1
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Rieland L, Wagner J, Bernhardt R, Wang T, Abdul-Aziz O, Stein P, Pogna EAA, Dal Conte S, Cerullo G, Hedayat H, van Loosdrecht PHM. Ultrafast Optical Control of Exciton Diffusion in WSe 2/Graphene Heterostructures Revealed by Heterodyne Transient Grating Spectroscopy. NANO LETTERS 2024. [PMID: 39056490 DOI: 10.1021/acs.nanolett.4c01516] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/28/2024]
Abstract
Using heterodyne transient grating spectroscopy, we observe a significant enhancement of exciton diffusion in a monolayer WSe2 stacked on graphene. The diffusion dynamics can be optically tuned within a few picoseconds by altering the photoexcited carrier density in graphene. The effective diffusion constant in initial picoseconds in the WSe2/graphene heterostructure is (40.3 ± 4.5) cm2 s-1, representing a substantial improvement over (2.1 ± 0.8) cm2 s-1, typical for an isolated WSe2 monolayer. This enhancement can be understood in terms of a transient screening of impurities, charge traps, and defect states in WSe2 by photoexcited charge carriers in graphene. Furthermore, diffusion within WSe2 is affected by interlayer interactions, such as charge transfer, varying with the incident excitation fluence. These findings underscore the dynamical nature of screening and diffusion processes in heterostructures of 2D semiconductors and graphene and provide insights for future applications of these systems in ultrafast optoelectronic devices.
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Affiliation(s)
- Lukas Rieland
- II. Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, Köln D-50937, Germany
| | - Julian Wagner
- II. Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, Köln D-50937, Germany
| | - Robin Bernhardt
- II. Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, Köln D-50937, Germany
| | - Tianyi Wang
- II. Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, Köln D-50937, Germany
| | - Omar Abdul-Aziz
- II. Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, Köln D-50937, Germany
| | - Philipp Stein
- II. Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, Köln D-50937, Germany
| | - Eva A A Pogna
- Istituto di Fotonica e Nanotecnologie, Consiglio Nazionale delle Ricerche, Piazza L. da Vinci 32, 20133 Milano, Italy
| | - Stefano Dal Conte
- Dipartimento di Fisica, Politecnico di Milano, Piazza L. da Vinci 32, 20133 Milan, Italy
| | - Giulio Cerullo
- Istituto di Fotonica e Nanotecnologie, Consiglio Nazionale delle Ricerche, Piazza L. da Vinci 32, 20133 Milano, Italy
- Dipartimento di Fisica, Politecnico di Milano, Piazza L. da Vinci 32, 20133 Milan, Italy
| | - Hamoon Hedayat
- II. Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, Köln D-50937, Germany
| | - Paul H M van Loosdrecht
- II. Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, Köln D-50937, Germany
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2
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Timmer D, Gittinger M, Quenzel T, Cadore AR, Rosa BLT, Li W, Soavi G, Lünemann DC, Stephan S, Silies M, Schulz T, Steinhoff A, Jahnke F, Cerullo G, Ferrari AC, De Sio A, Lienau C. Ultrafast Coherent Exciton Couplings and Many-Body Interactions in Monolayer WS 2. NANO LETTERS 2024; 24:8117-8125. [PMID: 38901032 PMCID: PMC11229071 DOI: 10.1021/acs.nanolett.4c01991] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/26/2024] [Revised: 06/03/2024] [Accepted: 06/12/2024] [Indexed: 06/22/2024]
Abstract
Transition metal dichalcogenides (TMDs) are quantum confined systems with interesting optoelectronic properties, governed by Coulomb interactions in the monolayer (1L) limit, where strongly bound excitons provide a sensitive probe for many-body interactions. Here, we use two-dimensional electronic spectroscopy (2DES) to investigate many-body interactions and their dynamics in 1L-WS2 at room temperature and with sub-10 fs time resolution. Our data reveal coherent interactions between the strongly detuned A and B exciton states in 1L-WS2. Pronounced ultrafast oscillations of the transient optical response of the B exciton are the signature of a coherent 50 meV coupling and coherent population oscillations between the two exciton states. Supported by microscopic semiconductor Bloch equation simulations, these coherent dynamics are rationalized in terms of Dexter-like interactions. Our work sheds light on the role of coherent exciton couplings and many-body interactions in the ultrafast temporal evolution of spin and valley states in TMDs.
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Affiliation(s)
- Daniel Timmer
- Institut
für Physik, Carl von Ossietzky Universität
Oldenburg, 26129 Oldenburg, Germany
| | - Moritz Gittinger
- Institut
für Physik, Carl von Ossietzky Universität
Oldenburg, 26129 Oldenburg, Germany
| | - Thomas Quenzel
- Institut
für Physik, Carl von Ossietzky Universität
Oldenburg, 26129 Oldenburg, Germany
| | - Alisson R. Cadore
- Cambridge
Graphene Centre, University of Cambridge, CB3 0FA Cambridge, United Kingdom
| | - Barbara L. T. Rosa
- Cambridge
Graphene Centre, University of Cambridge, CB3 0FA Cambridge, United Kingdom
| | - Wenshan Li
- Cambridge
Graphene Centre, University of Cambridge, CB3 0FA Cambridge, United Kingdom
| | - Giancarlo Soavi
- Cambridge
Graphene Centre, University of Cambridge, CB3 0FA Cambridge, United Kingdom
| | - Daniel C. Lünemann
- Institut
für Physik, Carl von Ossietzky Universität
Oldenburg, 26129 Oldenburg, Germany
| | - Sven Stephan
- Institut
für Physik, Carl von Ossietzky Universität
Oldenburg, 26129 Oldenburg, Germany
| | - Martin Silies
- Institut
für Physik, Carl von Ossietzky Universität
Oldenburg, 26129 Oldenburg, Germany
| | - Tommy Schulz
- Institute
for Theoretical Physics and Bremen Center for Computational Materials
Science, University of Bremen, P.O. Box 330 440, 28334 Bremen, Germany
| | - Alexander Steinhoff
- Institute
for Theoretical Physics and Bremen Center for Computational Materials
Science, University of Bremen, P.O. Box 330 440, 28334 Bremen, Germany
| | - Frank Jahnke
- Institute
for Theoretical Physics and Bremen Center for Computational Materials
Science, University of Bremen, P.O. Box 330 440, 28334 Bremen, Germany
| | - Giulio Cerullo
- Dipartimento
di Fisica, Politecnico di Milano, Piazza L. da Vinci 32, 20133 Milano, Italy
- Istituto
di Fotonica e Nanotecnologie-CNR, Piazza L. da Vinci 32, 20133 Milano, Italy
| | - Andrea C. Ferrari
- Cambridge
Graphene Centre, University of Cambridge, CB3 0FA Cambridge, United Kingdom
| | - Antonietta De Sio
- Institut
für Physik, Carl von Ossietzky Universität
Oldenburg, 26129 Oldenburg, Germany
- Center
for Nanoscale Dynamics (CENAD), Carl von
Ossietzky Universität Oldenburg, Institut für Physik, 26129 Oldenburg, Germany
| | - Christoph Lienau
- Institut
für Physik, Carl von Ossietzky Universität
Oldenburg, 26129 Oldenburg, Germany
- Center
for Nanoscale Dynamics (CENAD), Carl von
Ossietzky Universität Oldenburg, Institut für Physik, 26129 Oldenburg, Germany
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3
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Beaulieu S, Dong S, Christiansson V, Werner P, Pincelli T, Ziegler JD, Taniguchi T, Watanabe K, Chernikov A, Wolf M, Rettig L, Ernstorfer R, Schüler M. Berry curvature signatures in chiroptical excitonic transitions. SCIENCE ADVANCES 2024; 10:eadk3897. [PMID: 38941460 PMCID: PMC11212730 DOI: 10.1126/sciadv.adk3897] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/21/2023] [Accepted: 05/24/2024] [Indexed: 06/30/2024]
Abstract
The topology of the electronic band structure of solids can be described by its Berry curvature distribution across the Brillouin zone. We theoretically introduce and experimentally demonstrate a general methodology based on the measurement of energy- and momentum-resolved optical transition rates, allowing to reveal signatures of Berry curvature texture in reciprocal space. By performing time- and angle-resolved photoemission spectroscopy of atomically thin WSe2 using polarization-modulated excitations, we demonstrate that excitons become an asset in extracting the quantum geometrical properties of solids. We also investigate the resilience of our measurement protocol against ultrafast scattering processes following direct chiroptical transitions.
