Pub Date : 2024-07-11DOI: 10.1088/2053-1583/ad5f3f
Pratik S Kasbe, Muxuan Yang, Juan Bosch, Jinyu Bu, Christopher DellaCorte and Weinan Xu
Beyond conventional 2D layered materials such as graphene and transition metal dichalcogenides, 2D metal oxides have also received much interest in recent years. They have unique electronic (such as 2D TiO2 and MoO2), catalytic (such as 2D CeO2 and MnO2), and magnetic properties (such as 2D Fe2O3) compared with bulk metal oxides due to their atomically thin structures. Certain types of 2D metal oxides also have the potential to be a new type of high-performance solid lubricants due to the tunable interlayer interaction and possibility for 2D heterostructure formation, but this remains largely unexplored. In this work, we developed a scalable microwave-assisted solid-state synthesis of 2D Fe2O3 and their nanocomposites with reduced graphene oxide (rGO). The 2D Fe2O3/rGO nanocomposites were systematically characterized by electron microscopies and spectroscopies, and their utilization as solid lubricants was studied by pin-on-disk tribometer on both silicon and steel substrates. The results show that due to the easy sliding between 2D Fe2O3 and rGO nanosheets and their unique magnetic-induced assembled morphology, low coefficient of friction (COF) can be achieved for both steel-silicon and steel-steel interfaces. Superlubricity (COF ∼ 0.007) can be achieved for the 2D Fe2O3/rGO nanocomposite with a GO primer layer on a steel substrate. This work provides new insights into the development of functional 2D nanocomposites and expands their applications to solid lubrication and beyond.
{"title":"Two-dimensional iron oxide/graphene-based nanocomposites as high-performance solid lubricants","authors":"Pratik S Kasbe, Muxuan Yang, Juan Bosch, Jinyu Bu, Christopher DellaCorte and Weinan Xu","doi":"10.1088/2053-1583/ad5f3f","DOIUrl":"https://doi.org/10.1088/2053-1583/ad5f3f","url":null,"abstract":"Beyond conventional 2D layered materials such as graphene and transition metal dichalcogenides, 2D metal oxides have also received much interest in recent years. They have unique electronic (such as 2D TiO2 and MoO2), catalytic (such as 2D CeO2 and MnO2), and magnetic properties (such as 2D Fe2O3) compared with bulk metal oxides due to their atomically thin structures. Certain types of 2D metal oxides also have the potential to be a new type of high-performance solid lubricants due to the tunable interlayer interaction and possibility for 2D heterostructure formation, but this remains largely unexplored. In this work, we developed a scalable microwave-assisted solid-state synthesis of 2D Fe2O3 and their nanocomposites with reduced graphene oxide (rGO). The 2D Fe2O3/rGO nanocomposites were systematically characterized by electron microscopies and spectroscopies, and their utilization as solid lubricants was studied by pin-on-disk tribometer on both silicon and steel substrates. The results show that due to the easy sliding between 2D Fe2O3 and rGO nanosheets and their unique magnetic-induced assembled morphology, low coefficient of friction (COF) can be achieved for both steel-silicon and steel-steel interfaces. Superlubricity (COF ∼ 0.007) can be achieved for the 2D Fe2O3/rGO nanocomposite with a GO primer layer on a steel substrate. This work provides new insights into the development of functional 2D nanocomposites and expands their applications to solid lubrication and beyond.","PeriodicalId":6812,"journal":{"name":"2D Materials","volume":"24 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2024-07-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141611639","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-10DOI: 10.1088/2053-1583/ad5e92
Yueming Guo, Hu Miao, Qiang Zou, Mingming Fu, Athena S Sefat, Andrew R Lupini, Sergei V Kalinin and Zheng Gai
In type-II superconductors, electronic states within magnetic vortices hold crucial information about the paring mechanism and can reveal non-trivial topology. While scanning tunneling microscopy/spectroscopy (STM/S) is a powerful tool for imaging superconducting vortices, it is challenging to isolate the intrinsic electronic properties from extrinsic effects like subsurface defects and disorders. Here we combine STM/STS with basic machine learning to develop a method for screening out the vortices pinned by embedded disorder in iron-based superconductors. Through a principal component analysis of large STS data within vortices, we find that the vortex-core states in Ba(Fe0.96Ni0.04)2As2 start to split into two categories at certain magnetic field strengths, reflecting vortices with and without pinning by subsurface defects or disorders. Our machine-learning analysis provides an unbiased approach to reveal intrinsic vortex-core states in novel superconductors and shed light on ongoing puzzles in the possible emergence of a Majorana zero mode.
