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12 pages, 2721 KiB

Open AccessArticle

Synthesis and Characterization of TiO₂ Thin Films Modified with Anderson-Type Polyoxometalates (Ni, Co, and Fe)

by William Vallejo, Gabriel Corzo, Ricardo Berrio, Carlos Diaz-Uribe, Freider Duran, Ximena Zarate and Eduardo Schott

Coatings 2024, 14(11), 1362; https://doi.org/10.3390/coatings14111362 - 26 Oct 2024

Viewed by 615

Abstract

In this work, TiO₂ and Anderson-type polyoxometalates (Ni, Co, and Fe) thin-film composites were fabricated. The composites were characterized by FTIR and Raman spectroscopy, diffuse reflectance, and scanning electronic microscopy. The methylene blue (MB) photocatalytic degradation on the composites under UV irradiation [...] Read more.

In this work, TiO₂ and Anderson-type polyoxometalates (Ni, Co, and Fe) thin-film composites were fabricated. The composites were characterized by FTIR and Raman spectroscopy, diffuse reflectance, and scanning electronic microscopy. The methylene blue (MB) photocatalytic degradation on the composites under UV irradiation was studied. Spectroscopic results verified the modification of TiO₂ thin films. Optical and morphological properties changed after TiO₂ modification. The largest change in the optical band gap was observed for the FePOM/TiO₂ system, which reported a value of 3.05 eV. The POM/TiO₂ systems were more efficient in methylene blue (MB) adsorption than bare TiO₂. Furthermore, the modified films were more efficient than bare TiO₂ during MB photodegradation tests. The NiPOM/TiO₂ and the CoPOM/TiO₂ were the most efficient in the MB adsorption, reaching ~20%. The NiPOM/TiO₂ and the CoPOM/TiO₂ composites were the most efficient in the photodegradation process, reaching ~50% of MB removal. The stability tests indicated that composite films were moderately stable after the three performed reusability cycles. Thus, these results suggest that POM modification of TiO₂ can improve the adsorption and photodegradation capacity of semiconductors. Full article

(This article belongs to the Special Issue Optical Thin Films: Preparation, Application and Development)

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11 pages, 6595 KiB

Open AccessArticle

Study on the Degradation Performance of AlGaN-Based Deep Ultraviolet LEDs under Thermal and Electrical Stress

by Mingfeng Gong, Xuejiao Sun, Cheng Lei, Ting Liang, Fengchao Li, Yu Xie, Jinmin Li and Naixin Liu

Coatings 2024, 14(7), 904; https://doi.org/10.3390/coatings14070904 - 19 Jul 2024

Cited by 1 | Viewed by 899

Abstract

AlGaN-based deep-ultraviolet (DUV) LEDs could realize higher optical power output when adopting a p-AlGaN contact layer instead of a p-GaN contact layer. However, this new type DUV LEDs exhibit poor reliability. Thus, this study thoroughly investigates the degradation behaviors of AlGaN-based DUV LEDs [...] Read more.

AlGaN-based deep-ultraviolet (DUV) LEDs could realize higher optical power output when adopting a p-AlGaN contact layer instead of a p-GaN contact layer. However, this new type DUV LEDs exhibit poor reliability. Thus, this study thoroughly investigates the degradation behaviors of AlGaN-based DUV LEDs with a p-AlGaN contact layer through different aging tests, including single thermal stress, single electrical stress with air-cooling, single electrical stress, and thermoelectric complex stress. It can be found that both high temperature and large working current play crucial roles in accelerating the degradation of optoelectronic properties of the DUV LEDs, and the single high thermal stress without electrical stress can also bring obvious performance degradation to the DUV LEDs, which is a significantly different finding from previous studies. This is because thermal stress on DUV LED could bring some metal electrode elements entering the p-AlGaN layer. Thus, the degradation of optical and electrical properties under the thermal and electrical stress could be not only attributed to the degradation of the device’s ohmic contacts, but also due to the metal electrode elements entering the p-AlGaN layer through thermal diffusion, leading to the generation of tunneling current and the generation of defects within or around the active region. Despite that the peak wavelengths of the DUV LEDs remained stable, the turn-on voltage and series resistance increased. Particularly worth mentioning is that the value of the optical power degradation under thermoelectric conditions is larger than the sum of the single thermal and single electrical optical power degradation, which is a result of the mutual reinforcement of thermal and electrical stresses to exacerbate the defect generation and ohmic contact degradation. Based on the study above, preparing p-AlGaN layers with hyperfine gradient aluminum fractions and reducing the junction temperature may help to improve the reliability of AlGaN-based DUV LEDs with the p-AlGaN contact layer. Full article

(This article belongs to the Special Issue Optical Thin Films: Preparation, Application and Development)

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9 pages, 2143 KiB

Open AccessArticle

Fabrication of a Porous Low Refractive Index Anti-Reflective Coating with High Transmittance by Using the Porogen of Laureth-5 Carboxylic Acid

by Tao Li, Xinyu Tan, Weifeng Chen, Fatao Zhang, Xu Li, Shuangquan Liu, Wanjiang Jin, Ting Xiao and Lihua Jiang

Coatings 2024, 14(4), 440; https://doi.org/10.3390/coatings14040440 - 8 Apr 2024

Cited by 1 | Viewed by 1243

Abstract

A porous anti-reflective coating (P-ARC) with average transmittance in the visible range of 97.9% was fabricated through the sol-gel method, followed by calcination at a relatively low temperature (220 °C) using the porogen of Laureth-5 carboxylic acid via a one-step approach. The results [...] Read more.

