Focusing on Rhenium disulfide (ReS2), a group VII transition metal di-chalcogenides (TMDC), being a promising contender system for future nanoelectronics and optoelectronics, here, we present an innovative pathway to experimentally achieve an almost barrier-free contact for the ReS2 field effect transistors (FETs) by using few layered graphene as contact electrodes, further supported by comparative first-principles analysis. Such barrier-free contacts enable the observation of metal-to-insulator transition with enhanced room temperature carrier mobility up to 25 cm2/Vs, linear Ids-Vds characteristic down to 80 K, along with the reduction of 1/f noise by more than two orders of magnitude. We further demonstrate a highly responsive gate- tunable phototransistor (R > 106 A/W) at an illumination wavelength of 633 nm. This work demonstrates a straightforward strategy to unlock the full potential of ReS2 for CMOS compatible future electronic and optoelectronic devices.
{"title":"Achieving nearly barrier free transport in high mobility ReS2 phototransistors with van der Waals contacts","authors":"Shubhrasish Mukherjee, Gaurab Samanta, Md Nur Hasan, Shubhadip Moulick, Ruta Kulkarni, Kenji Watanabe, Takashi Taniguchi, Arumugum Thamizhavel, Debjani Karmakar, Atindra Nath Pal","doi":"10.1038/s41699-024-00507-3","DOIUrl":"10.1038/s41699-024-00507-3","url":null,"abstract":"Focusing on Rhenium disulfide (ReS2), a group VII transition metal di-chalcogenides (TMDC), being a promising contender system for future nanoelectronics and optoelectronics, here, we present an innovative pathway to experimentally achieve an almost barrier-free contact for the ReS2 field effect transistors (FETs) by using few layered graphene as contact electrodes, further supported by comparative first-principles analysis. Such barrier-free contacts enable the observation of metal-to-insulator transition with enhanced room temperature carrier mobility up to 25 cm2/Vs, linear Ids-Vds characteristic down to 80 K, along with the reduction of 1/f noise by more than two orders of magnitude. We further demonstrate a highly responsive gate- tunable phototransistor (R > 106 A/W) at an illumination wavelength of 633 nm. This work demonstrates a straightforward strategy to unlock the full potential of ReS2 for CMOS compatible future electronic and optoelectronic devices.","PeriodicalId":19227,"journal":{"name":"npj 2D Materials and Applications","volume":" ","pages":"1-9"},"PeriodicalIF":9.1,"publicationDate":"2024-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41699-024-00507-3.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142579815","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-11-05DOI: 10.1038/s41699-024-00511-7
Jakub Iwański, Krzysztof P. Korona, Mateusz Tokarczyk, Grzegorz Kowalski, Aleksandra K. Dąbrowska, Piotr Tatarczak, Izabela Rogala, Marta Bilska, Maciej Wójcik, Sławomir Kret, Anna Reszka, Bogdan J. Kowalski, Song Li, Anton Pershin, Adam Gali, Johannes Binder, Andrzej Wysmołek
Boron nitride exhibits various crystal structures. The subgroup of layered boron nitrides includes several polytypes such as hexagonal (hBN), Bernal (bBN), and rhombohedral (rBN) BN. The latter two are non-centrosymmetric, potentially leading to piezoelectric or ferroelectric properties. A key challenge related to the polytypism of sp2-bonded BN is distinguishing between these polytypes. We demonstrate that the optical response of the 4.1-eV defect can be used to differentiate hBN from rBN. Photoluminescence and cathodoluminescence measurements on samples grown by metalorganic vapor phase epitaxy (MOVPE) show a zero-phonon line at 4.096 eV for hBN and 4.143 eV for rBN. Our calculations confirm that the photoluminescence originates from a carbon dimer, CBCN (C2), which is sensitive to the local environments of different polytypes. We demonstrate that different polytypic compositions of hBN and rBN can be achieved by MOVPE, which could pave the way for future applications in large-area van der Waals heterostructures.
