Research

9 pages, 1848 KiB

Open AccessFeature PaperArticle

The Excitation of Ultrasound by Laser Radiation in Water Using an Optical Fiber Laser Converter with a 2D Colloidal Crystalline Coating

by Vladimir I. Bredikhin and Viacheslav V. Kazakov

Coatings 2019, 9(12), 857; https://doi.org/10.3390/coatings9120857 - 14 Dec 2019

Cited by 1 | Viewed by 2453

Abstract

The technology of applying a colloidal single-layer coating of transparent polystyrene (PS) Ø 1 μm spheres at the tip face of a quartz fiber has been proposed and tested. Such a coating plays, in a light absorbing liquid, the role of a converter [...] Read more.

The technology of applying a colloidal single-layer coating of transparent polystyrene (PS) Ø 1 μm spheres at the tip face of a quartz fiber has been proposed and tested. Such a coating plays, in a light absorbing liquid, the role of a converter of pulsed laser radiation into acoustic radiation. The generation of ultrasound in water using a converter based on a quartz fiber 1 mm in diameter with a 2D colloidal crystalline coating consisted of polystyrene spheres with a diameter of ~1 μm at the fiber end was investigated. When excited by laser radiation (λ = 1.064 µm), coating of polystyrene spheres created in the liquid a laser thermal microstructure with a characteristic size of fractions of ~λ and a maximum temperature up to 10⁻² degree at an energy in a short laser pulse of ~0.005 J. This short-lived thermal microstructure generated sound pulses in the liquid in the approximately 0.2–4 MHz range. The results of the experimental study of this effect are reported. The proposed laser radiation converter with colloidal coating of the optical fiber distal tip by a single layer of transparent spheres can be used for the development of new laser microtools for studying, processing of various objects in microsurgery, microstructuring of the surface, spot cleaning and restoration of objects of art and history. Full article

(This article belongs to the Special Issue Design, Manufacturing and Measurement of Optical Film Coatings)

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8 pages, 4953 KiB

Open AccessFeature PaperArticle

Structure of Highly Porous Silicon Dioxide Thin Film: Results of Atomistic Simulation

by F.V. Grigoriev, V.B. Sulimov and A.V. Tikhonravov

Coatings 2019, 9(9), 568; https://doi.org/10.3390/coatings9090568 - 05 Sep 2019

Cited by 12 | Viewed by 3510

Abstract

The high-energy glancing angle deposition of silicon dioxide films with alternation of deposition angle is studied using classical atomistic simulation. Both slow and fast alternations are investigated. The growth of vertical tree-like columns and chevron-like regular structures is demonstrated under fast and slow [...] Read more.

The high-energy glancing angle deposition of silicon dioxide films with alternation of deposition angle is studied using classical atomistic simulation. Both slow and fast alternations are investigated. The growth of vertical tree-like columns and chevron-like regular structures is demonstrated under fast and slow alternations, respectively. Due to high porosity, the density of the deposited silicon dioxide films is reduced to 1.3 ÷ 1.4 g/cm³. This results in reduction of the refractive index to 1.3, which agrees with known experimental data. For slow continuous substrate rotation, formation of a helical structure is demonstrated. Full article

(This article belongs to the Special Issue Design, Manufacturing and Measurement of Optical Film Coatings)

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Graphical abstract

13 pages, 10194 KiB

Open AccessArticle

Design and Manufacture of a Novel Sunlight Guiding Panel

by Wei-Hsuan Hsu and Yi-Zhang Xie

Coatings 2019, 9(9), 562; https://doi.org/10.3390/coatings9090562 - 03 Sep 2019

Cited by 2 | Viewed by 2321

Abstract

With technological advancement, energy consumption and lack of energy supply are inevitable. Approximately 20% of total energy consumption is used for artificial light in standard office buildings. To reduce energy consumption for illumination purposes, a sunlight guiding panel was used to increase the [...] Read more.