A porous anti-reflective coating (P-ARC) with average transmittance in the visible range of 97.9% was fabricated through the sol-gel method, followed by calcination at a relatively low temperature (220 °C) using the porogen of Laureth-5 carboxylic acid via a one-step approach. The results demonstrated the coating had an absolute value that was 7.5% higher than that of bare glass (92%). The prepared porous anti-reflective coating had a refractive index as low as 1.21. The coating remained undamaged during 3M tape stripping tests while maintaining excellent light transmittance. This work presents a film that has good thermal stability, chemical stability, and mechanical stability. Full article

(This article belongs to the Special Issue Optical Thin Films: Preparation, Application and Development)

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15 pages, 18951 KiB

Open AccessArticle

Comparison of the Optical Properties of Different Dielectric Materials (SnO₂, ZnO, AZO, or SiAlN_x) Used in Silver-Based Low-Emissivity Coatings

by Ana Cueva and Enrique Carretero

Coatings 2023, 13(10), 1709; https://doi.org/10.3390/coatings13101709 - 28 Sep 2023

Cited by 1 | Viewed by 1576

Abstract

This work analyzed and compared the optical and photoenergetic properties of low-emissivity coatings made from various dielectric materials deposited through magnetron sputtering following a systematic, comparable method. Different multilayer structures of silver-based low-emissivity coatings were studied using SnO₂, ZnO, SiAlN_x [...] Read more.

This work analyzed and compared the optical and photoenergetic properties of low-emissivity coatings made from various dielectric materials deposited through magnetron sputtering following a systematic, comparable method. Different multilayer structures of silver-based low-emissivity coatings were studied using SnO₂, ZnO, SiAlN_x, and aluminum-doped zinc oxide (AZO, which is inherently a semiconductor, but it fulfils an optical dielectric function in this type of structure). The properties of the coatings were determined by spectrophotometric and sheet resistance measurements. Coatings with AZO as the dielectric layers obtain the best photoenergetic performance because silver growth is more efficient on AZO. We also studied the effect of ion bombardment on AZO and SiAlN_x in an attempt to obtain a better low-emissivity coating, achieving better results when etching the dielectric layer with an ion gun. Regarding the structures’ visible transmission, the oxides produced better transmission results. Based on the above, we concluded that AZO had the best optical and photoenergetic properties in our deposition system, observing, in the best-case scenario, improvements in emissivity from 0.083 with SnO₂ to 0.058 with AZO and to 0.052 using an ion beam on AZO and improvements in visible transmission from 81.9% with SnO₂ to 86.8% with AZO. Full article

(This article belongs to the Special Issue Optical Thin Films: Preparation, Application and Development)

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21 pages, 1048 KiB

Open AccessFeature PaperArticle

Optical Characterization of Gadolinium Fluoride Films Using Universal Dispersion Model

by Daniel Franta, Jiří Vohánka, Jan Dvořák, Pavel Franta, Ivan Ohlídal, Petr Klapetek, Jaromír Březina and David Škoda

Coatings 2023, 13(2), 218; https://doi.org/10.3390/coatings13020218 - 17 Jan 2023

Cited by 3 | Viewed by 1593

Abstract

The optical characterization of gadolinium fluoride (GdF₃) films is performed in a wide spectral range using heterogeneous data-processing methods (the ellipsometric and spectrophotometric measurements for five samples with thicknesses ranging from 20 to 600 nm are processed simultaneously). The main result [...] Read more.

The optical characterization of gadolinium fluoride (GdF₃) films is performed in a wide spectral range using heterogeneous data-processing methods (the ellipsometric and spectrophotometric measurements for five samples with thicknesses ranging from 20 to 600 nm are processed simultaneously). The main result of the characterization is the optical constants of GdF₃ in the range from far infrared to vacuum ultraviolet, both in the form of a table and in the form of dispersion parameters of the universal dispersion model (UDM). Such reliable data in such a broad spectral range have not been published so far. The GdF₃ films exhibit several defects related to the porous polycrystalline structure, namely, surface roughness and a refractive index profile, which complicate the optical characterization. The main complication arises from the volatile adsorbed components, which can partially fill the pores. The presented optical method is based on the application of the UDM for the description of the optical response of GdF₃ films with partially filled pores. Using this dispersion model, it is possible to effectively separate the optical response of the host material from the response of the adsorbed components. Several recently published structural and dispersion models are used for optical characterization for the first time. For example, a model of inhomogeneous rough films based on Rayleigh–Rice theory or asymmetric peak approximation with a Voigt profile for the phonon spectra of polycrystalline materials. Full article

(This article belongs to the Special Issue Optical Thin Films: Preparation, Application and Development)

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10 pages, 3247 KiB

Open AccessArticle

Improvement of Electrical Properties of Silver Nanowires Transparent Conductive by Metal Oxide Nanoparticles Modification

by Wei Liu, Yuehui Hu, Yichuan Chen, Zhiqiang Hu, Ke Zhou, Zhijian Min, Huiwen Liu, Lilin Zhan and Yinjie Dai

Coatings 2022, 12(12), 1816; https://doi.org/10.3390/coatings12121816 - 24 Nov 2022

Cited by 5 | Viewed by 1747

Abstract

At present, silver nanowire transparent conductive films (AgNWs-TCFs) still have problems such as high resistance of AgNWs network nodes, uneven distribution of resistance and poor electrical performance stability, which restrict their commercial application. Different from chemical modification, in this paper, a method of [...] Read more.