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Affiliation(s)
- Samuel Beaulieu
- Université de Bordeaux - CNRS - CEA, CELIA, UMR5107, F33405 Talence, France
| | - Shuo Dong
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany
| | | | - Philipp Werner
- Department of Physics, University of Fribourg, 1700 Fribourg, Switzerland
| | - Tommaso Pincelli
- Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany
- Institut für Optik und Atomare Physik, Technische Universität Berlin, Strasse des 17 Juni 135, 10623 Berlin, Germany
| | - Jonas D. Ziegler
- Institute of Applied Physics and Würzburg-Dresden Cluster of Excellence ct.qmat, Technische Universität Dresden, 01062 Dresden, Germany
| | - Takashi Taniguchi
- Research Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Kenji Watanabe
- Research Center for Electronic and Optical Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Alexey Chernikov
- Institute of Applied Physics and Würzburg-Dresden Cluster of Excellence ct.qmat, Technische Universität Dresden, 01062 Dresden, Germany
| | - Martin Wolf
- Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany
| | - Laurenz Rettig
- Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany
| | - Ralph Ernstorfer
- Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany
- Institut für Optik und Atomare Physik, Technische Universität Berlin, Strasse des 17 Juni 135, 10623 Berlin, Germany
| | - Michael Schüler
- Laboratory for Materials Simulations, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
- Department of Physics, University of Fribourg, CH-1700 Fribourg, Switzerland
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4
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Xiang B, Wang R, Chen Y, Wang Y, Qin T, Zhang M, Watanabe K, Taniguchi T, Duan W, Tang P, Liu H, Xiong Q. Chirality-Dependent Dynamic Evolution for Trions in Monolayer WS 2. NANO LETTERS 2024; 24:6592-6600. [PMID: 38787539 DOI: 10.1021/acs.nanolett.4c01082] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2024]
Abstract
Monolayer transition metal dichalcogenides exhibit valley-dependent excitonic characters with a large binding energy, acting as the building block for future optoelectronic functionalities. Herein, combined with pump-probe ultrafast transient transmission spectroscopy and theoretical simulations, we reveal the chirality-dependent trion dynamics in h-BN encapsulated monolayer tungsten disulfide. By resonantly pumping trions in a single valley and monitoring their temporal evolution, we identify the temperature-dependent competition between two relaxation channels driven by chirality-dependent scattering processes. At room temperature, the phonon-assisted upconversion process predominates, converting excited trions to excitons within the same valley on a sub-picosecond (ps) time scale. As temperature decreases, this process becomes less efficient, while alternative channels, notably valley depolarization process for trions, assume importance, leading to an increase of trion density in the unpumped valley within a ps time scale. Our time-resolved valley-contrast results provide a comprehensive insight into trion dynamics in 2D materials, thereby advancing the development of novel valleytronic devices.
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Affiliation(s)
- Baixu Xiang
- State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing,100084, P. R. China
- Beijing Academy of Quantum Information Sciences, Beijing 100193, P. R. China
| | - Renqi Wang
- State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing,100084, P. R. China
| | - Yuzhong Chen
- Beijing Academy of Quantum Information Sciences, Beijing 100193, P. R. China
| | - Yubin Wang
- State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing,100084, P. R. China
- Beijing Academy of Quantum Information Sciences, Beijing 100193, P. R. China
| | - Tingxiao Qin
- Beijing Academy of Quantum Information Sciences, Beijing 100193, P. R. China
| | - Mengdi Zhang
- Beijing Academy of Quantum Information Sciences, Beijing 100193, P. R. China
| | - Kenji Watanabe
- Research Center for Electronic and Optical Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Takashi Taniguchi
- Research Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Wenhui Duan
- State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing,100084, P. R. China
- Institute for Advanced Study, Tsinghua University, Beijing 100084, P. R. China
- Frontier Science Center for Quantum Information, Beijing, 100084, P. R. China
| | - Peizhe Tang
- School of Materials Science and Engineering, Beihang University, Beijing 100191, P. R. China
- Max Planck Institute for the Structure and Dynamics of Matter, Center for Free Electron Laser Science, 22761 Hamburg, Germany
| | - Haiyun Liu
- Beijing Academy of Quantum Information Sciences, Beijing 100193, P. R. China
| | - Qihua Xiong
- State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing,100084, P. R. China
- Beijing Academy of Quantum Information Sciences, Beijing 100193, P. R. China
- Frontier Science Center for Quantum Information, Beijing, 100084, P. R. China
- Collaborative Innovation Center of Quantum Matter, Beijing, 100084, P.R. China
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5
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Rostami H, Cilento F, Cappelluti E. Pump-Driven Opto-Magnetic Properties in Semiconducting Transition-Metal Dichalcogenides: An Analytical Model. NANOMATERIALS (BASEL, SWITZERLAND) 2024; 14:707. [PMID: 38668201 PMCID: PMC11053629 DOI: 10.3390/nano14080707] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/11/2024] [Revised: 04/15/2024] [Accepted: 04/16/2024] [Indexed: 04/29/2024]
Abstract
Single-layer transition-metal dichalcogenides provide an unique intrinsic entanglement between the spin/valley/orbital degrees of freedom and the polarization of scattered photons. This scenario gives rise to the well-assessed optical dichroism observed by using both steady and time-resolved probes. In this paper, we provide compact analytical modeling of the onset of a finite Faraday/Kerr optical rotation upon shining with circularly polarized light. We identify different optical features displaying optical rotation at different characteristic energies, and we describe in an analytical framework the time-dependence of their intensities as a consequence of the main spin-conserving and spin-flip processes.
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Affiliation(s)
- Habib Rostami
- Department of Physics, University of Bath, Claverton Down, Bath BA2 7AY, UK;
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6
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Kim J, Park J, Choi H, Kim T, Cha S, Lee Y, Watanabe K, Taniguchi T, Kim J, Jo MH, Choi H. Correlation-driven nonequilibrium exciton site transition in a WSe 2/WS 2 moiré supercell. Nat Commun 2024; 15:3312. [PMID: 38632336 PMCID: PMC11024152 DOI: 10.1038/s41467-024-47768-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2023] [Accepted: 04/10/2024] [Indexed: 04/19/2024] Open
Abstract
Moiré superlattices of transition metal dichalcogenides offer a unique platform to explore correlated exciton physics with optical spectroscopy. Whereas the spatially modulated potentials evoke that the exciton resonances are distinct depending on a site in a moiré supercell, there have been no clear demonstration how the moiré excitons trapped in different sites dynamically interact with the doped carriers; so far the exciton-electron dynamic interactions were presumed to be site-dependent. Thus, the transient emergence of nonequilibrium correlations are open questions, but existing studies are limited to steady-state optical measurements. Here we report experimental fingerprints of site-dependent exciton correlations under continuous-wave as well as ultrashort optical excitations. In near-zero angle-aligned WSe2/WS2 heterobilayers, we observe intriguing polarization switching and strongly enhanced Pauli blocking near the Mott insulating state, dictating the dominant correlation-driven effects. When the twist angle is near 60°, no such correlations are observed, suggesting the strong dependence of atomic registry in moiré supercell configuration. Our studies open the door to largely unexplored nonequilibrium correlations of excitons in moiré superlattices.
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Affiliation(s)
- Jinjae Kim
- Department of Physics, Seoul National University, Seoul, 08826, Korea
- Institute of Applied Physics, Seoul National University, Seoul, 08826, Korea
| | - Jiwon Park
- Department of Physics, Seoul National University, Seoul, 08826, Korea
- Institute of Applied Physics, Seoul National University, Seoul, 08826, Korea
| | - Hyojin Choi
- Department of Physics, Seoul National University, Seoul, 08826, Korea
- Institute of Applied Physics, Seoul National University, Seoul, 08826, Korea
| | - Taeho Kim
- Department of Materials Science and Engineering, Pohang University of Science and Technology, Pohang, 37673, Korea
- Center for van der Waals Quantum Solids, Institute for Basic Science (IBS), Pohang, 37673, Korea
| | - Soonyoung Cha
- Department of Physics and Astronomy, University of California, Riverside, CA, 92521, USA
| | - Yewon Lee
- Department of Materials Science and Engineering, Pohang University of Science and Technology, Pohang, 37673, Korea
- Center for van der Waals Quantum Solids, Institute for Basic Science (IBS), Pohang, 37673, Korea
| | - Kenji Watanabe
- Advanced Materials Laboratory, National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044, Japan
| | - Takashi Taniguchi
- Advanced Materials Laboratory, National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044, Japan
| | - Jonghwan Kim
- Department of Materials Science and Engineering, Pohang University of Science and Technology, Pohang, 37673, Korea
- Center for van der Waals Quantum Solids, Institute for Basic Science (IBS), Pohang, 37673, Korea
| | - Moon-Ho Jo
- Department of Materials Science and Engineering, Pohang University of Science and Technology, Pohang, 37673, Korea
- Center for van der Waals Quantum Solids, Institute for Basic Science (IBS), Pohang, 37673, Korea
| | - Hyunyong Choi
- Department of Physics, Seoul National University, Seoul, 08826, Korea.
- Institute of Applied Physics, Seoul National University, Seoul, 08826, Korea.
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7
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Jeffries WR, Jawaid AM, Vaia RA, Knappenberger KL. Thickness-dependent electronic relaxation dynamics in solution-phase redox-exfoliated MoS2 heterostructures. J Chem Phys 2024; 160:144707. [PMID: 38597312 DOI: 10.1063/5.0200398] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2024] [Accepted: 03/20/2024] [Indexed: 04/11/2024] Open
Abstract
Electronic relaxation dynamics of solution-phase redox-exfoliated molybdenum disulfide (MoS2) monolayer and multilayer ensembles are described. MoS2 was exfoliated using polyoxometalate (POM) reductants. This process yields a colloidal heterostructure consisting of MoS2 2D sheet multilayers with surface-bound POM complexes. Using two-dimensional electronic spectroscopy, transient bleaching and photoinduced absorption signals were detected at excitation/detection energies of 1.82/1.87 and 1.82/1.80 eV, respectively. Approximate 100-fs bandgap renormalization (BGR) and subsequent defect- and phonon-mediated relaxation on the picosecond timescale were resolved for several MoS2 thicknesses spanning from 1 to 2 L to ∼20 L. BGR rates were independent of sample thickness and slightly slower than observations for chemical vapor deposition-grown MoS2 monolayers. However, defect-mediated relaxation accelerated ∼10-fold with increased sample thicknesses. The relaxation rates increased from 0.33 ± 0.05 to 1.2 ± 0.1 and 3.1 ± 0.4 ps-1 for 1-2 L, 3-4 L, and 20 L fractions. The thicknesses-dependent relaxation rates for POM-MoS2 heterostructures were modeled using a saturating exponential function that showed saturation at thirteen MoS2 layers. The results suggest that the increased POM surface coverage leads to larger defect density in the POM-MoS2 heterostructure. These are the first descriptions of the influence of sample thickness on electronic relaxation rates in solution-phase redox-exfoliated POM-MoS2 heterostructures. Outcomes of this work are expected to impact the development of solution-phase exfoliation of 2D metal-chalcogenide heterostructures.
