Materials

14 pages, 7651 KiB

Open AccessEditor’s ChoiceArticle

The Microstructure and Strength of UFG 6060 Alloy after Superplastic Deformation at a Lower Homologous Temperature

by Elena V. Bobruk, Pavel D. Dolzhenko, Maxim Yu. Murashkin, Ruslan Z. Valiev and Nariman A. Enikeev

Materials 2022, 15(19), 6983; https://doi.org/10.3390/ma15196983 - 8 Oct 2022

Cited by 7 | Viewed by 2204

Abstract

The paper reports on the features of low-temperature superplasticity of the heat-treatable aluminum Al-Mg-Si alloy in the ultrafine-grained state at temperatures below 0.5 times the melting point as well as on its post-deformation microstructure and tensile strength. We show that the refined microstructure [...] Read more.

The paper reports on the features of low-temperature superplasticity of the heat-treatable aluminum Al-Mg-Si alloy in the ultrafine-grained state at temperatures below 0.5 times the melting point as well as on its post-deformation microstructure and tensile strength. We show that the refined microstructure is retained after superplastic deformation in the range of deformation temperatures of 120–180 °C and strain rates of 5 × 10^–3 s^–1–10^–4 s^–1. In the absence of noticeable grain growth, the ultrafine-grained alloy maintains the strength up to 380 MPa after SP deformation, which considerably exceeds the value (250 MPa) for the alloy in the peak-aged coarse-grain state. This finding opens pathways to form high-strength articles of Al-Mg-Si alloys after superplastic forming. Full article

(This article belongs to the Special Issue Recent Advances on Mechanical Properties and Microstructural Features of Alloy/Steel)

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18 pages, 8332 KiB

Open AccessEditor’s ChoiceArticle

Influence of Grain Orientation and Grain Boundary Features on Local Stress State of Cu-8Al-11Mn Alloy Investigated Using Crystal Plasticity Finite Element Method

by Ce Zheng, Lijun Xu, Xiaohui Feng, Qiuyan Huang, Yingju Li, Zhongwu Zhang and Yuansheng Yang

Materials 2022, 15(19), 6950; https://doi.org/10.3390/ma15196950 - 7 Oct 2022

Cited by 3 | Viewed by 2211

Abstract

Reducing the local stress in the vicinity of the grain boundaries is a favorable way to improve the super-elastic properties of super-elastic alloys. The crystal plasticity finite element method (CPFEM) was applied in this study to simulate the deformation behavior and local stress [...] Read more.

Reducing the local stress in the vicinity of the grain boundaries is a favorable way to improve the super-elastic properties of super-elastic alloys. The crystal plasticity finite element method (CPFEM) was applied in this study to simulate the deformation behavior and local stress of a super-elastic Cu-8Al-11Mn (wt.%) alloy containing single grains with various orientations, columnar grains with different misorientation angles, and tri-crystals with distinct grain boundary morphologies. The results indicated that the stress distribution of single grains presented obvious orientation dependence during deformation. Uniformly distributed stress was observed in grains with orientations of 0° and 90° when more slip systems were activated during deformation. With the increase in the misorientation angles of columnar grains, the stresses in the vicinity of the grain boundaries increased, which was related to the difference in the shear stress of the slip systems in adjacent grains. When the difference in the shear stress of the slip systems in two adjacent grains was large, a local stress concentration formed in the vicinity of the grain boundary. Compared with the triple-junction grain boundaries, the local stresses of the straight and vertical grain boundaries were smaller, which was closely related to the number of activated slip systems on both sides of the grain boundary. The above results were obtained experimentally and could be used to design super-elastic alloys with high performance. Full article

(This article belongs to the Special Issue Application of Advanced Metal-Forming Technology in Light-Weight Alloys)

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60 pages, 33352 KiB

Open AccessEditor’s ChoiceReview

The Influence of Surface Texturing of Ceramic and Superhard Cutting Tools on the Machining Process—A Review

by Sergey N. Grigoriev, Thet Naing Soe, Khaled Hamdy, Yuri Pristinskiy, Alexander Malakhinsky, Islamutdin Makhadilov, Vadim Romanov, Ekaterina Kuznetsova, Pavel Podrabinnik, Alexandra Yu. Kurmysheva, Anton Smirnov and Nestor Washington Solís Pinargote

Materials 2022, 15(19), 6945; https://doi.org/10.3390/ma15196945 - 6 Oct 2022

Cited by 9 | Viewed by 3287

Abstract

Machining is an indispensable manufacturing process for a wide range of engineering materials, such as metals, ceramics, and composite materials, in which the tool wear is a serious problem, which affects not only the costs and productivity but also the quality of the [...] Read more.

Machining is an indispensable manufacturing process for a wide range of engineering materials, such as metals, ceramics, and composite materials, in which the tool wear is a serious problem, which affects not only the costs and productivity but also the quality of the machined components. Thus, the modification of the cutting tool surface by application of textures on their surfaces is proposed as a very promising method for improving tool life. Surface texturing is a relatively new surface engineering technology, where microscale or nanoscale surface textures are generated on the cutting tool through a variety of techniques in order to improve tribological properties of cutting tool surfaces by reducing the coefficient of friction and increasing wear resistance. In this paper, the studies carried out to date on the texturing of ceramic and superhard cutting tools have been reviewed. Furthermore, the most common methods for creating textures on the surfaces of different materials have been summarized. Moreover, the parameters that are generally used in surface texturing, which should be indicated in all future studies of textured cutting tools in order to have a better understanding of its effects in the cutting process, are described. In addition, this paper proposes a way in which to classify the texture surfaces used in the cutting tools according to their geometric parameters. This paper highlights the effect of ceramic and superhard textured cutting tools in improving the machining performance of difficult-to-cut materials, such as coefficient of friction, tool wear, cutting forces, cutting temperature, and machined workpiece roughness. Finally, a conclusion of the analyzed papers is given. Full article

(This article belongs to the Special Issue Advanced Ceramics and Composites: Design, Structure, Processing, Properties, and Applications)

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13 pages, 3942 KiB

Open AccessEditor’s ChoiceArticle

Relation between Ga Vacancies, Photoluminescence, and Growth Conditions of MOVPE-Prepared GaN Layers

by Alice Hospodková, Jakub Čížek, František Hájek, Tomáš Hubáček, Jiří Pangrác, Filip Dominec, Karla Kuldová, Jan Batysta, Maciej O. Liedke, Eric Hirschmann, Maik Butterling and Andreas Wagner

Materials 2022, 15(19), 6916; https://doi.org/10.3390/ma15196916 - 5 Oct 2022

Cited by 6 | Viewed by 2313

Abstract

A set of GaN layers prepared by metalorganic vapor phase epitaxy under different technological conditions (growth temperature carrier gas type and Ga precursor) were investigated using variable energy positron annihilation spectroscopy (VEPAS) to find a link between technological conditions, GaN layer properties, and [...] Read more.

A set of GaN layers prepared by metalorganic vapor phase epitaxy under different technological conditions (growth temperature carrier gas type and Ga precursor) were investigated using variable energy positron annihilation spectroscopy (VEPAS) to find a link between technological conditions, GaN layer properties, and the concentration of gallium vacancies (V_Ga). Different correlations between technological parameters and V_Ga concentration were observed for layers grown from triethyl gallium (TEGa) and trimethyl gallium (TMGa) precursors. In case of TEGa, the formation of V_Ga was significantly influenced by the type of reactor atmosphere (N₂ or H₂), while no similar behaviour was observed for growth from TMGa. V_Ga formation was suppressed with increasing temperature for growth from TEGa. On the contrary, enhancement of V_Ga concentration was observed for growth from TMGa, with cluster formation for the highest temperature of 1100 °C. From the correlation of photoluminescence results with V_Ga concentration determined by VEPAS, it can be concluded that yellow band luminescence in GaN is likely not connected with V_Ga; additionally, increased V_Ga concentration enhances excitonic luminescence. The probable explanation is that V_Ga prevent the formation of some other highly efficient nonradiative defects. Possible types of such defects are suggested. Full article

(This article belongs to the Special Issue Growth and Characteristics of Nitride Semiconductor Layers)

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14 pages, 4224 KiB

Open AccessEditor’s ChoiceArticle

Selective Etching of Si versus Si_1−xGe_x in Tetramethyl Ammonium Hydroxide Solutions with Surfactant

by Yongjoon Choi, Choonghee Cho, Dongmin Yoon, Joosung Kang, Jihye Kim, So Young Kim, Dong Chan Suh and Dae-Hong Ko

Materials 2022, 15(19), 6918; https://doi.org/10.3390/ma15196918 - 5 Oct 2022

Viewed by 2958

Abstract

We investigated the selective etching of Si versus Si_1−xGe_x with various Ge concentrations (x = 0.13, 0.21, 0.30, 0.44) in tetramethyl ammonium hydroxide (TMAH) solution. Our results show that the Si_1−xGe_x with a higher Ge concentration was [...] Read more.

We investigated the selective etching of Si versus Si_1−xGe_x with various Ge concentrations (x = 0.13, 0.21, 0.30, 0.44) in tetramethyl ammonium hydroxide (TMAH) solution. Our results show that the Si_1−xGe_x with a higher Ge concentration was etched slower due to the reduction in the Si(Ge)–OH bond. Owing to the difference in the etching rate, Si was selectively etched in the Si_0.7Ge_0.3/Si/Si_0.7Ge_0.3 multi-layer. The etching rate of Si depends on the Si surface orientation, as TMAH is an anisotropic etchant. The (111) and (010) facets were formed in TMAH, when Si was laterally etched in the <110> and <100> directions in the multi-layer, respectively. We also investigated the effect of the addition of Triton X-100 in TMAH on the wet etching process. Our results confirmed that the presence of 0.1 vol% Triton reduced the roughness of the etched Si and Si_1−xGe_x surfaces. Moreover, the addition of Triton to TMAH could change the facet formation from (010) to (011) during Si etching in the <100>-direction. The facet change could reduce the lateral etching rate of Si and consequently reduce selectivity. The decrease in the layer thickness also reduced the lateral Si etching rate in the multi-layer. Full article

(This article belongs to the Special Issue Anisotropic Functional Nanomaterials: Preparations, Characterizations, and Applications)

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11 pages, 13571 KiB

Open AccessEditor’s ChoiceArticle

Gold-Nanoparticle-Coated Magnetic Beads for ALP-Enzyme-Based Electrochemical Immunosensing in Human Plasma

by Seo-Eun Lee, Se-Eun Jeong, Jae-Sang Hong, Hyungsoon Im, Sei-Young Hwang, Jun Kyun Oh and Seong-Eun Kim

Materials 2022, 15(19), 6875; https://doi.org/10.3390/ma15196875 - 3 Oct 2022

Cited by 4 | Viewed by 3293

Abstract

A simple and sensitive AuNP-coated magnetic beads (AMB)-based electrochemical biosensor platform was fabricated for bioassay. In this study, AuNP-conjugated magnetic particles were successfully prepared using biotin–streptavidin conjugation. The morphology and structure of the nanocomplex were characterized by scanning electron microscopy (SEM) with energy-dispersive [...] Read more.

A simple and sensitive AuNP-coated magnetic beads (AMB)-based electrochemical biosensor platform was fabricated for bioassay. In this study, AuNP-conjugated magnetic particles were successfully prepared using biotin–streptavidin conjugation. The morphology and structure of the nanocomplex were characterized by scanning electron microscopy (SEM) with energy-dispersive X-ray analysis (EDX) and UV–visible spectroscopy. Moreover, cyclic voltammetry (CV) was used to investigate the effect of AuNP-MB on alkaline phosphatase (ALP) for electrochemical signal enhancement. An ALP-based electrochemical (EC) immunoassay was performed on the developed AuNP-MB complex with indium tin oxide (ITO) electrodes. Subsequently, the concentration of capture antibodies was well-optimized on the AMB complex via biotin–avidin conjugation. Lastly, the developed AuNP-MB immunoassay platform was verified with extracellular vesicle (EV) detection via immune response by showing the existence of EGFR proteins on glioblastoma multiforme (GBM)-derived EVs (10⁸ particle/mL) spiked in human plasma. Therefore, the signal-enhanced ALP-based EC biosensor on AuNP-MB was favorably utilized as an immunoassay platform, revealing the potential application of biosensors in immunoassays in biological environments. Full article

(This article belongs to the Special Issue Application of Nanoparticles as Biosensors in the Biomedical Field)

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17 pages, 4704 KiB

Open AccessEditor’s ChoiceArticle

Flexible Perfluoropolyethers-Functionalized CNTs-Based UHMWPE Composites: A Study on Hydrogen Evolution, Conductivity and Thermal Stability

by Maurizio Sansotera, Valeria Marona, Piergiorgio Marziani, Nadka Tzankova Dintcheva, Elisabetta Morici, Rossella Arrigo, Gianlorenzo Bussetti, Walter Navarrini and Luca Magagnin

Materials 2022, 15(19), 6883; https://doi.org/10.3390/ma15196883 - 3 Oct 2022

Cited by 3 | Viewed by 1769

Abstract

Flexible conductive composites based on ultra-high molecular weight polyethylene (UHMWPE) filled with multi-walled carbon nanotubes (CNTs) modified by perfluoropolyethers (PFPEs) were produced. The bonding of PFPE chains, added in 1:1 and 2:1 weight ratios, on CNTs influences the dispersion of nanotubes in the [...] Read more.

