Materials

11 pages, 3705 KiB

Open AccessEditor’s ChoiceArticle

Zirconium Oxide as a Novel Material for Post-Endodontically Treated Teeth: Comparative Fracture Behavior of 3D-Printed Cobalt–Chromium, Milled Zirconium Oxide, and Quartz Fiber Posts

by Armin Sokolowski, Fernando Gustavo Warchomicka, Lukas Seebacher, Bernhard Remschmidt, Marcus Rieder, Lumnije Kqiku-Biblekaj and Alwin Sokolowski

Materials 2024, 17(22), 5611; https://doi.org/10.3390/ma17225611 - 17 Nov 2024

Viewed by 1243

Abstract

This study evaluates the mechanical properties of materials used in the post-endodontic restoration of root-treated teeth and examines their performance under stress to provide insights for material selection in clinical applications. Particular attention is given to zirconium oxide, which demonstrates promising characteristics due [...] Read more.

This study evaluates the mechanical properties of materials used in the post-endodontic restoration of root-treated teeth and examines their performance under stress to provide insights for material selection in clinical applications. Particular attention is given to zirconium oxide, which demonstrates promising characteristics due to its esthetic color and favorable material properties, positioning it as a potential material for future use in post-endodontic treatments. Three materials—prefabricated quartz fiber-reinforced composite, milled zirconium oxide, and additively manufactured cobalt–chromium—were evaluated using compressive-deflection tests. The specimens were subjected to a 45° compressive load extending 5 mm from a metal core. Their mechanical properties were analyzed using one-way ANOVA and Tukey’s post hoc test. Significant differences were observed among the materials. Quartz fiber posts, with the lowest force resistance, buckled at lower loads (143.3 ± 9.9 N), while zirconia posts failed in a brittle manner at higher forces (246.1 ± 97.2 N). Cobalt–chromium posts demonstrated the highest maximal force (323.2 ± 10.5 N, p < 0.001) and, unlike the other materials, bent rather than fractured. The failure patterns of the tested materials underscore the importance of careful material selection when restoring root-treated teeth. Despite displaying distinct fracture characteristics, zirconium oxide, due to its color, rigidity, and hardness, stands out as a promising material for future dental applications. Further research through randomized clinical trials is recommended to refine treatment approaches and optimize clinical outcomes. Full article

(This article belongs to the Special Issue Recent Research in Restorative Dental Materials)

► Show Figures

Figure 1

18 pages, 5642 KiB

Open AccessEditor’s ChoiceArticle

A New Slicer-Based Method to Generate Infill Inspired by Sandwich-Patterns for Reduced Material Consumption

by Patrick Steck, Dominik Schuler, Christian Witzgall and Sandro Wartzack

Materials 2024, 17(22), 5596; https://doi.org/10.3390/ma17225596 - 15 Nov 2024

Viewed by 995

Abstract

This work presents a novel infill method for additive manufacturing, specifically designed to optimize material use and enhance stiffness in fused filament fabrication (FFF) parts through a geometry-aware, corrugated design inspired by sandwich structures. Unlike standard infill patterns, which typically employ uniform, space-filling [...] Read more.

This work presents a novel infill method for additive manufacturing, specifically designed to optimize material use and enhance stiffness in fused filament fabrication (FFF) parts through a geometry-aware, corrugated design inspired by sandwich structures. Unlike standard infill patterns, which typically employ uniform, space-filling grids that often disregard load-specific requirements, this method generates a cavity inside the component to be printed and fill the space between inner and outer contours with continuous, adaptable extrusion paths. This design enables consistent support and improved load distribution, making it particularly effective for parts under bending stresses, as it enhances structural resilience without requiring additional material. Simulations performed on a 10 cm³ test part using this method showed potential reductions in material consumption by up to 77% and a decrease in print time by 78%, while maintaining stiffness comparable to parts using conventional 100% grid infill. Additionally, simulations demonstrated that the new corrugated infill pattern provides near-isotropic stiffness, addressing the anisotropic limitations often seen in traditional infill designs that are sensitive to load orientation. This geometry-aware infill strategy thus contributes to balanced stiffness across complex geometries, enhancing reliability under mechanical loads. By integrating directly with slicer software, this approach simplifies advanced stiffness optimization without the necessity of finite element analysis-based topology optimization. Full article

(This article belongs to the Special Issue Advanced Additive Manufacturing and Application)

► Show Figures

Figure 1

13 pages, 7008 KiB

Open AccessEditor’s ChoiceArticle

Si Characterization on Thinning and Singulation Processes for 2.5/3D HBM Package Integration

by MiKyeong Choi, SeaHwan Kim, TaeJoon Noh, DongGil Kang and SeungBoo Jung

Materials 2024, 17(22), 5529; https://doi.org/10.3390/ma17225529 - 13 Nov 2024

Viewed by 1111

Abstract

As stacking technologies, such as 2.5D and 3D packages, continue to accelerate in advanced semiconductor components, the singulation and thinning of Si wafers are becoming increasingly critical. Despite their importance in producing thinner and more reliable Si chips, achieving high reliability remains a [...] Read more.

As stacking technologies, such as 2.5D and 3D packages, continue to accelerate in advanced semiconductor components, the singulation and thinning of Si wafers are becoming increasingly critical. Despite their importance in producing thinner and more reliable Si chips, achieving high reliability remains a challenge, and comprehensive research on the effects of these processing techniques on Si chip integrity is lacking. In this study, the impacts of wafer thinning and singulation on the fracture strength of Si wafers were systematically compared. Three different grinding processes, namely fine grinding, poly-grinding, and polishing, were used for thinning, and the resulting surface morphology and roughness were analyzed using scanning electron microscopy and an interferometer. In addition, the residual mechanical stress on the wafer surface was measured using Raman spectroscopy. The fracture strength of Si wafers and chips was assessed through three-point bending tests. Singulation, including blade dicing, laser dicing, and stealth dicing, was evaluated for its impact on fracture strength. Among these processes, polishing for wafer thinning exhibited the lowest full-width half maximum and intensity ratio of Raman shifts (I480/I520), indicating minimal residual stress and surface defects. Consequently, Si wafers and chips processed through polishing demonstrated the highest fracture strength. Moreover, the 60 µm thick Si wafers and chips showed the highest fracture strength compared with those with thicknesses of 90 and 120 µm, possibly because of the increased flexibility, which mitigates stress. Among the singulation methods, stealth dicing yielded the highest fracture strength, outperforming blade and laser dicing. The combination of wafer thinning via polishing and singulation via stealth dicing presents an optimal solution for producing highly reliable Si chips for 2.5D and 3D packaging. These findings may be valuable in selecting optimal processing technologies for high-reliability Si chip production in industrial settings. Full article

(This article belongs to the Section Advanced Materials Characterization)

► Show Figures

Figure 1

16 pages, 2999 KiB

Open AccessEditor’s ChoiceArticle

Modification of Poly(3-Hydroxybutyrate) with a Linear Polyurethane Modifier and Organic Nanofiller—Preparation and Structure–Property Relationship

by Iwona Zarzyka, Beata Krzykowska, Karol Hęclik, Wiesław Frącz, Grzegorz Janowski, Łukasz Bąk, Tomasz Klepka, Jarosław Bieniaś, Monika Ostapiuk, Aneta Tor-Świątek, Magda Droździel-Jurkiewicz, Adam Tomczyk, Anna Falkowska and Michał Kuciej

Materials 2024, 17(22), 5542; https://doi.org/10.3390/ma17225542 - 13 Nov 2024

Viewed by 879

Abstract

The growing demand for products made of polymeric materials, including the commonly used polypropylene (PP), is accompanied by the problem of storing and disposing of non-biodegradable waste, increasing greenhouse gas emissions, climate change and the creation of toxic products that constitute a health [...] Read more.

The growing demand for products made of polymeric materials, including the commonly used polypropylene (PP), is accompanied by the problem of storing and disposing of non-biodegradable waste, increasing greenhouse gas emissions, climate change and the creation of toxic products that constitute a health hazard of all living organisms. Moreover, most of the synthetic polymers used are made from petrochemical feedstocks from non-renewable resources. The use of petrochemical raw materials also causes degradation of the natural environment. A potential solution to these problems is the use of biopolymers. Biopolymers include biodegradable or biosynthesizable polymers, i.e., obtained from renewable sources or produced synthetically but from raw materials of natural origin. One of them is the poly(3-hydroxybutyrate) (P3HB) biopolymer, whose properties are comparable to PP. Unfortunately, it is necessary to modify its properties to improve its processing and operational properties. In the work, hybrid polymer nanobiocomposites based on P3HB, with the addition of chain, uncross-linked polyurethane (PU) and layered aluminosilicate modified with organic salts (Cloisite^®30B) were produced by extrusion process. The introduction of PU and Cloisite^®30B to the polymer matrix (P3HB) influenced the processing parameters beneficially and resulted in a decrease in the extrusion temperature of more than 10 °C. The influence of the simultaneous addition of a constant amount of PU (10 m/m%) and the different amounts of nanoadditives (1, 2 and 3 m/m%) on the compatibility, morphology and static mechanical properties of the resulted nanobiocomposites were examined. The component interactions by Fourier transformation infrared spectroscopy (FTIR) analysis, nano- and microscale structure studies using small-angle X-ray scattering (SAXS) and morphology by scanning electron microscopy (SEM) were carried out, and the hardness and tensile strength of the obtained polymer nanobiocomposites were determined. FTIR analysis identified the compatibility of the polyester matrix, PU, and organomodified montmorillonite, the greatest being 3 m/m% Cloisite30B content. The addition of PU to the polyester elasticizes the material and decreases the material’s strength and ductility. The presence of nanoclay enhanced the mechanical properties of nanobiocomposites. The resulting nanobiocomposites can be used in the production of short-life materials applied in gardening or agriculture. Full article

(This article belongs to the Special Issue Progressive Technologies and Materials in Mechanical and Materials Engineering)

► Show Figures

Figure 1

26 pages, 16106 KiB

Open AccessEditor’s ChoiceArticle

Physicochemical Characterization and Kinetics Study of Polymer Carriers with Vitamin C for Controlled Release Applications

by Magdalena Bańkosz

Materials 2024, 17(22), 5502; https://doi.org/10.3390/ma17225502 - 12 Nov 2024

Viewed by 999

Abstract

This study focuses on the selection and evaluation of a kinetic model for the release of vitamin C from different delivery systems, including microcapsules, hydrogels, and a hybrid system combining both. The microcapsules were synthesized from a 2% sodium alginate solution and with [...] Read more.

This study focuses on the selection and evaluation of a kinetic model for the release of vitamin C from different delivery systems, including microcapsules, hydrogels, and a hybrid system combining both. The microcapsules were synthesized from a 2% sodium alginate solution and with vitamin C incorporated in selected formulations. Hydrogels were obtained through photopolymerization using poly(ethylene glycol) diacrylate and polyvinyl alcohol, with and without the addition of vitamin C. The hybrid system incorporated the vitamin C-containing microcapsules within the hydrogel matrix. Physicochemical properties, such as density, porosity, and water vapor transmission rate (WVTR), were evaluated. Kinetic studies of vitamin C release were conducted under dynamic and static conditions, and the experimental data were fitted to six different kinetic models: zero-order, first-order, second-order, Higuchi, Korsmeyer–Peppas, and Hixson–Crowell. The Higuchi and Korsmeyer–Peppas models provided the best fit for most systems, indicating that the release is predominantly controlled by diffusion and, in dynamic conditions, swelling of the matrix. The hybrid system, while exhibiting slower release than the microcapsules and hydrogel alone, demonstrated more controlled and sustained release, which is advantageous for applications requiring prolonged action. Full article

(This article belongs to the Special Issue Research of Organic Molecules and Materials for Biological Application)

► Show Figures

Graphical abstract

39 pages, 8550 KiB

Open AccessEditor’s ChoiceReview

Enhancement of Magnetic Shielding Based on Low-Noise Materials, Magnetization Control, and Active Compensation: A Review

by Yijin Liu, Jianzhi Yang, Fuzhi Cao, Xu Zhang and Shiqiang Zheng

Materials 2024, 17(22), 5469; https://doi.org/10.3390/ma17225469 - 8 Nov 2024

Cited by 4 | Viewed by 2743

Abstract

Magnetic-shielding technologies play a crucial role in the field of ultra-sensitive physical measurement, medical imaging, quantum sensing, etc. With the increasing demand for the accuracy of magnetic measurement, the performance requirements of magnetic-shielding devices are also higher, such as the extremely weak magnetic [...] Read more.