在 II 型超导体中，磁涡旋内的电子状态蕴含着有关平分机制的重要信息，并能揭示非难拓扑结构。虽然扫描隧道显微镜/光谱学（STM/S）是超导漩涡成像的强大工具，但要将其内在电子特性与次表面缺陷和紊乱等外在效应分离开来却很有挑战性。在这里，我们将 STM/STS 与基本的机器学习相结合，开发出一种方法，用于筛选出铁基超导体中由嵌入式紊乱钉住的涡旋。通过对涡旋内的 STS 大数据进行主成分分析，我们发现 Ba(Fe0.96Ni0.04)2As2 中的涡旋核心态在特定磁场强度下开始分成两类，分别反映了有和没有被次表面缺陷或紊乱钉住的涡旋。我们的机器学习分析提供了一种无偏的方法来揭示新型超导体中的内在涡核态，并揭示了马约拉纳零模可能出现的谜题。
{"title":"Towards revealing intrinsic vortex-core states in Fe-based superconductors through statistical discovery","authors":"Yueming Guo, Hu Miao, Qiang Zou, Mingming Fu, Athena S Sefat, Andrew R Lupini, Sergei V Kalinin and Zheng Gai","doi":"10.1088/2053-1583/ad5e92","DOIUrl":"https://doi.org/10.1088/2053-1583/ad5e92","url":null,"abstract":"In type-II superconductors, electronic states within magnetic vortices hold crucial information about the paring mechanism and can reveal non-trivial topology. While scanning tunneling microscopy/spectroscopy (STM/S) is a powerful tool for imaging superconducting vortices, it is challenging to isolate the intrinsic electronic properties from extrinsic effects like subsurface defects and disorders. Here we combine STM/STS with basic machine learning to develop a method for screening out the vortices pinned by embedded disorder in iron-based superconductors. Through a principal component analysis of large STS data within vortices, we find that the vortex-core states in Ba(Fe0.96Ni0.04)2As2 start to split into two categories at certain magnetic field strengths, reflecting vortices with and without pinning by subsurface defects or disorders. Our machine-learning analysis provides an unbiased approach to reveal intrinsic vortex-core states in novel superconductors and shed light on ongoing puzzles in the possible emergence of a Majorana zero mode.","PeriodicalId":6812,"journal":{"name":"2D Materials","volume":"23 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2024-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141586486","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-04DOI: 10.1088/2053-1583/ad5bd6
Clotilde Ligaud, Lucie Le Van-Jodin, Bruno Reig, Pierre Trousset, Paul Brunet, Michaël Bertucchi, Clémence Hellion, Nicolas Gauthier, Le Van-Hoan, Hanako Okuno, Djordje Dosenovic, Stéphane Cadot, Remy Gassilloud and Matthieu Jamet
Two-dimensional (2D) materials like transition metal dichalcogenides (TMD) have proved to be serious candidates to replace silicon in several technologies with enhanced performances. In this respect, the two remaining challenges are the wafer scale growth of TMDs and their integration into operational devices using clean room compatible processes. In this work, two different CMOS-compatible protocols are developed for the fabrication of MoS2-based memristors, and the resulting performances are compared. The quality of MoS2 at each stage of the process is characterized by Raman spectroscopy and x-ray photoemission spectroscopy. In the first protocol, the structure of MoS2 is preserved during transfer and patterning processes. However, a polymer layer with a minimum thickness of 3 nm remains at the surface of MoS2 limiting the electrical switching performances. In the second protocol, the contamination layer is completely removed resulting in improved electrical switching performances and reproducibility. Based on physico-chemical and electrical results, the switching mechanism is discussed in terms of conduction through grain boundaries.
