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Coatings, Volume 9, Issue 5 (May 2019)

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Open AccessArticle
Improving the Environmental Sustainability of Low Noise Pavements: Comparative Life Cycle Assessment of Reclaimed Asphalt and Crumb Rubber Based Warm Mix Technologies
Coatings 2019, 9(5), 343; https://doi.org/10.3390/coatings9050343 (registering DOI)
Received: 31 March 2019 / Revised: 10 May 2019 / Accepted: 22 May 2019 / Published: 26 May 2019
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Abstract
Increasing environmental awareness is pushing towards sustainable approaches to the design and management of transport infrastructures. A life cycle assessment of low noise pavements is carried out here, with the aim to evaluate and compare the use of warm mix asphalts containing crumb [...] Read more.
Increasing environmental awareness is pushing towards sustainable approaches to the design and management of transport infrastructures. A life cycle assessment of low noise pavements is carried out here, with the aim to evaluate and compare the use of warm mix asphalts containing crumb rubber (CR) from end-of-life tires (ELTs) and reclaimed asphalt pavement (RAP). Different scenarios have been considered, taking into account production, construction, maintenance activities, and end-of-life of the pavement, according to a cradle to grave approach. Hot mix asphalt (HMA) was used as a reference wearing course. Results show that the simultaneous implementation of warm asphalt technologies and recycled materials can lead to a 50% reduction of the environmental burdens, compared to the standard scenario. The difference is mainly ascribed to the material depletion, the energy consumption, and the emissions associated with the frequency of maintenance of the wearing course. The use of asphalt rubber is environmentally advantageous, if compared to polymer modified binders (PMB); moreover, rubberized open-graded mixtures require the lowest bitumen content and maintenance. The findings of this research support the use of recycled materials and warm technologies as a way to improve the environmental sustainability of low noise pavements. Full article
(This article belongs to the Special Issue Pavement Surface Coatings)
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Open AccessArticle
Molecular Dynamics Study on the Tribological Properties of Phosphorene/Polyethylene Composites
Coatings 2019, 9(5), 342; https://doi.org/10.3390/coatings9050342 (registering DOI)
Received: 24 April 2019 / Revised: 20 May 2019 / Accepted: 22 May 2019 / Published: 26 May 2019
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Abstract
This study aimed to investigate the mechanism of phosphorene in enhancing the friction behaviors of polyethylene using molecular dynamics. A sliding model was constructed to investigate the coefficient of friction and abrasion rate of composites by applying a tangential velocity on a rigid [...] Read more.
This study aimed to investigate the mechanism of phosphorene in enhancing the friction behaviors of polyethylene using molecular dynamics. A sliding model was constructed to investigate the coefficient of friction and abrasion rate of composites by applying a tangential velocity on a rigid tip. Both the size and number of layers of phosphorene had positive effects on the friction force of composites but through different mechanisms. The former was because the interaction between phosphorene and polyethylene increased with the size of phosphorene, while the latter was through influencing the thermal transport across phosphorene and polyethylene interfaces. The rate of improvement decreased with the increased layer number of phosphorene due to the fact that the phosphorene tended to congregate together and thus formed multi-layer agglomerates. The friction behavior of the composites was highly anisotropic because of the high divergence of potential-energy on the phosphorene surface. These findings have provided insights into enhancing the friction behavior of polymer filled by phosphorene. Full article
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Open AccessArticle
Growth of Ultrathin Al2O3 Films on n-InP Substrates as Insulating Layers by RF Magnetron Sputtering and Study on the Optical and Dielectric Properties
Coatings 2019, 9(5), 341; https://doi.org/10.3390/coatings9050341 (registering DOI)
Received: 21 March 2019 / Revised: 20 May 2019 / Accepted: 23 May 2019 / Published: 26 May 2019
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Abstract
Here, we report an explorative study of an attempt to fabricate ultrathin aluminum oxide films on n-InP substrates by radio-frequency (RF) magnetron sputtering as a candidate for insulating layers in semiconductor lasers for optical communication. Film thickness and morphology were monitored to study [...] Read more.
Here, we report an explorative study of an attempt to fabricate ultrathin aluminum oxide films on n-InP substrates by radio-frequency (RF) magnetron sputtering as a candidate for insulating layers in semiconductor lasers for optical communication. Film thickness and morphology were monitored to study the film growth and to explore the minimum thickness of a continuous film that RF magnetron sputtering could achieve. Originating from the weak wettability between the n-InP substrate and the Al2O3 film, Al2O3 films firstly grew in an island pattern which then turned into a layer-by-layer pattern when those islands became connected and continuous. Uniform and compact Al2O3 films were obtained when the film thickness reached 40 nm. The average transmittance, optical band gap, and optical absorption coefficient at a wavelength of 1550 nm of this Al2O3 film were about 80%, 3.72 eV, and 3.0 × 104 cm−1, respectively. At a frequency of 1 MHz, the permittivity, dielectric loss, and electrical resistivity were 8.96, 0.31, and 5 × 1010 Ω·cm, respectively. This work provides valuable references for the application of Al2O3 ultrathin films as insulating layers in micro-and opto-electronics. Full article
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Open AccessArticle
Cavitation Erosion and Sliding Wear Mechanisms of AlTiN and TiAlN Films Deposited on Stainless Steel Substrate
Coatings 2019, 9(5), 340; https://doi.org/10.3390/coatings9050340 (registering DOI)
Received: 18 April 2019 / Revised: 21 May 2019 / Accepted: 23 May 2019 / Published: 25 May 2019
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Abstract
The resistance to cavitation erosion and sliding wear of stainless steel grade AISI 304 can be improved by using physical vapor deposited (PVD) coatings. The aim of this study was to investigate the cavitation erosion and sliding wear mechanisms of magnetron-sputtered AlTiN and [...] Read more.
