Materials

23 pages, 7382 KiB

Open AccessEditor’s ChoiceArticle

Combined Electrochemical, Raman Analysis and Machine Learning Assessments of the Inhibitive Properties of an 1,3,4-Oxadiazole-2-Thiol Derivative against Carbon Steel Corrosion in HCl Solution

by Simona Varvara, Camelia Berghian-Grosan, Gianina Damian, Maria Popa and Florin Popa

Materials 2022, 15(6), 2224; https://doi.org/10.3390/ma15062224 - 17 Mar 2022

Cited by 6 | Viewed by 2153

Abstract

The inhibiting properties of 5-(4-pyridyl)-1,3,4-oxadiazole-2-thiol (PyODT) on the corrosion of carbon steel in 1.0 M HCl solution were investigated by potentiodynamic polarization, electrochemical impedance spectroscopy, Raman spectroscopy, and SEM-EDX analysis. An approach based on machine learning algorithms and Raman data was also applied [...] Read more.

The inhibiting properties of 5-(4-pyridyl)-1,3,4-oxadiazole-2-thiol (PyODT) on the corrosion of carbon steel in 1.0 M HCl solution were investigated by potentiodynamic polarization, electrochemical impedance spectroscopy, Raman spectroscopy, and SEM-EDX analysis. An approach based on machine learning algorithms and Raman data was also applied to follow the carbon steel degradation in different experimental conditions. The electrochemical measurements revealed that PyODT behaves as a mixed-type corrosion inhibitor, reaching an efficiency of about 93.1% at a concentration of 5 mM, after 1 h exposure to 1.0 M HCl solution. Due to the molecular adsorption and structural organization of PyODT molecules on the C-steel surface, higher inhibitive effectiveness of about 97% was obtained at 24 h immersion. The surface analysis showed a significantly reduced degradation state of the carbon steel surface in the presence of PyODT due to the inhibitor adsorption revealed by Raman spectroscopy and the presence of N and S atoms in the EDX spectra. The combination of Raman spectroscopy and machine learning algorithms was proved to be a facile and reliable tool for an incipient identification of the corrosion sites on a metallic surface exposed to corrosive environments. Full article

(This article belongs to the Special Issue Corrosion and Corrosion Inhibition of Metals and Their Alloys)

► Show Figures

Figure 1

31 pages, 4478 KiB

Open AccessEditor’s ChoiceReview

Exploring the Journey of Zinc Oxide Nanoparticles (ZnO-NPs) toward Biomedical Applications

by Fahadul Islam, Sheikh Shohag, Md. Jalal Uddin, Md. Rezaul Islam, Mohamed H. Nafady, Aklima Akter, Saikat Mitra, Arpita Roy, Talha Bin Emran and Simona Cavalu

Materials 2022, 15(6), 2160; https://doi.org/10.3390/ma15062160 - 15 Mar 2022

Cited by 229 | Viewed by 12491

Abstract

The field of nanotechnology is concerned with the creation and application of materials having a nanoscale spatial dimensioning. Having a considerable surface area to volume ratio, nanoparticles have particularly unique properties. Several chemical and physical strategies have been used to prepare zinc oxide [...] Read more.

The field of nanotechnology is concerned with the creation and application of materials having a nanoscale spatial dimensioning. Having a considerable surface area to volume ratio, nanoparticles have particularly unique properties. Several chemical and physical strategies have been used to prepare zinc oxide nanoparticles (ZnO-NPs). Still, biological methods using green or natural routes in various underlying substances (e.g., plant extracts, enzymes, and microorganisms) can be more environmentally friendly and cost-effective than chemical and/or physical methods in the long run. ZnO-NPs are now being studied as antibacterial agents in nanoscale and microscale formulations. The purpose of this study is to analyze the prevalent traditional method of generating ZnO-NPs, as well as its harmful side effects, and how it might be addressed utilizing an eco-friendly green approach. The study’s primary focus is on the potential biomedical applications of green synthesized ZnO-NPs. Biocompatibility and biomedical qualities have been improved in green-synthesized ZnO-NPs over their traditionally produced counterparts, making them excellent antibacterial and cancer-fighting drugs. Additionally, these ZnO-NPs are beneficial when combined with the healing processes of wounds and biosensing components to trace small portions of biomarkers linked with various disorders. It has also been discovered that ZnO-NPs can distribute and sense drugs. Green-synthesized ZnO-NPs are compared to traditionally synthesized ones in this review, which shows that they have outstanding potential as a potent biological agent, as well as related hazardous properties. Full article

(This article belongs to the Special Issue Preparation, Physico-Chemical Properties and Biomedical Applications of Nanoparticles)

► Show Figures

Figure 1

11 pages, 5776 KiB

Open AccessEditor’s ChoiceArticle

The Effects of 3-Dimensional Bioprinting Calcium Silicate Cement/Methacrylated Gelatin Scaffold on the Proliferation and Differentiation of Human Dental Pulp Stem Cells

by Dakyung Choi, Manfei Qiu, Yun-Chan Hwang, Won-Mann Oh, Jeong-Tae Koh, Chan Park and Bin-Na Lee

Materials 2022, 15(6), 2170; https://doi.org/10.3390/ma15062170 - 15 Mar 2022

Cited by 17 | Viewed by 3527

Abstract

A calcium silicate cement/methacrylated gelatin (GelMa) scaffold has been applied in tissue engineering; however, the research on its applications in dental tissue regeneration remains lacking. We investigate the effect of this scaffold on human dental pulp stem cells (hDPSCs). hDPSCs were cultured in [...] Read more.

A calcium silicate cement/methacrylated gelatin (GelMa) scaffold has been applied in tissue engineering; however, the research on its applications in dental tissue regeneration remains lacking. We investigate the effect of this scaffold on human dental pulp stem cells (hDPSCs). hDPSCs were cultured in 3D-printed GelMa and MTA-GelMa scaffolds. Cell adhesion was evaluated using scanning electron microscopy images. Cells were cultured in an osteogenic differentiation medium, which contained a complete medium or α-MEM containing aqueous extracts of the 3D-printd GelMa or MTA-GelMa scaffold with 2% FBS, 10 mM β-glycerophosphate, 50 μg/mL ascorbic acid, and 10 nM dexamethasone; cell viability and differentiation were shown by WST-1 assay, Alizarin Red S staining, and alkaline phosphatase staining. Quantitative real-time PCR was used to measure the mRNA expression of DSPP and DMP-1. One-way analysis of variance followed by Tukey’s post hoc test was used to determine statistically significant differences, identified at p < 0.05. hDPSCs adhered to both the 3D-printed GelMa and MTA-GelMa scaffolds. There was no statistically significant difference between the GelMa and MTA-GelMa groups and the control group in the cell viability test. Compared with the control group, the 3D-printed MTA-GelMa scaffold promoted the odontogenic differentiation of hDPSCs. The 3D-printed MTA-GelMa scaffold is suitable for the growth of hDPSCs, and the scaffold extracts can better promote odontoblastic differentiation. Full article

(This article belongs to the Special Issue Hydrogel Biomaterials: Present and Future Challenges)

► Show Figures

Figure 1

19 pages, 5743 KiB

Open AccessEditor’s ChoiceArticle

Polyester and Epoxy Resins with Increased Thermal Conductivity and Reduced Surface Resistivity for Applications in Explosion-Proof Enclosures of Electrical Devices

by Małgorzata Szymiczek and Dawid Buła

Materials 2022, 15(6), 2171; https://doi.org/10.3390/ma15062171 - 15 Mar 2022

Cited by 4 | Viewed by 2411

Abstract

Composite materials are still finding new applications that require the modification of various properties and are characterized by the summary impact on selected operational features. Due to the operating conditions of electrical equipment enclosures in potentially explosive atmospheres, the surface resistivity ensuring anti-electrostatic [...] Read more.

Composite materials are still finding new applications that require the modification of various properties and are characterized by the summary impact on selected operational features. Due to the operating conditions of electrical equipment enclosures in potentially explosive atmospheres, the surface resistivity ensuring anti-electrostatic properties, i.e., below 10⁹ Ω and resistance to the flame while maintaining appropriate operational enclosure properties is very important. It is also crucial to dissipate heat while reducing weight. Currently metal or cast-iron enclosures are used for various types of electrical devices. As part of the work, a material that can be used for a composite matrix for the enclosure was developed. The study aimed to assess the influence of selected fillers and chemical modifications on the thermal conductivity coefficient, resistivity, and strength properties of matrix materials for the production of electrical device enclosures used in the mining industry. Selected resins were modified with graphite, copper, and carbon black. Tests were carried out on the coefficient of thermal conductivity, surface resistivity, flammability, and flexural strength. At the final stage of the work, a multi-criteria analysis was carried out, which allowed the selection of a composite that meets the assumed characteristics to the highest degree. It is a vinyl ester composite modified with 15 wt.% MG394 and 5 wt.% MG1596 graphite (W2). The thermal conductivity of composite W2 is 5.64 W/mK, the surface resistivity is 5.2 × 10³ Ω, the flexural strength is 50.61 MPa, and the flammability class is V0. Full article

(This article belongs to the Special Issue Polymer Composites: Microstructural, Thermal and Mechanical Properties)

► Show Figures

Figure 1

19 pages, 5911 KiB

Open AccessEditor’s ChoiceArticle

Activated Carbon Preparation from Sugarcane Leaf via a Low Temperature Hydrothermal Process for Aquaponic Treatment

by Kanyanat Tawatbundit and Sumrit Mopoung

Materials 2022, 15(6), 2133; https://doi.org/10.3390/ma15062133 - 14 Mar 2022

Cited by 5 | Viewed by 3655

Abstract

The effects of hydrothermal treatment, 0–5% KMnO₄ content, and 300–400 °C pyrolysis temperature, were studied for activated carbon preparation from sugar cane leaves in comparison with non-hydrothermal treatment. The percent yield of activated carbon prepared by the hydrothermal method (20.33–36.23%) was higher [...] Read more.

The effects of hydrothermal treatment, 0–5% KMnO₄ content, and 300–400 °C pyrolysis temperature, were studied for activated carbon preparation from sugar cane leaves in comparison with non-hydrothermal treatment. The percent yield of activated carbon prepared by the hydrothermal method (20.33–36.23%) was higher than that prepared by the non-hydrothermal method (16.40–36.50%) and was higher with conditions employing the same content of KMnO₄ (22.08–42.14%). The hydrothermal and pyrolysis temperatures have the effect of increasing the carbon content and aromatic nature of the synthesized activated carbons. In addition, KMnO₄ utilization increased the O/C ratio and the content of C-O, Mn-OH, O-Mn-O, and Mn-O surface functional groups. KMnO₄ also decreases zeta potential values throughout the pH range of 3 to 11 and the surface area and porosity of the pre-hydrothermal activated carbons. The use of the pre-hydrothermal activated carbon prepared with 3% KMnO₄ and pyrolyzed at 350 °C as a filter in an aquaponic system could improve the quality of water with pH of 7.2–7.4, DO of 9.6–13.3 mg/L, and the turbidity of 2.35–2.90 NTU. It could also reduce the content of ammonia, nitrite, and phosphate with relative removal rates of 86.84%, 73.17%, and 53.33%, respectively. These results promoted a good growth of catfish and red oak lettuce. Full article

(This article belongs to the Collection Advanced Biomass-Derived Carbon Materials)

► Show Figures

Figure 1

12 pages, 4733 KiB

Open AccessEditor’s ChoiceArticle

High-Frequency and High-Power Performance of n-Type GaN Epilayers with Low Electron Density Grown on Native Substrate

by Roman M. Balagula, Liudvikas Subačius, Justinas Jorudas, Vytautas Janonis, Pawel Prystawko, Mikolaj Grabowski and Irmantas Kašalynas

Materials 2022, 15(6), 2066; https://doi.org/10.3390/ma15062066 - 11 Mar 2022

Cited by 7 | Viewed by 2802

Abstract

The n-type GaN epilayers with low electron density were developed on a native substrate using the metalorganic vapour phase epitaxy method and investigated under pulsed electric fields until material breakdown and optically in the spectrum range from 0.1 THz to 60 THz [...] Read more.