Flexible conductive composites based on ultra-high molecular weight polyethylene (UHMWPE) filled with multi-walled carbon nanotubes (CNTs) modified by perfluoropolyethers (PFPEs) were produced. The bonding of PFPE chains, added in 1:1 and 2:1 weight ratios, on CNTs influences the dispersion of nanotubes in the UHMWPE matrix due to the non-polar nature of the polymer, facilitating the formation of nanofillers-rich conductive pathways and improving composites’ electrical conductivity (two to five orders of magnitude more) in comparison to UHMWPE-based nanocomposites obtained with pristine CNTs. Electrochemical atomic force microscopy (EC-AFM) was used to evaluate the morphological changes during cyclic voltammetry (CV). The decrease of the overpotential for hydrogen oxidation peaks in samples containing PFPE-functionalized CNTs and hydrogen production (approximately −1.0 V vs. SHE) suggests that these samples could find application in fuel cell technology as well as in hydrogen storage devices. Carbon black-containing composites were prepared for comparative study with CNTs containing nanocomposites. Full article

(This article belongs to the Section Advanced Composites)

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19 pages, 4196 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Bright UV-C Phosphors with Excellent Thermal Stability—Y_1−xSc_xPO₄ Solid Solutions

by Dmitry Spassky, Andrey Vasil’ev, Vitali Nagirnyi, Irina Kudryavtseva, Dina Deyneko, Ivan Nikiforov, Ildar Kondratyev and Boris Zadneprovski

Materials 2022, 15(19), 6844; https://doi.org/10.3390/ma15196844 - 2 Oct 2022

Cited by 10 | Viewed by 1939

Abstract

The structural and luminescence properties of undoped Y_1−xSc_xPO₄ solid solutions have been studied. An intense thermally stable emission with fast decay (τ_1/e ~ 10⁻⁷ s) and a band position varying from 5.21 to 5.94 eV [...] Read more.

The structural and luminescence properties of undoped Y_1−xSc_xPO₄ solid solutions have been studied. An intense thermally stable emission with fast decay (τ_1/e ~ 10⁻⁷ s) and a band position varying from 5.21 to 5.94 eV depending on the Sc/Y ratio is detected and ascribed to the 2p O-3d Sc self-trapped excitons. The quantum yield of the UV-C emission, also depending on the Sc/Y ratio, reaches 34% for the solid solution with x = 0.5 at 300 K. It is shown by a combined analysis of theoretical and experimental data that the formation of Sc clusters occurs in the solid solutions studied. The clusters facilitate the creation of energy wells at the conduction band bottom, which enables deep localization of electronic excitations and the creation of luminescence centers characterized by high quantum yield and thermal stability of the UV-C emission. Full article

(This article belongs to the Collection Luminescent Materials)

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17 pages, 9975 KiB

Open AccessEditor’s ChoiceArticle

Microstructure and Mechanical Properties of Hot-Extruded Mg–Zn–Ga–(Y) Biodegradable Alloys

by Viacheslav Bazhenov, Anna Li, Stanislav Tavolzhanskii, Andrey Bazlov, Natalia Tabachkova, Andrey Koltygin, Alexander Komissarov and Kwang Seon Shin

Materials 2022, 15(19), 6849; https://doi.org/10.3390/ma15196849 - 2 Oct 2022

Cited by 9 | Viewed by 2191

Abstract

Magnesium alloys are attractive candidates for use as temporary fixation devices in osteosynthesis because they have a density and Young’s modulus similar to those of cortical bone. One of the main requirements for biodegradable implants is its substitution by tissues during the healing [...] Read more.

Magnesium alloys are attractive candidates for use as temporary fixation devices in osteosynthesis because they have a density and Young’s modulus similar to those of cortical bone. One of the main requirements for biodegradable implants is its substitution by tissues during the healing process. In this article, the Mg–Zn–Ga–(Y) alloys were investigated that potentially can increase the bone growth rate by release of Ga ions during the degradation process. Previously, the effectiveness of Ga ions on bone tissue regeneration has been proved by clinical tests. This work is the first systematic study on the microstructure and mechanical properties of Mg–Zn–Y alloys containing Ga as an additional major alloying element prepared by the hot-extrusion process. The microstructure and phase composition of the Mg–Zn–Ga–(Y) alloys in as-cast, heat-treated, and extruded conditions were analyzed. In addition, it was shown that the use of hot extrusion produces Mg–Zn–Ga–(Y) alloys with favorable mechanical properties. The tensile yield strength, ultimate tensile strength, and elongation at fracture of the MgZn4Ga4 alloy extruded at 150 °C were 256 MPa, 343 MPa, and 14.2%, respectively. Overall, MgZn4Ga4 alloy is a perspective for applications in implants for osteosynthesis with improved bone regeneration ability. Full article

(This article belongs to the Special Issue Hot Deformation Behavior of Magnesium Alloys)

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12 pages, 3621 KiB

Open AccessEditor’s ChoiceArticle

Effects of Grain Refinement and Thermal Aging on Atomic Scale Local Structures of Ultra-Fine Explosives by X-ray Total Scattering

by Jiangtao Xing, Weili Wang, Shiliang Huang, Maohua Du, Bing Huang, Yousong Liu, Shanshan He, Tianle Yao, Shichun Li and Yu Liu

Materials 2022, 15(19), 6835; https://doi.org/10.3390/ma15196835 - 1 Oct 2022

Cited by 3 | Viewed by 1613

Abstract

The atomic scale local structures affect the initiation performance of ultra-fine explosives according to the stimulation results of hot spot formation. However, the experimental characterization of local structures in ultra-fine explosives has been rarely reported, due to the difficulty in application of characterization [...] Read more.

The atomic scale local structures affect the initiation performance of ultra-fine explosives according to the stimulation results of hot spot formation. However, the experimental characterization of local structures in ultra-fine explosives has been rarely reported, due to the difficulty in application of characterization methods having both high resolution in and small damage to unstable organic explosive materials. In this work, X-ray total scattering was explored to investigate the atomic scale local distortion of two widely applicable ultra-fine explosives, LLM-105 and HNS. The experimental spectra of atomic pair distribution function (PDF) derived from scattering results were fitted by assuming rigid ring structures in molecules. The effects of grain refinement and thermal aging on the atomic scale local structure were investigated, and the changes in both the length of covalent bonds have been identified. Results indicate that by decreasing the particle size of LLM-105 and HNS from hundreds of microns to hundreds of nanometers, the crystal structures remain, whereas the molecular configuration slightly changes and the degree of structural disorder increases. For example, the average length of covalent bonds in LLM-105 reduces from 1.25 Å to 1.15 Å, whereas that in HNS increases from 1.25 Å to 1.30 Å, which is possibly related to the incomplete crystallization process and internal stress. After thermal aging of ultra-fine LLM-105 and HNS, the degree of structural disorder decreases, and the distortion in molecules formed in the synthesis process gradually healed. The average length of covalent bonds in LLM-105 increases from 1.15 Å to 1.27 Å, whereas that in HNS reduces from 1.30 Å to 1.20 Å. The possible reason is that the atomic vibration in the molecule intensifies during the heat aging treatment, and the internal stress was released through changes in molecular configuration, and thus the atomic scale distortion gradually heals. The characterization method and findings in local structures obtained in this work may pave the path to deeply understand the relationship between the defects and performance of ultra-fine explosives. Full article

(This article belongs to the Section Advanced Materials Characterization)

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27 pages, 10406 KiB

Open AccessEditor’s ChoiceArticle

Three-Dimensional Numerical Simulation of Grain Growth during Selective Laser Melting of 316L Stainless Steel

by Feng Xu, Feiyu Xiong, Ming-Jian Li and Yanping Lian

Materials 2022, 15(19), 6800; https://doi.org/10.3390/ma15196800 - 30 Sep 2022

Cited by 10 | Viewed by 3503

Abstract

The grain structure of the selective laser melting additive manufactured parts has been shown to be heterogeneous and spatially non-uniform compared to the traditional manufacturing process. However, the complex formation mechanism of these unique grain structures is hard to reveal using the experimental [...] Read more.

The grain structure of the selective laser melting additive manufactured parts has been shown to be heterogeneous and spatially non-uniform compared to the traditional manufacturing process. However, the complex formation mechanism of these unique grain structures is hard to reveal using the experimental method alone. In this study, we presented a high-fidelity 3D numerical model to address the grain growth mechanisms during the selective laser melting of 316 stainless steel, including two heating modes, i.e., conduction mode and keyhole mode melting. In the numerical model, the powder-scale thermo-fluid dynamics are simulated using the finite volume method with the volume of fluid method. At the same time, the grain structure evolution is sequentially predicted by the cellular automaton method with the predicted temperature field and the as-melted powder bed configuration as input. The simulation results agree well with the experimental data available in the literature. The influence of the process parameters and the keyhole and keyhole-induced void on grain structure formation are addressed in detail. The findings of this study are helpful to the optimization of process parameters for tailoring the microstructure of fabricated parts with expected mechanical properties. Full article

(This article belongs to the Special Issue Experimental Research and Numerical Simulations of Metal Additive Manufacturing)

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16 pages, 8996 KiB

Open AccessEditor’s ChoiceArticle

Simulation of the Refractive Index Variation and Validation of the Form Deviation in Precisely Molded Chalcogenide Glass Lenses (IRG 26) Considering the Stress and Structure Relaxation

by Cheng Jiang, Carlos Marin Tovar, Jan-Helge Staasmeyer, Marcel Friedrichs, Tim Grunwald and Thomas Bergs

Materials 2022, 15(19), 6756; https://doi.org/10.3390/ma15196756 - 29 Sep 2022

Cited by 5 | Viewed by 2424

Abstract

Precise infrared (IR) optics are core elements of infrared cameras for thermal imaging and night vision applications and can be manufactured directly or using a replicative process. For instance, precision glass molding (PGM) is a replicative manufacturing method that meets the demand of [...] Read more.

Precise infrared (IR) optics are core elements of infrared cameras for thermal imaging and night vision applications and can be manufactured directly or using a replicative process. For instance, precision glass molding (PGM) is a replicative manufacturing method that meets the demand of producing precise and accurate glass optics in a cost-efficient manner. However, several iterations in the PGM process are applied to compensate the induced form deviation and the index drop after molding. The finite element method (FEM) is utilized to simulate the thermomechanical process, predicting the optical properties of molded chalcogenide lenses and thus preventing costly iterations. Prior to FEM modelling, self-developed glass characterization methods for the stress and structure relaxation of chalcogenide glass IRG 26 are implemented. Additionally, a ray-tracing method is developed in this work to calculate the optical path difference (OPD) based on the mesh structure results from the FEM simulation. The developed method is validated and conducted during the production of molded lenses. Full article

(This article belongs to the Section Optical and Photonic Materials)

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26 pages, 8954 KiB

Open AccessEditor’s ChoiceReview

Frontier and Hot Topics of Pulsed Fiber Lasers via CiteSpace Scientometric Analysis: Passively Mode-Locked Fiber Lasers with Real Saturable Absorbers Based on Two-Dimensional Materials

by Wen Zhou, Xiuyang Pang, Hanke Zhang, Qiang Yu, Fangqi Liu, Wenyue Wang, Yikun Zhao, Yan Lu and Zixin Yang

Materials 2022, 15(19), 6761; https://doi.org/10.3390/ma15196761 - 29 Sep 2022

Cited by 12 | Viewed by 3007

Abstract

Pulsed fiber lasers, with high peak power and narrow pulse widths, have been proven to be an important tool for a variety of fields of application. In this work, frontier and hot topics in pulsed fiber lasers were analyzed with 11,064 articles. Benefitting [...] Read more.

