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11 pages, 1335 KiB

Open AccessArticle

Towards Optimizing Width Modulation for Maximum Thermoelectric Efficiency

by Antonios-Dimitrios Stefanou and Xanthippi Zianni

Micromachines 2023, 14(12), 2176; https://doi.org/10.3390/mi14122176 - 29 Nov 2023

Cited by 1 | Viewed by 1027

Maximizing thermoelectric efficiency is typically addressed as identical to minimizing parasitic thermal conduction. Such an approach relies on the assumption that the adopted strategy mainly affects phonons, leaving electrons intact, and is not justified in many cases of non-uniform nanostructures such as width-modulated [...] Read more.

Maximizing thermoelectric efficiency is typically addressed as identical to minimizing parasitic thermal conduction. Such an approach relies on the assumption that the adopted strategy mainly affects phonons, leaving electrons intact, and is not justified in many cases of non-uniform nanostructures such as width-modulated nanowaveguides, where both electrons and phonons are significantly affected by width modulation. Here, we address the question of maximizing the thermoelectric efficiency of this class of metamaterials by exploring the effect of the modulation extent on both electron and phonon transport. We investigated the effect of increasing modulation degree on the thermoelectric efficiency, considering the cases of (a) a two-QD modulation and (b) multiple-QD modulations in periodic and aperiodic sequences. We show that the thermoelectric efficiency depends on the coupling between the modulation units and the interplay between periodicity and aperiodicity in the modulation profile. We reveal that the maximization of the thermoelectric power factor is for periodic width-modulation, whereas the maximization of the thermoelectric efficiency is for aperiodic width-modulation profiles that form quasi-localized states for electrons. Our work provides new insight that can be used to optimize width modulation for maximum thermoelectric efficiency. Full article

(This article belongs to the Special Issue Development of High Performance Thermoelectric Materials towards Applications)

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11 pages, 3399 KiB

Open AccessArticle

The Effect of Width-Mismatch of Modulated Nanowaveguides on the Thermoelectric Efficiency

by Antonios-Dimitrios Stefanou and Xanthippi Zianni

Micromachines 2023, 14(10), 1912; https://doi.org/10.3390/mi14101912 - 7 Oct 2023

Cited by 1 | Viewed by 1295

Abstract

Width-modulated nanowaveguides are promising for thermoelectric efficiency enhancement because electron and phonon transport properties can be geometrically tuned for improved performance. The shape of the modulation profile drastically affects the transport properties. Optimization of the width modulation for simultaneous maximum thermoelectric transport and [...] Read more.

Width-modulated nanowaveguides are promising for thermoelectric efficiency enhancement because electron and phonon transport properties can be geometrically tuned for improved performance. The shape of the modulation profile drastically affects the transport properties. Optimization of the width modulation for simultaneous maximum thermoelectric transport and minimum thermal transport is challenging because of the interconnected electron and phonon transport properties. We addressed this problem by analysing the effect of each characteristic dimension of a single rectangular modulation unit on electron and phonon transport. We identified distinct behaviours for electrons and phonons. We reveal that whereas phonon thermal conductance decreases with increasing width-mismatch, the electron thermoelectric power factor shows a non-monotonic dependence. It is pointed out that optimal width-mismatch that maximizes thermoelectric efficiency is mainly determined by electron transport and should be identified by maximizing the thermoelectric power. Our work points to a new strategy of optimizing geometry-modulated metamaterials for maximum thermoelectric efficiency. Full article

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20 pages, 5053 KiB

Open AccessArticle

Perfect Invisibility Modes in Dielectric Nanofibers

by Vasily V. Klimov and Dmitry V. Guzatov

Photonics 2023, 10(3), 248; https://doi.org/10.3390/photonics10030248 - 26 Feb 2023

Cited by 4 | Viewed by 1876

Abstract

With the help of the original mathematical method for solving Maxwell’s equations, it is shown that in dielectric waveguides along with usual waveguides and quasi-normal modes, there are perfect invisibility modes or perfect non-scattering modes. In contrast to the usual waveguide modes, at [...] Read more.