{"title":"Revealing polytypism in 2D boron nitride with UV photoluminescence","authors":"Jakub Iwański, Krzysztof P. Korona, Mateusz Tokarczyk, Grzegorz Kowalski, Aleksandra K. Dąbrowska, Piotr Tatarczak, Izabela Rogala, Marta Bilska, Maciej Wójcik, Sławomir Kret, Anna Reszka, Bogdan J. Kowalski, Song Li, Anton Pershin, Adam Gali, Johannes Binder, Andrzej Wysmołek","doi":"10.1038/s41699-024-00511-7","DOIUrl":"10.1038/s41699-024-00511-7","url":null,"abstract":"Boron nitride exhibits various crystal structures. The subgroup of layered boron nitrides includes several polytypes such as hexagonal (hBN), Bernal (bBN), and rhombohedral (rBN) BN. The latter two are non-centrosymmetric, potentially leading to piezoelectric or ferroelectric properties. A key challenge related to the polytypism of sp2-bonded BN is distinguishing between these polytypes. We demonstrate that the optical response of the 4.1-eV defect can be used to differentiate hBN from rBN. Photoluminescence and cathodoluminescence measurements on samples grown by metalorganic vapor phase epitaxy (MOVPE) show a zero-phonon line at 4.096 eV for hBN and 4.143 eV for rBN. Our calculations confirm that the photoluminescence originates from a carbon dimer, CBCN (C2), which is sensitive to the local environments of different polytypes. We demonstrate that different polytypic compositions of hBN and rBN can be achieved by MOVPE, which could pave the way for future applications in large-area van der Waals heterostructures.","PeriodicalId":19227,"journal":{"name":"npj 2D Materials and Applications","volume":" ","pages":"1-9"},"PeriodicalIF":9.1,"publicationDate":"2024-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41699-024-00511-7.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142595673","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-11-04DOI: 10.1038/s41699-024-00509-1
Seung Ju Kim, Hyeon-Ji Lee, Chul-Ho Lee, Ho Won Jang
Neuromorphic hardware enables energy-efficient computing, which is essential for a sustainable system. Recently, significant progress has been reported in neuromorphic hardware based on two-dimensional materials. However, traditional planar-integrated architectures still suffer from high energy consumption. This review systematically explores recent advances in the three-dimensional integration of two-dimensional material-based neuromorphic hardware to address these challenges. The materials, process, device physics, array, and integration levels are discussed, highlighting challenges and perspectives.
{"title":"2D materials-based 3D integration for neuromorphic hardware","authors":"Seung Ju Kim, Hyeon-Ji Lee, Chul-Ho Lee, Ho Won Jang","doi":"10.1038/s41699-024-00509-1","DOIUrl":"10.1038/s41699-024-00509-1","url":null,"abstract":"Neuromorphic hardware enables energy-efficient computing, which is essential for a sustainable system. Recently, significant progress has been reported in neuromorphic hardware based on two-dimensional materials. However, traditional planar-integrated architectures still suffer from high energy consumption. This review systematically explores recent advances in the three-dimensional integration of two-dimensional material-based neuromorphic hardware to address these challenges. The materials, process, device physics, array, and integration levels are discussed, highlighting challenges and perspectives.","PeriodicalId":19227,"journal":{"name":"npj 2D Materials and Applications","volume":" ","pages":"1-11"},"PeriodicalIF":9.1,"publicationDate":"2024-11-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41699-024-00509-1.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142574214","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Neuromorphic computing has emphasized the need for memristors with non-volatile, multiple conductance levels. This paper demonstrates the potential of hexagonal boron nitride (hBN)/graphene heterostructures to act as memristors with multiple resistance states that can be optically tuned using visible light. The number of resistance levels in graphene can be controlled by modulating doping levels, achieved by varying the electric field strength or adjusting the duration of optical illumination. Our measurements show that this photodoping of graphene results from the optical excitation of charge carriers from the nitrogen-vacancy levels of hBN to its conduction band, with these carriers then being transferred to graphene by the gate-induced electric field. We develop a qualitative model to describe our observations. Additionally, utilizing our device architecture, we propose a memristive crossbar array for vector-matrix multiplications.