At present, silver nanowire transparent conductive films (AgNWs-TCFs) still have problems such as high resistance of AgNWs network nodes, uneven distribution of resistance and poor electrical performance stability, which restrict their commercial application. Different from chemical modification, in this paper, a method of modifying AgNWs-TCFs with metal oxide nanoparticles (MONPs) is proposed, that is, ZnO, SnO₂, Al₂O₃ and TiO₂ etc., four transparent metal oxides are used as targets respectively in a magnetron sputtering process, modifying the silver nanowire network wire–wire junctions and silver nanowire in AgNWs-TCFs using active MONPs generated by magnetron sputtering. A series of AgNWs@MONPs for the AgNWs@ZnO-TCFs, AgNWs@SnO₂-TCFs, AgNWs@Al₂O₃-TCFs and AgNWs@TiO₂-TCFs were obtained. A significant decrease in the resistance of AgNWs-TCFs through the modification of MONPs was shown. Respectively, the reduction of resistance was 75.6%, 70.4%, 53.2% and 59.8% for AgNWs@ZnO-TCFs, AgNWs@SnO₂-TCFs, AgNWs@Al₂O₃-TCFs and AgNWs@TiO₂-TCFs. Correspondingly, its non-uniformity of resistance distribution was 12.5% (18.2% before), 10.0% (17.1% before), 10.1% (24.3% before) and 10.6% (13.4% before), respectively, which markedly improved the uniformity of electrical property. Respectively, their failure voltages reach 16, 16, 15 and 16 (V), so accordingly, the electrical stability is considerably enhanced. In addition, the uniformity of temperature distribution was also significantly optimized with its temperature non-uniformity of 10.4%, 8.7%, 10.3% and 9.6%, respectively. Contrast that with AgNWs@MONPs, and the failure voltages and temperature non-uniformity of AgNWs-TCFs are 12 V and 40.6%. Full article

(This article belongs to the Special Issue Optical Thin Films: Preparation, Application and Development)

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17 pages, 3811 KiB

Open AccessArticle

Laser Protection Properties of Multi-Band Non-Regularized Highly Reflective Films

by Xiaohong Deng and Junhong Su

Coatings 2022, 12(11), 1614; https://doi.org/10.3390/coatings12111614 - 23 Oct 2022

Cited by 1 | Viewed by 1928

Abstract

With the increasing exploitation of lasers, single-band laser protection has been extensively studied. However, single-band laser protection techniques have remained expensive and failed to meet protection requirements for multi-band lasers. In addition, the actual use of protective films requires a specific transmittance, which [...] Read more.

With the increasing exploitation of lasers, single-band laser protection has been extensively studied. However, single-band laser protection techniques have remained expensive and failed to meet protection requirements for multi-band lasers. In addition, the actual use of protective films requires a specific transmittance, which is generally not met by regular films. Here, we deposited three non-regularized highly reflective films using SiO₂ as the low-refractive-index material and TiO₂, HfO₂, and Ta₂O₅ as the high-refractive-index materials by thermal evaporation for achieving multi-band laser protection. To verify the effectiveness of the films, the variation in transmittance, damage threshold, standing-wave electric field, and damage morphology of the films were analyzed at two laser wavelengths, and their protection mechanisms were evaluated based on optical properties and damage resistance. The results showed that the reflectances of the prepared non-regularized films at 1064 nm and 532 nm were greater than 99%, and the laser-induced damage thresholds for TiO₂/SiO₂, HfO₂/SiO₂, and Ta₂O₅/SiO₂ films were 5.99, 5.89, and 9.99 J/cm² at 1064 nm and 3.04 J/cm², 1.48 J/cm², and 4.93 J/cm² at 532 nm, respectively, demonstrating good laser protection. The present work provides a practical and effective solution for multi-band laser protection and the prepared films may be used in numerous laser applications. Full article

(This article belongs to the Special Issue Optical Thin Films: Preparation, Application and Development)

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10 pages, 1589 KiB

Open AccessArticle

3-(N,N-Diphenylamino)carbazole Donor Containing Bipolar Derivatives with Very High Glass Transition Temperatures as Potential TADF Emitters for OLEDs

by Daiva Tavgeniene, Raminta Beresneviciute, Dovydas Blazevicius, Gintare Krucaite, Greta Jacunskaite, Sujith Sudheendran Swayamprabha, Jwo-Huei Jou and Saulius Grigalevicius

Coatings 2022, 12(7), 932; https://doi.org/10.3390/coatings12070932 - 1 Jul 2022

Cited by 4 | Viewed by 2156

Abstract

Well-defined electroactive bipolar derivatives of new structure have been synthesized from 3-(N,N-diphenylamino)-9H-carbazole and bis(4-fluorophenyl)sulfone, 4-fluorophenylsulfone or 4,4′-difluorobenzophenone, respectively. The full characterization of their structure is described. The amorphous materials with very high glass transition temperatures of 111–173 °C also [...] Read more.