Pulsed fiber lasers, with high peak power and narrow pulse widths, have been proven to be an important tool for a variety of fields of application. In this work, frontier and hot topics in pulsed fiber lasers were analyzed with 11,064 articles. Benefitting from the scientometric analysis capabilities of CiteSpace, the analysis found that passively mode-locked fiber lasers with saturable absorbers (SAs) based on two-dimensional (2D) materials have become a hot research topic in the field of pulsed fiber lasers due to the advantages of self-starting operation, high stability, and good compatibility. The excellent nonlinear optical properties exhibited by 2D materials at nanometer-scale thicknesses have become a particularly popular research topic; the research has paved the way for exploring its wider applications. We summarize the performance of several typical 2D materials in ultrafast fiber lasers, such as graphene, topological insulators (TIs), transition metal dichalcogenides (TMDs), and black phosphorus (BP). Meanwhile, we review and analyze the direction of the development of 2D SAs for ultrafast fiber lasers. Full article

(This article belongs to the Special Issue Fiber Lasers and Non-Linear Optics of Materials)

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10 pages, 2425 KiB

Open AccessEditor’s ChoiceArticle

Study of Carrier Mobilities in 4H-SiC MOSFETS Using Hall Analysis

by Suman Das, Yongju Zheng, Ayayi Ahyi, Marcelo A. Kuroda and Sarit Dhar

Materials 2022, 15(19), 6736; https://doi.org/10.3390/ma15196736 - 28 Sep 2022

Cited by 11 | Viewed by 3371

Abstract

The channel conduction in 4H-SiC metal–oxide–semiconductor field effect transistors (MOSFETs) are highly impacted by charge trapping and scattering at the interface. Even though nitridation reduces the interface trap density, scattering still plays a crucial role in increasing the channel resistance in these transistors. [...] Read more.

The channel conduction in 4H-SiC metal–oxide–semiconductor field effect transistors (MOSFETs) are highly impacted by charge trapping and scattering at the interface. Even though nitridation reduces the interface trap density, scattering still plays a crucial role in increasing the channel resistance in these transistors. In this work, the dominant scattering mechanisms are distinguished for inversion layer electrons and holes using temperature and body-bias-dependent Hall measurements on nitrided lateral 4H-SiC MOSFETs. The effect of the transverse electric field (

E_{e f f}

) on carrier mobility is analyzed under strong inversion condition where surface roughness scattering becomes prevalent. Power law dependencies of the electron and hole Hall mobility for surface roughness scattering are determined to be

E_{e f f}^{- 1.8}

and

E_{e f f}^{- 2.4}

, respectively, analogous to those of silicon MOSFETs. Moreover, for n-channel MOSFETs, the effect of phonon scattering is observed at zero body bias, whereas in p-channel MOSFETs, it is observed only under negative body biases. Along with the identification of regimes governed by different scattering mechanisms, these results highlight the importance of the selection of substrate doping and of

E_{e f f}

in controlling the value of channel mobility in 4H-SiC MOSFETs. Full article

(This article belongs to the Special Issue Silicon Carbide: Material Growth, Device Processing and Applications)

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17 pages, 3510 KiB

Open AccessEditor’s ChoiceArticle

Study on the Stability of Bio-Oil Modified Prime Coat Oil Based on Molecular Dynamics

by Shuang Shi, Lanqin Lin, Zhaoguang Hu, Linhao Gu and Yanning Zhang

Materials 2022, 15(19), 6737; https://doi.org/10.3390/ma15196737 - 28 Sep 2022

Cited by 11 | Viewed by 2087

Abstract

To explore the effect of different emulsifier contents on the stability performance of biomass-emulsified asphalt, three types of emulsified asphalt with 1%, 3%, and 5% anionic emulsifiers were prepared and analyzed by molecular dynamics simulation and macroscopic experiments. Firstly, we used molecular simulation [...] Read more.

To explore the effect of different emulsifier contents on the stability performance of biomass-emulsified asphalt, three types of emulsified asphalt with 1%, 3%, and 5% anionic emulsifiers were prepared and analyzed by molecular dynamics simulation and macroscopic experiments. Firstly, we used molecular simulation software (Material Studio, MS) to construct a model of biomass-emulsified asphalt with different emulsifier contents and analyzed the microscopic mechanism of the emulsifier to improve the stability of the emulsified asphalt by the radial distribution function, interaction energy, interfacial layer thickness, and solubility parameters of the emulsified asphalt system with different emulsifier contents. The results were validated by macro and micro tests including storage stability, particle size determination, and infrared spectroscopy. The results show that at low emulsifier contents, the emulsifier can reduce the interfacial tension between the oil–water interface and expand the transition region between the two phases (interfacial layer thickness), which will prevent interparticle agglomeration and reduce the emulsion particle size, thus reducing the settling rate and ensuring the stability of the emulsion. When the emulsifier content is further increased beyond the critical micelle concentration, the emulsifiers will agglomerate with each other and show larger peaks in the radial distribution function, and the phenomenon of emulsifier agglomeration will appear in the five-day storage stability test, resulting in a corresponding decrease in the proximity of the infrared absorption peak area ratio in the same wavelength band of the upper and lower layers of the biomass-emulsified asphalt, and the emulsion stability decreases instead. Full article

(This article belongs to the Special Issue Sustainable Recycling Techniques of Pavement Materials)

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13 pages, 5635 KiB

Open AccessEditor’s ChoiceArticle

Excellent Thermoelectric Performance of 2D CuMN₂ (M = Sb, Bi; N = S, Se) at Room Temperature

by Wenyu Fang, Yue Chen, Kuan Kuang and Mingkai Li

Materials 2022, 15(19), 6700; https://doi.org/10.3390/ma15196700 - 27 Sep 2022

Cited by 9 | Viewed by 2459

Abstract

2D copper-based semiconductors generally possess low lattice thermal conductivity due to their strong anharmonic scattering and quantum confinement effect, making them promising candidate materials in the field of high-performance thermoelectric devices. In this work, we proposed four 2D copper-based materials, namely CuSbS₂ [...] Read more.

2D copper-based semiconductors generally possess low lattice thermal conductivity due to their strong anharmonic scattering and quantum confinement effect, making them promising candidate materials in the field of high-performance thermoelectric devices. In this work, we proposed four 2D copper-based materials, namely CuSbS₂, CuSbSe₂, CuBiS₂, and CuBiSe₂. Based on the framework of density functional theory and Boltzmann transport equation, we revealed that the monolayers possess high stability and narrow band gaps of 0.57~1.10 eV. Moreover, the high carrier mobilities (10²~10³ cm²·V⁻¹·s⁻¹) of these monolayers lead to high conductivities (10⁶~10⁷ Ω⁻¹·m⁻¹) and high-power factors (18.04~47.34 mW/mK²). Besides, as the strong phonon-phonon anharmonic scattering, the monolayers also show ultra-low lattice thermal conductivities of 0.23~3.30 W/mK at 300 K. As results show, all the monolayers for both p-type and n-type simultaneously show high thermoelectric figure of merit (ZT) of about 0.91~1.53 at room temperature. Full article

(This article belongs to the Special Issue Materials Physics in Thermoelectric Materials)

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14 pages, 1178 KiB

Open AccessEditor’s ChoiceArticle

Evaluation of the Color Stability, Water Sorption, and Solubility of Current Resin Composites

by Wenkai Huang, Ling Ren, Yuyao Cheng, Minghua Xu, Wenji Luo, Desong Zhan, Hidehiko Sano and Jiale Fu

Materials 2022, 15(19), 6710; https://doi.org/10.3390/ma15196710 - 27 Sep 2022

Cited by 29 | Viewed by 3482

Abstract

This study aims to assess the color stability, water sorption, and solubility of 11 resin composites as commercially available dental products. Twenty samples (10 mm in diameter and 2 mm in thickness) of each material were fabricated using a customized silicone mold, followed [...] Read more.

This study aims to assess the color stability, water sorption, and solubility of 11 resin composites as commercially available dental products. Twenty samples (10 mm in diameter and 2 mm in thickness) of each material were fabricated using a customized silicone mold, followed by immersion in each of curry, coffee, wine, and distilled water for 28 days (n = 5). Baseline shade and color changes (ΔE) were measured using a reflection spectrophotometer. The CIE L*, a*, b* system was used to evaluate the color changes. Five samples of each resin composite were applied to test water sorption and solubility according to ISO 4049:2009. As a result, the ∆E values were significantly influenced by each of the three factors (composition of material, solution, time) and the interactions between them (p < 0.001). Highest resistance to discoloration was achieved by Ceram.X One Universal (CXU), followed by Magnafill Putty (MP). Generally, microhybrid composites showed fewer color changes than nanohybrid composites and giomers. DX. Universal and Filtek Z350 XT showed the highest ΔE values in all colorants. All materials tested in this study fulfilled the criteria of ISO 4049:2009; CXU and MP had the lowest water sorption and solubility. The Pearson test showed statistically significant positive correlations between water sorption and ΔE and between solubility and ΔE. Full article

(This article belongs to the Special Issue Advanced Restorative Dental Composite Resins: Research and Development)

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12 pages, 5057 KiB

Open AccessEditor’s ChoiceArticle

Ultrahigh Piezoelectric Strains in PbZr_1−xTi_xO₃ Single Crystals with Controlled Ti Content Close to the Tricritical Point

by Iwona Lazar, Roger William Whatmore, Andrzej Majchrowski, Anthony Mike Glazer, Dariusz Kajewski, Janusz Koperski, Andrzej Soszyński, Julita Piecha, Barbara Loska and Krystian Roleder

Materials 2022, 15(19), 6708; https://doi.org/10.3390/ma15196708 - 27 Sep 2022

Cited by 5 | Viewed by 1984

Abstract

Intensive investigations of PbZr_1-xTi_xO₃ (PZT) materials with the ABO₃ perovskite structure are connected with their extraordinary piezoelectric properties. Especially well known are PZT ceramics at the Morphotropic Phase Boundary (MPB), with x~0.48, whose applications are the most [...] Read more.

Intensive investigations of PbZr_1-xTi_xO₃ (PZT) materials with the ABO₃ perovskite structure are connected with their extraordinary piezoelectric properties. Especially well known are PZT ceramics at the Morphotropic Phase Boundary (MPB), with x~0.48, whose applications are the most numerous among ferroelectrics. These piezoelectric properties are often obtained by doping with various ions at the B sites. Interestingly, we have found similar properties for undoped PZT single crystals with low Ti content, for which we have confirmed the existence of the tricritical point near x~0.06. For a PbZr_{0.95 ± 0.01}Ti_0.05_{∓ 0.01}O₃ crystal, we describe the ultrahigh strain, dielectric, optical and piezoelectric properties. We interpret the ultrahigh strain observed in the region of the antiferroelectric–ferroelectric transition as an inverse piezoelectric effect generated by the coexistence of domains of different symmetries. The complex domain coexistence was confirmed by determining optical indicatrix orientations in domains. The piezoelectric coefficient in this region reached an extremely high value of 5000 pm/V. We also verified that the properties of the PZT single crystals from the region near the tricritical point are incredibly susceptible to a slight deviation in the Ti content. Full article

(This article belongs to the Special Issue Emerging Dielectric, Piezoelectric and Ferroelectric Ceramic and Crystalline Materials and Their Applications)

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13 pages, 4286 KiB

Open AccessEditor’s ChoiceArticle

Dissolution of β-C₂S Cement Clinker: Part 2 Atomistic Kinetic Monte Carlo (KMC) Upscaling Approach

by Mohammadreza Izadifar, Neven Ukrainczyk, Khondakar Mohammad Salah Uddin, Bernhard Middendorf and Eduardus Koenders

Materials 2022, 15(19), 6716; https://doi.org/10.3390/ma15196716 - 27 Sep 2022

Cited by 20 | Viewed by 2757

Abstract

Cement clinkers containing mainly belite (β-C₂S as a model crystal), replacing alite, offer a promising solution for the development of environmentally friendly solutions to reduce the high level of CO₂ emissions in the production of Portland cement. However, the much [...] Read more.