{"title":"Optical control of multiple resistance levels in graphene for memristic applications","authors":"Harsimran Kaur Mann, Mainak Mondal, Vivek Sah, Kenji Watanabe, Takashi Taniguchi, Akshay Singh, Aveek Bid","doi":"10.1038/s41699-024-00503-7","DOIUrl":"10.1038/s41699-024-00503-7","url":null,"abstract":"Neuromorphic computing has emphasized the need for memristors with non-volatile, multiple conductance levels. This paper demonstrates the potential of hexagonal boron nitride (hBN)/graphene heterostructures to act as memristors with multiple resistance states that can be optically tuned using visible light. The number of resistance levels in graphene can be controlled by modulating doping levels, achieved by varying the electric field strength or adjusting the duration of optical illumination. Our measurements show that this photodoping of graphene results from the optical excitation of charge carriers from the nitrogen-vacancy levels of hBN to its conduction band, with these carriers then being transferred to graphene by the gate-induced electric field. We develop a qualitative model to describe our observations. Additionally, utilizing our device architecture, we propose a memristive crossbar array for vector-matrix multiplications.","PeriodicalId":19227,"journal":{"name":"npj 2D Materials and Applications","volume":" ","pages":"1-7"},"PeriodicalIF":9.1,"publicationDate":"2024-10-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41699-024-00503-7.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142566010","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-26DOI: 10.1038/s41699-024-00500-w
Hannah C. Nerl, Juan Pablo Guerrero-Felipe, Ana M. Valencia, Khairi Fahad Elyas, Katja Höflich, Christoph T. Koch, Caterina Cocchi
Heterostructures obtained by combining two-dimensional (2D) sheets are widely investigated as a platform for designing new materials with customised characteristics. Transition metal dichalcogenides (TMDCs) are often combined with hexagonal boron nitride (hBN) to enhance their excitonic resonances. However, little is known about how stacking affects excitons and plasmons in TMDCs or their mutual interactions. Here, we combine momentum-resolved electron energy-loss spectroscopy with first-principles calculations to study the energy-momentum dispersion of plasmons in multi-layer WSe2-hBN heterostructures as well as in their isolated components. The dispersion of the high-momentum excitons of hBN, alone and in combination with WSe2, is mapped across the entire Brillouin zone. Signatures of hybridisation in the plasmon resonances and some of the excitons suggest that the contribution of hBN cannot be neglected when interpreting the response of such a heterostructure. The consequences of using hBN as an encapsulant for TMDCs are also discussed.
{"title":"Mapping the energy-momentum dispersion of hBN excitons and hybrid plasmons in hBN-WSe2 heterostructures","authors":"Hannah C. Nerl, Juan Pablo Guerrero-Felipe, Ana M. Valencia, Khairi Fahad Elyas, Katja Höflich, Christoph T. Koch, Caterina Cocchi","doi":"10.1038/s41699-024-00500-w","DOIUrl":"10.1038/s41699-024-00500-w","url":null,"abstract":"Heterostructures obtained by combining two-dimensional (2D) sheets are widely investigated as a platform for designing new materials with customised characteristics. Transition metal dichalcogenides (TMDCs) are often combined with hexagonal boron nitride (hBN) to enhance their excitonic resonances. However, little is known about how stacking affects excitons and plasmons in TMDCs or their mutual interactions. Here, we combine momentum-resolved electron energy-loss spectroscopy with first-principles calculations to study the energy-momentum dispersion of plasmons in multi-layer WSe2-hBN heterostructures as well as in their isolated components. The dispersion of the high-momentum excitons of hBN, alone and in combination with WSe2, is mapped across the entire Brillouin zone. Signatures of hybridisation in the plasmon resonances and some of the excitons suggest that the contribution of hBN cannot be neglected when interpreting the response of such a heterostructure. The consequences of using hBN as an encapsulant for TMDCs are also discussed.","PeriodicalId":19227,"journal":{"name":"npj 2D Materials and Applications","volume":" ","pages":"1-11"},"PeriodicalIF":9.1,"publicationDate":"2024-10-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41699-024-00500-w.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142519199","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-11DOI: 10.1038/s41699-024-00504-6
Jennifer Schmeink, Jens Osterfeld, Osamah Kharsah, Stephan Sleziona, Marika Schleberger
We investigate the effect of structural and substitutional defects in Janus MoSSe and the Janus alloys MoS2(1−x)Se2x by a comprehensive analysis. Distinct Raman signatures are associated with various defect types and densities, mirroring the evolution from MoSe2 to Janus alloys to ideal Janus MoSSe. By the corresponding stoichiometrical and structural changes, the band gap can be tuned from 1.50 eV up to 1.68 eV at room temperature. Electrical characterization in a field effect device uncovers the impact of defects on conductivity, mobility (up to 2.42 × 10−3 cm2 V−1 s−1), and threshold voltages. A decrease of n-type doping of 5.3 × 1011 cm−2 in Janus MoSSe compared to the Janus alloy points towards an increased work function and a reduction of defects. Our findings deepen the understanding of defect physics in 2D Janus materials and pave the way for tailored defect engineering strategies for advanced (opto-)electronic applications.