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Affiliation(s)
- William R Jeffries
- Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
| | - Ali M Jawaid
- Air Force Research Laboratory, 2941 Hobson Way, Wright Patterson Air Force Base, Dayton, Ohio 45433, USA
| | - Richard A Vaia
- Air Force Research Laboratory, 2941 Hobson Way, Wright Patterson Air Force Base, Dayton, Ohio 45433, USA
| | - Kenneth L Knappenberger
- Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
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8
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Zhang Y, Zhou T, Zhong F, Jiang G, Wang S, Yuan X, Zhang Q, Lu J, Ni Z, Wan D. Interfacial Effect on the Transient Dielectric Function and Charge Transfer in a Monolayer WS 2/Si Heterojunction. ACS APPLIED MATERIALS & INTERFACES 2023; 15:59981-59988. [PMID: 38100424 DOI: 10.1021/acsami.3c16009] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/17/2023]
Abstract
Monolayer tungsten disulfide (WS2) is a highly promising material for silicon photonics. Thus, the WS2/Si interface plays a very important role due to the interfacial complex effects and abundant states. Among them, the effect of charge transfer on exciton dynamics and the optoelectronic property is determined by the dielectric function, which is very crucial for the performance of optoelectronic devices. However, research on the exciton dynamics or the transient dielectric function of WS2 in such WS2/Si junctions is still rare. In this work, both the transient dielectric function and charge transfer of WS2/Si heterojunctions are analyzed based on the transient reflectance spectra measured by the pump-probe spectrometer. The dynamic processes of the A exciton, affected by charge transfer within the WS2/Si heterojunction, are interpreted. Moreover, the transient dielectric function of WS2 is quantitatively analyzed. The dielectric function of WS2 exhibits a notable 19% change, persisting for more than 180 ps within the WS2/Si heterojunction. These findings can pave the way for the advancement of silicon photonic devices based on WS2.
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Affiliation(s)
- Yuwei Zhang
- School of Physics and Key Laboratory of Quantum Materials and Devices of Ministry of Education, Southeast University, Nanjing 211189, China
| | - Tao Zhou
- School of Physics and Key Laboratory of Quantum Materials and Devices of Ministry of Education, Southeast University, Nanjing 211189, China
| | - Fan Zhong
- School of Physics and Key Laboratory of Quantum Materials and Devices of Ministry of Education, Southeast University, Nanjing 211189, China
| | - Guangsheng Jiang
- School of Physics and Key Laboratory of Quantum Materials and Devices of Ministry of Education, Southeast University, Nanjing 211189, China
| | - Shixuan Wang
- School of Physics and Key Laboratory of Quantum Materials and Devices of Ministry of Education, Southeast University, Nanjing 211189, China
| | - Xueyong Yuan
- School of Physics and Key Laboratory of Quantum Materials and Devices of Ministry of Education, Southeast University, Nanjing 211189, China
| | - Qi Zhang
- School of Physics and Key Laboratory of Quantum Materials and Devices of Ministry of Education, Southeast University, Nanjing 211189, China
| | - Junpeng Lu
- School of Physics and Key Laboratory of Quantum Materials and Devices of Ministry of Education, Southeast University, Nanjing 211189, China
| | - Zhenhua Ni
- School of Physics and Key Laboratory of Quantum Materials and Devices of Ministry of Education, Southeast University, Nanjing 211189, China
- Purple Mountain Laboratories, Nanjing 211111, China
| | - Dongyang Wan
- School of Physics and Key Laboratory of Quantum Materials and Devices of Ministry of Education, Southeast University, Nanjing 211189, China
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9
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Chi Z, Wei Z, Zhang G, Chen H, Weng YX. Determining Band Splitting and Spin-Flip Dynamics in Monolayer MoS 2. J Phys Chem Lett 2023; 14:9640-9645. [PMID: 37870497 DOI: 10.1021/acs.jpclett.3c02431] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2023]
Abstract
Femtosecond helicity-resolved pump-probe spectroscopy is performed to study the spin and valley dynamics in monolayer (ML) MoS2. Both the bright to dark intravalley exciton transition (∼50 fs) and the reverse transition process (<50 fs) are directly monitored. It suggests that the bright exciton state of ML MoS2 is lower in energy than the dark one, which is also confirmed by observing the temperature-dependent co-polarized photobleaching dynamics of A and B excitons. Furthermore, the band splitting in the conduction band of ML MoS2 with a value of 15 ± 0.3 meV is determined by fitting the temperature-dependent ratios of the population in bright and dark states using the Boltzmann distribution law. Such minor band splitting allows the phonon-mediated intravalley spin-flip to even occur from the lower to the upper conduction band within tens of femtoseconds, which will have non-negligible effects on the performance of these ML MoS2-based optoelectronic and photonic devices.
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Affiliation(s)
- Zhen Chi
- The Laboratory of Soft Matter Physics, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- School of Physics and Electronics, International Joint Research Laboratory of New Energy Materials and Devices of Henan Province, Henan University, Kaifeng 475004, China
| | - Zheng Wei
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - Guangyu Zhang
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- Songshan Lake Materials Laboratory, Dongguan, Guangdong 523808, China
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Hailong Chen
- The Laboratory of Soft Matter Physics, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- Songshan Lake Materials Laboratory, Dongguan, Guangdong 523808, China
| | - Yu-Xiang Weng
- The Laboratory of Soft Matter Physics, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- Songshan Lake Materials Laboratory, Dongguan, Guangdong 523808, China
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
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10
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Zheng SW, Wang HY, Wang H, Wang L. Excitonic Effect Drives Ultrafast Transition in Two-Dimensional Transition Metal Dichalcogenides. J Phys Chem Lett 2023; 14:9200-9206. [PMID: 37801730 DOI: 10.1021/acs.jpclett.3c02545] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/08/2023]
Abstract
Two-dimensional (2D) transition metal dichalcogenides (TMDCs) are ideal platforms for exploring excitonic physics because of the tightly bound excitons. In this work, we observed the onset of band-edge exciton formation in monolayer MoS2 (WS2) and bilayer MoS2-WS2 by measuring the transient optical response upon excitation with ultrashort laser pulses. In addition to wavelength dependence on excitation under nonresonant excitation, we found that the onset of band-edge exciton formation in monolayer MoS2 (WS2) pumped in the exciton state is significantly faster than that with pumping in the nonexciton state, which could be attributed to the effective transition between exciton states induced by the excitonic effect. Besides, the onset of band-edge exciton formation in van der Waals heterostructures is similar to that for monolayer TMDCs regardless of charge transfer at the interface. Our work contributes to a better understanding of exciton dynamics in 2D TMDCs, providing a solid basis of the rational design of the 2D optoelectronic applications based on TMDCs.
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Affiliation(s)
- Shu-Wen Zheng
- Henan Key Laboratory of Infrared Materials & Spectrum Measures and Applications School of Physics, Henan Normal University, 46 Jianshe Road, Xinxiang 453007, China
| | - Hai-Yu Wang
- State Key Laboratory of Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, 2699 Qianjin Street, Changchun 130012, China
| | - Hai Wang
- State Key Laboratory of Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, 2699 Qianjin Street, Changchun 130012, China
| | - Lei Wang
- State Key Laboratory of Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, 2699 Qianjin Street, Changchun 130012, China
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11
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Katzer M, Selig M, Christiansen D, Ballottin MV, Christianen PCM, Knorr A. Impact of Optically Pumped Nonequilibrium Steady States on Luminescence Emission of Atomically Thin Semiconductor Excitons. PHYSICAL REVIEW LETTERS 2023; 131:146201. [PMID: 37862631 DOI: 10.1103/physrevlett.131.146201] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/10/2022] [Revised: 06/01/2023] [Accepted: 08/22/2023] [Indexed: 10/22/2023]
Abstract
The interplay of the nonequivalent corners in the Brillouin zone of transition metal dichalcogenides (TMDCs) has been investigated extensively. While experimental and theoretical works contributed to a detailed understanding of the relaxation of selective optical excitations and the related relaxation rates, only limited microscopic descriptions of stationary experiments are available so far. Here we present microscopic calculations for the nonequilibrium steady state properties of excitons during continuous wave pumping exemplary for monolayer MoSe_{2}. We find sharp features in photoluminescence excitation spectra and degree of polarization which result from phonon assisted excitonic transitions dominating over exciton recombination and intervalley exchange coupling.