Cement clinkers containing mainly belite (β-C₂S as a model crystal), replacing alite, offer a promising solution for the development of environmentally friendly solutions to reduce the high level of CO₂ emissions in the production of Portland cement. However, the much lower reactivity of belite compared to alite limits the widespread use of belite cements. Therefore, this work presents a fundamental atomistic computational approach for comprehending and quantifying the mesoscopic forward dissolution rate of β-C₂S, applied to two reactive crystal facets of (100) and (

\bar{1} 00

). For this, an atomistic kinetic Monte Carlo (KMC) upscaling approach for cement clinker was developed. It was based on the calculated activation energies (ΔG*) under far-from-equilibrium conditions obtained by a molecular dynamic simulation using the combined approach of ReaxFF and metadynamics, as described in the Part 1 paper in this Special Issue. Thus, the individual atomistic dissolution rates were used as input parameters for implementing the KMC upscaling approach coded in MATLAB to study the dissolution time and morphology changes at the mesoscopic scale. Four different cases and 21 event scenarios were considered for the dissolution of calcium atoms (Ca) and silicate monomers. For this purpose, the (100) and (

\bar{1} 00

) facets of a β-C₂S crystal were considered using periodic boundary conditions (PBCs). In order to demonstrate the statistical nature of the KMC approach, 40 numerical realizations were presented. The major findings showed a striking layer-by-layer dissolution mechanism in the case of an ideal crystal, where the total dissolution rate was limited by the much slower dissolution of the silicate monomer compared to Ca. The introduction of crystal defects, namely cutting the edges at two crystal boundaries, increased the overall average dissolution rate by a factor of 519. Full article

(This article belongs to the Special Issue Mathematical Modeling of Building Materials)

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12 pages, 3274 KiB

Open AccessEditor’s ChoiceArticle

Immediate and Long-Term Radiopacity and Surface Morphology of Hydraulic Calcium Silicate-Based Materials

by Goda Bilvinaite, Saulius Drukteinis, Vilma Brukiene and Sivaprakash Rajasekharan

Materials 2022, 15(19), 6635; https://doi.org/10.3390/ma15196635 - 24 Sep 2022

Cited by 7 | Viewed by 2316

Abstract

The present study aimed to evaluate and compare the radiopacity and surface morphology of AH Plus Bioceramic Sealer (AHPB), Bio-C Sealer (BIOC), Biodentine (BD), BioRoot RCS (BR), Grey-MTAFlow (GMF), White-MTAFlow (WMF), TotalFill BC Sealer (TF), and TotalFill BC Sealer HiFlow (TFHF) at different [...] Read more.

The present study aimed to evaluate and compare the radiopacity and surface morphology of AH Plus Bioceramic Sealer (AHPB), Bio-C Sealer (BIOC), Biodentine (BD), BioRoot RCS (BR), Grey-MTAFlow (GMF), White-MTAFlow (WMF), TotalFill BC Sealer (TF), and TotalFill BC Sealer HiFlow (TFHF) at different time moments—30 min, 24 h, and 28 days. Ten specimens of each material were prepared according to the ISO-6876:2012 standard and radiographed next to an aluminum step wedge using a digital sensor. The specimens were stored in a gelatinized Hank’s balanced salt solution at 37 °C between assessments. The mean grayscale values of each specimen were converted into equivalent aluminum thickness by a linear regression model. Characterization of the surface morphology was performed by using a scanning electron microscope at ×4.0k and ×10.0k magnifications. The radiographic analysis revealed that all the tested materials exceeded the ISO-specified limit of 3 mm Al, with the highest radiopacity presented by AHPB and the lowest by BD. None of the tested materials demonstrated considerable variances between the 30 min and the 24 h radiopacity level (p < 0.05), and statistically significant long-term radiopacity changes were exhibited by BR, TFHF, and TF (p > 0.05). All the specimens demonstrated a common feature of limited precipitate formation, with numerous unreacted particles still presented on the surface after 24 h, whereas the particle rearrangement and the deposition of precipitates were clearly observed after 28 days. Full article

(This article belongs to the Special Issue Biomaterials for Medical and Dental Application)

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10 pages, 3795 KiB

Open AccessEditor’s ChoiceArticle

Effects of the Parent Alloy Microstructure on the Thermal Stability of Nanoporous Au

by Andrea Pinna, Giorgio Pia, Roberta Licheri and Luca Pilia

Materials 2022, 15(19), 6621; https://doi.org/10.3390/ma15196621 - 23 Sep 2022

Cited by 2 | Viewed by 1508

Abstract

Nanoporous (NP) metals represent a unique class of materials with promising properties for a wide set of applications in advanced technology, from catalysis and sensing to lightweight structural materials. However, they typically suffer from low thermal stability, which results in a coarsening behavior [...] Read more.

Nanoporous (NP) metals represent a unique class of materials with promising properties for a wide set of applications in advanced technology, from catalysis and sensing to lightweight structural materials. However, they typically suffer from low thermal stability, which results in a coarsening behavior not yet fully understood. In this work, we focused precisely on the coarsening process undergone by NP Au, starting from the analysis of data available in the literature and addressing specific issues with suitably designed experiments. We observe that annealing more easily induces densification in systems with short characteristic lengths. The NP Au structures obtained by dealloying of mechanically alloyed AuAg precursors exhibit lower thermal stability than several NP Au samples discussed in the literature. Similarly, NP Au samples prepared by annealing the precursor alloy before dealloying display enhanced resistance to coarsening. We suggest that the microstructure of the precursor alloy, and, in particular, the grain size of the metal phases, can significantly affect the thermal stability of the NP metal. Specifically, the smaller the grain size of the parent alloy, the lower the thermal stability. Full article

(This article belongs to the Special Issue Recent Advances in the Mechanical Properties and Microstructural Features of Porous Materials)

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24 pages, 11073 KiB

Open AccessEditor’s ChoiceArticle

Performance-Based Assessment of Bridges with Novel SMA-Washer-Based Self-Centering Rocking Piers

by Jiawei Chen, Dong Liang, Xin You and Hao Liang

Materials 2022, 15(19), 6589; https://doi.org/10.3390/ma15196589 - 22 Sep 2022

Cited by 4 | Viewed by 2107

Abstract

This study discussed a novel self-centering rocking (SCR) bridge system equipped with shape memory alloy (SMA)-based piers, with a particular focus on the benefit of the SCR bridge system in a life-cycle context. The study commences with an introduction of the SCR bridge [...] Read more.

This study discussed a novel self-centering rocking (SCR) bridge system equipped with shape memory alloy (SMA)-based piers, with a particular focus on the benefit of the SCR bridge system in a life-cycle context. The study commences with an introduction of the SCR bridge system; subsequently, a life-cycle loss and resilience assessment framework for the SCR bridge system is presented. Specifically, the seismic fragility, resilience, and life-cycle loss associated with the SCR and conventional bridge systems were addressed. The proposed life-cycle assessment framework was finally applied to two highway bridges with and without SMA washer-based rocking piers, considering the representative hazard scenarios that could happen within the investigated regions. The results revealed that the novel SCR pier bridge system slightly increased the bearing displacement but extensively reduced the pier curvature ductility due to the rocking mechanism. The SCR bridge system kept a lower life-cycle loss level and exhibited more resilient performance than the conventional bridge, especially in the region with higher seismic intensities. Indirect loss can be significantly larger than the direct loss, specifically for the earthquakes with a relatively low probability of occurrence. The SCR bridge system outperformed the conventional system in terms of recovery time, where a quick recovery after an earthquake and drastically decreased the social and economic losses. Full article

(This article belongs to the Special Issue Shape Memory Alloys for Civil Engineering)

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12 pages, 4339 KiB

Open AccessEditor’s ChoiceArticle

Electric Arc Furnace Dust Recycled in 7075 Aluminum Alloy Composites Fabricated by Spark Plasma Sintering (SPS)

by Elder Soares, Nadège Bouchonneau, Elizeth Alves, Kleber Alves, Oscar Araújo Filho, David Mesguich, Geoffroy Chevallier, Nouhaila Khalile, Christophe Laurent and Claude Estournès

Materials 2022, 15(19), 6587; https://doi.org/10.3390/ma15196587 - 22 Sep 2022

Cited by 3 | Viewed by 2039

Abstract

The reuse of industrial waste, such as electric arc furnace dust (EAFD) as reinforcement in aluminum matrix composites (AMC), is still little explored even though it has shown potential to improve the mechanical properties, such as hardness and mechanical strength, of AMCs. To [...] Read more.

The reuse of industrial waste, such as electric arc furnace dust (EAFD) as reinforcement in aluminum matrix composites (AMC), is still little explored even though it has shown potential to improve the mechanical properties, such as hardness and mechanical strength, of AMCs. To propose a new alternative for EAFD recycling, AA7075-EAFD composites were produced by spark plasma sintering (SPS). The starting powders were prepared by high-energy milling with different weight fractions of EAFD in two particle size ranges added to an AA7075 matrix. SEM shows that the distribution of reinforcement particles in the matrix is homogeneous with no agglomeration of the particles. XRD patterns of initial powders and the SPS-sintered (SPSed) samples suggest that there was no reaction during sintering (no additional peaks were detected). The relative density of all SPSed samples exceeded 96.5%. The Vickers microhardness of the composites tended to increase with increasing EAFD content, increasing from 108 HV (AA7075 without reinforcement) up to 168 HV (56% increase). The maximum microhardness value was obtained when using 15 wt.% EAFD with a particle size smaller than 53 μm (called G1), showing that EAFD presents a promising potential to be applied as reinforcement in AA7075 matrix composites. Full article

(This article belongs to the Special Issue Materials with Advanced Properties Fabricated by Spark Plasma Sintering)

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17 pages, 4643 KiB

Open AccessEditor’s ChoiceArticle

Investigating the Correlation between the Microstructure and Electrical Properties of FeSbO₄ Ceramics

by Carlos G. P. Moraes, Robert S. Matos, Cledson dos Santos, Ştefan Ţălu, John M. Attah-Baah, Romualdo S. Silva Junior, Marcelo S. da Silva, Marcos V. S. Rezende, Ronaldo S. Silva and Nilson S. Ferreira

Materials 2022, 15(19), 6555; https://doi.org/10.3390/ma15196555 - 21 Sep 2022

Cited by 6 | Viewed by 2426

Abstract

FeSbO₄ powder was prepared using the solid-state reaction method in this work. Afterward, the dense and porous ceramics were obtained by sintering the pressed powder calcined at temperatures of 900 and 1000 °C for 4 h. Rietveld profile analysis of the X-ray [...] Read more.

FeSbO₄ powder was prepared using the solid-state reaction method in this work. Afterward, the dense and porous ceramics were obtained by sintering the pressed powder calcined at temperatures of 900 and 1000 °C for 4 h. Rietveld profile analysis of the X-ray powder diffraction data showed that FeSbO₄ adopts the trirutile-type structure (space group P4₂/mnm, with a ≅ 4.63 Å and c ≅ 9.23 Å). SEM images showed that the powder calcined at 900 °C after being sintered at 1200 °C resulted in ceramics of higher crystallinity, larger grains, and consequently, low porosity. The dielectric properties were measured in the frequency range of 10⁻¹ Hz–1 MHz as a function of temperature (25–250 °C). The real (σ′) and imaginary (σ″) parts of the complex conductivity increase with rising annealing temperature for both samples. The real conductivity in the AC region for 𝑓 = 100 kHz was

1.59 \times 10^{- 6} S \cdot {cm}^{- 1}

and

7.04 \times 10^{- 7} S \cdot {cm}^{- 1}

for the ceramic samples obtained from the powder calcined at 900 (C-900) and 1000 °C (C-1000), respectively. Furthermore, the dielectric constants (k′) measured at room temperature and

f = 100 kHz

were

13.77

(C-900) and

6.27

(C-1000), while the activation energies of the grain region were E_a = 0.53 eV and E_a = 0.49 eV, respectively. Similar activation energy (E_a = 0.52 eV and 0.49 eV) was also obtained by the brick-layer model and confirmed by the adjustment of activation energy by DC measurements which indicated an absence of the porosity influence on the parameter. Additionally, loss factor values were obtained to be equal to 3.8 (C-900) and 5.99 (C-1000) for measurements performed at 100 Hz, suggesting a contribution of the conductivity originated from the combination or accommodation of the pores in the grain boundary region. Our results prove that the microstructural factors that play a critical role in the electrical and dielectric properties are the average grain size and the porosity interspersed with the grain boundary region. Full article

(This article belongs to the Special Issue New Progresses in the Development, Microstructure and Properties of Ceramic-Metal Composites (Cermets))

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12 pages, 3842 KiB

Open AccessEditor’s ChoiceArticle

Upconversion Emission Studies in Er^3+/Yb³⁺ Doped/Co-Doped NaGdF₄ Phosphor Particles for Intense Cathodoluminescence and Wide Temperature-Sensing Applications

by Abhishek Kumar, Helena Couto and Joaquim C. G. Esteves da Silva

Materials 2022, 15(19), 6563; https://doi.org/10.3390/ma15196563 - 21 Sep 2022

Cited by 7 | Viewed by 2226

Abstract

Er³⁺/Yb³⁺ doped/co-doped NaGdF₄ upconversion phosphor nanoparticles were synthesized via the thermal decomposition route of synthesis. The α-phase crystal structure and nanostructure of these particles were confirmed using XRD and FE-SEM analysis. In the power-dependent upconversion analysis, different emission bands [...] Read more.