The n-type GaN epilayers with low electron density were developed on a native substrate using the metalorganic vapour phase epitaxy method and investigated under pulsed electric fields until material breakdown and optically in the spectrum range from 0.1 THz to 60 THz at two temperatures of 77 K and 300 K. The epilayers demonstrated the low-field electron mobility and density values reaching up to 1021 cm²/V·s and 1.06 × 10¹⁶ cm⁻³ (at 300 K) and 2652 cm²/V·s and 0.21 × 10¹⁶ cm⁻³ (at 77 K), respectively. Maximum injected electric power value till the damage of the GaN epilayer was found to be up to 1.8 GW/cm³ and 5.1 GW/cm³ at 77 K and 300 K, respectively. The results indicate new practical possibilities of the GaN material controlled by an external electric field. Full article

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

► Show Figures

Graphical abstract

20 pages, 2045 KiB

Open AccessEditor’s ChoiceReview

Achievements and Future Perspectives of the Trivalent Thulium-Ion-Doped Mixed-Sesquioxide Ceramics for Laser Applications

by Angela Pirri, Roman N. Maksimov, Jiang Li, Matteo Vannini and Guido Toci

Materials 2022, 15(6), 2084; https://doi.org/10.3390/ma15062084 - 11 Mar 2022

Cited by 28 | Viewed by 3257

Abstract

This paper is devoted to reviewing the latest results achieved in solid-state lasers based on thulium-doped mixed-sesquioxide ceramics, i.e., (Lu,Sc,Y)₂O₃. The near- and mid-infrared regions are of interest for many applications, from medicine to remote sensing, as they match [...] Read more.

This paper is devoted to reviewing the latest results achieved in solid-state lasers based on thulium-doped mixed-sesquioxide ceramics, i.e., (Lu,Sc,Y)₂O₃. The near- and mid-infrared regions are of interest for many applications, from medicine to remote sensing, as they match molecular fingerprints and cover several atmospheric transparency windows. These matrices are characterized by a strong electron–phonon interaction—which results in a large splitting of the ground state—and by a spectral broadening of the optical transition suitable for developing tunable and short-pulse lasers. In particular, the manuscript reports on the trivalent thulium laser transitions at 1.5, 1.9, and 2.3 µm, along with the thermal and optical characteristics of the (Lu,Sc,Y)₂O₃ ceramics, including the fabrication techniques, spectroscopic and optical properties, and laser performances achieved in different pumping regimes, such as continuous-wave (CW), quasi-CW, and pulsed modes. A comparison of the performance obtained with these mixed-sesquioxide ceramics and with the corresponding crystals is reported. Full article

(This article belongs to the Special Issue Multiple Applications for Ceramic Materials)

► Show Figures

Figure 1

29 pages, 4254 KiB

Open AccessEditor’s ChoiceReview

Current Research and Challenges in Bitumen Emulsion Manufacturing and Its Properties

by Ahmed Al-Mohammedawi and Konrad Mollenhauer

Materials 2022, 15(6), 2026; https://doi.org/10.3390/ma15062026 - 9 Mar 2022

Cited by 19 | Viewed by 8973

Abstract

The global increase of road infrastructure and its impact on the environment requires serious attention to develop sustainable and environmentally friendly road materials. One group of those materials is produced by using bitumen emulsion. However, there are still scientific and technical obstacles standing [...] Read more.

The global increase of road infrastructure and its impact on the environment requires serious attention to develop sustainable and environmentally friendly road materials. One group of those materials is produced by using bitumen emulsion. However, there are still scientific and technical obstacles standing against its regular application. The bitumen emulsion formulation process and compositional optimization are subjected to a high number of degrees of freedom. Consequently, obtaining the desired product is mostly based on a series of random and tedious trials because of the enormous number of tests that are carried out to meet the required properties, such as emulsion stability, viscosity, droplet size (and distribution), and bitumen emulsion chemistry. Several pre-established formulation procedures have been presented in the literature. Some of them have technical limitations to be utilized for practical industrial application, whereas others are still not understood enough to be applied in bitumen emulsion formulation. Therefore, discussing some important issues in this field could be useful to offer a practical guide for bitumen emulsion manufacturers when trying to formulate a well-defined bitumen emulsion to best fit its use in pavement infrastructure rather than to simply to meet standard specifications. This review paper aims to enable the ultimate potential of bitumen emulsion by further reviewing the research progress of bitumen emulsion manufacturing and discussing the literature available up to now on this topic, in the realm of bitumen emulsion manufacturing and emulsion chemistry. Full article

(This article belongs to the Special Issue Feature Papers in Construction and Building Materials)

► Show Figures

Figure 1

19 pages, 4390 KiB

Open AccessEditor’s ChoiceReview

Production and Upgrading of Recovered Carbon Black from the Pyrolysis of End-of-Life Tires

by Sebastião M. R. Costa, David Fowler, Germano A. Carreira, Inês Portugal and Carlos M. Silva

Materials 2022, 15(6), 2030; https://doi.org/10.3390/ma15062030 - 9 Mar 2022

Cited by 38 | Viewed by 9732

Abstract

Increasing awareness regarding fossil fuel dependence, waste valorization, and greenhouse gas emissions have prompted the emergence of new solutions for numerous markets over the last decades. The tire industry is no exception to this, with a global production of more than 1.5 billion [...] Read more.

Increasing awareness regarding fossil fuel dependence, waste valorization, and greenhouse gas emissions have prompted the emergence of new solutions for numerous markets over the last decades. The tire industry is no exception to this, with a global production of more than 1.5 billion tires per year raising environmental concerns about their end-of-life recycling or disposal. Pyrolysis enables the recovery of both energy and material from end-of-life tires, yielding valuable gas, liquid, and solid fractions. The latter, known as recovered carbon black (rCB), has been extensively researched in the last few years to ensure its quality for market applications. These studies have shown that rCB quality depends on the feedstock composition and pyrolysis conditions such as type of reactor, temperature range, heating rate, and residence time. Recent developments of activation and demineralization techniques target the production of rCB with specific chemical, physical, and morphological properties for singular applications. The automotive industry, which is the highest consumer of carbon black, has set specific targets to incorporate recycled materials (such as rCB) following the principles of sustainability and a circular economy. This review summarizes the pyrolysis of end-of-life tires for the production of syngas, oil, and rCB, focusing on the process conditions and product yield and composition. A further analysis of the characteristics of the solid material is performed, including their influence on the rCB application as a substitute of commercial CB in the tire industry. Purification and modification post-treatment processes for rCB upgrading are also inspected. Full article

(This article belongs to the Special Issue Advance in Environmentally Friendly Materials)

► Show Figures

Figure 1

13 pages, 5794 KiB

Open AccessEditor’s ChoiceArticle

Acoustic Characteristics of Microcellular Foamed Ceramic Urethane

by Jin Hong and Sung Woon Cha

Materials 2022, 15(6), 2007; https://doi.org/10.3390/ma15062007 - 8 Mar 2022

Cited by 4 | Viewed by 2713

Abstract

Noise pollution critically degrades the quality of human life, and its effects are becoming more severe due to rapid population growth and the development of industry and transportation. Acoustic wave aggregation in the 30–8000 Hz band can have a negative impact on human [...] Read more.

Noise pollution critically degrades the quality of human life, and its effects are becoming more severe due to rapid population growth and the development of industry and transportation. Acoustic wave aggregation in the 30–8000 Hz band can have a negative impact on human health, especially following continuous exposure to low-frequency noise. This study investigates the acoustic performance of microcellular foams made of a mixture of brittle and soft materials and their potential use as absorption materials. It is common to use porous materials to improve acoustic properties. Specimens prepared by mixing ceramic and urethane were made into microcellular foamed ceramic urethane by a batch process using carbon dioxide. The specimens were expected to exhibit characteristics of porous sound-absorbing materials. After measuring the acoustic characteristics using an impedance tube, a significant sound-absorption coefficient at a specific frequency was noted, a characteristic of a resonance-type sound-absorbing material. However, the sound-absorption properties were generally worse than those before foaming. Differences based on the size, shape, and structure of the pores were also noted. It will be necessary to check the effects of cellular morphological differences on the absorption properties by controlling the variables of the microcellular foaming process in a future study. Full article

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

► Show Figures

Figure 1

14 pages, 3178 KiB

Open AccessEditor’s ChoiceArticle

Antimicrobial TiN-Ag Coatings in Leather Insole for Diabetic Foot

by Sandra M. Marques, Isabel Carvalho, Teófilo R. Leite, Mariana Henriques and Sandra Carvalho

Materials 2022, 15(6), 2009; https://doi.org/10.3390/ma15062009 - 8 Mar 2022

Cited by 7 | Viewed by 3006

Abstract

This work reports on TiN-Ag antimicrobial coatings deposited by d.c. magnetron sputtering on leather used for insoles on the footwear industry, studies involving the antimicrobial properties of Ag-based functionalized leathers by sputtering techniques are shown. The X-ray diffraction (XRD) results suggested the presence [...] Read more.

This work reports on TiN-Ag antimicrobial coatings deposited by d.c. magnetron sputtering on leather used for insoles on the footwear industry, studies involving the antimicrobial properties of Ag-based functionalized leathers by sputtering techniques are shown. The X-ray diffraction (XRD) results suggested the presence of crystalline fcc-TiN phase for the sample without silver, and also a fcc-Ag phase in the samples containing silver. According to the Scanning Electron Microscopy (SEM) analysis, the coatings were homogeneous and dispersed Ag clusters were detected on the surface of samples with silver content above 8 at. %. The Inductively coupled plasma—optical emission spectrometry (ICP-OES) analysis showed that the ionization of silver over time depends on the morphology of the coatings. The samples did not present cytotoxicity and only samples with incorporated silver presented antibacterial and antifungal activity, highlighting the potential of the TiN-Ag insole coatings for diseases such as diabetic foot. Full article

(This article belongs to the Special Issue Fabrication, Characterization, and Application of Coatings and Thin Films)

► Show Figures

Figure 1

16 pages, 5817 KiB

Open AccessEditor’s ChoiceArticle

Biocompatibility of a New Calcium Silicate-Based Root Canal Sealer Mediated via the Modulation of Macrophage Polarization in a Rat Model

by Xiaoqian Yang, Jun Tian, Mengjie Li, Weiyang Chen, He Liu, Zhejun Wang, Markus Haapasalo, Ya Shen and Xi Wei

Materials 2022, 15(5), 1962; https://doi.org/10.3390/ma15051962 - 7 Mar 2022

Cited by 15 | Viewed by 3312

Abstract

(1) Background: The EndoSequence BC Sealer HiFlow (Brasseler, Savannah, GA, USA) has recently been introduced in clinical applications. Thus, the aims of the present study are to determine its biocompatibility in vivo and to examine its ability to drive macrophage polarization in vitro [...] Read more.

(1) Background: The EndoSequence BC Sealer HiFlow (Brasseler, Savannah, GA, USA) has recently been introduced in clinical applications. Thus, the aims of the present study are to determine its biocompatibility in vivo and to examine its ability to drive macrophage polarization in vitro and in vivo. (2) Methods: HiFlow was implanted into rat connective tissue for 7, 30 and 150 days. The microstructures and elemental compositions were determined by scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDX). Hematoxylin–eosin, immunofluorescence, RT–qPCR and flow cytometry were used to elucidate the effects on inflammatory responses and macrophage polarization. (3) Results: SEM-EDX revealed the formation of surface hydroxyapatite crystal layers. Histological evaluation showed that HiFlow exhibited long-term biocompatibility because it decreased inflammatory responses and reduced the number of macrophages over time; however, tissue necrosis was observed in all the groups. RT–qPCR verified that HiFlow regulated the expression of inflammatory factors to inhibit the inflammatory response. Immunofluorescence analysis performed on in vivo samples revealed that HiFlow promoted M2-like macrophage polarization, and these results were confirmed by flow cytometry in vitro. (4) Conclusion: After 150 days of investigation, HiFlow was considered biologically acceptable, and the formation of apatite crystal layers and the promotion of M2-like macrophage polarization may contribute to its favorable biocompatibility. Full article

(This article belongs to the Special Issue Endodontics)

► Show Figures

Figure 1

12 pages, 2780 KiB

Open AccessEditor’s ChoiceCommunication

Carbon Nanotube-Based Thermoelectric Modules Enhanced by ZnO Nanowires

by Patrycja Taborowska, Tomasz Wasiak, Mika Sahlman, Mari Lundström and Dawid Janas

Materials 2022, 15(5), 1924; https://doi.org/10.3390/ma15051924 - 4 Mar 2022

Cited by 8 | Viewed by 2370

Abstract

Carbon nanotubes (CNTs) have a wide range of unique properties, which have kept them at the forefront of research in recent decades. Due to their electrical and thermal characteristics, they are often evaluated as key components of thermogenerators. One can create thermogenerators exclusively [...] Read more.