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Affiliation(s)
- Manuel Katzer
- Nichtlineare Optik und Quantenelektronik, Institut für Theoretische Physik, Technische Universität Berlin, 10623 Berlin, Germany
| | - Malte Selig
- Nichtlineare Optik und Quantenelektronik, Institut für Theoretische Physik, Technische Universität Berlin, 10623 Berlin, Germany
| | - Dominik Christiansen
- Nichtlineare Optik und Quantenelektronik, Institut für Theoretische Physik, Technische Universität Berlin, 10623 Berlin, Germany
| | - Mariana V Ballottin
- High Field Magnet Laboratory (HFML-EMFL), Radboud University, Toernooiveld 7, Nijmegen 6525 ED, The Netherlands
| | - Peter C M Christianen
- High Field Magnet Laboratory (HFML-EMFL), Radboud University, Toernooiveld 7, Nijmegen 6525 ED, The Netherlands
| | - Andreas Knorr
- Nichtlineare Optik und Quantenelektronik, Institut für Theoretische Physik, Technische Universität Berlin, 10623 Berlin, Germany
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12
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Abstract
Valley degrees of freedom in transition metal dichalcogenides thoroughly influence electron-phonon coupling and its nonequilibrium dynamics. We conducted a first-principles study of the quantum kinetics of chiral phonons following valley-selective carrier excitation with circularly polarized light. Our numerical investigations treat the ultrafast dynamics of electrons and phonons on equal footing within a parameter-free ab initio framework. We report the emergence of valley-polarized phonon populations in monolayer MoS2 that can be selectively excited at either the K or K' valleys depending on the light helicity. The resulting vibrational state is characterized by a distinctive chirality, which lifts time-reversal symmetry of the lattice on transient time scales. We show that chiral valley phonons can further lead to fingerprints of vibrational dichroism detectable by ultrafast diffuse scattering and persist beyond 10 ps. The valley polarization of nonequilibrium phonon populations could be exploited as an information carrier, thereby extending the paradigm of valleytronics to the domain of vibrational excitations.
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Affiliation(s)
- Yiming Pan
- Institut für Theoretische Physik und Astrophysik, Christian-Albrechts-Universität zu Kiel, D-24118 Kiel, Germany
| | - Fabio Caruso
- Institut für Theoretische Physik und Astrophysik, Christian-Albrechts-Universität zu Kiel, D-24118 Kiel, Germany
- Kiel Nano, Surface and Interface Science KiNSIS, Christian-Albrechts-Universität zu Kiel, D-24118 Kiel, Germany
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13
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Fanciulli M, Bresteau D, Gaudin J, Dong S, Géneaux R, Ruchon T, Tcherbakoff O, Minár J, Heckmann O, Richter MC, Hricovini K, Beaulieu S. Ultrafast Hidden Spin Polarization Dynamics of Bright and Dark Excitons in 2H-WSe_{2}. PHYSICAL REVIEW LETTERS 2023; 131:066402. [PMID: 37625042 DOI: 10.1103/physrevlett.131.066402] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/17/2023] [Accepted: 07/06/2023] [Indexed: 08/27/2023]
Abstract
We performed spin-, time- and angle-resolved extreme ultraviolet photoemission spectroscopy of excitons prepared by photoexcitation of inversion-symmetric 2H-WSe_{2} with circularly polarized light. The very short probing depth of XUV photoemission permits selective measurement of photoelectrons originating from the top-most WSe_{2} layer, allowing for direct measurement of hidden spin polarization of bright and momentum-forbidden dark excitons. Our results reveal efficient chiroptical control of bright excitons' hidden spin polarization. Following optical photoexcitation, intervalley scattering between nonequivalent K-K^{'} valleys leads to a decay of bright excitons' hidden spin polarization. Conversely, the ultrafast formation of momentum-forbidden dark excitons acts as a local spin polarization reservoir, which could be used for spin injection in van der Waals heterostructures involving multilayer transition metal dichalcogenides.
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Affiliation(s)
- Mauro Fanciulli
- Laboratoire de Physique des Matériaux et Surfaces, CY Cergy Paris Université, 95031 Cergy-Pontoise, France
- Université Paris-Saclay, CEA, CNRS, LIDYL, Gif-sur-Yvette, 91191, France
| | - David Bresteau
- Université Paris-Saclay, CEA, CNRS, LIDYL, Gif-sur-Yvette, 91191, France
| | - Jérôme Gaudin
- Université de Bordeaux-CNRS-CEA, CELIA, UMR5107, F33405 Talence, France
| | - Shuo Dong
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - Romain Géneaux
- Université Paris-Saclay, CEA, CNRS, LIDYL, Gif-sur-Yvette, 91191, France
| | - Thierry Ruchon
- Université Paris-Saclay, CEA, CNRS, LIDYL, Gif-sur-Yvette, 91191, France
| | | | - Ján Minár
- University of West Bohemia, New Technologies Research Centre, 301 00 Plzeň, Czech Republic
| | - Olivier Heckmann
- Laboratoire de Physique des Matériaux et Surfaces, CY Cergy Paris Université, 95031 Cergy-Pontoise, France
- Université Paris-Saclay, CEA, CNRS, LIDYL, Gif-sur-Yvette, 91191, France
| | - Maria Christine Richter
- Laboratoire de Physique des Matériaux et Surfaces, CY Cergy Paris Université, 95031 Cergy-Pontoise, France
- Université Paris-Saclay, CEA, CNRS, LIDYL, Gif-sur-Yvette, 91191, France
| | - Karol Hricovini
- Laboratoire de Physique des Matériaux et Surfaces, CY Cergy Paris Université, 95031 Cergy-Pontoise, France
- Université Paris-Saclay, CEA, CNRS, LIDYL, Gif-sur-Yvette, 91191, France
| | - Samuel Beaulieu
- Université de Bordeaux-CNRS-CEA, CELIA, UMR5107, F33405 Talence, France
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14
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Soni A, Kushavah D, Lu LS, Chang WH, Pal SK. Efficient Multiple Exciton Generation in Monolayer MoS 2. J Phys Chem Lett 2023; 14:2965-2972. [PMID: 36939637 DOI: 10.1021/acs.jpclett.3c00306] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/18/2023]
Abstract
Utilization of the excess energy of photoexcitation that is otherwise lost as thermal effects can improve the efficiency of next-generation light-harvesting devices. Multiple exciton generation (MEG) in semiconducting materials yields two or more excitons by absorbing a single high-energy photon, which can break the Shockley-Queisser limit for the conversion efficiency of photovoltaic devices. Recently, monolayer transition metal dichalcogenides (TMDs) have emerged as promising light-harvesting materials because of their high absorption coefficient. Here, we report efficient MEGs with low threshold energy and high (86%) efficiency in a van der Waals (vdW) layered material, MoS2. Through different experimental approaches, we demonstrate the signature of exciton multiplication and discuss the possible origin of decisive MEG in monolayer MoS2. Our results reveal that vdW-layered materials could be a potential candidate for developing mechanically flexible and highly efficient next-generation solar cells and photodetectors.
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Affiliation(s)
- Ashish Soni
- School of Physical Sciences, Indian Institute of Technology Mandi, Kamand, Mandi 175005, Himachal Pradesh, India
- Advanced Materials Research Centre, Indian Institute of Technology Mandi, Kamand, Mandi 175005, Himachal Pradesh, India
| | - Dushyant Kushavah
- School of Physical Sciences, Indian Institute of Technology Mandi, Kamand, Mandi 175005, Himachal Pradesh, India
- Advanced Materials Research Centre, Indian Institute of Technology Mandi, Kamand, Mandi 175005, Himachal Pradesh, India
| | - Li-Syuan Lu
- Department of Electrophysics, National Yang Ming Chiao Tung University, Hsinchu 30010, Taiwan
| | - Wen-Hao Chang
- Department of Electrophysics, National Yang Ming Chiao Tung University, Hsinchu 30010, Taiwan
- Research Center for Applied Sciences, Academia Sinica, Nankang, Taipei 11529, Taiwan
| | - Suman Kalyan Pal
- School of Physical Sciences, Indian Institute of Technology Mandi, Kamand, Mandi 175005, Himachal Pradesh, India
- Advanced Materials Research Centre, Indian Institute of Technology Mandi, Kamand, Mandi 175005, Himachal Pradesh, India
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15
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Koutenský P, Slobodeniuk A, Bartoš M, Trojánek F, Malý P, Kozák M. Ultrafast Dynamics of Valley-Polarized Excitons in WSe 2 Monolayer Studied by Few-Cycle Laser Pulses. NANOMATERIALS (BASEL, SWITZERLAND) 2023; 13:1207. [PMID: 37049301 PMCID: PMC10096652 DOI: 10.3390/nano13071207] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/21/2023] [Revised: 03/20/2023] [Accepted: 03/27/2023] [Indexed: 06/19/2023]
Abstract
We report on the experimental investigation of the ultrafast dynamics of valley-polarized excitons in monolayer WSe2 using transient reflection spectroscopy with few-cycle laser pulses with 7 fs duration. We observe that at room temperature, the anisotropic valley population of excitons decays on two different timescales. The shorter decay time of approximately 120 fs is related to the initial hot exciton relaxation related to the fast direct recombination of excitons from the radiative zone, while the slower picosecond dynamics corresponds to valley depolarization induced by Coloumb exchange-driven transitions of excitons between two inequivalent valleys.
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Affiliation(s)
- Petr Koutenský
- Department of Chemical Physics and Optics, Faculty of Mathematics and Physics, Charles University, Ke Karlovu 3, 121 16 Prague, Czech Republic
| | - Artur Slobodeniuk
- Department of Condensed Matter Physics, Faculty of Mathematics and Physics, Charles University, Ke Karlovu 5, 121 16 Prague, Czech Republic
| | - Miroslav Bartoš
- Central European Institute of Technology, Brno University of Technology, Purkyňova 656/123, 612 00 Brno, Czech Republic
| | - František Trojánek
- Department of Condensed Matter Physics, Faculty of Mathematics and Physics, Charles University, Ke Karlovu 5, 121 16 Prague, Czech Republic
| | - Petr Malý
- Department of Condensed Matter Physics, Faculty of Mathematics and Physics, Charles University, Ke Karlovu 5, 121 16 Prague, Czech Republic
| | - Martin Kozák
- Department of Condensed Matter Physics, Faculty of Mathematics and Physics, Charles University, Ke Karlovu 5, 121 16 Prague, Czech Republic
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16
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Kunin A, Chernov S, Bakalis J, Li Z, Cheng S, Withers ZH, White MG, Schönhense G, Du X, Kawakami RK, Allison TK. Momentum-Resolved Exciton Coupling and Valley Polarization Dynamics in Monolayer WS_{2}. PHYSICAL REVIEW LETTERS 2023; 130:046202. [PMID: 36763432 DOI: 10.1103/physrevlett.130.046202] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/14/2022] [Accepted: 12/22/2022] [Indexed: 06/18/2023]
Abstract
Using time- and angle-resolved photoemission, we present momentum- and energy-resolved measurements of exciton coupling in monolayer WS_{2}. We observe strong intravalley coupling between the B_{1s} exciton and A_{n>1} states. Our measurements indicate that the dominant valley depolarization mechanism conserves the exciton binding energy and momentum. While this conservation is consistent with Coulomb exchange-driven valley depolarization, we do not observe a momentum or energy dependence to the depolarization rate as would be expected for the exchange-based mechanism.