Well-defined electroactive bipolar derivatives of new structure have been synthesized from 3-(N,N-diphenylamino)-9H-carbazole and bis(4-fluorophenyl)sulfone, 4-fluorophenylsulfone or 4,4′-difluorobenzophenone, respectively. The full characterization of their structure is described. The amorphous materials with very high glass transition temperatures of 111–173 °C also possess high thermal stability, with onset decomposition temperatures of 351–398 °C. Some of the compounds having the best solubility were tested as the emitters dispersed in 4,4′-bis(N-carbazolyl)-1,1′-biphenyl (CBP) host for preparation of organic light emitting diodes (OLEDs). A device containing 15 wt% of the guest bis[4-{3-(N,N-diphenylamino)carbazol-9-yl}phenyl] sulfone demonstrated the best overall characteristics with maximum brightness exceeding 2630 cd/m², current efficiency of 3.2 cd/A, power efficiency of 2.2 lm/W, and external quantum efficiency exceeding 1.7% at 100 cd/m². Full article

(This article belongs to the Special Issue Optical Thin Films: Preparation, Application and Development)

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14 pages, 1949 KiB

Open AccessArticle

Noble Infrared Optical Thickness Monitoring System Based on the Algorithm of Phase-Locked Output Current–Reflectivity Coefficient

by Suotao Dong, Xiuhua Fu and Cheng Li

Coatings 2022, 12(6), 782; https://doi.org/10.3390/coatings12060782 - 6 Jun 2022

Cited by 5 | Viewed by 2101

Abstract

With the rapid development of modern science and technology, the application of infrared (IR) optical thin films is increasingly widespread, including in aerospace, autonomous driving, military development, and the fight against Coronavirus Disease 2019 (COVID-19), in which thin film devices play an important [...] Read more.

With the rapid development of modern science and technology, the application of infrared (IR) optical thin films is increasingly widespread, including in aerospace, autonomous driving, military development, and the fight against Coronavirus Disease 2019 (COVID-19), in which thin film devices play an important role. Similarly, with the improvement of user requirements, the precision requirements for the preparation of optical films are also developing and improving. In this paper, the IR optical thickness monitoring system is studied with the noble algorithm introducing the phase-locked amplifier current and single film reflectivity coefficient. An optical control system is developed to monitor the IR thin film accurately, which aids the IR narrow-band filter film research. Full article

(This article belongs to the Special Issue Optical Thin Films: Preparation, Application and Development)

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15 pages, 7993 KiB

Open AccessArticle

Spin-Current Oscillations in Diluted Magnetic Semiconductor Multibarrier GaMnAs/GaAs: Role of Temperature and Bias Voltage

by Najla S. Al-Shameri and Hassen Dakhlaoui

Coatings 2022, 12(4), 504; https://doi.org/10.3390/coatings12040504 - 8 Apr 2022

Cited by 2 | Viewed by 1534

Abstract

This paper has studied the electronic properties of multi-diluted magnetic semiconductor (DMS) layers Ga_{(1 − x)}Mn_xAs interposed between nonmagnetic GaAs layers. The asymmetry of confining potential on the transmission coefficient by tuning the temperature and the size of the [...] Read more.

This paper has studied the electronic properties of multi-diluted magnetic semiconductor (DMS) layers Ga_{(1 − x)}Mn_xAs interposed between nonmagnetic GaAs layers. The asymmetry of confining potential on the transmission coefficient by tuning the temperature and the size of the (DMS) layers was discussed. The diluted magnetic layers Ga_{(1 − x)}Mn_xAs behave as barriers for spin-up holes and quantum wells for spin-down holes. Furthermore, we have addressed the impact of an applied bias voltage and the temperature on the variation of the spin-polarization and spin current densities. Our findings reveal that the transmission coefficients present an oscillating behavior due to the resonant states and strongly depend on the temperature of the system and the number of magnetic layers. Furthermore, the obtained results demonstrated that the number of these states is multiplied by augmenting the magnetic layers. Moreover, we demonstrate that the asymmetric structure presents a completely different transmission of holes than the symmetric structure. Furthermore, the negative differential resistance (NDR) is demonstrated in the current density variations. Especially, this (NDR) was more intense for spin-up holes than spin-down holes. The findings in the present paper can be useful in manufacturing spin-filters by adjusting the values of the temperature and the external voltages. Full article

(This article belongs to the Special Issue Optical Thin Films: Preparation, Application and Development)

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12 pages, 5203 KiB

Open AccessArticle

Effect of Seed Layer on the Growth of Zinc Oxide Nanowires by Chemical Bath Deposition Method

by Zaidatul Hanis Azmi, Siti Nurnadiah Mohd Aris, Shamsu Abubakar, Suresh Sagadevan, Rikson Siburian and Suriati Paiman

Coatings 2022, 12(4), 474; https://doi.org/10.3390/coatings12040474 - 31 Mar 2022

Cited by 22 | Viewed by 4515

Abstract

This study concentrated on the effect of the ZnO seed layer on the growth of ZnO nanowires by the chemical bath deposition method. Multilayer coatings were used to control the thickness of the seed layer of one layer, three layers, and five layers. [...] Read more.

This study concentrated on the effect of the ZnO seed layer on the growth of ZnO nanowires by the chemical bath deposition method. Multilayer coatings were used to control the thickness of the seed layer of one layer, three layers, and five layers. The seed layer thickness was measured using a profilometer at 14.43, 33.31, and 53.13 nm for one-layer, three-layer, and five-layer samples, respectively. The samples were then immersed in a chemical bath deposition solution at 90 °C for 3 h to allow ZnO nanowires to grow. The X-ray diffraction (XRD) pattern of seed layers revealed a polycrystalline wurtzite structure with (101) orientation as the dominant peak in all samples. Field emission scanning electron microscopy (FESEM) revealed that ZnO nanowires grown in a single layer have a flower-like structure, whereas ZnO nanowires grown in three and five layers have a rod-like structure. Further, ImageJ software revealed that the diameter and length of the ZnO nanowires were in the 40–90 nm and 100–900 nm ranges, respectively. The five-layer sample had the highest density of ZnO nanowires at 668 µm⁻², followed by the three-layer sample and the one-layer sample. However, the ZnO nanowires in the five-layer and one-layer samples are not vertically aligned. On the other hand, the three-layer sample had the best vertical alignment of this group of samples. Full article