{"title":"Unraveling the influence of defects in Janus MoSSe and Janus alloys MoS2(1−x)Se2x","authors":"Jennifer Schmeink, Jens Osterfeld, Osamah Kharsah, Stephan Sleziona, Marika Schleberger","doi":"10.1038/s41699-024-00504-6","DOIUrl":"10.1038/s41699-024-00504-6","url":null,"abstract":"We investigate the effect of structural and substitutional defects in Janus MoSSe and the Janus alloys MoS2(1−x)Se2x by a comprehensive analysis. Distinct Raman signatures are associated with various defect types and densities, mirroring the evolution from MoSe2 to Janus alloys to ideal Janus MoSSe. By the corresponding stoichiometrical and structural changes, the band gap can be tuned from 1.50 eV up to 1.68 eV at room temperature. Electrical characterization in a field effect device uncovers the impact of defects on conductivity, mobility (up to 2.42 × 10−3 cm2 V−1 s−1), and threshold voltages. A decrease of n-type doping of 5.3 × 1011 cm−2 in Janus MoSSe compared to the Janus alloy points towards an increased work function and a reduction of defects. Our findings deepen the understanding of defect physics in 2D Janus materials and pave the way for tailored defect engineering strategies for advanced (opto-)electronic applications.","PeriodicalId":19227,"journal":{"name":"npj 2D Materials and Applications","volume":" ","pages":"1-10"},"PeriodicalIF":9.1,"publicationDate":"2024-10-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41699-024-00504-6.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142431087","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-10DOI: 10.1038/s41699-024-00505-5
Jan N. Kirchhof, Kirill I. Bolotin
{"title":"Author Correction: Mechanically-tunable bandgap closing in 2D graphene phononic crystals","authors":"Jan N. Kirchhof, Kirill I. Bolotin","doi":"10.1038/s41699-024-00505-5","DOIUrl":"10.1038/s41699-024-00505-5","url":null,"abstract":"","PeriodicalId":19227,"journal":{"name":"npj 2D Materials and Applications","volume":" ","pages":"1-1"},"PeriodicalIF":9.1,"publicationDate":"2024-10-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41699-024-00505-5.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142431088","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-02DOI: 10.1038/s41699-024-00502-8
Martin Dahlqvist, Johanna Rosen
MXenes are a diverse family of two-dimensional (2D) transition metal carbides, nitrides, and carbonitrides. They can be synthesized through both top-down approaches, such as selective etching of A-layers from MAX phases using acids or molten salts, and bottom-up approaches, such as direct synthesis using chemical vapor deposition. However, the degree of the surface termination coverage depends on the synthesis route and is one key parameter for controlling its properties. This study focuses on halogen- and chalcogen-terminated MXenes, particularly M2CTx where M = Ti, Zr, V, Nb, Ta, and T = S, Se, Te, Cl, Br, I, and with surface termination coverage ranging from 100% (ideal, x = 2) to 50% (x = 1). The incorporation of oxygen on vacant termination sites was also evaluated. Using density functional theory (DFT) calculations, we investigated the structural, electronic, and mechanical properties of these MXenes. Our findings reveal that non-ideal termination coverage (x < 2) is more favorable for MXenes terminated with a larger size of T, such as Ti2CBrx, Nb2CClx, and Ta2CClx, and leads to mixed termination sites and lower binding energies. A reduced binding energy may facilitate delamination into single sheets, however, too low termination coverage may also cause structural collapse. Electronic properties showed an increased number of states at the Fermi level under non-ideal coverage, potentially enhancing the conductivity. Mechanically, we find the moduli of MXenes to be comparable to other 2D materials, such as transition metal chalcogenides and hexagonal boron nitride, indicating their suitability for applications requiring flexibility and durability. This study underscores the potential of tailoring MXene properties through precise control of termination coverage and composition, paving the way for enhanced application-specific performance.
