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28 pages, 2319 KiB

Open AccessReview

Advancements in Free-Standing Ferroelectric Films: Paving the Way for Transparent Flexible Electronics

by Riya Pathak, Gopinathan Anoop and Shibnath Samanta

J. Compos. Sci. 2025, 9(2), 71; https://doi.org/10.3390/jcs9020071 - 5 Feb 2025

Cited by 2 | Viewed by 1423

Free-standing ferroelectric films have emerged as a transformative technology in the field of flexible electronics, offering unique properties that enable a wide range of applications, including sensors, actuators, and energy harvesting devices. This review paper explores recent advancements in the fabrication, characterization, and [...] Read more.

Free-standing ferroelectric films have emerged as a transformative technology in the field of flexible electronics, offering unique properties that enable a wide range of applications, including sensors, actuators, and energy harvesting devices. This review paper explores recent advancements in the fabrication, characterization, and application of free-standing ferroelectric films, highlighting innovative techniques such as multilayer structures and van der Waals epitaxy that enhance their performance while maintaining mechanical flexibility. We discuss the critical role of these films in next-generation devices, emphasizing their potential for integration into multifunctional systems that combine energy harvesting and sensing capabilities. Additionally, we address challenges related to leakage currents, polarization stability, and scalability that must be overcome to facilitate commercialization. By synthesizing current research findings and identifying future directions, this paper aims to provide a comprehensive overview of the state-of-the-art in free-standing ferroelectric films and their impact on the development of sustainable and efficient flexible electronic technologies. Full article

(This article belongs to the Section Composites Applications)

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11 pages, 4947 KiB

Open AccessArticle

Growth of Hg_0.7Cd_0.3Te on Van Der Waals Mica Substrates via Molecular Beam Epitaxy

by Shuo Ma, Wenwu Pan, Xiao Sun, Zekai Zhang, Renjie Gu, Lorenzo Faraone and Wen Lei

Molecules 2024, 29(16), 3947; https://doi.org/10.3390/molecules29163947 - 21 Aug 2024

Viewed by 4122

Abstract

In this paper, we present a study on the direct growth of

{H g}_{0.7} {C d}_{0.3} T e

thin films on layered transparent van der Waals mica (001) substrates through weak interface interaction through molecular beam epitaxy. The preferred orientation for [...] Read more.

In this paper, we present a study on the direct growth of

{H g}_{0.7} {C d}_{0.3} T e

thin films on layered transparent van der Waals mica (001) substrates through weak interface interaction through molecular beam epitaxy. The preferred orientation for growing

{H g}_{0.7} {C d}_{0.3} T e

on mica (001) substrates is found to be the (111) orientation due to a better lattice match between the

{H g}_{0.7} {C d}_{0.3} T e

layer and the underlying mica substrate. The influence of growth parameters (mainly temperature and Hg flux) on the material quality of epitaxial

{H g}_{0.7} {C d}_{0.3} T e

thin films is studied, and the optimal growth temperature and Hg flux are found to be approximately 190 °C and 4.5 ×

10^{- 4}

Torr as evidenced by higher crystalline quality and better surface morphology.

{H g}_{0.7} {C d}_{0.3} T e

thin films (3.5 µm thick) grown under these optimal growth conditions present a full width at half maximum of 345.6 arc sec for the X-ray diffraction rocking curve and a root-mean-square surface roughness of 6 nm. However, a significant number of microtwin defects are observed using cross-sectional transmission electron microscopy, which leads to a relatively high etch pit density (mid-

10^{7}

{c m}^{- 2}

) in the

{H g}_{0.7} {C d}_{0.3} T e

thin films. These findings not only facilitate the growth of HgCdTe on mica substrates for fabricating curved IR sensors but also contribute to a better understanding of growth of traditional zinc-blende semiconductors on layered substrates. Full article

(This article belongs to the Special Issue Recent Advances in Epitaxial Growth: Materials and Methods)

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29 pages, 8536 KiB

Open AccessReview

Hexagonal Boron Nitride Based Photonic Quantum Technologies

by Madhava Krishna Prasad, Mike P. C. Taverne, Chung-Che Huang, Jonathan D. Mar and Ying-Lung Daniel Ho

Materials 2024, 17(16), 4122; https://doi.org/10.3390/ma17164122 - 20 Aug 2024

Cited by 5 | Viewed by 2937

Abstract

Hexagonal boron nitride is rapidly gaining interest as a platform for photonic quantum technologies, due to its two-dimensional nature and its ability to host defects deep within its large band gap that may act as room-temperature single-photon emitters. In this review paper we [...] Read more.