Magnetic-shielding technologies play a crucial role in the field of ultra-sensitive physical measurement, medical imaging, quantum sensing, etc. With the increasing demand for the accuracy of magnetic measurement, the performance requirements of magnetic-shielding devices are also higher, such as the extremely weak magnetic field, gradient, and low-frequency noise. However, the conventional method to improve the shielding performance by adding layers of materials is restricted by complex construction and inherent materials noise. This paper provides a comprehensive review about the enhancement of magnetic shielding in three aspects, including low-noise materials, magnetization control, and active compensation. The generation theorem and theoretical calculation of materials magnetic noise is summarized first, focusing on the development of spinel ferrites, amorphous, and nanocrystalline. Next, the principles and applications of two magnetization control methods, degaussing and magnetic shaking, are introduced. In the review of the active magnetic compensation system, the forward and inverse design methods of coil and the calculation method of the coupling effect under the ferromagnetic boundary of magnetic shield are explained in detail, and their applications, especially in magnetocardiography (MCG) and magnetoencephalogram (MEG), are also mainly described. In conclusion, the unresolved challenges of different enhancement methods in materials preparation, optimization of practical implementation, and future applications are proposed, which provide comprehensive and instructive references for corresponding research. Full article

(This article belongs to the Special Issue Preparation, Electromagnetic Absorption and Shielding Properties of Electromagnetic Functional Materials)

► Show Figures

Figure 1

26 pages, 21893 KiB

Open AccessEditor’s ChoiceArticle

An Example of Using Low-Cost LiDAR Technology for 3D Modeling and Assessment of Degradation of Heritage Structures and Buildings

by Piotr Kędziorski, Marcin Jagoda, Paweł Tysiąc and Jacek Katzer

Materials 2024, 17(22), 5445; https://doi.org/10.3390/ma17225445 - 7 Nov 2024

Cited by 1 | Viewed by 1083

Abstract

This article examines the potential of low-cost LiDAR technology for 3D modeling and assessment of the degradation of historic buildings, using a section of the Koszalin city walls in Poland as a case study. Traditional terrestrial laser scanning (TLS) offers high accuracy but [...] Read more.

This article examines the potential of low-cost LiDAR technology for 3D modeling and assessment of the degradation of historic buildings, using a section of the Koszalin city walls in Poland as a case study. Traditional terrestrial laser scanning (TLS) offers high accuracy but is expensive. The study assessed whether more accessible LiDAR options, such as those integrated with mobile devices such as the Apple iPad Pro, can serve as viable alternatives. This study was conducted in two phases—first assessing measurement accuracy and then assessing degradation detection—using tools such as the FreeScan Combo scanner and the Z+F 5016 IMAGER TLS. The results show that, while low-cost LiDAR is suitable for small-scale documentation, its accuracy decreases for larger, complex structures compared to TLS. Despite these limitations, this study suggests that low-cost LiDAR can reduce costs and improve access to heritage conservation, although further development of mobile applications is recommended. Full article

(This article belongs to the Special Issue Advanced Materials & Methods for Heritage & Archaeology (Second Edition))

► Show Figures

Figure 1

22 pages, 3931 KiB

Open AccessEditor’s ChoiceReview

Securing Rare Earth Permanent Magnet Needs for Sustainable Energy Initiatives

by Dan-Cristian Popa and Loránd Szabó

Materials 2024, 17(22), 5442; https://doi.org/10.3390/ma17225442 - 7 Nov 2024

Cited by 1 | Viewed by 1944

Abstract

Rare earth permanent magnets are vital in various sectors, including renewable energy conversion, where they are widely used in permanent magnet generators. However, the global supply and availability of these materials present significant risks, and their mining and processing have raised serious environmental [...] Read more.

Rare earth permanent magnets are vital in various sectors, including renewable energy conversion, where they are widely used in permanent magnet generators. However, the global supply and availability of these materials present significant risks, and their mining and processing have raised serious environmental concerns. This paper reviews the necessary legislative, economic, and technological measures that must be implemented to address these issues. While it may not be feasible to eliminate the risks associated with the availability of rare earth materials, researchers in the field of electrical generators can play a crucial role in significantly reducing the demand for newly mined and processed such materials, thereby mitigating the negative environmental impacts of their extraction and production. Full article

(This article belongs to the Special Issue Advances in Sustainable Energy Materials and Devices)

► Show Figures

Figure 1

14 pages, 6179 KiB

Open AccessEditor’s ChoiceArticle

Preparation and Characterization of Mechanical Properties of HAP/45S5 Bioglass Laminated Ceramic Composites via Spark Plasma Sintering

by Ye Meng, Xinge Li and Bing Yun

Materials 2024, 17(22), 5413; https://doi.org/10.3390/ma17225413 - 6 Nov 2024

Cited by 2 | Viewed by 937

Abstract

Hydroxyapatite (HAP) displays a high degree of similarity to the inorganic components that make up roughly 70% of human hard tissue, and it possesses exceptional biological activity and biocompatibility. It is currently internationally recognized as the most biologically active hard tissue implant material. [...] Read more.

Hydroxyapatite (HAP) displays a high degree of similarity to the inorganic components that make up roughly 70% of human hard tissue, and it possesses exceptional biological activity and biocompatibility. It is currently internationally recognized as the most biologically active hard tissue implant material. However, its substandard mechanical properties have significantly limited the application of HAP in areas requiring load bearing or in the repair of large bone defects. In this study, HAP/45S5 bioglass laminated ceramic composites were consolidated using the spark plasma sintering (SPS) technique. The grain growth and phase transformation of HAP and 45S5 bioglass were examined at various sintering temperatures. The mechanical properties of the laminated composites were investigated. At 950 °C, the flexural strength and fracture work of the sintered body were (153.22 ± 7.7) MPa and (2049 ± 34) J·m⁻², respectively. These results corresponded to the load–displacement curves and showed that the composites met the mechanical performance requirements of the support material. Full article

(This article belongs to the Section Advanced and Functional Ceramics and Glasses)

► Show Figures

Figure 1

21 pages, 1766 KiB

Open AccessEditor’s ChoiceReview

Advanced Biomaterials for Lacrimal Tissue Engineering: A Review

by Kevin Y. Wu, Archan Dave, Patrick Daigle and Simon D. Tran

Materials 2024, 17(22), 5425; https://doi.org/10.3390/ma17225425 - 6 Nov 2024

Cited by 1 | Viewed by 1616

Abstract

The lacrimal gland (LG) is vital for ocular health, producing tears that lubricate and protect the eye. Dysfunction of the LG leads to aqueous-deficient dry eye disease (DED), significantly impacting quality of life. Current treatments mainly address symptoms rather than the underlying LG [...] Read more.

The lacrimal gland (LG) is vital for ocular health, producing tears that lubricate and protect the eye. Dysfunction of the LG leads to aqueous-deficient dry eye disease (DED), significantly impacting quality of life. Current treatments mainly address symptoms rather than the underlying LG dysfunction, highlighting the need for regenerative therapies. Tissue engineering offers a promising solution, with biomaterials playing crucial roles in scaffolding and supporting cell growth for LG regeneration. This review focuses on recent advances in biomaterials used for tissue engineering of the lacrimal gland. We discuss both natural and synthetic biomaterials that mimic the extracellular matrix and provide structural support for cell proliferation and differentiation. Natural biomaterials, such as Matrigel, decellularized extracellular matrices, chitosan, silk fibroin hydrogels, and human amniotic membrane are evaluated for their biocompatibility and ability to support lacrimal gland cells. Synthetic biomaterials, like polyethersulfone, polyesters, and biodegradable polymers (PLLA and PLGA), are assessed for their mechanical properties and potential to create scaffolds that replicate the complex architecture of the LG. We also explore the integration of growth factors and stem cells with these biomaterials to enhance tissue regeneration. Challenges such as achieving proper vascularization, innervation, and long-term functionality of engineered tissues are discussed. Advances in 3D bioprinting and scaffold fabrication techniques are highlighted as promising avenues to overcome current limitations. Full article

(This article belongs to the Section Biomaterials)

► Show Figures

Figure 1

10 pages, 2301 KiB

Open AccessEditor’s ChoiceArticle

Fibrillated Films for Suspension Catalyst Immobilization—A Kinetic Study of the Nitrobenzene Hydrogenation

by Chiara Boscagli, Enrico Lepre, Oliver Hofmann, Lukas Wengeler, Marcel Schmitt, Ivana Jevtovikj, Carlos Lizandara-Pueyo and Stephan A. Schunk

Materials 2024, 17(22), 5411; https://doi.org/10.3390/ma17225411 - 6 Nov 2024

Viewed by 919

Abstract

The immobilization of suspension catalysts in flexible, fibrillated films offers a promising solution to the mass transfer limitations often encountered in three-phase hydrogenation reactions. This study investigates the catalytic performance and mass transfer properties of fibrillated films in the hydrogenation of nitrobenzene to [...] Read more.

The immobilization of suspension catalysts in flexible, fibrillated films offers a promising solution to the mass transfer limitations often encountered in three-phase hydrogenation reactions. This study investigates the catalytic performance and mass transfer properties of fibrillated films in the hydrogenation of nitrobenzene to aniline, comparing them to free-flowing powdered catalysts. Fibrillated films were prepared from Pd/C catalysts with varying thicknesses (100–400 µm), and their performance was evaluated through kinetic studies in both batch reactors and microreactors. The specific activity of the films was significantly influenced by film thickness with thinner films demonstrating lower mass transfer limitations. However, mass transfer limitations were observed in thicker films, prompting the development of alternative film designs, including enhanced macro-porous films and sandwich structures. These modifications successfully minimized diffusion limitations, achieving similar specific activity to the powder catalysts while maintaining the mechanical stability of the films. This work demonstrates the feasibility of using fibrillated films for continuous catalytic processes and highlights their potential for efficient catalyst reuse, avoiding filtration steps and enhancing process sustainability. Furthermore, while PTFE remains indispensable for producing such films due to its mechanical and thermal stability, ongoing research focuses on identifying more environmentally friendly alternatives without compromising performance. Full article

(This article belongs to the Special Issue Recent Developments in Catalytic Materials)

► Show Figures

Graphical abstract

21 pages, 13768 KiB

Open AccessEditor’s ChoiceArticle

Cyclic Fatigue Failure of Perforated 3D-Printed Polylactide (PLA) Specimens by Inserted Pin Loading

by J. S. Hertel, Y. W. Kwon and D. Sachau

Materials 2024, 17(22), 5394; https://doi.org/10.3390/ma17225394 - 5 Nov 2024

Viewed by 1003

Abstract

The failure of 3D-printed Polylactide (PLA) specimens with circular holes was studied under tensile and cyclic loading, respectively, by an inserted pin. Experiments were conducted for the perforated PLA specimens with various print angles from 0° to 90°, as well as [0°/90°]s and [...] Read more.

The failure of 3D-printed Polylactide (PLA) specimens with circular holes was studied under tensile and cyclic loading, respectively, by an inserted pin. Experiments were conducted for the perforated PLA specimens with various print angles from 0° to 90°, as well as [0°/90°]s and [0°/±45°/90°]s. The hole locations varied along the specimens. The PLA specimens showed two different failure modes: one through the print lines and the other between the print lines. Different print angles resulted in different tensile failure stresses under pin loading. The cyclic tests of different print angles showed very similar S-N data as the applied stresses were normalized to their tensile failure stresses if the failure mode was through the print lines. On the other hand, cyclic failure between print lines showed distinctly separated S-N data, even with the normalized applied stresses. The tensile failure stresses, failure locations, and orientations were successfully predicted using the failure criterion that is based on both stress and stress gradient conditions. A proposed mathematical interpolation equation provided good estimations of the tensile failure stresses and S-N curves of specimens with different print angles once the failure stresses were known for the 0° to 90° specimens. Full article

(This article belongs to the Special Issue Numerical Modeling and Dynamic Analysis of Composite Materials)

► Show Figures

Figure 1

24 pages, 11388 KiB

Open AccessEditor’s ChoiceArticle

Enhancement of 5-Fluorouracil Drug Delivery in a Graphene Oxide Containing Electrospun Chitosan/Polyvinylpyrrolidone Construct

by Jamie J. Grant, Suresh C. Pillai, Tatiana S. Perova, Barry Brennan, Steven J. Hinder, Marion McAfee, Sarah Hehir and Ailish Breen

Materials 2024, 17(21), 5300; https://doi.org/10.3390/ma17215300 - 31 Oct 2024

Viewed by 1038

Abstract

Electrospun nanofibrous mats, consisting of chitosan (CS) and polyvinylpyrrolidone (PVP), were constructed with the addition of graphene oxide (GO) for enhancement of delivery of the 5-Fluorouracil (5-Fu) chemotherapy drug. Upon studying the range of GO concentrations in CS/PVP, the concentration of 0.2% w [...] Read more.

