Editorial

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4 pages, 208 KiB

Open AccessEditorial

Special Issue: Optical Properties of Crystals and Thin Films

by Piotr Potera

Coatings 2022, 12(7), 920; https://doi.org/10.3390/coatings12070920 - 29 Jun 2022

Cited by 1 | Viewed by 1173

Abstract

Crystalline materials and coatings can be found almost everywhere in the modern world [...] Full article

(This article belongs to the Special Issue Optical Properties of Crystals and Thin Films)

Research

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11 pages, 2767 KiB

Open AccessFeature PaperArticle

Reverse Engineering Analysis of Optical Properties of (Ti,Cu)Ox Gradient Thin Film Coating

by Jarosław Domaradzki, Michał Mazur, Damian Wojcieszak, Artur Wiatrowski, Ewa Mańkowska and Paweł Chodasewicz

Coatings 2023, 13(6), 1012; https://doi.org/10.3390/coatings13061012 - 30 May 2023

Viewed by 1177

Abstract

Analysis of the optical properties of a gradient (Ti,Cu)Ox thin film is presented in this paper. The thin film was prepared using reactive co-sputtering of Ti and Cu targets. The desired elemental concentration profiles of Cu and Ti versus the thin film thickness [...] Read more.

Analysis of the optical properties of a gradient (Ti,Cu)Ox thin film is presented in this paper. The thin film was prepared using reactive co-sputtering of Ti and Cu targets. The desired elemental concentration profiles of Cu and Ti versus the thin film thickness were obtained by changing the power delivered to the magnetron equipped with Cu, while the powering of the magnetron equipped with the Ti target was maintained at a constant level during the film deposition. Optical properties were analysed using the reverse engineering method, based on simultaneously measured optical transmittance and reflectance. Detailed microstructure analysis performed using transmission electron microscopy investigations revealed that the thin film consisted of at least four areas with different structural properties. Finding a satisfying fit of theoretical to experimental data required taking into account the heterogeneity in the material composition and microstructure in relation to the depth in the prepared gradient thin film. On the basis of the built equivalent layer stack model, the composition profile and porosity at the cross-section of the prepared gradient film were evaluated, which agreed well with the obtained elemental and microscopy studies. Full article

(This article belongs to the Special Issue Optical Properties of Crystals and Thin Films)

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9 pages, 1926 KiB

Open AccessArticle

Tunable Low-Threshold Optical Bistability in Optical Tamm Plasmon Superlattices

by Fengyu Li, Jiao Xu, Wei Li, Jianbo Li, Yuxiang Peng and Mengdong He

Coatings 2023, 13(5), 938; https://doi.org/10.3390/coatings13050938 - 17 May 2023

Cited by 1 | Viewed by 901

Abstract

We propose a scheme to obtain tunable low-threshold optical bistability of reflected beams in optical Tamm plasmon superlattices (TPS). The low-threshold optical bistability is triggered due to the strong third-order non-linearity of graphene and the local field enhancement in the TPS. Our results [...] Read more.

We propose a scheme to obtain tunable low-threshold optical bistability of reflected beams in optical Tamm plasmon superlattices (TPS). The low-threshold optical bistability is triggered due to the strong third-order non-linearity of graphene and the local field enhancement in the TPS. Our results show that the optical Tamm plasmon superlattices have the ability to lower the bistable threshold even further than the single optical Tamm state. The results show that the hysteresis behavior and optical bistability threshold can be continuously adjusted by changing the applied voltage and the number of graphene layers (N ≤ 4). In particular, the optical bistability in the TPS is affected by the incident angle. Our results introduce a new possible route for low threshold optical bistability in the THz range and provide a new method in the field of all-optical switching applications. Full article

(This article belongs to the Special Issue Optical Properties of Crystals and Thin Films)

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11 pages, 3312 KiB

Open AccessArticle

Low-Threshold Optical Bistability Based on Photonic Crystal Fabry–Perot Cavity with Three-Dimensional Dirac Semimetal

by Fengyu Li, Jiao Xu, Jianbo Li, Yuxiang Peng and Mengdong He

Coatings 2023, 13(5), 936; https://doi.org/10.3390/coatings13050936 - 17 May 2023

Cited by 1 | Viewed by 1176

Abstract

In this paper, we investigate theoretically the tunable low threshold optical bistability (OB) in the terahertz range based on photonic crystals’ Fabry–Perot (FP) cavity with a three-dimensional Dirac semimetal (3D DSM). On the one hand, a 3D DSM with a high nonlinear refractive [...] Read more.

