Pub Date : 2024-04-05DOI: 10.1088/2515-7639/ad3b6e
Chaobo Luo, Zongyu Huang, H. Qiao, Xiang Qi, Xiangyang Peng
Valleytronics uses valleys to encode information. It combines other degrees of freedom to produce a more comprehensive, stable, and efficient information processing system. However, in nonmagnetic valleytronic materials, the valley polarization is transient and the depolarization occurs once the external excitation is withdrawn. Introduction of magnetic field is an effective approach to realizing the spontaneous valley polarization by breaking the time-reversal symmetry. In hexagonal magnetic valleytronic materials, the inequivalent valleys at the K and -K Dirac cones have asymmetric energy gaps and Berry curvatures. The time-reversal symmetry in nonmagnetic materials can be broken by applying an external magnetic field, adding a magnetic substrate or doping magnetic atoms. Recent theoretical studies have demonstrated that valleytronic materials with intrinsic ferromagnetism, now termed as ferrovalley materials, exhibit spontaneous valley polarization without the need for external fields to maintain the polarization. The coupling of the valley and spin degrees of freedom enables stable and unequal distribution of electrons in the two valleys and thus facilitating nonvolatile information storage. Hence, ferrovalley materials are promising materials for valleytronic devices. In this review, we first briefly overview valleytronics and its related properties, the ways to realize valley polarization in nonmagnetic valleytronic materials. Then we focus on the recent developments in two-dimensional ferrovalley materials, which can be classified according to their molecular formula and crystal structure: MX2; M(XY)2, M(XY2) and M(XYZ)2; M2X3, M3X8 and MNX6; MNX2Y2, M2X2Y6 and MNX2Y6; and the Janus structure ferrovalley materials. In the inequivalent valleys, the Berry curvatures have opposite signs with unequal absolute values, leading to anomalous valley Hall effect. When the valley polarization is large, the ferrovalleys can be selectively excited even with unpolarized light. Intrinsic valley polarization in two-dimensional ferrovalley materials is of great importance. It opens a new avenue for information-related applications and hence is under rapid development.
{"title":"Valleytronics in two-dimensional magnetic materials","authors":"Chaobo Luo, Zongyu Huang, H. Qiao, Xiang Qi, Xiangyang Peng","doi":"10.1088/2515-7639/ad3b6e","DOIUrl":"https://doi.org/10.1088/2515-7639/ad3b6e","url":null,"abstract":"\u0000 Valleytronics uses valleys to encode information. It combines other degrees of freedom to produce a more comprehensive, stable, and efficient information processing system. However, in nonmagnetic valleytronic materials, the valley polarization is transient and the depolarization occurs once the external excitation is withdrawn. Introduction of magnetic field is an effective approach to realizing the spontaneous valley polarization by breaking the time-reversal symmetry. In hexagonal magnetic valleytronic materials, the inequivalent valleys at the K and -K Dirac cones have asymmetric energy gaps and Berry curvatures. The time-reversal symmetry in nonmagnetic materials can be broken by applying an external magnetic field, adding a magnetic substrate or doping magnetic atoms. Recent theoretical studies have demonstrated that valleytronic materials with intrinsic ferromagnetism, now termed as ferrovalley materials, exhibit spontaneous valley polarization without the need for external fields to maintain the polarization. The coupling of the valley and spin degrees of freedom enables stable and unequal distribution of electrons in the two valleys and thus facilitating nonvolatile information storage. Hence, ferrovalley materials are promising materials for valleytronic devices. In this review, we first briefly overview valleytronics and its related properties, the ways to realize valley polarization in nonmagnetic valleytronic materials. Then we focus on the recent developments in two-dimensional ferrovalley materials, which can be classified according to their molecular formula and crystal structure: MX2; M(XY)2, M(XY2) and M(XYZ)2; M2X3, M3X8 and MNX6; MNX2Y2, M2X2Y6 and MNX2Y6; and the Janus structure ferrovalley materials. In the inequivalent valleys, the Berry curvatures have opposite signs with unequal absolute values, leading to anomalous valley Hall effect. When the valley polarization is large, the ferrovalleys can be selectively excited even with unpolarized light. Intrinsic valley polarization in two-dimensional ferrovalley materials is of great importance. It opens a new avenue for information-related applications and hence is under rapid development.","PeriodicalId":501825,"journal":{"name":"Journal of Physics: Materials","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-04-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140737850","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-03-28DOI: 10.1088/2515-7639/ad367b
Onurcan Kaya, Luigi Colombo, Aleandro Antidormi, Marco A Villena, Mario Lanza, Ivan Cole, Stephan Roche
Interconnect materials with ultralow dielectric constant, and good thermal and mechanical properties are crucial for the further miniaturization of electronic devices. Recently, it has been demonstrated that ultrathin amorphous boron nitride (aBN) films have a very low dielectric constant, high density (above 2.1 g cm−3), high thermal stability, and mechanical properties. The excellent properties of aBN derive from the nature and degree of disorder, which can be controlled at fabrication, allowing tuning of the physical properties for desired applications. Here, we report an improvement in the stability and mechanical properties of aBN upon hydrogen doping. With the introduction of a Gaussian approximation potential for atomistic simulations, we investigate the changing morphology of aBN with varying H doping concentrations. We found that for 8 at% of H doping, the concentration of sp3-hybridized atoms reaches to a maximum which leads to an improvement of thermal stability and mechanical properties by 20%. These results will be a guideline for experimentalists and process engineers to tune the growth conditions of aBN films for numerous applications.