The resistance to cavitation erosion and sliding wear of stainless steel grade AISI 304 can be improved by using physical vapor deposited (PVD) coatings. The aim of this study was to investigate the cavitation erosion and sliding wear mechanisms of magnetron-sputtered AlTiN and TiAlN films deposited with different contents of chemical elements onto a stainless steel SS304 substrate. The surface morphology and structure of samples were examined by optical profilometry, light optical microscopy (LOM) and scanning electron microscopy (SEM-EDS). Mechanical properties (hardness, elastic modulus) were tested using a nanoindentation tester. Adhesion of the deposited coatings was determined by the scratch test and Rockwell adhesion tests. Cavitation erosion tests were performed according to ASTM G32 (vibratory apparatus) in compliance with the stationary specimen procedure. Sliding wear tests were conducted with the use of a nano-tribo tester, i.e. ball-on-disc apparatus. Results demonstrate that the cavitation erosion mechanism of the TiAlN and AlTiN coatings rely on embrittlement, which can be attributed to fatigue processes causing film rupture and internal decohesion in flake spallation, and thus leading to coating detachment and substrate exposition. At moderate loads, the sliding wear of thin films takes the form of grooving, micro-scratching, micro-ploughing and smearing of the columnar grain top hills. Compared to the SS reference sample, the PVD films exhibit superior resistance to sliding wear and cavitation erosion. Full article
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Open AccessArticle
Protective Performance of Zn-Al-Mg-TiO2 Coating Prepared by Cold Spraying on Marine Steel Equipment
Coatings 2019, 9(5), 339; https://doi.org/10.3390/coatings9050339 (registering DOI)
Received: 11 April 2019 / Revised: 21 May 2019 / Accepted: 22 May 2019 / Published: 25 May 2019
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Abstract
According to research, we have learned that zinc has excellent cathodic protection performance, that the corrosion products of aluminum and magnesium can form dense and stable passivation films to protect internal materials of coatings, and that TiO2 has excellent photocatalytic self-cleaning performance [...] Read more.
According to research, we have learned that zinc has excellent cathodic protection performance, that the corrosion products of aluminum and magnesium can form dense and stable passivation films to protect internal materials of coatings, and that TiO2 has excellent photocatalytic self-cleaning performance which will form a physical adsorption film on the surface to isolate the external corrosion solution. In this paper, a Zn-Al-Mg-TiO2 pseudo alloy coating was prepared by cold spray technique on a Q235 substrate. The protective performance of Zn-Al-Mg-TiO2 for marine metal equipment was studied using dynamic salt water corrosion testing, electrochemical testing, and friction and wear testing. The microstructure, composition, and wear marks of coatings were observed using a scanning electron microscope (SEM), energy dispersive spectrometer (EDS), and white-light interferometer. The results show that the Zn-Al-Mg-TiO2 coating has excellent corrosion and wear resistance, which can provide long-term and stable protection for the substrate. Full article
Open AccessFeature PaperArticle
Microstructure and Mechanical Property Investigation of TaSiN Thin Films Deposited by Reactive Magnetron Sputtering
Coatings 2019, 9(5), 338; https://doi.org/10.3390/coatings9050338 (registering DOI)
Received: 11 April 2019 / Revised: 16 May 2019 / Accepted: 23 May 2019 / Published: 25 May 2019
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Abstract
Tantalum silicon nitride (Ta–Si–N) films were synthesized on Si substrate via magnetron sputtering. The structure and properties of the Ta–Si–N films were investigated as a function of the N2 content in the N2/Ar gas mixture. Increasing the N2 percentage [...] Read more.
Tantalum silicon nitride (Ta–Si–N) films were synthesized on Si substrate via magnetron sputtering. The structure and properties of the Ta–Si–N films were investigated as a function of the N2 content in the N2/Ar gas mixture. Increasing the N2 percentage in the gas mixture from 7% to 20% changed the film structure from textured hexagonal (hex) Ta2N to nontextured hex Ta2N to a mixture of face-centered cubic (fcc) TaN and hex Ta2N, and finally to fcc TaN. X-ray photoelectron spectroscopy showed Ta–N and Si–N bonds in the films. The film microstructure was found to change from columnar morphology with visible amorphous boundaries (at 13% N2) to columnar morphology with absence of amorphous boundaries (at 15% N2). Increasing N2 content increased hardness in the films with those deposited with 13–15% N2 displaying the highest hardness of ~40 ± 2 GPa. In addition, the 13% N2 films showed a ratio of H/E* > 0.11, elastic recovery of ~60%, low coefficient of friction of 0.6, reduced wear rate (7.09 × 10−6 mm3/N·m), and remained thermally stable up to 800 °C. The results suggest that the Ta–Si–N films have high potential as hard tribological nanocomposite coatings. Full article
(This article belongs to the Special Issue Mechanical Properties of Nanostructured Coatings)
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Open AccessFeature PaperArticle
Gas Sensing with Nanoplasmonic Thin Films Composed of Nanoparticles (Au, Ag) Dispersed in a CuO Matrix
Coatings 2019, 9(5), 337; https://doi.org/10.3390/coatings9050337 (registering DOI)
Received: 6 May 2019 / Revised: 22 May 2019 / Accepted: 23 May 2019 / Published: 25 May 2019
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Abstract
Magnetron sputtered nanocomposite thin films composed of monometallic Au and Ag, and bimetallic Au-Ag nanoparticles, dispersed in a CuO matrix, were prepared, characterized, and tested, which aimed to find suitable nano-plasmonic platforms capable of detecting the presence of gas molecules. The Localized Surface [...] Read more.
Magnetron sputtered nanocomposite thin films composed of monometallic Au and Ag, and bimetallic Au-Ag nanoparticles, dispersed in a CuO matrix, were prepared, characterized, and tested, which aimed to find suitable nano-plasmonic platforms capable of detecting the presence of gas molecules. The Localized Surface Plasmon Resonance phenomenon, LSPR, induced by the morphological changes of the nanoparticles (size, shape, and distribution), and promoted by the thermal annealing of the films, was used to tailor the sensitivity to the gas molecules. Results showed that the monometallic films, Au:CuO and Ag:CuO, present LSPR bands at ~719 and ~393 nm, respectively, while the bimetallic Au-Ag:CuO film has two LSPR bands, which suggests the presence of two noble metal phases. Through transmittance-LSPR measurements, the bimetallic films revealed to have the highest sensitivity to the refractive index changes, as well as high signal-to-noise ratios, respond consistently to the presence of a test gas. Full article
(This article belongs to the Special Issue Advanced Strategies in Thin Film Engineering by Magnetron Sputtering)
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Open AccessArticle
Effect of Heating Treatment on the Microstructure and Properties of Cr–Mo Duplex-Alloyed Coating Prepared by Double Glow Plasma Surface Alloying
Coatings 2019, 9(5), 336; https://doi.org/10.3390/coatings9050336 (registering DOI)
Received: 18 May 2019 / Revised: 23 May 2019 / Accepted: 23 May 2019 / Published: 25 May 2019
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Abstract
In this study, Cr–Mo duplex-alloyed coating was prepared on carbon steel by double glow plasma surface alloying (DGPSA). The effect of annealing and quenching and tempering (Q&T) treatments on the microstructure and performance of the coating was investigated by X-ray diffraction (XRD), energy [...] Read more.