In this paper, we investigate theoretically the tunable low threshold optical bistability (OB) in the terahertz range based on photonic crystals’ Fabry–Perot (FP) cavity with a three-dimensional Dirac semimetal (3D DSM). On the one hand, a 3D DSM with a high nonlinear refractive index coefficient creates conditions for the generation of OB. Additionally, the finite film thickness of 3D DSMs leads to significantly a enhanced interaction volume compared to graphene, which allows easier preparation and has stable properties. On the other hand, the resonance of the FP cavity plays a positive role in promoting the tunable low-threshold OB. It was found that the OB threshold and hysteresis curve can be continuously adjusted by manipulating the Fermi energy and relaxation times of a 3D DSM. Additionally, the bistable curve of the composite structure is also closely related to the angle of incident light. Through parameter optimization, OB with a threshold approaching 10⁵ V/m can be obtained. The photonic crystal’s FP cavity with a 3D DSM structure provides a feasible way to achieve low-threshold OB and a building block for future integrated all-optical devices. Full article

(This article belongs to the Special Issue Optical Properties of Crystals and Thin Films)

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14 pages, 2288 KiB

Open AccessEditor’s ChoiceArticle

Linear and Nonlinear Optical Properties of Iridium Nanoparticles Grown via Atomic Layer Deposition

by Paul Schmitt, Pallabi Paul, Weiwei Li, Zilong Wang, Christin David, Navid Daryakar, Kevin Hanemann, Nadja Felde, Anne-Sophie Munser, Matthias F. Kling, Sven Schröder, Andreas Tünnermann and Adriana Szeghalmi

Coatings 2023, 13(4), 787; https://doi.org/10.3390/coatings13040787 - 18 Apr 2023

Cited by 2 | Viewed by 1874

Abstract

Nonlinear optical phenomena enable novel photonic and optoelectronic applications. Especially, metallic nanoparticles and thin films with nonlinear optical properties offer the potential for micro-optical system integration. For this purpose, new nonlinear materials need to be continuously identified, investigated, and utilized for nonlinear optical [...] Read more.

Nonlinear optical phenomena enable novel photonic and optoelectronic applications. Especially, metallic nanoparticles and thin films with nonlinear optical properties offer the potential for micro-optical system integration. For this purpose, new nonlinear materials need to be continuously identified, investigated, and utilized for nonlinear optical applications. While noble-metal nanoparticles, nanostructures, and thin films of silver and gold have been widely studied, iridium (Ir) nanoparticles and ultrathin films have not been investigated for nonlinear optical applications yet. Here, we present a combined theoretical and experimental study on the linear and nonlinear optical properties of iridium nanoparticles deposited via atomic layer deposition (ALD). Linear optical constants, such as the effective refractive index and extinction coefficient, were evaluated at different growth stages of nanoparticle formation. Both linear and nonlinear optical properties of these Ir ALD coatings were calculated theoretically using the Maxwell Garnett theory. The third-order susceptibility of iridium nanoparticle samples was experimentally investigated using the z-scan technique. According to the experiment, for an Ir ALD coating with 45 cycles resulting in iridium nanoparticles, the experimentally determined nonlinear third-order susceptibility is about χ_Ir⁽³⁾ = (2.4 − i2.1) × 10⁻¹⁷ m²/V² at the fundamental wavelength of 700 nm. The theory fitted to the experimental results predicts a 5 × 10⁶-fold increase around 230 nm. This strong increase is due to the proximity to the Mie resonance of iridium nanoparticles. Full article

(This article belongs to the Special Issue Optical Properties of Crystals and Thin Films)

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23 pages, 8402 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Heterostructure Films of SiO₂ and HfO₂ for High-Power Laser Optics Prepared by Plasma-Enhanced Atomic Layer Deposition

by Shawon Alam, Pallabi Paul, Vivek Beladiya, Paul Schmitt, Olaf Stenzel, Marcus Trost, Steffen Wilbrandt, Christian Mühlig, Sven Schröder, Gabor Matthäus, Stefan Nolte, Sebastian Riese, Felix Otto, Torsten Fritz, Alexander Gottwald and Adriana Szeghalmi

Coatings 2023, 13(2), 278; https://doi.org/10.3390/coatings13020278 - 26 Jan 2023

Cited by 2 | Viewed by 1888

Abstract

Absorption losses and laser-induced damage threshold (LIDT) are considered to be the major constraints for development of optical coatings for high-power laser optics. Such coatings require paramount properties, such as low losses due to optical absorption, high mechanical stability, and enhanced damage resistance, [...] Read more.

