Special Issue "Optical Characterization of Novel Composite and Optically Active Materials"

A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Structure Analysis and Characterization".

Deadline for manuscript submissions: closed (31 December 2020).

Special Issue Editor

Prof. Dr. Tatiana Perova
E-Mail Website1 Website2
Guest Editor
Department of Electronic and Electrical Engineering, Trinity College Dublin, College Green, 2 Dublin, Ireland
Interests: infrared and Raman spectroscopy of condensed matter; semiconductor quantum dots; silicon photonic crystals; 2D materials; metal nanoparticles
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Special Issue Information

Dear Colleagues,

There has been increasing interest over the last decade in novel optical composite materials. These materials, which demonstrate unique properties, are based on semiconductor nanocrystals of different shapes, viz. quantum dots, wires, and platelets, or simple metal nanoparticles. These materials are used in a variety of photonic and plasmonic applications. Applications include advanced light sources, photovoltaics, biosensing, bioimaging, and photonic circuitry with novel architectures. The synthesis and fabrication of these innovative composite materials requires a knowledge and understanding of the relationship between the chemical structure and interactions in these systems, as well as their optical characteristics when targeting specific applications.

This Special Issue will be devoted to the optical characterization of new composite and optically active materials, including UV-VIS, CD, infrared, and Raman spectroscopies. Original research papers and review articles related to these areas are cordially invited.

Prof. Tatiana S. Perova
Guest Editor

Manuscript Submission Information

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Keywords

  • infrared and Raman spectroscopy of condensed matter
  • semiconductor quantum dots
  • silicon photonic crystals
  • 2D materials
  • metal nanoparticles

Published Papers (12 papers)

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Editorial

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Editorial
Special Issue: Optical Characterizations of Novel Composite and Optically Active Materials
Materials 2020, 13(22), 5263; https://doi.org/10.3390/ma13225263 - 21 Nov 2020
Viewed by 355
Abstract
Market pressures have placed new demands on modern photonic and opto-electronic materials, including requirements for miniaturization, higher efficiency, tunable and controllable optical and electrical properties, and consistent performance [...] Full article