Electrospun nanofibrous mats, consisting of chitosan (CS) and polyvinylpyrrolidone (PVP), were constructed with the addition of graphene oxide (GO) for enhancement of delivery of the 5-Fluorouracil (5-Fu) chemotherapy drug. Upon studying the range of GO concentrations in CS/PVP, the concentration of 0.2% w/v GO was chosen for inclusion in the drug delivery model. SEM showed bead-free, homogenous fibres within this construct. This construct also proved to be non-toxic to CaCo-2 cells over 24 and 48 h exposure. The construction of a drug delivery vehicle whereby 5-Fu was loaded with and without GO in various concentrations showed several interesting findings. The presence of CS/PVP was revealed through XPS, FTIR and Raman spectroscopies. FTIR was also imperative for the analysis of 5-Fu while Raman exclusively highlighted the presence of GO in the samples. In particular, a detailed analysis of the IR spectra recorded using two FTIR spectrometers, several options for determining the concentration of 5-Fu in composite fibre systems CS/PVP/5-Fu and GO/CS/PVP/5-Fu were demonstrated. By analysis of Raman spectra in the region of D and G bands, a linear dependence of ratios of integrated intensities of A_D and A_G on the intensity of host polymer band at 1425 cm⁻¹ vs. GO content was found. Both methods, therefore, can be used for monitoring of GO content and 5-Fu release in studied complex systems. After incorporating the chemotherapy drug 5-Fu into the constructs, cell viability studies were also performed. This study demonstrated that GO/CS/PVP/5-Fu constructs have potential in chemotherapy drug delivery systems. Full article

(This article belongs to the Special Issue Synthesis, Physicochemical Properties, and Applications of Low-Dimensional Materials)

► Show Figures

Figure 1

19 pages, 1977 KiB

Open AccessEditor’s ChoiceArticle

Measuring the Electro-Optical Kerr Effect Against the Background of Electro-Absorption Modulation in Liquids

by Rafał Ledzion, Marek Izdebski and Anita Rambo

Materials 2024, 17(21), 5346; https://doi.org/10.3390/ma17215346 - 31 Oct 2024

Viewed by 806

Abstract

A new approach to the dynamic polarimetric method is proposed, which allows for the decoupling of electro-optical Kerr effect measurements from the electro-absorption effect in partially transparent liquids. The method is illustrated by using the results of engine oil measurements as a function [...] Read more.

A new approach to the dynamic polarimetric method is proposed, which allows for the decoupling of electro-optical Kerr effect measurements from the electro-absorption effect in partially transparent liquids. The method is illustrated by using the results of engine oil measurements as a function of temperature and modulating field frequency. It was shown that the birefringence induced in the sample, the modulation of the ordinary wave transmission, and the modulation of the extraordinary wave transmission in the sample can be shifted in phase with respect to the square of the applied alternating modulating field. Each of these three phase shifts can depend differently on the temperature and frequency. Neglecting the influence of electro-absorption on electro-optical measurements in liquids or considering electro-absorption as an effect correlated in phase with induced birefringence may lead to significant measurement errors. This indicates that the Kerr constant and the electro-absorption coefficients for an alternating electric field should be considered as complex quantities instead of real values, as they have been traditionally. The proposed approach fills an important gap in measurement techniques described in the literature, which may provide erroneous results for measurements of the Kerr constant in partially transparent liquids including many industrially important liquids. Full article

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

► Show Figures

Figure 1

11 pages, 9506 KiB

Open AccessEditor’s ChoiceArticle

Multiscale Analysis of Surface Topography for Engineering Applications in the Casting Industry

by Damian Gogolewski, Tomasz Kozior and Paweł Zmarzły

Materials 2024, 17(21), 5272; https://doi.org/10.3390/ma17215272 - 30 Oct 2024

Viewed by 645

Abstract

This paper presents the results of studies aimed at assessing the impact of the molding process on the variability of surface irregularities of casting models. This research was conducted using a selected multiscale method, i.e., wavelet transformation, in both discrete and continuous perspective. [...] Read more.

This paper presents the results of studies aimed at assessing the impact of the molding process on the variability of surface irregularities of casting models. This research was conducted using a selected multiscale method, i.e., wavelet transformation, in both discrete and continuous perspective. The test samples were made both based on traditional methods of manufacturing casting models, i.e., machining of aluminum and wood, as well as using three additive technologies. The impact of the forming process on the variability of the topography of the produced models was evaluated. This research comprehensively relates to the assessment of the applicability of additive technologies, which are increasingly used in various industrial areas, as well as the impact of the process on surface topography in relation to scale. The statistical assessment based on the ANOVA analysis demonstrated that it is possible to distinguish between the surfaces before and after a specific number of forming cycles. Studies have shown that the impact of the forming process is relatively small, mainly affecting the long-term irregularity components, and there are no functional dependencies in terms of the impact of the forming process on the variation in surface topography in relation to the manufacturing method or its parameters. Full article

(This article belongs to the Special Issue Recent Trends in Roughness Measurement and Data Analysis of Machined Surfaces (2nd Edition))

► Show Figures

Figure 1

18 pages, 3418 KiB

Open AccessEditor’s ChoiceArticle

On the Influence of Welding Parameters and Their Interdependence During Robotic Continuous Ultrasonic Welding of Carbon Fibre Reinforced Thermoplastics

by Filipp Köhler, Irene Fernandez Villegas, Clemens Dransfeld and Axel Herrmann

Materials 2024, 17(21), 5282; https://doi.org/10.3390/ma17215282 - 30 Oct 2024

Viewed by 1042

Abstract

Ultrasonic welding of fibre-reinforced thermoplastics is a joining technology with high potential for short welding times and low energy consumption. While the majority of the current studies on continuous ultrasonic welding have so far focused on woven reinforcements, unidirectional materials are preferred for [...] Read more.

Ultrasonic welding of fibre-reinforced thermoplastics is a joining technology with high potential for short welding times and low energy consumption. While the majority of the current studies on continuous ultrasonic welding have so far focused on woven reinforcements, unidirectional materials are preferred for highly loaded aerospace components due to their better mechanical performance. Therefore, this paper investigates the influence and interdependence of the welding speed, amplitude, and energy director thickness on the weld quality of adherends made of unidirectional composites. The quality of the welded joints is assessed by a single-lap shear strength and fracture surface analysis complemented by the microscopic analysis of cross-sections and comparison to a co-consolidated reference. The results showed that the welding process is highly affected by changing welding speeds for a given amplitude. Furthermore, while lower amplitudes lead to significant scatter in the welding quality, higher amplitudes result in increased heating rates and a fully molten energy director even for high welding speeds. Nevertheless, insufficient consolidation at high welding speeds results in porosity in the weld line. Finally, it was observed that thicker, and therefore more compliant, energy directors lead to more uniform melting of the energy director and less deviation in the weld quality for a wider range of welding speeds. Full article

(This article belongs to the Special Issue Ultrasound for Material Characterization and Processing (3rd Edition))

► Show Figures

Figure 1

12 pages, 4520 KiB

Open AccessEditor’s ChoiceArticle

Magnetic CuFe₂O₄ Spinel–Polypyrrole Pseudocapacitive Composites for Energy Storage

by Mahmoud Awad and Igor Zhitomirsky

Materials 2024, 17(21), 5249; https://doi.org/10.3390/ma17215249 - 28 Oct 2024

Viewed by 960

Abstract

This investigation focused on the fabrication of ceramic ferrimagnetic CuFe₂O₄–conductive polypyrrole (PPy) composites for energy storage. CuFe₂O₄ with a crystal size of 20–30 nm and saturation magnetization of 31.4 emu g⁻¹ was prepared by hydrothermal [...] Read more.

This investigation focused on the fabrication of ceramic ferrimagnetic CuFe₂O₄–conductive polypyrrole (PPy) composites for energy storage. CuFe₂O₄ with a crystal size of 20–30 nm and saturation magnetization of 31.4 emu g⁻¹ was prepared by hydrothermal synthesis, and PPy was prepared by chemical polymerization. High-active-mass composite electrodes were fabricated for energy storage in supercapacitors for operation in a sodium sulfate electrolyte. The addition of PPy to CuFe₂O₄ resulted in a decrease in charge transfer resistance and an increase in capacitance in the range from 1.20 F cm⁻² (31 F g⁻¹) to 4.52 F cm⁻² (117.4 F g⁻¹) at a 1 mV s⁻¹ sweep rate and from 1.17 F cm⁻² (29.9 F g⁻¹) to 4.60 F cm⁻² (120.1 F g⁻¹) at a 3 mA cm⁻² current density. The composites showed higher capacitance than other magnetic ceramic composites of the same mass containing PPy in the same potential range and exhibited improved cyclic stability. The magnetic behavior of the composites was influenced by the magnetic properties of ferrimagnetic CuFe₂O₄ and paramagnetic PPy. The composites showed a valuable combination of capacitive and magnetic properties and enriched materials science of magnetic supercapacitors for novel applications based on magnetoelectric and magnetocapacitive properties. Full article

(This article belongs to the Special Issue Processing, Characterization and Applications of Ceramic Matrix Composites)

► Show Figures

Figure 1

16 pages, 5871 KiB

Open AccessEditor’s ChoiceArticle

Effect of Natural Inhibitors on the Corrosion Properties of Grade 2 Titanium Alloy

by Mehrdad Faraji, Luca Pezzato, Arshad Yazdanpanah, Giacomo Nardi, Mojtaba Esmailzadeh and Irene Calliari

Materials 2024, 17(21), 5202; https://doi.org/10.3390/ma17215202 - 25 Oct 2024

Cited by 2 | Viewed by 973

Abstract

This study investigates the effects of natural inhibitors (pomegranate, algae, and tomato extracts) on the corrosion resistance of titanium (grade 2). To deepen understanding the inhibition mechanism, Molecular Dynamic (MD) and Monte Carlo (MC) simulations were employed to analyze adsorption behaviors and identify [...] Read more.

This study investigates the effects of natural inhibitors (pomegranate, algae, and tomato extracts) on the corrosion resistance of titanium (grade 2). To deepen understanding the inhibition mechanism, Molecular Dynamic (MD) and Monte Carlo (MC) simulations were employed to analyze adsorption behaviors and identify optimal adsorption sites on titanium oxide (TiO₂) surfaces for compounds within the inhibitors. Results indicate non-flat adsorption orientations, with pomegranate peel extract components showing superior inhibition capabilities, attributed to the formation of strong O-H chemical bonds with the TiO₂ surface. In the experimental part of the study Electrochemical Impedance Spectroscopy (EIS) and Potentiodynamic Polarization (PDP) were conducted. Two electrolytes were tested: a solution 3.5% NaCl and a solution 0.5 M NaOH. All the tests were performed with 5% of inhibitor and with the reference solution. Also, inhibition efficiency was calculated on the base of PDP tests. The study found that pomegranate extract can act as a good corrosion inhibitor for titanium alloy in aqueous solutions 0.5 M NaOH. This was demonstrated by the increase in the corrosion potential and impedance modulus and decrease in the corrosion current density after the addition of pomegranate extract to the solution. However, in a 3.5% NaCl solution, the efficacy of pomegranate extract was less pronounced, probably due to the high aggressivity of the electrolyte. Tomato and algae extract have instead shown very low inhibition effects in all the tested conditions. Full article

(This article belongs to the Special Issue Corrosion Behavior and Mechanical Properties of Metallic Materials)

► Show Figures

Figure 1

15 pages, 4658 KiB

Open AccessEditor’s ChoiceArticle

The Impact of the Final Sintering Temperature on the Microstructure and Dielectric Properties of Ba_0.75Ca_0.25TiO₃ Perovskite Ceramics

by Kamil Feliksik, Małgorzata Adamczyk-Habrajska, Jolanta Makowska, Joanna A. Bartkowska, Tomasz Pikula, Rafał Panek and Oliwia Starczewska

Materials 2024, 17(21), 5210; https://doi.org/10.3390/ma17215210 - 25 Oct 2024

Cited by 1 | Viewed by 808

Abstract

Ba_0.75Ca_0.25TiO₃ ceramics were successfully synthesized by a simple solid-state reaction method. This study examined the influence of sintering temperature on the structure, microstructure, dielectric properties and electrical behavior of the material. The XRD analysis reveals that the tetragonal [...] Read more.