Absorption losses and laser-induced damage threshold (LIDT) are considered to be the major constraints for development of optical coatings for high-power laser optics. Such coatings require paramount properties, such as low losses due to optical absorption, high mechanical stability, and enhanced damage resistance, to withstand high-intensity laser pulses. In this work, heterostructures were developed by sub-nanometer thin films of SiO₂ and HfO₂ using the plasma-enhanced atomic layer deposition (PEALD) technique. Thin-film characterization techniques, such as spectroscopic ellipsometry, spectrophotometry, substrate curvature measurements, X-ray reflectivity, and Fourier transform infrared spectroscopy, were employed for extracting optical constants, residual stress, layer formation, and functional groups present in the heterostructures, respectively. These heterostructures demonstrate tunable refractive index, bandgap, and improved optical losses and LIDT properties. The films were incorporated into antireflection coatings (multilayer stacks and graded-index coatings) and the LIDT was determined at 355 nm wavelength by the R-on-1 method. Optical absorptions at the reported wavelengths were characterized using photothermal common-path interferometry and laser-induced deflection techniques. Full article

(This article belongs to the Special Issue Optical Properties of Crystals and Thin Films)

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13 pages, 4260 KiB

Open AccessFeature PaperArticle

Optical Properties of ITO/Glass Substrates Modified by Silver Nanoparticles for PV Applications

by Grzegorz Wisz, Piotr Potera, Paulina Sawicka-Chudy and Katarzyna Gwóźdź

Coatings 2023, 13(1), 61; https://doi.org/10.3390/coatings13010061 - 29 Dec 2022

Cited by 2 | Viewed by 2156

Abstract

The paper describes the research on optical properties of glass/ITO/Ag thin layers obtained on glass/ITO substrates with different properties. The authors will discuss the influence of silver particles and silver layer thickness on the transmission and reflection spectra of the layers and parameters, [...] Read more.

The paper describes the research on optical properties of glass/ITO/Ag thin layers obtained on glass/ITO substrates with different properties. The authors will discuss the influence of silver particles and silver layer thickness on the transmission and reflection spectra of the layers and parameters, such as the width of the optical band gap, refractive index, and dieelectric function. For example, the presence of silver leads to a decrease in the transmission of the layers (compared to ITO/glass) regardless of the thickness of the silver layer, and in the case of reflection, both its increase and decrease were observed, depending on the thickness of the silver layer and the type of glass/ITO substrate used. The average transmission value in the visible region depends on the thickness of the silver nanoparticle layer and varies from ~50% to ~90%. The average refractive index takes values from the range ~1.4 to ~1.65 and does not depend on the presence and thickness of the silver layer. Full article

(This article belongs to the Special Issue Optical Properties of Crystals and Thin Films)

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14 pages, 5235 KiB

Open AccessFeature PaperArticle

Generation of High-Frequency Ultrasound in a Liquid upon Excitation by Laser Radiation through a Light Guide with a Converter of Transparent Spheres

by Vladimir I. Bredikhin and Viacheslav V. Kazakov

Coatings 2023, 13(1), 55; https://doi.org/10.3390/coatings13010055 - 28 Dec 2022

Viewed by 1201

Abstract

One of the important tasks in optoacoustics today is the development of methods and tools for generating high-frequency ultrasound (above 1 MHz) in liquids and other media. To expand the frequency range of ultrasound, it was proposed to use coatings consisting of focusing [...] Read more.

One of the important tasks in optoacoustics today is the development of methods and tools for generating high-frequency ultrasound (above 1 MHz) in liquids and other media. To expand the frequency range of ultrasound, it was proposed to use coatings consisting of focusing spheres on a fiber tip. The methodology of calculating the ultrasound spectra depending on the sphere size, index of refraction, and parameters of laser radiation was developed. Two cases of small and large spheres in strongly and weakly absorbing media were simulated. The experimental results were analyzed in the approximations allowing a fairly accurate estimation of the spectrum and indicatrix of the generated ultrasound upon laser excitation through a converter based on a coating of transparent spheres. A good agreement between the model and experimental result was obtained. Full article

(This article belongs to the Special Issue Optical Properties of Crystals and Thin Films)

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13 pages, 4747 KiB

Open AccessEditor’s ChoiceArticle

Effect of Annealing on the Microstructure, Opto-Electronic and Hydrogen Sensing Properties of V₂O₅ Thin Films Deposited by Magnetron Sputtering

by Michał Mazur, Szymon Kiełczawa and Jarosław Domaradzki

Coatings 2022, 12(12), 1885; https://doi.org/10.3390/coatings12121885 - 04 Dec 2022

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Abstract

This paper reports results of investigations on selected properties of vanadium oxide thin films deposited using gas impulse magnetron sputtering and annealed at temperatures in the range of 423 K to 673 K. Post-process annealing was shown to allow phase transition of as-deposited [...] Read more.