In this study, Cr–Mo duplex-alloyed coating was prepared on carbon steel by double glow plasma surface alloying (DGPSA). The effect of annealing and quenching and tempering (Q&T) treatments on the microstructure and performance of the coating was investigated by X-ray diffraction (XRD), energy dispersive spectrometry (EDS), backscattering electron imaging (BSEI) and electron backscattering diffraction (EBSD) techniques. The results show that a gradient structured coating composed of an Fe–Cr–Mo solid solution (Fe–Cr–Mo SS) layer and an alloyed pearlite layer was obtained on the steel surface. The affected layer was adjacent to the coating. After annealing or Q&T, more carbides precipitated in the Fe–Cr–Mo SS layer and alloyed pearlite layer. Most of the C atoms in the subsurface were dragged into the coating to form carbides in the Fe–Cr–Mo SS and alloyed pearlite layers of the coating, transforming the affected layers into a carbon-poor zone. Annealing and Q&T hardly modified the thickness of the coating, but greatly changed the hardness and corrosion resistance of the coating. The Q&T treated samples had higher hardness and better corrosion resistance than the as-DGPSA treated and the annealed samples. Full article
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Open AccessReview
Current Status on Pulsed Laser Deposition of Coatings from Animal-Origin Calcium Phosphate Sources
Coatings 2019, 9(5), 335; https://doi.org/10.3390/coatings9050335
Received: 30 April 2019 / Revised: 16 May 2019 / Accepted: 22 May 2019 / Published: 24 May 2019
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Abstract
The aim of this paper is to present the current status on animal-origin hydroxyapatite (HA) coatings synthesized by Pulsed Laser Deposition (PLD) technique for medical implant applications. PLD as a thin film synthesis method, although limited in terms of surface covered area, still [...] Read more.
The aim of this paper is to present the current status on animal-origin hydroxyapatite (HA) coatings synthesized by Pulsed Laser Deposition (PLD) technique for medical implant applications. PLD as a thin film synthesis method, although limited in terms of surface covered area, still gathers interest among researchers due to its advantages such as stoichiometric transfer, thickness control, film adherence, and relatively simple experimental set-up. While animal-origin HA synthesized by bacteria or extracted from animal bones, eggshells, and clams was tested in the form of thin films or scaffolds as a bioactive agent before, the reported results on PLD coatings from HA materials extracted from natural sources were not gathered and compared until the present study. Since natural apatite contains trace elements and new functional groups, such as CO32– and HPO42– in its complex molecules, physical-chemical results on the transfer of animal-origin HA by PLD are extremely interesting due to the stoichiometric transfer possibilities of this technique. The points of interest of this paper are the origin of HA from various sustainable resources, the extraction methods employed, the supplemental functional groups, and ions present in animal-origin HA targets and coatings as compared to synthetic HA, the coatings’ morphology function of the type of HA, and the structure and crystalline status after deposition (where properties were superior to synthetic HA), and the influence of various dopants on these properties. The most interesting studies published in the last decade in scientific literature were compared and morphological, elemental, structural, and mechanical data were compiled and interpreted. The biological response of different types of animal-origin apatites on a variety of cell types was qualitatively assessed by comparing MTS assay data of various studies, where the testing conditions were possible. Antibacterial and antifungal activity of some doped animal-origin HA coatings was also discussed. Full article
(This article belongs to the Special Issue Current Research in Pulsed Laser Deposition)
Open AccessArticle
Characterization of Sol-Gel Derived Calcium Hydroxyapatite Coatings Fabricated on Patterned Rough Stainless Steel Surface
Coatings 2019, 9(5), 334; https://doi.org/10.3390/coatings9050334
Received: 16 April 2019 / Revised: 14 May 2019 / Accepted: 21 May 2019 / Published: 24 May 2019
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Abstract
Sol-gel derived calcium hydroxyapatite (Ca10(PO4)6(OH)2; CHA) thin films were deposited on stainless steel substrates with transverse and longitudinal patterned roughness employing a spin-coating technique. Each layer in the preparation of CHA multilayers was separately annealed [...] Read more.
Sol-gel derived calcium hydroxyapatite (Ca10(PO4)6(OH)2; CHA) thin films were deposited on stainless steel substrates with transverse and longitudinal patterned roughness employing a spin-coating technique. Each layer in the preparation of CHA multilayers was separately annealed at 850 °C in air. Fabricated CHA coatings were placed in simulated body fluid (SBF) for 2, 3, and 4 weeks and investigated after withdrawal. For the evaluation of obtained and treated with SBF coatings, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), X-ray diffraction (XRD) analysis, Raman spectroscopy, XPS spectroscopy, scanning electron microscopy (SEM) analysis, and contact angle measurements were used. The tribological properties of the CHA coatings were also investigated in this study. Full article
(This article belongs to the Special Issue Functional Ceramic Coatings)
Open AccessArticle
Antifungal Starch–Gellan Edible Coatings with Thyme Essential Oil for the Postharvest Preservation of Apple and Persimmon
Coatings 2019, 9(5), 333; https://doi.org/10.3390/coatings9050333
Received: 9 May 2019 / Revised: 20 May 2019 / Accepted: 21 May 2019 / Published: 24 May 2019
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Abstract
Starch–gellan (80:20) coating formulations were applied to apples and persimmons to analyse their effectiveness controlling the weight loss, respiration rate, fruit firmness, and fungal decay during postharvest. Thyme essential oil (EO) was incorporated (0.25 and 0.5 g per g of polymer) directly or [...] Read more.