Ba_0.75Ca_0.25TiO₃ ceramics were successfully synthesized by a simple solid-state reaction method. This study examined the influence of sintering temperature on the structure, microstructure, dielectric properties and electrical behavior of the material. The XRD analysis reveals that the tetragonal phase (P4mm) is dominant in all the synthesized materials, with those sintered at T = 1400 °C and T = 1450 °C being single-phase, while others exhibit a minor orthorhombic phase (Pbnm). Higher sintering temperatures promoted better grain boundary formation and larger grain sizes. The electric permittivity increased with temperature up to T = 1400 °C, followed by a sharp decline at T = 1450 °C. Additionally, the Curie temperature decreased with increasing sintering temperature, indicating changes in phase transition characteristics. Thermal analysis showed that higher sintering temperatures led to sharper heat capacity peaks, while pyroelectric and thermally stimulated depolarization currents were maximized at T = 1400 °C due to oxygen vacancies. These findings highlight the significant impact of sintering temperature on the material’s structural and functional properties. Full article

(This article belongs to the Special Issue Synergy in Polyphase Materials: Harnessing the Power of Glass and Ceramics)

► Show Figures

Figure 1

15 pages, 14562 KiB

Open AccessEditor’s ChoiceArticle

Multiple Broadband Infrared Topological Photonic Crystal Valley States Based on Liquid Crystals

by Jinying Zhang, Bingnan Wang, Rui Wang, Jiacheng Wang, Xinye Wang and Yexiaotong Zhang

Materials 2024, 17(21), 5212; https://doi.org/10.3390/ma17215212 - 25 Oct 2024

Viewed by 838

Abstract

Spectral tunable technology has to meet the requirements of strong robustness and wide spectral range. We propose a method for the transmission and manipulation of infrared topological photonic crystal valley states based on tunable refractive index method that exhibits broad-spectrum and multi-band characteristics, [...] Read more.

Spectral tunable technology has to meet the requirements of strong robustness and wide spectral range. We propose a method for the transmission and manipulation of infrared topological photonic crystal valley states based on tunable refractive index method that exhibits broad-spectrum and multi-band characteristics, along with a tunable emission angle. With this structure, different rotational directions of vortex light sources can independently excite the K valley and K′ valley within the frequency band ranging from 75.64 THz to 99.61 THz. At frequencies from 142.60 THz to 171.12 THz, it is possible to simultaneously excite both the K valley and K′ valley. The dual refractive index tunable design allows for the adjustment of the emission angle at a fixed frequency, enabling control over the independent excitation of either a single K valley or K′ valley, as well as their simultaneous excitation. This capability has significant implications for photonic computation and tunable filtering, offering enhanced operational flexibility and expanded functionality for future optical communications and integrated optical circuits. Full article

(This article belongs to the Special Issue Terahertz Materials and Technologies in Materials Science)

► Show Figures

Figure 1

17 pages, 5515 KiB

Open AccessEditor’s ChoiceArticle

Comparative Analysis of Anodized TiO₂ Nanotubes and Hydrothermally Synthesized TiO₂ Nanotubes: Morphological, Structural, and Photoelectrochemical Properties

by Syrine Sassi, Amal Bouich, Brahim Bessais, Lotfi Khezami, Bernabé Mari Soucase and Anouar Hajjaji

Materials 2024, 17(21), 5182; https://doi.org/10.3390/ma17215182 - 24 Oct 2024

Cited by 3 | Viewed by 5814

Abstract

This study presents a comparative analysis of anodization and hydrothermal techniques for synthesizing TiO₂ nanotubes directly on titanium foil. It emphasizes its advantages as a substrate due to its superior conductivity and efficient charge transfer. Optimized synthesis conditions enable a thorough evaluation [...] Read more.

This study presents a comparative analysis of anodization and hydrothermal techniques for synthesizing TiO₂ nanotubes directly on titanium foil. It emphasizes its advantages as a substrate due to its superior conductivity and efficient charge transfer. Optimized synthesis conditions enable a thorough evaluation of the resulting nanotubes’ morphology, structure, and optical properties, ultimately assessing their photoelectrochemical and photocatalytic performances. Scanning electron microscopy (SEM) reveals differences in tube diameter and organization. An X-ray diffraction (XRD) analysis shows a dominant anatase (101) crystal phase in both methods, with the hydrothermally synthesized nanotubes exhibiting a biphase structure after annealing at 500 °C. UV–Vis and photoluminescence analyses indicate slight variations in band gaps (around 0.02 eV) and recombination rates. The anodized TiO₂ nanotubes, exhibiting superior hydrophilicity and order, demonstrate significantly enhanced photocatalytic degradation of a model pollutant, amido black (80 vs. 78%), and achieve a 0.1% higher photoconversion efficiency compared to the hydrothermally synthesized tubes. This study underscores the potential advantages of the anodization method for photocatalytic applications, particularly by demonstrating the efficacy of direct TiO₂ nanotube growth on titanium foil for efficient photocatalysis. Full article

(This article belongs to the Section Advanced Materials Characterization)

► Show Figures

Figure 1

35 pages, 20307 KiB

Open AccessEditor’s ChoiceArticle

An Enhanced Progressive Damage Model for Laminated Fiber-Reinforced Composites Using the 3D Hashin Failure Criterion: A Multi-Level Analysis and Validation

by Yichen Zhang, Wim Van Paepegem and Wouter De Corte

Materials 2024, 17(21), 5176; https://doi.org/10.3390/ma17215176 - 24 Oct 2024

Cited by 4 | Viewed by 2072

Abstract

This paper presents a progressive damage model (PDM) based on the 3D Hashin failure criterion within the ABAQUS/Explicit^TM 2021 framework via a VUMAT subroutine, enhancing the characterization of the mechanical performance and damage evolution in the elastic and softening stages of composite [...] Read more.

This paper presents a progressive damage model (PDM) based on the 3D Hashin failure criterion within the ABAQUS/Explicit^TM 2021 framework via a VUMAT subroutine, enhancing the characterization of the mechanical performance and damage evolution in the elastic and softening stages of composite materials via the accurate calculation of damage variables and accommodation of non-monotonic loading conditions. In the subsequent multi-level verification, it is found that the model accurately simulates the primary failure modes at the element level and diminishes the influence of element size, ensuring a reliable behavior representation under non-monotonic loading. At the laminate level, it also accurately forecasts the elastic behavior and damage evolution in open-hole lamina and laminates, demonstrating the final crack band at ultimate failure. This paper also emphasizes the importance of correct characteristic length selection and how to minimize mesh size impact by selecting appropriate values. Compared to ABAQUS’s built-in 2D model, the 3D VUMAT subroutine shows superior accuracy and effectiveness, proving its value in characterizing the mechanical behavior and damage mechanisms of fiber-reinforced polymer (FRP) materials. The enhanced 3D PDM accurately characterizes the softening processes in composite materials under simple or complex stress states during monotonic or non-monotonic loading, effectively minimizes the mesh dependency, and reasonably captures failure crack bands, making it suitable for future simulations and resolutions of numerical issues in composite material models under complex, three-dimensional stress states. Full article

(This article belongs to the Special Issue Numerical Modeling and Dynamic Analysis of Composite Materials)

► Show Figures

Graphical abstract

31 pages, 18671 KiB

Open AccessEditor’s ChoiceArticle

Effect of Artificial Saliva Modification on Corrosion Resistance of Metal Oxide Coatings on Co-Cr-Mo Dental Alloy

by Bożena Łosiewicz, Patrycja Osak, Karolina Górka-Kulikowska and Joanna Maszybrocka

Materials 2024, 17(21), 5166; https://doi.org/10.3390/ma17215166 - 23 Oct 2024

Cited by 3 | Viewed by 997

Abstract

Surface modifications not only improve the corrosion resistance of Co-Cr-Mo dental alloys (Bego Wirobond^® C) but also ensure their long-term performance and reliability in dental applications. This paper describes the preparation of single-layer TiO₂-ZrO₂ sol–gel coatings on the Co-Cr-Mo [...] Read more.

Surface modifications not only improve the corrosion resistance of Co-Cr-Mo dental alloys (Bego Wirobond^® C) but also ensure their long-term performance and reliability in dental applications. This paper describes the preparation of single-layer TiO₂-ZrO₂ sol–gel coatings on the Co-Cr-Mo dental alloy using the method of dip-coating. The TiO₂-ZrO₂ sol–gel coatings were sintered at 300 and 500 °C. SEM analysis shows that sintering at 300 °C produces a uniform, slightly dense structure without micro-cracks, while sintering at 500 °C results in a denser structure with micro-cracks due to higher stress and shrinkage. EDS confirms that sintering temperature affects the elemental composition of the coating, with higher temperatures causing the volatilization or diffusion of Ti and Zr. Roughness measurements indicate that the Ra value increases with the sintering temperature, meeting dental application requirements. Electrochemical measurements by open-circuit potential, EIS, and cyclic potentiodynamic curves demonstrate that sintering temperature and saliva composition affect corrosion resistance, with NaF and mouthwashes (Listerine Total Care Teeth Protection^® and Meridol^®) generally increasing charge transfer resistance and double-layer capacitance. The ceramic TiO₂-ZrO₂ coatings significantly reduce pitting corrosion susceptibility at physiological and acidic pH, with the 500 °C sintered coating showing better protective properties. These findings highlight the potential of TiO₂-ZrO₂ coatings in enhancing the performance of Co-Cr-Mo dental alloys. Full article

(This article belongs to the Special Issue Corrosion Behavior and Mechanical Properties of Metallic Materials)

► Show Figures

Figure 1

13 pages, 16956 KiB

Open AccessEditor’s ChoiceArticle

A Study on Pigment Composition of Buddhist Cave Paintings Based on Hyperspectral Technology

by Xiang Shi, Xiaogang Lin, Yu Lei, Jinyu Wu, Xiao Lv and Yong Zhou

Materials 2024, 17(21), 5147; https://doi.org/10.3390/ma17215147 - 22 Oct 2024

Viewed by 999

Abstract

The value of the Buddhist cave lies not only in the Buddha statues but also in the surface painting. Hyperspectral imaging technology, as an emerging and effective method for component identification, offers a non-contact and non-destructive approach to the preservation and restoration of [...] Read more.

The value of the Buddhist cave lies not only in the Buddha statues but also in the surface painting. Hyperspectral imaging technology, as an emerging and effective method for component identification, offers a non-contact and non-destructive approach to the preservation and restoration of oil paintings. This study employed hyperspectral cameras to capture common pigments on the surfaces of Buddhist caves. Then, the results were processed and used as a database to identify the paintings. Additionally, a series of experiments were conducted to examine the impact of binder, substrate types, and pigment sizes on the reflectance spectrum of the paints. The Spectral Angle Matching (SAM) algorithm was then used to analyze the Yuanjue Cave and Qiqushan Stone Carvings of the Tang Dynasty in China. The findings revealed that the position of absorption peaks in the reflectance spectra is not significantly influenced by the substrate but is affected by the binder. Moreover, the absorption depth varies regularly with particle size. Furthermore, the spectral matching results demonstrate that components can be accurately identified even for similar colors. Based on the pigment distribution, the study also inferred specific details of ancient paintings, including the painting steps and hidden information in the manuscript layout. These findings hold significant implications for the restoration of representative surface paintings of the Tang Dynasty Buddhist cave, providing a reference for the selection of restoration materials and methods. Full article

(This article belongs to the Special Issue Advanced Materials & Methods for Heritage & Archaeology (Second Edition))

► Show Figures

Graphical abstract

17 pages, 6110 KiB

Open AccessEditor’s ChoiceArticle

Definition, Fabrication, and Compression Testing of Sandwich Structures with Novel TPMS-Based Cores

by Alexandru Vasile, Dan Mihai Constantinescu, Iulian Constantin Coropețchi, Ștefan Sorohan and Dragoș Alexandru Apostol

Materials 2024, 17(21), 5150; https://doi.org/10.3390/ma17215150 - 22 Oct 2024

Cited by 4 | Viewed by 1190

Abstract

Triply periodic minimal surfaces (TPMSs) constitute a type of metamaterial, deriving their unique characteristics from their microstructure topology. They exhibit wide parameterization possibilities, but their behavior is hard to predict. This study focuses on using an implicit modeling method that can effectively generate [...] Read more.