Er³⁺/Yb³⁺ doped/co-doped NaGdF₄ upconversion phosphor nanoparticles were synthesized via the thermal decomposition route of synthesis. The α-phase crystal structure and nanostructure of these particles were confirmed using XRD and FE-SEM analysis. In the power-dependent upconversion analysis, different emission bands at 520 nm, 540 nm, and 655 nm were obtained. The sample was also examined for cathodoluminescence (CL) analysis at different filament currents of an electron beam. Through CL analysis, different emission bands of 526 nm, 550 nm, 664 nm, and 848 nm were obtained. The suitability of the present sample for temperature-sensing applications at a wide range of temperatures, from room temperature to 1173 K, was successfully demonstrated. Full article

(This article belongs to the Special Issue Advances in Luminescent Materials)

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10 pages, 2439 KiB

Open AccessEditor’s ChoiceArticle

Biocompatibility of Zinc Matrix Biodegradable Composites Reinforced by Graphene Nanosheets

by Mei Fan, Fei Zhao, Shanshan Peng, Qianfei Dai, Yuan Liu, Sheng Yin and Zongkui Zhang

Materials 2022, 15(18), 6481; https://doi.org/10.3390/ma15186481 - 19 Sep 2022

Cited by 9 | Viewed by 2282

Abstract

As a new type of biodegradable implant material, zinc matrix composites have excellent potential in the application of biodegradable implants because of their better corrosion resistance than magnesium matrix materials. Our previous studies have shown that graphene nanosheet reinforced zinc matrix composites (Zn-GNS) [...] Read more.

As a new type of biodegradable implant material, zinc matrix composites have excellent potential in the application of biodegradable implants because of their better corrosion resistance than magnesium matrix materials. Our previous studies have shown that graphene nanosheet reinforced zinc matrix composites (Zn-GNS) prepared by spark plasma sintering (SPS) have good mechanical properties and suitable degradation rate. However, the biocompatibility of zinc matrix composites is still a problem of concern. The cytocompatibility and blood compatibility of pure zinc and Zn-GNS composites in vitro were studied. The results showed that Zn-GNS composites had acceptable toxicity to MG-63 human osteosarcoma cells. In addition, the hemolysis rate of pure zinc and its composites were less than 3%, which has no adverse effect on adhered platelets, and has good antithrombotic and antiadhesion platelets properties. In conclusion, the addition of GNS did not adversely affect the biocompatibility of Zn-GNS composites, which indicated that Zn-GNS composites are a promising candidate for bone implantation. Full article

(This article belongs to the Special Issue On the Residual Strength and Damage Identification of Damaged Composite Structure)

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17 pages, 4845 KiB

Open AccessEditor’s ChoiceArticle

A Mesoscale Study on the Dilation of Actively Confined Concrete under Axial Compression

by Peng Chen, Xiaomeng Cui, Huijun Zheng and Shengpu Si

Materials 2022, 15(18), 6490; https://doi.org/10.3390/ma15186490 - 19 Sep 2022

Cited by 4 | Viewed by 2066

Abstract

The confinement of concrete enhances its strength and ductility by restraining lateral dilation. The accuracy of a confinement model depends on how well it captures the dilation of concrete. In the current paper, a mesoscale model is established to study the dilation properties [...] Read more.

The confinement of concrete enhances its strength and ductility by restraining lateral dilation. The accuracy of a confinement model depends on how well it captures the dilation of concrete. In the current paper, a mesoscale model is established to study the dilation properties of concrete in active confinement, where the heterogeneity of concrete is considered. The stress–strain and lateral–axial strain curves of concrete in active confinement were used to demonstrate the validity of the mesoscale model. Subsequently, the distribution of lateral strain and the influences of the strength grade and confinement ratio on the dilation of concrete were investigated in a simulation. The results show that the distribution of the lateral strain along the radial or longitudinal directions is not uniform on the specimen when compressive failure occurs. The confinement ratio has a more significant influence on the concrete’s transverse dilation than the strength grade. Finally, an expression of the lateral–axial strain relationship of concrete in active confinement is proposed. The proposed formula can reflect the simulation results of the mesoscale model and is in good agreement with the prediction of existing formulas. Full article

(This article belongs to the Special Issue Life-Cycle Performance of Green Cementitious Composites under Complex Environmental Conditions)

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15 pages, 10896 KiB

Open AccessEditor’s ChoiceArticle

Halochromic Inks Applied on Cardboard for Food Spoilage Monitorization

by Liliana Leite, Inês Boticas, Miguel Navarro, Luís Nobre, João Bessa, Fernando Cunha, Pedro Neves and Raúl Fangueiro

Materials 2022, 15(18), 6431; https://doi.org/10.3390/ma15186431 - 16 Sep 2022

Cited by 1 | Viewed by 2673

Abstract

Control of food spoilage is a critical concern in the current world scenario, not only to ensure the quality and safety of food but also to avoid the generation of food waste. This paper evaluates a dual-sensor strategy using six different pH indicators [...] Read more.

Control of food spoilage is a critical concern in the current world scenario, not only to ensure the quality and safety of food but also to avoid the generation of food waste. This paper evaluates a dual-sensor strategy using six different pH indicators stamped on cardboard for the detection of spoilage in three different foods: beef, salmon, and strawberries. After function validation and formulation optimizations in the laboratory, the halochromic sensors methyl orange and bromocresol purple 2% (w/v) were stamped on cardboard and, in contact with the previously mentioned foods, were able to produce an easily perceptible signal for spoilage by changing color. Additionally, when it comes to mechanical characterization the inks showed high abrasion (>100 cycles) and adhesion resistance (>91%). Full article

(This article belongs to the Special Issue Recent Studies of Additives and Materials for Smart Packaging Applications)

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14 pages, 6153 KiB

Open AccessEditor’s ChoiceArticle

Amino-Functionalized Titanate Nanotubes: pH and Kinetic Study of a Promising Adsorbent for Acid Dye in Aqueous Solution

by Débora A. Sales, Paloma N. S. Lima, Lucinaldo S. Silva, Thalles M. F. Marques, Suziete B. S. Gusmão, Odair P. Ferreira, Anupama Ghosh, Yuset Guerra, Alan Í. S. Morais, Roosevelt D. S. Bezerra, Edson C. Silva-Filho and Bartolomeu C. Viana

Materials 2022, 15(18), 6393; https://doi.org/10.3390/ma15186393 - 15 Sep 2022

Cited by 3 | Viewed by 2029

Abstract

This work reports the functionalization of sodium titanate nanotubes with amine groups obtained from the reaction of titanate nanotubes with [3-(2-Aminoethylamino)propyl]trimethoxysilane, NaTiNT−2NH, and 3-[2-(2-Aminoethylamino)ethylamino]propyltrimethoxysilane, NaTiNT−3NH. It was verified that the crystalline and morphological structures of NaTiNT were preserved after the functionalization, spectroscopies showed [...] Read more.

This work reports the functionalization of sodium titanate nanotubes with amine groups obtained from the reaction of titanate nanotubes with [3-(2-Aminoethylamino)propyl]trimethoxysilane, NaTiNT−2NH, and 3-[2-(2-Aminoethylamino)ethylamino]propyltrimethoxysilane, NaTiNT−3NH. It was verified that the crystalline and morphological structures of NaTiNT were preserved after the functionalization, spectroscopies showed that aminosilane interacted covalently with the surface of NaTiNT, and the incorporation of the aminosilane groups on the surface of NaTiNT can be confirmed. The adsorbent matrices NaTiNT−2NH and NaTiNT−3NH were used to remove the anionic dye from remazol blue R (RB) in aqueous medium, and the highest adsorption capacity was around 365.84 mg g

^{- 1}

(NaTiNT−2NH) and 440.70 mg g

^{- 1}

(NaTiNT−3NH) in the range of pH 5.0 to 10.0 and the equilibrium time was reached in 210 min (NaTiNT−2NH) and 270 min (NaTiNT−3NH). Furthermore, the Elovich model, which reports the adsorption in heterogeneous sites and with different activation energies in the chemisorption process, was the most appropriate to describe the adsorption kinetics. Thus, these adsorbent matrices can be used as an alternative potential for dye removal RB in aqueous solution. Full article

(This article belongs to the Special Issue Recent Advances of Adsorbents: Materials, Characterization, Applications, Kinetics and Equilibrium Models)

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10 pages, 2137 KiB

Open AccessEditor’s ChoiceArticle

Electric-Field Control of Spin Diffusion Length and Electric-Assisted D’yakonov–Perel’ Mechanism in Ultrathin Heavy Metal and Ferromagnetic Insulator Heterostructure

by Shijie Xu, Bingqian Dai, Houyi Cheng, Lixuan Tai, Lili Lang, Yadong Sun, Zhong Shi, Kang L. Wang and Weisheng Zhao

Materials 2022, 15(18), 6368; https://doi.org/10.3390/ma15186368 - 14 Sep 2022

Cited by 1 | Viewed by 2691

Abstract

Electric-field control of spin dynamics is significant for spintronic device applications. Thus far, effectively electric-field control of magnetic order, magnetic damping factor and spin–orbit torque (SOT) has been studied in magnetic materials, but the electric field control of spin relaxation still remains unexplored. [...] Read more.

Electric-field control of spin dynamics is significant for spintronic device applications. Thus far, effectively electric-field control of magnetic order, magnetic damping factor and spin–orbit torque (SOT) has been studied in magnetic materials, but the electric field control of spin relaxation still remains unexplored. Here, we use ionic liquid gating to control spin-related property in the ultra-thin (4 nm) heavy metal (HM) platinum (Pt) and ferromagnetic insulator (FMI) yttrium iron garnet (Y₃Fe₅O₁₂, YIG) heterostructure. It is found that the anomalous Hall effect (AHE), spin relaxation time and spin diffusion length can be effectively controlled by the electric field. The anomalous Hall resistance is almost twice as large as at 0 voltage after applying a small voltage of 5.5 V. The spin relaxation time can vary by more than 50 percent with the electric field, from 41.6 to 64.5 fs. In addition, spin relaxation time at different gate voltage follows the reciprocal law of the electron momentum scattering time, which indicates that the D’yakonov–Perel’ mechanism is dominant in the Pt/YIG system. Furthermore, the spin diffusion length can be effectively controlled by an ionic gate, which can be well explained by voltage-modulated interfacial spin scattering. These results help us to improve the interface spin transport properties in magnetic materials, with great contributions to the exploration of new physical mechanisms and spintronics device. Full article

(This article belongs to the Special Issue Recent Advances in Functional Magnetic Nanomaterials)

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14 pages, 6431 KiB

Open AccessEditor’s ChoiceArticle

Dissolution of β-C₂S Cement Clinker: Part 1 Molecular Dynamics (MD) Approach for Different Crystal Facets

by Khondakar Mohammad Salah Uddin, Mohammadreza Izadifar, Neven Ukrainczyk, Eduardus Koenders and Bernhard Middendorf

Materials 2022, 15(18), 6388; https://doi.org/10.3390/ma15186388 - 14 Sep 2022

Cited by 7 | Viewed by 2532

Abstract

A major concern in the modern cement industry is considering how to minimize the CO₂ footprint. Thus, cements based on belite, an impure clinker mineral (CaO)₂SiO₂ (C₂S in cement chemistry notation), which forms at lower temperatures, is [...] Read more.