Starch–gellan (80:20) coating formulations were applied to apples and persimmons to analyse their effectiveness controlling the weight loss, respiration rate, fruit firmness, and fungal decay during postharvest. Thyme essential oil (EO) was incorporated (0.25 and 0.5 g per g of polymer) directly or encapsulated in lecithin to enhance antifungal action. Coatings did not reduce weight loss or firmness changes in apples, but they prevented water loss in persimmons. In contrast, no significant effect of the coatings was observed on the respiration rates and the respiration quotient of persimmons, whereas the respiration rates and quotient was increased in apples. On the other hand, the coatings without lecithin reduced the incidence and severity of black spot caused by Alternaria alternata in persimmons, regardless of the content of essential oil. Likewise, these reduced the severity of gray mold caused by Botrytis cinerea in apples. No positive effect of lecithin in coatings was observed on the postharvest quality and decay in either apples or persimmons, nor did EO exert antifungal action despite its proven effectiveness in in vitro tests. Full article
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Open AccessArticle
Flow Kinetics of Molten Silicates through Thermal Barrier Coating: A Numerical Study
Coatings 2019, 9(5), 332; https://doi.org/10.3390/coatings9050332
Received: 16 April 2019 / Revised: 20 May 2019 / Accepted: 21 May 2019 / Published: 23 May 2019
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Abstract
Infiltration of molten calcium–magnesium–alumina–silicates (CMAS) through thermal barrier coatings (TBCs) causes structural degradation of TBC layers. The infiltration kinetics can be altered by careful tailoring of the electron beam physical vapor deposition (EB-PVD) microstructure such as feather arm lengths and inter-columnar gaps, etc. [...] Read more.
Infiltration of molten calcium–magnesium–alumina–silicates (CMAS) through thermal barrier coatings (TBCs) causes structural degradation of TBC layers. The infiltration kinetics can be altered by careful tailoring of the electron beam physical vapor deposition (EB-PVD) microstructure such as feather arm lengths and inter-columnar gaps, etc. Morphology of the feathery columns and their inherent porosities directly influences the infiltration kinetics of molten CMAS. To understand the influence of columnar morphology on the kinetics of the CAMS flow, a finite element based parametric model was developed for describing a variety of EB-PVD top coat microstructures. A detailed numerical study was performed considering fluid-solid interactions (FSI) between the CMAS and TBC top coat (TC). The CMAS flow characteristics through these microstructures were assessed quantitatively and qualitatively. Finally, correlations between the morphological parameters and CMAS flow kinetics were established. It was shown that the rate of longitudinal and lateral infiltration could be minimized by reducing the gap between columns and increasing the length of the feather arms. The results also show that the microstructures with long feather arms having a lower lateral inclination decrease the CMAS infiltration rate, therefore, reduce the CMAS infiltration depth. The analyses allow the identification of key morphological features that are important for mitigating the CMAS infiltration. Full article
(This article belongs to the Special Issue Environmental Barrier Coatings)
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Open AccessArticle
The Effect of Transglutaminase to Improve the Quality of Either Traditional or Pectin-Coated Falafel (Fried Middle Eastern Food)
Coatings 2019, 9(5), 331; https://doi.org/10.3390/coatings9050331
Received: 16 April 2019 / Revised: 13 May 2019 / Accepted: 21 May 2019 / Published: 23 May 2019
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Abstract
In this study, the effect of transglutaminase (TGase) (5 or 20 U/g of chickpea proteins) on falafel dough was investigated. The resulting falafel balls were either treated or not by dipping them into a pectin (PEC 1%) coating solution. Acrylamide (ACR), oil, and [...] Read more.
In this study, the effect of transglutaminase (TGase) (5 or 20 U/g of chickpea proteins) on falafel dough was investigated. The resulting falafel balls were either treated or not by dipping them into a pectin (PEC 1%) coating solution. Acrylamide (ACR), oil, and water content were then evaluated. Texture profile analyses and in vitro gastric digestion experiments were also carried out. The ACR content was reduced by 10.8% and by 34.4% in the samples prepared with 5 and 20 U TGase/g, respectively. In PEC-coated samples, the reduction of ACR was equal to 59.3%, 65.3%, and 84.5%, in falafel balls prepared either without TGase or containing 5 U or 20 U of the enzyme, respectively. However, TGase treatment did not affect oil content, while the PEC coating reduced oil uptake by 23.5%. No difference was observed in the texture properties between the control sample and the one dipped in PEC, while these properties changed in samples prepared with the enzyme. Finally, digestion studies, carried out under physiological conditions, demonstrated that the falafels prepared in the presence of TGase were efficiently digested in the gastric environment. Full article
(This article belongs to the Special Issue Coatings and Interfacial Films for Food Applications)
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Open AccessArticle
The CRATI Project: New Insights on the Consolidation of Salt Weathered Stone and the Case Study of San Domenico Church in Cosenza (South Calabria, Italy)
Coatings 2019, 9(5), 330; https://doi.org/10.3390/coatings9050330
Received: 16 April 2019 / Revised: 8 May 2019 / Accepted: 20 May 2019 / Published: 22 May 2019
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Abstract
This paper presents the results of a laboratory experimentation carried out on stone materials in the framework of the CRATI project (Knowledge and Restoration through Advanced Integrated Technologies) aimed at testing new products with consolidating properties by means of an integrated methodological approach. [...] Read more.
This paper presents the results of a laboratory experimentation carried out on stone materials in the framework of the CRATI project (Knowledge and Restoration through Advanced Integrated Technologies) aimed at testing new products with consolidating properties by means of an integrated methodological approach. After the preliminary characterization of stone materials collected in the pilot site, the second stage of the activities within the project were focused on the formulation and testing of products for the conservation of the same materials against decay, especially salt crystallization, one of the most aggressive and common degrading processes. The San Domenico Church, located in the old town of Cosenza (Calabria, Southern Italy) has been chosen as the pilot site and for the in situ tests. Several specimens with the same features of the stone materials used in San Domenico church were collected from a historical quarry near the city of Cosenza. These specimens were treated and then artificially degraded by salt crystallization tests in order to evaluate their susceptibility to weathering intensity. Three different consolidating products were used; respectively, two commercial and another one formulated in laboratory: (a) a suspension of nanosilica (Nano Estel®); (b) a suspension of nanolime (CaLoSiL®), and (c) a suspension of nano calcium-hydroxide dispersed in isopropyl alcohol and then mixed with diammonium hydrogen phosphate. A systematic approach, including minero-petrographic, geochemical and physico-mechanical techniques, was applied to evaluate (a) the nature and main features of materials; (b) the efficacy of consolidating treatments, and (c) the resistance of treated stone to the salt crystallization processes. The tested products demonstrated a significant efficiency to consolidate and protect stone material samples, enhancing their resistance to salt crystallization. Thus, such a case history may be useful in order to plan appropriate restoration interventions that consider the interactions between the building stone and the protective/consolidating product. Full article
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Open AccessArticle
The Effects of Ti Additions and Deposition Parameters on the Structural and Mechanical Properties of Stainless Steel-Nitride Thin Films
Coatings 2019, 9(5), 329; https://doi.org/10.3390/coatings9050329
Received: 1 April 2019 / Revised: 9 May 2019 / Accepted: 16 May 2019 / Published: 21 May 2019
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Abstract
This study examines the structure and properties of stainless steel coatings deposited to incorporate large concentrations of nitrogen along with varying amounts of titanium. Deposition was carried out using magnetron co-sputtering of stainless steel and titanium from separate targets in a mixed Ar/N [...] Read more.