Triply periodic minimal surfaces (TPMSs) constitute a type of metamaterial, deriving their unique characteristics from their microstructure topology. They exhibit wide parameterization possibilities, but their behavior is hard to predict. This study focuses on using an implicit modeling method that can effectively generate novel thin-walled metamaterials, proposing eight shell-based TPMS topologies and one stochastic structure, along with the gyroid acting as a reference. After insights into the printability and design parameters of the proposed samples are presented, a cell homogeneity analysis is conducted, indicating the level of anisotropy of each cellular structure. For each of the designed metamaterials, multiple samples were printed using a stereolithography (SLA) method, using a constant 0.3 relative density and 50 µm resolution. To provide an understanding of their behavior, compression tests of sandwich-type specimens were performed and specific deformation modes were identified. Furthermore, the study estimates the general mechanical behavior of the novel TPMS cores at different relative densities using an open cell mathematical model. Alterations of the uniform topologies are then suggested and the way these modifications affect the compressive response are presented. Thus, this paper demonstrates that an implicit modeling method could easily generate novel thin-walled TPMSs and stochastic structures, which led to identifying an artificially designed structure with superior properties to already mature topologies, such as the gyroid. Full article

(This article belongs to the Special Issue Advances in Metamaterials: Structure, Properties and Applications)

► Show Figures

Graphical abstract

19 pages, 7079 KiB

Open AccessEditor’s ChoiceArticle

Molecular Dynamics, Dielectric Properties, and Textures of Protonated and Selectively Deuterated 4′-Pentyl-4-biphenylcarbonitrile Liquid Crystal

by Jadwiga Tritt-Goc, Magdalena Knapkiewicz, Piotr Harmata, Jakub Herman and Michał Bielejewski

Materials 2024, 17(20), 5106; https://doi.org/10.3390/ma17205106 - 19 Oct 2024

Viewed by 1375

Abstract

Using liquid crystals in near-infrared applications suffers from effects related to processes like parasitic absorption and high sensitivity to UV-light exposure. One way of managing these disadvantages is to use deuterated systems. The combined ¹H and ²H nuclear magnetic resonance relaxometry [...] Read more.

Using liquid crystals in near-infrared applications suffers from effects related to processes like parasitic absorption and high sensitivity to UV-light exposure. One way of managing these disadvantages is to use deuterated systems. The combined ¹H and ²H nuclear magnetic resonance relaxometry method (FFC NMR), dielectric spectroscopy (DS), optical microscopy (POM), and differential scanning calorimetry (DSC) approach was applied to investigate the influence of selective deuteration on the molecular dynamics, thermal properties, self-organization, and electric-field responsiveness to a 4′-pentyl-4-biphenylcarbonitrile (5CB) liquid crystal. The NMR relaxation dispersion (NMRD) profiles were analyzed using theoretical models for the description of dynamics processes in different mesophases. Obtained optical textures of selectively deuterated 5CB showed the occurrence of the domain structure close to the I/N phase transition. The dielectric measurements showed a substantial difference in switching fields between fully protonated/deuterated 5CB and selectively deuterated molecules. The DSC thermograms showed a more complex phase transition sequence for partially deuterated 5CB with respect to fully protonated/deuterated molecules. Full article

(This article belongs to the Special Issue Liquid Crystals and Other Partially Disordered Molecular Systems)

► Show Figures

Figure 1

27 pages, 2743 KiB

Open AccessEditor’s ChoiceReview

Exploring the Potential of Cold Sintering for Proton-Conducting Ceramics: A Review

by Andrea Bartoletti, Elisa Mercadelli, Angela Gondolini and Alessandra Sanson

Materials 2024, 17(20), 5116; https://doi.org/10.3390/ma17205116 - 19 Oct 2024

Cited by 4 | Viewed by 3412

Abstract

Proton-conducting ceramic materials have emerged as effective candidates for improving the performance of solid oxide cells (SOCs) and electrolyzers (SOEs) at intermediate temperatures. BaCeO₃ and BaZrO₃ perovskites doped with rare-earth elements such as Y₂O₃ (BCZY) are well known [...] Read more.

Proton-conducting ceramic materials have emerged as effective candidates for improving the performance of solid oxide cells (SOCs) and electrolyzers (SOEs) at intermediate temperatures. BaCeO₃ and BaZrO₃ perovskites doped with rare-earth elements such as Y₂O₃ (BCZY) are well known for their high proton conductivity, low operating temperature, and chemical stability, which lead to SOCs’ improved performance. However, the high sintering temperature and extended processing time needed to obtain dense BCZY-type electrolytes (typically > 1350 °C) to be used as SOC electrolytes can cause severe barium evaporation, altering the stoichiometry of the system and consequently reducing the performance of the final device. The cold sintering process (CSP) is a novel sintering technique that allows a drastic reduction in the sintering temperature needed to obtain dense ceramics. Using the CSP, materials can be sintered in a short time using an appropriate amount of a liquid phase at temperatures < 300 °C under a few hundred MPa of uniaxial pressure. For these reasons, cold sintering is considered one of the most promising ways to obtain ceramic proton conductors in mild conditions. This review aims to collect novel insights into the application of the CSP with a focus on BCZY-type materials, highlighting the opportunities and challenges and giving a vision of future trends and perspectives. Full article

(This article belongs to the Section Advanced and Functional Ceramics and Glasses)

► Show Figures

Graphical abstract

20 pages, 12921 KiB

Open AccessEditor’s ChoiceArticle

Parameter Optimization for Laser Peen Forming on 6005A-T6 Aluminum Alloy Plates to Enhance the Constrained Deformation of Integral Stiffened Plates

by Gaoqiang Jiang, Jianzhong Zhou, Jian Wu, Shu Huang, Xiankai Meng and Yongxiang Hu

Materials 2024, 17(20), 5090; https://doi.org/10.3390/ma17205090 - 18 Oct 2024

Cited by 2 | Viewed by 796

Abstract

Multiscale parameter optimization for laser peen forming (LPF) on 6005A-T6 aluminum alloy plates was conducted through a combination of simulation and experimentation. By obtaining the optimal parameter, this study aims to explore the constrained deformation and forming laws of the integral stiffened plates. [...] Read more.

Multiscale parameter optimization for laser peen forming (LPF) on 6005A-T6 aluminum alloy plates was conducted through a combination of simulation and experimentation. By obtaining the optimal parameter, this study aims to explore the constrained deformation and forming laws of the integral stiffened plates. Detailed descriptions were provided regarding the dynamic response process and transient behavior of aluminum alloy plates under ultrahigh strain rates, along with an in-depth analysis of the stress evolution. The results reveal that laser beam diameter and laser beam energy can achieve large range forming, while the number of tracks facilitates the precise deformation adjustment. During the 12-track LPF process, there is an overall upward trend in deformation values accompanied by a dynamic increase in the bend curvature. After static relaxation, the deformation value recovers to 55.2% of the final bending curvature. The chord direction scanning of stiffened plates exhibits a larger bending curvature, indicating its greater forming capacity for large-sized single unfolding direction formation; whereas, the unfolding direction scanning of stiffened plates excels in achieving efficient integrated two-way forming. Full article

(This article belongs to the Special Issue Laser Processing of Metals and Alloys: Structures, Properties, and Applications)

► Show Figures

Graphical abstract

13 pages, 5081 KiB

Open AccessEditor’s ChoiceArticle

Low-Power Field-Deployable Interdigital Transducer-Based Scanning Laser Doppler Vibrometer for Wall-Thinning Detection in Plates

by To Kang, Soonwoo Han, Yun-Taek Yeom and Ho-Yong Lee

Materials 2024, 17(20), 5098; https://doi.org/10.3390/ma17205098 - 18 Oct 2024

Viewed by 711

Abstract

Lamb waves have become a focal point in ultrasonic testing owing to their potential for long-range and inaccessible detection. However, accurately estimating the flaws in plates using Lamb waves remains challenging because of scattering, mode conversion, and dispersion effects. Recent advances in laser [...] Read more.

Lamb waves have become a focal point in ultrasonic testing owing to their potential for long-range and inaccessible detection. However, accurately estimating the flaws in plates using Lamb waves remains challenging because of scattering, mode conversion, and dispersion effects. Recent advances in laser ultrasonic wave techniques have introduced innovative visualization methods that exploit the dispersion effect of Lamb waves to visualize defects via, for example, acoustic wavenumber spectroscopy. In this study, we developed an interdigital transducer (IDT)-based scanning laser Doppler vibrometer (SLDV) system without a power amplifier using a low-power IDT fabricated from lead magnesium niobate–lead zirconate titanate single crystals. To validate the proposed low-power IDT-based SLDV, four different defective plates were measured for defects. A comparison between a conventional IDT-based SLDV, a dry-coupled IDT-based SLDV, and the proposed method demonstrated that the latter is highly reliable for measuring thin plate defects. Full article

(This article belongs to the Special Issue Non-Destructive Testing of Materials and Parts: Techniques, Case Studies and Practical Applications)

► Show Figures

Figure 1

10 pages, 4132 KiB

Open AccessEditor’s ChoiceArticle

Ion Beam-Induced Luminescence (IBIL) for Studying Manufacturing Conditions in Ceramics: An Application to Ceramic Body Tiles

by Victoria Corregidor, José Luis Ruvalcaba-Sil, Maria Isabel Prudêncio, Maria Isabel Dias and Luís C. Alves

Materials 2024, 17(20), 5075; https://doi.org/10.3390/ma17205075 - 17 Oct 2024

Viewed by 924

Abstract

The first experimental results obtained by the ion beam-induced luminescence technique from the ceramic bodies of ancient tiles are reported in this work. The photon emission from the ceramic bodies is related to the starting minerals and the manufacturing conditions, particularly the firing [...] Read more.

The first experimental results obtained by the ion beam-induced luminescence technique from the ceramic bodies of ancient tiles are reported in this work. The photon emission from the ceramic bodies is related to the starting minerals and the manufacturing conditions, particularly the firing temperature and cooling processes. Moreover, the results indicate that this non-destructive technique, performed under a helium-rich atmosphere instead of an in-vacuum setup and with acquisition times of only a few seconds, presents a promising alternative to traditional, often destructive, compositional characterisation methods. Additionally, by adding other ion beam-based techniques such as PIXE (Particle-Induced X-ray Emission) and PIGE (Particle-Induced Gamma-ray Emission), compositional information from light elements such as Na can also be inferred, helping to also identify the raw materials used. Full article

(This article belongs to the Section Advanced Materials Characterization)

► Show Figures

Graphical abstract

21 pages, 9532 KiB

Open AccessEditor’s ChoiceArticle

Dual-Function Femtosecond Laser: β-TCP Structuring and AgNP Synthesis via Photoreduction with Azorean Green Tea for Enhanced Osteointegration and Antibacterial Properties

by Marco Oliveira, Liliya Angelova, Liliana Grenho, Maria Helena Fernandes and Albena Daskalova

Materials 2024, 17(20), 5057; https://doi.org/10.3390/ma17205057 - 16 Oct 2024

Viewed by 1340

Abstract

β-Tricalcium phosphate (β-TCP) is a well-established biomaterial for bone regeneration, highly regarded for its biocompatibility and osteoconductivity. However, its clinical efficacy is often compromised by susceptibility to bacterial infections. In this study, we address this limitation by integrating femtosecond (fs)-laser processing with the [...] Read more.

β-Tricalcium phosphate (β-TCP) is a well-established biomaterial for bone regeneration, highly regarded for its biocompatibility and osteoconductivity. However, its clinical efficacy is often compromised by susceptibility to bacterial infections. In this study, we address this limitation by integrating femtosecond (fs)-laser processing with the concurrent synthesis of silver nanoparticles (AgNPs) mediated by Azorean green tea leaf extract (GTLE), which is known for its rich antioxidant and anti-inflammatory properties. The fs laser was employed to modify the surface of β-TCP scaffolds by varying scanning velocities, fluences, and patterns. The resulting patterns, formed at lower scanning velocities, display organized nanostructures, along with enhanced roughness and wettability, as characterized by Scanning Electron Microscopy (SEM), optical profilometry, and contact angle measurements. Concurrently, the femtosecond laser facilitated the photoreduction of silver ions in the presence of GTLE, enabling the efficient synthesis of small, spherical AgNPs, as confirmed by UV–vis spectroscopy, Transmission Electron Microscopy (TEM), and Fourier Transform Infrared Spectroscopy (FTIR). The resulting AgNP-embedded β-TCP scaffolds exhibited a significantly improved cell viability and elongation of human bone marrow mesenchymal stem cells (hBM-MSCs), alongside significant antibacterial activity against Staphylococcus aureus (S. aureus). This study underscores the transformative potential of combining femtosecond laser surface modification with GTLE-mediated AgNP synthesis, presenting a novel and effective strategy for enhancing the performance of β-TCP scaffolds in bone-tissue engineering. Full article

(This article belongs to the Special Issue Size-Dependent Effects in Materials for Environmental Protection and Energy Application (2nd Edition))

► Show Figures

Figure 1

24 pages, 11670 KiB

Open AccessEditor’s ChoiceArticle

Influence of the Traverse Speed of the Stylus Tip on Changes in the Areal Texture Parameters of Machined Surfaces

by Pawel Pawlus, Rafal Reizer and Wiesław Żelasko

Materials 2024, 17(20), 5052; https://doi.org/10.3390/ma17205052 - 16 Oct 2024

Cited by 1 | Viewed by 862

Abstract

Measurements of areal (3D) surface texture using optical methods are very popular because of the short measurement time compared to the stylus tip technique. However, they are very sensitive to measurement errors. In some cases, optical measurements are not recommended. The stylus measurement [...] Read more.