A major concern in the modern cement industry is considering how to minimize the CO₂ footprint. Thus, cements based on belite, an impure clinker mineral (CaO)₂SiO₂ (C₂S in cement chemistry notation), which forms at lower temperatures, is a promising solution to develop eco-efficient and sustainable cement-based materials, used in enormous quantities. The slow reactivity of belite plays a critical role, but the dissolution mechanisms and kinetic rates at the atomistic scale are not known completely yet. This work aims to understand the dissolution behavior of different facets of β-C₂S providing missing input data and an upscaling modeling approach to connect the atomistic scale to the sub-micro scale. First, a combined ReaxFF and metadynamics-based molecular dynamic approach are applied to compute the atomistic forward reaction rates (R_D) of calcium (Ca) and silicate species of (100) facet of β-C₂S considering the influence of crystal facets and crystal defects. To minimize the huge number of atomistic events possibilities, a generalized approach is proposed, based on the systematic removal of nearest neighbors’ crystal sites. This enables us to tabulate data on the forward reaction rates of most important atomistic scenarios, which are needed as input parameters to implement the Kinetic Monte Carlo (KMC) computational upscaling approach. The reason for the higher reactivity of the (100) facet compared to the (010) is explained. Full article

(This article belongs to the Special Issue Mathematical Modeling of Building Materials)

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27 pages, 12806 KiB

Open AccessEditor’s ChoiceArticle

Seismic Performance Evaluation of Corrosion-Damaged Reinforced Concrete Columns Controlled by Shear Based on Experiment and FEA

by Young-Shik Kim, Bok-Gi Lee, Ju-Seong Jung and Kang-Seok Lee

Materials 2022, 15(18), 6361; https://doi.org/10.3390/ma15186361 - 13 Sep 2022

Cited by 2 | Viewed by 2065

Abstract

It is extremely important to investigate the effect of the seismic performance of corrosion-damaged reinforced concrete (RC) members, in terms of strength and deformability, on the seismic performance of the entire building. This will allow a more accurate assessment of the seismic performance [...] Read more.

It is extremely important to investigate the effect of the seismic performance of corrosion-damaged reinforced concrete (RC) members, in terms of strength and deformability, on the seismic performance of the entire building. This will allow a more accurate assessment of the seismic performance of RC structures with corroded members, including beams and columns. However, current methods of evaluating the seismic performance of RC structures fail to fully consider the influence of reinforcement corrosion and other performance deterioration of RC members. The main objective of this study is to propose a practical method of evaluating the seismic performance of RC structures with corrosion-damaged members, identifying factors contributing to structural performance deterioration based on strength and deformability for direct, quantitative evaluation of seismic performance. To achieve the aforementioned objective, the authors examined the effects of reinforcement corrosion on the structural behavior of RC beams and factors contributing to structural performance deterioration. Past experiments verified the strong correlation between the half-cell potential (HCP) before and after reinforcement corrosion and the reduction factor based on energy absorption capacity. However, current research evaluates the correlation between the extent of corrosion and structural performance deterioration of RC beam members, which are not members that resist lateral force. As such, the results cannot be directly applied to the evaluation of the seismic performance of RC structures containing corrosion-damaged members. To achieve this study’s main purpose of proposing a practical method of evaluating the seismic performance of RC structures comprised of corrosion-damaged members, analytical methods including structural experiments should be applied to corrosion-damaged lateral resisting members, namely, column members of the shear failure type with non-seismic details. This study performed cyclic loading tests on columns of the shear failure type having reinforcement corrosion to examine the correlation between HCP before and after corrosion and seismic performance deterioration. At the same time, finite element analysis (FEA) was carried out in consideration of the weakened bonding between steel and concrete, so as to analyze the correlation between structural performance deterioration before and after corrosion of shear columns. Through a comparison of the experimental findings and FEA results, this study proposed a seismic performance reduction factor in relation to the extent of corrosion of shear columns. Full article

(This article belongs to the Special Issue Advance in Corrosion and Protection of Metals)

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25 pages, 6749 KiB

Open AccessEditor’s ChoiceArticle

Assembling of Carbon Fibre/PEEK Composites: Comparison of Ultrasonic, Induction, and Transmission Laser Welding

by Adrian Korycki, Christian Garnier, Margot Bonmatin, Elisabeth Laurent and France Chabert

Materials 2022, 15(18), 6365; https://doi.org/10.3390/ma15186365 - 13 Sep 2022

Cited by 16 | Viewed by 3916

Abstract

In the present work, an ultrasonic, an induction, and a through transmission laser welding were compared to join carbon fibre reinforced polyetheretherketone (CF/PEEK) composites. The advantages and drawbacks of each process are discussed, as well as the material properties required to fit each [...] Read more.

In the present work, an ultrasonic, an induction, and a through transmission laser welding were compared to join carbon fibre reinforced polyetheretherketone (CF/PEEK) composites. The advantages and drawbacks of each process are discussed, as well as the material properties required to fit each process. CF/PEEK plates were consolidated at 395 °C with an unidirectional sequence and cross-stacking ply orientation. In some configurations, a polyetherimide (PEI) layer or substrate was used. The thermal, mechanical, and optical properties of the materials were measured to highlight the specific properties required for each process. The drying conditions were defined as 150 °C during at least 8 h for PEI and 24 h for CF/PEEK to avoid defects due to water. The optical transmission factor of PEI is above 40% which makes it suitable for through transmission laser welding. The thermal conductivity of CF/PEEK is at most 55 W·(m·K)⁻¹, which allows it to weld by induction without a metallic susceptor. Ultrasonic welding is the most versatile process as it does not necessitate any specific properties. Then, the mechanical resistance of the welds was measured by single lap shear. For CF/PEEK on CF/PEEK, the maximum lap shear strength (LSS) of 28.6 MPa was reached for a joint obtained by ultrasonic welding, while an induction one brought 17.6 MPa. The maximum LSS of 15.2 MPa was obtained for PEI on CF/PEEK assemblies by laser welding. Finally, interfacial resistances were correlated to the fracture modes through observations of the fractured surfaces. CF/PEEK on CF/PEEK joints resulted in mixed cohesive/adhesive failure at the interface and within the inner layers of both substrates. This study presents a guideline to select the suitable welding process when assembling composites for the aerospace industry. Full article

(This article belongs to the Special Issue Fusion Bonding/Welding of Polymer Composites)

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35 pages, 4542 KiB

Open AccessEditor’s ChoiceReview

Designing a Biomaterial Approach to Control the Adaptive Response to a Skin Injury

by Dale Feldman

Materials 2022, 15(18), 6366; https://doi.org/10.3390/ma15186366 - 13 Sep 2022

Cited by 2 | Viewed by 1916

Abstract

The goal of this review is to explain how to design a biomaterial approach to control the adaptive response to injury, with an emphasis on skin wounds. The strategies will be selected based on whether they have a reasonable probability of meeting the [...] Read more.

The goal of this review is to explain how to design a biomaterial approach to control the adaptive response to injury, with an emphasis on skin wounds. The strategies will be selected based on whether they have a reasonable probability of meeting the desired clinical outcome vs. just comparing the pros and cons of different strategies. To do this, the review will look at the normal adaptive response in adults and why it does not meet the desired clinical outcome in most cases. In addition, the adaptive response will be looked at in cases where it does meet the clinical performance requirements including animals that regenerate and for fetal wound healing. This will lead to how biomaterials can be used to alter the overall adaptive response to allow it to meet the desired clinical outcome. The important message of the review is that you need to use the engineering design process, not the scientific method, to design a clinical treatment. Also, the clinical performance requirements are functional, not structural. The last section will give some specific examples of controlling the adaptive response for two skin injuries: burns and pressure ulcers. For burns, it will cover some preclinical studies used to justify a clinical study as well as discuss the results of a clinical study using this system. For pressure ulcers, it will cover some preclinical studies for two different approaches: electrical stimulation and degradable/regenerative scaffolds. For electrical stimulation, the results of a clinical study will be presented. Full article

(This article belongs to the Special Issue Biological Materials in Health and Disease)

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18 pages, 3496 KiB

Open AccessEditor’s ChoiceArticle

Benchmarking for Strain Evaluation in CFRP Laminates Using Computer Vision: Machine Learning versus Deep Learning

by Jónatas Valença, Habibu Mukhandi, André G. Araújo, Micael S. Couceiro and Eduardo Júlio

Materials 2022, 15(18), 6310; https://doi.org/10.3390/ma15186310 - 11 Sep 2022

Cited by 17 | Viewed by 3412

Abstract

The strengthening of concrete structures with laminates of Carbon-Fiber-Reinforced Polymers (CFRP) is a widely adopted technique. retained The application is more effective if pre-stressed CFRP laminates are adopted. The measurement of the strain level during the pre-stress application usually involves laborious and time-consuming [...] Read more.

The strengthening of concrete structures with laminates of Carbon-Fiber-Reinforced Polymers (CFRP) is a widely adopted technique. retained The application is more effective if pre-stressed CFRP laminates are adopted. The measurement of the strain level during the pre-stress application usually involves laborious and time-consuming applications of instrumentation. Thus, the development of expedited approaches to accurately measure the pre-stressed application in the laminates represents an important contribution to the field. This paper proposes and benchmarks contact-free architecture for measuring the strain level of CFRP laminate based on computer vision. The main objective is to provide a solution that might be economically feasible, automated, easy to use, and accurate. The architecture is fed by digitally deformed synthetic images, generated based on a low-resolution camera. The adopted methods range from traditional machine learning to deep learning. Furthermore, dropout and cross-validation methods for quantifying traditional machine learning algorithms and neural networks are used to efficiently provide uncertainty estimates. ResNet34 deep learning architecture provided the most accurate results, reaching a root mean square error (RMSE) of 0.057‰ for strain prediction. Finally, it is important to highlight that the architecture presented is contact-free, automatic, cost-effective, and measures directly on the laminate surfaces, which allows them to be widely used in the application of pre-stressed laminates. Full article

(This article belongs to the Special Issue Damage Analysis and Reliability Assessment for Composite Materials)

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18 pages, 8289 KiB

Open AccessEditor’s ChoiceArticle

Designing for Shape Memory in Additive Manufacturing of Cu–Al–Ni Shape Memory Alloy Processed by Laser Powder Bed Fusion

by Mikel Pérez-Cerrato, Itziar Fraile, José Fernando Gómez-Cortés, Ernesto Urionabarrenetxea, Isabel Ruiz-Larrea, Iban González, María Luisa Nó, Nerea Burgos and Jose M. San Juan

Materials 2022, 15(18), 6284; https://doi.org/10.3390/ma15186284 - 9 Sep 2022

Cited by 24 | Viewed by 3442

Abstract

Shape memory alloys (SMAs) are functional materials that are being applied in practically all industries, from aerospace to biomedical sectors, and at present the scientific and technologic communities are looking to gain the advantages offered by the new processing technologies of additive manufacturing [...] Read more.

Shape memory alloys (SMAs) are functional materials that are being applied in practically all industries, from aerospace to biomedical sectors, and at present the scientific and technologic communities are looking to gain the advantages offered by the new processing technologies of additive manufacturing (AM). However, the use of AM to produce functional materials, like SMAs, constitutes a real challenge due to the particularly well controlled microstructure required to exhibit the functional property of shape memory. In the present work, the design of the complete AM processing route, from powder atomization to laser powder bed fusion for AM and hot isostatic pressing (HIP), is approached for Cu–Al–Ni SMAs. The microstructure of the different processing states is characterized in relationship with the processing parameters. The thermal martensitic transformation, responsible for the functional properties, is analyzed in a comparative way for each one of the different processed samples. The present results demonstrate that a final post–processing thermal treatment to control the microstructure is crucial to obtain the expected functional properties. Finally, it is demonstrated that using the designed processing route of laser powder bed fusion followed by a post–processing HIP and a final specific thermal treatment, a satisfactory shape memory behavior can be obtained in Cu–Al–Ni SMAs, paving the road for further applications. Full article

(This article belongs to the Special Issue Design, Characterization and Novel Applications of Shape Memory Alloys)

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15 pages, 21705 KiB

Open AccessEditor’s ChoiceArticle

Charge Storage and Reliability Characteristics of Nonvolatile Memory Capacitors with HfO₂/Al₂O₃-Based Charge Trapping Layers

by Dencho Spassov, Albena Paskaleva, Elżbieta Guziewicz, Wojciech Wozniak, Todor Stanchev, Tsvetan Ivanov, Joanna Wojewoda-Budka and Marta Janusz-Skuza

Materials 2022, 15(18), 6285; https://doi.org/10.3390/ma15186285 - 9 Sep 2022

Cited by 10 | Viewed by 3082

Abstract

Flash memories are the preferred choice for data storage in portable gadgets. The charge trapping nonvolatile flash memories are the main contender to replace standard floating gate technology. In this work, we investigate metal/blocking oxide/high-k charge trapping layer/tunnel oxide/Si (MOHOS) structures from the [...] Read more.

