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Khalil L, Pierucci D, Velez-Fort E, Avila J, Vergnaud C, Dudin P, Oehler F, Chaste J, Jamet M, Lhuillier E, Pala M, Ouerghi A. Hybridization and localized flat band in the WSe 2/MoSe 2heterobilayer. NANOTECHNOLOGY 2022; 34:045702. [PMID: 36252554 DOI: 10.1088/1361-6528/ac9abe] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/18/2022] [Accepted: 10/17/2022] [Indexed: 06/16/2023]
Abstract
Nearly localized moiré flat bands in momentum space, arising at particular twist angles, are the key to achieve correlated effects in transition-metal dichalcogenides. Here, we use angle-resolved photoemission spectroscopy (ARPES) to visualize the presence of a flat band near the Fermi level of van der Waals WSe2/MoSe2heterobilayer grown by molecular beam epitaxy. This flat band is localized near the Fermi level and has a width of several hundred meVs. By combining ARPES measurements with density functional theory calculations, we confirm the coexistence of different domains, namely the reference 2H stacking without layer misorientation and regions with arbitrary twist angles. For the 2H-stacked heterobilayer, our ARPES results show strong interlayer hybridization effects, further confirmed by complementary micro- Raman spectroscopy measurements. The spin-splitting of the valence band atKis determined to be 470 meV. The valence band maximum (VBM) position of the heterobilayer is located at the Γ point. The energy difference between the VBM at Γ and theKpoint is of -60 meV, which is a stark difference compared to individual single monolayer WSe2and monolayer WSe2, showing both a VBM atK.
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Affiliation(s)
- Lama Khalil
- Université Paris-Saclay, CNRS, Centre de Nanosciences et de Nanotechnologies, F-91120, Palaiseau, France
| | - Debora Pierucci
- Université Paris-Saclay, CNRS, Centre de Nanosciences et de Nanotechnologies, F-91120, Palaiseau, France
| | - Emilio Velez-Fort
- Université Grenoble Alpes, CEA, CNRS, Grenoble INP, IRIG-Spintec, F-38054, Grenoble, France
| | - José Avila
- Synchrotron-SOLEIL, Université Paris-Saclay, Saint-Aubin, BP48, F-91192 Gif sur Yvette, France
| | - Céline Vergnaud
- Université Grenoble Alpes, CEA, CNRS, Grenoble INP, IRIG-Spintec, F-38054, Grenoble, France
| | - Pavel Dudin
- Synchrotron-SOLEIL, Université Paris-Saclay, Saint-Aubin, BP48, F-91192 Gif sur Yvette, France
| | - Fabrice Oehler
- Université Paris-Saclay, CNRS, Centre de Nanosciences et de Nanotechnologies, F-91120, Palaiseau, France
| | - Julien Chaste
- Université Paris-Saclay, CNRS, Centre de Nanosciences et de Nanotechnologies, F-91120, Palaiseau, France
| | - Matthieu Jamet
- Université Grenoble Alpes, CEA, CNRS, Grenoble INP, IRIG-Spintec, F-38054, Grenoble, France
| | - Emmanuel Lhuillier
- Sorbonne Université, CNRS, Institut des NanoSciences de Paris, INSP, F-75005 Paris, France
| | - Marco Pala
- Université Paris-Saclay, CNRS, Centre de Nanosciences et de Nanotechnologies, F-91120, Palaiseau, France
| | - Abdelkarim Ouerghi
- Université Paris-Saclay, CNRS, Centre de Nanosciences et de Nanotechnologies, F-91120, Palaiseau, France
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Fan L, Xu J, Hong Y. Defects in graphene-based heterostructures: topological and geometrical effects. RSC Adv 2022; 12:6772-6782. [PMID: 35424609 PMCID: PMC8982235 DOI: 10.1039/d1ra08884j] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2021] [Accepted: 01/31/2022] [Indexed: 12/25/2022] Open
Abstract
The combination of graphene (Gr) and graphene-like materials provides the possibility of using two-dimensional (2D) atomic layer building blocks to create unprecedented architectures. The most attractive characteristics are strongly dependent on the various spatial structures, mainly including in-plane heterostructures butt-joined at the side of an atomic monolayer through covalent bonds, van der Waals (vdW) heterostructures involving a vertically stacked hybrid structure, and their combinations. Heterostructures can not only overcome the limitations inherent to each material but may also obtain new features by appropriate material combination. However, heterostructures made of vdW force superposition or covalent bond splicing are prone to defects. The introduction of external and internal defects causes local deformation and stress in the material, thereby affecting the physical properties of the material, such as its transport properties and mechanical properties. Therefore, research, utilization and control of these defects are highly critical. This paper reviews the vacancy, topological and geometrical effects of defects in modulating the structures and mechanical responses of Gr-based heterostructures. Moreover, the coupling effects of various defects on the Gr-based heterostructures in multi-physics fields are also discussed. This work aims to improve the understanding of the physical mechanism of defective configurations and their association in low dimensions, so as to realize various configurations and to aid the search for new usages. The combination of graphene (Gr) and graphene-like materials provides the possibility of using two-dimensional (2D) atomic layer building blocks to create unprecedented architectures.![]()
