article

(This article belongs to the Special Issue Solar Cells)

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