{"title":"Development and optimization of large-scale integration of 2D material in memristors","authors":"Clotilde Ligaud, Lucie Le Van-Jodin, Bruno Reig, Pierre Trousset, Paul Brunet, Michaël Bertucchi, Clémence Hellion, Nicolas Gauthier, Le Van-Hoan, Hanako Okuno, Djordje Dosenovic, Stéphane Cadot, Remy Gassilloud and Matthieu Jamet","doi":"10.1088/2053-1583/ad5bd6","DOIUrl":"https://doi.org/10.1088/2053-1583/ad5bd6","url":null,"abstract":"Two-dimensional (2D) materials like transition metal dichalcogenides (TMD) have proved to be serious candidates to replace silicon in several technologies with enhanced performances. In this respect, the two remaining challenges are the wafer scale growth of TMDs and their integration into operational devices using clean room compatible processes. In this work, two different CMOS-compatible protocols are developed for the fabrication of MoS2-based memristors, and the resulting performances are compared. The quality of MoS2 at each stage of the process is characterized by Raman spectroscopy and x-ray photoemission spectroscopy. In the first protocol, the structure of MoS2 is preserved during transfer and patterning processes. However, a polymer layer with a minimum thickness of 3 nm remains at the surface of MoS2 limiting the electrical switching performances. In the second protocol, the contamination layer is completely removed resulting in improved electrical switching performances and reproducibility. Based on physico-chemical and electrical results, the switching mechanism is discussed in terms of conduction through grain boundaries.","PeriodicalId":6812,"journal":{"name":"2D Materials","volume":"9 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2024-07-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141553260","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-01DOI: 10.1088/2053-1583/ad58f1
Irina Chircă, AbdulAziz AlMutairi, Barat Achinuq, Rongsheng Cai, Sarah J Haigh and Stephan Hofmann
Facile mapping of 2D heterostructures and resolving anisotropic formation kinetics down to the monolayer level are critical to developing scalable interfacing solutions and unlocking their application potential in emerging nano-optoelectronics. We adapt a Kramers–Kronig constrained variational fitting algorithm for spectroscopic imaging ellipsometry (SIE) to facilitate multi-scale heterostructure analysis comprising films with unknown complex dielectric functions and demonstrate how this enables non-destructive, scalable mapping and operando capability for the model system of HfS2 oxidation. This methodology proves highly accurate for assessing the thickness of buried HfS2 layers, oxide quality, and lateral and vertical uniformity. We capture dynamic stack evolution during thermal oxidation up to 400 ∘C, providing insights into the temperature and time-dependent nature of self-limiting oxide growth and reaction kinetics that involve the localised trapping and release of sulphur reaction products. Our methodology is versatile in material and device horizons, and advantageously agnostic to the underlying substrate. Combined with the various modes of SIE operation, it unlocks fast, high-throughput, large-area capability to accelerate process development at the atomic scale.