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Affiliation(s)
- Lei Fan
- School of Civil Engineering and Architecture, Zhejiang University of Science & Technology, Hangzhou, PR China
| | - Jin Xu
- School of Civil Engineering and Architecture, Zhejiang University of Science & Technology, Hangzhou, PR China
| | - Yihong Hong
- Shanghai Urban Construction Vocational College, Shanghai, China
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Dappe YJ, Almadori Y, Dau MT, Vergnaud C, Jamet M, Paillet C, Journot T, Hyot B, Pochet P, Grévin B. Charge transfers and charged defects in WSe 2/graphene-SiC interfaces. NANOTECHNOLOGY 2020; 31:255709. [PMID: 32182596 DOI: 10.1088/1361-6528/ab8083] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
We report on Kelvin probe force microscopy (KPFM) and density functional theory (DFT) investigations of charge transfers in vertical heterojunctions between tungsten diselenide (WSe2) layers and graphene on silicon carbide substrates. The experimental data reveal the existence of an interface dipole, which is shown by DFT to originate from the neutralization of the graphene n-doping by an electron transfer towards the transition metal dichalcogenide (TMD) layer. The relative vacuum level shift probed by KPFM between the TMD and the substrate stays constant when passing from monolayer to bilayer graphene, which confirms that the Schottky-Mott model can be rigorously applied to these interfaces by taking into account the charge transfer from the substrate to the TMD. DFT calculations show that the first TMD layer absorbs almost all the excess charges contained in the graphene, and that the second TMD layer shall not play a significant role in the electrostatics of the system. Negatively charged defect at the TMD edges contribute however to the electrostatic landscape probed by KPFM on both TMD layers.
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Affiliation(s)
- Y J Dappe
- SPEC, CEA, CNRS, Université Paris Saclay, CEA Saclay, 91191 Gif-sur-Yvette Cedex France
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4
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Vergnaud C, Dau MT, Grévin B, Licitra C, Marty A, Okuno H, Jamet M. New approach for the molecular beam epitaxy growth of scalable WSe 2 monolayers. NANOTECHNOLOGY 2020; 31:255602. [PMID: 32187582 DOI: 10.1088/1361-6528/ab80fe] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
The search for high-quality transition metal dichalcogenides mono- and multi-layers grown on large areas is still a very active field of investigation. Here, we use molecular beam epitaxy to grow WSe2 on 15 × 15 mm large mica in the van der Waals regime. By screening one-step growth conditions, we find that very high temperature (>900 °C) and very low deposition rate (<0.15 Å min-1) are necessary to obtain high quality WSe2 films. The domain size can be as large as 1 µm and the in-plane rotational misorientation of 1.25°. The WSe2 monolayer is also robust against air exposure, can be easily transferred over 1 cm2 on SiN/SiO2 and exhibits strong photoluminescence signal. Moreover, by combining grazing incidence x-ray diffraction and transmission electron microscopy, we could detect the presence of few misoriented grains. A two-dimensional model based on atomic coincidences between the WSe2 and mica crystals allows us to explain the formation of these misoriented grains and gives insight to achieve highly crystalline WSe2.
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Affiliation(s)
- Céline Vergnaud
- Univ. Grenoble Alpes, CEA, CNRS, Grenoble INP, IRIG-Spintec, 38000 Grenoble, France
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5
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Abstract
The Hall effect can be extended by inducing a temperature gradient in lieu of electric field that is known as the Nernst (-Ettingshausen) effect. The recently discovered spin Nernst effect in heavy metals continues to enrich the picture of Nernst effect-related phenomena. However, the collection would not be complete without mentioning the valley degree of freedom benchmarked by the valley Hall effect. Here we show the experimental evidence of its missing counterpart, the valley Nernst effect. Using millimeter-sized WSe\documentclass[12pt]{minimal}
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\begin{document}$${}_{2}$$\end{document}2 mono-multi-layers and the ferromagnetic resonance-spin pumping technique, we are able to apply a temperature gradient by off-centering the sample in the radio frequency cavity and address a single valley through spin-valley coupling. The combination of a temperature gradient and the valley polarization leads to the valley Nernst effect in WSe\documentclass[12pt]{minimal}
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\begin{document}$${}_{2}$$\end{document}2 that we detect electrically at room temperature. The valley Nernst coefficient is in good agreement with the predicted value. Atomically thin transition metal dichalcogenides possess a valley degree of freedom, which could enrich the physics underpinning the conventional Nernst effect observed in traditional solids. Here, the authors report experimental evidence of the valley Nernst effect in WSe2 at room temperature.