具有超低介电常数、良好热性能和机械性能的互连材料对于电子设备的进一步微型化至关重要。最近的研究表明，超薄无定形氮化硼（aBN）薄膜具有极低的介电常数、高密度（高于 2.1 g cm-3）、高热稳定性和机械性能。氮化硼的优异特性源于其无序的性质和程度，而无序的性质和程度可在制造过程中加以控制，从而调整其物理性质以满足所需的应用。在此，我们报告了氢掺杂对 aBN 的稳定性和机械性能的改善。通过在原子模拟中引入高斯近似势，我们研究了 aBN 在不同氢掺杂浓度下的形态变化。我们发现，当氢掺杂浓度为 8 at% 时，sp3 杂化原子的浓度达到最大值，从而使热稳定性和机械性能提高了 20%。这些结果将为实验人员和工艺工程师提供指导，帮助他们调整 aBN 薄膜的生长条件，使其应用于多种领域。
{"title":"Impact of hydrogenation on the stability and mechanical properties of amorphous boron nitride","authors":"Onurcan Kaya, Luigi Colombo, Aleandro Antidormi, Marco A Villena, Mario Lanza, Ivan Cole, Stephan Roche","doi":"10.1088/2515-7639/ad367b","DOIUrl":"https://doi.org/10.1088/2515-7639/ad367b","url":null,"abstract":"Interconnect materials with ultralow dielectric constant, and good thermal and mechanical properties are crucial for the further miniaturization of electronic devices. Recently, it has been demonstrated that ultrathin amorphous boron nitride (aBN) films have a very low dielectric constant, high density (above 2.1 g cm<sup>−3</sup>), high thermal stability, and mechanical properties. The excellent properties of aBN derive from the nature and degree of disorder, which can be controlled at fabrication, allowing tuning of the physical properties for desired applications. Here, we report an improvement in the stability and mechanical properties of aBN upon hydrogen doping. With the introduction of a Gaussian approximation potential for atomistic simulations, we investigate the changing morphology of aBN with varying H doping concentrations. We found that for 8 at% of H doping, the concentration of <italic toggle=\"yes\">sp</italic>\u0000<sup>3</sup>-hybridized atoms reaches to a maximum which leads to an improvement of thermal stability and mechanical properties by 20%. These results will be a guideline for experimentalists and process engineers to tune the growth conditions of aBN films for numerous applications.","PeriodicalId":501825,"journal":{"name":"Journal of Physics: Materials","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-03-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140587578","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Element substitutions with magnetic or non-magnetic atoms are known to significantly impact the magnetic structure and related transport properties of magnets. To clarify the change of magnetic structure of B20-type magnets with element doping, we conduct real-space observations of spin textures and their temperature (T)-magnetic field (H) phase diagrams of a helimagnet FeGe with partially substituting Fe and Ge with Co and Si, respectively. The helical period (λ) changes dramatically by the element doping: λ increases by 147% to 103 nm in 30% Co-doped FeGe, whereas it decreases by around 70% to 49 nm in 30% Si-doped FeGe, compared to the λ =70 nm in FeGe. Upon applying the magnetic field normally to (001), (110), and (111) thin plates of both FeSi0.3Ge0.7 and Fe0.7Co0.3Ge, the hexagonal skyrmion crystal (SkX) state emerges. The magnetic phase diagrams observed through the real-space imaging reveal that (1) the SkX can extend to a larger T-H window by reducing the sample thickness or by cooling the sample under specific magnetic fields from temperatures above the transition temperature (TC); (2) the stability of the SkX phase differs between Si-doped and Co-doped FeGe: the SkX phase is most unstable in the (111) FeSi0.3Ge0.7, while it remains robust in the (111) Fe0.7Co0.3Ge. These differences indicate distinct anisotropic behavior in FeGe with magnetic (Co) and non-magnetic-element (Si) dopants.