This study examines the structure and properties of stainless steel coatings deposited to incorporate large concentrations of nitrogen along with varying amounts of titanium. Deposition was carried out using magnetron co-sputtering of stainless steel and titanium from separate targets in a mixed Ar/N2 gas atmosphere. Composition analysis by X-ray photoelectron spectroscopy showed that while films with up to 4 at.% Ti exhibited little change in nitrogen content (compared to films deposited without Ti) and remained sub-stoichiometric with respect to N content. Films with 7–8 at.% Ti had a higher N level and further increasing the Ti level to 11–12 at.% resulted in stoichiometric N levels. X-ray diffraction showed that the films all had a nominally FCC structure with no additional phases. However, the peak locations for the (111) and (200) reflections indicated a distorted lattice characteristic of the S-phase, with calculated c/a values ranging from 1.007 to 1.033. The Ti additions, along with the corresponding increase in N content, helped reduce the extent of lattice distortion. The film microstructure of the higher (11–12 at.%) Ti films also showed higher density, lower surface roughness, and a finer grain structure. As a result, these films had a higher hardness compared to the sub-stoichiometric films, with hardness levels in the range of 18–23 GPa, typical of transition metal nitrides coatings. Full article
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Open AccessArticle
Layered Double Hydroxide Clusters as Precursors of Novel Multifunctional Layers: A Bottom-Up Approach
Coatings 2019, 9(5), 328; https://doi.org/10.3390/coatings9050328
Received: 26 April 2019 / Revised: 14 May 2019 / Accepted: 16 May 2019 / Published: 21 May 2019
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Abstract
The specific microstructure of aluminum alloys is herein explored to grow spatially-resolved layered double hydroxide (SR-LDH) clusters on their surface. Upon chemical modification of LDHs via intercalation, adsorption and grafting with different functional molecules, novel surface-engineered surfaces were obtained. Crystal structure and phase [...] Read more.
The specific microstructure of aluminum alloys is herein explored to grow spatially-resolved layered double hydroxide (SR-LDH) clusters on their surface. Upon chemical modification of LDHs via intercalation, adsorption and grafting with different functional molecules, novel surface-engineered surfaces were obtained. Crystal structure and phase composition were analyzed by X-ray diffraction (XRD) and surface morphology was observed by scanning electron microscopy (SEM). X-ray photoelectron spectroscopy (XPS) and glow discharge optical emission spectrometry (GDOES) were used to correlate structural changes upon ion-exchange and interfacial modifications with chemical composition and surface profiles of the SR-LDH films, respectively. The protection conferred by these films against localized corrosion was investigated at microscale using the scanning vibrating electrode technique (SVET). LDH-NO3 phase was obtained by direct growth onto AA2024 surface, as evidenced by (003) and (006) XRD diffraction reflections. After anion exchange of nitrate with 2-mercaptobenzothiazole (MBT) there was a decrease in the SR-LDH thickness inferred from GDOES profiles. The subsequent surface functionalization with HTMS was confirmed by the presence of Si signal in XPS and GDOES analyses, leading to an increase in the water contact angle (c.a 144° ± 3°). SVET measurements of the SR-LDH films revealed exceptional corrosion resistance, whereas the bioluminescent bacteria assay proved the anti-microbial character of the obtained films. Overall the results obtained show an effective corrosion protection of the SR-LDHs when compared to the bare substrate and the potential of these films for biofouling applications as new Cr-free pre-treatments. Full article
(This article belongs to the Special Issue Advanced Hybrid Coatings and Thin Films for Surface Functionalization)
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Open AccessArticle
Icariin-Functionalized Coating on TiO2 Nanotubes Surface to Improve Osteoblast Activity In Vitro and Osteogenesis Ability In Vivo
Coatings 2019, 9(5), 327; https://doi.org/10.3390/coatings9050327
Received: 24 April 2019 / Revised: 14 May 2019 / Accepted: 15 May 2019 / Published: 18 May 2019
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Abstract
Surface modification of titanium is encouraged to facilitate early osseointegration in dental and orthopedic fields. Icariin is the main active constituents of Herba Epimedii, which has good bone-promoting ability. We established an icariin-functionalized coating composed of icariin and poly (lactic-co-glycolic acid) (PLGA) on [...] Read more.
Surface modification of titanium is encouraged to facilitate early osseointegration in dental and orthopedic fields. Icariin is the main active constituents of Herba Epimedii, which has good bone-promoting ability. We established an icariin-functionalized coating composed of icariin and poly (lactic-co-glycolic acid) (PLGA) on TiO2 nanotubes surface (NT-ICA-PLGA) to promote osteoblast cell activity and early osseointegration. Surface topography, wettability and drug release pattern of the established NT-ICA-PLGA surface were characterized by scanning electron microscopy (SEM), contact angle test and drug release test. MC3T3-E1 osteoblast cell activity tests were performed using SEM, immunofluorescent staining, cell counting kit-8 and alkaline phosphatase assays. The osteogenic effects of different surfaces were observed using a rat model. Surface characterization proved the successful fabrication of the icariin-functionalized coating on the TiO2 nanotube structure, with increased wettability. The NT-ICA-PLGA substrate showed sustained release of icariin until two weeks. Osteoblast cells grown on the NT-ICA-PLGA substrate displayed improved cell adhesion, proliferation and differentiation ability than the control Ti surface. The in vivo experiment also revealed superior bone forming ability on the NT-ICA-PLGA surface, compared to the pure Ti control. These results imply that the developed NT-ICA-PLGA substrate has a promising future use as functionalized coating for implant surface modification. Full article
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Open AccessCommunication
Differentiating Generic versus Branded Pharmaceutical Tablets Using Ultra-High-Resolution Optical Coherence Tomography
Coatings 2019, 9(5), 326; https://doi.org/10.3390/coatings9050326
Received: 7 April 2019 / Revised: 14 May 2019 / Accepted: 15 May 2019 / Published: 17 May 2019
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Abstract
Optical coherence tomography (OCT) has recently been demonstrated as a powerful tool to image through pharmaceutical film coatings. Majority of the existing systems can, however, resolve film coatings for thickness greater than 10 µm. Here we report on an ultra-high-resolution (UHR) OCT system, [...] Read more.