(This article belongs to the Special Issue Optical Thin Films: Preparation, Application and Development)

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18 pages, 6469 KiB

Open AccessArticle

Top-Down Formulation of Goethite Nanosuspensions for the Production of Transparent, Inorganic Glass Coatings

by Christoph Peppersack, Karsten Wermbter, Arno Kwade, Georg Garnweitner and Sandra Breitung-Faes

Coatings 2022, 12(3), 330; https://doi.org/10.3390/coatings12030330 - 2 Mar 2022

Cited by 1 | Viewed by 2347

Abstract

This study presents a simple but effective process route for the production of transparent coatings on glass substrates from inorganic pigment goethite. For this purpose, coating suspensions were prepared by wet milling with a stirred media mill. A water/ethanol mixture was used as [...] Read more.

This study presents a simple but effective process route for the production of transparent coatings on glass substrates from inorganic pigment goethite. For this purpose, coating suspensions were prepared by wet milling with a stirred media mill. A water/ethanol mixture was used as the liquid medium to take advantage of the resulting low surface tension for the coating process. In this manner, stable suspensions with particles of down to 50 nm in size were obtained, which already showed a significant increase in transparency. With regard to grinding characteristics, particularly low stress energies proved to be energetically reasonable. The coating step was performed by wet film deposition, achieving coating thicknesses in a range of 0.5–2.5 µm via dip coating. Highly transparent coatings were obtained by applying small particles of 50 nm, which exhibited a significantly lower scattering loss of light (≈3%) in comparison to particles of around 300 nm (70–80%). Additionally, the film color could be adjusted through a variation of the drying temperature due to a conversion of goethite to hematite by dehydration. Since transparency was not affected, this provides an easy-to-implement process adaptation for controlling coating colors. Full article

(This article belongs to the Special Issue Optical Thin Films: Preparation, Application and Development)

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15 pages, 1600 KiB

Open AccessArticle

Experimental Study of Irradiation of Thin Oxide and Mo/Si Multilayers by High Brightness Broadband VUV/UV Radiation and Their Degradation

by Victor D. Telekh, Aleksei V. Pavlov, Daniil V. Kirillov, Evgeny V. Vorob’ev, Alexander G. Turyanskiy, Viacheslav M. Senkov, Petr A. Tsygankov, Freddy F. Parada-Becerra, Vladimir R. Vesnin and Andrei S. Skriabin

Coatings 2022, 12(2), 290; https://doi.org/10.3390/coatings12020290 - 21 Feb 2022

Cited by 7 | Viewed by 2637

Abstract

This study discusses the main features of the irradiation of prospective multilayer coatings by VUV/UV radiation from compressed plasma flows. Such radiation is characterized by a broadband spectrum and high brightness fluxes. Oxide and Mo/Si bilayers were used as the basis of the [...] Read more.

This study discusses the main features of the irradiation of prospective multilayer coatings by VUV/UV radiation from compressed plasma flows. Such radiation is characterized by a broadband spectrum and high brightness fluxes. Oxide and Mo/Si bilayers were used as the basis of the reflective multilayers for the visible and UV ranges. A gas-dynamic response from the irradiated surfaces was studied with schlieren photography. The properties of original and irradiated multilayers were described with ultra violet visible infrared spectroscopy (UV-Vis-IR), X-ray diffraction (XRD), X-ray reflectometry, scanning electron microscopy (SEM) and other techniques. Data on the degradation of optical properties and surface morphology were obtained. Full article

(This article belongs to the Special Issue Optical Thin Films: Preparation, Application and Development)

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12 pages, 7339 KiB

Open AccessArticle

Impact of Multi-Walled CNT Incorporation on Dielectric Properties of PVDF-BaTiO₃ Nanocomposites and Their Energy Harvesting Possibilities

by Abu Sadat M. Iftekhar Uddin, Dongin Lee, Chanseob Cho and Bonghwan Kim

Coatings 2022, 12(1), 77; https://doi.org/10.3390/coatings12010077 - 10 Jan 2022

Cited by 22 | Viewed by 3603

Abstract

The current study investigated the fabrication of multi-walled carbon nanotubes (MWCNTs) adhering to Barium titanate (BaTiO₃) nanoparticles and poly(vinylidene fluoride) (PVDF) nanocomposites, as well as the impact of MWCNT on the PVDF-BaTiO₃ matrix in terms of dielectric constant and dielectric [...] Read more.

The current study investigated the fabrication of multi-walled carbon nanotubes (MWCNTs) adhering to Barium titanate (BaTiO₃) nanoparticles and poly(vinylidene fluoride) (PVDF) nanocomposites, as well as the impact of MWCNT on the PVDF-BaTiO₃ matrix in terms of dielectric constant and dielectric loss with a view to develop a high performance piezoelectric energy harvester in future. The capacity and potential of as-prepared nanocomposite films for the fabrication of high-performance flexible piezoelectric nanogenerator (PNG) were also investigated in this work. In particular, five distinct types of nanocomposites and films were synthesized: PB (bare PVDF–BaTiO₃), PBC-1 (PVDF–BaTiO₃-0.1 wt% CNT), PBC-2 (PVDF–BaTiO₃-0.3 wt% CNT), PBC-3 (PVDF–BaTiO₃-0.5 wt% CNT), and PBC-4 (PVDF–BaTiO₃-1 wt% CNT). The dielectric constant and dielectric loss increased as MWCNT concentration increased. Sample PBC-3 had the optimum dielectric characteristics of all the as-prepared samples, with the maximum output voltage and current of 4.4 V and 0.66 μA, respectively, with an applied force of ~2N. Fine-tuning the BaTiO₃ content and thickness of the PNGs is likely to increase the harvester’s performance even more. It is anticipated that the work would make it easier to fabricate high-performance piezoelectric films and would be a suitable choice for creating high-performance PNG. Full article