Hexagonal boron nitride is rapidly gaining interest as a platform for photonic quantum technologies, due to its two-dimensional nature and its ability to host defects deep within its large band gap that may act as room-temperature single-photon emitters. In this review paper we provide an overview of (1) the structure, properties, growth and transfer of hexagonal boron nitride; (2) the creationof colour centres in hexagonal boron nitride and assignment of defects by comparison with ab initio calculations for applications in photonic quantum technologies; and (3) heterostructure devices for the electrical tuning and charge control of colour centres that form the basis for photonic quantum technology devices. The aim of this review is to provide readers a summary of progress in both defect engineering and device fabrication in hexagonal boron nitride based photonic quantum technologies. Full article

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11 pages, 2530 KiB

Open AccessArticle

Direct Selective Epitaxy of 2D Sb₂Te₃ onto Monolayer WS₂ for Vertical p–n Heterojunction Photodetectors

by Baojun Pan, Zhenjun Dou, Mingming Su, Ya Li, Jialing Wu, Wanwan Chang, Peijian Wang, Lijie Zhang, Lei Zhao, Mei Zhao and Sui-Dong Wang

Nanomaterials 2024, 14(10), 884; https://doi.org/10.3390/nano14100884 - 19 May 2024

Cited by 3 | Viewed by 2056

Abstract

Two-dimensional transition metal dichalcogenides (2D-TMDs) possess appropriate bandgaps and interact via van der Waals (vdW) forces between layers, effectively overcoming lattice compatibility challenges inherent in traditional heterojunctions. This property facilitates the creation of heterojunctions with customizable bandgap alignments. However, the prevailing method for [...] Read more.

Two-dimensional transition metal dichalcogenides (2D-TMDs) possess appropriate bandgaps and interact via van der Waals (vdW) forces between layers, effectively overcoming lattice compatibility challenges inherent in traditional heterojunctions. This property facilitates the creation of heterojunctions with customizable bandgap alignments. However, the prevailing method for creating heterojunctions with 2D-TMDs relies on the low-efficiency technique of mechanical exfoliation. Sb₂Te₃, recognized as a notable p-type semiconductor, emerges as a versatile component for constructing diverse vertical p–n heterostructures with 2D-TMDs. This study presents the successful large-scale deposition of 2D Sb₂Te₃ onto inert mica substrates, providing valuable insights into the integration of Sb₂Te₃ with 2D-TMDs to form heterostructures. Building upon this initial advancement, a precise epitaxial growth method for Sb₂Te₃ on pre-existing WS₂ surfaces on SiO₂/Si substrates is achieved through a two-step chemical vapor deposition process, resulting in the formation of Sb₂Te₃/WS₂ heterojunctions. Finally, the development of 2D Sb₂Te₃/WS₂ optoelectronic devices is accomplished, showing rapid response times, with a rise/decay time of 305 μs/503 μs, respectively. Full article

(This article belongs to the Special Issue 2D Materials and van der Waals Heterostructures for Optoelectronic Devices)

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15 pages, 11880 KiB

Open AccessEditor’s ChoiceArticle

Epitaxial Growth of GaN Films on Chemical-Vapor-Deposited 2D MoS₂ Layers by Plasma-Assisted Molecular Beam Epitaxy

by Iwan Susanto, Hong-Shan Liu, Yen-Ten Ho and Ing-Song Yu

Nanomaterials 2024, 14(8), 732; https://doi.org/10.3390/nano14080732 - 22 Apr 2024

Cited by 2 | Viewed by 2730

Abstract

The van der Waals epitaxy of wafer-scale GaN on 2D MoS₂ and the integration of GaN/MoS₂ heterostructures were investigated in this report. GaN films have been successfully grown on 2D MoS₂ layers using three different Ga fluxes via a plasma-assisted [...] Read more.