Optical coherence tomography (OCT) has recently been demonstrated as a powerful tool to image through pharmaceutical film coatings. Majority of the existing systems can, however, resolve film coatings for thickness greater than 10 µm. Here we report on an ultra-high-resolution (UHR) OCT system, with 1 µm axial and 1.6 µm lateral resolutions, which can resolve thin coatings at approximately 4 µm. We further demonstrate a novel application of the system for differentiating generic and branded suppliers of paracetamol tablets. Full article
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Open AccessArticle
Doped PANI Coated Nano-Ag Electrode for Rapid In-Situ Detection of Bromide in Seawater
Coatings 2019, 9(5), 325; https://doi.org/10.3390/coatings9050325
Received: 7 April 2019 / Revised: 11 May 2019 / Accepted: 16 May 2019 / Published: 17 May 2019
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Abstract
In this paper, we successfully fabricated a novel bromide ion selective electrode (Br-ISE), which was coated by bromine ion doped polyaniline as sensitive film. Using Ag wire as the substrate, a uniform and dense nano-silver layer was electroplated to enhance the specific surface [...] Read more.
In this paper, we successfully fabricated a novel bromide ion selective electrode (Br-ISE), which was coated by bromine ion doped polyaniline as sensitive film. Using Ag wire as the substrate, a uniform and dense nano-silver layer was electroplated to enhance the specific surface area of the electrode. Subsequently, a polyaniline (PANI) film was coated onto the electrode by cyclic voltammetry in a 0.3 M aniline and 1 M HCl solution and was in-situ doped by 0.1 M KBr solution. The morphology and performance of the electrode were characterized by scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), and other electrochemical analysis methods, respectively. The prepared Br-ISE exhibited a wide linear dynamic range between 1.0 × 10−1 and 1.0 × 10−7 M with a near-Nernst slope of 57.33 mV/decade. In addition, the electrode possessed extremely fast response time (<1 s) and low impedance (300 Ω), high sensitivity, and good selectivity. The electrode potential drifted within 2 mV in 8 h. The lifespan was larger than three months. Full article
(This article belongs to the Special Issue Corrosion and Electrochemical Behavior of Metals Coating)
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Open AccessArticle
Experiment Study of Rapid Laser Polishing of Freeform Steel Surface by Dual-Beam
Coatings 2019, 9(5), 324; https://doi.org/10.3390/coatings9050324
Received: 28 April 2019 / Revised: 11 May 2019 / Accepted: 13 May 2019 / Published: 16 May 2019
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Abstract
One of the challenges regarding widespread use of parts made from alloy steel is their time-consuming polishing process. A rough freeform surface of part has been often expected to be polished rapidly up to a smooth surface finish. The focus of this study [...] Read more.
One of the challenges regarding widespread use of parts made from alloy steel is their time-consuming polishing process. A rough freeform surface of part has been often expected to be polished rapidly up to a smooth surface finish. The focus of this study is to develop a fast polishing method of freeform surface by using dual-beam lasers. The dual-beam laser system consists of continuous laser (CW) and pulsed laser based on a five-axis CNC device. In this study, a series of experiments of CW laser polishing present the effects of different spot irradiation on surface topography, then the combination trajectory of zigzag and square waveform of pulsed laser is explored to realize a “melting peak for filling into valley” (MPFV) method. The polishing experiment on a semisphere of S136H steel polished by dual-beam shows that a rough semisphere surface was rapidly polished from initial state value of Sa (=877 nm) to post-polished value of Sa (=142 nm), and the polishing efficiency is as high as 2890 cm2/H. Full article
(This article belongs to the Special Issue Surface Treatment by Laser-Assisted Techniques)
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Open AccessArticle
Improvements of Nano-TiO2 on the Long-Term Chloride Resistance of Concrete with Polymer Coatings
Coatings 2019, 9(5), 323; https://doi.org/10.3390/coatings9050323
Received: 1 May 2019 / Revised: 11 May 2019 / Accepted: 15 May 2019 / Published: 16 May 2019
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Abstract
The long-term chloride resistance of concrete treated with nano-TiO2-modified polymer coatings was studied. Three types of organic film-forming paints: polyurethane, epoxy resin, and chlorinated rubber were selected, and concrete specimens with nano-TiO2-modified coatings were fabricated. Then, specimens were subjected [...] Read more.
The long-term chloride resistance of concrete treated with nano-TiO2-modified polymer coatings was studied. Three types of organic film-forming paints: polyurethane, epoxy resin, and chlorinated rubber were selected, and concrete specimens with nano-TiO2-modified coatings were fabricated. Then, specimens were subjected to periodical ultraviolet-accelerated aging and subsequent Coulomb electric flux experiments. Nanomodified coatings before and after ultraviolet aging were observed through scanning electron microcopy. Results indicate that the nano-TiO2 particles can effectively reduce the microdefects in coating films and alleviate damages due to aging. As a result, nano-TiO2 can significantly reduce the Coulomb fluxes of coated concrete before and after coating aging, and the average reduction amplitudes reached 66% and 44%. That is, nano-TiO2 can remarkably improve the long-term chloride resistance of coated concrete. In addition, we established the development models of the ultraviolet aging and chloride resistance of coated concrete according to an S-shaped curve. Full article
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Open AccessArticle
Glycerol-Plasticized Films Obtained from Whey Proteins Denatured at Alkaline pH
Coatings 2019, 9(5), 322; https://doi.org/10.3390/coatings9050322
Received: 11 April 2019 / Revised: 12 May 2019 / Accepted: 14 May 2019 / Published: 16 May 2019
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Abstract
Whey represents the major by-product of cheese industry. One possibility to recycle the whey wastes is the use of their globular proteins as a polymer source for the production of biodegradable plastic materials. Whey protein (WP)-based films are usually obtained by protein heat [...] Read more.