(This article belongs to the Special Issue Optical Thin Films: Preparation, Application and Development)

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13 pages, 3013 KiB

Open AccessArticle

Application of Artificial Neural Networks in Analysis of Time-Variable Optical Reflectance Spectra in Digital Light Projection Spectroscopy

by Marek Gąsiorowski, Piotr Szymak, Leszek Bychto and Aleksy Patryn

Coatings 2022, 12(1), 37; https://doi.org/10.3390/coatings12010037 - 28 Dec 2021

Cited by 4 | Viewed by 1850

Abstract

This article undertakes the subject matter of applying artificial neural networks to analyze optical reflectance spectra of objects exhibiting a change of optical properties in the domain of time. A compact Digital Light Projection NIRscan Nano Evaluation Module spectrometer was used to record [...] Read more.

This article undertakes the subject matter of applying artificial neural networks to analyze optical reflectance spectra of objects exhibiting a change of optical properties in the domain of time. A compact Digital Light Projection NIRscan Nano Evaluation Module spectrometer was used to record spectra. Due to the miniature spectrometer’s size and its simplicity of measurement, it can be used to conduct tests outside of a laboratory. A series of plant-derived objects were used as test subjects with rapidly changing optical properties in the presented research cycle. The application of artificial neural networks made it possible to determine the aging time of plants with a relatively low mean squared error, reaching 0.56 h for the Levenberg–Marquardt backpropagation training method. The results of the other ten training methods for artificial neural networks have been included in the paper. Full article

(This article belongs to the Special Issue Optical Thin Films: Preparation, Application and Development)

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9 pages, 2366 KiB

Open AccessArticle

Optical and Recombination Parameters of CdS_1−xTe_x Thin Films Obtained by the CMBD Method

by Takhir M. Razykov, Aleksy Patryn, Mirosław Maliński, Leszek Bychto, Bobur Ergashev, Kudratulia Kouchkarov, Akbarjon Shukurov, Mirzavkiy Makhmudov and Diyorbek Isaqov

Coatings 2022, 12(1), 5; https://doi.org/10.3390/coatings12010005 - 22 Dec 2021

Viewed by 2152

Abstract

This paper presents the results of the photoacoustic, SEM, and surface photovoltage experiments performed on the series of CdS_1−xTe_x thin films. These CdS_1−xTe_x (0 ≤ x ≤ 1) thin films were obtained on the glass substrate by [...] Read more.

This paper presents the results of the photoacoustic, SEM, and surface photovoltage experiments performed on the series of CdS_1−xTe_x thin films. These CdS_1−xTe_x (0 ≤ x ≤ 1) thin films were obtained on the glass substrate by the chemical molecular beam deposition (CMBD) method. The polycrystalline character of these films was revealed by SEM pictures. From the experimental optical characteristics, the optical absorption coefficient spectra of the samples and values of their energy gaps vs. their composition were determined. From the surface photovoltage characteristics, the diffusion lengths of the carriers were also determined. Full article

(This article belongs to the Special Issue Optical Thin Films: Preparation, Application and Development)

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13 pages, 5712 KiB

Open AccessArticle

Condition Assessment of Solar Modules by Flash Test and Electroluminescence Test

by István Bodnár, Dávid Matusz-Kalász, Rafael Ruben Boros and Róbert Lipták

Coatings 2021, 11(11), 1361; https://doi.org/10.3390/coatings11111361 - 4 Nov 2021

Cited by 5 | Viewed by 3840

Abstract

The Hungarian society and the Hungarian state are constantly increasing their solar capacity. More and more solar power plants are being put into operation. The largest of these has a 100 MW peak capacity. Such power plants do not require constant maintenance. However, [...] Read more.

The Hungarian society and the Hungarian state are constantly increasing their solar capacity. More and more solar power plants are being put into operation. The largest of these has a 100 MW peak capacity. Such power plants do not require constant maintenance. However, in the case of low productivity, a conditional assessment is required. The reason for production loss can also be manufacturing, installation, and operational errors. A flying drone was used for finding failures by thermographic scouting. Furthermore, electroluminescent (EL) and flash tests give a comprehensive view of the real state of the modules in a mobile laboratory. We had the opportunity to summarize these test results of more than a thousand modules operating in a solar power plant. The report on the power plant shows that a significant part of the modules became unusable in a short time. After four years, 10% of the 260 Wp modules suffered a performance reduction of more than 10%. Full article

(This article belongs to the Special Issue Optical Thin Films: Preparation, Application and Development)

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14 pages, 4232 KiB

Open AccessArticle

Modifying Precursor Solutions to Obtain Screen-Printable Inks for Tungsten Oxides Electrochromic Film Preparation

by Kaiyue Guo, Guanguang Zhang, Yujie Long, Honglong Ning, Zhuohui Xu, Tian Qiu, Dongxiang Luo, Muyun Li, Rihui Yao and Junbiao Peng

Coatings 2021, 11(8), 872; https://doi.org/10.3390/coatings11080872 - 22 Jul 2021

Cited by 8 | Viewed by 3097

Abstract

Tungsten trioxide (WO₃) is used to prepare the important electrochromic layer of the electrochromic device as a wide bandgap semiconductor material. In this study, WO₃ electrochromic film was successfully prepared by screen printing. To modify the thixotropy and wettability of [...] Read more.