轻松绘制二维异质结构图并将各向异性的形成动力学解析到单层水平，对于开发可扩展的接口解决方案和释放其在新兴纳米光电子学中的应用潜力至关重要。我们为光谱成像椭偏仪（SIE）调整了克雷默-克罗尼格约束变分拟合算法，以促进由具有未知复杂介电函数的薄膜组成的多尺度异质结构分析，并演示了如何实现无损、可扩展的制图和 HfS2 氧化模型系统的操作能力。事实证明，这种方法可以非常准确地评估埋藏的 HfS2 层厚度、氧化物质量以及横向和纵向均匀性。我们捕捉了高达 400 ℃ 的热氧化过程中堆栈的动态演变，深入了解了自限制氧化物生长和反应动力学随温度和时间变化的性质，其中涉及硫反应产物的局部捕获和释放。我们的方法适用于各种材料和器件，而且与底层基底无关。结合 SIE 的各种运行模式，它可以释放出快速、高通量、大面积的能力，从而加速原子尺度的工艺开发。
{"title":"Versatile fitting approach for operando spectroscopic imaging ellipsometry of HfS2 oxidation","authors":"Irina Chircă, AbdulAziz AlMutairi, Barat Achinuq, Rongsheng Cai, Sarah J Haigh and Stephan Hofmann","doi":"10.1088/2053-1583/ad58f1","DOIUrl":"https://doi.org/10.1088/2053-1583/ad58f1","url":null,"abstract":"Facile mapping of 2D heterostructures and resolving anisotropic formation kinetics down to the monolayer level are critical to developing scalable interfacing solutions and unlocking their application potential in emerging nano-optoelectronics. We adapt a Kramers–Kronig constrained variational fitting algorithm for spectroscopic imaging ellipsometry (SIE) to facilitate multi-scale heterostructure analysis comprising films with unknown complex dielectric functions and demonstrate how this enables non-destructive, scalable mapping and operando capability for the model system of HfS2 oxidation. This methodology proves highly accurate for assessing the thickness of buried HfS2 layers, oxide quality, and lateral and vertical uniformity. We capture dynamic stack evolution during thermal oxidation up to 400 ∘C, providing insights into the temperature and time-dependent nature of self-limiting oxide growth and reaction kinetics that involve the localised trapping and release of sulphur reaction products. Our methodology is versatile in material and device horizons, and advantageously agnostic to the underlying substrate. Combined with the various modes of SIE operation, it unlocks fast, high-throughput, large-area capability to accelerate process development at the atomic scale.","PeriodicalId":6812,"journal":{"name":"2D Materials","volume":"24 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141501426","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-06-27DOI: 10.1088/2053-1583/ad59b4
Marko Milivojević, Martin Gmitra, Marcin Kurpas, Ivan Štich and Jaroslav Fabian
We analyze the spin–orbit coupling effects in a 3∘-degree twisted bilayer heterostructure made of graphene and an in-plane ferroelectric SnTe, with the goal of transferring the spin–orbit coupling from SnTe to graphene, via the proximity effect. Our results indicate that the point-symmetry breaking due to the incompatible mutual symmetry of the twisted monolayers and a strong hybridization has a massive impact on the spin splitting in graphene close to the Dirac point, with the spin splitting values greater than 20 meV. The band structure and spin expectation values of graphene close to the Dirac point can be described using a symmetry-free model, triggering different types of interaction with respect to the threefold symmetric graphene/transition-metal dichalcogenide heterostructure. We show that the strong hybridization of the Dirac cone’s right movers with the SnTe band gives rise to a large asymmetric spin splitting in the momentum space. Furthermore, we discover that the ferroelectricity-induced Rashba spin–orbit coupling in graphene is the dominant contribution to the overall Rashba field, with the effective in-plane electric field that is almost aligned with the (in-plane) ferroelectricity direction of the SnTe monolayer. We also predict an anisotropy of the in-plane spin relaxation rates. Our results demonstrate that the group-IV monochalcogenides MX (M = Sn, Ge; X = S, Se, Te) are a viable alternative to transition-metal dichalcogenides for inducing strong spin–orbit coupling in graphene.