Carbon nanotubes (CNTs) have a wide range of unique properties, which have kept them at the forefront of research in recent decades. Due to their electrical and thermal characteristics, they are often evaluated as key components of thermogenerators. One can create thermogenerators exclusively from CNTs, without any metal counterpart, by properly selecting dopants to obtain n- and p-doped CNTs. However, the performance of CNT thermogenerators remains insufficient to reach wide commercial implementation. This study shows that molecular doping and the inclusion of ZnO nanowires (NWs) can greatly increase their application potential. Moreover, prototype modules, based on single-walled CNTs (SWCNTs), ZnO NWs, polyethyleneimine, and triazole, reveal notable capabilities for generating electrical energy, while ensuring fully scalable performance. Upon doping and the addition of ZnO nanowires, the electrical conductivity of pure SWCNTs (211 S/cm) was increased by a factor of three. Moreover, the proposed strategy enhanced the Power Factor values from 18.99 (unmodified SWCNTs) to 34.9 and 42.91 µW/m∙K² for CNTs triazole and polyethyleneimine + ZnO NWs inclusion, respectively. Full article

(This article belongs to the Special Issue Synthesis, Characterization and Applications of Thermoelectric Materials)

► Show Figures

Figure 1

20 pages, 4929 KiB

Open AccessEditor’s ChoiceArticle

Decellularized Pig Kidney with a Micro-Nano Secondary Structure Contributes to Tumor Progression in 3D Tumor Model

by Shuangjia Yang, Le Zheng, Zilong Chen, Zeren Jiao, Tianqing Liu, Yi Nie, Yue Kang, Bo Pan and Kedong Song

Materials 2022, 15(5), 1935; https://doi.org/10.3390/ma15051935 - 4 Mar 2022

Cited by 8 | Viewed by 2939

Abstract

In spite of many anti-cancer drugs utilized in clinical treatment, cancer is still one of the diseases with the highest morbidity and mortality worldwide, owing to the complexity and heterogeneity of the tumor microenvironment. Compared with conventional 2D tumor models, 3D scaffolds could [...] Read more.

In spite of many anti-cancer drugs utilized in clinical treatment, cancer is still one of the diseases with the highest morbidity and mortality worldwide, owing to the complexity and heterogeneity of the tumor microenvironment. Compared with conventional 2D tumor models, 3D scaffolds could provide structures and a microenvironment which stimulate native tumor tissues more accurately. The extracellular matrix (ECM) is the main component of the cell in the microenvironment that is mainly composed of three-dimensional nanofibers, which can form nanoscale fiber networks, while the decellularized extracellular matrix (dECM) has been widely applied to engineered scaffolds. In this study, pig kidney was used as the source material to prepare dECM scaffolds. A chemical crosslinking method was used to improve the mechanical properties and other physical characteristics of the decellularized pig kidney-derived scaffold. Furthermore, a human breast cancer cell line (MCF-7) was used to further investigate the biocompatibility of the scaffold to fabricate a tumor model. The results showed that the existence of nanostructures in the scaffold plays an important role in cell adhesion, proliferation, and differentiation. Therefore, the pig kidney-derived matrix scaffold prepared by decellularization could provide more cell attachment sites, which is conducive to cell adhesion and proliferation, physiological activities, and tumor model construction. Full article

(This article belongs to the Special Issue Biofunctionalized Scaffold in Regenerative Medicine-Series II)

► Show Figures

Graphical abstract

9 pages, 4130 KiB

Open AccessEditor’s ChoiceArticle

Band Structure of Organic-Ion-Intercalated (EMIM)_xFeSe Superconductor

by Lyudmila V. Begunovich and Maxim M. Korshunov

Materials 2022, 15(5), 1856; https://doi.org/10.3390/ma15051856 - 2 Mar 2022

Cited by 1 | Viewed by 2213

Abstract

The band structure and the Fermi surface of the recently discovered superconductor (EMIM)

_{x}

FeSe are studied within the density functional theory in the generalized gradient approximation. We show that the bands near the Fermi level are formed primarily by Fe-d orbitals. [...] Read more.

The band structure and the Fermi surface of the recently discovered superconductor (EMIM)

_{x}

FeSe are studied within the density functional theory in the generalized gradient approximation. We show that the bands near the Fermi level are formed primarily by Fe-d orbitals. Although there is no direct contribution of EMIM orbitals to the near-Fermi level states, the presence of organic cations leads to a shift of the chemical potential. It results in the appearance of small electron pockets in the quasi-two-dimensional Fermi surface of (EMIM)

_{x}

FeSe. Full article

(This article belongs to the Special Issue Structure and Electronic Properties of Emerging Superconductor and Related Materials)

► Show Figures

Figure 1

14 pages, 2282 KiB

Open AccessEditor’s ChoiceArticle

Simple Strategies to Modulate the pH-Responsiveness of Lignosulfonate-Based Delivery Systems

by Massimo Sgarzi, Matteo Gigli, Charlotte Giuriato and Claudia Crestini

Materials 2022, 15(5), 1857; https://doi.org/10.3390/ma15051857 - 2 Mar 2022

Cited by 8 | Viewed by 2881

Abstract

The extensive use of non-degradable microplastics in a wide plethora of daily life products is causing serious pollution problems. More ecofriendly solutions are therefore urgently needed. In this context, the use of lignin, a largely available aromatic polymer, may represent a viable option. [...] Read more.

The extensive use of non-degradable microplastics in a wide plethora of daily life products is causing serious pollution problems. More ecofriendly solutions are therefore urgently needed. In this context, the use of lignin, a largely available aromatic polymer, may represent a viable option. Due to the self-assembly ability of its molecules, lignin is in fact an ideal matrix for the fabrication of nanostructures. In this study, lignosulfonate microcapsules containing a limonene core were prepared and characterized in terms of their dimensions and of the physicochemical characteristics of the capsule-forming lignosulfonate molecules. The main purpose is to elucidate the key properties governing the pH-responsive behavior of the capsules to be able to achieve better control over the release kinetics of the entrapped compound(s). The results demonstrate that both the molecular weight and the concentration of sulfonate groups are the most important factors in this respect. Based on these findings, two strategies were followed to further tailor the capsules’ behavior: (i) fractionation of the starting lignosulfonate by solvent extraction and (ii) introduction of a specific additive in the formulation. The first approach permitted to fabricate highly resistant capsules both in acidic, as well as in alkaline conditions, while in the second case the chemical structure of the additive, the diester diveratryl sebacate, allowed for fast kinetics of release, as values above 70% were reached after 24 h of incubation at pH 4 and pH 12. Full article

(This article belongs to the Special Issue Sustainable Polymers: From Synthesis to Functional Properties)

► Show Figures

Figure 1

11 pages, 5081 KiB

Open AccessEditor’s ChoiceReview

Eu³⁺ as a Powerful Structural and Spectroscopic Tool for Glass Photonics

by Thi Ngoc Lam Tran, Alessandro Chiasera, Anna Lukowiak and Maurizio Ferrari

Materials 2022, 15(5), 1847; https://doi.org/10.3390/ma15051847 - 1 Mar 2022

Cited by 13 | Viewed by 2690

Abstract

The unique properties of the Eu³⁺ ion make it a powerful spectroscopic tool to investigate structure or follow processes and mechanisms in several high-tech application areas such as biology and health, structural engineering, environment monitoring systems and quantum technology, mainly concerning photonics. [...] Read more.

The unique properties of the Eu³⁺ ion make it a powerful spectroscopic tool to investigate structure or follow processes and mechanisms in several high-tech application areas such as biology and health, structural engineering, environment monitoring systems and quantum technology, mainly concerning photonics. The traditional method is to exploit the unique photoluminescent properties of Eu³⁺ ions to understand complex dynamical processes and obtain information useful to develop materials with specific characteristics. The objective of this review is to focus on the use of Eu³⁺ optical spectroscopy in some condensed matter issues. After a short presentation of the more significant properties of the Eu³⁺ ion, some examples regarding its use as a probe of the local structure in sol–gel systems are presented. Another section is devoted to dynamical processes such as the important technological role of nanocrystals as rare-earth sensitizers. The appealing effect of the site-selection memory, observed when exciting different sites into the ⁵D₁ state, which the ⁵D₀ → ⁷F₀ emission band reflects following the sites’ distribution, is also mentioned. Finally, a section is devoted to the use of Eu³⁺ in the development of a rare-earth-based platform for quantum technologies. Full article

(This article belongs to the Special Issue Structural and Optical Studies of Eu³⁺ Doped Materials)

► Show Figures

Figure 1

10 pages, 1920 KiB

Open AccessEditor’s ChoiceArticle

Structure and Electrical Properties of Microwave Sintered BTS-BCT-xBF Lead-Free Piezoelectric Ceramics

by Tao Wang, Jian Ma, Bo Wu, Fenghua Wang, Shiyu Wang, Min Chen and Wenjuan Wu

Materials 2022, 15(5), 1789; https://doi.org/10.3390/ma15051789 - 27 Feb 2022

Cited by 3 | Viewed by 2277

Abstract

Barium titanate (BT)-based ceramics are one of the promising piezoelectric materials for environment-friendly electro-mechanical transformation. However, high performance materials are often sintered at high temperatures, resulting in volatile components and increased energy consumption. Here, 0.82Ba(Ti_0.89Sn_0.11)O₃-(0.18-x)(Ba [...] Read more.

Barium titanate (BT)-based ceramics are one of the promising piezoelectric materials for environment-friendly electro-mechanical transformation. However, high performance materials are often sintered at high temperatures, resulting in volatile components and increased energy consumption. Here, 0.82Ba(Ti_0.89Sn_0.11)O₃-(0.18-x)(Ba_0.7Ca_0.3)TiO₃-xBiFeO₃ (BTS-BCT-xBF) piezoelectric ceramics were prepared by microwave sintering (MWS) method, and the structure and properties were emphatically studied, aiming to reveal the regulatory mechanism of MWS on the structure and properties. Compared with conventional solid sintering (CS), the phase structure presents a similar evolution in MWS ceramics as a function of BF, while the more refined grain size and the denser structure are observed in MWS ceramics. The electrical properties (e.g., d₃₃, ε_r, tan δ, etc.) of MWS ceramics are superior to the CS ceramics owing to the refined grain size and denser microstructure. It is worth noting that the energy storage performance (e.g., energy storage density, energy storage efficiency) significantly outperformed expectations due to the slender hysteresis loop resulting from the smaller grain and high cubic phase. Therefore, the MWS sintering mechanism can further drive practical application of BT-based ceramics. Full article

(This article belongs to the Special Issue Electronic Functional Materials: Synthesis, Structure, Property, Mechanism and Application)

► Show Figures

Figure 1

11 pages, 2867 KiB

Open AccessEditor’s ChoiceArticle

Evaluation of Acoustic Waves in Acousto-Optical Devices by Ultrasonic Imaging

by Sergey A. Titov, Alexander S. Machikhin and Vitold Ed. Pozhar

Materials 2022, 15(5), 1792; https://doi.org/10.3390/ma15051792 - 27 Feb 2022

Cited by 6 | Viewed by 2424

Abstract

The structure of the acoustic field defines the key parameters of acousto-optical (AO) devices. To confirm their compliance with the expected values in the presence of multiple real factors, AO crystalline cells require accurate experimental investigation of the acoustic field after being totally [...] Read more.

The structure of the acoustic field defines the key parameters of acousto-optical (AO) devices. To confirm their compliance with the expected values in the presence of multiple real factors, AO crystalline cells require accurate experimental investigation of the acoustic field after being totally assembled. For this purpose, we propose to detect and quantify all the acoustic waves propagating in AO cells using an impulse acoustic microscopy technique. To validate this approach, we have analyzed both theoretically and experimentally the modes, amplitudes, propagation trajectories, and other features of the ultrasonic waves generated inside an AO modulator made of fused quartz. Good correspondence between theoretical and experimental data confirms the effectiveness of the proposed technique. Full article

(This article belongs to the Special Issue Acousto-Optical Spectral Technologies)

► Show Figures

Figure 1

13 pages, 3559 KiB

Open AccessEditor’s ChoiceArticle

Atomic Layer Deposition of Ultrathin La₂O₃/Al₂O₃ Nanolaminates on MoS₂ with Ultraviolet Ozone Treatment

by Jibin Fan, Yimeng Shi, Hongxia Liu, Shulong Wang, Lijun Luan, Li Duan, Yan Zhang and Xing Wei

Materials 2022, 15(5), 1794; https://doi.org/10.3390/ma15051794 - 27 Feb 2022

Cited by 4 | Viewed by 2181

Abstract

Due to the chemically inert surface of MoS₂, uniform deposition of ultrathin high-κ dielectric using atomic layer deposition (ALD) is difficult. However, this is crucial for the fabrication of field-effect transistors (FETs). In this work, the atomic layer deposition growth of [...] Read more.

