Special Issue "Optical Thin Films and Structures: Design and Advanced Applications"

A special issue of Coatings (ISSN 2079-6412).

Deadline for manuscript submissions: closed (20 April 2020).

Special Issue Editor

Prof. Dr. Tsvetanka Babeva
Website
Guest Editor
Institute of Optical Materials and Technologies, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
Interests: thin films optics; multilayered structures; sensors with optical read-out; porous thin films and structures; zeolite nanocomposites
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Special Issue Information

Dear Colleagues,

You are cordially invited to submit your original work to this Special Issue devoted to “Optical Thin Films and Structures: Design and Advanced Applications”. Diverse types of materials such as polymers, glasses, metals, ceramics, zeolites, etc., could be prepared as thin films with high optical quality, thus finding applications in photonics, optical sensing, photocatalysis, optoelectronics, linear and non-linear optics, holography, etc. Different production strategies, including ‘dry’ and ‘wet’ deposition methods, are developed and optimized. In order for these thin films and structures to be utilized in different optical devices, unambiguous methods for their design and characterization are required. Additionally, in-situ optical monitoring of their properties will be beneficial for proper device operation.

This Special Issue will cover the recent progress and new developments in the area of the design, deposition, characterization, and application of optical thin films and structures.

In particular, the topics of interest include, but are not limited to the following:

  • Design of complex thin films and structures;
  • Deposition strategies for optical thin films and multilayered structures;
  • Antireflective thin film coatings;
  • Thin films and structures for optical sensing of humidity, VOC’s, gases, heavy metal ions, etc.;
  • Optical thin films in photocatalysis;
  • Optical thin films in solar cells;
  • Optical thin films in light emitting devices;
  • Transparent and conductive thin films and structures;
  • Optical thin films and structures for security devices.

Prof. Dr. Tsvetanka Babeva
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Coatings is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Published Papers (11 papers)

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Editorial

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Open AccessEditorial
Special Issue: “Optical Thin Films and Structures: Design and Advanced Applications”
Coatings 2020, 10(11), 1140; https://doi.org/10.3390/coatings10111140 - 23 Nov 2020
Abstract
This Special Issue is devoted on design and application of thin films and structures with special emphasis on optical applications. It comprises ten papers, five featured and five regular papers, authored by respective scientists all over the world. Diverse materials are studied and [...] Read more.
This Special Issue is devoted on design and application of thin films and structures with special emphasis on optical applications. It comprises ten papers, five featured and five regular papers, authored by respective scientists all over the world. Diverse materials are studied and their possible applications are demonstrated and discussed: transparent conductive coatings and structures from ZnO doped with Al and Ga and Ti-doped SnO2, polymer and nanosized zeolite thin films for optical sensing, TiO2 with linear and non-linear optical properties, organic diamagnetic materials, broadband optical coatings, CrWN glass molding coatings and silicon on insulator waveguides. Full article
(This article belongs to the Special Issue Optical Thin Films and Structures: Design and Advanced Applications)
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Research