{"title":"Giant asymmetric proximity-induced spin–orbit coupling in twisted graphene/SnTe heterostructure","authors":"Marko Milivojević, Martin Gmitra, Marcin Kurpas, Ivan Štich and Jaroslav Fabian","doi":"10.1088/2053-1583/ad59b4","DOIUrl":"https://doi.org/10.1088/2053-1583/ad59b4","url":null,"abstract":"We analyze the spin–orbit coupling effects in a 3∘-degree twisted bilayer heterostructure made of graphene and an in-plane ferroelectric SnTe, with the goal of transferring the spin–orbit coupling from SnTe to graphene, via the proximity effect. Our results indicate that the point-symmetry breaking due to the incompatible mutual symmetry of the twisted monolayers and a strong hybridization has a massive impact on the spin splitting in graphene close to the Dirac point, with the spin splitting values greater than 20 meV. The band structure and spin expectation values of graphene close to the Dirac point can be described using a symmetry-free model, triggering different types of interaction with respect to the threefold symmetric graphene/transition-metal dichalcogenide heterostructure. We show that the strong hybridization of the Dirac cone’s right movers with the SnTe band gives rise to a large asymmetric spin splitting in the momentum space. Furthermore, we discover that the ferroelectricity-induced Rashba spin–orbit coupling in graphene is the dominant contribution to the overall Rashba field, with the effective in-plane electric field that is almost aligned with the (in-plane) ferroelectricity direction of the SnTe monolayer. We also predict an anisotropy of the in-plane spin relaxation rates. Our results demonstrate that the group-IV monochalcogenides MX (M = Sn, Ge; X = S, Se, Te) are a viable alternative to transition-metal dichalcogenides for inducing strong spin–orbit coupling in graphene.","PeriodicalId":6812,"journal":{"name":"2D Materials","volume":"3 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2024-06-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141517792","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-06-13DOI: 10.1088/2053-1583/ad4ef1
Thomas Olsen
We present a perspective on the status of antiferromagnetism in two-dimensional (2D) materials. Various types of spin-compensated orders are discussed and include non-collinear order, spin spirals and altermagnetism. Spin–orbit effects ultimately determine, whether compounds exhibit long range order, Kosterlitz-Thouless physics, or multiferroic properties and we discuss the basic magnetic prototypes that may arise in 2D materials depending on the magnetic anisotropy and ordering vector. A summary of 2D antiferromagnets that have been characterized experimentally is provided—with particular emphasis on magnetic anisotropies and Neel temperatures. We then outline the ingredients needed to describe the magnetic properties using density functional theory. In particular, the systematic determination of magnetic ground states from the generalized Bloch theorem and the magnetic force theorem, which may be used to calculate magnetic excitations from the Heisenberg model with parameters determined from first principles. The methods are exemplified by application to the monolayer helimagnet NiBr2. Finally, we present a summary of predicted and prospective 2D antiferromagnets and discuss the challenges associated with the prediction of Néel temperatures from first principles.
{"title":"Antiferromagnetism in two-dimensional materials: progress and computational challenges","authors":"Thomas Olsen","doi":"10.1088/2053-1583/ad4ef1","DOIUrl":"https://doi.org/10.1088/2053-1583/ad4ef1","url":null,"abstract":"We present a perspective on the status of antiferromagnetism in two-dimensional (2D) materials. Various types of spin-compensated orders are discussed and include non-collinear order, spin spirals and altermagnetism. Spin–orbit effects ultimately determine, whether compounds exhibit long range order, Kosterlitz-Thouless physics, or multiferroic properties and we discuss the basic magnetic prototypes that may arise in 2D materials depending on the magnetic anisotropy and ordering vector. A summary of 2D antiferromagnets that have been characterized experimentally is provided—with particular emphasis on magnetic anisotropies and Neel temperatures. We then outline the ingredients needed to describe the magnetic properties using density functional theory. In particular, the systematic determination of magnetic ground states from the generalized Bloch theorem and the magnetic force theorem, which may be used to calculate magnetic excitations from the Heisenberg model with parameters determined from first principles. The methods are exemplified by application to the monolayer helimagnet NiBr2. Finally, we present a summary of predicted and prospective 2D antiferromagnets and discuss the challenges associated with the prediction of Néel temperatures from first principles.","PeriodicalId":6812,"journal":{"name":"2D Materials","volume":"78 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2024-06-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141501394","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In-plane optical properties of two-dimensional bismuth oxychalcogenides Bi2O2X (X = S, Se, and Te) are reported for a wide spectral range of 0.73–6.42 eV and at temperatures of 4.5–500 K by spectroscopic ellipsometry. At room temperature, Bi2O2S, Bi2O2Se, and Bi2O2Te exhibit an indirect band gap of 1.18 ± 0.02, 0.95 ± 0.01, and 0.60 ± 0.01 eV, respectively. As the temperature decreases, the indirect absorption edge of Bi2O2S undergoes a blueshift, while the indirect band gap of Bi2O2Se shows a redshift, and Bi2O2Te remains independent of temperature. The chalcogenide-dependent behavior as a function of temperature may be relevant to electron–phonon interactions in Bi2O2X materials. The observed pseudo-isotropic complex dielectric function and optical absorption coefficient by spectroscopic ellipsometry are directly compared with the first-principles calculations with a hybrid functional approach.
