Strain sensors based on porous conductive polymers (CPCs) have garnered growing research interest for their potential applications in motion detection, healthcare, human–computer interaction, and artificial intelligence. However, the complexity of CPC processing makes it difficult to achieve the controlled design of microscopic porous structures, leading to simple and random porous structures, thus limiting their further use in the field of pressure sensing. This paper presents a strain sensor with a high-performance, wood-like structure composed of flexible conductive carbon black/plastic polyurethane foam (BWCT) using a bidirectional freeze casting process. The results show that, compared with conventional random freezing and unidirectional freezing, the bidirectional freeze casting process can effectively realize multiscale control of the composite structure, which results in a good laminar porous structure of the prepared BWCT. This parallel laminar structure not only contributes to the layered transfer of stresses but also avoids the local concentration of stresses. At the same time, it significantly increases the directional electrical conduction ability, which results in high sensing stability performance. In particular, the BWCT sensors had a wide detection range (80%), a lower limit of detection (0.2%), rapid response and relaxation times (200 ms), as well as exceptional durability (>2000 cycles). Furthermore, the BWCT was integrated into a wearable sensor to monitor various human motions, including arm bending, squatting, and walking, demonstrating reliable detection performance. Altogether, the BWCT sensors are promising in expanding the application but also offer guidance for designing high-performance wearable strain sensors.
{"title":"Nature-inspired wood-like TPU/CB aerogels for high performance flexible strain sensors","authors":"Guanyu Wang, Yadong Yang, Wenzhe Cao, Caichao Wan","doi":"10.1063/5.0205597","DOIUrl":"https://doi.org/10.1063/5.0205597","url":null,"abstract":"Strain sensors based on porous conductive polymers (CPCs) have garnered growing research interest for their potential applications in motion detection, healthcare, human–computer interaction, and artificial intelligence. However, the complexity of CPC processing makes it difficult to achieve the controlled design of microscopic porous structures, leading to simple and random porous structures, thus limiting their further use in the field of pressure sensing. This paper presents a strain sensor with a high-performance, wood-like structure composed of flexible conductive carbon black/plastic polyurethane foam (BWCT) using a bidirectional freeze casting process. The results show that, compared with conventional random freezing and unidirectional freezing, the bidirectional freeze casting process can effectively realize multiscale control of the composite structure, which results in a good laminar porous structure of the prepared BWCT. This parallel laminar structure not only contributes to the layered transfer of stresses but also avoids the local concentration of stresses. At the same time, it significantly increases the directional electrical conduction ability, which results in high sensing stability performance. In particular, the BWCT sensors had a wide detection range (80%), a lower limit of detection (0.2%), rapid response and relaxation times (200 ms), as well as exceptional durability (>2000 cycles). Furthermore, the BWCT was integrated into a wearable sensor to monitor various human motions, including arm bending, squatting, and walking, demonstrating reliable detection performance. Altogether, the BWCT sensors are promising in expanding the application but also offer guidance for designing high-performance wearable strain sensors.","PeriodicalId":7985,"journal":{"name":"APL Materials","volume":"9 1","pages":""},"PeriodicalIF":6.1,"publicationDate":"2024-05-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140930590","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
S. Krishnia, B. Bony, E. Rongione, L. Moreno Vicente-Arche, T. Denneulin, A. Pezo, Y. Lu, R. E. Dunin-Borkowski, S. Collin, A. Fert, J.-M. George, N. Reyren, V. Cros, H. Jaffrès
The generation of large spin currents, and the associated spin torques, which are at the heart of modern spintronics, has long been achieved by charge-to-spin conversion mechanisms, i.e., the spin Hall effect and/or the Rashba–Edelstein effect, intrinsically linked to strong spin–orbit coupling. Recently, a novel path has been predicted and observed for achieving significant current-induced torques originating from light elements, hence possessing weak spin–orbit interaction. These findings point out to the potential involvement of the orbital counterpart of electrons, namely the orbital Hall and orbital Rashba–Edelstein effects. In this study, we aim at quantifying these orbital-related contributions to the effective torques acting on a thin Co layer in different systems. First, we demonstrate in Pt|Co|Cu|AlOx stacking a comparable torque strength coming from the conversion due to the orbital Rashba–Edelstein effect at the Cu|AlOx interface and the one from the effective spin Hall effect in the bottom Pt|Co system. Second, in order to amplify the orbital-to-spin conversion, we investigate the impact of an intermediate Pt layer in Co|Pt|Cu|CuOx. From the Pt thickness dependence of the effective torques determined by harmonic Hall measurements complemented by spin Hall magneto-resistance and THz spectroscopy experiments, we demonstrate that a large orbital Rashba–Edelstein effect is present at the Cu|CuOx interface, leading to a twofold enhancement of the net torques on Co for the optimal Pt thickness. Our findings not only demonstrate the crucial role that orbital currents can play in low-dimensional systems with weak spin–orbit coupling but also reveal that they enable more energy efficient manipulation of magnetization in spintronic devices.