Flash memories are the preferred choice for data storage in portable gadgets. The charge trapping nonvolatile flash memories are the main contender to replace standard floating gate technology. In this work, we investigate metal/blocking oxide/high-k charge trapping layer/tunnel oxide/Si (MOHOS) structures from the viewpoint of their application as memory cells in charge trapping flash memories. Two different stacks, HfO₂/Al₂O₃ nanolaminates and Al-doped HfO₂, are used as the charge trapping layer, and SiO₂ (of different thickness) or Al₂O₃ is used as the tunneling oxide. The charge trapping and memory windows, and retention and endurance characteristics are studied to assess the charge storage ability of memory cells. The influence of post-deposition oxygen annealing on the memory characteristics is also studied. The results reveal that these characteristics are most strongly affected by post-deposition oxygen annealing and the type and thickness of tunneling oxide. The stacks before annealing and the 3.5 nm SiO₂ tunneling oxide have favorable charge trapping and retention properties, but their endurance is compromised because of the high electric field vulnerability. Rapid thermal annealing (RTA) in O₂ significantly increases the electron trapping (hence, the memory window) in the stacks; however, it deteriorates their retention properties, most likely due to the interfacial reaction between the tunneling oxide and the charge trapping layer. The O₂ annealing also enhances the high electric field susceptibility of the stacks, which results in better endurance. The results strongly imply that the origin of electron and hole traps is different—the hole traps are most likely related to HfO₂, while electron traps are related to Al₂O₃. These findings could serve as a useful guide for further optimization of MOHOS structures as memory cells in NVM. Full article

(This article belongs to the Special Issue Physics, Electrical and Structural Properties of Dielectric Layers)

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12 pages, 13146 KiB

Open AccessEditor’s ChoiceArticle

Phonon Structure, Infra-Red and Raman Spectra of Li₂MnO₃ by First-Principles Calculations

by Ruth Pulido, Nelson Naveas, Raúl J. Martin-Palma, Fernando Agulló-Rueda, Victor R. Ferró, Jacobo Hernández-Montelongo, Gonzalo Recio-Sánchez, Ivan Brito and Miguel Manso-Silván

Materials 2022, 15(18), 6237; https://doi.org/10.3390/ma15186237 - 8 Sep 2022

Cited by 6 | Viewed by 3623

Abstract

The layer-structured monoclinic Li₂MnO₃ is a key material, mainly due to its role in Li-ion batteries and as a precursor for adsorbent used in lithium recovery from aqueous solutions. In the present work, we used first-principles calculations based on density [...] Read more.

The layer-structured monoclinic Li₂MnO₃ is a key material, mainly due to its role in Li-ion batteries and as a precursor for adsorbent used in lithium recovery from aqueous solutions. In the present work, we used first-principles calculations based on density functional theory (DFT) to study the crystal structure, optical phonon frequencies, infra-red (IR), and Raman active modes and compared the results with experimental data. First, Li₂MnO₃ powder was synthesized by the hydrothermal method and successively characterized by XRD, TEM, FTIR, and Raman spectroscopy. Secondly, by using Local Density Approximation (LDA), we carried out a DFT study of the crystal structure and electronic properties of Li₂MnO₃. Finally, we calculated the vibrational properties using Density Functional Perturbation Theory (DFPT). Our results show that simulated IR and Raman spectra agree well with the observed phonon structure. Additionally, the IR and Raman theoretical spectra show similar features compared to the experimental ones. This research is useful in investigations involving the physicochemical characterization of Li₂MnO₃ material. Full article

(This article belongs to the Special Issue Advances in Density Functional Theory (DFT) Studies of Solids (Second Volume))

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50 pages, 5934 KiB

Open AccessEditor’s ChoiceReview

Graphene: A Path-Breaking Discovery for Energy Storage and Sustainability

by Deepam Goyal, Rajeev Kumar Dang, Tarun Goyal, Kuldeep K. Saxena, Kahtan A. Mohammed and Saurav Dixit

Materials 2022, 15(18), 6241; https://doi.org/10.3390/ma15186241 - 8 Sep 2022

Cited by 28 | Viewed by 3332

Abstract

The global energy situation requires the efficient use of resources and the development of new materials and processes for meeting current energy demand. Traditional materials have been explored to large extent for use in energy saving and storage devices. Graphene, being a path-breaking [...] Read more.

The global energy situation requires the efficient use of resources and the development of new materials and processes for meeting current energy demand. Traditional materials have been explored to large extent for use in energy saving and storage devices. Graphene, being a path-breaking discovery of the present era, has become one of the most-researched materials due to its fascinating properties, such as high tensile strength, half-integer quantum Hall effect and excellent electrical/thermal conductivity. This paper presents an in-depth review on the exploration of deploying diverse derivatives and morphologies of graphene in various energy-saving and environmentally friendly applications. Use of graphene in lubricants has resulted in improvements to anti-wear characteristics and reduced frictional losses. This comprehensive survey facilitates the researchers in selecting the appropriate graphene derivative(s) and their compatibility with various materials to fabricate high-performance composites for usage in solar cells, fuel cells, supercapacitor applications, rechargeable batteries and automotive sectors. Full article

(This article belongs to the Special Issue Multifunction Materials, Interfaces, and Composites: Design and Applications)

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21 pages, 2835 KiB

Open AccessEditor’s ChoiceArticle

Investigation of Multicomponent Fluoridated Borate Glasses through a Design of Mixtures Approach

by Kathleen MacDonald and Daniel Boyd

Materials 2022, 15(18), 6247; https://doi.org/10.3390/ma15186247 - 8 Sep 2022

Cited by 4 | Viewed by 2296

Abstract

Due to their enhanced dissolution, solubility and reaction speed, borate glasses offer potential advantages for the design and development of therapeutic ion-release systems. However, the field remains poorly understood relative to traditional phosphosilicate and silicate bioglasses. The increased structural complexity and relative lack [...] Read more.

Due to their enhanced dissolution, solubility and reaction speed, borate glasses offer potential advantages for the design and development of therapeutic ion-release systems. However, the field remains poorly understood relative to traditional phosphosilicate and silicate bioglasses. The increased structural complexity and relative lack of published data relating to borates, particularly borofluorates, also decreases the accuracy of artificial intelligence models, which are used to predict glass properties. To develop predictive models for borofluorate networks, this paper uses a design of mixtures approach for rapid screening of composition–property relationships, including the development of polynomial equations that comprehensively establish the predictive capabilities for glass transition, density, mass loss and fluoride release. A broad range of glass compositions, extending through the boron anomaly range, were investigated, with the inclusion of 45 to 95 mol% B₂O₃ along with 1–50 mol% MgO, CaO and Na₂O as well as 1–30% KF and NaF. This design space allows for the investigation of the impact of fluorine as well as mixed alkali–alkaline earth effects. Glass formation was found to extend past 30 mol% KF or NaF without a negative impact on glass degradation in contrast to the trends observed in phosphosilicates. The data demonstrates that fluoroborate materials offer an exceptional base for the development of fluoride-releasing materials. Full article

(This article belongs to the Special Issue Bioceramics and Bioactive Glass-Based Composites)

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11 pages, 3687 KiB

Open AccessEditor’s ChoiceArticle

Poly(lactic acid) Matrix Reinforced with Diatomaceous Earth

by Izabela Zglobicka, Magdalena Joka-Yildiz, Rafal Molak, Michal Kawalec, Adrian Dubicki, Jakub Wroblewski, Kamil Dydek, Anna Boczkowska and Krzysztof J. Kurzydlowski

Materials 2022, 15(18), 6210; https://doi.org/10.3390/ma15186210 - 7 Sep 2022

Cited by 7 | Viewed by 2140

Abstract

The poly(lactic acid) (PLA) biodegradable polymer, as well as natural, siliceous reinforcement in the form of diatomaceous earth, fit perfectly into the circular economy trend. In this study, various kinds of commercial PLA have been reinforced with diatomaceous earth (DE) to prepare biodegradable [...] Read more.

The poly(lactic acid) (PLA) biodegradable polymer, as well as natural, siliceous reinforcement in the form of diatomaceous earth, fit perfectly into the circular economy trend. In this study, various kinds of commercial PLA have been reinforced with diatomaceous earth (DE) to prepare biodegradable composites via the extrusion process. The structure of the manufactured composites as well as adhesion between the matrix and the filler were investigated using scanning electron microscopy (SEM). Differential scanning calorimetry (DSC) analyses were carried out to determine crystallinity of PLA matrix as function of DE additions. Additionally, the effect of the ceramic-based reinforcement on the mechanical properties (Young’s modulus, elongation to failure, ultimate tensile strength) of PLA has been investigated. The results are discussed in terms of possible applications of PLA + DE composites. Full article

(This article belongs to the Section Advanced Composites)

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24 pages, 4351 KiB

Open AccessEditor’s ChoiceReview

Developing Insulating Polymeric Foams: Strategies and Research Needs from a Circular Economy Perspective

by Lucia Doyle, Ingo Weidlich and Ernesto Di Maio

Materials 2022, 15(18), 6212; https://doi.org/10.3390/ma15186212 - 7 Sep 2022

Cited by 16 | Viewed by 4030

Abstract

Insulating polymeric foams have an important role to play in increasing energy efficiency and therefore contributing to combating climate change. Their development in recent years has been driven towards the reduction of thermal conductivity and achievement of the required mechanical properties as main [...] Read more.

Insulating polymeric foams have an important role to play in increasing energy efficiency and therefore contributing to combating climate change. Their development in recent years has been driven towards the reduction of thermal conductivity and achievement of the required mechanical properties as main targets towards sustainability. This perception of sustainability has overseen the choice of raw materials, which are often toxic, or has placed research efforts on optimizing one constituent while the other necessary reactants remain hazardous. The transition to the circular economy requires a holistic understanding of sustainability and a shift in design methodology and the resulting research focus. This paper identifies research needs and possible strategies for polymeric foam development compatible with Circular Product Design and Green Engineering, based on an extensive literature review. Identified research needs include material characterization of a broader spectrum of polymer melt–gas solutions, ageing behavior, tailoring of the polymer chains, detailed understanding and modeling of the effects of shear on cell nucleation, and the upscaling of processing tools allowing for high and defined pressure drop rates. Full article

(This article belongs to the Special Issue Polymer Foams: Materials, Processing and Properties)

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17 pages, 4370 KiB

Open AccessEditor’s ChoiceArticle

High-Energy Computed Tomography as a Prospective Tool for In Situ Monitoring of Mass Transfer Processes inside High-Pressure Reactors—A Case Study on Ammonothermal Bulk Crystal Growth of Nitrides including GaN

by Saskia Schimmel, Michael Salamon, Daisuke Tomida, Steffen Neumeier, Tohru Ishiguro, Yoshio Honda, Shigefusa F. Chichibu and Hiroshi Amano

Materials 2022, 15(17), 6165; https://doi.org/10.3390/ma15176165 - 5 Sep 2022

Cited by 3 | Viewed by 3080

Abstract

For the fundamental understanding and the technological development of the ammonothermal method for the synthesis and crystal growth of nitrides, an in situ monitoring technique for tracking mass transport of the nitride throughout the entire autoclave volume is desirable. The feasibility of using [...] Read more.

For the fundamental understanding and the technological development of the ammonothermal method for the synthesis and crystal growth of nitrides, an in situ monitoring technique for tracking mass transport of the nitride throughout the entire autoclave volume is desirable. The feasibility of using high-energy computed tomography for this purpose was therefore evaluated using ex situ measurements. Acceleration voltages of 600 kV were estimated to yield suitable transparency in a lab-scale ammonothermal setup for GaN crystal growth designed for up to 300 MPa operating pressure. The total scan duration was estimated to be in the order of 20 to 40 min, which was sufficient given the comparatively slow crystal growth speed in ammonothermal growth. Even shorter scan durations or, alternatively, lower acceleration voltages for improved contrast or reduced X-ray shielding requirements, were estimated to be feasible in the case of ammonoacidic growth, as the lower pressure requirements for this process variant allow for thinned autoclave walls in an adapted setup designed for improved X-ray transparency. Promising nickel-base and cobalt-base alloys for applications in ammonothermal reactors with reduced X-ray absorption in relation to the maximum operating pressure were identified. The applicability for the validation of numerical simulations of the growth process of GaN, in addition to the applicability of the technique to further nitride materials, as well as larger reactors and bulk crystals, were evaluated. Full article

(This article belongs to the Special Issue Wide and Ultra-Wide Bandgap Semiconductor Materials for Power Devices)

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32 pages, 3128 KiB

Open AccessEditor’s ChoiceReview

Lignin as a Renewable Building Block for Sustainable Polyurethanes

by Fernanda Rosa Vieira, Sandra Magina, Dmitry V. Evtuguin and Ana Barros-Timmons

Materials 2022, 15(17), 6182; https://doi.org/10.3390/ma15176182 - 5 Sep 2022

Cited by 37 | Viewed by 7128

Abstract

Currently, the pulp and paper industry generates around 50–70 million tons of lignin annually, which is mainly burned for energy recovery. Lignin, being a natural aromatic polymer rich in functional hydroxyl groups, has been drawing the interest of academia and industry for its [...] Read more.