Tungsten trioxide (WO₃) is used to prepare the important electrochromic layer of the electrochromic device as a wide bandgap semiconductor material. In this study, WO₃ electrochromic film was successfully prepared by screen printing. To modify the thixotropy and wettability of the ink, polyvinyl alcohol (PVA) and 2-perfluoroalkyl ethanol (FSO) were added in the ammonium meta-tungstate (AMT) solution. We found that the PVA additive could improve the dynamic viscosity of the solution and modify the uniformity of the film. 2-Perfluoroalkyl ethanol (FSO) could lower the surface tension and increase the wettability of the AMT solution on the substrate. By observing the morphology of the printed films, the ink formulas for screen printing were selected. We found the annealing process could help remove PVA. Through characterization of electrochromic performance, it was found that the best performing device had 42.57% modulation and 93.25 cm²·C⁻¹ coloration efficiency (CE) for 600 nm light. This study showed great potential in the preparation of WO₃ electrochromic devices by a low-cost screen-printing method. Full article

(This article belongs to the Special Issue Optical Thin Films: Preparation, Application and Development)

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15 pages, 4359 KiB

Open AccessArticle

Optimization of the Active Layer P3HT:PCBM for Organic Solar Cell

by Mohamed Shaban, Mohamed Benghanem, Abdullah Almohammedi and Mohamed Rabia

Coatings 2021, 11(7), 863; https://doi.org/10.3390/coatings11070863 - 19 Jul 2021

Cited by 34 | Viewed by 6658

Abstract

ITO/PEDOT:PSS/P3HT:PC₆₀BM/Mg-Al organic solar cells (OSCs) were fabricated depending on optimization of Poly(3-hexylthiophene-2,5-diyl) (P3HT) and phenyl-C61-Butyric-Acid-Methyl Ester (PC₆₀BM). The optimization of the active layer, P3HT:PC₆₀BM, was carried out under different spin frequencies coating from 900 to 3000 rpm. [...] Read more.

ITO/PEDOT:PSS/P3HT:PC₆₀BM/Mg-Al organic solar cells (OSCs) were fabricated depending on optimization of Poly(3-hexylthiophene-2,5-diyl) (P3HT) and phenyl-C61-Butyric-Acid-Methyl Ester (PC₆₀BM). The optimization of the active layer, P3HT:PC₆₀BM, was carried out under different spin frequencies coating from 900 to 3000 rpm. The post-production annealing temperature of all prepared OSC was studied from 130 to 190 °C. The holes transport layer, poly(3,4-ethylene dioxythiophene) polystyrene sulfonate (PEDOT:PSS), was prepared under constant conditions of 3000 rpm for 35 s, and annealing temperature 178 °C for 15 min. From our study, the optimum conditions for P3HT:PC₆₀BM were spin coating of 3000 rpm, and annealing temperature of 160 °C for 5 min. The optimum J-V parameters values for the prepared OSC were J_SC = 12.01 mA/cm², V_OC = 660 mV, FF = 59%, PCE = 4.65%, and EQE = 61%. A complete OSC with acceptable efficiency was designed using simple and low-cost techniques that may be utilized in the industry. Furthermore, the cost of the synthesized solar cell is projected to be around 1 $/cm², with the goal of lowering the cost and increasing efficiency in the future by incorporating more commercial nanostructured electron/hole transport components. Full article

(This article belongs to the Special Issue Optical Thin Films: Preparation, Application and Development)

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11 pages, 3637 KiB

Open AccessArticle

LED Light Improved by an Optical Filter to Visible Solar-Like Light with High Color Rendering

by Li-Siang Shen, Hsing-Yu Wu, Li-Jen Hsiao, Chih-Hsuan Shih and Jin-Cherng Hsu

Coatings 2021, 11(7), 763; https://doi.org/10.3390/coatings11070763 - 25 Jun 2021

Cited by 5 | Viewed by 2421

Abstract

In this study, a new, cost-effective, rapid, and easy method to produce a sunlight-like D65 light source from a typical white light-emitting diode (LED) is discussed. The novelty of this method is that the emission spectrum of a typical white LED is measured [...] Read more.

In this study, a new, cost-effective, rapid, and easy method to produce a sunlight-like D65 light source from a typical white light-emitting diode (LED) is discussed. The novelty of this method is that the emission spectrum of a typical white LED is measured first, then the reverse spectrum is used to design and fabricate a double-sided multilayer coating filter to set in front of the typical white LED. This can be verified experimentally to improve the color-rendering index of the white LED to 95.8 at the D65 color temperature. The optical thicknesses of the multilayer film are designed at a quarter wavelength. The layer-thickness errors during the deposition process are reduced due to easy monitoring with the turning-point method. By lowering both the cost and level of technology required to produce D65 light sources, in addition to the most direct consequences of increased D65 availability and affordability, the cost and level of technology required for research that heavily utilizes D65 light sources can also be lowered in turn, especially in the fields of clinical science, medicine, and related industries. Full article

(This article belongs to the Special Issue Optical Thin Films: Preparation, Application and Development)

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10 pages, 2479 KiB

Open AccessFeature PaperArticle

Effect of Target Sintering Temperature on the Morphological and Optical Properties of Pulsed Laser Deposited TiO₂ Thin Films

by Laid Kadri, Georgiana Bulai, Aurelian Carlescu, Stoian George, Silviu Gurlui, Liviu Leontie, Corneliu Doroftei and Mohamed Adnane

Coatings 2021, 11(5), 561; https://doi.org/10.3390/coatings11050561 - 11 May 2021

Cited by 5 | Viewed by 3472

Abstract

In this paper, we report on the effect of titanium dioxide (TiO₂) target sintering temperature on the morphological and optical properties of amorphous titanium dioxide thin films synthesized by pulsed laser deposition (PLD) on indium tin oxide (ITO) glass substrate and [...] Read more.