Due to the chemically inert surface of MoS₂, uniform deposition of ultrathin high-κ dielectric using atomic layer deposition (ALD) is difficult. However, this is crucial for the fabrication of field-effect transistors (FETs). In this work, the atomic layer deposition growth of sub-5 nm La₂O₃/Al₂O₃ nanolaminates on MoS₂ using different oxidants (H₂O and O₃) was investigated. To improve the deposition, the effects of ultraviolet ozone treatment on MoS₂ surface are also evaluated. It is found that the physical properties and electrical characteristics of La₂O₃/Al₂O₃ nanolaminates change greatly for different oxidants and treatment processes. These changes are found to be associated with the residual of metal carbide caused by the insufficient interface reactions. Ultraviolet ozone pretreatment can substantially improve the initial growth of sub-5 nm H₂O-based or O₃-based La₂O₃/Al₂O₃ nanolaminates, resulting in a reduction of residual metal carbide. All results indicate that O₃-based La₂O₃/Al₂O₃ nanolaminates on MoS₂ with ultraviolet ozone treatment yielded good electrical performance with low leakage current and no leakage dot, revealing a straightforward approach for realizing sub-5 nm uniform La₂O₃/Al₂O₃ nanolaminates on MoS₂. Full article

(This article belongs to the Section Thin Films and Interfaces)

► Show Figures

Figure 1

16 pages, 37723 KiB

Open AccessEditor’s ChoiceArticle

Fabrication of Cu₂ZnSnS₄ Light Absorber Using a Cost-Effective Mechanochemical Method for Photovoltaic Applications

by Meenakshi Sahu, Vasudeva Reddy Minnam Reddy, Bomyung Kim, Bharati Patro, Chinho Park, Woo Kyoung Kim and Pratibha Sharma

Materials 2022, 15(5), 1708; https://doi.org/10.3390/ma15051708 - 24 Feb 2022

Cited by 62 | Viewed by 3517

Abstract

In the present study, we adopt an easy and cost-effective route for preparing Cu₂ZnSnS₄ (CZTS)-absorber nanoparticles by a mechanochemical method using non-toxic and environmentally benign solvents (butanol, methyl ethyl ketone, and ethanol). The gram-scale synthesis of absorber nanoparticles was achieved [...] Read more.

In the present study, we adopt an easy and cost-effective route for preparing Cu₂ZnSnS₄ (CZTS)-absorber nanoparticles by a mechanochemical method using non-toxic and environmentally benign solvents (butanol, methyl ethyl ketone, and ethanol). The gram-scale synthesis of absorber nanoparticles was achieved in a non-hazardous, zero-waste process without using high-vacuum equipment. The effects of annealing and Na incorporation on the properties of spin-coated CZTS thin films were scrutinized. The deposited samples showed kesterite crystal structure and single phase. The morphological results revealed an improvement in the surface morphology after annealing. The optical bandgaps of the thin films lied in the range of 1.50–1.57 eV with p-type nature. Finally, photovoltaic devices were fabricated, and their cell performance parameters were studied. An efficiency of 0.16% was observed. The present study provides a potential route for the cost-effective fabrication of CZTS-based photovoltaic devices. Full article

(This article belongs to the Special Issue Thin Films: Growth, Characterization, and Optoelectronic Device Applications)

► Show Figures

Figure 1

13 pages, 2956 KiB

Open AccessEditor’s ChoiceArticle

Thioether-Linked Liquid Crystal Trimers: Odd–Even Effects of Spacers and the Influence of Thioether Bonds on Phase Behavior

by Yuki Arakawa, Kenta Komatsu, Yuko Ishida, Takuma Shiba and Hideto Tsuji

Materials 2022, 15(5), 1709; https://doi.org/10.3390/ma15051709 - 24 Feb 2022

Cited by 13 | Viewed by 2814

Abstract

We report the synthesis, phase-transition behavior, and mesophase structures of the first homologous series of thioether-linked liquid crystal (LC) trimers, 4,4′-bis[ω-(4-cyanobiphenyl-4′-ylthio)alkoxy]biphenyls (CBSnOBOnSCB with a wide range of spacer carbon numbers, n = 3–11). All CBSnOBOnSCB [...] Read more.

We report the synthesis, phase-transition behavior, and mesophase structures of the first homologous series of thioether-linked liquid crystal (LC) trimers, 4,4′-bis[ω-(4-cyanobiphenyl-4′-ylthio)alkoxy]biphenyls (CBSnOBOnSCB with a wide range of spacer carbon numbers, n = 3–11). All CBSnOBOnSCB homologs exhibited LC phases. Interestingly, even-n and odd-n homologs showed monotropic layered smectic A (SmA) and pseudo-layered twist-bend nematic (N_TB) phases, respectively, below a nematic (N) phase. This alternate formation, which depends on spacer chain parity, is attributed to different average molecular shapes, which are associated with the relative orientations of the biphenyl moieties: linear and bent shapes for even-n and odd-n homologs, respectively. In addition, X-ray diffraction analysis indicated a strong cybotactic N phase tendency, with a triply intercalated structure. The phase-transition behavior and LC phase structures of thioether-linked CBSnOBOnSCB were compared with those of the all-ether-linked classic LC trimers CBOnOBOnOCB. Overall, thioether linkages endowed CBSnOBOnSCB with a monotropic LC tendency and lowered phase-transition temperatures, compared to those of CBOnOBOnOCB, for the same n. This is attributed to enhanced flexibility and bending (less molecular anisotropy) of the molecules, caused by the greater bond flexibility and smaller inner bond angles of the C–S–C bonds, compared to those of the C–O–C bonds. Full article

(This article belongs to the Special Issue Advances in Liquid Crystals)

► Show Figures

Graphical abstract

12 pages, 3152 KiB

Open AccessEditor’s ChoiceArticle

Sunlike White Light-Emitting Diodes Based on Rare-Earth-Free Luminescent Materials

by Amador Menéndez-Velázquez, Dolores Morales and Ana Belén García-Delgado

Materials 2022, 15(5), 1680; https://doi.org/10.3390/ma15051680 - 23 Feb 2022

Cited by 19 | Viewed by 2779

Abstract

Solid-state lighting (SSL) sources based on light-emitting diodes represent the new generation of highly efficient illumination systems that significantly impact energy-saving. The development of white light-emitting diodes (WLEDs) with a combination of high color rendering index (CRI) and high deep-red color rendering R [...] Read more.

Solid-state lighting (SSL) sources based on light-emitting diodes represent the new generation of highly efficient illumination systems that significantly impact energy-saving. The development of white light-emitting diodes (WLEDs) with a combination of high color rendering index (CRI) and high deep-red color rendering R₉ is an important challenge in the field of solid-state lighting. On the other hand, most WLEDs use rare-earth inorganic luminescent materials. The annual demand for rare-earth metals has doubled to 125,000 tons in 15 years, and the demand is projected to reach 315,000 tons in 2030. The explosion in demand for these materials, combined with a monopolistic supply source, represents a real risk for the development of WLEDs in the next few years. Luminescent organic materials are a relevant and promising alternative. Here, we report a WLED with a very high CRI of 95.7 and R₉ of 78.7, obtained using a combination of a blue LED chip (excitation source) and two organic luminescent dyes (Coumarin 6 and Lumogen Red) acting as spectral converters in a multilayer remote phosphor configuration. To the best of our knowledge, this is the first rare-earth-free WLED with such high values of CRI and R₉. Full article

(This article belongs to the Special Issue Advanced Materials for Optical Applications and Devices)

► Show Figures

Figure 1

23 pages, 6668 KiB

Open AccessEditor’s ChoiceReview

MXene (Ti₃C₂T_x)-Embedded Nanocomposite Hydrogels for Biomedical Applications: A Review

by Fouad Damiri, Md. Habibur Rahman, Mehrukh Zehravi, Aeshah A. Awaji, Mohammed Z. Nasrullah, Heba A. Gad, Mutasem Z. Bani-Fwaz, Rajender S. Varma, Mousa O. Germoush, Hamdan S. Al-malky, Amany A. Sayed, Satish Rojekar, Mohamed M. Abdel-Daim and Mohammed Berrada

Materials 2022, 15(5), 1666; https://doi.org/10.3390/ma15051666 - 23 Feb 2022

Cited by 57 | Viewed by 7448

Abstract

Polymeric nanocomposites have been outstanding functional materials and have garnered immense attention as sustainable materials to address multi-disciplinary problems. MXenes have emerged as a newer class of 2D materials that produce metallic conductivity upon interaction with hydrophilic species, and their delamination affords monolayer [...] Read more.

Polymeric nanocomposites have been outstanding functional materials and have garnered immense attention as sustainable materials to address multi-disciplinary problems. MXenes have emerged as a newer class of 2D materials that produce metallic conductivity upon interaction with hydrophilic species, and their delamination affords monolayer nanoplatelets of a thickness of about one nm and a side size in the micrometer range. Delaminated MXene has a high aspect ratio, making it an alluring nanofiller for multifunctional polymer nanocomposites. Herein, we have classified and discussed the structure, properties and application of major polysaccharide-based electroactive hydrogels (hyaluronic acid (HA), alginate sodium (SA), chitosan (CS) and cellulose) in biomedical applications, starting with the brief historical account of MXene’s development followed by successive discussions on the synthesis methods, structures and properties of nanocomposites encompassing polysaccharides and MXenes, including their biomedical applications, cytotoxicity and biocompatibility aspects. Finally, the MXenes and their utility in the biomedical arena is deliberated with an eye on potential opportunities and challenges anticipated for them in the future, thus promoting their multifaceted applications. Full article

(This article belongs to the Special Issue MXenes and Their Composites for Emerging Applications)

► Show Figures

Figure 1

17 pages, 10153 KiB

Open AccessEditor’s ChoiceArticle

Comparison of Corrosion Performance of Extruded and Forged WE43 Mg Alloy

by Guonan Liu, Jilei Xu, Baojing Feng, Jinhui Liu, Dongqing Qi, Wenzhan Huang, Peixu Yang and Shaojun Zhang

Materials 2022, 15(5), 1622; https://doi.org/10.3390/ma15051622 - 22 Feb 2022

Cited by 11 | Viewed by 2629

Abstract

Adjusting the microstructure through the deformation process is one of the ways to improve the properties of Mg alloys. Most studies have focused on the influence of the microstructure after deformation treatment on the mechanical properties of Mg alloys. In this paper, extruded [...] Read more.

Adjusting the microstructure through the deformation process is one of the ways to improve the properties of Mg alloys. Most studies have focused on the influence of the microstructure after deformation treatment on the mechanical properties of Mg alloys. In this paper, extruded and forged Mg-Gd-Y-Nd-Zr alloys were selected to investigate the corrosion performance of two deformed magnesium alloys immersed in 0.6 M NaCl solution using a hydrogen evolution test, a weight loss test, an immersion experiment, and an electrochemical test. The results showed that WE43 alloys undergoing different deformation treatments presented different microstructures, which led to different corrosion behaviors and corrosion resistance. The extruded WE43 alloy showed uniform corrosion, while the forged WE43 alloy suffered severe local galvanic corrosion. Meanwhile, the corrosion rate of the forged WE43 alloy was about four times faster than that of the extruded WE43 alloy. Full article

(This article belongs to the Special Issue Corrosion and Corrosion Inhibition of Metals and Their Alloys)

► Show Figures

Figure 1

15 pages, 4882 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Progress and Challenges of InGaN/GaN-Based Core–Shell Microrod LEDs

by Johanna Meier and Gerd Bacher

Materials 2022, 15(5), 1626; https://doi.org/10.3390/ma15051626 - 22 Feb 2022

Cited by 15 | Viewed by 3696

Abstract

LEDs based on planar InGaN/GaN heterostructures define an important standard for solid-state lighting. However, one drawback is the polarization field of the wurtzite heterostructure impacting both electron–hole overlap and emission energy. Three-dimensional core–shell microrods offer field-free sidewalls, thus improving radiative recombination rates while [...] Read more.