Currently, the pulp and paper industry generates around 50–70 million tons of lignin annually, which is mainly burned for energy recovery. Lignin, being a natural aromatic polymer rich in functional hydroxyl groups, has been drawing the interest of academia and industry for its valorization, especially for the development of polymeric materials. Among the different types of polymers that can be derived from lignin, polyurethanes (PUs) are amid the most important ones, especially due to their wide range of applications. This review encompasses available technologies to isolate lignin from pulping processes, the main approaches to convert solid lignin into a liquid polyol to produce bio-based polyurethanes, the challenges involving its characterization, and the current technology assessment. Despite the fact that PUs derived from bio-based polyols, such as lignin, are important in contributing to the circular economy, the use of isocyanate is a major environmental hot spot. Therefore, the main strategies that have been used to replace isocyanates to produce non-isocyanate polyurethanes (NIPUs) derived from lignin are also discussed. Full article

(This article belongs to the Special Issue Synthesis and Application of New Lignin-Based Polymers and Composites)

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16 pages, 5626 KiB

Open AccessEditor’s ChoiceArticle

Theoretical Modelling of the Degradation Processes Induced by Freeze–Thaw Cycles on Bond-Slip Laws of Fibres in High-Performance Fibre-Reinforced Concrete

by Rosa Penna, Luciano Feo, Enzo Martinelli and Marco Pepe

Materials 2022, 15(17), 6122; https://doi.org/10.3390/ma15176122 - 3 Sep 2022

Cited by 7 | Viewed by 1719

Abstract

High-performance fibre-reinforced concrete (HPFRC) is a composite material in which the advantages of fibre-reinforced concrete (FRC) are combined with those of a high-performance concrete (HPC), which mitigates the weaknesses of conventional concrete and improves its overall performance. With the aim to reduce the [...] Read more.

High-performance fibre-reinforced concrete (HPFRC) is a composite material in which the advantages of fibre-reinforced concrete (FRC) are combined with those of a high-performance concrete (HPC), which mitigates the weaknesses of conventional concrete and improves its overall performance. With the aim to reduce the long-term maintenance costs of structures, such as heavily loaded bridges, HPFRC is highly recommended due to its major durability performance. Specifically, its good antifreezing property makes it suitable for application in cold regions where cyclic freeze–thaw conditions cause the concrete to degrade. In this paper, a numerical simulation of the degradation processes induced by freeze–thaw cycles on bond-slip laws in HPFRC beam specimens has been developed so as to assess their effect on the flexural response of specimens as the fibres’ volume percentage changes. Their cracking strength, postcracking strength, and toughness were predicted, with the present model being able to predict the cracking strength, postcracking strength and toughness of the HPFRC beam element under bending load conditions. Its accuracy was confirmed by comparing the model predictions with experimental results. Full article

(This article belongs to the Special Issue Advances in Sustainable Inorganic Matrix Composites for Construction)

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14 pages, 5445 KiB

Open AccessEditor’s ChoiceArticle

A Novel Method for Carbendazim High-Sensitivity Detection Based on the Combination of Metamaterial Sensor and Machine Learning

by Ruizhao Yang, Yun Li, Jincun Zheng, Jie Qiu, Jinwen Song, Fengxia Xu and Binyi Qin

Materials 2022, 15(17), 6093; https://doi.org/10.3390/ma15176093 - 2 Sep 2022

Cited by 7 | Viewed by 2129

Abstract

Benzimidazole fungicide residue in food products poses a risk to consumer health. Due to its localized electric-field enhancement and high-quality factor value, the metamaterial sensor is appropriate for applications regarding food safety detection. However, the previous detection method based on the metamaterial sensor [...] Read more.

Benzimidazole fungicide residue in food products poses a risk to consumer health. Due to its localized electric-field enhancement and high-quality factor value, the metamaterial sensor is appropriate for applications regarding food safety detection. However, the previous detection method based on the metamaterial sensor only considered the resonance dip shift. It neglected other information contained in the spectrum. In this study, we proposed a method for highly sensitive detection of benzimidazole fungicide using a combination of a metamaterial sensor and mean shift machine learning method. The unit cell of the metamaterial sensor contained a cut wire and two split-ring resonances. Mean shift, an unsupervised machine learning method, was employed to analyze the THz spectrum. The experiment results show that our proposed method could detect carbendazim concentrations as low as 0.5 mg/L. The detection sensitivity was enhanced 200 times compared to that achieved using the metamaterial sensor only. Our present work demonstrates a potential application of combining a metamaterial sensor and mean shift in benzimidazole fungicide residue detection. Full article

(This article belongs to the Special Issue Design and Applications of Terahertz Metamaterials)

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24 pages, 7048 KiB

Open AccessEditor’s ChoiceArticle

3D Printing of Cellulase-Laden Cellulose Nanofiber/Chitosan Hydrogel Composites: Towards Tissue Engineering Functional Biomaterials with Enzyme-Mediated Biodegradation

by Arnaud Kamdem Tamo, Tuan Anh Tran, Ingo Doench, Shaghayegh Jahangir, Aastha Lall, Laurent David, Carlos Peniche-Covas, Andreas Walther and Anayancy Osorio-Madrazo

Materials 2022, 15(17), 6039; https://doi.org/10.3390/ma15176039 - 1 Sep 2022

Cited by 33 | Viewed by 5530

Abstract

The 3D printing of a multifunctional hydrogel biomaterial with bioactivity for tissue engineering, good mechanical properties and a biodegradability mediated by free and encapsulated cellulase was proposed. Bioinks of cellulase-laden and cellulose nanofiber filled chitosan viscous suspensions were used to 3D print enzymatic [...] Read more.

The 3D printing of a multifunctional hydrogel biomaterial with bioactivity for tissue engineering, good mechanical properties and a biodegradability mediated by free and encapsulated cellulase was proposed. Bioinks of cellulase-laden and cellulose nanofiber filled chitosan viscous suspensions were used to 3D print enzymatic biodegradable and biocompatible cellulose nanofiber (CNF) reinforced chitosan (CHI) hydrogels. The study of the kinetics of CNF enzymatic degradation was studied in situ in fibroblast cell culture. To preserve enzyme stability as well as to guarantee its sustained release, the cellulase was preliminarily encapsulated in chitosan–caseinate nanoparticles, which were further incorporated in the CNF/CHI viscous suspension before the 3D printing of the ink. The incorporation of the enzyme within the CHI/CNF hydrogel contributed to control the decrease of the CNF mechanical reinforcement in the long term while keeping the cell growth-promoting property of chitosan. The hydrolysis kinetics of cellulose in the 3D printed scaffolds showed a slow but sustained degradation of the CNFs with enzyme, with approximately 65% and 55% relative activities still obtained after 14 days of incubation for the encapsulated and free enzyme, respectively. The 3D printed composite hydrogels showed excellent cytocompatibility supporting fibroblast cell attachment, proliferation and growth. Ultimately, the concomitant cell growth and biodegradation of CNFs within the 3D printed CHI/CNF scaffolds highlights the remarkable potential of CHI/CNF composites in the design of tissue models for the development of 3D constructs with tailored in vitro/in vivo degradability for biomedical applications. Full article

(This article belongs to the Special Issue 3D Printing Functional Biomaterials)

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17 pages, 3368 KiB

Open AccessEditor’s ChoiceReview

Direct Writing of Functional Layer by Selective Laser Sintering of Nanoparticles for Emerging Applications: A Review

by Eunseung Hwang, Jungmin Hong, Jonghun Yoon and Sukjoon Hong

Materials 2022, 15(17), 6006; https://doi.org/10.3390/ma15176006 - 31 Aug 2022

Cited by 10 | Viewed by 3548

Abstract

Selective laser sintering of nanoparticles enables the direct and rapid formation of a functional layer even on heat-sensitive flexible and stretchable substrates, and is rising as a pioneering fabrication technology for future-oriented applications. To date, laser sintering has been successfully applied to various [...] Read more.

Selective laser sintering of nanoparticles enables the direct and rapid formation of a functional layer even on heat-sensitive flexible and stretchable substrates, and is rising as a pioneering fabrication technology for future-oriented applications. To date, laser sintering has been successfully applied to various target nanomaterials including a wide range of metal and metal-oxide nanoparticles, and extensive investigation of relevant experimental schemes have not only reduced the minimum feature size but also have further expanded the scalability of the process. In the beginning, the selective laser sintering process was regarded as an alternative method to conventional manufacturing processes, but recent studies have shown that the unique characteristics of the laser-sintered layer may improve device performance or even enable novel functionalities which were not achievable using conventional fabrication techniques. In this regard, we summarize the current developmental status of the selective laser sintering technique for nanoparticles, affording special attention to recent emerging applications that adopt the laser sintering scheme. Full article

(This article belongs to the Special Issue Feature Paper in Section Smart Materials)

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13 pages, 1877 KiB

Open AccessEditor’s ChoiceArticle

Effects of Mono- and Bifunctional Surface Ligands of Cu–In–Se Quantum Dots on Photoelectrochemical Hydrogen Production

by Soo Ik Park, Sung-Mok Jung, Jae-Yup Kim and Jiwoong Yang

Materials 2022, 15(17), 6010; https://doi.org/10.3390/ma15176010 - 31 Aug 2022

Cited by 7 | Viewed by 2861

Abstract

Semiconductor nanocrystal quantum dots (QDs) are promising materials for solar energy conversion because of their bandgap tunability, high absorption coefficient, and improved hot-carrier generation. CuInSe₂ (CISe)-based QDs have attracted attention because of their low toxicity and wide light-absorption range, spanning visible to [...] Read more.

Semiconductor nanocrystal quantum dots (QDs) are promising materials for solar energy conversion because of their bandgap tunability, high absorption coefficient, and improved hot-carrier generation. CuInSe₂ (CISe)-based QDs have attracted attention because of their low toxicity and wide light-absorption range, spanning visible to near-infrared light. In this work, we study the effects of the surface ligands of colloidal CISe QDs on the photoelectrochemical characteristics of QD-photoanodes. Colloidal CISe QDs with mono- and bifunctional surface ligands are prepared and used in the fabrication of type-II heterojunction photoanodes by adsorbing QDs on mesoporous TiO₂. QDs with monofunctional ligands are directly attached on TiO₂ through partial ligand detachment, which is beneficial for electron transfer between QDs and TiO₂. In contrast, bifunctional ligands bridge QDs and TiO₂, increasing the amount of QD adsorption. Finally, photoanodes fabricated with oleylamine-passivated QDs show a current density of ~8.2 mA/cm², while those fabricated with mercaptopropionic-acid-passivated QDs demonstrate a current density of ~6.7 mA/cm² (at 0.6 V_RHE under one sun illumination). Our study provides important information for the preparation of QD photoelectrodes for efficient photoelectrochemical hydrogen generation. Full article

(This article belongs to the Special Issue Advances in Nanostructured Catalysts)

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7 pages, 6198 KiB

Open AccessEditor’s ChoiceArticle

Double-Resolved Beam Steering by Metagrating-Based Tamm Plasmon Polariton

by Rashid G. Bikbaev, Dmitrii N. Maksimov, Kuo-Ping Chen and Ivan V. Timofeev

Materials 2022, 15(17), 6014; https://doi.org/10.3390/ma15176014 - 31 Aug 2022

Cited by 14 | Viewed by 2459

Abstract

We consider Tamm plasmon polariton in a subwavelength grating patterned on top of a Bragg reflector. We demonstrate dynamic control of the phase and amplitude of a plane wave reflected from such metagrating due to resonant coupling with the Tamm plasmon polariton. The [...] Read more.

We consider Tamm plasmon polariton in a subwavelength grating patterned on top of a Bragg reflector. We demonstrate dynamic control of the phase and amplitude of a plane wave reflected from such metagrating due to resonant coupling with the Tamm plasmon polariton. The tunability of the phase and amplitude of the reflected wave arises from modulation of the refractive index of a transparent conductive oxide layer by applying the bias voltage. The electrical switching of diffracted beams of the ±1st order is shown. The possibility of doubling the angular resolution of beam steering by using asymmetric reflected phase distribution with integer and half-integer periods of the metagrating is demonstrated. Full article

(This article belongs to the Special Issue Soft Photonic Crystals and Metamaterials)

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