Whey represents the major by-product of cheese industry. One possibility to recycle the whey wastes is the use of their globular proteins as a polymer source for the production of biodegradable plastic materials. Whey protein (WP)-based films are usually obtained by protein heat treatment in the presence of glycerol (GLY) as plasticizer at pH 7, a method which would require commercially high costing process. In this work we explored the possibility of producing manageable whey-derived materials without any heat-treatment but under alkaline conditions. The reported results demonstrated that the casting at pH 12 of the unheated WP film forming solutions (FFSs), containing either 40% or 50% GLY, led to produce more resistant and flexible materials than the ones obtained at pH 7. Film opacity was observed significantly increased, being higher in the samples obtained at alkaline pH without WP heating and with higher GLY concentrations. Finally, moisture content decreased with the reduction of GLY content, both in heated and unheated WP-based films, whereas water uptake of the different films prepared at pH 12 did not significantly change. Full article
(This article belongs to the Special Issue Edible Films and Coatings: Fundamentals and Applications)
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Open AccessArticle
Synthesis and Characteristics of Zn-Doped CuCrO2 Transparent Conductive Thin Films
Coatings 2019, 9(5), 321; https://doi.org/10.3390/coatings9050321
Received: 23 February 2019 / Revised: 18 April 2019 / Accepted: 30 April 2019 / Published: 15 May 2019
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Abstract
The effects of doping a p-type CuCrO2 film with zinc on its structural and optoelectronic properties were investigated by experiments using CuCr1−xZnxO2 thin films (x = 0, 0.025, 0.065, 0.085). An increase in the amount [...] Read more.
The effects of doping a p-type CuCrO2 film with zinc on its structural and optoelectronic properties were investigated by experiments using CuCr1−xZnxO2 thin films (x = 0, 0.025, 0.065, 0.085). An increase in the amount of zinc dopant in the thin films affected the lattice constant and increased its Gibbs free energy of phase transformation. Cross-sectional images of the CuCrO2 thin film samples exhibited a dense polygonal microstructure and a surface morphology with protruding nanoscale granules. With the increase in the amount of Zn dopant, the surface roughness decreased, thereby increasing the amount of incident photons as well as the visible-light transmittance and ultraviolet-light absorption of the thin films. With the zinc doping in the CuCrO2 thin films, the band gap increased from 3.09 to 3.11 eV. The substitution of Cr3+ with Zn2+ forms hole carriers in the crystals, which was demonstrated by X-ray photoelectron spectroscopy and Hall effect measurements. The conductivities and carrier concentrations of the Zn-doped CuCrO2 thin films were greater than those of undoped CuCrO2. The CuCr1−xZnxO2 film (x = 0.065) exhibited the best optoelectronic properties; its carrier concentration and resistivity were 1.88 × 1017 cm−3 and 3.82 Ωcm, respectively. Full article
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Open AccessArticle
Reactive-Sputtered Prepared Tin Oxide Thin Film as an Electron Transport Layer for Planar Perovskite Solar Cells
Coatings 2019, 9(5), 320; https://doi.org/10.3390/coatings9050320
Received: 21 March 2019 / Revised: 29 April 2019 / Accepted: 6 May 2019 / Published: 14 May 2019
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Abstract
Currently, tin oxide (SnO2) is a highly sought-after semiconductor material used in perovskite solar cells (PSCs) because of its good transmittance, the appropriate energy level, high electron mobility, high conductivity, ideal band gap and excellent chemical stability. In this study, SnO [...] Read more.
Currently, tin oxide (SnO2) is a highly sought-after semiconductor material used in perovskite solar cells (PSCs) because of its good transmittance, the appropriate energy level, high electron mobility, high conductivity, ideal band gap and excellent chemical stability. In this study, SnO2 film was successfully prepared by radio frequency reactive magnetron sputtering (RS) under room temperature conditions. The obtained SnO2 thin films not only exhibited high transmittance in the visible region as well as the pure phase, but also had a suitable energy band structure and lower surface roughness than FTO (SnO2:F) glass substrate, which contributes to the improvement of the adjacent interface morphology. The SnO2 films prepared by reactive sputtering could effectively suppress carrier recombination and act as an electron transport layer. Moreover, the maximum efficiency of the device based on reactive sputtering of SnO2 as the electron transport layer (ETL) for planar perovskite solar cells (PSCs) was 14.63%. This study mainly described the preparation of SnO2 by reactive sputtering under room temperature conditions. Full article
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Open AccessArticle
Synthesis and Characterization of a Polyurethane Phase Separated to Nano Size in an Epoxy Polymer
Coatings 2019, 9(5), 319; https://doi.org/10.3390/coatings9050319
Received: 2 April 2019 / Revised: 22 April 2019 / Accepted: 7 May 2019 / Published: 13 May 2019
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Abstract
Epoxy resins are widely applicable in the aircraft, automobile, coating, and adhesive industries because of their good chemical resistance and excellent mechanical and thermal properties. However, upon external impact, the crack propagation of epoxy polymers weakens the overall impact resistance of these materials. [...] Read more.
Epoxy resins are widely applicable in the aircraft, automobile, coating, and adhesive industries because of their good chemical resistance and excellent mechanical and thermal properties. However, upon external impact, the crack propagation of epoxy polymers weakens the overall impact resistance of these materials. Therefore, many impact modifiers have been developed to reduce the brittleness of epoxy polymers. Polyurethanes, as impact modifiers, can improve the toughness of polymers. Although it is well known that polyurethanes (PUs) are phase-separated in the polymer matrix after curing, connecting PUs to the polymer matrix for enhancing the mechanical properties of polymers has proven to be challenging. In this study, we introduced epoxy functional groups into polyol backbones, which is different from other studies that focused on modifying capping agents to achieve a network structure between the polymer matrix and PU. We confirmed the molecular weight of the prepared PU via gel permeation chromatography. Moreover, the prepared material was added to the epoxies and the resulting mechanical and thermal properties of the materials were evaluated. Furthermore, we conducted tensile, flexural strength, and impact resistance measurements. The addition of PU to the epoxy compositions enhanced their impact strength and maintained their mechanical strength up to 10 phr of PU. Furthermore, the morphologies observed with field emission scanning electron microscopy and transmission electron microscopy proved that the PU was phase separated in the epoxy matrix. Full article
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Open AccessArticle
Channel Characteristics of InAs/AlSb Heterojunction Epitaxy: Comparative Study on Epitaxies with Different Thickness of InAs Channel and AlSb Upper Barrier
Coatings 2019, 9(5), 318; https://doi.org/10.3390/coatings9050318
Received: 11 April 2019 / Revised: 7 May 2019 / Accepted: 9 May 2019 / Published: 13 May 2019
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Abstract
Because of the high electron mobility and electron velocity in the channel, InAs/AlSb high electron mobility transistors (HEMTs) have excellent physical properties, compared with the other traditional III-V semiconductor components, such as ultra-high cut-off frequency, very low power consumption and good noise performance. [...] Read more.