Measurements of areal (3D) surface texture using optical methods are very popular because of the short measurement time compared to the stylus tip technique. However, they are very sensitive to measurement errors. In some cases, optical measurements are not recommended. The stylus measurement method is well known and can be the reference technique for surface texture measurement. The main disadvantage is the long measuring time. This time can be shortened using higher speeds of measurement. The effect of the speed of the measurement of stylus profilometer on changes in surface texture parameters was studied. Fifty surface topographies were measured using the stylus profilometer at speeds 0.5, 1, 2, 3, 4, and 5 mm/s in the same places. Surfaces after lapping, polishing, grinding, milling, laser texturing, and two-process random surfaces were measured and analyzed. Changes in parameters caused by the increase in the traverse speed depend on the characteristics and parameters of the surfaces. The random surfaces changed more than the deterministic ones. The increase in the traverse speed from 0.5 to 1 mm/s caused small changes in the parameters. Full article

(This article belongs to the Special Issue Material Surface Topography Measurement, Analysis and Characterization)

► Show Figures

Figure 1

12 pages, 2780 KiB

Open AccessEditor’s ChoiceArticle

Fabrication and Characterization of Flexible CuI-Based Photodetectors on Mica Substrates by a Low-Temperature Solution Process

by Chien-Yie Tsay, Yun-Chi Chen, Hsuan-Meng Tsai and Kai-Hsiang Liao

Materials 2024, 17(20), 5011; https://doi.org/10.3390/ma17205011 - 14 Oct 2024

Viewed by 1047

Abstract

Both CuI and CuI:Zn semiconductor thin films, along with MSM-structured UV photodetectors, were prepared on flexible mica substrates at low temperature (150 °C) by a wet chemical method. The two CuI-based films exhibited a polycrystalline phase with an optical bandgap energy close to [...] Read more.

Both CuI and CuI:Zn semiconductor thin films, along with MSM-structured UV photodetectors, were prepared on flexible mica substrates at low temperature (150 °C) by a wet chemical method. The two CuI-based films exhibited a polycrystalline phase with an optical bandgap energy close to 3.0 eV. Hall effect measurements indicated that the CuI thin film sample had p-type conductivity, while the CuI:Zn thin film sample exhibited n-type conductivity, with the latter showing a higher carrier mobility of 14.78 cm²/Vs compared to 7.67 cm²/Vs for the former. The I-V curves of both types of photodetectors showed asymmetric rectification characteristics with rectification ratios at ±3 V of 5.23 and 14.3 for the CuI and CuI:Zn devices, respectively. Flexible CuI:Zn devices exhibited significantly better sensitivity, responsivity, and specific detectivity than CuI devices both before and after static bending tests. It was found that, while the optoelectronic performance of flexible CuI-based photodetectors degraded under tensile stress during static bending tests, they still exhibited good reproducibility and repeatability in their photoresponses. Full article

(This article belongs to the Special Issue Current Research in Thin-Film Deposition: From Principles and Technologies to Film Properties and Applications)

► Show Figures

Figure 1

14 pages, 11311 KiB

Open AccessEditor’s ChoiceArticle

Effect of Cooling Rate on α Variant Selection and Microstructure Evolution in TB17 Titanium Alloy

by Guoqiang Shang, Xueping Gan, Xinnan Wang, Jinyang Ge, Chao Li, Zhishou Zhu, Xiaoyong Zhang and Kechao Zhou

Materials 2024, 17(20), 5010; https://doi.org/10.3390/ma17205010 - 13 Oct 2024

Cited by 2 | Viewed by 1484

Abstract

The α variant selection and microstructure evolution in a new metastable β titanium alloy TB17 were studied in depth by DTA, microhardness, XRD, SEM, and EBSD characterization methods. Under the rapid cooling rate conditions (150 °C/min–400 °C/min), only a very small amount of [...] Read more.

The α variant selection and microstructure evolution in a new metastable β titanium alloy TB17 were studied in depth by DTA, microhardness, XRD, SEM, and EBSD characterization methods. Under the rapid cooling rate conditions (150 °C/min–400 °C/min), only a very small amount of granular α_WM (α Widmanstatten precipitates within the grains) precipitated within the grains. The secondary α phase precipitated in the alloy changed from granular to fine needle-like at moderate cooling rates (15 °C/min–20 °C/min). When continuing to slow down the cooling rates (10 °C/min and 1 °C/min), the α_GB (α precipitates along the β grain boundaries), α_WGB (α Widmanstatten precipitates that developed from β grain boundaries or α_GB) and α_WM grew rapidly. Moreover, the continuous cooling transformation (CCT) diagram illustrated the effect of cooling rate on the β/α phase transition. EBSD analysis revealed that the variants selection of α near the original β grain boundary is mainly divided into three categories. (i) The double-BOR (Burgers orientation relationship) α_WGB colonies within neighboring β grains grow in different directions but have the same crystallographic orientation. (ii) The double-BOR α_WGB colonies within neighboring β grains have different growth directions and different crystallographic orientations. (iii) The double-BOR α_WGB colonies within the same grain have the same growth direction, but different crystallographic directions. And these double-BOR α_WGB colonies correspond to two variants of the given {0001}α//{110}β. Full article

(This article belongs to the Special Issue Research on Performance Improvement of Advanced Alloys)

► Show Figures

Figure 1

21 pages, 18454 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Image-Based Peridynamic Modeling-Based Micro-CT for Failure Simulation of Composites

by Zhuo Wang, Ling Zhang, Jiandong Zhong, Yichao Peng, Yi Ma and Fei Han

Materials 2024, 17(20), 4987; https://doi.org/10.3390/ma17204987 - 12 Oct 2024

Viewed by 1508

Abstract

By utilizing computed tomography (CT) technology, we can gain a comprehensive understanding of the specific details within the material. When combined with computational mechanics, this approach allows us to predict the structural response through numerical simulation, thereby avoiding the high experimental costs. In [...] Read more.

By utilizing computed tomography (CT) technology, we can gain a comprehensive understanding of the specific details within the material. When combined with computational mechanics, this approach allows us to predict the structural response through numerical simulation, thereby avoiding the high experimental costs. In this study, the tensile cracking behavior of carbon–silicon carbide (C/SiC) composites is numerically simulated using the bond-based peridynamics model (BB-PD), which is based on geometric models derived from segmented images of three-dimensional (3D) CT data. To obtain results efficiently and accurately, we adopted a deep learning-based image recognition model to identify the kinds of material and then the pixel type that corresponds to the material point, which can be modeled by BB-PD for failure simulation. The numerical simulations of the composites indicate that the proposed image-based peridynamics (IB-PD) model can accurately reconstruct the actual composite microstructure. It can effectively simulate various fracture phenomena such as interfacial debonding, crack propagation affected by defects, and damage to the matrix. Full article

(This article belongs to the Special Issue Alloys and Composites: Structural and Functional Applications, Second Edition)

► Show Figures

Figure 1

14 pages, 42919 KiB

Open AccessEditor’s ChoiceArticle

Effect of Eu Ions Concentration in Y₂O₃-Based Transparent Ceramics on the Electron Irradiation Induced Luminescence and Damage

by Wenhui Lou, Yang Tang, Haohong Chen, Yisong Lei, Hui Lin, Ruijin Hong, Zhaoxia Han and Dawei Zhang

Materials 2024, 17(20), 4954; https://doi.org/10.3390/ma17204954 - 10 Oct 2024

Viewed by 1020

Abstract

Eu³⁺-doped Y₂O₃-based luminescent materials can be used as a scintillator for electron or high energy β-ray irradiation, which are essential for applications such as electron microscopy and nuclear batteries. Therefore, it is essential to understand their defect [...] Read more.

Eu³⁺-doped Y₂O₃-based luminescent materials can be used as a scintillator for electron or high energy β-ray irradiation, which are essential for applications such as electron microscopy and nuclear batteries. Therefore, it is essential to understand their defect mechanisms and to develop materials with excellent properties. In this paper, Y₂O₃-based transparent ceramics with different Eu³⁺ doping concentrations were prepared by solid-state reactive vacuum sintering. This series of transparent ceramic samples exhibits strong red emission under electron beam excitation at the keV level. However, color change appears after the high-energy electron irradiation due to the capture of electrons by the traps in the Y₂O₃ lattice. Optical transmittance, laser-excited luminescence, X-ray photoelectron spectroscopy (XPS), and other analyses indicated that the traps, or the color change, mainly originate from the residual oxygen vacancies, which can be suppressed by high Eu doping. Seen from the cathodoluminescence (CL) spectra, higher doping concentrations of Eu³⁺ showed stronger resistance to electron irradiation damage, but also resulted in lower emissions due to concentration quenching. Therefore, 10% doping of Eu was selected in this work to keep the high emission intensity and strong radiation resistance both. This work helps to enhance the understanding of defect formation mechanisms in the Y₂O₃ matrix and will be of benefit for the modification of scintillation properties for functional materials systems. Full article

(This article belongs to the Section Advanced and Functional Ceramics and Glasses)

► Show Figures

Graphical abstract

15 pages, 4643 KiB

Open AccessEditor’s ChoiceArticle

Composites Based on Electrodeposited WO₃ and TiO₂ Nanoparticles for Photoelectrochemical Water Splitting

by Ramunas Levinas, Elizabeth Podlaha, Natalia Tsyntsaru and Henrikas Cesiulis

Materials 2024, 17(19), 4914; https://doi.org/10.3390/ma17194914 - 8 Oct 2024

Viewed by 1296

Abstract

Photoelectrochemically active WO₃ films were fabricated by electrodeposition from an acidic (pH 2), hydrogen-peroxide-containing electrolyte at −0.5 V vs. SCE. WO₃-TiO₂ composites were then synthesized under the same conditions, but with 0.2 g/L of anatase TiO₂ nanoparticles (⌀ [...] Read more.

Photoelectrochemically active WO₃ films were fabricated by electrodeposition from an acidic (pH 2), hydrogen-peroxide-containing electrolyte at −0.5 V vs. SCE. WO₃-TiO₂ composites were then synthesized under the same conditions, but with 0.2 g/L of anatase TiO₂ nanoparticles (⌀ 36 nm), mechanically suspended in the solution by stirring. After synthesis, the films were annealed at 400 °C. Structural characterization by XRD showed that the WO₃ films exhibit the crystalline structure of a non-stoichiometric hydrate, whereas, in WO₃-TiO₂, the WO₃ phase was monoclinic. The oxidation of tungsten, as revealed by XPS, was W⁶⁺ for both materials. Ti was found to exist mainly as Ti⁴⁺ in the composite, with a weak Ti³⁺ signal. The efficiency of the WO₃ films and composites as an oxygen evolution reaction (OER) photo-electrocatalyst was examined. The composite would generate approximately three times larger steady-state photocurrents at 1.2 V vs. SCE in a neutral 0.5 M Na₂SO₄ electrolyte compared to WO₃ alone. The surface recombination of photogenerated electron–hole pairs was characterized by intensity-modulated photocurrent spectroscopy (IMPS). Photogenerated charge transfer efficiencies were calculated from the spectra, and at 1.2 V vs. SCE, were 86.6% for WO₃ and 62% for WO₃-TiO₂. Therefore, the composite films suffered from relatively more surface recombination but generated larger photocurrents, which resulted in overall improved photoactivity. Full article

(This article belongs to the Special Issue Electrochemical Material Science and Electrode Processes)

► Show Figures

Graphical abstract

26 pages, 9412 KiB

Open AccessEditor’s ChoiceArticle

Mechanisms of Chemically Promoted Material Removal Examined for Molybdenum and Copper CMP in Weakly Alkaline Citrate-Based Slurries

by K. U. Gamagedara and D. Roy

Materials 2024, 17(19), 4905; https://doi.org/10.3390/ma17194905 - 7 Oct 2024

Cited by 3 | Viewed by 2165

Abstract

Chemical mechanical planarization (CMP) of metal components is an essential step in the fabrication of integrated circuits. Metal CMP is a complex process where strategically activated (electro)chemical reactions serve to structurally weaken the surface layers of the material being processed, and the resulting [...] Read more.