With the help of the original mathematical method for solving Maxwell’s equations, it is shown that in dielectric waveguides along with usual waveguides and quasi-normal modes, there are perfect invisibility modes or perfect non-scattering modes. In contrast to the usual waveguide modes, at eigenfrequencies of the perfect invisibility modes, light can propagate in free space. The properties of the invisibility modes in waveguides of circular and elliptical cross-sections are analyzed in detail. It is shown that at the eigenfrequencies of the perfect invisibility modes, the power of the light scattered from the waveguide tends to zero and the optical fiber becomes invisible. The found modes can be used to create highly sensitive nanosensors and other optical nanodevices, where radiation and scattering losses should be minimal. Full article

(This article belongs to the Special Issue Advances in Optical Microcavities)

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11 pages, 5226 KiB

Open AccessArticle

Low Loss Vertical TiO₂/Polymer Hybrid Nano-Waveguides

by Isaac Doughan, Kehinde Oyemakinwa, Olli Ovaskainen and Matthieu Roussey

Nanomaterials 2023, 13(3), 469; https://doi.org/10.3390/nano13030469 - 24 Jan 2023

Cited by 2 | Viewed by 2469

Abstract

This article proposes a novel demonstration of a low-loss polymer channel hybridized with a titania core leading to a nano-waveguide elongated in the normal direction to the substrate. It is aimed at using the quasi-transverse magnetic (TM) mode as the predominant mode in [...] Read more.

This article proposes a novel demonstration of a low-loss polymer channel hybridized with a titania core leading to a nano-waveguide elongated in the normal direction to the substrate. It is aimed at using the quasi-transverse magnetic (TM) mode as the predominant mode in compact photonic circuitry. A detailed design analysis shows how a thin layer of a higher-refractive index material in a trench within the core of the waveguide can increase the confinement and reduce the propagation losses. This thin layer, produced by atomic layer deposition, covers the entire polymer structure in a conformal manner, ensuring both a reduction of the surface roughness and a stronger field confinement. The trench can be made at any place within the polymer channel and therefore its position can be tuned to obtain asymmetric modal distribution. The waveguide is demonstrated at telecom wavelengths, although the material’s properties enable operation over a large part of the electromagnetic spectrum. We measured propagation losses as low as 1.75 ± 0.32 dB/cm in a 200 nm

\times

900 nm section of the waveguide core. All processes being mass-production compatible, this study opens a path towards easier integrated-component manufacture. Full article

(This article belongs to the Special Issue Nanophotonics and Integrated Optics Devices)

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7 pages, 1601 KiB

Open AccessArticle

Metallic On-Chip Light Concentrators Fabricated by In Situ Plasmonic Etching Technique

by Lihua Cha and Pan Li

Nanomaterials 2022, 12(23), 4195; https://doi.org/10.3390/nano12234195 - 25 Nov 2022

Viewed by 1417

Abstract

One-dimensional tapered metallic nanostructures are highly interesting for nanophotonic applications because of their plasmonic waveguiding and field-focusing properties. Here, we developed an in situ etching technique for unique tapered crystallized silver nanowire fabrication. Under the focused laser spot, plasmon-induced charge separation of chemically [...] Read more.

One-dimensional tapered metallic nanostructures are highly interesting for nanophotonic applications because of their plasmonic waveguiding and field-focusing properties. Here, we developed an in situ etching technique for unique tapered crystallized silver nanowire fabrication. Under the focused laser spot, plasmon-induced charge separation of chemically synthesized nanowires is excited, which triggers the uniaxial etching of silver nanowires along the radial direction with decreasing rate, forming tapered structures several micrometers long and with diameter attenuating from hundreds to tens of nanometers. These tapered metallic nanowires have smooth surfaces showing excellent performance for plasmonic waveguiding, and can be good candidates for nanocircuits and remote-excitation sources. Full article

(This article belongs to the Special Issue Advance in Nanophotonics)

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12 pages, 4635 KiB

Open AccessArticle

Symmetric Graphene Dielectric Nanowaveguides as Ultra-Compact Photonic Structures

by Da Teng, Yuncheng Wang, Tianzi Xu, Huayu Wang, Qinqin Shao and Yanan Tang

Nanomaterials 2021, 11(5), 1281; https://doi.org/10.3390/nano11051281 - 13 May 2021

Cited by 18 | Viewed by 3112

Abstract

A symmetric graphene plasmon waveguide (SGPWG) is proposed here to achieve excellent subwavelength waveguiding performance of mid-infrared waves. The modal properties of the fundamental graphene plasmon mode are investigated by use of the finite element method. Due to the naturally rounded tips, the [...] Read more.