作为现代自旋电子学核心的大自旋电流和相关自旋转矩的产生，长期以来一直是通过电荷-自旋转换机制（即自旋霍尔效应和/或拉什巴-爱德斯坦效应）实现的，这与强自旋轨道耦合有着内在联系。最近，人们预测并观察到了一种新的途径，即通过轻元素（因此具有弱自旋轨道相互作用）实现显著的电流诱导转矩。这些发现指出了电子轨道对应物的潜在参与，即轨道霍尔效应和轨道拉什巴-爱德斯坦效应。在本研究中，我们旨在量化这些轨道效应对不同体系中作用于 Co 薄层的有效转矩的贡献。首先，我们证明了在 Pt|Co|Cu|AlOx 堆叠中，Cu|AlOx 界面的轨道 Rashba-Edelstein 效应和底部 Pt|Co 系统的有效自旋霍尔效应所产生的转换扭矩强度相当。其次，为了放大轨道到自旋的转换，我们研究了 Co|Pt|Cu|CuOx 中中间铂层的影响。通过谐波霍尔测量以及自旋霍尔磁阻和太赫兹光谱实验确定的有效转矩的铂厚度依赖性，我们证明了在 Cu|CuOx 界面存在着巨大的轨道拉什巴-爱德斯坦效应，从而导致在最佳铂厚度下 Co 上的净转矩增强了两倍。我们的发现不仅证明了轨道电流在自旋轨道耦合较弱的低维系统中可以发挥关键作用，而且揭示了轨道电流可以在自旋电子器件中实现更高效的磁化操纵。
{"title":"Quantifying the large contribution from orbital Rashba–Edelstein effect to the effective damping-like torque on magnetization","authors":"S. Krishnia, B. Bony, E. Rongione, L. Moreno Vicente-Arche, T. Denneulin, A. Pezo, Y. Lu, R. E. Dunin-Borkowski, S. Collin, A. Fert, J.-M. George, N. Reyren, V. Cros, H. Jaffrès","doi":"10.1063/5.0198970","DOIUrl":"https://doi.org/10.1063/5.0198970","url":null,"abstract":"The generation of large spin currents, and the associated spin torques, which are at the heart of modern spintronics, has long been achieved by charge-to-spin conversion mechanisms, i.e., the spin Hall effect and/or the Rashba–Edelstein effect, intrinsically linked to strong spin–orbit coupling. Recently, a novel path has been predicted and observed for achieving significant current-induced torques originating from light elements, hence possessing weak spin–orbit interaction. These findings point out to the potential involvement of the orbital counterpart of electrons, namely the orbital Hall and orbital Rashba–Edelstein effects. In this study, we aim at quantifying these orbital-related contributions to the effective torques acting on a thin Co layer in different systems. First, we demonstrate in Pt|Co|Cu|AlOx stacking a comparable torque strength coming from the conversion due to the orbital Rashba–Edelstein effect at the Cu|AlOx interface and the one from the effective spin Hall effect in the bottom Pt|Co system. Second, in order to amplify the orbital-to-spin conversion, we investigate the impact of an intermediate Pt layer in Co|Pt|Cu|CuOx. From the Pt thickness dependence of the effective torques determined by harmonic Hall measurements complemented by spin Hall magneto-resistance and THz spectroscopy experiments, we demonstrate that a large orbital Rashba–Edelstein effect is present at the Cu|CuOx interface, leading to a twofold enhancement of the net torques on Co for the optimal Pt thickness. Our findings not only demonstrate the crucial role that orbital currents can play in low-dimensional systems with weak spin–orbit coupling but also reveal that they enable more energy efficient manipulation of magnetization in spintronic devices.","PeriodicalId":7985,"journal":{"name":"APL Materials","volume":"16 1","pages":""},"PeriodicalIF":6.1,"publicationDate":"2024-05-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140930667","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Olivio Chiatti, Johannes Boy, Christian Heyn, Wolfgang Hansen, Saskia F. Fischer