众所周知，磁性或非磁性原子的元素置换会显著影响磁体的磁性结构和相关传输特性。为了弄清掺杂元素后 B20 型磁体磁性结构的变化，我们对分别用 Co 和 Si 部分取代 Fe 和 Ge 的螺旋磁体 FeGe 的自旋纹理及其温度（T）-磁场（H）相图进行了实空间观测。螺旋周期（λ）因元素掺杂而发生显著变化：与 FeGe 中的λ = 70 nm 相比，掺杂 30% Co 的 FeGe 中的λ 增加了 147% 至 103 nm，而掺杂 30% Si 的 FeGe 中的λ 则减少了约 70% 至 49 nm。在对FeSi0.3Ge0.7和Fe0.7Co0.3Ge的(001)、(110)和(111)薄板正常施加磁场时，会出现六方天幕晶体（SkX）态。通过实空间成像观察到的磁相图显示：(1) 通过减小样品厚度或在特定磁场下从高于转变温度 (TC) 的温度开始冷却样品，SkX 可以扩展到更大的 T-H 窗口；(2) 掺 Si 和掺 Co 的 FeGe 中 SkX 相的稳定性不同：在 (111) FeSi0.3Ge0.7 中 SkX 相最不稳定，而在 (111) Fe0.7Co0.3Ge 中则保持稳定。这些差异表明，掺杂磁性元素（Co）和非磁性元素（Si）的 FeGe 具有不同的各向异性。
{"title":"Topological stability of spin textures in Si/Co-doped helimagnet FeGe","authors":"Yao Guang, Yukako Fujishiro, Aito Tanaka, Licong Peng, Yoshio Kaneko, Naoya Kanazawa, Yoshinori Tokura, Xiuzhen Yu","doi":"10.1088/2515-7639/ad2ec4","DOIUrl":"https://doi.org/10.1088/2515-7639/ad2ec4","url":null,"abstract":"Element substitutions with magnetic or non-magnetic atoms are known to significantly impact the magnetic structure and related transport properties of magnets. To clarify the change of magnetic structure of B20-type magnets with element doping, we conduct real-space observations of spin textures and their temperature (<italic toggle=\"yes\">T</italic>)-magnetic field (<italic toggle=\"yes\">H</italic>) phase diagrams of a helimagnet FeGe with partially substituting Fe and Ge with Co and Si, respectively. The helical period (<italic toggle=\"yes\">λ</italic>) changes dramatically by the element doping: <italic toggle=\"yes\">λ</italic> increases by 147% to 103 nm in 30% Co-doped FeGe, whereas it decreases by around 70% to 49 nm in 30% Si-doped FeGe, compared to the <italic toggle=\"yes\">λ =</italic>70 nm in FeGe. Upon applying the magnetic field normally to (001), (110), and (111) thin plates of both FeSi<sub>0.3</sub>Ge<sub>0.7</sub> and Fe<sub>0.7</sub>Co<sub>0.3</sub>Ge, the hexagonal skyrmion crystal (SkX) state emerges. The magnetic phase diagrams observed through the real-space imaging reveal that (1) the SkX can extend to a larger <italic toggle=\"yes\">T-H</italic> window by reducing the sample thickness or by cooling the sample under specific magnetic fields from temperatures above the transition temperature (<italic toggle=\"yes\">T<sub>C</sub>\u0000</italic>); (2) the stability of the SkX phase differs between Si-doped and Co-doped FeGe: the SkX phase is most unstable in the (111) FeSi<sub>0.3</sub>Ge<sub>0.7</sub>, while it remains robust in the (111) Fe<sub>0.7</sub>Co<sub>0.3</sub>Ge. These differences indicate distinct anisotropic behavior in FeGe with magnetic (Co) and non-magnetic-element (Si) dopants.","PeriodicalId":501825,"journal":{"name":"Journal of Physics: Materials","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-03-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140316980","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-03-13DOI: 10.1088/2515-7639/ad33a4
Chonghui Zhang, Y. Zhao
The progress of machine learning (ML) in the past years has opened up new opportunities to the design of auxetic metamaterials. However, successful implementation of ML algorithms remains challenging, particularly for complex problems such as domain performance prediction and inverse design. In this paper, we first reviewed classic auxetic designs and summarized their variants in different applications. The enormous variant design space leads to challenges using traditional design or topology optimization. Therefore, we also investigated how ML techniques can help address design challenges of auxetic metamaterials and when researchers should deploy them. The theories behind the techniques are explained, along with practical application examples from the analysed literature. The advantages and limitations of different ML algorithms are discussed and trends in the field are highlighted. Finally, two practical problems of ML-aided design, design scales and data collection are discussed.