{"title":"Temperature-dependent indirect gaps for two-dimensional bismuth oxychalcogenides probed by spectroscopic ellipsometry","authors":"Hsiang-Lin Liu, Hsiao-Wen Chen, Nguyen Tuan Hung, Yi-Cheng Chen, Heng-Jui Liu, Chieh-Ting Chen, Yu-Lun Chueh, Ying-Hao Chu and Riichiro Saito","doi":"10.1088/2053-1583/ad50ad","DOIUrl":"https://doi.org/10.1088/2053-1583/ad50ad","url":null,"abstract":"In-plane optical properties of two-dimensional bismuth oxychalcogenides Bi2O2X (X = S, Se, and Te) are reported for a wide spectral range of 0.73–6.42 eV and at temperatures of 4.5–500 K by spectroscopic ellipsometry. At room temperature, Bi2O2S, Bi2O2Se, and Bi2O2Te exhibit an indirect band gap of 1.18 ± 0.02, 0.95 ± 0.01, and 0.60 ± 0.01 eV, respectively. As the temperature decreases, the indirect absorption edge of Bi2O2S undergoes a blueshift, while the indirect band gap of Bi2O2Se shows a redshift, and Bi2O2Te remains independent of temperature. The chalcogenide-dependent behavior as a function of temperature may be relevant to electron–phonon interactions in Bi2O2X materials. The observed pseudo-isotropic complex dielectric function and optical absorption coefficient by spectroscopic ellipsometry are directly compared with the first-principles calculations with a hybrid functional approach.","PeriodicalId":6812,"journal":{"name":"2D Materials","volume":"5 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2024-06-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141517793","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-06-11DOI: 10.1088/2053-1583/ad518d
Andrew M Fitzgerald, Emily Sutherland, Tarek Ali El-Melegy, Mary Qin Hassig, Julia L Martin, Erika Colin-Ulloa, Ken Ngo, Ronald L Grimm, Joshua R Uzarski, Michel W Barsoum, N Aaron Deskins, Lyubov V Titova and Kateryna Kushnir Friedman
Two-dimensional, 2D, niobium carbide MXene, Nb2CTx, has attracted attention due to its extraordinarily high photothermal conversion efficiency that has applications ranging from medicine, for tumor ablation, to solar energy conversion. Here, we characterize its electronic properties and investigate the ultrafast dynamics of its photoexcitations with a goal of shedding light onto the origins of its unique properties. Through density functional theory, DFT, calculations, we find that Nb2CTx is metallic, with a small but finite DOS at the Fermi level for all experimentally relevant terminations that can be achieved using HF or molten salt etching of the parent MAX phase, including –OH, –O, –F, –Cl, –Br, –I. In agreement with this prediction, THz spectroscopy reveals an intrinsic long-range conductivity of ∼60 Ω−1 cm−1, with significant charge carrier localization and a charge carrier density (∼1020 cm−3) comparable to Mo-based MXenes. Excitation with 800 nm pulses results in a rapid enhancement in photoconductivity, which decays to less than 25% of its peak value within several picoseconds, underlying efficient photothermal conversion. At the same time, a small fraction of photoinjected excess carriers persists for hundreds of picoseconds, and can potentially be utilized in photocatalysis or other energy conversion applications.