The crossover from quasi-two- to quasi-one-dimensional electron transport subject to transverse electric fields and perpendicular magnetic fields is studied in the diffusive to quasi-ballistic and zero-field to quantum Hall regime. In-plane gates and Hall-bars have been fabricated from an InGaAs/InAlAs/InAs quantum well hosting a 2DEG with a carrier density of about 6.8 × 1011 cm−2, a mobility of 1.8 × 105 cm2/Vs, and an effective mass of 0.042me after illumination. Magnetotransport measurements at temperatures down to 50 mK and fields up to 12 T yield a high effective Landé factor of g*=16, enabling the resolution of spin-split subbands at magnetic fields of 2.5 T. In the quantum Hall regime, electrostatic control of an effective constriction width enables steering of the reflection and transmission of edge channels, allowing a separation of fully spin-polarized edge channels at filling factors ν = 1 und ν = 2. A change in the orientation of a transverse in-plane electric field in the constriction shifts the transition between Zeeman-split quantum Hall plateaus by ΔB ≈ 0.1 T and is consistent with an effective magnetic field of Beff ≈ 0.13 T by spin-dependent backscattering, indicating a change in the spin-split density of states.
{"title":"In-plane gate induced transition asymmetry of spin-resolved Landau levels in InAs-based quantum wells","authors":"Olivio Chiatti, Johannes Boy, Christian Heyn, Wolfgang Hansen, Saskia F. Fischer","doi":"10.1063/5.0203097","DOIUrl":"https://doi.org/10.1063/5.0203097","url":null,"abstract":"The crossover from quasi-two- to quasi-one-dimensional electron transport subject to transverse electric fields and perpendicular magnetic fields is studied in the diffusive to quasi-ballistic and zero-field to quantum Hall regime. In-plane gates and Hall-bars have been fabricated from an InGaAs/InAlAs/InAs quantum well hosting a 2DEG with a carrier density of about 6.8 × 1011 cm−2, a mobility of 1.8 × 105 cm2/Vs, and an effective mass of 0.042me after illumination. Magnetotransport measurements at temperatures down to 50 mK and fields up to 12 T yield a high effective Landé factor of g*=16, enabling the resolution of spin-split subbands at magnetic fields of 2.5 T. In the quantum Hall regime, electrostatic control of an effective constriction width enables steering of the reflection and transmission of edge channels, allowing a separation of fully spin-polarized edge channels at filling factors ν = 1 und ν = 2. A change in the orientation of a transverse in-plane electric field in the constriction shifts the transition between Zeeman-split quantum Hall plateaus by ΔB ≈ 0.1 T and is consistent with an effective magnetic field of Beff ≈ 0.13 T by spin-dependent backscattering, indicating a change in the spin-split density of states.","PeriodicalId":7985,"journal":{"name":"APL Materials","volume":"42 1","pages":""},"PeriodicalIF":6.1,"publicationDate":"2024-05-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140930444","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Isabel Streicher, Patrik Straňák, Lutz Kirste, Mario Prescher, Stefan Müller, Stefano Leone
Wurtzite AlN alloyed with group 3 elements Sc and Y boosts the performance of GaN-based high-electron-mobility transistors (HEMTs) significantly as they increase the spontaneous polarization of the barrier layer and, thus, enhance the charge carrier density ns in the two-dimensional electron gas (2DEG) formed at the interface with the GaN channel. The emerging nitride Al1−xYxN additionally features an a lattice parameter matching to that of GaN at x = 0.07–0.11, allowing for the growth of strain-free barriers. Here, we demonstrate the growth of Al1−xYxN/GaN heterostructures for HEMTs by metal–organic chemical vapor deposition for the first time. The effect of the Y concentrations on the 2DEG is investigated in a Y concentration range from 3% to 15%. At 8% Y, a record mobility of 3200 cm2/(Vs) was measured at