过去几年中，机器学习（ML）的进步为辅助超材料的设计带来了新的机遇。然而，成功实施 ML 算法仍具有挑战性，尤其是对于域性能预测和反设计等复杂问题。在本文中，我们首先回顾了经典的辅助设计，并总结了它们在不同应用中的变体。巨大的变体设计空间给传统设计或拓扑优化带来了挑战。因此，我们还研究了 ML 技术如何帮助解决辅助超材料的设计难题，以及研究人员应在何时使用这些技术。我们解释了这些技术背后的理论，并列举了分析文献中的实际应用实例。讨论了不同 ML 算法的优势和局限性，并强调了该领域的发展趋势。最后，讨论了 ML 辅助设计的两个实际问题：设计规模和数据收集。
{"title":"A Critical Review on the Application of Machine Learning in Supporting Auxetic Metamaterial Design","authors":"Chonghui Zhang, Y. Zhao","doi":"10.1088/2515-7639/ad33a4","DOIUrl":"https://doi.org/10.1088/2515-7639/ad33a4","url":null,"abstract":"\u0000 The progress of machine learning (ML) in the past years has opened up new opportunities to the design of auxetic metamaterials. However, successful implementation of ML algorithms remains challenging, particularly for complex problems such as domain performance prediction and inverse design. In this paper, we first reviewed classic auxetic designs and summarized their variants in different applications. The enormous variant design space leads to challenges using traditional design or topology optimization. Therefore, we also investigated how ML techniques can help address design challenges of auxetic metamaterials and when researchers should deploy them. The theories behind the techniques are explained, along with practical application examples from the analysed literature. The advantages and limitations of different ML algorithms are discussed and trends in the field are highlighted. Finally, two practical problems of ML-aided design, design scales and data collection are discussed.","PeriodicalId":501825,"journal":{"name":"Journal of Physics: Materials","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-03-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140247773","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-03-12DOI: 10.1088/2515-7639/ad2ec5
T Z Ward, R P Wilkerson, B L Musicó, A Foley, M Brahlek, W J Weber, K E Sickafus, A R Mazza
Compositionally complex materials have demonstrated extraordinary promise for structural robustness in extreme environments. Of these, the most commonly thought of are high entropy alloys, where chemical complexity grants uncommon combinations of hardness, ductility, and thermal resilience. In contrast to these metal–metal bonded systems, the addition of ionic and covalent bonding has led to the discovery of high entropy ceramics (HECs). These materials also possess outstanding structural, thermal, and chemical robustness but with a far greater variety of functional properties which enable access to continuously controllable magnetic, electronic, and optical phenomena. In this experimentally focused perspective, we outline the potential for HECs in functional applications under extreme environments, where intrinsic stability may provide a new path toward inherently hardened device design. Current works on high entropy carbides, actinide bearing ceramics, and high entropy oxides are reviewed in the areas of radiation, high temperature, and corrosion tolerance where the role of local disorder is shown to create pathways toward self-healing and structural robustness. In this context, new strategies for creating future electronic, magnetic, and optical devices to be operated in harsh environments are outlined.