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Open AccessFeature PaperEditor’s ChoiceArticle
Atomic Layer-Deposited Al-Doped ZnO Thin Films for Display Applications
Coatings 2020, 10(6), 539; https://doi.org/10.3390/coatings10060539 - 31 May 2020
Cited by 2
Abstract
The integration of high uniformity, conformal and compact transparent conductive layers into next generation indium tin oxide (ITO)-free optoelectronics, including wearable and bendable structures, is a huge challenge. In this study, we demonstrate the transparent and conductive functionality of aluminum-doped zinc oxide (AZO) [...] Read more.
The integration of high uniformity, conformal and compact transparent conductive layers into next generation indium tin oxide (ITO)-free optoelectronics, including wearable and bendable structures, is a huge challenge. In this study, we demonstrate the transparent and conductive functionality of aluminum-doped zinc oxide (AZO) thin films deposited on glass as well as on polyethylene terephthalate (PET) flexible substrates by using an atomic layer deposition (ALD) technique. AZO thin films possess high optical transmittance at visible and near-infrared spectral range and electrical properties competitive to commercial ITO layers. AZO layers deposited on flexible PET substrates demonstrate stable sheet resistance over 1000 bending cycles. Based on the performed optical and electrical characterizations, several applications of ALD AZO as transparent conductive layers are shown—AZO/glass-supported liquid crystal (LC) display and AZO/PET-based flexible polymer-dispersed liquid crystal (PDLC) devices. Full article
(This article belongs to the Special Issue Optical Thin Films and Structures: Design and Advanced Applications)
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Open AccessFeature PaperArticle
Amphiphilic Poly(vinyl Alcohol) Copolymers Designed for Optical Sensor Applications—Synthesis and Properties
Coatings 2020, 10(5), 460; https://doi.org/10.3390/coatings10050460 - 09 May 2020
Cited by 1
Abstract
A possible approach for enhancement of Poly(vinyl alcohol) (PVA) humidity-sensing performance using hydrophobically modified PVA copolymers is studied. Series of poly(vinylalcohol-co-vinylacetal)s (PVA–Ac) of acetal content in the range 18%–28% are synthesized by partial acetalization of hydroxyl groups of PVA with acetaldehyde [...] Read more.
A possible approach for enhancement of Poly(vinyl alcohol) (PVA) humidity-sensing performance using hydrophobically modified PVA copolymers is studied. Series of poly(vinylalcohol-co-vinylacetal)s (PVA–Ac) of acetal content in the range 18%–28% are synthesized by partial acetalization of hydroxyl groups of PVA with acetaldehyde and thin films are deposited by spin-coating using silicon substrates and glass substrates covered with Au–Pd thin film with thickness of 30 nm. Sensing properties are probed through reflectance measurements at relative humidity (RH) in the range 5%–95% RH. The influence of film thickness, post-deposition annealing temperature, and substrate type/configuration on hysteresis, sensitivity, and accuracy/resolution of humidity sensing is studied for partially acetalized PVA copolymer films, and comparison with neat PVA is made. Enhancement of sensing behavior through preparation of polymer–silica hybrids is demonstrated. The possibility of color sensing is discussed. Full article
(This article belongs to the Special Issue Optical Thin Films and Structures: Design and Advanced Applications)
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Open AccessFeature PaperArticle
In-Situ Ellipsometric Study of the Optical Properties of LTL-Doped Thin Film Sensors for Copper(II) Ion Detection
Coatings 2020, 10(4), 423; https://doi.org/10.3390/coatings10040423 - 24 Apr 2020
Cited by 2
Abstract
Optical sensors fabricated in zeolite nanoparticle composite films rely on changes in their optical properties (refractive index, n, and thickness, d) to produce a measurable response in the presence of a target analyte. Here, ellipsometry is used to characterize the changes [...] Read more.
Optical sensors fabricated in zeolite nanoparticle composite films rely on changes in their optical properties (refractive index, n, and thickness, d) to produce a measurable response in the presence of a target analyte. Here, ellipsometry is used to characterize the changes in optical properties of Linde Type L (LTL) zeolite thin films in the presence of Cu2+ ions in solution, with a view to improving the design of optical sensors that involve the change of n and/or d due to the adsorption of Cu2+ ions. The suitability of two different ellipsometry techniques (single wavelength and spectroscopic) for the evaluation of changes in n and d of both undoped and zeolite-doped films during exposure to water and Cu2+-containing solutions was investigated. The influence of pre-immersion thermal treatment conditions on sensor response was also studied. Due to the high temporal resolution, single wavelength ellipsometry facilitated the identification of a Cu2+ concentration response immediately after Cu2+ introduction, indicating that the single wavelength technique is suitable for dynamic studies of sensor–analyte interactions over short time scales. In comparison, spectroscopic ellipsometry produced a robust analysis of absolute changes in film n and d, as well as yielding insight into the net influence of competing and simultaneous changes in n and d inside the zeolite-doped films arising due to water adsorption and the ion exchange of potassium (K+) cations by copper (Cu2+). Full article
(This article belongs to the Special Issue Optical Thin Films and Structures: Design and Advanced Applications)
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Open AccessArticle