The van der Waals epitaxy of wafer-scale GaN on 2D MoS₂ and the integration of GaN/MoS₂ heterostructures were investigated in this report. GaN films have been successfully grown on 2D MoS₂ layers using three different Ga fluxes via a plasma-assisted molecular beam epitaxy (PA-MBE) system. The substrate for the growth was a few-layer 2D MoS₂ deposited on sapphire using chemical vapor deposition (CVD). Three different Ga fluxes were provided by the gallium source of the K-cell at temperatures of 825, 875, and 925 °C, respectively. After the growth, RHEED, HR-XRD, and TEM were conducted to study the crystal structure of GaN films. The surface morphology was obtained using FE-SEM and AFM. Chemical composition was confirmed by XPS and EDS. Raman and PL spectra were carried out to investigate the optical properties of GaN films. According to the characterizations of GaN films, the van der Waals epitaxial growth mechanism of GaN films changed from 3D to 2D with the increase in Ga flux, provided by higher temperatures of the K-cell. GaN films grown at 750 °C for 3 h with a K-cell temperature of 925 °C demonstrated the greatest crystal quality, chemical composition, and optical properties. The heterostructure of 3D GaN on 2D MoS₂ was integrated successfully using the low-temperature PA-MBE technique, which could be applied to novel electronics and optoelectronics. Full article

(This article belongs to the Special Issue III-Nitride Semiconductors: Design, Characterization, Applications, and Devices)

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11 pages, 5235 KiB

Open AccessArticle

Electrostimulation and Nanomanipulation of Two-Dimensional MoO_3-x Layers Grown on Graphite

by Aleksandra Nadolska, Dorota A. Kowalczyk, Iaroslav Lutsyk, Michał Piskorski, Paweł Krukowski, Paweł Dąbrowski, Maxime Le Ster, Witold Kozłowski, Rafał Dunal, Przemysław Przybysz, Wojciech Ryś, Klaudia Toczek, Paweł J. Kowalczyk and Maciej Rogala

Crystals 2023, 13(6), 905; https://doi.org/10.3390/cryst13060905 - 1 Jun 2023

Cited by 5 | Viewed by 2199

Abstract

Molybdenum trioxide shows many attractive properties, such as a wide electronic band gap and a high relative permittivity. Monolayers of this material are particularly important, as they offer new avenues in optoelectronic devices, e.g., to alter the properties of graphene electrodes. Nanoscale electrical [...] Read more.

Molybdenum trioxide shows many attractive properties, such as a wide electronic band gap and a high relative permittivity. Monolayers of this material are particularly important, as they offer new avenues in optoelectronic devices, e.g., to alter the properties of graphene electrodes. Nanoscale electrical characterization is essential for potential applications of monolayer molybdenum trioxide. We present a conductive atomic force microscopy study of an epitaxially grown 2D molybdenum oxide layer on a graphene-like substrate, such as highly oriented pyrolytic graphite (HOPG). Monolayers were also investigated using X-ray photoelectron spectroscopy, atomic force microscopy (semi-contact and contact mode), Kelvin probe force microscopy, and lateral force microscopy. We demonstrate mobility of the unpinned island under slight mechanical stress as well as shaping and detachment of the material with applied electrical stimulation. Non-stoichiometric MoO_3-x monolayers show heterogeneous behavior in terms of electrical conductivity, which can be related to the crystalline domains and defects in the structure. Different regions show various I–V characteristics, which are correlated with their susceptibility to electrodegradation. In this work, we cover the existing gap regarding nanomanipulation and electrical nanocharacterization of the MoO₃ monolayer. Full article

(This article belongs to the Special Issue Electronic Phenomena of Transition Metal Oxides Volume II)