{"title":"High entropy ceramics for applications in extreme environments","authors":"T Z Ward, R P Wilkerson, B L Musicó, A Foley, M Brahlek, W J Weber, K E Sickafus, A R Mazza","doi":"10.1088/2515-7639/ad2ec5","DOIUrl":"https://doi.org/10.1088/2515-7639/ad2ec5","url":null,"abstract":"Compositionally complex materials have demonstrated extraordinary promise for structural robustness in extreme environments. Of these, the most commonly thought of are high entropy alloys, where chemical complexity grants uncommon combinations of hardness, ductility, and thermal resilience. In contrast to these metal–metal bonded systems, the addition of ionic and covalent bonding has led to the discovery of high entropy ceramics (HECs). These materials also possess outstanding structural, thermal, and chemical robustness but with a far greater variety of functional properties which enable access to continuously controllable magnetic, electronic, and optical phenomena. In this experimentally focused perspective, we outline the potential for HECs in functional applications under extreme environments, where intrinsic stability may provide a new path toward inherently hardened device design. Current works on high entropy carbides, actinide bearing ceramics, and high entropy oxides are reviewed in the areas of radiation, high temperature, and corrosion tolerance where the role of local disorder is shown to create pathways toward self-healing and structural robustness. In this context, new strategies for creating future electronic, magnetic, and optical devices to be operated in harsh environments are outlined.","PeriodicalId":501825,"journal":{"name":"Journal of Physics: Materials","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-03-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140317004","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-03-07DOI: 10.1088/2515-7639/ad2d5e
Alfons G Schuck, Sebastian Kölsch, Adrian Valadkhani, Igor I Mazin, Roser Valentí, Michael Huth
Europium intermetallic compounds show a variety of different ground states and anomalous physical properties due to the interactions between the localized 4f electrons and the delocalized electronic states. Europium is also the most reactive of the rare earth metals which might be the reason why very few works are concerned with the properties of Eu-based thin films. Here we address the low-temperature magnetic properties of ferromagnetic EuPd2 thin films prepared by molecular beam epitaxy. The epitaxial (111)-oriented thin films grow on MgO (100) with eight different domain orientations. We analyze the low-temperature magnetic hysteresis behavior by means of micromagnetic simulations taking the multi-domain morphology explicitly into account and quantify the magnetic crystal anisotropy contribution. By ab initio calculations we trace back the microscopic origin of the magnetic anisotropy to thin film-induced uniform biaxial strain.
由于局域 4f 电子和脱局域电子态之间的相互作用，铕金属间化合物显示出各种不同的基态和异常物理性质。铕也是稀土金属中反应性最强的一种，这可能是很少有人研究铕基薄膜特性的原因。在此，我们探讨了分子束外延法制备的铁磁性 EuPd2 薄膜的低温磁性能。外延 (111) 取向薄膜生长在氧化镁 (100) 上，具有八种不同的畴取向。我们通过微磁模拟分析了低温磁滞行为，明确考虑了多畴体形态，并量化了磁晶体各向异性的贡献。通过 ab initio 计算，我们将磁各向异性的微观起源追溯到薄膜引起的均匀双轴应变。
{"title":"Strain-induced magnetic anisotropy of multi-domain epitaxial EuPd2 thin films","authors":"Alfons G Schuck, Sebastian Kölsch, Adrian Valadkhani, Igor I Mazin, Roser Valentí, Michael Huth","doi":"10.1088/2515-7639/ad2d5e","DOIUrl":"https://doi.org/10.1088/2515-7639/ad2d5e","url":null,"abstract":"Europium intermetallic compounds show a variety of different ground states and anomalous physical properties due to the interactions between the localized 4f electrons and the delocalized electronic states. Europium is also the most reactive of the rare earth metals which might be the reason why very few works are concerned with the properties of Eu-based thin films. Here we address the low-temperature magnetic properties of ferromagnetic EuPd<sub>2</sub> thin films prepared by molecular beam epitaxy. The epitaxial (111)-oriented thin films grow on MgO (100) with eight different domain orientations. We analyze the low-temperature magnetic hysteresis behavior by means of micromagnetic simulations taking the multi-domain morphology explicitly into account and quantify the magnetic crystal anisotropy contribution. By <italic toggle=\"yes\">ab initio</italic> calculations we trace back the microscopic origin of the magnetic anisotropy to thin film-induced uniform biaxial strain.","PeriodicalId":501825,"journal":{"name":"Journal of Physics: Materials","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-03-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140311424","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-03-04DOI: 10.1088/2515-7639/ad2b7b
Yueting Yang, Zhuojun Duan, Huimin Li, Song Liu
The twist angle regulation strategy provides a feasible tool for studying the emerging properties of transition metal dichalcogenides (TMDCs). For the twisted TMDCs (t-TMDCs), there is the lattice mismatch and twist between layers, thus forming moiré superlattice. The formation of moiré superlattice brings about innovative properties to the t-TMDCs. These innovative properties have attracted more and more attention from researchers. This review firstly focuses on the synthesis methods of t-TMDCs, as well as the merits and shortcomings of each method. Secondly, the common spectral characterization and microscopic characterization methods are discussed. Thirdly, the prominent properties of t-TMDCs are briefly demonstrated, including ferroelectricity, flat band, and interlaminar excitons. Finally, we look forward to the potential application prospect and research direction of t-TMDCs.