Optoelectronic Properties of Ti-doped SnO2 Thin Films Processed under Different Annealing Temperatures
Coatings 2020, 10(4), 394; https://doi.org/10.3390/coatings10040394 - 16 Apr 2020
Cited by 2
Abstract
Ti-doped SnO2 transparent conductive oxide (TCO) thin films are deposited on glass substrates using a radio frequency (RF) magnetron sputtering system and then are annealed at temperatures in the range of 200–500 °C for 30 min. The effects of the annealing temperature [...] Read more.
Ti-doped SnO2 transparent conductive oxide (TCO) thin films are deposited on glass substrates using a radio frequency (RF) magnetron sputtering system and then are annealed at temperatures in the range of 200–500 °C for 30 min. The effects of the annealing temperature on the structural properties, surface roughness, electrical properties, and optical transmittance of the thin films are then systematically explored. The results show that a higher annealing temperature results in lower surface roughness and larger crystal size. Moreover, an annealing temperature of 300 °C leads to the minimum electrical resistivity of 5.65 × 10−3 Ω·cm. The mean optical transmittance increases with an increase in temperature and achieves a maximum value of 74.2% at an annealing temperature of 500 °C. Overall, the highest figure of merit (ΦTC) (3.99 × 10−4 Ω−1) is obtained at an annealing temperature of 500 °C. Full article
(This article belongs to the Special Issue Optical Thin Films and Structures: Design and Advanced Applications)
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Open AccessArticle
Low-Temperature Fabrication of High-Performance and Stable GZO/Ag/GZO Multilayer Structures for Transparent Electrode Applications
Coatings 2020, 10(3), 269; https://doi.org/10.3390/coatings10030269 - 13 Mar 2020
Cited by 4
Abstract
Presently, research and development of indium-free stable highly transparent conductive (TC) materials is of paramount importance for the blooming world of information display systems and solar energy conversion. Development of devices based on flexible organic substrates further narrows the choice of possible TC [...] Read more.
Presently, research and development of indium-free stable highly transparent conductive (TC) materials is of paramount importance for the blooming world of information display systems and solar energy conversion. Development of devices based on flexible organic substrates further narrows the choice of possible TC materials due to the need for lower deposition and process temperatures. In our work, the structural, electrical, and optical performances of Ga-doped ZnO/Ag/Ga-doped ZnO (GZO/Ag/GZO) multilayered structures deposited on glass substrates by direct current (DC) magnetron sputtering in a pure Ar medium without any purposeful substrate heating have been investigated. The highest figure of merit achieved was 5.15 × 10−2 Ω−1 for the symmetric GZO/Ag/GZO multilayer, featuring GZO and Ag thicknesses of 40 and 10 nm, respectively, while the average optical transmittance was over 81% in the visible range of wavelengths and the resistivity was 2.2 × 10−5 Ω·cm. Additionally, the good durability of the performances of the multilayer structures was demonstrated by their testing in the context of long-term storage (over 500 days) in standard environmental conditions. Full article
(This article belongs to the Special Issue Optical Thin Films and Structures: Design and Advanced Applications)
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Open AccessArticle
Investigation for Sidewall Roughness Caused Optical Scattering Loss of Silicon-on-Insulator Waveguides with Confocal Laser Scanning Microscopy
Coatings 2020, 10(3), 236; https://doi.org/10.3390/coatings10030236 - 04 Mar 2020
Cited by 4
Abstract
Sidewall roughness-caused optical loss of waveguides is one of the critical limitations to the proliferation of the silicon photonic integrated circuits in fiber-optic communications and optical interconnects in computers, so it is imperative to investigate the distribution characteristics of sidewall roughness and its [...] Read more.
Sidewall roughness-caused optical loss of waveguides is one of the critical limitations to the proliferation of the silicon photonic integrated circuits in fiber-optic communications and optical interconnects in computers, so it is imperative to investigate the distribution characteristics of sidewall roughness and its impact upon the optical losses. In this article, we investigated the distribution properties of waveguide sidewall roughness (SWR) with the analysis for the three-dimensional (3-D) SWR of dielectric waveguides, and, then the accurate SWR measurements for silicon-on-insulator (SOI) waveguide were carried out with confocal laser scanning microscopy (CLSM). Further, we composed a theoretical/experimental combinative model of the SWR-caused optical propagation loss. Consequently, with the systematic simulations for the characteristics of optical propagation loss of SOI waveguides, the two critical points were found: (i) the sidewall roughness-caused optical loss was synchronously dependent on the correlation length and the waveguide width in addition to the SWR and (ii) the theoretical upper limit of the correlation length was the bottleneck to compressing the roughness-induced optical loss. The simulation results for the optical loss characteristics, including the differences between the TE and TM modes, were in accord with the experimental data published in the literature. The above research outcomes are very sustainable to the selection of coatings before/after the SOI waveguide fabrication. Full article
(This article belongs to the Special Issue Optical Thin Films and Structures: Design and Advanced Applications)
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Open AccessArticle