LEDs based on planar InGaN/GaN heterostructures define an important standard for solid-state lighting. However, one drawback is the polarization field of the wurtzite heterostructure impacting both electron–hole overlap and emission energy. Three-dimensional core–shell microrods offer field-free sidewalls, thus improving radiative recombination rates while simultaneously increasing the light-emitting area per substrate size. Despite those promises, microrods have still not replaced planar devices. In this review, we discuss the progress in device processing and analysis of microrod LEDs and emphasize the perspectives related to the 3D device architecture from an applications point of view. Full article

(This article belongs to the Special Issue Optoelectronic Devices: 2021)

► Show Figures

Figure 1

20 pages, 7142 KiB

Open AccessEditor’s ChoiceArticle

The Influence of Microstructure on the Flexural Properties of 3D Printed Zirconia Part via Digital Light Processing Technology

by Boran Wang, Ali Arab, Jing Xie and Pengwan Chen

Materials 2022, 15(4), 1602; https://doi.org/10.3390/ma15041602 - 21 Feb 2022

Cited by 18 | Viewed by 3504

Abstract

In recent years, additive manufacturing of ceramics is becoming of increasing interest due to the possibility of the fabrication of complex shaped parts. However, the fabrication of a fully dense bulk ceramic part without cracks and defects is still challenging. In the presented [...] Read more.

In recent years, additive manufacturing of ceramics is becoming of increasing interest due to the possibility of the fabrication of complex shaped parts. However, the fabrication of a fully dense bulk ceramic part without cracks and defects is still challenging. In the presented work, the digital light processing method was introduced for fabricating zirconia parts. The flexural properties of the printed zirconia were systematically investigated via a three-point bending test with the digital image correlation method, scanning electron microscopy observation and fractography analysis. Due to the anisotropy of the sample, the bending deformation behaviors of the zirconia samples in the parallel and vertical printing directions were significantly different. The flexural strength and the related elastic modulus of the samples under vertical loading were higher than that of the parallel loading, as the in-plane strength is higher than that of the interlayer strength. The maximum horizontal strain always appeared at the bottom center before the failure for the parallel loading case; while the maximum horizontal strain for the vertical loading moved upward from the bottom center to the top center. There was a clear dividing line between the minimum perpendicular strain and the maximum perpendicular strain of the samples under parallel loading; however, under vertical loading, the perpendicular strain declined from the bottom to the top along the crack path. The surrounding dense part of the sintered sample (a few hundred microns) was mainly composed of large and straight cracks between printing layers, whereas the interior contained numerous small winding cracks. The intense cracks inside the sample led to a low flexural property compared to other well-prepared zirconia samples, which the inadequate additive formulations would be the main reason for the generation of cracks. A better understanding of the additive formulation (particularly the dispersant) and the debinding-sintering process are necessary for future improvement. Full article

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

► Show Figures

Figure 1

39 pages, 72409 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Photothermal and Photodynamic Therapy of Tumors with Plasmonic Nanoparticles: Challenges and Prospects

by Alla B. Bucharskaya, Nikolai G. Khlebtsov, Boris N. Khlebtsov, Galina N. Maslyakova, Nikita A. Navolokin, Vadim D. Genin, Elina A. Genina and Valery V. Tuchin

Materials 2022, 15(4), 1606; https://doi.org/10.3390/ma15041606 - 21 Feb 2022

Cited by 48 | Viewed by 6597

Abstract

Cancer remains one of the leading causes of death in the world. For a number of neoplasms, the efficiency of conventional chemo- and radiation therapies is insufficient because of drug resistance and marked toxicity. Plasmonic photothermal therapy (PPT) using local hyperthermia induced by [...] Read more.

Cancer remains one of the leading causes of death in the world. For a number of neoplasms, the efficiency of conventional chemo- and radiation therapies is insufficient because of drug resistance and marked toxicity. Plasmonic photothermal therapy (PPT) using local hyperthermia induced by gold nanoparticles (AuNPs) has recently been extensively explored in tumor treatment. However, despite attractive promises, the current PPT status is limited by laboratory experiments, academic papers, and only a few preclinical studies. Unfortunately, most nanoformulations still share a similar fate: great laboratory promises and fair preclinical trials. This review discusses the current challenges and prospects of plasmonic nanomedicine based on PPT and photodynamic therapy (PDT). We start with consideration of the fundamental principles underlying plasmonic properties of AuNPs to tune their plasmon resonance for the desired NIR-I, NIR-2, and SWIR optical windows. The basic principles for simulation of optical cross-sections and plasmonic heating under CW and pulsed irradiation are discussed. Then, we consider the state-of-the-art methods for wet chemical synthesis of the most popular PPPT AuNPs such as silica/gold nanoshells, Au nanostars, nanorods, and nanocages. The photothermal efficiencies of these nanoparticles are compared, and their applications to current nanomedicine are shortly discussed. In a separate section, we discuss the fabrication of gold and other nanoparticles by the pulsed laser ablation in liquid method. The second part of the review is devoted to our recent experimental results on laser-activated interaction of AuNPs with tumor and healthy tissues and current achievements of other research groups in this application area. The unresolved issues of PPT are the significant accumulation of AuNPs in the organs of the mononuclear phagocyte system, causing potential toxic effects of nanoparticles, and the possibility of tumor recurrence due to the presence of survived tumor cells. The prospective ways of solving these problems are discussed, including developing combined antitumor therapy based on combined PPT and PDT. In the conclusion section, we summarize the most urgent needs of current PPT-based nanomedicine. Full article

(This article belongs to the Special Issue Feature Paper in Optical and Photonic Materials)

► Show Figures

Figure 1

19 pages, 6261 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Advanced Carbon Reinforced Concrete Technologies for Façade Elements of Nearly Zero-Energy Buildings

by Robert Kraft, Alexander Kahnt, Otto Grauer, Mike Thieme, Daniel Sebastian Wolz, Dominik Schlüter, Matthias Tietze, Manfred Curbach, Klaus Holschemacher, Hubert Jäger and Robert Böhm

Materials 2022, 15(4), 1619; https://doi.org/10.3390/ma15041619 - 21 Feb 2022

Cited by 12 | Viewed by 4492

Abstract

The building sector accounts for approx. 40% of total energy consumption and approx. 36% of all greenhouse gas emissions in Europe. As the EU climate targets for 2030 call for a reduction of greenhouse gas emissions by more than half compared to the [...] Read more.

The building sector accounts for approx. 40% of total energy consumption and approx. 36% of all greenhouse gas emissions in Europe. As the EU climate targets for 2030 call for a reduction of greenhouse gas emissions by more than half compared to the emissions of 1990 and also aim for climate neutrality by 2050, there is an urgent need to achieve a significant decrease in the energy use in buildings towards Nearly Zero-Energy Buildings (nZEBs). As the energy footprint of buildings includes the energy and greenhouse gas consumption both in the construction phase and during service life, nZEB solutions have to provide energy-efficient and less carbon-intensive building materials, specific thermal insulation solutions, and a corresponding design of the nZEB. Carbon reinforced concrete (CRC) materials have proven to be excellent candidate materials for concrete-based nZEBs since they are characterized by a significantly lower CO₂ consumption during component production and much a longer lifecycle. The corresponding CRC technology has been successively implemented in the last two decades and first pure CRC-based buildings are currently being built. This article presents a novel material system that combines CRC technology and suitable multifunctional insulation materials as a sandwich system in order to meet future nZEB requirements. Because of its importance for the life cycle stage of production, cost-efficient carbon fibers (CF) from renewable resources like lignin are used as reinforcing material, and reinforcement systems based on such CF are developed. Cutting edge approaches to produce ultra-thin lightweight CF reinforced concrete panels are discussed with regard to their nZEB relevance. For the life cycle stage of the utilization phase, the thermal insulation properties of core materials are optimized. In this context, novel sandwich composites with thin CRC layers and a cellular lightweight concrete core are proposed as a promising solution for façade elements as the sandwich core can additionally be combined with an aerogel-based insulation. The concepts to realize such sandwich façade elements will be described here along with a fully automated manufacturing process to produce such structures. The findings of this study provide clear evidence on the promising capabilities of the CRC technology for nZEBs on the one hand and on the necessity for further research on optimizing the energy footprint of CRC-based structural elements on the other hand. Full article

(This article belongs to the Special Issue Composite Materials for Nearly Zero Emission Applications)

► Show Figures

Figure 1

16 pages, 3357 KiB

Open AccessEditor’s ChoiceArticle

Synthesis and Structural Characterization of CaO-P₂O₅-CaF:CuO Glasses with Antitumoral Effect on Skin Cancer Cells

by Nicoleta Simona Vedeanu, Cristian Lujerdean, Marius Zăhan, Daniel Severus Dezmirean, Lucian Barbu-Tudoran, Grigore Damian and Răzvan Ștefan

Materials 2022, 15(4), 1526; https://doi.org/10.3390/ma15041526 - 18 Feb 2022

Cited by 2 | Viewed by 2087

Abstract

Copper is one of the most used therapeutic metallic elements in biomedicine, ranging from antibacterial approaches to developing new complexes in cancer therapy. In the present investigation, we developed a novel xCuO∙(100 − x) [CaF₂∙3P₂O₅∙CaO] glass system [...] Read more.

Copper is one of the most used therapeutic metallic elements in biomedicine, ranging from antibacterial approaches to developing new complexes in cancer therapy. In the present investigation, we developed a novel xCuO∙(100 − x) [CaF₂∙3P₂O₅∙CaO] glass system with 0 ≤ x ≤ 16 mol% in order to determine the influence of doping on the composition structure of glasses. The samples were characterized by dissolution tests, pH measurements, Fourier-transform infrared spectroscopy (FT-IR), electron paramagnetic resonance (EPR), Scanning Electron Microscopy with energy dispersive spectroscopy (SEM-EDX) and afterward, their antitumor character was assessed. The glasses were mostly soluble in the aqueous medium, their dissolution rate being directly proportional to the increase in pH and the level of doping up to x = 8 mol%. FT-IR spectra of glass samples show the presence of all structural units characteristic to P₂O₅ in different rates and directly depending on the depolymerization process. SEM-EDX results revealed the presence of an amorphous glass structure composed of P, O, Ca, and Cu elements. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) reduction assay showed strong cytotoxicity for tumoral cells A375 even in low concentrations for Cu-treatment. In contrast, the copper-free matrix (without Cu) determined a proliferative effect of over 70% viability for all concentrations used. Full article

(This article belongs to the Special Issue Optical and Magnetic Properties of Glass and Glass Ceramics)

► Show Figures

Figure 1

37 pages, 548 KiB

Open AccessEditor’s ChoiceArticle

Analytical Methods for Causality Evaluation of Photonic Materials

by Tomasz P. Stefański, Jacek Gulgowski and Kosmas L. Tsakmakidis

Materials 2022, 15(4), 1536; https://doi.org/10.3390/ma15041536 - 18 Feb 2022

Cited by 3 | Viewed by 1642

Abstract

We comprehensively review several general methods and analytical tools used for causality evaluation of photonic materials. Our objective is to call to mind and then formulate, on a mathematically rigorous basis, a set of theorems which can answer the question whether a considered [...] Read more.

We comprehensively review several general methods and analytical tools used for causality evaluation of photonic materials. Our objective is to call to mind and then formulate, on a mathematically rigorous basis, a set of theorems which can answer the question whether a considered material model is causal or not. For this purpose, a set of various distributional theorems presented in literature is collected as the distributional version of the Titchmarsh theorem, allowing for evaluation of causality in complicated electromagnetic systems. Furthermore, we correct the existing material models with the use of distribution theory in order to obtain their causal formulations. In addition to the well-known Kramers–Krönig (K–K) relations, we overview four further methods which can be used to assess causality of given dispersion relations, when calculations of integrals involved in the K–K relations are challenging or even impossible. Depending on the given problem, optimal approaches allowing us to prove either the causality or lack thereof are pointed out. These methodologies should be useful for scientists and engineers analyzing causality problems in electrodynamics and optics, particularly with regard to photonic materials, when the involved mathematical distributions have to be invoked. Full article

(This article belongs to the Special Issue Photonic Materials for Optical Waveguide Application)

► Show Figures

Figure 1

26 pages, 14735 KiB

Open AccessEditor’s ChoiceReview

Carbon Nanotube Devices for Quantum Technology

by Andrey Baydin, Fuyang Tay, Jichao Fan, Manukumara Manjappa, Weilu Gao and Junichiro Kono

Materials 2022, 15(4), 1535; https://doi.org/10.3390/ma15041535 - 18 Feb 2022

Cited by 44 | Viewed by 9389

Abstract

Carbon nanotubes, quintessentially one-dimensional quantum objects, possess a variety of electrical, optical, and mechanical properties that are suited for developing devices that operate on quantum mechanical principles. The states of one-dimensional electrons, excitons, and phonons in carbon nanotubes with exceptionally large quantization energies [...] Read more.