{"title":"Advance in twisted transition metal dichalcogenides: synthesis, characterization, and properties","authors":"Yueting Yang, Zhuojun Duan, Huimin Li, Song Liu","doi":"10.1088/2515-7639/ad2b7b","DOIUrl":"https://doi.org/10.1088/2515-7639/ad2b7b","url":null,"abstract":"The twist angle regulation strategy provides a feasible tool for studying the emerging properties of transition metal dichalcogenides (TMDCs). For the twisted TMDCs (t-TMDCs), there is the lattice mismatch and twist between layers, thus forming moiré superlattice. The formation of moiré superlattice brings about innovative properties to the t-TMDCs. These innovative properties have attracted more and more attention from researchers. This review firstly focuses on the synthesis methods of t-TMDCs, as well as the merits and shortcomings of each method. Secondly, the common spectral characterization and microscopic characterization methods are discussed. Thirdly, the prominent properties of t-TMDCs are briefly demonstrated, including ferroelectricity, flat band, and interlaminar excitons. Finally, we look forward to the potential application prospect and research direction of t-TMDCs.","PeriodicalId":501825,"journal":{"name":"Journal of Physics: Materials","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-03-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140311485","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-03-01DOI: 10.1088/2515-7639/ad2983
Arslan Mazitov, Maximilian A Springer, Nataliya Lopanitsyna, Guillaume Fraux, Sandip De, Michele Ceriotti
High-entropy alloys (HEAs), containing several metallic elements in near-equimolar proportions, have long been of interest for their unique mechanical properties. More recently, they have emerged as a promising platform for the development of novel heterogeneous catalysts, because of the large design space, and the synergistic effects between their components. In this work we use a machine-learning potential that can model simultaneously up to 25 transition metals to study the tendency of different elements to segregate at the surface of a HEA. We use as a starting point a potential that was previously developed using exclusively crystalline bulk phases, and show that, thanks to the physically-inspired functional form of the model, adding a much smaller number of defective configurations makes it capable of describing surface phenomena. We then present several computational studies of surface segregation, including both a simulation of a 25-element alloy, that provides a rough estimate of the relative surface propensity of the various elements, and targeted studies of CoCrFeMnNi and IrFeCoNiCu, which provide further validation of the model, and insights to guide the modeling and design of alloys for heterogeneous catalysis.
{"title":"Surface segregation in high-entropy alloys from alchemical machine learning","authors":"Arslan Mazitov, Maximilian A Springer, Nataliya Lopanitsyna, Guillaume Fraux, Sandip De, Michele Ceriotti","doi":"10.1088/2515-7639/ad2983","DOIUrl":"https://doi.org/10.1088/2515-7639/ad2983","url":null,"abstract":"High-entropy alloys (HEAs), containing several metallic elements in near-equimolar proportions, have long been of interest for their unique mechanical properties. More recently, they have emerged as a promising platform for the development of novel heterogeneous catalysts, because of the large design space, and the synergistic effects between their components. In this work we use a machine-learning potential that can model simultaneously up to 25 transition metals to study the tendency of different elements to segregate at the surface of a HEA. We use as a starting point a potential that was previously developed using exclusively crystalline bulk phases, and show that, thanks to the physically-inspired functional form of the model, adding a much smaller number of defective configurations makes it capable of describing surface phenomena. We then present several computational studies of surface segregation, including both a simulation of a 25-element alloy, that provides a rough estimate of the relative surface propensity of the various elements, and targeted studies of CoCrFeMnNi and IrFeCoNiCu, which provide further validation of the model, and insights to guide the modeling and design of alloys for heterogeneous catalysis.","PeriodicalId":501825,"journal":{"name":"Journal of Physics: Materials","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140311518","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-02-14DOI: 10.1088/2515-7639/ad261a
K Nepal, C Ugwumadu, A Gautam, Keerti Kappagantula, D A Drabold
This paper explores the transport properties of aluminum-carbon composite material via ab initio methods. Interfacial and electronic dynamics of the aluminum-graphene interface structure were investigated using models of amorphous graphene added to an aluminum matrix. We examine the impact on electronic conduction caused by the presence of nitrogen impurities within the interfacial amorphous graphene layer. We elucidate the conduction mechanisms by using a projection of the electronic conductivity into space.