Thermal Stability of CrWN Glass Molding Coatings after Vacuum Annealing
Coatings 2020, 10(3), 198; https://doi.org/10.3390/coatings10030198 - 25 Feb 2020
Cited by 1
Abstract
CrWN glass molding coatings were deposited by plasma enhanced magnetron sputtering (PEMS). The microstructure and thermal stability of these coatings were investigated by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscope, transmission electron microscope, atomic force microscope and nanoindentation tests. The as-deposited coating [...] Read more.
CrWN glass molding coatings were deposited by plasma enhanced magnetron sputtering (PEMS). The microstructure and thermal stability of these coatings were investigated by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscope, transmission electron microscope, atomic force microscope and nanoindentation tests. The as-deposited coating exhibited an aggravated lattice expansion resulting in a constant hardness enhancement. The vacuum annealing induced surface coarsening and the spinodal decomposition of the coating accompanied by the formation of nm-sized c-CrN, c-W2N, and h-WN domains. The annealed coating with low W content had mainly a face-centered cubic (f.c.c) matrix, strain fields caused by lattice mismatch caused hardness enhancement. Following an increase in W content, the annealed coating showed a mixed face-centered cubic (f.c.c) and hexagonal close-packed (h.c.p) matrix. The large volume fraction of h-WN phases seriously weakened the coating strengthening effect and caused an obvious drop in hardness. Full article
(This article belongs to the Special Issue Optical Thin Films and Structures: Design and Advanced Applications)
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Open AccessArticle
Linear and Nonlinear Absorption of Titanium Dioxide Films Produced by Plasma Ion-Assisted Electron Beam Evaporation: Modeling and Experiments
Coatings 2020, 10(1), 59; https://doi.org/10.3390/coatings10010059 - 09 Jan 2020
Cited by 1
Abstract
Titanium dioxide films were prepared by plasma ion-assisted electron beam evaporation. Linear optical properties were investigated in terms of spectrophotometry using the beta-distributed oscillator (ß_do) model as a parametrized dispersion law. The nonlinear two-photon absorption coefficient of titanium dioxide was determined by means [...] Read more.
Titanium dioxide films were prepared by plasma ion-assisted electron beam evaporation. Linear optical properties were investigated in terms of spectrophotometry using the beta-distributed oscillator (ß_do) model as a parametrized dispersion law. The nonlinear two-photon absorption coefficient of titanium dioxide was determined by means of the laser-induced deflection technique at a wavelength of 800 nm. The obtained values of (2–5) × 10−11 cm/W were consistent with published experimental values for rutile as well as for simulations performed in the frames of the ß_do and Sheik–Bahae models. Full article
(This article belongs to the Special Issue Optical Thin Films and Structures: Design and Advanced Applications)
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Open AccessFeature PaperArticle
Strategies of Broadband Monitoring Aimed at Minimizing Deposition Errors
Coatings 2019, 9(12), 809; https://doi.org/10.3390/coatings9120809 - 01 Dec 2019
Cited by 1
Abstract
This article presents a computational approach for comparing various broadband monitoring strategies, taking into account the positive and negative effects associated with the correlation of thickness errors caused by the monitoring procedure. The approach is based on statistical estimates of the strength of [...] Read more.
This article presents a computational approach for comparing various broadband monitoring strategies, taking into account the positive and negative effects associated with the correlation of thickness errors caused by the monitoring procedure. The approach is based on statistical estimates of the strength of the error self-compensation effect and the expected level of thickness errors. Its application is demonstrated by using a 50-layer, nonpolarizing edge filter. The presented approach is general and can be applied to verify the prospects of broadband monitoring for the production of various types of optical coatings. Full article
(This article belongs to the Special Issue Optical Thin Films and Structures: Design and Advanced Applications)
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Open AccessEditor’s ChoiceArticle
Thin Films of Tolane Aggregates for Faraday Rotation: Materials and Measurement
Coatings 2019, 9(10), 669; https://doi.org/10.3390/coatings9100669 - 16 Oct 2019
Cited by 2
Abstract
We present organic, diamagnetic materials based on structurally simple (hetero-)tolane derivatives. They form crystalline thin-film aggregates that are suitable for Faraday rotation (FR) spectroscopy. The resulting new materials are characterized appropriately by common spectroscopic (NMR, UV-Vis), microscopy (POM), and XRD techniques. The spectroscopic [...] Read more.
We present organic, diamagnetic materials based on structurally simple (hetero-)tolane derivatives. They form crystalline thin-film aggregates that are suitable for Faraday rotation (FR) spectroscopy. The resulting new materials are characterized appropriately by common spectroscopic (NMR, UV-Vis), microscopy (POM), and XRD techniques. The spectroscopic studies give extremely high FR activities, thus making these materials promising candidates for future practical applications. Other than a proper explanation, we insist on the complexity of designing efficient FR materials starting from single molecules. Full article
(This article belongs to the Special Issue Optical Thin Films and Structures: Design and Advanced Applications)
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