MXenes 是二维（2D）过渡金属碳化物、氮化物和碳氮化物的一个多样化家族。它们既可以通过自上而下的方法合成，如使用酸或熔盐从 MAX 相中选择性蚀刻 A 层，也可以通过自下而上的方法合成，如使用化学气相沉积直接合成。然而，表面终止覆盖的程度取决于合成途径，也是控制其特性的一个关键参数。本研究的重点是卤素和缩醛基封端 MXenes，特别是 M2CTx，其中 M = Ti、Zr、V、Nb、Ta，T = S、Se、Te、Cl、Br、I，表面封端覆盖率从 100% （理想 x = 2）到 50% （x = 1）不等。此外，还评估了氧在空置终止位点上的结合情况。利用密度泛函理论（DFT）计算，我们研究了这些 MXenes 的结构、电子和机械特性。我们的研究结果表明，非理想终止覆盖（x <2）更有利于以较大尺寸的 T（如 Ti2CBrx、Nb2CClx 和 Ta2CClx）终止的 MXenes，并导致混合终止位点和较低的结合能。结合能的降低可能会促进单片的分层，但过低的终止覆盖率也可能导致结构崩溃。电子特性显示，在非理想覆盖率下，费米级上的状态数量增加，从而有可能提高导电性。在力学方面，我们发现 MXenes 的模量与其他二维材料（如过渡金属瑀和六方氮化硼）相当，这表明它们适用于需要灵活性和耐久性的应用。这项研究强调了通过精确控制终止覆盖和组成来定制 MXene 特性的潜力，为提高特定应用性能铺平了道路。
{"title":"Chalcogen and halogen surface termination coverage in MXenes—structure, stability, and properties","authors":"Martin Dahlqvist, Johanna Rosen","doi":"10.1038/s41699-024-00502-8","DOIUrl":"10.1038/s41699-024-00502-8","url":null,"abstract":"MXenes are a diverse family of two-dimensional (2D) transition metal carbides, nitrides, and carbonitrides. They can be synthesized through both top-down approaches, such as selective etching of A-layers from MAX phases using acids or molten salts, and bottom-up approaches, such as direct synthesis using chemical vapor deposition. However, the degree of the surface termination coverage depends on the synthesis route and is one key parameter for controlling its properties. This study focuses on halogen- and chalcogen-terminated MXenes, particularly M2CTx where M = Ti, Zr, V, Nb, Ta, and T = S, Se, Te, Cl, Br, I, and with surface termination coverage ranging from 100% (ideal, x = 2) to 50% (x = 1). The incorporation of oxygen on vacant termination sites was also evaluated. Using density functional theory (DFT) calculations, we investigated the structural, electronic, and mechanical properties of these MXenes. Our findings reveal that non-ideal termination coverage (x < 2) is more favorable for MXenes terminated with a larger size of T, such as Ti2CBrx, Nb2CClx, and Ta2CClx, and leads to mixed termination sites and lower binding energies. A reduced binding energy may facilitate delamination into single sheets, however, too low termination coverage may also cause structural collapse. Electronic properties showed an increased number of states at the Fermi level under non-ideal coverage, potentially enhancing the conductivity. Mechanically, we find the moduli of MXenes to be comparable to other 2D materials, such as transition metal chalcogenides and hexagonal boron nitride, indicating their suitability for applications requiring flexibility and durability. This study underscores the potential of tailoring MXene properties through precise control of termination coverage and composition, paving the way for enhanced application-specific performance.","PeriodicalId":19227,"journal":{"name":"npj 2D Materials and Applications","volume":" ","pages":"1-13"},"PeriodicalIF":9.1,"publicationDate":"2024-10-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41699-024-00502-8.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142377213","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-30DOI: 10.1038/s41699-024-00499-0
R. Roemer, D. H. D. Lee, S. Smit, X. Zhang, S. Godin, V. Hamza, T. Jian, J. Larkin, H. Shin, C. Liu, M. Michiardi, G. Levy, Z. Zhang, R. J. Green, C. Kim, D. Muller, A. Damascelli, M. J. Han, K. Zou
Two-dimensional (2D) van der Waals (vdW) magnets have sparked widespread attention due to their potential in spintronic applications as well as in fundamental physics. Ferromagnetic vdW compound Fe3GeTe2 (FGT) and its Ga variants have garnered significant interest due to their itinerant magnetism, correlated states, and high magnetic transition temperature. Experimental studies have demonstrated the tunability of FGT’s Curie temperature, TC, through adjustments in quintuple layer numbers (QL) and carrier concentrations, n. However, the underlying mechanism remains elusive. In this study, we employ molecular beam epitaxy (MBE) to synthesize 2D FGT films down to 1 QL with precise layer control, facilitating an exploration of the band structure and the evolution of itinerant carrier density. Angle-resolved photoemission spectroscopy (ARPES) reveals significant band structure changes at the ultra-thin limit, while first-principles calculations elucidate the band evolution from 1 QL to bulk, largely governed by interlayer coupling. Additionally, we find that n is intrinsically linked to the number of QL and temperature, with a critical value triggering the magnetic phase transition. Our findings underscore the pivotal role of band structure and itinerant electrons in governing magnetic phase transitions in such 2D vdW magnetic materials.