Carbon nanotubes, quintessentially one-dimensional quantum objects, possess a variety of electrical, optical, and mechanical properties that are suited for developing devices that operate on quantum mechanical principles. The states of one-dimensional electrons, excitons, and phonons in carbon nanotubes with exceptionally large quantization energies are promising for high-operating-temperature quantum devices. Here, we discuss recent progress in the development of carbon-nanotube-based devices for quantum technology, i.e., quantum mechanical strategies for revolutionizing computation, sensing, and communication. We cover fundamental properties of carbon nanotubes, their growth and purification methods, and methodologies for assembling them into architectures of ordered nanotubes that manifest macroscopic quantum properties. Most importantly, recent developments and proposals for quantum information processing devices based on individual and assembled nanotubes are reviewed. Full article

(This article belongs to the Special Issue Materials Opportunities and Challenges for Quantum Information Processors)

► Show Figures

Figure 1

17 pages, 5003 KiB

Open AccessEditor’s ChoiceArticle

Dissolution of Portlandite in Pure Water: Part 2 Atomistic Kinetic Monte Carlo (KMC) Approach

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

Materials 2022, 15(4), 1442; https://doi.org/10.3390/ma15041442 - 15 Feb 2022

Cited by 26 | Viewed by 3452

Abstract

Portlandite, as a most soluble cement hydration reaction product, affects mechanical and durability properties of cementitious materials. In the present work, an atomistic kinetic Monte Carlo (KMC) upscaling approach is implemented in MATLAB code in order to investigate the dissolution time and morphology [...] Read more.

Portlandite, as a most soluble cement hydration reaction product, affects mechanical and durability properties of cementitious materials. In the present work, an atomistic kinetic Monte Carlo (KMC) upscaling approach is implemented in MATLAB code in order to investigate the dissolution time and morphology changes of a hexagonal platelet portlandite crystal. First, the atomistic rate constants of individual Ca dissolution events are computed by a transition state theory equation based on inputs of the computed activation energies (ΔG*) obtained through the metadynamics computational method (Part 1 of paper). Four different facets (100 or

\bar{1} 00

, 010 or 0

\bar{1}

0,

\bar{1} 10

or

1 \bar{1} 0

, and 001 or 00

\bar{1}

) are considered, resulting in a total of 16 different atomistic event scenarios. Results of the upscaled KMC simulations demonstrate that dissolution process initially takes place from edges, sides, and facets of 010 or 0

\bar{1}

0 of the crystal morphology. The steady-state dissolution rate for the most reactive facets (010 or 0

\bar{1} 0

) was computed to be 1.0443 mol/(s cm²); however, 0.0032 mol/(s cm²) for

\bar{1} 10

or

1 \bar{1} 0

, 2.672 × 10⁻⁷ mol/(s cm²) for 001 or 00

\bar{1}

, and 0.31 × 10⁻¹⁶ mol/(s cm²) for 100 or

\bar{1} 00

were represented in a decreasing order for less reactive facets. Obtained upscaled dissolution rates between each facet resulted in a huge (16 orders of magnitude) difference, reflecting the importance of crystallographic orientation of the exposed facets. Full article

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

► Show Figures

Figure 1

11 pages, 6224 KiB

Open AccessEditor’s ChoiceArticle

Evaluating the X-ray-Shielding Performance of Graphene-Oxide-Coated Nanocomposite Fabric

by Serhat Süha Türkaslan, Şule Sultan Ugur, Banu Esencan Türkaslan and Nicholas Fantuzzi

Materials 2022, 15(4), 1441; https://doi.org/10.3390/ma15041441 - 15 Feb 2022

Cited by 23 | Viewed by 3955

Abstract

Exposure to ionizing radiation (IR) during diagnostic medical procedures brings certain risks, especially when experiencing recurrent exposures. The fabrication of nano-based composites, doped with different nanoparticles, have been suggested as effective shielding materials to replace conventional lead-based ones in material sciences and nanotechnology. [...] Read more.

Exposure to ionizing radiation (IR) during diagnostic medical procedures brings certain risks, especially when experiencing recurrent exposures. The fabrication of nano-based composites, doped with different nanoparticles, have been suggested as effective shielding materials to replace conventional lead-based ones in material sciences and nanotechnology. In this study, commercially available fabrics, used to produce scrubs and gowns for clinical staff, are modified utilizing graphene oxide (GO) nanoparticles using a layer-by-layer (LBL) technique. GO was obtained from graphite through environmentally friendly technology by using a modified–improved Hummers’ method without NaNO₃. Lightweight, flexible, air- and water-permeable shielding materials are produced that are wearable in all-day clinical practice. The nanoparticles are kept to a minimum at 1 wt%; however, utilizing the LBL technique they are distributed evenly along the fibers of the fabrics to achieve as much shielding effect as possible. The evaluation of samples is accomplished by simulating real-time routine clinical procedures and the radiographic programs and devices used daily. The GO-coated nanocomposite fabrics demonstrated promising results for X-ray shielding. Full article

(This article belongs to the Special Issue Radiation Shielding Materials)

► Show Figures

Figure 1

8 pages, 9530 KiB

Open AccessEditor’s ChoiceArticle

Microstructure and Mechanical Properties of Co₃₂Cr₂₈Ni₃₂.₉₄Al₄.₀₆Ti₃ High-Entropy Alloy

by Jinquan Guo, Chaozhongzheng Tang and Huan Sheng Lai

Materials 2022, 15(4), 1444; https://doi.org/10.3390/ma15041444 - 15 Feb 2022

Cited by 9 | Viewed by 2346

Abstract

High-entropy alloys have good application prospects in nuclear power plants due to their excellent mechanical properties and radiation resistance. In this paper, the microstructure of the Co₃₂Cr₂₈Ni₃₂.₉₄Al₄.₀₆Ti₃ high-entropy alloy was [...] Read more.

High-entropy alloys have good application prospects in nuclear power plants due to their excellent mechanical properties and radiation resistance. In this paper, the microstructure of the Co₃₂Cr₂₈Ni₃₂.₉₄Al₄.₀₆Ti₃ high-entropy alloy was researched using metallurgical microscopy, X-ray diffraction, and scanning electron microscopy. The mechanical properties were tested using a Vickers microhardness tester and a tensile testing machine, respectively. The results showed that Co₃₂Cr₂₈Ni₃₂.₉₄Al₄.₀₆Ti₃ had a single-phase, disordered, face-centered, cubic solid-solution structure and was strengthened by solid solution. The alloy lattice parameter and density were estimated as 0.304 nm and 7.89 g/cm³, respectively. The test results indicated that the alloy had satisfactory mechanical properties with yield stress and tensile strength of about 530 MPa and 985 MPa, respectively. Full article

(This article belongs to the Special Issue Advances in Smart Materials and Structures)

► Show Figures

Figure 1

10 pages, 1777 KiB

Open AccessEditor’s ChoiceArticle

Superplastic Deformation of Alumina Composites Reinforced with Carbon Nanofibers and with Graphene Oxide Sintered by SPS—Experimental Testing and Theoretical Interpretation

by Rafael Cano-Crespo, César Retamal, Miguel Lagos and Francisco Luis Cumbrera

Materials 2022, 15(4), 1396; https://doi.org/10.3390/ma15041396 - 14 Feb 2022

Viewed by 1631

Abstract

The superplastic behavior of alumina-based nanostructured ceramics (Al₂O₃) is an important issue in the world of materials. The main body of this paper is an analysis of the creep behavior of polycrystals, with grain boundary sliding as the main [...] Read more.

The superplastic behavior of alumina-based nanostructured ceramics (Al₂O₃) is an important issue in the world of materials. The main body of this paper is an analysis of the creep behavior of polycrystals, with grain boundary sliding as the main deformation mechanism at high temperatures. Concomitant accommodation of grain shapes to preserve spatial continuity has a comparatively small effect on the strain rate. The constitutive equations for small deformations, relating strain and strain rate, derived from two models for grain sliding, are compared with the experimental data with their respective uncertainties. The data follow from experiments on the plastic deformation of alumina composites reinforced, on the one hand by graphene oxide, and on the other hand by carbon nanofibers sintered by SPS. The results show good agreement between experiment and theory for these advanced ceramics, particularly for one of the assumed models. The values obtained of ξ² for model A were in the interval 0.0002–0.1189, and for model B were in the interval 0.000001–0.0561. The values obtained of R² for model A were in the interval 0.9122–0.9994, and for model B were in the interval 0.9586–0.9999. The threshold stress was between (3.05 · 10⁻¹⁵–25.68) MPa. Full article

(This article belongs to the Special Issue Mechanical Properties and Electrical Conductivity of Ceramics)

► Show Figures

Figure 1

23 pages, 185666 KiB

Open AccessEditor’s ChoiceArticle

Passive Photonic Integrated Circuits Elements Fabricated on a Silicon Nitride Platform

by Marcin Lelit, Mateusz Słowikowski, Maciej Filipiak, Marcin Juchniewicz, Bartłomiej Stonio, Bartosz Michalak, Krystian Pavłov, Marcin Myśliwiec, Piotr Wiśniewski, Andrzej Kaźmierczak, Krzysztof Anders, Stanisław Stopiński, Romuald B. Beck and Ryszard Piramidowicz

Materials 2022, 15(4), 1398; https://doi.org/10.3390/ma15041398 - 14 Feb 2022

Cited by 17 | Viewed by 5954

Abstract

The fabrication processes for silicon nitride photonic integrated circuits evolved from microelectronics components technology—basic processes have common roots and can be executed using the same type of equipment. In comparison to that of electronics components, passive photonic structures require fewer manufacturing steps and [...] Read more.

The fabrication processes for silicon nitride photonic integrated circuits evolved from microelectronics components technology—basic processes have common roots and can be executed using the same type of equipment. In comparison to that of electronics components, passive photonic structures require fewer manufacturing steps and fabricated elements have larger critical dimensions. In this work, we present and discuss our first results on design and development of fundamental building blocks for silicon nitride integrated photonic platform. The scope of the work covers the full design and manufacturing chain, from numerical simulations of optical elements, design, and fabrication of the test structures to optical characterization and analysis the results. In particular, technological processes were developed and evaluated for fabrication of the waveguides (WGs), multimode interferometers (MMIs), and arrayed waveguide gratings (AWGs), which confirmed the potential of the technology and correctness of the proposed approach. Full article

(This article belongs to the Special Issue Trends in Electronic and Optoelectronic Materials)

► Show Figures

Figure 1

13 pages, 4334 KiB

Open AccessEditor’s ChoiceArticle

Pressure-Induced Superconductivity in Iron-Based Spin-Ladder Compound BaFe_2+δ(S_1−xSe_x)₃

by Hiroki Takahashi, Ryosuke Kikuchi, Chizuru Kawashima, Satoshi Imaizumi, Takuya Aoyama and Kenya Ohgushi

Materials 2022, 15(4), 1401; https://doi.org/10.3390/ma15041401 - 14 Feb 2022

Cited by 2 | Viewed by 3054

Abstract

The iron-based superconductors had a significant impact on condensed matter physics. They have a common structural motif of a two-dimensional square iron lattice and exhibit fruitful physical properties as a strongly correlated electron system. During the extensive investigations, quasi-one-dimensional iron-based spin-ladder compounds attracted [...] Read more.

The iron-based superconductors had a significant impact on condensed matter physics. They have a common structural motif of a two-dimensional square iron lattice and exhibit fruitful physical properties as a strongly correlated electron system. During the extensive investigations, quasi-one-dimensional iron-based spin-ladder compounds attracted much attention as a platform for studying the interplay between magnetic and orbital ordering. In these compounds, BaFe₂S₃ and BaFe₂Se₃ were found to exhibit superconductivity under high pressure, having a different crystal and magnetic structure at low temperature. We report a brief review of the iron-based spin-ladder compound and recent studies for BaFe_2+δ(S_1−xSe_x)₃. BaFe₂(S_0.75 Se_0.25)₃ is in the vicinity of the boundary of two different magnetic phases and it is intriguing to perform high pressure experiments for studying superconductivity, since effects of large magnetic fluctuations on superconductivity are expected. The effect of iron stoichiometry on the interplay between magnetism and superconductivity is also studied by changing the iron concentration in BaFe_2+δSe₃. Full article

(This article belongs to the Special Issue Quantum Materials and Emergent Phenomena under Extreme Conditions)

► Show Figures

Figure 1

13 pages, 6985 KiB

Open AccessEditor’s ChoiceArticle

Dissolution of Portlandite in Pure Water: Part 1 Molecular Dynamics (MD) Approach

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

Materials 2022, 15(4), 1404; https://doi.org/10.3390/ma15041404 - 14 Feb 2022

Cited by 16 | Viewed by 3671

Abstract

The current contribution proposes a multi-scale bridging modeling approach for the dissolution of crystals to connect the atomistic scale to the (sub-) micro-scale. This is demonstrated in the example of dissolution of portlandite, as a relatively simple benchmarking example for cementitious materials. Moreover, [...] Read more.