a low temperature (7 K). Room and low-temperature ns was at 1–2 × 1013 cm−2. Al0.92Y0.08N barriers were coherently strained to the GaN channel for barrier thicknesses from 5 to 15 nm. Finally, the deposition of Al1−xYxN/GaN heterostructures deposited on 4″ 4H–SiC wafers had a room-temperature mobility close to 1400 cm2/(Vs). AlYN/GaN heterostructures may offer advantages over AlScN/GaN heterostructures not only for the lower price and higher abundance of the raw material but also in terms of electrical characteristics and may be more suitable for power amplifying applications due to increased electron mobility.
{"title":"Two-dimensional electron gases in AlYN/GaN heterostructures grown by metal–organic chemical vapor deposition","authors":"Isabel Streicher, Patrik Straňák, Lutz Kirste, Mario Prescher, Stefan Müller, Stefano Leone","doi":"10.1063/5.0203156","DOIUrl":"https://doi.org/10.1063/5.0203156","url":null,"abstract":"Wurtzite AlN alloyed with group 3 elements Sc and Y boosts the performance of GaN-based high-electron-mobility transistors (HEMTs) significantly as they increase the spontaneous polarization of the barrier layer and, thus, enhance the charge carrier density ns in the two-dimensional electron gas (2DEG) formed at the interface with the GaN channel. The emerging nitride Al1−xYxN additionally features an a lattice parameter matching to that of GaN at x = 0.07–0.11, allowing for the growth of strain-free barriers. Here, we demonstrate the growth of Al1−xYxN/GaN heterostructures for HEMTs by metal–organic chemical vapor deposition for the first time. The effect of the Y concentrations on the 2DEG is investigated in a Y concentration range from 3% to 15%. At 8% Y, a record mobility of 3200 cm2/(Vs) was measured at a low temperature (7 K). Room and low-temperature ns was at 1–2 × 1013 cm−2. Al0.92Y0.08N barriers were coherently strained to the GaN channel for barrier thicknesses from 5 to 15 nm. Finally, the deposition of Al1−xYxN/GaN heterostructures deposited on 4″ 4H–SiC wafers had a room-temperature mobility close to 1400 cm2/(Vs). AlYN/GaN heterostructures may offer advantages over AlScN/GaN heterostructures not only for the lower price and higher abundance of the raw material but also in terms of electrical characteristics and may be more suitable for power amplifying applications due to increased electron mobility.","PeriodicalId":7985,"journal":{"name":"APL Materials","volume":"24 1","pages":""},"PeriodicalIF":6.1,"publicationDate":"2024-05-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140930592","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Oxide ionotronics is an interdisciplinary field in which systems and devices rely on the migration of ions/ionic defects to alter or drive functionality. In this perspective, we focus on epitaxial oxide heterostructures and the contributing roles of oxygen vacancies and interfaces in ionotronics. We begin with a description of oxygen vacancy behavior, with a focus on vacancy ordering and the effects of interfaces and electric fields on particular epitaxial oxide systems. We then emphasize the use of synchrotron x-ray techniques for investigating system structure and dynamics in situ at interfaces and surfaces. Finally, an outlook on the future of epitaxial oxide ionotronics is provided, and several key areas for research are identified, such as freestanding heterostructures, combinatorial synthesis and machine learning, and next-generation synchrotron x-ray characterization.
