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Boora M, Lin YC, Chen C, Trainor N, Robinson JA, Redwing JM, Suh JY. Low-Frequency Raman Study of Large-Area Twisted Bilayers of WS 2 Stacked by an Etchant-Free Transfer Method. ACS APPLIED MATERIALS & INTERFACES 2024; 16:2902-2911. [PMID: 38166373 DOI: 10.1021/acsami.3c14708] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/04/2024]
Abstract
Monolayer transition metal dichalcogenides have strong intracovalent bonding. When stacked in multilayers, however, weak van der Waals interactions dominate interlayer mechanical coupling and, thus, influence their lattice vibrations. This study presents the frequency evolution of interlayer phonons in twisted WS2 bilayers, highly subject to the twist angle. The twist angle between the layers is controlled to modulate the spacing between the layers, which, in turn, affects the interlayer coupling that is probed by Raman spectroscopy. The shifts of high-frequency E2g1 (Γ) and A1g (Γ) phonon modes and their frequency separations are dependent on the twist angle, reflecting the correlation between the interlayer mechanical coupling and twist angle. In this work, we fabricated large-area, twisted bilayer WS2 with a clean interface with controlled twist angles. Polarized Raman spectroscopy identified new interlayer modes, which were not previously reported, depending on the twist angle. The appearance of breathing modes in Raman phonon spectra provides evidence of strong interlayer coupling in bilayer structures. We confirm that the twist angle can alter the exciton and trion dynamics of bilayers as indicated by the photoluminescence peak shift. These large-area controlled twist angle samples have practical applications in optoelectronic device fabrication and twistronics.
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Affiliation(s)
- Manpreet Boora
- Department of Physics, Michigan Technological University, Houghton, Michigan 49931, United States
| | - Yu-Chuan Lin
- Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
- Department of Materials Science and Engineering, National Yang Ming Chiao Tung University, Hsinchu City 300093, Taiwan
| | - Chen Chen
- Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - Nicholas Trainor
- Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - Joshua A Robinson
- Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
- 2D Crystal Consortium Materials Innovation Platform, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
- Department of Chemistry and Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - Joan M Redwing
- Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
- 2D Crystal Consortium Materials Innovation Platform, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - Jae Yong Suh
- Department of Physics, Michigan Technological University, Houghton, Michigan 49931, United States
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Nunn JE, McEllistrim A, Weston A, Garcia-Ruiz A, Watson MD, Mucha-Kruczynski M, Cacho C, Gorbachev RV, Fal'ko VI, Wilson NR. ARPES Signatures of Few-Layer Twistronic Graphenes. NANO LETTERS 2023. [PMID: 37235208 DOI: 10.1021/acs.nanolett.3c01173] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Diverse emergent correlated electron phenomena have been observed in twisted-graphene layers. Many electronic structure predictions have been reported exploring this new field, but with few momentum-resolved electronic structure measurements to test them. We use angle-resolved photoemission spectroscopy to study the twist-dependent (1° < θ < 8°) band structure of twisted-bilayer, monolayer-on-bilayer, and double-bilayer graphene (tDBG). Direct comparison is made between experiment and theory, using a hybrid k·p model for interlayer coupling. Quantitative agreement is found across twist angles, stacking geometries, and back-gate voltages, validating the models and revealing field-induced gaps in twisted graphenes. However, for tDBG at θ = 1.5 ± 0.2°, close to the magic angle θ = 1.3°, a flat band is found near the Fermi level with measured bandwidth Ew = 31 ± 5 meV. An analysis of the gap between the flat band and the next valence band shows deviations between experiment (Δh = 46 ± 5 meV) and theory (Δh = 5 meV), indicative of lattice relaxation in this regime.
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Affiliation(s)
- James E Nunn
- Diamond Light Source, Division of Science, Didcot OX11 0DE, U.K
- Department of Physics, University of Warwick, Coventry CV4 7AL, U.K
| | - Andrew McEllistrim
- School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, U.K
- National Graphene Institute, University of Manchester, Booth St East, Manchester M13 9PL, U.K
| | - Astrid Weston
- School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, U.K
- National Graphene Institute, University of Manchester, Booth St East, Manchester M13 9PL, U.K
| | - Aitor Garcia-Ruiz
- School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, U.K
- National Graphene Institute, University of Manchester, Booth St East, Manchester M13 9PL, U.K
| | | | - Marcin Mucha-Kruczynski
- Centre for Nanoscience and Nanotechnology, Department of Physics, University of Bath, Bath BA2 7AY, U.K
| | - Cephise Cacho
- Diamond Light Source, Division of Science, Didcot OX11 0DE, U.K
| | - Roman V Gorbachev
- School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, U.K
- National Graphene Institute, University of Manchester, Booth St East, Manchester M13 9PL, U.K
| | - Vladimir I Fal'ko
- School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, U.K
- National Graphene Institute, University of Manchester, Booth St East, Manchester M13 9PL, U.K
| | - Neil R Wilson
- Department of Physics, University of Warwick, Coventry CV4 7AL, U.K
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