Research

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Article
Optical Characterization of AsxTe100−x Films Grown by Plasma Deposition Based on the Advanced Optimizing Envelope Method
Materials 2020, 13(13), 2981; https://doi.org/10.3390/ma13132981 - 03 Jul 2020
Cited by 2 | Viewed by 593
Abstract
Three AsxTe100x films with different x and dissimilar average thickness d¯ are characterized mainly from one interference transmittance spectrum T(λ = 300 to 3000 nm) of such film on a substrate based on the advanced [...] Read more.
Three AsxTe100x films with different x and dissimilar average thickness d ¯ are characterized mainly from one interference transmittance spectrum T(λ = 300 to 3000 nm) of such film on a substrate based on the advanced optimizing envelope method (AOEM). A simple dual transformation of T(λ) is proposed and used for increasing the accuracy of computation of its envelopes T+(λ) and T(λ) accounting for the significant glass substrate absorption especially for λ > 2500 nm. The refractive index n(λ) of As40Te60 and As98Te2 films is determined with a relative error <0.30%. As far as we know, the As80Te20 film is the only one with anomalous dispersion and the thickest, with estimated d ¯ = 1.1446 nm, ever characterized by an envelope method. It is also shown and explained why the extinction coefficient k(λ) of any of the three AsxTe100x films is computed more accurately from the quantity Ti(λ) = [T+(λ)T(λ)]0.5 compared to its commonly employed computation from T+(λ). The obtained results strengthen our conviction that the AOEM has a capacity for providing most accurate optical characterization of almost every dielectric or semiconductor film with d ¯ > 300 nm on a substrate, compared to all the other methods for characterization of such films only from T(λ). Full article
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Article
Enhanced Photoluminescence of Hydrogenated Amorphous Silicon Carbide Thin Films by Means of a Fast Thermal Annealing Process
Materials 2020, 13(11), 2643; https://doi.org/10.3390/ma13112643 - 10 Jun 2020
Cited by 2 | Viewed by 859
Abstract
In this paper, the photoluminescence (PL) of hydrogenated amorphous silicon carbide (a-Si1−xCx:H) thin films obtained by Plasma Enhancement Chemical Vapor Deposition (PECVD) is reported. Strong PL is obtained after a fast annealing process for 60 s at temperatures of [...] Read more.
In this paper, the photoluminescence (PL) of hydrogenated amorphous silicon carbide (a-Si1−xCx:H) thin films obtained by Plasma Enhancement Chemical Vapor Deposition (PECVD) is reported. Strong PL is obtained after a fast annealing process for 60 s at temperatures of 200, 400, 600, and 800 °C. The thin films are characterized using Fourier Transform Infrared spectroscopy (FTIR), PL spectroscopy, and Energy-Dispersive X-ray Spectroscopy (EDS). According to the results of the structural characterization, it is deduced that a structural rearrangement of the amorphous matrix is carried out during the fast annealing process, which results in different degrees of oxidation on the a-Si1−xCx:H films. The PL peak position shifts towards higher energies as the temperature increases. The sample deposited with a silane/methane flux ratio of 37.5 at an Radio Frequency (RF) power of 6 W experiences an increase in PL intensity of more than nine times, with a displacement in the peak position from 2.5 eV to 2.87 eV, at 800 °C. From the PL analysis, we observe two emission bands: one centered in the near infrared and other in the visible range (with a blue peak). This study opens the possibility to use such thin films in the development of optoelectronics devices, with potential for application in solar cells. Full article
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Article
Accounting for the Local Field When Determining the Dielectric Loss Spectra of Metals in the Region of the Frequencies of Volume, Surface and Localized Plasmon Oscillations
Materials 2020, 13(3), 631; https://doi.org/10.3390/ma13030631 - 31 Jan 2020
Cited by 1 | Viewed by 670
Abstract
The optical constant of bulk metal is used to determine the dispersion of the local field under one-dimensional (1D), two-dimensional (2D) and three-dimensional (3D) confinement. 3D confinement, expressed as ε2mic(ω3D), corresponds to the [...] Read more.
The optical constant of bulk metal is used to determine the dispersion of the local field under one-dimensional (1D), two-dimensional (2D) and three-dimensional (3D) confinement. 3D confinement, expressed as ε 2 m i c ( ω 3 D ) , corresponds to the dielectric loss spectra of spherical particles with a diameter, d, much less than the wavelength of the beam used to measure the spectrum (d << λ). Excellent agreement with the results of Mie theory and experimental data for solid colloids within alkali halide crystals was observed. The function expressed as ε 2 m i c ( ω 1 D ) allows the measurement of spectral micro-characteristics in the frequency range of the longitudinal collective motion of the free electrons. This corresponds to the spectrum of dielectric losses of bulk plasma oscillations. The function ε 2 m i c ( ω 2 D ) describes the spectra of the dielectric losses of surface plasma oscillations in thin metal films. It is shown that the peak positions of ε 2 m i c ( ω 3 D ) , ε 2 m i c ( ω 2 D ) and ε 2 m i c ( ω 1 D ) spectra for simple metals, viz. alkali metals as well as Al, Be, Mg, Ga, In, Sn and Si, are in agreement with experimental results from electron-energy-loss spectroscopy and various optical techniques. Full article
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Article
Functionalized rGO Interlayers Improve the Fill Factor and Current Density in PbS QDs-Based Solar Cells
Materials 2019, 12(24), 4221; https://doi.org/10.3390/ma12244221 - 16 Dec 2019
Cited by 4 | Viewed by 896
Abstract
Graphene-quantum dot nanocomposites attract significant attention for novel optoelectronic devices, such as ultrafast photodetectors and third-generation solar cells. Combining the remarkable optical properties of quantum dots (QDs) with the exceptional electrical properties of graphene derivatives opens a vast perspective for further growth in [...] Read more.