Chemical mechanical planarization (CMP) of metal components is an essential step in the fabrication of integrated circuits. Metal CMP is a complex process where strategically activated (electro)chemical reactions serve to structurally weaken the surface layers of the material being processed, and the resulting overburdens are removed under low-force abrasion. Understanding the tribo-electrochemical mechanisms of this process is crucial to successfully designing the consumable materials for advanced CMP slurries that are needed for the new technology nodes. Using a model CMP system involving copper (wiring material in interconnect structures) and molybdenum (a new diffusion barrier material for copper), the present work illustrates a tribo-electroanalytical scheme for studying various mechanistic details of metal CMP. Electroanalytical probes are employed both in the absence and in the presence of surface polishing to quantify the interplay between mechanical abrasion and chemical surface modification. Weakly alkaline slurry formulations are tested with variable concentrations of silica abrasives and a complexing agent, citric acid. The results serve to examine the link between material removal and tribo-corrosion and to identify the functions of the active slurry additives in governing the rates and selectivity of material removal for CMP. Full article

(This article belongs to the Section Materials Chemistry)

► Show Figures

Figure 1

14 pages, 2370 KiB

Open AccessEditor’s ChoiceArticle

Nd³⁺-Doped Scheelite-Type Multifunctional Materials—Their Thermal Stability and Magnetic Properties

by Elżbieta Tomaszewicz, Grażyna Dąbrowska, Hubert Fuks and Paweł Kochmański

Materials 2024, 17(19), 4883; https://doi.org/10.3390/ma17194883 - 4 Oct 2024

Viewed by 1305

Abstract

New Nd³⁺-doped cadmium molybdato-tungstates with the chemical formula of Cd_1−3x▯_xNd_2x(MoO₄)_1−3x(WO₄)_3x (where x = 0.0283, 0.0455, 0.0839, 0.1430, 0.1875, 0.2000, 0.2500, and ▯ denotes a [...] Read more.

New Nd³⁺-doped cadmium molybdato-tungstates with the chemical formula of Cd_1−3x▯_xNd_2x(MoO₄)_1−3x(WO₄)_3x (where x = 0.0283, 0.0455, 0.0839, 0.1430, 0.1875, 0.2000, 0.2500, and ▯ denotes a vacant site in the crystal lattice) were successfully synthesized by the high-temperature solid state reaction method, using CdMoO₄ and Nd₂(WO₄)₃ as the initial reactants. The structure and change in their lattice parameters as a function of Nd³⁺ ion concentration were investigated by the XRD (X-ray diffraction) method. The surface morphology and grain size of the doped materials were characterized by SEM (scanning electron microscopy). Their thermal properties and initial reactants were analyzed by DTA-TG (differential thermal analysis coupled with thermogravimetry) techniques. The optical properties of the Nd³⁺-doped cadmium molybdato-tungstates, such as optical band gap, were determined by UV–vis–NIR (ultraviolet–visible–near infrared) spectroscopy. The EPR (electron paramagnetic resonance) technique provided information on the type of magnetic interactions between Nd³⁺ ions. Full article

(This article belongs to the Special Issue Obtaining and Characterization of New Materials (5th Edition))

► Show Figures

Graphical abstract

11 pages, 5962 KiB

Open AccessEditor’s ChoiceArticle

Stable Single-Mode 795 nm Vertical-Cavity Surface-Emitting Laser for Quantum Sensing

by Yongli Wang, Yang Zhang, Chuanchuan Li, Jian Li, Xin Wei and Lianghui Chen

Materials 2024, 17(19), 4872; https://doi.org/10.3390/ma17194872 - 4 Oct 2024

Viewed by 1687

Abstract

Vertical-cavity surface-emitting lasers (VCSELs) are essential for exhibiting single-transverse-mode output characteristics, which are critical for applications in quantum sensing, optical interconnection, and laser printing. In this study, we achieved stable single-transverse-mode lasing using extended-2λ-cavity with an oxide aperture diameter of 7.08 μm. The [...] Read more.

Vertical-cavity surface-emitting lasers (VCSELs) are essential for exhibiting single-transverse-mode output characteristics, which are critical for applications in quantum sensing, optical interconnection, and laser printing. In this study, we achieved stable single-transverse-mode lasing using extended-2λ-cavity with an oxide aperture diameter of 7.08 μm. The device demonstrated a high output power of 6.8 mW and a narrow linewidth of 49.8 MHz at room temperature. Additionally, it maintained stable single-mode emission at 794.8 nm and achieved a side-mode suppression ratio (SMSR) exceeding 40 dB within the temperature range of 25 °C~85 °C, thereby meeting the requirements of ⁸⁷Rb atom quantum sensors. The fabricated device obtained high-power and narrow linewidth single-transverse-mode operation by a monolithic extended cavity without introducing additional processing procedures, which is expected to promote the commercial viability of VCSELs in quantum sensing. Full article

(This article belongs to the Special Issue Advances in Nanophotonic Materials, Devices, and Applications)

► Show Figures

Figure 1

37 pages, 4470 KiB

Open AccessEditor’s ChoiceReview

A Review of Natural Fibres and Biopolymer Composites: Progress, Limitations, and Enhancement Strategies

by Innes McKay, Johnattan Vargas, Liu Yang and Reda M. Felfel

Materials 2024, 17(19), 4878; https://doi.org/10.3390/ma17194878 - 4 Oct 2024

Cited by 3 | Viewed by 2646

Abstract

The interest in natural fibres and biopolymers for developing bio-composites has greatly increased in recent years, motivated by the need to reduce the environmental impact of traditional synthetic, fossil fuel-derived materials. However, several limitations associated with the use of natural fibres and polymers [...] Read more.

The interest in natural fibres and biopolymers for developing bio-composites has greatly increased in recent years, motivated by the need to reduce the environmental impact of traditional synthetic, fossil fuel-derived materials. However, several limitations associated with the use of natural fibres and polymers should be addressed if they are to be seriously considered mainstream fibre reinforcements. These include poor compatibility of natural fibres with polymer matrices, variability, high moisture absorption, and flammability. Various surface treatments have been studied to tackle these drawbacks, such as alkalisation, silane treatment, acetylation, plasma treatment, and polydopamine coating. This review paper considers the classification, properties, and limitations of natural fibres and biopolymers in the context of bio-composite materials. An overview of recent advancements and enhancement strategies to overcome such limitations will also be discussed, with a focus on mechanical performance, moisture absorption behaviour, and flammability of composites. The limitations of natural fibres, biopolymers, and their bio-composites should be carefully addressed to enable the widespread use of bio-composites in various applications, including electronics, automotive, and construction. Full article

(This article belongs to the Section Advanced Composites)

► Show Figures

Figure 1

12 pages, 4941 KiB

Open AccessEditor’s ChoiceArticle

Self-Adaptive Intelligent Metasurface Cloak System with Integrated Sensing Units

by Panyi Li, Jiwei Zhao, Caofei Luo, Zhicheng Pei, Hui Jin, Yitian Huang, Wei Zhou and Bin Zheng

Materials 2024, 17(19), 4863; https://doi.org/10.3390/ma17194863 - 2 Oct 2024

Viewed by 3630

Abstract

Metasurfaces, which are ultrathin planar metamaterials arranged in certain global sequences, interact uniquely with the surrounding light field and exhibit unusual effects of light modulation. Many interesting applications have been discovered based on metasurfaces, particularly in invisibility cloaks. However, most invisibility cloaks are [...] Read more.

Metasurfaces, which are ultrathin planar metamaterials arranged in certain global sequences, interact uniquely with the surrounding light field and exhibit unusual effects of light modulation. Many interesting applications have been discovered based on metasurfaces, particularly in invisibility cloaks. However, most invisibility cloaks are limited to working in specific directions. Achieving effectiveness in multiple directions requires the metasurface to be designed with both perception and modulation capabilities. Current multi-directional metasurface cloak systems are implemented with discrete components rather than an integrated sensing component. Here, we propose an intelligent metasurface cloak system that integrates sensing units, resulting in the cloaking effect with the help of a real-time direction sensor and an adaptive feedback control system. A reconfigurable reflective meta-atom based on phase modulation is presented. Sensing units replace parts of the meta-atoms in the designed tunable metasurface, integrating with an FPGA responsible for measuring the direction and frequency of the incident wave, constituting a closed-loop system together with the feedback parts. Experimental results demonstrate that the metasurface cloak system can recognize the different directions of the incoming wave, and can adaptively manipulate the reflected phase of EM waves to conceal objects without any human participation. Full article

(This article belongs to the Special Issue Advances in Metamaterials: Structure, Properties and Applications)

► Show Figures

Figure 1

35 pages, 4084 KiB

Open AccessEditor’s ChoiceArticle

Electrostatically Interacting Wannier Qubits in Curved Space

by Krzysztof Pomorski

Materials 2024, 17(19), 4846; https://doi.org/10.3390/ma17194846 - 30 Sep 2024

Cited by 2 | Viewed by 1341

Abstract

A derivation of a tight-binding model from Schrödinger formalism for various topologies of position-based semiconductor qubits is presented in the case of static and time-dependent electric fields. The simplistic tight-binding model enables the description of single-electron devices at a large integration scale. The [...] Read more.

A derivation of a tight-binding model from Schrödinger formalism for various topologies of position-based semiconductor qubits is presented in the case of static and time-dependent electric fields. The simplistic tight-binding model enables the description of single-electron devices at a large integration scale. The case of two electrostatically Wannier qubits (also known as position-based qubits) in a Schrödinger model is presented with omission of spin degrees of freedom. The concept of programmable quantum matter can be implemented in the chain of coupled semiconductor quantum dots. Highly integrated and developed cryogenic CMOS nanostructures can be mapped to coupled quantum dots, the connectivity of which can be controlled by a voltage applied across the transistor gates as well as using an external magnetic field. Using the anti-correlation principle arising from the Coulomb repulsion interaction between electrons, one can implement classical and quantum inverters (Classical/Quantum Swap Gate) and many other logical gates. The anti-correlation will be weakened due to the fact that the quantumness of the physical process brings about the coexistence of correlation and anti-correlation at the same time. One of the central results presented in this work relies on the appearance of dissipation-like processes and effective potential renormalization building effective barriers in both semiconductors and in superconductors between not bended nanowire regions both in classical and in quantum regimes. The presence of non-straight wire regions is also expressed by the geometrical dissipative quantum Aharonov–Bohm effect in superconductors/semiconductors when one obtains a complex value vector potential-like field. The existence of a Coulomb interaction provides a base for the physical description of an electrostatic Q-Swap gate with any topology using open-loop nanowires, with programmable functionality. We observe strong localization of the wavepacket due to nanowire bending. Therefore, it is not always necessary to build a barrier between two nanowires to obtain two quantum dot systems. On the other hand, the results can be mapped to the problem of an electron in curved space, so they can be expressed with a programmable position-dependent metric embedded in Schrödinger’s equation. The semiconductor quantum dot system is capable of mimicking curved space, providing a bridge between fundamental and applied science in the implementation of single-electron devices. Full article

(This article belongs to the Section Quantum Materials)

► Show Figures

Figure 1

14 pages, 4622 KiB

Open AccessEditor’s ChoiceArticle

Fatigue Behavior of Cord-Rubber Composite Materials under Different Loading Conditions

by Julian Torggler, Martin Leitner, Christian Buzzi, Tobias Faethe, Heiko Müller and Eduardo Machado Charry

Materials 2024, 17(19), 4771; https://doi.org/10.3390/ma17194771 - 28 Sep 2024

Cited by 2 | Viewed by 895

Abstract

Cord-rubber composites are subjected to a wide range of loads in various applications. However, their fatigue behavior remains relatively under-researched. To address this gap, a set of representative specimens was developed, and a validated numerical model was employed to assess fatigue-relevant parameters. In [...] Read more.