With technological advancement, energy consumption and lack of energy supply are inevitable. Approximately 20% of total energy consumption is used for artificial light in standard office buildings. To reduce energy consumption for illumination purposes, a sunlight guiding panel was used to increase the amount of sunlight available indoors. However, in most designs of a sunlight guiding panel, the panel has to be placed on the outdoor surface of a window glass. This type of design is inconvenient for assembling and cleaning. To enhance the practicality of a sunlight guiding panel, we attempted to place the sunlight guiding panel on the indoor surface of a window glass. The simulation results revealed that when the sunlight guiding panel was placed on the indoor surface of a window glass, the aspect ratio of the light-guiding structure of the sunlight guiding panel had to be increased for guiding the sunlight from outdoors so as to increase the amount of sunlight indoors. To fabricate the proposed sunlight guiding panel, UV nanoimprint lithography was applied to pattern the light-guiding structure of the sunlight guiding panel. Moreover, a mold with a high-precision light-guiding structure was used in UV nanoimprint lithography. The mold was fabricated using ultraprecision machining technology. Both analytical and experimental investigations were conducted to confirm the proposed design. The average light-guiding efficiency was 89.9% with a solar elevation angle range of 35° to 65°, and the experimental results agreed well with the simulation results. This study elucidates light-guiding efficiency when the sunlight guiding panel is placed on the indoor surface of a window glass, which can increase the usage convenience and application potential of sunlight guiding panels. Full article

(This article belongs to the Special Issue Design, Manufacturing and Measurement of Optical Film Coatings)

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8 pages, 2847 KiB

Open AccessArticle

Effect of Wet Expansion Behavior on Polyimide Membrane Diffractive Lens

by Guohan Gao, Danbo Mao, Bin Fan and Chunlin Guan

Coatings 2019, 9(9), 559; https://doi.org/10.3390/coatings9090559 - 02 Sep 2019

Cited by 8 | Viewed by 2092

Abstract

Optical polyimide (PI) membrane is a potential substrate to fabricate a diffractive primary lens in large aperture space-borne telescope. In this paper, we investigated the wet expansion behavior of PI via a strain gauge method and measured the coefficient of wet expansion (CWE) [...] Read more.

Optical polyimide (PI) membrane is a potential substrate to fabricate a diffractive primary lens in large aperture space-borne telescope. In this paper, we investigated the wet expansion behavior of PI via a strain gauge method and measured the coefficient of wet expansion (CWE) of PI membrane supported by different fixtures. The CWE of silica-fixed, ring-fixed, and free state PI membrane were near zero, 5 ppm/%, and 10 ppm/% respectively. It is found that Fresnel zone lens (FZL), based on PI membrane with lower CWE, achieve a better imaging quality with smaller wave-front errors. The underlying mechanisms and methods to improve imaging quality of ring-fixed FZL are discussed. This work provides direction in fabricating a flexible membrane diffractive lens with applicable imaging quality. Full article

(This article belongs to the Special Issue Design, Manufacturing and Measurement of Optical Film Coatings)

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10 pages, 2871 KiB

Open AccessArticle

Study of Birefringence and Stress Distribution of SiO₂ Film Optical Waveguide on Silicon Wafer

by Qingyu Sun, DeGui Sun, Hongpeng Shang, Ting Yu, Liyuan Chang, Zheyu Sun, Wenchao Xing and Mingxue Dong

Coatings 2019, 9(5), 316; https://doi.org/10.3390/coatings9050316 - 10 May 2019

Cited by 2 | Viewed by 4031

Abstract

Silica waveguide planar lightwave circuit (PLC) technology is driving the broad applications of various functional components to meet the increasing demands of the industry due to its advanced performance in large-scale wafer mass production. Despite the intense research interests in understanding and relaxing [...] Read more.

Silica waveguide planar lightwave circuit (PLC) technology is driving the broad applications of various functional components to meet the increasing demands of the industry due to its advanced performance in large-scale wafer mass production. Despite the intense research interests in understanding and relaxing the stress causing the optical birefringence, not much research has been devoted to investigating the stress distribution. In this article, the thermal stress, growth-caused stress, and structural stress are comparably studied. The birefringence distribution of a 6 μm-thick SiO₂ film from the center to the edge on a 6-inch silicon wafer was measured to be 0.0006 to 0.0038, leading to an equivalent stress distribution cross the wafer from −170 to −1000 MPa. This implies that the compressive stress of the thick SiO₂ film on the wafer was nonuniformly distributed; however, it gradually increased from the center to the edge. Meanwhile, the measured stress of a SiO₂ film decreased with the flow rate of the doped GeH₄ gas. The algebraic sum of the above three stresses reached excellent agreement with the measurement results in both distribution form and amplitude. In both research and production, the agreeable optical property distributions between the theoretical calculations and experimental measurements are more sustainable to further improving the yields of SiO₂ thick film PLC products. Full article

(This article belongs to the Special Issue Design, Manufacturing and Measurement of Optical Film Coatings)

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19 pages, 6785 KiB

Open AccessEditor’s ChoiceArticle

Development of Belt-Type Microstructure Array Flexible Mold and Asymmetric Hot Roller Embossing Process Technology

by Yung-Jin Weng

Coatings 2019, 9(4), 274; https://doi.org/10.3390/coatings9040274 - 22 Apr 2019

Cited by 5 | Viewed by 3617

Abstract

This study proposed the belt-type microstructure array flexible mold designed hot roller embossing process technology. An extrusion molding system was integrated with belt-type hot roller embossing process technology and, deriving the asymmetric principle as the basis of prediction, designed a belt-type microstructure array [...] Read more.