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Affiliation(s)
- Alice Kunin
- Department of Chemistry, Stony Brook University, Stony Brook, New York 11794, USA
| | - Sergey Chernov
- Department of Chemistry, Stony Brook University, Stony Brook, New York 11794, USA
| | - Jin Bakalis
- Department of Chemistry, Stony Brook University, Stony Brook, New York 11794, USA
| | - Ziling Li
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
| | - Shuyu Cheng
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
| | - Zachary H Withers
- Department of Physics and Astronomy, Stony Brook University, Stony Brook, New York 11794, USA
| | - Michael G White
- Department of Chemistry, Stony Brook University, Stony Brook, New York 11794, USA
- Chemistry Division, Brookhaven National Laboratory, Upton, New York 11973, USA
| | - Gerd Schönhense
- Johannes Gutenberg-Universität, Institut für Physik, D-55099 Mainz, Germany
| | - Xu Du
- Department of Physics and Astronomy, Stony Brook University, Stony Brook, New York 11794, USA
| | - Roland K Kawakami
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
| | - Thomas K Allison
- Department of Chemistry, Stony Brook University, Stony Brook, New York 11794, USA
- Department of Physics and Astronomy, Stony Brook University, Stony Brook, New York 11794, USA
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17
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Ye L, Xu X, He S, Liu Y, Jin Y, Yang YM, Zhu H. Molecular Triplet Sensitization of Monolayer Semiconductors in 2D Organic/Inorganic Hybrid Heterostructures. ACS NANO 2022; 16:12532-12540. [PMID: 35900068 DOI: 10.1021/acsnano.2c03995] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Hybrid heterostructures (HSs) comprising organic and two-dimensional (2D) monolayer semiconductors hold great promise for optoelectronic applications. So far, research efforts on organic/2D HSs have exclusively focused on coupling directly photoexcited singlets to monolayer semiconductors. It remains unexplored whether and how the optically dark triplets in organic semiconductors with intriguing properties (e.g., long lifetime) can be implemented for modulating light-matter interactions of hybrid HSs. Herein, we investigate the triplet sensitization of monolayer semiconductors by time-resolved spectroscopic studies on Pd-octaethylporphyrin (PdOEP)/WSe2 and PdOEP/WS2 HSs with type I and type II band alignment, respectively. We show that PdOEP triplets formed in ∼5 ps from intersystem crossing can transfer energy or charge to WSe2 or WS2 monolayers, respectively, leading to a significant photoluminescence enhancement (180%) in WSe2 or long-lived charge separation (>2 ns) in WS2. The triplet transfer occurs in ∼100 ns, which is more than 3 orders of magnitude slower than singlet and can be attributed to its tightly localized nature. Further study of thickness dependence reveals the dictating role of triplet diffusion for triplet sensitization in organic/2D HSs. This study shows the great promise of much less explored molecular triplets on sensitizing 2D monolayer semiconductors and provides the guidance to achieve long-range light harvesting and energy migration in organic/2D HSs for enhanced optoelectronic applications.
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Affiliation(s)
- Lei Ye
- Key Laboratory of Excited-State Materials of Zhejiang Province, Department of Chemistry, Zhejiang University, Hangzhou 310027, China
- ZJU-Hangzhou Global Scientific and Technological Innovation Center, Hangzhou 310014, China
| | - Xuehui Xu
- State Key Laboratory of Modern Optical Instrumentation, College of Optical Science and Engineering, Zhejiang University, Hangzhou 310027, China
| | - Siyu He
- Key Laboratory of Excited-State Materials of Zhejiang Province, Department of Chemistry, Zhejiang University, Hangzhou 310027, China
| | - Yanping Liu
- Key Laboratory of Excited-State Materials of Zhejiang Province, Department of Chemistry, Zhejiang University, Hangzhou 310027, China
| | - Yizheng Jin
- Key Laboratory of Excited-State Materials of Zhejiang Province, Department of Chemistry, Zhejiang University, Hangzhou 310027, China
| | - Yang Michael Yang
- State Key Laboratory of Modern Optical Instrumentation, College of Optical Science and Engineering, Zhejiang University, Hangzhou 310027, China
| | - Haiming Zhu
- Key Laboratory of Excited-State Materials of Zhejiang Province, Department of Chemistry, Zhejiang University, Hangzhou 310027, China
- ZJU-Hangzhou Global Scientific and Technological Innovation Center, Hangzhou 310014, China
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18
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Trovatello C, Katsch F, Li Q, Zhu X, Knorr A, Cerullo G, Dal Conte S. Disentangling Many-Body Effects in the Coherent Optical Response of 2D Semiconductors. NANO LETTERS 2022; 22:5322-5329. [PMID: 35759746 PMCID: PMC9284612 DOI: 10.1021/acs.nanolett.2c01309] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
In single-layer (1L) transition metal dichalcogenides, the reduced Coulomb screening results in strongly bound excitons which dominate the linear and the nonlinear optical response. Despite the large number of studies, a clear understanding on how many-body and Coulomb correlation effects affect the excitonic resonances on a femtosecond time scale is still lacking. Here, we use ultrashort laser pulses to measure the transient optical response of 1L-WS2. In order to disentangle many-body effects, we perform exciton line-shape analysis, and we study its temporal dynamics as a function of the excitation photon energy and fluence. We find that resonant photoexcitation produces a blue shift of the A exciton, while for above-resonance photoexcitation the transient response at the optical bandgap is largely determined by a reduction of the exciton oscillator strength. Microscopic calculations based on excitonic Heisenberg equations of motion quantitatively reproduce the nonlinear absorption of the material and its dependence on excitation conditions.
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Affiliation(s)
- Chiara Trovatello
- Dipartimento
di Fisica, Politecnico di Milano, Piazza L. da Vinci 32, I-20133 Milano, Italy
| | - Florian Katsch
- Institut
für Theoretische Physik, Nichtlineare Optik und Quantenelektronik, Technische Universität Berlin, 10623 Berlin, Germany
| | - Qiuyang Li
- Department
of Chemistry, Columbia University, New York, New York 10027, United States
| | - Xiaoyang Zhu
- Department
of Chemistry, Columbia University, New York, New York 10027, United States
| | - Andreas Knorr
- Institut
für Theoretische Physik, Nichtlineare Optik und Quantenelektronik, Technische Universität Berlin, 10623 Berlin, Germany
| | - Giulio Cerullo
- Dipartimento
di Fisica, Politecnico di Milano, Piazza L. da Vinci 32, I-20133 Milano, Italy
| | - Stefano Dal Conte
- Dipartimento
di Fisica, Politecnico di Milano, Piazza L. da Vinci 32, I-20133 Milano, Italy
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19
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Zhang C, Lu G, Zhang Y, Fang Z, He H, Zhu H. Long-range transport and ultrafast interfacial charge transfer in perovskite/monolayer semiconductor heterostructure for enhanced light absorption and photocarrier lifetime. J Chem Phys 2022; 156:244701. [DOI: 10.1063/5.0097617] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Atomically thin two-dimensional transition metal dichalcogenides (TMDs) have shown great potential for optoelectronic applications, including photodetectors, phototransistors, and spintronic devices. However, the applications of TMD-based optoelectronic devices are severely restricted by their weak light absorption and short exciton lifetime due to their atomically thin nature and strong excitonic effect. To simultaneously enhance the light absorption and photocarrier lifetime of monolayer semiconductors, here, we report 3D/2D perovskite/TMD type II heterostructures by coupling solution processed highly smooth and ligand free CsPbBr3 film with MoS2 and WS2 monolayers. By time-resolved spectroscopy, we show interfacial hole transfer from MoS2 (WS2) to the perovskite layer occurs in an ultrafast time scale (100 and 350 fs) and interfacial electron transfer from ultrathin CsPbBr3 to MoS2 (WS2) in ∼3 (9) ps, forming a long-lived charge separation with a lifetime of >20 ns. With increasing CsPbBr3 thickness, the electron transfer rate from CsPbBr3 to TMD is slower, but the efficiency remains to be near-unity due to coupled long-range diffusion and ultrafast interfacial electron transfer. This study indicates that coupling solution processed lead halide perovskites with strong light absorption and long carrier diffusion length to monolayer semiconductors to form a type II heterostructure is a promising strategy to simultaneously enhance the light harvesting capability and photocarrier lifetime of monolayer semiconductors.