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11 pages, 3117 KiB

Open AccessArticle

Temperature−Dependent Raman Scattering Investigation on vdW Epitaxial PbI₂/CrOCl Heterostructure

by Siwen You, Xiao Guo, Junjie Jiang, Dingbang Yang, Mingjun Li, Fangping Ouyang, Haipeng Xie, Han Huang and Yongli Gao

Crystals 2023, 13(1), 104; https://doi.org/10.3390/cryst13010104 - 6 Jan 2023

Cited by 5 | Viewed by 3016

Abstract

Van der Waals (vdW) epitaxial growth provides an efficient strategy to prepare heterostructures with atomically and electronically sharp interfaces. Herein, PbI₂ was in situ thermally deposited onto exfoliated thin−layered CrOCl nanoflakes in high vacuum to fabricate vdW PbI₂/CrOCl heterostructures. Optical [...] Read more.

Van der Waals (vdW) epitaxial growth provides an efficient strategy to prepare heterostructures with atomically and electronically sharp interfaces. Herein, PbI₂ was in situ thermally deposited onto exfoliated thin−layered CrOCl nanoflakes in high vacuum to fabricate vdW PbI₂/CrOCl heterostructures. Optical microscopy, atomic force microscopy, X−ray diffraction, and temperature−dependent Raman spectroscopy were used to investigate the structural properties and phonon behaviors of the heterostructures. The morphology of PbI₂ films on the CrOCl substrate obviously depended on the substrate temperature, changing from hemispherical granules to 2D nanoflakes with flat top surfaces. In addition, anomalous blueshift of the

A_{g}^{1}

and

A_{u}^{2}

modes as the temperature increased in PbI₂/CrOCl heterostructure was observed for the first time. Our results provide a novel material platform for the vdW heterostructure and a possible method for optimizing heterostructure growth behaviors. Full article

(This article belongs to the Topic Advanced Structural Crystals)

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24 pages, 7885 KiB

Open AccessReview

‘Molecular Beam Epitaxy’ on Organic Semiconductor Single Crystals: Characterization of Well-Defined Molecular Interfaces by Synchrotron Radiation X-ray Diffraction Techniques

by Yasuo Nakayama, Ryohei Tsuruta and Tomoyuki Koganezawa

Materials 2022, 15(20), 7119; https://doi.org/10.3390/ma15207119 - 13 Oct 2022

Cited by 9 | Viewed by 3230

Abstract

Epitaxial growth, often termed “epitaxy”, is one of the most essential techniques underpinning semiconductor electronics, because crystallinities of the materials seriously dominate operation efficiencies of the electronic devices such as power gain/consumption, response speed, heat loss, and so on. In contrast to already [...] Read more.

Epitaxial growth, often termed “epitaxy”, is one of the most essential techniques underpinning semiconductor electronics, because crystallinities of the materials seriously dominate operation efficiencies of the electronic devices such as power gain/consumption, response speed, heat loss, and so on. In contrast to already well-established epitaxial growth methodologies for inorganic (covalent or ionic) semiconductors, studies on inter-molecular (van der Waals) epitaxy for organic semiconductors is still in the initial stage. In the present review paper, we briefly summarize recent works on the epitaxial inter-molecular junctions built on organic semiconductor single-crystal surfaces, particularly on single crystals of pentacene and rubrene. Experimental methodologies applicable for the determination of crystal structures of such organic single-crystal-based molecular junctions are also illustrated. Full article

(This article belongs to the Special Issue Physicochemical Properties of Organic and Hybrid Semiconductor Materials)

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13 pages, 16844 KiB

Open AccessEditor’s ChoiceArticle

Revisiting the van der Waals Epitaxy in the Case of (Bi_0.4Sb_0.6)₂Te₃ Thin Films on Dissimilar Substrates

by Liesbeth Mulder, Daan H. Wielens, Yorick A. Birkhölzer, Alexander Brinkman and Omar Concepción

Nanomaterials 2022, 12(11), 1790; https://doi.org/10.3390/nano12111790 - 24 May 2022

Cited by 4 | Viewed by 2745

Abstract

Ultrathin films of the ternary topological insulator (Bi

_{0.4}

Sb

_{0.6}

)

_{2}

Te

_{3}

are fabricated by molecular beam epitaxy. Although it is generally assumed that the ternary topological insulator tellurides grow by van der Waals epitaxy, our results show that the [...] Read more.