氧化物离子电子学是一个跨学科领域，其中的系统和器件依靠离子/离子缺陷的迁移来改变或驱动功能。在这一视角中，我们重点关注外延氧化物异质结构以及氧空位和界面在离子电子学中的作用。我们首先描述了氧空位行为，重点是空位排序以及界面和电场对特定外延氧化物系统的影响。然后，我们强调使用同步辐射 X 射线技术在界面和表面现场研究系统结构和动力学。最后，我们展望了外延氧化物离子电子学的未来，并确定了几个关键的研究领域，如独立异质结构、组合合成和机器学习，以及下一代同步辐射 X 射线表征。
{"title":"Epitaxial oxide ionotronics: Interfaces and oxygen vacancies","authors":"Jill K. Wenderott, Tadesse Billo, Dillon D. Fong","doi":"10.1063/5.0206822","DOIUrl":"https://doi.org/10.1063/5.0206822","url":null,"abstract":"Oxide ionotronics is an interdisciplinary field in which systems and devices rely on the migration of ions/ionic defects to alter or drive functionality. In this perspective, we focus on epitaxial oxide heterostructures and the contributing roles of oxygen vacancies and interfaces in ionotronics. We begin with a description of oxygen vacancy behavior, with a focus on vacancy ordering and the effects of interfaces and electric fields on particular epitaxial oxide systems. We then emphasize the use of synchrotron x-ray techniques for investigating system structure and dynamics in situ at interfaces and surfaces. Finally, an outlook on the future of epitaxial oxide ionotronics is provided, and several key areas for research are identified, such as freestanding heterostructures, combinatorial synthesis and machine learning, and next-generation synchrotron x-ray characterization.","PeriodicalId":7985,"journal":{"name":"APL Materials","volume":"47 1","pages":""},"PeriodicalIF":6.1,"publicationDate":"2024-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140832860","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The magneto-optical Kerr effect (MOKE) in monodomain bismuth ferrite (BiFeO3) thin films was investigated under applied electric fields and light irradiation. The field-swept MOKE measurements show that the Kerr rotation of BiFeO3 changes under applied electric fields or light irradiation. The piezoresponse force microscopy measurements found that the variation in electrical polarization at the BiFeO3 surface was similar under an applied electric field and ultraviolet irradiation, confirming that the Kerr rotation of BiFeO3 can be controlled using both electric fields and light irradiation. This paper presents a method to couple a magnetic field with an electric field or light irradiation via the Kerr angle measurements of BiFeO3, providing a concept for fabricating multifunctional devices in oxide electronics.
{"title":"Measurement of the coupling of magnetism with electricity or light irradiation in BiFeO3 using the Kerr angle","authors":"Siwat Polin, Peerawat Laohana, Jirapat Kullapapinyokol, Warakorn Jindata, Supansa Musikajaroen, Aissara Rasritat, Hideki Nakajima, Wittawat Saenrang, Santi Maensiri, Chang-Beom Eom, Worawat Meevasana","doi":"10.1063/5.0194274","DOIUrl":"https://doi.org/10.1063/5.0194274","url":null,"abstract":"The magneto-optical Kerr effect (MOKE) in monodomain bismuth ferrite (BiFeO3) thin films was investigated under applied electric fields and light irradiation. The field-swept MOKE measurements show that the Kerr rotation of BiFeO3 changes under applied electric fields or light irradiation. The piezoresponse force microscopy measurements found that the variation in electrical polarization at the BiFeO3 surface was similar under an applied electric field and ultraviolet irradiation, confirming that the Kerr rotation of BiFeO3 can be controlled using both electric fields and light irradiation. This paper presents a method to couple a magnetic field with an electric field or light irradiation via the Kerr angle measurements of BiFeO3, providing a concept for fabricating multifunctional devices in oxide electronics.","PeriodicalId":7985,"journal":{"name":"APL Materials","volume":"95 1","pages":""},"PeriodicalIF":6.1,"publicationDate":"2024-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140833084","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Dianxiang Ji, Yi Zhang, Wei Mao, Min Gu, Yiping Xiao, Yang Yang, Wei Guo, Zhengbin Gu, Jian Zhou, Peng Wang, Yuefeng Nie, Xiaoqing Pan
Atomic-level control of complex oxide heterostructure interfaces has resulted in unprecedented properties and functionalities. The majority of oxide heterointerfaces being intensively investigated maintain lattice coherence and exhibit a flawless epitaxial alignment between the films and the substrates. Here, we report the engineering of a charged incoherent BiFeO3/SrTiO3 interface using a tailored deposition sequence in reactive oxide molecular beam epitaxy. By introducing an additional iron oxide layer to disrupt the lattice coherence at the interface, the overlying BiFeO3 is stabilized in a tetragonal phase with its enhanced ferroelectric polarization pointing toward the SrTiO3 substrate, which drives free electrons to accumulate at the incoherent interface. Our findings reveal how controlling lattice coherence at oxide heterointerfaces can open new avenues for fabricating artificial oxide heterostructures with unique properties through precise interface engineering.