{"title":"Photoexcited charge carrier dynamics and electronic properties of two-dimensional MXene, Nb2CT x","authors":"Andrew M Fitzgerald, Emily Sutherland, Tarek Ali El-Melegy, Mary Qin Hassig, Julia L Martin, Erika Colin-Ulloa, Ken Ngo, Ronald L Grimm, Joshua R Uzarski, Michel W Barsoum, N Aaron Deskins, Lyubov V Titova and Kateryna Kushnir Friedman","doi":"10.1088/2053-1583/ad518d","DOIUrl":"https://doi.org/10.1088/2053-1583/ad518d","url":null,"abstract":"Two-dimensional, 2D, niobium carbide MXene, Nb2CTx, has attracted attention due to its extraordinarily high photothermal conversion efficiency that has applications ranging from medicine, for tumor ablation, to solar energy conversion. Here, we characterize its electronic properties and investigate the ultrafast dynamics of its photoexcitations with a goal of shedding light onto the origins of its unique properties. Through density functional theory, DFT, calculations, we find that Nb2CTx is metallic, with a small but finite DOS at the Fermi level for all experimentally relevant terminations that can be achieved using HF or molten salt etching of the parent MAX phase, including –OH, –O, –F, –Cl, –Br, –I. In agreement with this prediction, THz spectroscopy reveals an intrinsic long-range conductivity of ∼60 Ω−1 cm−1, with significant charge carrier localization and a charge carrier density (∼1020 cm−3) comparable to Mo-based MXenes. Excitation with 800 nm pulses results in a rapid enhancement in photoconductivity, which decays to less than 25% of its peak value within several picoseconds, underlying efficient photothermal conversion. At the same time, a small fraction of photoinjected excess carriers persists for hundreds of picoseconds, and can potentially be utilized in photocatalysis or other energy conversion applications.","PeriodicalId":6812,"journal":{"name":"2D Materials","volume":"57 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2024-06-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141501225","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-05-29DOI: 10.1088/2053-1583/ad4c73
Marko Milivojević, Marko Orozović, Silvia Picozzi, Martin Gmitra and Srđan Stavrić
Gaining growing attention in spintronics is a class of magnets displaying zero net magnetization and spin-split electronic bands called altermagnets. Here, by combining density functional theory and symmetry analysis, we show that RuF4 monolayer is a two-dimensional (2D) d-wave altermagnet. Spin–orbit coupling leads to pronounced spin splitting of the electronic bands at the Γ point by and turns the RuF4 into a weak ferromagnet due to nontrivial spin-momentum locking that cants the Ru magnetic moments. The net magnetic moment scales linearly with the spin–orbit coupling strength. Using group theory we derive an effective spin Hamiltonian capturing the spin-splitting and spin-momentum locking of the electronic bands. Disentanglement of the altermagnetic and spin–orbit coupling induced spin splitting uncovers to which extent the altermagnetic properties are affected by the spin–orbit coupling. Our results move the spotlight to the nontrivial spin-momentum locking and weak ferromagnetism in the 2D altermagnets relevant for novel venues in this emerging field of material science research.