Graphene-quantum dot nanocomposites attract significant attention for novel optoelectronic devices, such as ultrafast photodetectors and third-generation solar cells. Combining the remarkable optical properties of quantum dots (QDs) with the exceptional electrical properties of graphene derivatives opens a vast perspective for further growth in solar cell efficiency. Here, we applied (3-mercaptopropyl) trimethoxysilane functionalized reduced graphene oxide (f-rGO) to improve the QDs-based solar cell active layer. The different strategies of f-rGO embedding are explored. When f-rGO interlayers are inserted between PbS QD layers, the solar cells demonstrate a higher current density and a better fill factor. A combined study of the morphological and electrical parameters of the solar cells shows that the improved efficiency is associated with better layer homogeneity, lower trap-state densities, higher charge carrier concentrations, and the blocking of the minor charge carriers. Full article
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Article
Electrophoretic Deposition of Quantum Dots and Characterisation of Composites
Materials 2019, 12(24), 4089; https://doi.org/10.3390/ma12244089 - 07 Dec 2019
Cited by 7 | Viewed by 1048
Abstract
Electrophoretic deposition (EPD) is an emerging technique in nanomaterial-based device fabrication. Here, we report an in-depth study of this approach as a means to deposit colloidal quantum dots (CQDs), in a range of solvents. For the first time, we report the significant improvement [...] Read more.
Electrophoretic deposition (EPD) is an emerging technique in nanomaterial-based device fabrication. Here, we report an in-depth study of this approach as a means to deposit colloidal quantum dots (CQDs), in a range of solvents. For the first time, we report the significant improvement of EPD performance via the use of dichloromethane (DCM) for deposition of CQDs, producing a corresponding CQD-TiO2 composite with a near 10-fold increase in quantum dot loading relative to more commonly used solvents such as chloroform or toluene. We propose this effect is due to the higher dielectric constant of the solvent relative to more commonly used and therefore the stronger effect of EPD in this medium, though there remains the possibility that changes in zeta potential may also play an important role. In addition, this solvent choice enables the true universality of QD EPD to be demonstrated, via the sensitization of porous TiO2 electrodes with a range of ligand capped CdSe QDs and a range of group II-VI CQDs including CdS, CdSe/CdS, CdS/CdSe and CdTe/CdSe, and group IV-VI PbS QDs. Full article
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Article
Investigation of AgInS2/ZnS Quantum Dots by Magnetic Circular Dichroism Spectroscopy
Materials 2019, 12(21), 3616; https://doi.org/10.3390/ma12213616 - 04 Nov 2019
Cited by 6 | Viewed by 1310
Abstract
Over recent years, quantum dots (QDs) based on ternary metal dichalcogenides have attracted a lot of attention due to their unique properties and a range of potential applications. Here, we review the latest studies on the optical properties of AgInS2/ZnS QDs [...] Read more.
Over recent years, quantum dots (QDs) based on ternary metal dichalcogenides have attracted a lot of attention due to their unique properties and a range of potential applications. Here, we review the latest studies on the optical properties of AgInS2/ZnS QDs with emphasis on their theoretical modeling, and present our investigations of electronic transitions invisible in unstructured absorption spectra of AgInS2/ZnS QDs. The analysis of the absorption, photoluminescence excitation (PLE), and magnetic circular dichroism (MCD) spectra of hydrophobic and hydrophilic AgInS2/ZnS QDs of different sizes enables us to determine positions of electron transitions in these QDs. We demonstrate that the use of the second derivative of PLE spectra provides more unequivocal data on the position of the energy transitions compared with the second derivative of absorption spectra. Analysis of the MCD spectra reveals that the magnetic field induces energy level mixing in AgInS2/ZnS QDs in contrast to the traditional Cd-based QDs, where MCD is associated only with removing degeneracy of the excited energy level. Full article
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Article
Optical Properties, Morphology, and Stability of Iodide-Passivated Lead Sulfide Quantum Dots
Materials 2019, 12(19), 3219; https://doi.org/10.3390/ma12193219 - 01 Oct 2019
Cited by 5 | Viewed by 1140
Abstract
Iodide atomic surface passivation of lead chalcogenides has spawned a race in efficiency of quantum dot (QD)-based optoelectronic devices. Further development of QD applications requires a deeper understanding of the passivation mechanisms. In the first part of the current study, we compare optics [...] Read more.
Iodide atomic surface passivation of lead chalcogenides has spawned a race in efficiency of quantum dot (QD)-based optoelectronic devices. Further development of QD applications requires a deeper understanding of the passivation mechanisms. In the first part of the current study, we compare optics and electrophysical properties of lead sulfide (PbS) QDs with iodine ligands, obtained from different iodine sources. Methylammonium iodide (MAI), lead iodide (PbI2), and tetrabutylammonium iodide (TBAI) were used as iodine precursors. Using ultraviolet photoelectron spectroscopy, we show that different iodide sources change the QD HOMO/LUMO levels, allowing their fine tuning. AFM measurements suggest that colloidally-passivated QDs result in formation of more uniform thin films in one-step deposition. The second part of this paper is devoted to the PbS QDs with colloidally-exchanged shells (i.e., made from MAI and PbI2). We especially focus on QD optical properties and their stability during storage in ambient conditions. Colloidal lead iodide treatment is found to reduce the QD film resistivity and improve photoluminescence quantum yield (PLQY). At the same time stability of such QDs is reduced. MAI-treated QDs are found to be more stable in the ambient conditions but tend to agglomerate, which leads to undesirable changes in their optics. Full article
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Article