{"title":"Engineering of a charged incoherent BiFeO3/SrTiO3 interface","authors":"Dianxiang Ji, Yi Zhang, Wei Mao, Min Gu, Yiping Xiao, Yang Yang, Wei Guo, Zhengbin Gu, Jian Zhou, Peng Wang, Yuefeng Nie, Xiaoqing Pan","doi":"10.1063/5.0203518","DOIUrl":"https://doi.org/10.1063/5.0203518","url":null,"abstract":"Atomic-level control of complex oxide heterostructure interfaces has resulted in unprecedented properties and functionalities. The majority of oxide heterointerfaces being intensively investigated maintain lattice coherence and exhibit a flawless epitaxial alignment between the films and the substrates. Here, we report the engineering of a charged incoherent BiFeO3/SrTiO3 interface using a tailored deposition sequence in reactive oxide molecular beam epitaxy. By introducing an additional iron oxide layer to disrupt the lattice coherence at the interface, the overlying BiFeO3 is stabilized in a tetragonal phase with its enhanced ferroelectric polarization pointing toward the SrTiO3 substrate, which drives free electrons to accumulate at the incoherent interface. Our findings reveal how controlling lattice coherence at oxide heterointerfaces can open new avenues for fabricating artificial oxide heterostructures with unique properties through precise interface engineering.","PeriodicalId":7985,"journal":{"name":"APL Materials","volume":"30 1","pages":""},"PeriodicalIF":6.1,"publicationDate":"2024-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140833142","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Shuyu Cheng, Binzhi Liu, Igor Lyalin, Wenyi Zhou, Jinwoo Hwang, Roland K. Kawakami
Kagome lattices have garnered substantial interest because their band structure consists of topological flat bands and Dirac cones. The RMn6Sn6 (R = rare earth) compounds are particularly interesting because of the existence of the large intrinsic anomalous Hall effect (AHE), which originates from the gapped Dirac cones near the Fermi level. This makes RMn6Sn6 an outstanding candidate for realizing the high-temperature quantum AHE. The growth of RMn6Sn6 thin films is beneficial for both fundamental research and potential applications. However, most of the studies on RMn6Sn6 have focused on bulk crystals, and the synthesis of RMn6Sn6 thin films has not been reported so far. Here, we report the atomic layer molecular beam epitaxy growth, structural and magnetic characterizations, and transport properties of ErMn6Sn6 and TbMn6Sn6 thin films. It is especially noteworthy that TbMn6Sn6 thin films have out-of-plane magnetic anisotropy, which is important for realizing the quantum AHE. Our work paves the avenue toward the control of the AHE using devices patterned from RMn6Sn6 thin films.