{"title":"Unraveling the electronic structure and magnetic transition evolution across monolayer, bilayer, and multilayer ferromagnetic Fe3GeTe2","authors":"R. Roemer, D. H. D. Lee, S. Smit, X. Zhang, S. Godin, V. Hamza, T. Jian, J. Larkin, H. Shin, C. Liu, M. Michiardi, G. Levy, Z. Zhang, R. J. Green, C. Kim, D. Muller, A. Damascelli, M. J. Han, K. Zou","doi":"10.1038/s41699-024-00499-0","DOIUrl":"10.1038/s41699-024-00499-0","url":null,"abstract":"Two-dimensional (2D) van der Waals (vdW) magnets have sparked widespread attention due to their potential in spintronic applications as well as in fundamental physics. Ferromagnetic vdW compound Fe3GeTe2 (FGT) and its Ga variants have garnered significant interest due to their itinerant magnetism, correlated states, and high magnetic transition temperature. Experimental studies have demonstrated the tunability of FGT’s Curie temperature, TC, through adjustments in quintuple layer numbers (QL) and carrier concentrations, n. However, the underlying mechanism remains elusive. In this study, we employ molecular beam epitaxy (MBE) to synthesize 2D FGT films down to 1 QL with precise layer control, facilitating an exploration of the band structure and the evolution of itinerant carrier density. Angle-resolved photoemission spectroscopy (ARPES) reveals significant band structure changes at the ultra-thin limit, while first-principles calculations elucidate the band evolution from 1 QL to bulk, largely governed by interlayer coupling. Additionally, we find that n is intrinsically linked to the number of QL and temperature, with a critical value triggering the magnetic phase transition. Our findings underscore the pivotal role of band structure and itinerant electrons in governing magnetic phase transitions in such 2D vdW magnetic materials.","PeriodicalId":19227,"journal":{"name":"npj 2D Materials and Applications","volume":" ","pages":"1-8"},"PeriodicalIF":9.1,"publicationDate":"2024-09-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41699-024-00499-0.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142377215","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Titanium diselenide (TiSe2) is a layered material that under a critical temperature of Tc ≈ 200 K features a periodic modulation of the electron density, known as charge density wave (CDW), which finds applications in quantum information and emerging electronic devices. Here, we present first-principles calculations showing the suppression of the CDW via photoexcitation and consequent stabilization of the undistorted high-temperature phase, in agreement with experimental observations. Interestingly, the unfolded CDW melting is accompanied by a sizable reduction in the thermal conductivity, κ, of up to 25% and a large entropy increase of ~10 J K−1 kg−1. The significant κ variation is almost entirely originated from photoinduced changes in the phonon–phonon scattering processes involving a high-symmetry soft phonon mode. Our results open new possibilities in the design of devices for thermal management and phonon-based logic, and suggest original applications in the of context solid-state cooling.
{"title":"Phonon transport manipulation in TiSe2 via reversible charge density wave melting","authors":"Martí Raya-Moreno, Claudio Cazorla, Enric Canadell, Riccardo Rurali","doi":"10.1038/s41699-024-00501-9","DOIUrl":"10.1038/s41699-024-00501-9","url":null,"abstract":"Titanium diselenide (TiSe2) is a layered material that under a critical temperature of Tc ≈ 200 K features a periodic modulation of the electron density, known as charge density wave (CDW), which finds applications in quantum information and emerging electronic devices. Here, we present first-principles calculations showing the suppression of the CDW via photoexcitation and consequent stabilization of the undistorted high-temperature phase, in agreement with experimental observations. Interestingly, the unfolded CDW melting is accompanied by a sizable reduction in the thermal conductivity, κ, of up to 25% and a large entropy increase of ~10 J K−1 kg−1. The significant κ variation is almost entirely originated from photoinduced changes in the phonon–phonon scattering processes involving a high-symmetry soft phonon mode. Our results open new possibilities in the design of devices for thermal management and phonon-based logic, and suggest original applications in the of context solid-state cooling.","PeriodicalId":19227,"journal":{"name":"npj 2D Materials and Applications","volume":" ","pages":"1-9"},"PeriodicalIF":9.1,"publicationDate":"2024-09-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41699-024-00501-9.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142377214","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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