The current contribution proposes a multi-scale bridging modeling approach for the dissolution of crystals to connect the atomistic scale to the (sub-) micro-scale. This is demonstrated in the example of dissolution of portlandite, as a relatively simple benchmarking example for cementitious materials. Moreover, dissolution kinetics is also important for other industrial processes, e.g., acid gas absorption and pH control. In this work, the biased molecular dynamics (metadynamics) coupled with reactive force field is employed to calculate the reaction path as a free energy surface of calcium dissolution at 298 K in water from the different crystal facets of portlandite. It is also explained why the reactivity of the (010), (100), and (1

\bar{1}

0) crystal facet is higher compared to the (001) facet. In addition, the influence of neighboring Ca crystal sites arrangements on the atomistic dissolution rates is explained as necessary scenarios for the upscaling. The calculated rate constants of all atomistic reaction scenarios provided an input catalog ready to be used in an upscaling kinetic Monte Carlo (KMC) approach. Full article

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

► Show Figures

Figure 1

13 pages, 9087 KiB

Open AccessEditor’s ChoiceArticle

A CuNi-Loaded Porous Magnetic Soft Material: Preparation, Characterization and Magnetic Field-Controlled Modulus

by Jingyuan Bai, Xuejiao Wang, Meilin Zhang, Jin Zhang, Xiaolin Chen, Yanan An and Renguo Guan

Materials 2022, 15(4), 1412; https://doi.org/10.3390/ma15041412 - 14 Feb 2022

Cited by 1 | Viewed by 2120

Abstract

Novel porous magnetic soft materials (pMSMs) based on a poly (vinyl alcohol) (PVA) porous matrix filled with CuNi nanoparticles (NPs) of around 70 nm were synthesized. Initially, magnetic CuNi NPs were fabricated by the reduction of Ni and Cu ions with hydrazine hydrate [...] Read more.

Novel porous magnetic soft materials (pMSMs) based on a poly (vinyl alcohol) (PVA) porous matrix filled with CuNi nanoparticles (NPs) of around 70 nm were synthesized. Initially, magnetic CuNi NPs were fabricated by the reduction of Ni and Cu ions with hydrazine hydrate in ethylene glycol medium in the absence of other capping agents. The pMSMs are subsequently fabricated by mixing CuNi NPs and PVA through freezing-drying process. The as-obtained pMSMs can respond to a magnetic field, i.e., the compressive modulus increase under a magnetic field of 0.23 T. The experimental results indicate that CuNi NPs can easily move to form chain-like structures under the application of a magnetic field. A combination of direct observation and finite element modeling has shown that under the influence of a magnetic field, chain-like aggregates of CuNi NPs lead to self-reinforcement of the pMSMs and, thus, to the increased compressive modulus. From a technological point of view, these materials with good magnetic responsiveness and moderate mechanical strength have potential applications in artificial muscle, soft actuators and drug release, to name a few. Full article

(This article belongs to the Section Materials Physics)

► Show Figures

Graphical abstract

19 pages, 3402 KiB

Open AccessEditor’s ChoicePerspective

LIPSS Applied to Wide Bandgap Semiconductors and Dielectrics: Assessment and Future Perspectives

by Matteo Mastellone, Maria Lucia Pace, Mariangela Curcio, Nicola Caggiano, Angela De Bonis, Roberto Teghil, Patrizia Dolce, Donato Mollica, Stefano Orlando, Antonio Santagata, Valerio Serpente, Alessandro Bellucci, Marco Girolami, Riccardo Polini and Daniele Maria Trucchi

Materials 2022, 15(4), 1378; https://doi.org/10.3390/ma15041378 - 13 Feb 2022

Cited by 27 | Viewed by 4456

Abstract

With the aim of presenting the processes governing the Laser-Induced Periodic Surface Structures (LIPSS), its main theoretical models have been reported. More emphasis is given to those suitable for clarifying the experimental structures observed on the surface of wide bandgap semiconductors (WBS) and [...] Read more.

With the aim of presenting the processes governing the Laser-Induced Periodic Surface Structures (LIPSS), its main theoretical models have been reported. More emphasis is given to those suitable for clarifying the experimental structures observed on the surface of wide bandgap semiconductors (WBS) and dielectric materials. The role played by radiation surface electromagnetic waves as well as Surface Plasmon Polaritons in determining both Low and High Spatial Frequency LIPSS is briefly discussed, together with some experimental evidence. Non-conventional techniques for LIPSS formation are concisely introduced to point out the high technical possibility of enhancing the homogeneity of surface structures as well as tuning the electronic properties driven by point defects induced in WBS. Among these, double- or multiple-fs-pulse irradiations are shown to be suitable for providing further insight into the LIPSS process together with fine control on the formed surface structures. Modifications occurring by LIPSS on surfaces of WBS and dielectrics display high potentialities for their cross-cutting technological features and wide applications in which the main surface and electronic properties can be engineered. By these assessments, the employment of such nanostructured materials in innovative devices could be envisaged. Full article

(This article belongs to the Special Issue New Advances in Low-Dimensional Materials and Nanostructures)

► Show Figures

Figure 1

10 pages, 4102 KiB

Open AccessEditor’s ChoiceArticle

Face Mask Wastes as Cementitious Materials: A Possible Solution to a Big Concern

by Marta Castellote, Eva Jiménez-Relinque, María Grande, Francisco J. Rubiano and Ángel Castillo

Materials 2022, 15(4), 1371; https://doi.org/10.3390/ma15041371 - 12 Feb 2022

Cited by 22 | Viewed by 8486

Abstract

After more than two years wearing surgical masks due to the COVID-19 pandemic, used masks have become a significant risk for ecosystems, as they are producing wastes in huge amounts. They are a potential source of disturbance by themselves and as microplastic contamination [...] Read more.

After more than two years wearing surgical masks due to the COVID-19 pandemic, used masks have become a significant risk for ecosystems, as they are producing wastes in huge amounts. They are a potential source of disturbance by themselves and as microplastic contamination in the water system. As 5500 tons of face masks are estimated to be used each year, there is an urgent need to manage them according to the circular economy principles and avoid their inadequate disposal. In this paper, surgical wear masks (WM), without any further pretreatment, have been introduced as addition to mortars up to 5% in the weight of cement. Mechanical and microstructural characterization have been carried out. The results indicate that adding MW to the cement supposes a decrease in the properties of the material, concerning both strength and durability behavior. However, even adding a 5% of WM in weight of cement, the aspect of the mortars is quite good, the flexural strength is not significantly affected, and the strength and durability parameters are maintained at levels that—even lower than the reference—are quite reasonable for use. Provided that the worldwide production of cement is around 4.1 Bt/year, the introduction of a 5% of WM in less than 1% of the cement produced, would make it possible to get rid of the mask waste being produced. Full article

(This article belongs to the Special Issue Sustainability in Construction and Building Materials)

► Show Figures

Graphical abstract

26 pages, 7881 KiB

Open AccessEditor’s ChoiceArticle

Cathodic Protection of Mild Steel Using Aluminium-Based Alloys

by Maria del Rosario Silva Campos, Carsten Blawert, Nico Scharnagl, Michael Störmer and Mikhail L. Zheludkevich

Materials 2022, 15(4), 1301; https://doi.org/10.3390/ma15041301 - 10 Feb 2022

Cited by 29 | Viewed by 5084

Abstract

Typically, steel is protected from corrosion by employing sacrificial anodes or coatings based on Zn, Mg, Al or Cd. However, stricter environmental regulations require new environmentally friendly alternatives to replace Cd. Traditionally, Al-based anodes have been employed to cathodically protect steel in marine [...] Read more.

Typically, steel is protected from corrosion by employing sacrificial anodes or coatings based on Zn, Mg, Al or Cd. However, stricter environmental regulations require new environmentally friendly alternatives to replace Cd. Traditionally, Al-based anodes have been employed to cathodically protect steel in marine applications or as ion vapour deposition (IVD)-Al sacrificial coatings for aerospace applications. However, Al tends to passivate, thus losing its protective effect. Therefore, it is important to identify possible alloys that can provide a constantly sufficient current. In this study, Al-X alloys (X = Ag, Bi, Ca, Cr, Cu, Ga, Gd, In, Mg, Mn, Ni, Sb, Si, Sn, V, Ti, Zn and Zr) were firstly tested for a screening of the sacrificial properties of binary systems. Al-0.5Cr, Al-1Sn, Al-0.2Ga, Al-0.1In, Al-2Si and Al-5Zn alloys were suggested as promising sacrificial Al-based alloys. Suitable heat treatments for each system were implemented to reduce the influence of the secondary phases on the corrosion properties by minimising localised attack. extensive evaluation of the corrosion properties, including galvanic coupling of these alloys to steel, was performed in the NaCl electrolyte. A comparative analysis was conducted in order to choose the most promising alloy(s) for avoiding the passivation of Al and for efficient cathodic protection to steel. Full article

(This article belongs to the Section Corrosion)

► Show Figures

Graphical abstract

15 pages, 17149 KiB

Open AccessEditor’s ChoiceArticle

Improving the Thermomechanical Properties of Poly(lactic acid) via Reduced Graphene Oxide and Bioderived Poly(decamethylene 2,5-furandicarboxylate)

by Giulia Fredi, Mahdi Karimi Jafari, Andrea Dorigato, Dimitrios N. Bikiaris and Alessandro Pegoretti

Materials 2022, 15(4), 1316; https://doi.org/10.3390/ma15041316 - 10 Feb 2022

Cited by 12 | Viewed by 3164

Abstract

Polylactide (PLA) is the most widely used biopolymer, but its poor ductility and scarce gas barrier properties limit its applications in the packaging field. In this work, for the first time, the properties of PLA solvent-cast films are improved by the addition of [...] Read more.

Polylactide (PLA) is the most widely used biopolymer, but its poor ductility and scarce gas barrier properties limit its applications in the packaging field. In this work, for the first time, the properties of PLA solvent-cast films are improved by the addition of a second biopolymer, i.e., poly(decamethylene 2,5-furandicarboxylate) (PDeF), added in a weight fraction of 10 wt%, and a carbon-based nanofiller, i.e., reduced graphene oxide (rGO), added in concentrations of 0.25–2 phr. PLA and PDeF are immiscible, as evidenced by scanning electron microscopy (SEM) and Fourier-transform infrared (FTIR) spectroscopy, with PDeF spheroidal domains showing poor adhesion to PLA. The addition of 0.25 phr of rGO, which preferentially segregates in the PDeF domains, makes them smaller and considerably rougher and improves the interfacial interaction. Differential scanning calorimetry (DSC) confirms the immiscibility of the two polymer phases and highlights that rGO enhances the crystallinity of both polymer phases (especially of PDeF). Thermogravimetric analysis (TGA) highlights the positive impact of rGO and PDeF on the thermal degradation resistance of PLA. Quasi-static tensile tests evidence that adding 10 wt% of PDeF and a small fraction of rGO (0.25 phr) to PLA considerably enhances the strain at break, which raises from 5.3% of neat PLA to 10.0% by adding 10 wt% of PDeF, up to 75.8% by adding also 0.25 phr of rGO, thereby highlighting the compatibilizing role of rGO on this blend. On the other hand, a further increase in rGO concentration decreases the strain at break due to agglomeration but enhances the mechanical stiffness and strength up to an rGO concentration of 1 phr. Overall, these results highlight the positive and synergistic contribution of PDeF and rGO in enhancing the thermomechanical properties of PLA, and the resulting nanocomposites are promising for packaging applications. Full article

(This article belongs to the Special Issue Green Composites: Challenges and Opportunities)

► Show Figures

Figure 1

23 pages, 6027 KiB

Open AccessEditor’s ChoiceArticle

A Ternary Seismic Metamaterial for Low Frequency Vibration Attenuation

by Chen Chen, Jincheng Lei and Zishun Liu

Materials 2022, 15(3), 1246; https://doi.org/10.3390/ma15031246 - 8 Feb 2022

Cited by 24 | Viewed by 3470

Abstract

Structural vibration induced by low frequency elastic waves presents a great threat to infrastructure such as buildings, bridges, and nuclear structures. In order to reduce the damage of low frequency structural vibration, researchers proposed the structure of seismic metamaterial, which can be used [...] Read more.