Ultrathin films of the ternary topological insulator (Bi

_{0.4}

Sb

_{0.6}

)

_{2}

Te

_{3}

are fabricated by molecular beam epitaxy. Although it is generally assumed that the ternary topological insulator tellurides grow by van der Waals epitaxy, our results show that the influence of the substrate is substantial and governs the formation of defects, mosaicity, and twin domains. For this comparative study, InP (111)A, Al

_{2}

O

_{3}

(001), and SrTiO

_{3}

(111) substrates were selected. While the films deposited on lattice-matched InP (111)A show van der Waals epitaxial relations, our results point to a quasi-van der Waals epitaxy for the films grown on substrates with a larger lattice mismatch. Full article

(This article belongs to the Special Issue Advances in Topological Materials: Fundamentals, Challenges and Outlook)

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15 pages, 6502 KiB

Open AccessArticle

Van der Waals Epitaxial Growth of ZnO Films on Mica Substrates in Low-Temperature Aqueous Solution

by Hou-Guang Chen, Yung-Hui Shih, Huei-Sen Wang, Sheng-Rui Jian, Tzu-Yi Yang and Shu-Chien Chuang

Coatings 2022, 12(5), 706; https://doi.org/10.3390/coatings12050706 - 20 May 2022

Cited by 6 | Viewed by 3341

Abstract

In this article, we demonstrate the van der Waals (vdW) epitaxial growth of ZnO layers on mica substrates through a low-temperature hydrothermal process. The thermal pretreatment of mica substrates prior to the hydrothermal growth of ZnO is essential for growing ZnO crystals in [...] Read more.

In this article, we demonstrate the van der Waals (vdW) epitaxial growth of ZnO layers on mica substrates through a low-temperature hydrothermal process. The thermal pretreatment of mica substrates prior to the hydrothermal growth of ZnO is essential for growing ZnO crystals in epitaxy with the mica substrates. The addition of sodium citrate into the growth solution significantly promotes the growth of ZnO crystallites in a lateral direction to achieve fully coalesced, continuous ZnO epitaxial layers. As confirmed through transmission electron microscopy, the epitaxial paradigm of the ZnO layer on the mica substrate was regarded as an incommensurate van der Waals epitaxy. Furthermore, through the association of the Mist-CVD process, the high-density and uniform distribution of ZnO seeds preferentially occurred on mica substrates, leading to greatly improving the epitaxial qualities of the hydrothermally grown ZnO layers and obtaining flat surface morphologies. The electrical and optoelectrical properties of the vdW epitaxial ZnO layer grown on mica substrates were comparable with those grown on sapphire substrates through conventional solution-based epitaxy techniques. Full article

(This article belongs to the Special Issue Recent Advances in the Growth and Characterizations of Thin Films)

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10 pages, 4246 KiB

Open AccessArticle

MOVPE Growth of GaN via Graphene Layers on GaN/Sapphire Templates

by Kazimieras Badokas, Arūnas Kadys, Dominykas Augulis, Jūras Mickevičius, Ilja Ignatjev, Martynas Skapas, Benjaminas Šebeka, Giedrius Juška and Tadas Malinauskas

Nanomaterials 2022, 12(5), 785; https://doi.org/10.3390/nano12050785 - 25 Feb 2022

Cited by 11 | Viewed by 3865

Abstract

The remote epitaxy of GaN epilayers on GaN/sapphire templates was studied by using different graphene interlayer types. Monolayer, bilayer, double-stack of monolayer, and triple-stack of monolayer graphenes were transferred onto GaN/sapphire templates using a wet transfer technique. The quality of the graphene interlayers [...] Read more.