Because of the high electron mobility and electron velocity in the channel, InAs/AlSb high electron mobility transistors (HEMTs) have excellent physical properties, compared with the other traditional III-V semiconductor components, such as ultra-high cut-off frequency, very low power consumption and good noise performance. In this paper, both the structure and working principle of InAs/AlSb HEMTs were studied, the energy band distribution of the InAs/AlSb heterojunction epitaxy was analyzed, and the generation mechanism and scattering mechanism of two-dimensional electron gas (2DEG) in InAs channel were demonstrated, based on the software simulation in detail. In order to discuss the impact of different epitaxial structures on the 2DEG and electron mobility in channel, four kinds of epitaxies with different thickness of InAs channel and AlSb upper-barrier were manufactured. The samples were evaluated with the contact Hall test. It is found the sample with a channel thickness of 15 nm and upper-barrier layer of 17 nm shows a best compromised sheet carrier concentration of 2.56 × 1012 cm−2 and electron mobility of 1.81 × 104 cm2/V·s, and a low sheet resistivity of 135 Ω/□, which we considered to be the optimized thickness of channel layer and upper-barrier layer. This study is a reference to further design InAs/AlSb HEMT, by ensuring a good device performance. Full article
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Open AccessArticle
Structure and Conductivity Studies of Scandia and Alumina Doped Zirconia Thin Films
Coatings 2019, 9(5), 317; https://doi.org/10.3390/coatings9050317
Received: 22 March 2019 / Revised: 2 May 2019 / Accepted: 8 May 2019 / Published: 12 May 2019
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Abstract
In this work, scandia-doped zirconia (ScSZ) and scandia–alumina co-doped zirconia (ScSZAl) thin films were prepared by electron beam vapor deposition. X-ray diffraction (XRD) results indicated a presence of ZrO2 cubic phase structure, yet Raman analysis revealed the existence of secondary tetragonal and [...] Read more.
In this work, scandia-doped zirconia (ScSZ) and scandia–alumina co-doped zirconia (ScSZAl) thin films were prepared by electron beam vapor deposition. X-ray diffraction (XRD) results indicated a presence of ZrO2 cubic phase structure, yet Raman analysis revealed the existence of secondary tetragonal and rhombohedral phases. Thus, XRD measurements were supported by Raman spectroscopy in order to comprehensively analyze the structure of formed ScSZ and ScSZAl thin films. It was also found that Al dopant slows down the formation of the cubic phase. The impedance measurements affirmed the correlation of the amount of secondary phases with the conductivity results and nonlinear crystallite size dependence. Full article
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Open AccessArticle
Study of Birefringence and Stress Distribution of SiO2 Film Optical Waveguide on Silicon Wafer
Coatings 2019, 9(5), 316; https://doi.org/10.3390/coatings9050316
Received: 10 April 2019 / Revised: 5 May 2019 / Accepted: 8 May 2019 / Published: 10 May 2019
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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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Open AccessArticle
Optical Analysis of RF Sputtering Plasma through Colour Characterization
Coatings 2019, 9(5), 315; https://doi.org/10.3390/coatings9050315
Received: 24 February 2019 / Revised: 30 April 2019 / Accepted: 6 May 2019 / Published: 10 May 2019
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Abstract
The photometric properties of an radio frequency (RF)-based sputtering plasma source were monitored through optical spectroscopy. The colour of the plasma source was deduced based on conventional chromaticity index analysis and it was compared to the direct spectral data plots of the emission [...] Read more.
The photometric properties of an radio frequency (RF)-based sputtering plasma source were monitored through optical spectroscopy. The colour of the plasma source was deduced based on conventional chromaticity index analysis and it was compared to the direct spectral data plots of the emission peaks to investigate the possibility of characterising the plasma based on its specific colour and exploring the potential of defining a new method by which the plasma sputtering process can be addressed based on the plasma colour parameters. The intention of this investigation is to evaluate the possibility of simplifying the monitoring and assessment of the sputtering process for applied scientists operating plasma sputter deposition systems. We demonstrate a viable potential for this technique in terms of providing information regarding the stability of the plasma, chamber pressure, and plasma power; however, further work is underway to verify and assess a relationship between the quality of the thin film coating and the colour characteristics of the deposition plasma. Here, we only focus on the feasibility of such an approach and demonstrate interesting observations. We observed a linear relationship between the colour functions and the plasma power, while the stability of the sputtering plasma can be assessed based on the plasma colour functions. The colour functions also follow a unique pattern when the working gas pressure is increased. Full article
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Open AccessArticle
Observation of the Magnetization Reorientation in Self-Assembled Metallic Fe-Silicide Nanowires at Room Temperature by Spin-Polarized Scanning Tunneling Spectromicroscopy
Coatings 2019, 9(5), 314; https://doi.org/10.3390/coatings9050314
Received: 4 March 2019 / Revised: 5 May 2019 / Accepted: 8 May 2019 / Published: 10 May 2019
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Abstract
The quasi-periodic magnetic domains in metallic Fe-silicide nanowires self-assembled on the Si(110)-16 × 2 surface have been observed at room temperature by direct imaging of both the topographic and magnetic structures using spin-polarized scanning tunneling microscopy/spectroscopy. The spin-polarized differential conductance (dI/d [...] Read more.
The quasi-periodic magnetic domains in metallic Fe-silicide nanowires self-assembled on the Si(110)-16 × 2 surface have been observed at room temperature by direct imaging of both the topographic and magnetic structures using spin-polarized scanning tunneling microscopy/spectroscopy. The spin-polarized differential conductance (dI/dV) map of the rectangular-sectional Fe-silicide nanowire with a width and height larger than 36 and 4 nm, respectively, clearly shows an array of almost parallel streak domains that alternate an enhanced (reduced) density of states over in-plane (out-of-plane) magnetized domains with a magnetic period of 5.0 ± 1.0 nm. This heterostructure of magnetic Fe-silicide nanowires epitaxially integrated with the Si(110)-16 × 2 surface will have a significant impact on the development of Si-based spintronic nanodevices. Full article
(This article belongs to the Special Issue Metal-Semiconductor and Insulator-Semiconductor Interfaces)
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