Structural vibration induced by low frequency elastic waves presents a great threat to infrastructure such as buildings, bridges, and nuclear structures. In order to reduce the damage of low frequency structural vibration, researchers proposed the structure of seismic metamaterial, which can be used to block the propagation of low frequency elastic wave by adjusting the frequency range of elastic wave propagation. In this study, based on the concept of phononic crystal, a ternary seismic metamaterial is proposed to attenuate low frequency vibration by generating band gaps. The proposed metamaterial structure is periodically arranged by cube units, which consist of rubber coating, steel scatter, and soft matrix (like soil). The finite element analysis shows that the proposed metamaterial structure has a low frequency band gap with 8.5 Hz bandwidth in the range of 0–20 Hz, which demonstrates that the metamaterial can block the elastic waves propagation in a fairly wide frequency range within 0–20 Hz. The frequency response analysis demonstrates that the proposed metamaterial can effectively attenuate the low frequency vibration. A simplified equivalent mass–spring model is further proposed to analyze the band gap range which agrees well with the finite element results. This model provides a more convenient method to calculate the band gap range. Combining the proposed equivalent mass–spring model with finite element analysis, the effect of material parameters and geometric parameters on the band gap characteristic is investigated. This study can provide new insights for low frequency vibration attenuation. Full article

(This article belongs to the Section Mechanics of Materials)

► Show Figures

Figure 1

15 pages, 7332 KiB

Open AccessEditor’s ChoiceArticle

Strain Rate and Stress Amplitude Effects on the Mechanical Behavior of Carbon Paste Used in the Hall–Héroult Process and Subjected to Cyclic Loadings

by Zahraa Kansoun, Hicham Chaouki, Donald Picard, Julien Lauzon-Gauthier, Houshang Alamdari and Mario Fafard

Materials 2022, 15(3), 1263; https://doi.org/10.3390/ma15031263 - 8 Feb 2022

Cited by 4 | Viewed by 1819

Abstract

Carbon products such as anodes and ramming paste must have well-defined physical, mechanical, chemical, and electrical properties to perform their functions effectively in the aluminum electrolysis cell. The physical and mechanical properties of these products are assigned during the shaping procedure in which [...] Read more.

Carbon products such as anodes and ramming paste must have well-defined physical, mechanical, chemical, and electrical properties to perform their functions effectively in the aluminum electrolysis cell. The physical and mechanical properties of these products are assigned during the shaping procedure in which compaction stresses are applied to the green carbon paste. The optimization of the shaping process is crucial to improving the properties of the carbon products and consequently to increasing the energy efficiency and decreasing the greenhouse gas emissions of the Hall–Héroult process. The objective of this study is to experimentally investigate the effect(s) of the strain rate, of the stress maximum amplitude, and of the unloading level on the behavior of a green carbon paste subjected to cyclic loading. To this end, experiments consisting of (1) cyclic compaction tests at different maximum stress amplitudes and strain rates, and (2) cyclic compaction tests with different unloading levels were carried out. The study obtained the following findings about the behavior of carbon paste subjected to cyclic loads. The strain rate in the studied range had no effect either on the evolution of the permanent strain as a function of the cycle number, nor on the shape of the stress–strain hysteresis during the cyclic loading. Moreover, samples of the same density that had been subjected to different maximum stress amplitudes in their loading history did not have the same shape of the stress–strain curve. On the other hand, despite having different densities, samples subjected to the same number of cycles produce the same stress–strain curve during loading even though they were subjected to different maximum stress amplitudes in their loading histories. Finally, the level of unloading during each cycle of a cyclic test proved significant; when the sample was unloaded to a lower level of stress during each cycle, the permanent strain as a function of the cycle number was higher. Full article

(This article belongs to the Section Carbon Materials)

► Show Figures

Figure 1

17 pages, 6845 KiB

Open AccessEditor’s ChoiceArticle

Effect of Loading Rate and Initial Strain on Seismic Performance of an Innovative Self-Centering SMA Brace

by Yigang Jia, Bo Zhang, Sizhi Zeng, Fenghua Tang, Shujun Hu and Wenping Chen

Materials 2022, 15(3), 1234; https://doi.org/10.3390/ma15031234 - 7 Feb 2022

Cited by 9 | Viewed by 2129

Abstract

In order to improve the energy dissipation capacity and to reduce the residual deformation of civil structures simultaneously, this paper puts forwards an innovative self-centering shape memory alloy (SMA) brace that is based on the design concepts of SMA’s superelasticity and low friction [...] Read more.

In order to improve the energy dissipation capacity and to reduce the residual deformation of civil structures simultaneously, this paper puts forwards an innovative self-centering shape memory alloy (SMA) brace that is based on the design concepts of SMA’s superelasticity and low friction slip. Seven self-centering SMA brace specimens were tested under cyclic loading, and the hysteresis curves, bond curves, secant stiffness, energy dissipation coefficient, equivalent damping coefficient, and the self-centering capacity ratio of these specimens were investigated, allowing us to provide an evaluation of the effects of the loading rate and initial strain on the seismic performance. The test results show that the self-centering SMA braces have an excellent energy dissipation capacity, bearing capacity, and self-centering capacity, while the steel plates remain elastic, and the SMA in the specimens that are always under tension are able to return to the initial state. The hysteresis curves of all of the specimens are idealized as a flag shape with low residual deformation, and the self-centering capacity ratio reached 89.38%. In addition, both the loading rate and the initial strain were shown to have a great influence on the seismic performance of the self-centering SMA brace. The improved numerical models combined with the Graesser model and Bouc–Wen model in MATLAB were used to simulate the seismic performance of the proposed braces with different loading rates and initial strains, and the numerical results are consistent with the test results under the same conditions, meaning that they can accurately predict the seismic performance of the self-centering SMA brace proposed here. Full article

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

► Show Figures

Figure 1

29 pages, 9696 KiB

Open AccessEditor’s ChoiceArticle

The Use of a High-Pressure Water-Ice Jet for Removing Worn Paint Coating in Renovation Process

by Grzegorz Chomka, Jarosław Chodór, Leon Kukiełka and Maciej Kasperowicz

Materials 2022, 15(3), 1168; https://doi.org/10.3390/ma15031168 - 3 Feb 2022

Cited by 4 | Viewed by 2644

Abstract

The paper presents the results of investigations into the possibility of using ahigh-pressure water-ice jet as a new method for removing a worn-out paint coating from the surface of metal parts (including those found in means of transportation) and for preparing the base [...] Read more.

The paper presents the results of investigations into the possibility of using ahigh-pressure water-ice jet as a new method for removing a worn-out paint coating from the surface of metal parts (including those found in means of transportation) and for preparing the base surface for the application of renovation paint coating. Experimental investigations were carried out in four stages, on flat specimens, sized S × H = 75 × 115 mm, cut from sheet metal made of various materials such as steel X5CrNi18-10, PA2 aluminium alloy and PMMA polymethyl methacrylate (plastic). In the first stage, the surfaces of the samples were subjected to observation of surface morphology under a scanning electron microscope, and surface topography (ST) measurements were made on a profilographometer. Two ST parameters were analysed in detail: the maximum height of surface roughness Sz and the arithmetic mean surface roughness Sa. Next, paint coatings were applied to the specimens as a base. In the third stage, the paint coating applied was removed by means of a high-pressure water-ice jet (HPWIJ) by changing the values of the technological parameters, i.e., water jet pressure p_w, dry ice mass flow rate

{\dot{m}}_{L}

, distance between the sprinkler head outlet and the surface being treated (the so-called working jet length) l₂ and spray angle κ for the following constants: the number of TS = 4 holes, water hole diameter φ = 1.2 mm and sprinkler head length L_k = 200 mm. Afterwards, the surface morphology was observed again and the surface topography of the specimen was investigated by measuring selected 3D parameters of the ST structure, Sz and Sa. The results of investigations into the influence of selected HPWIJ treatment parameters on the surface Q_F removal efficiency obtained are also presented. Univariate regression functions were developed for the mean stripping efficiency based on the following: dry ice mass flow rate

{\dot{m}}_{L}

, working jet length l₂ and spray angle κ. Based on these functions, the values of optimal parameters were determined that allow the maximum efficiency of the process to be obtained. A 95% confidence region for the regression function was also developed. The results demonstrated that HPWIJ treatment does not interfere with the geometric structure of the base material, and they confirmed the possibility of using this treatment as an efficient method of removing a worn paint layer from bases made of various metal and plastic materials, and preparing it for applying a new layer during renovation. Full article

(This article belongs to the Special Issue Feature Papers in Materials Simulation and Design)

► Show Figures

Figure 1

33 pages, 7644 KiB

Open AccessEditor’s ChoiceReview

Application of Graphene-Related Materials in Organic Solar Cells

by Lara Velasco Davoise, Ana M. Díez-Pascual and Rafael Peña Capilla

Materials 2022, 15(3), 1171; https://doi.org/10.3390/ma15031171 - 3 Feb 2022

Cited by 32 | Viewed by 5076

Abstract

Graphene-related materials (GRMs) such as graphene quantum dots (GQDs), graphene oxide (GO), reduced graphene oxide (rGO), graphene nanoribbons (GNRs), and so forth have recently emerged as photovoltaic (PV) materials due to their nanodimensional structure and outstanding properties such as high electrical and thermal [...] Read more.

Graphene-related materials (GRMs) such as graphene quantum dots (GQDs), graphene oxide (GO), reduced graphene oxide (rGO), graphene nanoribbons (GNRs), and so forth have recently emerged as photovoltaic (PV) materials due to their nanodimensional structure and outstanding properties such as high electrical and thermal conductivity, large specific surface, and unique combination of mechanical strength and flexibility. They can be a crucial part of transparent electrodes, hole/electron transport materials, and active layers in organic solar cells (OSCs). Besides their role in charge extraction and transport, GRMs act as device protectors against environmental degradation through their compact bidimensional structure and offer good durability. This review briefly presents the synthesis methods of GRMs and describes the current progress in GRM-based OSCs. PV parameters (short circuit current, open circuit voltage, power conversion efficiency, and fill factor) are summarized and comparatively discussed for the different structures. The efficiency recently surpassed 15% for an OSC incorporating polymer-modified graphene as a transparent electrode. The long-term stability of OSCs incorporating GRMs is also discussed. Finally, conclusions and the outlook for future investigation into GRM-based devices for PVs are presented. Full article

(This article belongs to the Special Issue Advanced Materials for Photonics and Photovoltaics Applications)

► Show Figures

Figure 1

26 pages, 8120 KiB

Open AccessEditor’s ChoiceReview

by Zeyu Chi, Jacob J. Asher, Michael R. Jennings, Ekaterine Chikoidze and Amador Pérez-Tomás

Materials 2022, 15(3), 1164; https://doi.org/10.3390/ma15031164 - 2 Feb 2022

Cited by 46 | Viewed by 9079

Abstract

Currently, a significant portion (~50%) of global warming emissions, such as CO₂, are related to energy production and transportation. As most energy usage will be electrical (as well as transportation), the efficient management of electrical power is thus central to achieve [...] Read more.

Currently, a significant portion (~50%) of global warming emissions, such as CO₂, are related to energy production and transportation. As most energy usage will be electrical (as well as transportation), the efficient management of electrical power is thus central to achieve the XXI century climatic goals. Ultra-wide bandgap (UWBG) semiconductors are at the very frontier of electronics for energy management or energy electronics. A new generation of UWBG semiconductors will open new territories for higher power rated power electronics and solar-blind deeper ultraviolet optoelectronics. Gallium oxide—Ga₂O₃ (4.5–4.9 eV), has recently emerged pushing the limits set by more conventional WBG (~3 eV) materials, such as SiC and GaN, as well as for transparent conducting oxides (TCO), such asIn₂O₃, ZnO and SnO₂, to name a few. Indeed, Ga₂O₃ as the first oxide used as a semiconductor for power electronics, has sparked an interest in oxide semiconductors to be investigated (oxides represent the largest family of UWBG). Among these new power electronic materials, Al_xGa_1-xO₃ may provide high-power heterostructure electronic and photonic devices at bandgaps far beyond all materials available today (~8 eV) or ZnGa₂O₄ (~5 eV), enabling spinel bipolar energy electronics for the first time ever. Here, we review the state-of-the-art and prospects of some ultra-wide bandgap oxide semiconductor arising technologies as promising innovative material solutions towards a sustainable zero emission society. Full article

(This article belongs to the Special Issue Feature Papers in Electronic Materials Section)

► Show Figures

Figure 1

Journal Menu

Journal Browser

Editor’s Choice Articles

Further Information

Guidelines

MDPI Initiatives

Follow MDPI