This study proposed the belt-type microstructure array flexible mold designed hot roller embossing process technology. An extrusion molding system was integrated with belt-type hot roller embossing process technology and, deriving the asymmetric principle as the basis of prediction, designed a belt-type microstructure array hot roller embossing process system. This study first focused on the design and manufacturing of a belt-type hot roller embossing process system (roll to belt-type). It then carried out system integration and testing, along with the film extrusion system, to fabrication microstructure array production. Hot embossing was used to replicate the array of the plastic micro lens as the microstructure mold. The original master mold was fabricated with micro electromechanical technology and the PC micro lens array as the microstructure (inner layer) film using the gas-assisted hot embossing technology. A microstructure composite belt and magnetic belt were produced on the hot roller embossing by an innovated coated casting technique. The forming accuracy of the belt-type microstructure array flexible mold hot roller embossing process and the prediction precision of numerically simulated forming were discussed. The proposed process technology is expected to effectively reduce the process cycle time with the advantages of being a fast and continuous process. Full article

(This article belongs to the Special Issue Design, Manufacturing and Measurement of Optical Film Coatings)

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10 pages, 5024 KiB

Open AccessArticle

Analysis of High-Efficiency Mo-Based Solar Selective Absorber by Admittance Locus Method

by Hung-Pin Chen, Chao-Te Lee, Wei-Bo Liao, Ya-Chen Chang, Yu-Sheng Chen, Meng-Chi Li, Cheng-Chung Lee and Chien-Cheng Kuo

Coatings 2019, 9(4), 256; https://doi.org/10.3390/coatings9040256 - 17 Apr 2019

Cited by 7 | Viewed by 3311

Abstract

High absorptivity and low emissivity are characteristics needed in an ideal solar selective absorber. In high-temperature applications, such as a solar concentration power system in which the solar surface works under a long-term high temperature (about 400 to 800 °C), the absorber material [...] Read more.

High absorptivity and low emissivity are characteristics needed in an ideal solar selective absorber. In high-temperature applications, such as a solar concentration power system in which the solar surface works under a long-term high temperature (about 400 to 800 °C), the absorber material has to maintain high absorption in the visible region, high reflectance in the infrared region, and excellent thermal stability at high temperature. In this research, the design of a molybdenum-based (Mo-based) solar selective absorber was analyzed by the admittance locus method, and the films were deposited by magnetron sputtering. The ratio of the extinction coefficient to the refractive index of the Mo layer was close to 1, so that the Mo-based solar selective absorber had a broad absorption band, high absorption, and good solar selectivity. Its average reflectance in the visible region was less than 0.4%. The experimental absorption was 97.1% (simulated absorption was 98%) and the emissivity was from 13% to 20% (simulated emissivity was 8% to 26%) as the temperature increased from 400 to 800 °C. Full article

(This article belongs to the Special Issue Design, Manufacturing and Measurement of Optical Film Coatings)

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6 pages, 2891 KiB

Open AccessArticle

The Fabrication of a UV Notch Filter by Using Solid State Diffusion

by Hung-Pin Chen, Wen-Hao Cho, Wei-Chun Chen, Chao-Te Lee and Cheng-Chung Lee

Coatings 2019, 9(3), 208; https://doi.org/10.3390/coatings9030208 - 23 Mar 2019

Cited by 1 | Viewed by 2851

Abstract

One of the methods used to obtain notch filters involves one or several gradient index layers. In this method, the indices are decreased and then increased step by step to create a sinusoidal-like gradient layer. This paper reports a sinusoidal-like gradient layer fabrication [...] Read more.