This paper reports results of investigations on selected properties of vanadium oxide thin films deposited using gas impulse magnetron sputtering and annealed at temperatures in the range of 423 K to 673 K. Post-process annealing was shown to allow phase transition of as-deposited films from amorphous to nanocrystalline V₂O₅ with crystallite sizes in the range of 23 to 27 nm. Simultaneously, annealing resulted in an increase in surface roughness and grain size. Moreover, a decrease in transparency was observed in the visible wavelength range of approximately 50% to 30%, while the resistivity of formed vanadium pentoxide thin films was almost unchanged and was in the order of 10² Ω·cm. Simultaneously, the best optoelectronic performance, testified by evaluated figure of merit parameter, indicated the as-deposited amorphous films. Performed Seebeck coefficient measurements indicated the electron type of electrical conduction of each prepared thin film. Furthermore, gas sensing properties towards diluted hydrogen were investigated for annealed V₂O₅ thin films, and it was found that the highest senor response was obtained for a thin film annealed at 673 K and measured at operating temperature of 623 K. Full article

(This article belongs to the Special Issue Optical Properties of Crystals and Thin Films)

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12 pages, 3769 KiB

Open AccessArticle

Correlation between Thickness and Optical Properties in Nanocrystalline γ-Monoclinic WO₃ Thin Films

by Renee J. Sáenz-Hernández, Guillermo M. Herrera-Pérez, Jesús S. Uribe-Chavira, María C. Grijalva-Castillo, José Trinidad Elizalde-Galindo and José A. Matutes-Aquino

Coatings 2022, 12(11), 1727; https://doi.org/10.3390/coatings12111727 - 12 Nov 2022

Cited by 6 | Viewed by 1448

Abstract

Results from the analysis of the variation of structural defects, such as oxygen vacancies indicate that by adjusting the thickness of the WO₃ films, fabricated by DC reactive sputtering, it is possible to modulate the oxygen vacancies concentration. This has a tremendous [...] Read more.

Results from the analysis of the variation of structural defects, such as oxygen vacancies indicate that by adjusting the thickness of the WO₃ films, fabricated by DC reactive sputtering, it is possible to modulate the oxygen vacancies concentration. This has a tremendous influence on the applications of these semiconductor materials. The thicknesses analyzed here are 42, 66, and 131 nm. After the annealing process at 500 °C, films were directly transformed to a stable γ-monoclinic crystal structure with P2₁/n space group, with a preferential orientation in the (200) plane. Atomic force microscopy exhibits nanometer range particle size with the highest roughness and higher surface area for the thinner film. FTIR analysis shows the presence of characteristic bands of the double bond stretching vibrational modes (W=O) and stretching vibrations of the γ(W-O-W) bonds corresponding to the monoclinic WO₃. Raman bands located at 345, and 435 cm⁻¹ are ascribed to the presence of W⁵⁺ species that induces the formation of oxygen vacancies VO. The thinner film shows a decrease in the optical indirect band gap attributed to the formation of oxygen vacancies in combination with W⁵⁺ species that induce the formation of energy states within the forbidden band gap range. Full article

(This article belongs to the Special Issue Optical Properties of Crystals and Thin Films)

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12 pages, 3442 KiB

Open AccessFeature PaperArticle

Transparent Conductive Indium Zinc Oxide Films: Temperature and Oxygen Dependences of the Electrical and Optical Properties

by Akhmed K. Akhmedov, Eldar K. Murliev, Abil S. Asvarov, Arsen E. Muslimov and Vladimir M. Kanevsky

Coatings 2022, 12(10), 1583; https://doi.org/10.3390/coatings12101583 - 19 Oct 2022

Cited by 5 | Viewed by 2058

Abstract

Achieving high-efficiency optoelectronic devices often requires the development of high transparency in the extended range and high-conductivity materials, which can be ensured by the high mobility of charge carriers being used as the electrode. Among the candidate materials, transparent conductive indium zinc oxide [...] Read more.