A symmetric graphene plasmon waveguide (SGPWG) is proposed here to achieve excellent subwavelength waveguiding performance of mid-infrared waves. The modal properties of the fundamental graphene plasmon mode are investigated by use of the finite element method. Due to the naturally rounded tips, the plasmon mode in SGPWG could achieve a normalized mode field area of ~10⁻⁵ (or less) and a figure of merit over 400 by tuning the key geometric structure parameters and the chemical potential of graphene. In addition, results show that the modal performance of SGPWG seems to improve over its circular counterparts. Besides the modal properties, crosstalk analysis indicates that the proposed waveguide exhibits extremely low crosstalk, even at a separation distance of 64 nm. Due to these excellent characteristics, the proposed waveguide has promising applications in ultra-compact integrated photonic components and other intriguing nanoscale devices. Full article

(This article belongs to the Special Issue Nanophotonics and Integrated Optics Devices)

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9 pages, 3012 KiB

Open AccessArticle

Manipulation Technique for Precise Transfer of Single Perovskite Nanoparticles

by Filipp Komissarenko, George Zograf, Sergey Makarov, Mikhail Petrov and Ivan Mukhin

Nanomaterials 2020, 10(7), 1306; https://doi.org/10.3390/nano10071306 - 3 Jul 2020

Cited by 11 | Viewed by 3418

Abstract

In this article, we present the pick-and-place technique for the manipulation of single nanoparticles on non-conductive substrates using a tungsten tip irradiated by a focused electron beam from a scanning electron microscope. The developed technique allowed us to perform the precise transfer of [...] Read more.

In this article, we present the pick-and-place technique for the manipulation of single nanoparticles on non-conductive substrates using a tungsten tip irradiated by a focused electron beam from a scanning electron microscope. The developed technique allowed us to perform the precise transfer of single BaTiO₃ nanoparticles from one substrate to another in order to carry out measurements of elastic light scattering as well as second harmonic generation. Also, we demonstrate a fabricated structure made by finely tuning the position of a BaTiO₃ nanoparticle on top of a dielectric nanowaveguide deposited on a glass substrate. The presented technique is based on the electrostatic interaction between the sharp tungsten tip charged by the electron beam and the nanoscale object. A mechanism for nanoparticle transfer to a non-conductive substrate is proposed and the forces involved in the manipulation process are evaluated. The presented technique can be widely utilized for the fabrication of nanoscale structures on optically transparent non-conductive substrates, which presents a wide range of applications for nanophotonics. Full article

(This article belongs to the Special Issue Perovskite Nanophotonics)

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5 pages, 688 KiB

Open AccessProceeding Paper

Nanofabrication of SOI-Based Photonic Waveguide Resonators for Gravimetric Molecule Detection

by Tony Granz, Julia Sophie Böke, Gerry Hamdana, Michael Martens, Arijit Misra, Stefan Preußler, Meinhard Schilling, Erwin Peiner, Thomas Schneider and Andreas Waag

Proceedings 2018, 2(13), 1055; https://doi.org/10.3390/proceedings2131055 - 13 Feb 2019

Viewed by 2937

Abstract

A silicon photonic microresonator comprising two curved vertical grating couplers and a single suspended Si nanowaveguide (NWG) is developed to investigate the giant enhanced Brillouin scattering in subwavelength NWGs caused by photon-phonon interaction. Finite element modelling based on COMSOL Multiphysics is conducted to [...] Read more.

A silicon photonic microresonator comprising two curved vertical grating couplers and a single suspended Si nanowaveguide (NWG) is developed to investigate the giant enhanced Brillouin scattering in subwavelength NWGs caused by photon-phonon interaction. Finite element modelling based on COMSOL Multiphysics is conducted to optimize the critical device parameters (e.g., waveguide width, height, and length). As the smallest structures that need to be resolved are down to ~15 nm in size, electron-beam nanolithography is employed. In this case, dosage tests are carried out to minimize proximity charging effects during the nanopatterning of the silicon-on-insulator (SOI) surface, resulting in appropriate adaptive current area dosage distributions for the periodic gratings, couplers peripheral areas, and NWG, respectively. Furthermore, an enhanced inductively coupled plasma dry reactive ion etching (ICP-DRIE) process at a cryogenic temperature is used to realize smooth vertical sidewalls. Finally, buffered hydrofluoric acid (BHF)-based wet chemical etching is carried out to remove the buried oxide resulting in a suspended Si waveguide. Full article

(This article belongs to the Proceedings of EUROSENSORS 2018)

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