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Affiliation(s)
- Chi Zhang
- State Key Laboratory of Modern Optical Instrumentation, Key Laboratory of Excited-State Materials of Zhejiang Province, Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang 310027, China
| | - Guochao Lu
- School of Materials Science and Engineering, State Key Laboratory of Silicon Materials, Zhejiang University, Hangzhou 310027, China
| | - Yao Zhang
- State Key Laboratory of Modern Optical Instrumentation, Key Laboratory of Excited-State Materials of Zhejiang Province, Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang 310027, China
| | - Zhishan Fang
- School of Materials Science and Engineering, State Key Laboratory of Silicon Materials, Zhejiang University, Hangzhou 310027, China
| | - Haiping He
- School of Materials Science and Engineering, State Key Laboratory of Silicon Materials, Zhejiang University, Hangzhou 310027, China
| | - Haiming Zhu
- State Key Laboratory of Modern Optical Instrumentation, Key Laboratory of Excited-State Materials of Zhejiang Province, Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang 310027, China
- ZJU-Hangzhou Global Scientific and Technological Innovation Center, Hangzhou, Zhejiang 311200, China
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20
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Zheng SW, Wang D, Wang HY, Wang H, Chen X, Zhao LY, Wang L, Li XB, Sun HB. Spin-Valley Depolarization in van der Waals Heterostructures. J Phys Chem Lett 2022; 13:5501-5507. [PMID: 35695739 DOI: 10.1021/acs.jpclett.2c01414] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
The appearance of van der Waals heterostructures offers a new solution to valleytronics. Here, we observe the spin-valley depolarization process of electrons and holes in type-II MoS2-WSe2 heterostructures simultaneously for the first time by valley-resolved broad-band femtosecond pump-probe experiments. The different depolarization paths between electrons and holes make them have different spin-valley polarization lifetimes. The spin-valley depolarization pathway of holes is mainly dominated by a phonon-assisted intervalley scattering process, while intra- and intervalley coupling can trigger additional depolarization pathways for electrons. The hole polarization lifetime can be further prolonged to more than three times in trilayer heterostructure 2MoS2-WSe2. For MoS2-WS2 that has strong orbital hybridization of Mo and W atoms, both electrons and holes lose the spin-valley polarization extremely soon after charge separation, behaving similarly to intraexcitons in a monolayer. Our work advances the basic understanding of spin-valley depolarization of van der Waals heterostructures and facilitates the effort toward longer lifetime valleytronic devices for information transfer and storage applications.
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Affiliation(s)
- Shu-Wen Zheng
- State Key Laboratory of Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, 2699 Qianjin Street, Changchun 130012, China
| | - Dan Wang
- Department of Mechanical Engineering and Materials Science, Yale University, New Haven, Connecticut 06511, United States
| | - Hai-Yu Wang
- State Key Laboratory of Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, 2699 Qianjin Street, Changchun 130012, China
| | - Hai Wang
- State Key Laboratory of Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, 2699 Qianjin Street, Changchun 130012, China
| | - Xin Chen
- State Key Laboratory of Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, 2699 Qianjin Street, Changchun 130012, China
| | - Le-Yi Zhao
- State Key Laboratory of Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, 2699 Qianjin Street, Changchun 130012, China
| | - Lei Wang
- State Key Laboratory of Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, 2699 Qianjin Street, Changchun 130012, China
| | - Xian-Bin Li
- State Key Laboratory of Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, 2699 Qianjin Street, Changchun 130012, China
| | - Hong-Bo Sun
- State Key Laboratory of Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, 2699 Qianjin Street, Changchun 130012, China
- State Key Laboratory of Precision Measurement Technology and Instruments, Department of Precision Instrument, Tsinghua University, Haidian, Beijing 100084, China
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21
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Mondal N, Azam N, Gartstein YN, Mahjouri-Samani M, Malko AV. Photoexcitation Dynamics and Long-Lived Excitons in Strain-Engineered Transition Metal Dichalcogenides. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2022; 34:e2110568. [PMID: 35355335 DOI: 10.1002/adma.202110568] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/27/2021] [Revised: 03/17/2022] [Indexed: 06/14/2023]
Abstract
Strain-engineering in 2D transition metal dichalcogenide (TMD) semiconductors has garnered intense research interest in tailoring the optical properties via strain-induced modifications of the electronic bands in TMDs, while its impact on the exciton dynamics remains less understood. To address this, an extensive study of transient optical absorption (TA) of both W- and Mo-based single-crystalline monolayer TMDs grown by a recently developed laser-assisted evaporation method is performed. All spectral features of the monolayers as grown on fused silica substrates exhibit appreciable redshifts relating to the existence of strain due to growth conditions. Moreover, these systems exhibit a dramatic slowing down of exciton dynamics (100s of picoseconds to few nanoseconds) with an increase in carrier densities, which strongly contrasts with the monolayers in their freestanding form as well as in comparison with more traditionally grown TMDs. The observations are related to the modifications of the electronic bands as expected from the strain and associated population of the intervalley dark excitons that can now interplay with intravalley excitations. These findings are consistent across both the Mo- and W-based TMD families, providing key information about the influence of the growth conditions on the nature of optical excitations and fostering emerging optoelectronic applications of monolayer TMDs.
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Affiliation(s)
- Navendu Mondal
- Department of Physics, The University of Texas at Dallas, Richardson, TX, 75080, USA
| | - Nurul Azam
- Department of Electrical and Computer Engineering, Auburn University, Auburn, AL, 36849, USA
| | - Yuri N Gartstein
- Department of Physics, The University of Texas at Dallas, Richardson, TX, 75080, USA
| | - Masoud Mahjouri-Samani
- Department of Electrical and Computer Engineering, Auburn University, Auburn, AL, 36849, USA
| | - Anton V Malko
- Department of Physics, The University of Texas at Dallas, Richardson, TX, 75080, USA
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22
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Li Z, Yan Y, Song MS, Xin JY, Wang HY, Wang H, Wang Y. Exciton-Phonon Coupling of Chiral One-Dimensional Lead-Free Hybrid Metal Halides at Room Temperature. J Phys Chem Lett 2022; 13:4073-4081. [PMID: 35499477 DOI: 10.1021/acs.jpclett.2c00698] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
The interaction between organic cations and inorganic metal halide octahedral units strongly affects the properties of organic-inorganic hybrid metal halides. The "soft" property of the lattice provides the possibility of its strong exciton-phonon interaction. Here we report one-dimensional (1D) lead-free chiral organic-inorganic hybrid metal halide single crystals of (R/S)-methylbenzylamine bismuth iodide (R/S-MBA)2Bi2I8, which exhibits a high level of octahedral bond distortion. The introduction of chiral amines leads to a strong chiroptical response in the range of 200-600 nm. The strong exciton-phonon coupling can be observed through the coherent oscillation spectrum of transient absorption dynamics at room temperature. The coherent phonon oscillation frequencies are ∼97 and ∼130 cm-1, corresponding to the symmetrical stretching or bending of the Bi-I octahedron. Our work provides new insights for the study of exciton-phonon coupling in 1D chiral hybrid metal halides.
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Affiliation(s)
- Zhen Li
- State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, 2699 Qianjin Street, Changchun 130012, P. R. China
| | - Yan Yan
- State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, 2699 Qianjin Street, Changchun 130012, P. R. China
| | - Mu-Sen Song
- State Key Laboratory of Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, 2699 Qianjin Street, Changchun 130012, P. R. China
| | - Jia-Yu Xin
- State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, 2699 Qianjin Street, Changchun 130012, P. R. China
| | - Hai-Yu Wang
- State Key Laboratory of Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, 2699 Qianjin Street, Changchun 130012, P. R. China
| | - Hai Wang
- State Key Laboratory of Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, 2699 Qianjin Street, Changchun 130012, P. R. China
| | - Yu Wang
- State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, 2699 Qianjin Street, Changchun 130012, P. R. China
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23
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Zhou H, Sun C, Xin W, Li Y, Chen Y, Zhu H. Spatiotemporally Coupled Electron-Hole Dynamics in Two Dimensional Heterostructures. NANO LETTERS 2022; 22:2547-2553. [PMID: 35285224 DOI: 10.1021/acs.nanolett.2c00479] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Coulomb interactions play a crucial role in low-dimensional semiconductor materials, e.g., 2D layered semiconductors, dictating their electronic and optical properties. However, fundamental questions remain as to whether and how Coulomb interactions affect the charge or energy flow in 2D heterostructures, which is essential for their light-electricity conversions. Herein, using ultrafast spectroscopy, we report real space coupled electron-hole dynamics in 2D heterostructures. We show in (WSe2/)WS2/MoTe2 with a controlled energy gradient for the hole and a near flat band for electron transfer, the fate of the electron is controlled by the hole in coupled dynamics. The interfacial electron transfer from WS2 to MoTe2 follows the hole closely and can be facilitated or suppressed by dynamic Coulomb interaction. In parallel to the band alignment, this study reveals the critical role of Coulomb interactions on the fate of photogenerated charges in 2D heterostructures, providing experimental evidence for coupled electron-hole dynamics and a new knob for steering nanoscale charge or energy transfer process.