{"title":"Atomic layer molecular beam epitaxy of kagome magnet RMn6Sn6 (R = Er, Tb) thin films","authors":"Shuyu Cheng, Binzhi Liu, Igor Lyalin, Wenyi Zhou, Jinwoo Hwang, Roland K. Kawakami","doi":"10.1063/5.0182595","DOIUrl":"https://doi.org/10.1063/5.0182595","url":null,"abstract":"Kagome lattices have garnered substantial interest because their band structure consists of topological flat bands and Dirac cones. The RMn6Sn6 (R = rare earth) compounds are particularly interesting because of the existence of the large intrinsic anomalous Hall effect (AHE), which originates from the gapped Dirac cones near the Fermi level. This makes RMn6Sn6 an outstanding candidate for realizing the high-temperature quantum AHE. The growth of RMn6Sn6 thin films is beneficial for both fundamental research and potential applications. However, most of the studies on RMn6Sn6 have focused on bulk crystals, and the synthesis of RMn6Sn6 thin films has not been reported so far. Here, we report the atomic layer molecular beam epitaxy growth, structural and magnetic characterizations, and transport properties of ErMn6Sn6 and TbMn6Sn6 thin films. It is especially noteworthy that TbMn6Sn6 thin films have out-of-plane magnetic anisotropy, which is important for realizing the quantum AHE. Our work paves the avenue toward the control of the AHE using devices patterned from RMn6Sn6 thin films.","PeriodicalId":7985,"journal":{"name":"APL Materials","volume":"155 1","pages":""},"PeriodicalIF":6.1,"publicationDate":"2024-04-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140805617","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We explore the distinctive properties associated with a type-II Dirac point in a simply structured phononic crystal with a lattice deformation. This type-II Dirac point emerges at the Brillouin zone boundary, resulting from the lifting of two degenerate bands and featuring a conical-like Fermi surface in the equi-frequency curve. A practical implementation of such a phononic crystal is achieved with LEGO bricks. Upon introducing a periodic parity-time (PT) symmetric non-Hermitian perturbation, the phononic crystal undergoes a transition from PT-symmetric phase to PT-broken phase, causing the deformation of type-II Dirac point into an oval of exceptional points in the band structure. Based on the eigenmodes of the type-II Dirac point, a k⃗⋅p⃗ perturbation theory can be used to characterize these systems before and after the phase transition. Using a scattering matrix, we analyze the symmetric and broken phases and demonstrate that broadband unidirectional transparency and a coherent perfect absorber and laser can be realized with such a phononic crystal slab.
我们探索了具有晶格变形的简单结构声子晶体中的 II 型狄拉克点的独特性质。这种 II 型狄拉克点出现在布里渊区边界，是两个退化带抬升的结果，在等频曲线上具有锥形费米面。这种声子晶体的实际应用是通过乐高积木实现的。在引入周期性奇偶时（PT）对称非赫密特扰动后，声子晶体经历了从 PT 对称相到 PT 断裂相的转变，导致带结构中的 II 型狄拉克点变形为椭圆形的特殊点。基于 II 型狄拉克点的特征模，k⃗⋅p⃗扰动理论可用于描述相变前后这些系统的特征。利用散射矩阵，我们分析了对称相和破碎相，并证明这种声子晶体板可以实现宽带单向透明以及相干完美吸收器和激光器。
{"title":"Type-II Dirac phonons in a two-dimensional phononic crystal","authors":"Changqing Xu, Jun Mei, Guancong Ma, Ying Wu","doi":"10.1063/5.0189354","DOIUrl":"https://doi.org/10.1063/5.0189354","url":null,"abstract":"We explore the distinctive properties associated with a type-II Dirac point in a simply structured phononic crystal with a lattice deformation. This type-II Dirac point emerges at the Brillouin zone boundary, resulting from the lifting of two degenerate bands and featuring a conical-like Fermi surface in the equi-frequency curve. A practical implementation of such a phononic crystal is achieved with LEGO bricks. Upon introducing a periodic parity-time (PT) symmetric non-Hermitian perturbation, the phononic crystal undergoes a transition from PT-symmetric phase to PT-broken phase, causing the deformation of type-II Dirac point into an oval of exceptional points in the band structure. Based on the eigenmodes of the type-II Dirac point, a k⃗⋅p⃗ perturbation theory can be used to characterize these systems before and after the phase transition. Using a scattering matrix, we analyze the symmetric and broken phases and demonstrate that broadband unidirectional transparency and a coherent perfect absorber and laser can be realized with such a phononic crystal slab.","PeriodicalId":7985,"journal":{"name":"APL Materials","volume":"32 1","pages":""},"PeriodicalIF":6.1,"publicationDate":"2024-04-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140805612","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Jonathan Rommelfangen, Marco A. Gonzalez-Angulo, Devendra Pareek, Levent Gütay, Phillip J. Dale, Alex Redinger