本文通过 ab initio 方法探讨了铝碳复合材料的传输特性。利用添加到铝基体中的无定形石墨烯模型，研究了铝-石墨烯界面结构的界面动力学和电子动力学。我们研究了界面无定形石墨烯层中氮杂质的存在对电子传导的影响。我们利用电子传导性的空间投影来阐明传导机制。
{"title":"Electronic conductivity in metal-graphene composites: the role of disordered carbon structures, defects, and impurities","authors":"K Nepal, C Ugwumadu, A Gautam, Keerti Kappagantula, D A Drabold","doi":"10.1088/2515-7639/ad261a","DOIUrl":"https://doi.org/10.1088/2515-7639/ad261a","url":null,"abstract":"This paper explores the transport properties of aluminum-carbon composite material via <italic toggle=\"yes\">ab initio</italic> methods. Interfacial and electronic dynamics of the aluminum-graphene interface structure were investigated using models of amorphous graphene added to an aluminum matrix. We examine the impact on electronic conduction caused by the presence of nitrogen impurities within the interfacial amorphous graphene layer. We elucidate the conduction mechanisms by using a projection of the electronic conductivity into space.","PeriodicalId":501825,"journal":{"name":"Journal of Physics: Materials","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-02-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140010680","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-02-09DOI: 10.1088/2515-7639/ad229a
Esteban Rojas-Gatjens, David Otto Tiede, Katherine A Koch, Carlos Romero-Perez, Juan F Galisteo-López, Mauricio E Calvo, Hernán Míguez, Ajay Ram Srimath Kandada
The surface chemistry and inter-connectivity within perovskite nanocrystals play a critical role in determining the electronic interactions. They manifest in the Coulomb screening of electron–hole correlations and the carrier relaxation dynamics, among other many-body processes. Here, we characterize the coupling between the exciton and free carrier states close to the band-edge in a ligand-free formamidinium lead bromide nanocrystal assembly via two-dimensional coherent spectroscopy. The optical signatures observed in this work show: (i) a nonlinear spectral lineshape reminiscent of Fano-like interference that evidences the coupling between discrete electronic states and a continuum, (ii) symmetric excited state absorption cross-peaks that suggest the existence of a coupled exciton-carrier excited state, and (iii) ultrafast carrier thermalization and exciton formation. Our results highlight the presence of coherent coupling between exciton and free carriers, particularly in the sub-100 femtosecond timescales.
{"title":"Exciton-carrier coupling in a metal halide perovskite nanocrystal assembly probed by two-dimensional coherent spectroscopy","authors":"Esteban Rojas-Gatjens, David Otto Tiede, Katherine A Koch, Carlos Romero-Perez, Juan F Galisteo-López, Mauricio E Calvo, Hernán Míguez, Ajay Ram Srimath Kandada","doi":"10.1088/2515-7639/ad229a","DOIUrl":"https://doi.org/10.1088/2515-7639/ad229a","url":null,"abstract":"The surface chemistry and inter-connectivity within perovskite nanocrystals play a critical role in determining the electronic interactions. They manifest in the Coulomb screening of electron–hole correlations and the carrier relaxation dynamics, among other many-body processes. Here, we characterize the coupling between the exciton and free carrier states close to the band-edge in a ligand-free formamidinium lead bromide nanocrystal assembly via two-dimensional coherent spectroscopy. The optical signatures observed in this work show: (i) a nonlinear spectral lineshape reminiscent of Fano-like interference that evidences the coupling between discrete electronic states and a continuum, (ii) symmetric excited state absorption cross-peaks that suggest the existence of a coupled exciton-carrier excited state, and (iii) ultrafast carrier thermalization and exciton formation. Our results highlight the presence of coherent coupling between exciton and free carriers, particularly in the sub-100 femtosecond timescales.","PeriodicalId":501825,"journal":{"name":"Journal of Physics: Materials","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-02-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139770107","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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