{"title":"Interplay of altermagnetism and weak ferromagnetism in two-dimensional RuF4","authors":"Marko Milivojević, Marko Orozović, Silvia Picozzi, Martin Gmitra and Srđan Stavrić","doi":"10.1088/2053-1583/ad4c73","DOIUrl":"https://doi.org/10.1088/2053-1583/ad4c73","url":null,"abstract":"Gaining growing attention in spintronics is a class of magnets displaying zero net magnetization and spin-split electronic bands called altermagnets. Here, by combining density functional theory and symmetry analysis, we show that RuF4 monolayer is a two-dimensional (2D) d-wave altermagnet. Spin–orbit coupling leads to pronounced spin splitting of the electronic bands at the Γ point by and turns the RuF4 into a weak ferromagnet due to nontrivial spin-momentum locking that cants the Ru magnetic moments. The net magnetic moment scales linearly with the spin–orbit coupling strength. Using group theory we derive an effective spin Hamiltonian capturing the spin-splitting and spin-momentum locking of the electronic bands. Disentanglement of the altermagnetic and spin–orbit coupling induced spin splitting uncovers to which extent the altermagnetic properties are affected by the spin–orbit coupling. Our results move the spotlight to the nontrivial spin-momentum locking and weak ferromagnetism in the 2D altermagnets relevant for novel venues in this emerging field of material science research.","PeriodicalId":6812,"journal":{"name":"2D Materials","volume":"43 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2024-05-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141198355","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-05-23DOI: 10.1088/2053-1583/ad4720
Shoaib Khalid, Anderson Janotti and Bharat Medasani
Like in any other semiconductor, point defects in transition-metal dichalcogenides (TMDs) are expected to strongly impact their electronic and optical properties. However, identifying defects in these layered two-dimensional materials has been quite challenging with controversial conclusions despite the extensive literature in the past decade. Using first-principles calculations, we revisit the role of chalcogen vacancies and hydrogen impurity in bulk TMDs, reporting formation energies and thermodynamic and optical transition levels. We show that the S vacancy can explain recently observed cathodoluminescence spectra of MoS2 flakes and predict similar optical levels in the other TMDs. In the case of the H impurity, we find it more stable sitting on an interstitial site in the Mo plane, acting as a shallow donor, and possibly explaining the often observed n-type conductivity in some TMDs. We also predict the frequencies of the local vibration modes for the H impurity, aiding its identification through Raman or infrared spectroscopy.
与其他半导体一样，过渡金属二卤化物（TMDs）中的点缺陷预计会对其电子和光学特性产生强烈影响。然而，尽管过去十年间有大量文献报道，但识别这些层状二维材料中的缺陷一直颇具挑战性，而且结论也存在争议。利用第一原理计算，我们重新审视了查尔根空位和氢杂质在块状 TMD 中的作用，报告了形成能量以及热力学和光学转变水平。我们发现，S 空位可以解释最近观测到的 MoS2 薄片阴极发光光谱，并预测其他 TMD 中也存在类似的光学水平。至于 H 杂质，我们发现它位于 Mo 平面的一个间隙位点上更为稳定，起到浅供体的作用，并可能解释在某些 TMD 中经常观察到的 n 型导电性。我们还预测了 H 杂质的局部振动模式频率，有助于通过拉曼光谱或红外光谱对其进行识别。
{"title":"Role of chalcogen vacancies and hydrogen in the optical and electrical properties of bulk transition-metal dichalcogenides","authors":"Shoaib Khalid, Anderson Janotti and Bharat Medasani","doi":"10.1088/2053-1583/ad4720","DOIUrl":"https://doi.org/10.1088/2053-1583/ad4720","url":null,"abstract":"Like in any other semiconductor, point defects in transition-metal dichalcogenides (TMDs) are expected to strongly impact their electronic and optical properties. However, identifying defects in these layered two-dimensional materials has been quite challenging with controversial conclusions despite the extensive literature in the past decade. Using first-principles calculations, we revisit the role of chalcogen vacancies and hydrogen impurity in bulk TMDs, reporting formation energies and thermodynamic and optical transition levels. We show that the S vacancy can explain recently observed cathodoluminescence spectra of MoS2 flakes and predict similar optical levels in the other TMDs. In the case of the H impurity, we find it more stable sitting on an interstitial site in the Mo plane, acting as a shallow donor, and possibly explaining the often observed n-type conductivity in some TMDs. We also predict the frequencies of the local vibration modes for the H impurity, aiding its identification through Raman or infrared spectroscopy.","PeriodicalId":6812,"journal":{"name":"2D Materials","volume":"692 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2024-05-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141147607","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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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