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Affiliation(s)
- Hongzhi Zhou
- State Key Laboratory of Modern Optical Instrumentation, Key Laboratory of Excited-State Materials of Zhejiang Province, Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang 310027, China
| | - Cheng Sun
- State Key Laboratory of Modern Optical Instrumentation, Key Laboratory of Excited-State Materials of Zhejiang Province, Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang 310027, China
| | - Wei Xin
- Key Laboratory of UV-Emitting Materials and Technology, Ministry of Education, Northeast Normal University, Changchun, Jilin 130024, China
| | - Yujie Li
- State Key Laboratory of Modern Optical Instrumentation, Key Laboratory of Excited-State Materials of Zhejiang Province, Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang 310027, China
| | - Yuzhong Chen
- State Key Laboratory of Modern Optical Instrumentation, Key Laboratory of Excited-State Materials of Zhejiang Province, Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang 310027, China
| | - Haiming Zhu
- State Key Laboratory of Modern Optical Instrumentation, Key Laboratory of Excited-State Materials of Zhejiang Province, Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang 310027, China
- Hangzhou Global Scientific and Technological Innovation Center, Zhejiang University, Hangzhou 310014, P. R. China
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24
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Hahn T, Vaclavkova D, Bartos M, Nogajewski K, Potemski M, Watanabe K, Taniguchi T, Machnikowski P, Kuhn T, Kasprzak J, Wigger D. Destructive Photon Echo Formation in Six-Wave Mixing Signals of a MoSe 2 Monolayer. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2022; 9:e2103813. [PMID: 34716672 PMCID: PMC8728888 DOI: 10.1002/advs.202103813] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/30/2021] [Revised: 10/05/2021] [Indexed: 05/30/2023]
Abstract
Monolayers of transition metal dichalcogenides display a strong excitonic optical response. Additionally encapsulating the monolayer with hexagonal boron nitride allows to reach the limit of a purely homogeneously broadened exciton system. On such a MoSe2 -based system, ultrafast six-wave mixing spectroscopy is performed and a novel destructive photon echo effect is found. This process manifests as a characteristic depression of the nonlinear signal dynamics when scanning the delay between the applied laser pulses. By theoretically describing the process within a local field model, an excellent agreement with the experiment is reached. An effective Bloch vector representation is developed and thereby it is demonstrated that the destructive photon echo stems from a destructive interference of successive repetitions of the heterodyning experiment.
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Affiliation(s)
- Thilo Hahn
- Institute of Solid State TheoryUniversity of MünsterMünster48149Germany
- Department of Theoretical PhysicsWrocław University of Science and TechnologyWrocław50‐370Poland
| | - Diana Vaclavkova
- Laboratiore National des Champs Magnétiques IntensesLNCMI‐EMFLCNRS UPR3228, Univ. Grenoble Alpes, Univ. Toulouse, Univ. Toulouse 3, INSA‐TGrenoble and ToulouseFrance
| | - Miroslav Bartos
- Laboratiore National des Champs Magnétiques IntensesLNCMI‐EMFLCNRS UPR3228, Univ. Grenoble Alpes, Univ. Toulouse, Univ. Toulouse 3, INSA‐TGrenoble and ToulouseFrance
- Central European Institute of TechnologyBrno University of TechnologyBrnoCzech61200Republic
| | - Karol Nogajewski
- Institute of Experimental PhysicsFaculty of PhysicsUniversity of WarsawWarszawa02‐093Poland
| | - Marek Potemski
- Laboratiore National des Champs Magnétiques IntensesLNCMI‐EMFLCNRS UPR3228, Univ. Grenoble Alpes, Univ. Toulouse, Univ. Toulouse 3, INSA‐TGrenoble and ToulouseFrance
- Institute of Experimental PhysicsFaculty of PhysicsUniversity of WarsawWarszawa02‐093Poland
| | - Kenji Watanabe
- Research Center for Functional MaterialsNational Institute for Materials ScienceTsukuba305‐0044Japan
| | - Takashi Taniguchi
- International Center for Materials NanoarchitectonicsNational Institute for Materials ScienceTsukuba305‐0044Japan
| | - Paweł Machnikowski
- Department of Theoretical PhysicsWrocław University of Science and TechnologyWrocław50‐370Poland
| | - Tilmann Kuhn
- Institute of Solid State TheoryUniversity of MünsterMünster48149Germany
| | - Jacek Kasprzak
- Université Grenoble AlpesCNRS, Grenoble INP, Institut NéelGrenoble38000France
| | - Daniel Wigger
- Department of Theoretical PhysicsWrocław University of Science and TechnologyWrocław50‐370Poland
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25
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Chen X, Zheng S, Wang XP, Wang HY. Ultrafast dynamics of spin relaxation in monolayer WSe2 and WSe2/graphene heterojunction. Phys Chem Chem Phys 2022; 24:16538-16544. [DOI: 10.1039/d2cp02105f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Excitonic devices based on two-dimensional (2D) transition metal dichalcogenides (TMDCs) can combine spintronics with valleytronics due to its special energy band structure. In this work, we studied the generation and...
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26
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Li S, Liu Y, Chen D, Jiang Y, Nie Z, Pan F. Encoding the atomic structure for machine learning in materials science. WIRES COMPUTATIONAL MOLECULAR SCIENCE 2022. [DOI: 10.1002/wcms.1558] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Affiliation(s)
- Shunning Li
- School of Advanced Materials Peking University, Shenzhen Graduate School Shenzhen China
| | - Yuanji Liu
- School of Advanced Materials Peking University, Shenzhen Graduate School Shenzhen China
| | - Dong Chen
- School of Advanced Materials Peking University, Shenzhen Graduate School Shenzhen China
| | - Yi Jiang
- School of Advanced Materials Peking University, Shenzhen Graduate School Shenzhen China
| | - Zhiwei Nie
- School of Advanced Materials Peking University, Shenzhen Graduate School Shenzhen China
| | - Feng Pan
- School of Advanced Materials Peking University, Shenzhen Graduate School Shenzhen China
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27
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Thompson JJP, Brem S, Fang H, Antón-Solanas C, Han B, Shan H, Dash SP, Wieczorek W, Schneider C, Malic E. Valley-exchange coupling probed by angle-resolved photoluminescence. NANOSCALE HORIZONS 2021; 7:77-84. [PMID: 34796891 DOI: 10.1039/d1nh00302j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
The optical properties of monolayer transition metal dichalcogenides are dominated by tightly-bound excitons. They form at distinct valleys in reciprocal space, and can interact via the valley-exchange coupling, modifying their dispersion considerably. Here, we predict that angle-resolved photoluminescence can be used to probe the changes of the excitonic dispersion. The exchange-coupling leads to a unique angle dependence of the emission intensity for both circularly and linearly-polarised light. We show that these emission characteristics can be strongly tuned by an external magnetic field due to the valley-specific Zeeman-shift. We propose that angle-dependent photoluminescence measurements involving both circular and linear optical polarisation as well as magnetic fields should act as strong verification of the role of valley-exchange coupling on excitonic dispersion and its signatures in optical spectra.
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Affiliation(s)
- Joshua J P Thompson
- Department of Physics, Chalmers University of Technology, Gothenburg 412 96, Sweden.
| | - Samuel Brem
- Department of Physics, Philipps-Universität Marburg, Renthof 7, Marburg 35032, Germany
| | - Hanlin Fang
- Department of Microtechnology and Nanoscience (MC2), Chalmers University of Technology, Gothenburg 412 96, Sweden
| | | | - Bo Han
- Institute of Physics, University of Oldenburg, 26129 Oldenburg, Germany
| | - Hangyong Shan
- Institute of Physics, University of Oldenburg, 26129 Oldenburg, Germany
| | - Saroj P Dash
- Department of Microtechnology and Nanoscience (MC2), Chalmers University of Technology, Gothenburg 412 96, Sweden
| | - Witlef Wieczorek
- Department of Microtechnology and Nanoscience (MC2), Chalmers University of Technology, Gothenburg 412 96, Sweden
| | | | - Ermin Malic
- Department of Physics, Chalmers University of Technology, Gothenburg 412 96, Sweden.
- Department of Physics, Philipps-Universität Marburg, Renthof 7, Marburg 35032, Germany
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28
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Zheng SW, Wang L, Wang HY, Xu CY, Luo Y, Sun HB. Observation of quantum-confined exciton states in monolayer WS 2 quantum dots by ultrafast spectroscopy. NANOSCALE 2021; 13:17093-17100. [PMID: 34623366 DOI: 10.1039/d1nr04868f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Monolayer transition metal dichalcogenide quantum dots (TMDC QDs) could exhibit unique photophysical properties, because of both lateral quantum confinement effect and edge effect. However, there is little fundamental study on the quantum-confined exciton dynamics in monolayer TMDC QDs, to date. Here, by selective excitations of monolayer WS2 QDs in broadband transient absorption (TA) spectroscopy experiments, the excitation-wavelength-dependent ground state bleaching signals corresponding to the quantum-confined exciton states are directly observed. Compared to the time-resolved photophysical properties of WS2 nanosheets, the selected monolayer WS2 QDs only show one ground state bleaching peak with larger initial values for the linear polarization anisotropy of band-edge excitons, probably due to the expired spin-orbit coupling. This suggests a complete change of the band structure for monolayer WS2 QDs. In the femtosecond time-resolved circular polarization anisotropy experiments, a valley depolarization time of ∼100 fs is observed for WS2 nanosheets at room temperature, which is not observed for monolayer WS2 QDs. Our findings suggest a strong state-mixing of band-edge valley excitons responsible for the large linear polarization in monolayer WS2 QDs, which could be helpful for understanding the exciton relaxation mechanisms in colloidal monolayer TMDC QDs.