Achieving high-efficiency optoelectronic devices often requires the development of high transparency in the extended range and high-conductivity materials, which can be ensured by the high mobility of charge carriers being used as the electrode. Among the candidate materials, transparent conductive indium zinc oxide (IZO) has attracted significant interest because of its superior electron mobility (5−60 cm²/V·s) and the thermal stability of its structure. In this study, the IZO films were deposited by the radio frequency magnetron sputtering of the IZO ceramic target (containing 10 wt.% ZnO) by varying the two variables of the substrate temperature and the oxygen content in the working gas. Here, the importance of the deposition of the IZO films at a low substrate temperature, not exceeding 100 °C, in order to get the minimum values of the film resistivity is revealed. At a substrate temperature of 100 °C, the film deposited in pure argon demonstrated a minimum resistance of 3.4 × 10⁻⁴ Ω·cm. Despite the fact that, with the addition of O₂ in the working gas, an increase in resistivity was observed, the IZO film that deposited under 0.4% O₂ content demonstrated the highest mobility (μ = 35 cm²/V·s at ρ = 6.0 × 10⁻⁴ Ω·cm) and enhanced transparency in the visible (VIS, 400−800 nm) and near-infrared (NIR, 800−1250 nm) ranges (T_VIS ≥ 77% and T_NIR ≥ 76%). At an oxygen content above 0.4%, a significant deterioration in electrical properties and a decrease in optical characteristics were observed. SEM and XRD studies of the microstructure of the IZO films allowed the clarification of the effect of both the substrate temperature and the oxygen content on the functional characteristics of the transparent conducting IZO films. Full article

(This article belongs to the Special Issue Optical Properties of Crystals and Thin Films)

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13 pages, 3433 KiB

Open AccessArticle

Boron Nitride Thin Films with Anisotropic Optical Properties from Microscale Particle Density Distributions

by Lyubov V. Kotova, Linar A. Altynbaev, Maria O. Zhukova, Bogdan R. Borodin, Vladimir P. Kochereshko, Anna Baldycheva and Benjamin T. Hogan

Coatings 2022, 12(10), 1571; https://doi.org/10.3390/coatings12101571 - 18 Oct 2022

Viewed by 2113

Abstract

Unusual optical anisotropy was experimentally observed in hexagonal boron nitride thin films produced from bulk boron nitride via ultrasonication. Both the linear and circular polarisation demonstrated a well-defined single axis of anisotropy over a large sample area. To understand this phenomenon, we employed [...] Read more.

Unusual optical anisotropy was experimentally observed in hexagonal boron nitride thin films produced from bulk boron nitride via ultrasonication. Both the linear and circular polarisation demonstrated a well-defined single axis of anisotropy over a large sample area. To understand this phenomenon, we employed statistical analysis of optical microscopy images and atomic force microscopy to reveal an ordered particle density distribution at the microscopic level corresponding to the optical axis observed in the polarisation data. The direction of the observed ordering matched the axis of anisotropy. Hence, we attribute the measured optical anisotropy of the thin films to microscopic variations in the particle density distribution. Full article

(This article belongs to the Special Issue Optical Properties of Crystals and Thin Films)

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Review

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25 pages, 5673 KiB

Open AccessReview

Microstructured All-Optical Switching Based on Two-Dimensional Material

by Jiao Xu, Yuxiang Peng, Shengyou Qian and Leyong Jiang

Coatings 2023, 13(5), 876; https://doi.org/10.3390/coatings13050876 - 06 May 2023

Cited by 3 | Viewed by 1883

Abstract

Microstructured all-optical switching, possessing the unique function of light controlling light, is an important part of the on-chip ultra-fast optical connectivity network and integrated logic computing chip. Microstructured all-optical switching has attracted extensive research interest, the latest great developments of which have also [...] Read more.

Microstructured all-optical switching, possessing the unique function of light controlling light, is an important part of the on-chip ultra-fast optical connectivity network and integrated logic computing chip. Microstructured all-optical switching has attracted extensive research interest, the latest great developments of which have also yielded progress in nanophotonics, nonlinear optics, optical communications, and integrated optics, etc. The emergence of two-dimensional materials with good third-order optical nonlinearity provides an important driving force for the improvement of all-optical switches. This paper reviews the implementation principles, novel configurations, improved performance indexes, and research progress based on different two-dimensional materials for micro/nano all-optical switching. Not only is a systematic discussion of the current state provided, but also, a brief outlook is afforded on the remaining challenges in the pursuit of the application of practical on-chip microstructured all-optical switching that is based on two-dimensional materials. Full article

(This article belongs to the Special Issue Optical Properties of Crystals and Thin Films)

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