The remote epitaxy of GaN epilayers on GaN/sapphire templates was studied by using different graphene interlayer types. Monolayer, bilayer, double-stack of monolayer, and triple-stack of monolayer graphenes were transferred onto GaN/sapphire templates using a wet transfer technique. The quality of the graphene interlayers was examined by Raman spectroscopy. The impact of the interlayer type on GaN nucleation was analyzed by scanning electron microscopy. The graphene interface and structural quality of GaN epilayers were studied by transmission electron microscopy and X-ray diffraction, respectively. The influence of the graphene interlayer type is discussed in terms of the differences between remote epitaxy and van der Waals epitaxy. The successful exfoliation of GaN membrane is demonstrated. Full article

(This article belongs to the Topic Application of Graphene-Based Materials)

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9 pages, 2634 KiB

Open AccessArticle

MnBi₂Se₄-Based Magnetic Modulated Heterostructures

by Evgeniy K. Petrov, Vladimir M. Kuznetsov and Sergey V. Eremeev

Magnetism 2022, 2(1), 1-9; https://doi.org/10.3390/magnetism2010001 - 4 Jan 2022

Cited by 1 | Viewed by 3192

Abstract

Thin films of magnetic topological insulators (TIs) are expected to exhibit a quantized anomalous Hall effect when the magnetizations on the top and bottom surfaces are parallel and a quantized topological magnetoelectric effect when the magnetizations have opposite orientations. Progress in the observation [...] Read more.

Thin films of magnetic topological insulators (TIs) are expected to exhibit a quantized anomalous Hall effect when the magnetizations on the top and bottom surfaces are parallel and a quantized topological magnetoelectric effect when the magnetizations have opposite orientations. Progress in the observation of these quantum effects was achieved earlier in the films with modulated magnetic doping. On the other hand, the molecular-beam-epitaxy technique allowing the growth of stoichiometric magnetic van der Waals blocks in combination with blocks of topological insulator was developed. This approach should allow the construction of modulated heterostructures with the desired architecture. In the present paper, based on the first-principles calculations, we study the electronic structure of symmetric thin film heterostructures composed of magnetic MnBi

_{2}

Se

_{4}

blocks (septuple layers, SLs) and blocks of Bi

_{2}

Se

_{3}

TI (quintuple layers, QLs) in dependence on the depth of the magnetic SLs relative to the film surface and the TI spacer between them. Among considered heterostructures we have revealed those characterized by nontrivial band topology. Full article

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10 pages, 1628 KiB

Open AccessCommunication

Epitaxial Growth of Diamond-Shaped Au_1/2Ag_1/2CN Nanocrystals on Graphene

by Chunggeun Park, Jimin Ham, Yun Jung Heo and Won Chul Lee

Materials 2021, 14(24), 7569; https://doi.org/10.3390/ma14247569 - 9 Dec 2021

Cited by 2 | Viewed by 2785

Abstract

Epitaxial synthesis of inorganic nanomaterials on pristine 2D materials is of interest in the development of nanostructured devices and nanocomposite materials, but is quite difficult because pristine surfaces of 2D materials are chemically inert. Previous studies found a few exceptions including AuCN, AgCN, [...] Read more.

Epitaxial synthesis of inorganic nanomaterials on pristine 2D materials is of interest in the development of nanostructured devices and nanocomposite materials, but is quite difficult because pristine surfaces of 2D materials are chemically inert. Previous studies found a few exceptions including AuCN, AgCN, CuCN, and Cu_0.5Au_0.5CN, which can be preferentially synthesized and epitaxially aligned onto various 2D materials. Here, we discover that Au_1/2Ag_1/2CN forms diamond-shaped nanocrystals epitaxially grown on pristine graphene surfaces. The nanocrystals synthesized by a simple drop-casting method are crystallographically aligned to lattice structures of the underlying graphene. Our experimental investigations on 3D structures and the synthesis conditions of the nanocrystals imply that the rhombic 2D geometries originate from different growth rates depending on orientations along and perpendicular to 1D molecular chains of Au_1/2Ag_1/2CN. We also perform in situ TEM observations showing that Au_1/2Ag_1/2CN nanocrystals are decomposed to Au and Ag alloy nanocrystals under electron beam irradiation. Our experimental results provide an additional example of 1D cyanide chain families that form ordered nanocrystals epitaxially aligned on 2D materials, and reveal basic physical characteristics of this rarely investigated nanomaterial. Full article