Periodic Metallo-Dielectric Structures: Electromagnetic Absorption and its Related Developed Temperatures
Materials 2019, 12(13), 2108; https://doi.org/10.3390/ma12132108 - 30 Jun 2019
Cited by 3 | Viewed by 1160
Abstract
Multi-layer, metallo-dielectric structures (screens) have long been employed as electromagnetic band filters, either in transmission or in reflection modes. Here we study the radiation energy not transmitted or reflected by these structures (trapped radiation, which is denoted—absorption). The trapped radiation leads to hot [...] Read more.
Multi-layer, metallo-dielectric structures (screens) have long been employed as electromagnetic band filters, either in transmission or in reflection modes. Here we study the radiation energy not transmitted or reflected by these structures (trapped radiation, which is denoted—absorption). The trapped radiation leads to hot surfaces. In these bi-layer screens, the top (front) screen is made of metallic hole-array and the bottom (back) screen is made of metallic disk-array. The gap between them is filled with an array of dielectric spheres. The spheres are embedded in a dielectric host material, which is made of either a heat-insulating (air, polyimide) or heat-conducting (MgO) layer. Electromagnetic intensity trapping of 97% is obtained when a 0.15 micron gap is filled with MgO and Si spheres, which are treated as pure dielectrics (namely, with no added absorption loss). Envisioned applications are anti-fogging surfaces, electromagnetic shields, and energy harvesting structures. Full article
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Article
DFT Analysis of NO Adsorption on the Undoped and Ce-Doped LaCoO3 (011) Surface
Materials 2019, 12(9), 1379; https://doi.org/10.3390/ma12091379 - 28 Apr 2019
Cited by 8 | Viewed by 1431
Abstract
Using the density functional theory (DFT) method, we investigated the adsorption of NO on the undoped and Ce-doped LaCoO3 (011) surface. According to our calculations, the best adsorption site is not changed after Ce doping. When the NO molecule is adsorbed on [...] Read more.
Using the density functional theory (DFT) method, we investigated the adsorption of NO on the undoped and Ce-doped LaCoO3 (011) surface. According to our calculations, the best adsorption site is not changed after Ce doping. When the NO molecule is adsorbed on the perfect LaO-terminated LaCoO3 (011) surface, the most stable adsorption site is hollow-top, which corresponds to the hollow-NO configuration in our study. After the substitution of La with Ce, the adsorption energy of hollow-NO configuration is increased. For the perfect CoO2-terminated LaCoO3 (011) surface, it is found that Co-NO configuration is the preferential adsorption structure. Its adsorption energy can also be enhanced after Ce doping. When NO molecule is adsorbed on the undoped and Ce-doped LaO-terminated LaCoO3 (011) surface with hollow-NO configuration, it serves as the acceptor and electrons transfer from the surface to it in the adsorption process. On the contrary, for the Co-NO configuration of undoped and Ce-doped CoO2-terminated LaCoO3 (011) surface, NO molecule becomes the donor and loses electrons to the surface. Full article
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Article
TiO2 Self-Assembled, Thin-Walled Nanotube Arrays for Photonic Applications
Materials 2019, 12(8), 1332; https://doi.org/10.3390/ma12081332 - 24 Apr 2019
Cited by 4 | Viewed by 1199
Abstract
Two-dimensional arrays of hollow nanotubes made of TiO2 are a promising platform for sensing, spectroscopy and light harvesting applications. Their straightforward fabrication via electrochemical anodization, growing nanotube pillars of finite length from a Ti foil, allows precise tailoring of geometry and, thus, [...] Read more.
Two-dimensional arrays of hollow nanotubes made of TiO 2 are a promising platform for sensing, spectroscopy and light harvesting applications. Their straightforward fabrication via electrochemical anodization, growing nanotube pillars of finite length from a Ti foil, allows precise tailoring of geometry and, thus, material properties. We theoretically investigate these photonic crystal structures with respect to reduction of front surface reflection, achievable field enhancement, and photonic bands. Employing the Rigorous Coupled Wave Analysis (RCWA), we study the optical response of photonic crystals made of thin-walled nanotubes relative to their bare Ti foil substrate, including under additional charge carrier doping which might occur during the growth process. Full article
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Review

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Review
Lead-Free Perovskites for Lighting and Lasing Applications: A Minireview
Materials 2019, 12(23), 3845; https://doi.org/10.3390/ma12233845 - 22 Nov 2019
Cited by 15 | Viewed by 2058
Abstract
Research on materials with perovskite crystal symmetry for photonics applications represent a rapidly growing area of the photonics development due to their unique optical and electrical properties. Among them are high charge carrier mobility, high photoluminescence quantum yield, and high extinction coefficients, which [...] Read more.
Research on materials with perovskite crystal symmetry for photonics applications represent a rapidly growing area of the photonics development due to their unique optical and electrical properties. Among them are high charge carrier mobility, high photoluminescence quantum yield, and high extinction coefficients, which can be tuned through all visible range by a controllable change in chemical composition. To date, most of such materials contain lead atoms, which is one of the obstacles for their large-scale implementation. This disadvantage can be overcome via the substitution of lead with less toxic chemical elements, such as Sn, Bi, Yb, etc., and their mixtures. Herein, we summarized the scientific works from 2016 related to the lead-free perovskite materials with stress on the lasing and lighting applications. The synthetic approaches, chemical composition, and morphology of materials, together with the optimal device configurations depending on the material parameters are summarized with a focus on future challenges. Full article
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