Precise control of the optical and electrical properties of mono-layer (ML) thin MoS2 is crucial for future applications in functional devices. Depending on the synthesis route and the post-deposition annealing protocols, the number of sulfur vacancies in the material is different, which has a profound impact on the properties of the 2D layer. Here, we show that the sulfur vacancy-rich ML MoS2 films oxidize already at room temperature, which changes the photoluminescence (PL) yield, the MoS2–Al2O3 substrate interaction, and the structural integrity of the films. We used x-ray photoelectron spectroscopy to monitor the formation of MoO3 and possibly MoS3−xOx after exposure to air and to quantify the number of sulfur defects in the films. Atomic force microscopy measurements allow us to pinpoint the exact regions of oxidation and develop a dedicated low temperature heating procedure to remove oxidized species, leading to MoO3-free MoS2 films. AFM and Kelvin probe force microscopy show that the MoS2–Al2O3 substrate coupling is changed. The reduction in the MoS2–substrate coupling, combined with a preferential oxidation of sulfur vacancies, leads to a sevenfold increase in the PL intensity, and the ratio between trions and neutral excitons is changed. Our work highlights the importance of oxidized sulfur vacancies and provides useful methods to measure and manipulate their number in MoS2. Furthermore, changes in the MoS2–substrate interaction via sulfur vacancies and oxidation offer an elegant pathway to tune the optoelectronic properties of the two-dimensional films.
{"title":"Modification of mono-layer MoS2 through post-deposition treatment and oxidation for enhanced optoelectronic properties","authors":"Jonathan Rommelfangen, Marco A. Gonzalez-Angulo, Devendra Pareek, Levent Gütay, Phillip J. Dale, Alex Redinger","doi":"10.1063/5.0189378","DOIUrl":"https://doi.org/10.1063/5.0189378","url":null,"abstract":"Precise control of the optical and electrical properties of mono-layer (ML) thin MoS2 is crucial for future applications in functional devices. Depending on the synthesis route and the post-deposition annealing protocols, the number of sulfur vacancies in the material is different, which has a profound impact on the properties of the 2D layer. Here, we show that the sulfur vacancy-rich ML MoS2 films oxidize already at room temperature, which changes the photoluminescence (PL) yield, the MoS2–Al2O3 substrate interaction, and the structural integrity of the films. We used x-ray photoelectron spectroscopy to monitor the formation of MoO3 and possibly MoS3−xOx after exposure to air and to quantify the number of sulfur defects in the films. Atomic force microscopy measurements allow us to pinpoint the exact regions of oxidation and develop a dedicated low temperature heating procedure to remove oxidized species, leading to MoO3-free MoS2 films. AFM and Kelvin probe force microscopy show that the MoS2–Al2O3 substrate coupling is changed. The reduction in the MoS2–substrate coupling, combined with a preferential oxidation of sulfur vacancies, leads to a sevenfold increase in the PL intensity, and the ratio between trions and neutral excitons is changed. Our work highlights the importance of oxidized sulfur vacancies and provides useful methods to measure and manipulate their number in MoS2. Furthermore, changes in the MoS2–substrate interaction via sulfur vacancies and oxidation offer an elegant pathway to tune the optoelectronic properties of the two-dimensional films.","PeriodicalId":7985,"journal":{"name":"APL Materials","volume":"48 1","pages":""},"PeriodicalIF":6.1,"publicationDate":"2024-04-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140637015","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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