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22 pages, 8670 KiB

Open AccessArticle

Proven Anti-Wetting Properties of Molybdenum Tested for High-Temperature Corrosion-Resistance with Potential Application in the Aluminum Industry

by François Gitzhofer, James Aluha, Pierre-Olivier Langlois, Faranak Barandehfard, Thabang A. Ntho and Nicolas Abatzoglou

Materials 2021, 14(18), 5355; https://doi.org/10.3390/ma14185355 - 16 Sep 2021

Cited by 2 | Viewed by 2919

Abstract

The behavior of Mo in contact with molten Al was modelled by classical molecular dynamics (CMD) simulation of a pure Mo solid in contact with molten Al at 1200 K using the Materials Studio^®. Results showed that no reaction or cross [...] Read more.

The behavior of Mo in contact with molten Al was modelled by classical molecular dynamics (CMD) simulation of a pure Mo solid in contact with molten Al at 1200 K using the Materials Studio^®. Results showed that no reaction or cross diffusion of atoms occurs at the Mo(s)–Al(l) interface, and that molten Al atoms exhibit an epitaxial alignment with the exposed solid Mo crystal morphology. Furthermore, the two phases {Mo(s) and Al(l)} are predicted to interact with weak van der Waals forces and give interfacial energy of about 203 mJ/m². Surface energy measurements by the sessile drop experiment using the van Oss–Chaudhury–Good (VCG) theory established a Mo(s)–Al(l) interface energy equivalent to 54 mJ/m², which supports the weak van der Waals interaction. The corrosion resistance of a high purity (99.97%) Mo block was then tested in a molten alloy of 5% Mg mixed in Al (Al-5 wt.%Mg) at 1123 K for 96 h, using the ALCAN’s standard “immersion” test, and the results are presented. No Mo was found to be dissolved in the molten Al-Mg alloy. However, a 20% mass loss in the Mo block was due to intergranular corrosion scissoring the Mo block in the ALCAN test, but not as a result of the reaction of pure Mo with the molten Al-Mg alloy. It was observed that the Al-Mg alloy did not stick to the Mo block. Full article

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10 pages, 39661 KiB

Open AccessArticle

Preparation and Research of Monolayer WS₂ FETs Encapsulated by h-BN Material

by Tao Han, Hongxia Liu, Shupeng Chen, Shulong Wang and Kun Yang

Micromachines 2021, 12(9), 1006; https://doi.org/10.3390/mi12091006 - 24 Aug 2021

Cited by 5 | Viewed by 3065

Abstract

Functional devices that use vertical van der Waals (vdWs) heterostructure material can effectively combine the properties of single component materials, and the strong interlayer coupling effect can change their electronic and optical properties. According to our research, WS₂/h-BN vertical vdWs heterostructure [...] Read more.

Functional devices that use vertical van der Waals (vdWs) heterostructure material can effectively combine the properties of single component materials, and the strong interlayer coupling effect can change their electronic and optical properties. According to our research, WS₂/h-BN vertical vdWs heterostructure material can be synthesized by chemical vapor deposition (CVD) and wet transfer methods. Monolayer WS₂ material and WS₂/h-BN vertical vdWs heterostructure material can be tested and characterized using XPS, SEM, EDS, AFM and Raman spectroscopy, which can prove the existence of corresponding materials. When the thickness of the material decreases, the Coulomb scattering amongst two-dimensional (2D) layered materials increases. This is because both the shielding effect and the distance between the channel and the interface layer decrease. FET devices are then fabricated on WS₂/h-BN vdWs heterostructure material by the electron beam lithography and evaporation processes. The effects of vdWs epitaxy on electrical transmission when WS₂/h-BN vdWs heterostructure material is formed are explored. Finally, the related electrical performance of FET devices is tested and analyzed. Our experimental research provides guidance for the use of electronic devices with vdWs heterostructure material. Full article

(This article belongs to the Special Issue Electronic and Optoelectronic Devices Based on 2D Materials)

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