In this paper, we report on the effect of titanium dioxide (TiO₂) target sintering temperature on the morphological and optical properties of amorphous titanium dioxide thin films synthesized by pulsed laser deposition (PLD) on indium tin oxide (ITO) glass substrate and subsequently heat-treated in air at low temperature (150 °C). Three types of targets were used, unsintered (pressed at room temperature), sintered at 500 °C and sintered at 1000 °C. The surface morphology of the samples was investigated by scanning electron microscopy (SEM), and profilometry was used for thickness measurements. The structural properties of the films were examined by X-ray diffraction (XRD), while their optical properties were studied by UV‒vis spectroscopy. The obtained TiO₂ thin films have an amorphous nature, as shown by XRD analysis. Profilometer showed that sintered target samples have more reliable thicknesses than unsintered ones. The SEM studies revealed the sufficient structural homogeneity of sintered target nanosized TiO₂ films and agglomerates in the case of unsintered target film. The UV‒vis transmittance spectra showed high transparency in the visible range of PLD films, proportional to the target sintering temperature. The optical band gaps of the films deposited using the 500 °C and 1000 °C sintered targets are closer to those of anatase and rutile phases, respectively, which provides a promising approach to the challenges of amorphous TiO₂-based nanostructures. Full article

(This article belongs to the Special Issue Optical Thin Films: Preparation, Application and Development)

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8 pages, 4217 KiB

Open AccessCommunication

Non-invasive Optical Technical Identification of Red Pigments on Chinese Paper Notes

by Jie Ren, Cunjin Gao, Jigang Wang, Yang Shen, Jilong Shi, Quanxiao Liu and Wei Chen

Coatings 2021, 11(4), 410; https://doi.org/10.3390/coatings11040410 - 1 Apr 2021

Cited by 1 | Viewed by 2125

Abstract

Red pigments with bright colors were widely used in ancient Chinese painted pottery, books, antiques, calligraphy, and paintings. Herein, red pigments of traditional paper notes were investigated by non-invasive optical technology in order to enrich the Chinese historical pigments knowledge base. The results [...] Read more.

Red pigments with bright colors were widely used in ancient Chinese painted pottery, books, antiques, calligraphy, and paintings. Herein, red pigments of traditional paper notes were investigated by non-invasive optical technology in order to enrich the Chinese historical pigments knowledge base. The results of laser Raman spectroscopy tests on five paper notes clearly identified the inorganic mineral pigments including ocher and cinnabar. Infrared spectroscopy measurements indicated that an artificial synthetic magenta was employed as the organic pigment. Inorganic and organic red pigments were applied together on the same samples 2 and 5 which can be speculated to serve an anti-counterfeiting function. In addition, SEM-EDS analysis of sample 5 clearly showed that the red pigment was composed of lead oxides and ZnS was added as color modulator. Combined with the abovementioned non-invasive techniques, analysis of printed pigments can provide a feasible method to authenticate and conserve paper notes. Full article

(This article belongs to the Special Issue Optical Thin Films: Preparation, Application and Development)

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15 pages, 6411 KiB

Open AccessArticle

Optimization of Thickness Uniformity Distribution on a Large-Aperture Concave Reflective Mirror and Shadow Mask Design in a Planetary Rotation System

by Gang Wang, Yunli Bai, Jing Zhao, Li Wang, Jiyou Zhang and Yuming Zhou

Coatings 2021, 11(2), 140; https://doi.org/10.3390/coatings11020140 - 27 Jan 2021

Cited by 2 | Viewed by 2378

Abstract

Improving the spatial resolution of remote sensing satellites has long been a challenge in the field of optical designing. Although the use of large-aperture reflective mirrors significantly improves the resolution of optical systems, controlling the film thickness uniformity remains an issue. The planetary [...] Read more.

Improving the spatial resolution of remote sensing satellites has long been a challenge in the field of optical designing. Although the use of large-aperture reflective mirrors significantly improves the resolution of optical systems, controlling the film thickness uniformity remains an issue. The planetary rotation system (PRS) has received significant attention owing to the excellent uniformity of the coating applied to the large-aperture reflective mirror. However, the development of the PRS remains hindered by a lack of research on its properties and the design method of the shadow mask. To address this, we performed a theoretical analysis of the distribution of film thickness and uniformity in the PRS, which is impacted by parameters of geometric configuration in the vacuum chamber. We present a film thickness expression based on Knudsen’s law and the geometric configuration of the vacuum chamber that incorporates an additional shading function. Moreover, the variation of uniformity in the standard and counter PRSs was elucidated by changing the location of the evaporation source. Finally, a fixed-position shadow mask, which was obtained by theoretical design, allows the nonuniformity of the concave reflective mirror (with a 700 mm aperture) to reduce from 2.43% to 0.7%, highlighting the importance of initial shape design. Full article

(This article belongs to the Special Issue Optical Thin Films: Preparation, Application and Development)

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