Cord-rubber composites are subjected to a wide range of loads in various applications. However, their fatigue behavior remains relatively under-researched. To address this gap, a set of representative specimens was developed, and a validated numerical model was employed to assess fatigue-relevant parameters. In this study, we present the results from two series of tests with different strain ratios (R values). One series was subjected to a pure pulsating tensile strain (R ~0), while the second series experienced an increased mean strain with an R ratio between 0.2 and 0.3. A direct comparison of the two series demonstrated that a higher strain ratio results in a longer service life. This is reflected in an increase in the slope (k) from 13 to 23, as well as an increase in the ultimate fiber strain from 8% to 11% at N_d = 50,000 load cycles for a survival probability of 50%. Both series indicate a comparable scatter in the test results. This comparative analysis shows that the strain ratio significantly impacts the fatigue behavior of cord-rubber composite materials based on cyclic tests under different loading conditions. The findings of this study demonstrate the necessity of considering different load situations when evaluating or designing components. Full article

(This article belongs to the Special Issue Mechanical Performance of Advanced Composite Materials and Structures (2nd Edition))

► Show Figures

Figure 1

9 pages, 1716 KiB

Open AccessEditor’s ChoiceArticle

Adsorption and Catalytic Reduction of Nitrogen Oxides (NO, N₂O) on Disulfide Cluster Complexes of Cobalt and Iron—A Density Functional Study

by Ellie L. Uzunova and Ivelina M. Georgieva

Materials 2024, 17(19), 4764; https://doi.org/10.3390/ma17194764 - 28 Sep 2024

Viewed by 916

Abstract

The reactivity of nitrogen oxide, NO, as a ligand in complexes with [Fe2-S2] and [Co2-S2] non-planar rhombic cores is examined by density functional theory (DFT). The cobalt-containing nitrosyl complexes are less stable than the iron complexes because the Co-S bonds in the [Co2-S2] [...] Read more.

The reactivity of nitrogen oxide, NO, as a ligand in complexes with [Fe2-S2] and [Co2-S2] non-planar rhombic cores is examined by density functional theory (DFT). The cobalt-containing nitrosyl complexes are less stable than the iron complexes because the Co-S bonds in the [Co2-S2] core are weakened upon NO coordination. Various positions of NO were examined, including its binding to sulfur centers. The release of NO molecules can be monitored photochemically. The ability of NO to form a (NO)₂ dimer provides a favorable route of electrochemical reduction, as protonation significantly stabilizes the dimeric species over the monomers. The quasilinear dimer ONNO, with trans-orientation of oxygen atoms, gains higher stability under protonation and reduction via proton–electron transfer. The first two reduction steps lead to an N₂O intermediate, whose reduction is more energy demanding: in the two latter reaction steps the highest energy barrier for Co₂S₂(CO)₆ is 109 kJ mol⁻¹, and for Fe₂S₂(CO)₆, it is 133 kJ mol⁻¹. Again, the presence of favorable light absorption bands allows for a photochemical route to overcome these energy barriers. All elementary steps are exothermic, and the final products are molecular nitrogen and water. Full article

(This article belongs to the Special Issue Transition Metal Nanomaterials: Synthesis and Photo/Electrocatalytic Performance)

► Show Figures

Figure 1

13 pages, 10154 KiB

Open AccessEditor’s ChoiceArticle

An Improved Mampel Model of the Non-Isothermal Crystallization Kinetics of Fiber-Reinforced Thermoplastic Composites

by Zengrui Song, Huiming Ning, Feng Liu, Ning Hu and Youkun Gong

Materials 2024, 17(19), 4747; https://doi.org/10.3390/ma17194747 - 27 Sep 2024

Cited by 1 | Viewed by 721

Abstract

Fiber-reinforced thermoplastic composites (FRTPs) are gaining increasing attention and widespread use in engineering applications due to their high specific strength and stiffness, excellent toughness, and recyclability. The mechanical properties of these composites are closely tied to their crystallization process, making it crucial to [...] Read more.

Fiber-reinforced thermoplastic composites (FRTPs) are gaining increasing attention and widespread use in engineering applications due to their high specific strength and stiffness, excellent toughness, and recyclability. The mechanical properties of these composites are closely tied to their crystallization process, making it crucial to accurately describe this phenomenon. Existing theoretical models for analyzing the non-isothermal crystallization of thermoplastic composites often face challenges relating to the complexity of obtaining multiple parameters and the difficulty of achieving a final relative crystallinity of 1. To address these issues, this paper introduces a novel functional form of the crystallization rate parameter K(T), tailored for engineering applications, and proposes an improved Mampel model. This model assumes K(T) to be zero before the onset of crystallization and also to be linearly dependent on temperature thereafter, ensuring that the final relative crystallinity reaches 1. The model requires only two easily accessible parameters: the initial crystallization temperature (T_s) and the linear slope (k). The simplicity of the model makes it particularly well suited to engineering applications. This provides a straightforward and effective tool for describing the non-isothermal crystallization kinetics of fiber-reinforced thermoplastic composites. Full article

(This article belongs to the Special Issue Advances in Functional Polymers and Nanocomposites)

► Show Figures

Graphical abstract

8 pages, 2626 KiB

Open AccessEditor’s ChoiceArticle

Improvement of the Stability of Quantum-Dot Light Emitting Diodes Using Inorganic HfO_x Hole Transport Layer

by Jung Min Yun, Min Ho Park, Yu Bin Kim, Min Jung Choi, Seunghwan Kim, Yeonjin Yi, Soohyung Park and Seong Jun Kang

Materials 2024, 17(19), 4739; https://doi.org/10.3390/ma17194739 - 27 Sep 2024

Viewed by 1419

Abstract

One of the major challenges in QLED research is improving the stability of the devices. In this study, we fabricated all inorganic quantum-dot light emitting diodes (QLEDs) using hafnium oxide (HfO_x) as the hole transport layer (HTL), a material commonly used [...] Read more.

One of the major challenges in QLED research is improving the stability of the devices. In this study, we fabricated all inorganic quantum-dot light emitting diodes (QLEDs) using hafnium oxide (HfO_x) as the hole transport layer (HTL), a material commonly used for insulator. Oxygen vacancies in HfO_x create defect states below the Fermi level, providing a pathway for hole injection. The concentration of these oxygen vacancies can be controlled by the annealing temperature. We optimized the all-inorganic QLEDs with HfO_x as the HTL by changing the annealing temperature. The optimized QLEDs with HfO_x as the HTL showed a maximum luminance and current efficiency of 66,258 cd/m² and 9.7 cd/A, respectively. The fabricated all-inorganic QLEDs exhibited remarkable stability, particularly when compared to devices using organic materials for the HTL. Under extended storage in ambient conditions, the all-inorganic device demonstrated a significantly enhanced operating lifetime (T₅₀) of 5.5 h, which is 11 times longer than that of QLEDs using an organic HTL. These results indicate that the all-inorganic QLEDs structure, with ITO/MoO₃/HfO_x/QDs/ZnMgO/Al, exhibits superior stability compared to organic-inorganic hybrid QLEDs. Full article

(This article belongs to the Special Issue Feature Papers in Materials Physics (2nd Edition))

► Show Figures

Graphical abstract

12 pages, 1462 KiB

Open AccessEditor’s ChoiceArticle

Comparison of Flexural Strength and Wear of Injectable, Flowable and Paste Composite Resins

by Hadi Rajabi, Michael Denny, Kostas Karagiannopoulos and Haralampos Petridis

Materials 2024, 17(19), 4749; https://doi.org/10.3390/ma17194749 - 27 Sep 2024

Cited by 5 | Viewed by 2053

Abstract

(1) Objectives: This study investigated and compared the wear and flexural strength of two highly filled (injectable), one flowable and one paste composite. (2) Methods: Two highly filled flowable composites (G-aenial Universal Injectable and Beautifil Plus F00), a paste composite (Empress Direct) and [...] Read more.

(1) Objectives: This study investigated and compared the wear and flexural strength of two highly filled (injectable), one flowable and one paste composite. (2) Methods: Two highly filled flowable composites (G-aenial Universal Injectable and Beautifil Plus F00), a paste composite (Empress Direct) and a conventional flowable (Tetric EvoFlow) were tested. A two-body wear test was carried out using 10 disc-shaped samples from each group, which were subjected to 200,000 wear machine cycles to simulate wear, followed by Scanning Electron Microscope analysis. Flexural strength was tested using a three-point bend test using 15 beam samples for each of the four groups. Values were statistically compared using one-way analysis of variance (ANOVA) for flexural strength and a Kruskal–Wallis test for wear. (3) Results: The median volume loss for G-aenial Universal Injectable and Beautifil Plus F00 was statistically lower than that of both Empress Direct and Tetric EvoFlow. For flexural strength the two highly filled flowable composites both exhibited statistically higher mean flexural strength values compared to Empress Direct (p < 0.004) and Tetric Evoflow (p < 0.001). There were no statistically significant differences in the values of wear and flexural strength between the two highly filled flowable composites. (4) Conclusions/significance: Highly filled flowable composite resins with nano filler particles outperformed a conventional flowable and a paste composite resin in terms of wear resistance and flexural strength, and may be suitable to use in occlusal, load-bearing areas. Full article

(This article belongs to the Special Issue Materials for Dentistry: Biofunctional Properties and Their Improvement)

► Show Figures

Figure 1

15 pages, 8933 KiB

Open AccessEditor’s ChoiceArticle

Giant Elastocaloric Effect and Improved Cyclic Stability in a Directionally Solidified (Ni₅₀Mn₃₁Ti₁₉)₉₉B₁ Alloy

by Honglin Wang, Yueping Wang, Guoyao Zhang, Zongbin Li, Jiajing Yang, Jinwei Li, Bo Yang, Haile Yan and Liang Zuo

Materials 2024, 17(19), 4756; https://doi.org/10.3390/ma17194756 - 27 Sep 2024

Cited by 1 | Viewed by 1189

Abstract

Superelastic shape memory alloys with an integration of large elastocaloric response and good cyclability are crucially demanded for the advancement of solid-state elastocaloric cooling technology. In this study, we demonstrate a giant elastocaloric effect with improved cyclic stability in a <001>_A textured [...] Read more.

Superelastic shape memory alloys with an integration of large elastocaloric response and good cyclability are crucially demanded for the advancement of solid-state elastocaloric cooling technology. In this study, we demonstrate a giant elastocaloric effect with improved cyclic stability in a <001>_A textured polycrystalline (Ni₅₀Mn₃₁Ti₁₉)₉₉B₁ alloy developed through directional solidification. It is shown that large adiabatic temperature variation (|ΔT_ad|) values more than 15 K are obtained across the temperature range from 283 K to 373 K. In particular, a giant ΔT_ad up to −27.2 K is achieved by unloading from a relatively low compressive stress of 412 MPa at 303 K. Moreover, persistent |ΔT_ad| values exceeding 8.5 K are sustained for over 12,000 cycles, exhibiting a very low attenuation behavior with a rate of 7.5 × 10⁻⁵ K per cycle. The enhanced elastocaloric properties observed in the present alloy are ascribed to the microstructure texturing as well as the introduction of a secondary phase due to boron alloying. Full article

(This article belongs to the Special Issue Phase Transformation, Functional Properties, and Crystallography of Advanced Materials (Second Volume))

► Show Figures

Figure 1

21 pages, 2292 KiB

Open AccessEditor’s ChoiceReview

Recent Progress in Laser Powder Bed Fusions Processes of Advanced High-Strength Steels

by Aleksandra Królicka and Julia Malawska

Materials 2024, 17(19), 4699; https://doi.org/10.3390/ma17194699 - 25 Sep 2024

Viewed by 1548

Abstract

This review is focused on the perspectives of the application of Advanced High Strength Steels (AHSSs) in the field of additive technologies directed at the laser powder bed fusion/selective laser melting processes. In principle, AHSSs require significant attention due to their promising mechanical [...] Read more.

This review is focused on the perspectives of the application of Advanced High Strength Steels (AHSSs) in the field of additive technologies directed at the laser powder bed fusion/selective laser melting processes. In principle, AHSSs require significant attention due to their promising mechanical properties for usage in the automotive industry towards reducing the weight of vehicles. Although additive manufacturing represents a promising perspective towards expanding the industrialization of AHSSs in a wider area of their applications, they have not been sufficiently investigated concerning their usage in LPBF/SLM processes. AM techniques enable the fabrication of complex machine parts, including those with a cellular structure, which can contribute to further reducing the weight of vehicles or structures. Maraging steels have recently attracted the attention of researchers, and today are a common grade of steel produced by LPBF techniques. The other group of AHSSs are high-Mn steels with an austenitic matrix characterized by the TRIP and TWIP effects. Less published research has been conducted on medium-Mn steels, which require additional intercritical annealing and preheating during printing. Moreover, the advanced bainitic steels and low-density, high-strength steels represent a new window for further research into the use of the LPBF processes for their fabrication. Full article

(This article belongs to the Special Issue Enhancing In-Use Properties of Advanced Steels)

► Show Figures

Graphical abstract

Journal Menu

Journal Browser

Editor’s Choice Articles

Further Information

Guidelines

MDPI Initiatives

Follow MDPI