One of the methods used to obtain notch filters involves one or several gradient index layers. In this method, the indices are decreased and then increased step by step to create a sinusoidal-like gradient layer. This paper reports a sinusoidal-like gradient layer fabrication method based on solid state diffusion. Al₂O₃/MgO/Al₂O₃ (AMA) was deposited by electron beam evaporation and then post-annealed at 800 °C for 4 h. Through inner diffusion, the MgO layers became a low refractive index material with a porous structure (the average refractive index was 1.55) such that the MgAl₂O₄ spinel was formed as an inhomogeneous layer with an average refractive index of 1.69. This allowed simply using a structured multilayer, (Al₂O₃/MgO)⁸ Al₂O₃, and post-annealing to form a sinusoidal-like gradient layer for a UV notch filter. Full article

(This article belongs to the Special Issue Design, Manufacturing and Measurement of Optical Film Coatings)

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18 pages, 12546 KiB

Open AccessArticle

Comparison of the Optical and Electrical Properties of Al-Doped ZnO Films Using a Lorentz Model

by Jin-Cherng Hsu and Yu-Yun Chen

Coatings 2019, 9(1), 4; https://doi.org/10.3390/coatings9010004 - 21 Dec 2018

Cited by 7 | Viewed by 3645

Abstract

In this research, zinc oxide (ZnO) films are doped with various amounts of Al dopants, from 0 to 13 at.%, using ion-beam co-sputtering for Zn and Al metallic targets at room temperature. The Al-doped ZnO (AZO) films appear to have lower transmittances in [...] Read more.

In this research, zinc oxide (ZnO) films are doped with various amounts of Al dopants, from 0 to 13 at.%, using ion-beam co-sputtering for Zn and Al metallic targets at room temperature. The Al-doped ZnO (AZO) films appear to have lower transmittances in the UV and near-IR ranges. The electrical and optical properties of each film are successfully analyzed by using the spectroscopic ellipsometry of two Lorentz oscillators for the two lower transmittances. The optimal AZO film is deposited with an Al-dopant of 1.5 at.% at an oxygen partial pressure of 0.12 mTorr; it has the smallest resistivity of 7.8 × 10⁻⁴ Ω cm and high transmittance of > 80% in the visible regions. The free carrier concentration and mobility evaluated using ellipsometry are different from those measured using the Hall effect. This phenomenon was the result of the grain boundary scattering due to the small ~20-nm grain size of the AZO film used in this study. Full article

(This article belongs to the Special Issue Design, Manufacturing and Measurement of Optical Film Coatings)

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12 pages, 6827 KiB

Open AccessFeature PaperArticle

Extinction Properties of Obliquely Deposited TiN Nanorod Arrays

by Yi-Jun Jen, Wei-Chien Wang, Kai-Lun Wu and Meng-Jie Lin

Coatings 2018, 8(12), 465; https://doi.org/10.3390/coatings8120465 - 14 Dec 2018

Cited by 11 | Viewed by 3786

Abstract

Plasmonic titanium nitride (TiN) nanorod arrays (NRA) were fabricated by glancing angle deposition in a DC magnetron reactive sputtering system. The morphology of the TiN NRA was varied by collimating the vapor flux. The transmittance, reflectance, and extinctance of slanted TiN nanorods with [...] Read more.

Plasmonic titanium nitride (TiN) nanorod arrays (NRA) were fabricated by glancing angle deposition in a DC magnetron reactive sputtering system. The morphology of the TiN NRA was varied by collimating the vapor flux. The transmittance, reflectance, and extinctance of slanted TiN nanorods with different lengths as functions of wavelength and angle of incidence were measured and analyzed. The extinction peaks in the spectra reveal the transverse and longitudinal plasmonic modes of TiN NRA upon excitation by s-polarized and p-polarized light, respectively. The near-field simulation was performed to elucidate localized field enhancements that correspond to high extinction. The extension of the high extinction band with an increasing length of the nanorods results in broadband and wide-angle light extinction for a TiN NRA with a thickness greater than 426 nm. Full article

(This article belongs to the Special Issue Design, Manufacturing and Measurement of Optical Film Coatings)

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8 pages, 2554 KiB

Open AccessArticle

Design and Fabrication of a Narrow Bandpass Filter with Low Dependence on Angle of Incidence

by Yi-Jun Jen and Meng-Jie Lin

Coatings 2018, 8(7), 231; https://doi.org/10.3390/coatings8070231 - 29 Jun 2018

Cited by 17 | Viewed by 4932

Abstract

A multilayer narrow bandpass filter that consists of silver and silicon thin films is designed using the admittance tracing method. Owing to the low loss of silicon in the infrared range, the peak transmittance at a wavelength of 950 nm exceeds 85%. To [...] Read more.

A multilayer narrow bandpass filter that consists of silver and silicon thin films is designed using the admittance tracing method. Owing to the low loss of silicon in the infrared range, the peak transmittance at a wavelength of 950 nm exceeds 85%. To eliminate the sidebands that are adjacent to the passband, a compact four-layered structure is proposed to generate an angle-insensitive spectrum. In fabrication, a silver-silicon multilayer is deposited to approach the design. Full article

(This article belongs to the Special Issue Design, Manufacturing and Measurement of Optical Film Coatings)

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