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Dai Y, Ren X, Zhang J, Liu J, Liu H, Ho W, Dai X, Jin C, Xie M. Multifarious Interfaces, Band Alignments, and Formation Asymmetry of WSe 2-MoSe 2 Heterojunction Grown by Molecular-Beam Epitaxy. ACS APPLIED MATERIALS & INTERFACES 2019; 11:43766-43773. [PMID: 31657201 DOI: 10.1021/acsami.9b16189] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Monolayer (ML) transition-metal dichalcogenides (TMDs) continue to attract research attention, and the heterojunctions formed by vertically stacking or laterally stitching two different TMDs, e.g., MoSe2 and WSe2, may have many interesting electronic and optical properties and thus are at the center stage of current research. Experimentally realizing such heterojunctions with desired interface morphologies and electronic properties is of great demand. In this work, we report a diverse interface structure in molecular-beam epitaxial WSe2-MoSe2 heterojunction. The corresponding electronic bands show type-II band alignment for both monolayer ML-ML and ML-bilayer lateral junctions irrespective of the presence or absence of step states. Interestingly, a strong anisotropy in lateral heterojunction formation is observed, where sharp interfaces are obtained only when WSe2 deposition precedes MoSe2. Reversing the deposition order leads to alloying of the two materials without a notable boundary. This is explained by a step segregation process as suggested by the first-principles total energy calculations.
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Affiliation(s)
- Yawei Dai
- Physics Department , The University of Hong Kong , Pokfulam Road , Hong Kong , China
| | - Xibiao Ren
- State Key Laboratory of Silicon Materials, School of Materials and Engineering , Zhejiang University , Hangzhou , Zhejiang 310027 , China
| | - Junqiu Zhang
- Physics Department , The University of Hong Kong , Pokfulam Road , Hong Kong , China
| | - Jing Liu
- School of Physics , Henan Normal University , Xinxiang , Henan 453007 , China
| | - Hongjun Liu
- Physics Department , The University of Hong Kong , Pokfulam Road , Hong Kong , China
- Institute of Functional Crystals , Tianjin University of Technology , Tianjin 300384 , China
| | - Wingkin Ho
- Physics Department , The University of Hong Kong , Pokfulam Road , Hong Kong , China
| | - Xianqi Dai
- School of Physics , Henan Normal University , Xinxiang , Henan 453007 , China
| | - Chuanhong Jin
- State Key Laboratory of Silicon Materials, School of Materials and Engineering , Zhejiang University , Hangzhou , Zhejiang 310027 , China
| | - Maohai Xie
- Physics Department , The University of Hong Kong , Pokfulam Road , Hong Kong , China
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7
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Zhu S, Pochet P, Johnson HT. Controlling Rotation of Two-Dimensional Material Flakes. ACS NANO 2019; 13:6925-6931. [PMID: 31082256 DOI: 10.1021/acsnano.9b01794] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Interlayer rotational alignment in van der Waals (vdW) structures of two-dimensional (2D) materials couples strongly to electronic properties and, therefore, has significant technological implications. Nevertheless, controlling the rotation of an arbitrary 2D material flake remains a challenge in the development of rotation-tunable electronics, for the emerging field of twistronics. In this article, we reveal a general moiré-driven mechanism that governs the interlayer rotation. Controlling the moiré can therefore hold promise for controlling the interlayer rotation. We further demonstrate mismatch strain engineering as a useful tool to design the interlayer rotation via changing the energy landscape of moiré within a finite-sized region. The robustness and programmable nature of our approach arise from moiré symmetry, energetics, and mechanics. Our approach provides another possibility to the on-demand design of rotation-tunable electronics.
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Affiliation(s)
- Shuze Zhu
- Department of Mechanical Science and Engineering , University of Illinois at Urbana-Champaign , Urbana , Illinois 61801 , United States
| | - Pascal Pochet
- Laboratory of Atomistic Simulation (L_Sim) , Univ. Grenoble Alpes 38054 Grenoble , France
| | - Harley T Johnson
- Department of Mechanical Science and Engineering , University of Illinois at Urbana-Champaign , Urbana , Illinois 61801 , United States
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