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Affiliation(s)
- Shu-Wen Zheng
- State Key Laboratory of Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, 2699 Qianjin Street, Changchun 130012, China.
| | - Lei Wang
- State Key Laboratory of Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, 2699 Qianjin Street, Changchun 130012, China.
| | - Hai-Yu Wang
- State Key Laboratory of Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, 2699 Qianjin Street, Changchun 130012, China.
| | - Chen-Yu Xu
- State Key Laboratory of Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, 2699 Qianjin Street, Changchun 130012, China.
| | - Yang Luo
- Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033, China
| | - Hong-Bo Sun
- State Key Laboratory of Precision Measurement Technology and Instruments, Department of Precision Instrument, Tsinghua University, Haidian, Beijing 100084, China
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29
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Ye L, Liu Y, Zhou Q, Tao W, Li Y, Wang Z, Zhu H. Ultrafast Singlet Energy Transfer before Fission in a Tetracene/WSe 2 Type II Hybrid Heterostructure. J Phys Chem Lett 2021; 12:8440-8446. [PMID: 34436908 DOI: 10.1021/acs.jpclett.1c02540] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Hybrid heterostructures comprising organic and two-dimensional (2D) layered semiconductors hold great promise for light harvesting and optoelectronic applications. Among them, organic materials that exhibit singlet fission (SF) in which one singlet exciton generates two triplet excitons are particularly attractive and can potentially improve the performance of the device. However, SF-enhanced devices require that SF can compete with direct energy/charge transfer from the singlet exciton. Here, we performed ultrafast spectroscopic studies on a prototypical heterostructure consisting of tetracene (Tc) and monolayer WSe2. We show a type II band alignment with 16.5 ps hole transfer from photoexcited WSe2 to tetracene and a long-lived (∼565 ps) charge separation. Importantly, we show ultrafast (∼3.4 ps) singlet exciton energy transfer from photoexcited tetracene to WSe2, prior to the slow SF process (>20 ps) in tetracene. This study raises the challenge and calls for the careful design of SF-enhanced 2D optoelectronic devices.
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Affiliation(s)
- Lei Ye
- State Key Laboratory of Modern Optical Instrumentation, Key Laboratory of Excited-State Materials of Zhejiang Province, Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang 310027, China
| | - Yanping Liu
- State Key Laboratory of Modern Optical Instrumentation, Key Laboratory of Excited-State Materials of Zhejiang Province, Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang 310027, China
| | - Qiaohui Zhou
- State Key Laboratory of Modern Optical Instrumentation, Key Laboratory of Excited-State Materials of Zhejiang Province, Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang 310027, China
| | - Weijian Tao
- State Key Laboratory of Modern Optical Instrumentation, Key Laboratory of Excited-State Materials of Zhejiang Province, Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang 310027, China
| | - Yujie Li
- State Key Laboratory of Modern Optical Instrumentation, Key Laboratory of Excited-State Materials of Zhejiang Province, Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang 310027, China
| | - Zukun Wang
- State Key Laboratory of Modern Optical Instrumentation, Key Laboratory of Excited-State Materials of Zhejiang Province, Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang 310027, China
| | - Haiming Zhu
- State Key Laboratory of Modern Optical Instrumentation, Key Laboratory of Excited-State Materials of Zhejiang Province, Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang 310027, China
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30
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Zhou H, Chen Y, Zhu H. Deciphering asymmetric charge transfer at transition metal dichalcogenide-graphene interface by helicity-resolved ultrafast spectroscopy. SCIENCE ADVANCES 2021; 7:7/34/eabg2999. [PMID: 34417175 PMCID: PMC8378813 DOI: 10.1126/sciadv.abg2999] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/23/2020] [Accepted: 07/01/2021] [Indexed: 05/27/2023]
Abstract
Transition metal dichalcogenide (TMD)/graphene (Gr) heterostructures constitute a key component for two-dimensional devices. The operation of TMD/Gr devices relies on interfacial charge/energy transfer processes, which remains unclear and challenging to unravel. Fortunately, the coupled spin and valley index in TMDs adds a new degree of freedom to the charges and, thus, another dimension to spectroscopy. Here, by helicity-resolved ultrafast spectroscopy, we find that photoexcitation in TMDs transfers to graphene by asynchronous charge transfer, with one type of charge transferring in the order of femtoseconds and the other in picoseconds. The rate correlates well with energy offset between TMD and graphene, regardless of compositions and charge species. Spin-polarized hole injection or long-lived polarized hole can be achieved with deliberately designed heterostructures. This study shows helicity-resolved ultrafast spectroscopy as a powerful and facile approach to reveal the fundamental and complex charge/spin dynamics in TMD-based heterostructures, paving the way toward valleytronic and optoelectronic applications.
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Affiliation(s)
- Hongzhi Zhou
- State Key Laboratory of Modern Optical Instrumentation, Key Laboratory of Excited-State Materials of Zhejiang Province, Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang 310027, China
| | - Yuzhong Chen
- State Key Laboratory of Modern Optical Instrumentation, Key Laboratory of Excited-State Materials of Zhejiang Province, Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang 310027, China
| | - Haiming Zhu
- State Key Laboratory of Modern Optical Instrumentation, Key Laboratory of Excited-State Materials of Zhejiang Province, Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang 310027, China.
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31
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Goswami T, Bhatt H, Babu KJ, Kaur G, Ghorai N, Ghosh HN. Ultrafast Insights into High Energy (C and D) Excitons in Few Layer WS 2. J Phys Chem Lett 2021; 12:6526-6534. [PMID: 34242025 DOI: 10.1021/acs.jpclett.1c01627] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
High energy (C and D) excitons possess extraordinary influence over the optical properties of atomically thin transition metal dichalcogenides (TMDCs), and the comprehensive understanding of these would play a pivotal role in advancing research on 2D optoelectronics. Herein, we employed transient absorption spectroscopy to monitor the underlying photophysical processes involved with different excitonic features in few layer WS2, modeled as a TMDC representative. We observed a strong intervalley coupling across the momentum space and proposed the most plausible relaxation pathway for different excitons in few layer scenario. C and D exciton dynamics were significantly slower as compared to canonical A and B excitons, as a consequence of the indirect Λ-Γ relaxation in C and D and direct K-K combination in A and B. Most importantly, all four excitons emerge in the system and influence each other irrespective of the incident photon energy, which would be extremely impactful in fabricating wide range photonic devices.
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Affiliation(s)
- Tanmay Goswami
- Institute of Nano Science and Technology, Knowledge City, Sector 81, SAS Nagar, Punjab 140306, India
| | - Himanshu Bhatt
- Institute of Nano Science and Technology, Knowledge City, Sector 81, SAS Nagar, Punjab 140306, India
| | - K Justice Babu
- Institute of Nano Science and Technology, Knowledge City, Sector 81, SAS Nagar, Punjab 140306, India
| | - Gurpreet Kaur
- Institute of Nano Science and Technology, Knowledge City, Sector 81, SAS Nagar, Punjab 140306, India
| | - Nandan Ghorai
- Institute of Nano Science and Technology, Knowledge City, Sector 81, SAS Nagar, Punjab 140306, India
| | - Hirendra N Ghosh
- Institute of Nano Science and Technology, Knowledge City, Sector 81, SAS Nagar, Punjab 140306, India
- Radiation and Photochemistry Division, Bhabha Atomic Research Centre, Mumbai 400085, India
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32
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Lloyd LT, Wood RE, Mujid F, Sohoni S, Ji KL, Ting PC, Higgins JS, Park J, Engel GS. Sub-10 fs Intervalley Exciton Coupling in Monolayer MoS 2 Revealed by Helicity-Resolved Two-Dimensional Electronic Spectroscopy. ACS NANO 2021; 15:10253-10263. [PMID: 34096707 DOI: 10.1021/acsnano.1c02381] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
The valley pseudospin at the K and K' high-symmetry points in monolayer transition metal dichalcogenides (TMDs) has potential as an optically addressable degree of freedom in next-generation optoelectronics. However, intervalley scattering and relaxation of charge carriers leads to valley depolarization and limits practical applications. In addition, enhanced Coulomb interactions lead to pronounced excitonic effects that dominate the optical response and initial valley depolarization dynamics but complicate the interpretation of ultrafast spectroscopic experiments at short time delays. Employing broadband helicity-resolved two-dimensional electronic spectroscopy (2DES), we observe ultrafast (∼10 fs) intervalley coupling between all A and B valley exciton states that results in a complete breakdown of the valley index in large-area monolayer MoS2 films. These couplings and subsequent dynamics exhibit minimal excitation fluence or temperature dependence and are robust toward changes in sample grain size and inherent strain. Our observations strongly suggest that this direct intervalley coupling on the time scale of optical excitation is an inherent property of large-area MoS2 distinct from dynamic carrier or exciton scattering, phonon-driven processes, and multiexciton effects. This ultrafast intervalley coupling poses a fundamental challenge for exciton-based valleytronics in monolayer TMDs and must be overcome to fully realize large-area valleytronic devices.
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Affiliation(s)
- Lawson T Lloyd
- Department of Chemistry, The University of Chicago, Chicago, Illinois 60637, United States
- James Franck Institute, The University of Chicago, Chicago, Illinois 60637, United States
- Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, United States
| | - Ryan E Wood
- Department of Chemistry, The University of Chicago, Chicago, Illinois 60637, United States
- James Franck Institute, The University of Chicago, Chicago, Illinois 60637, United States
- Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, United States
| | - Fauzia Mujid
- Department of Chemistry, The University of Chicago, Chicago, Illinois 60637, United States
- James Franck Institute, The University of Chicago, Chicago, Illinois 60637, United States
| | - Siddhartha Sohoni
- Department of Chemistry, The University of Chicago, Chicago, Illinois 60637, United States
- James Franck Institute, The University of Chicago, Chicago, Illinois 60637, United States
- Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, United States
| | - Karen L Ji
- Department of Chemistry, The University of Chicago, Chicago, Illinois 60637, United States
- James Franck Institute, The University of Chicago, Chicago, Illinois 60637, United States
- Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, United States
| | - Po-Chieh Ting
- Department of Chemistry, The University of Chicago, Chicago, Illinois 60637, United States
- James Franck Institute, The University of Chicago, Chicago, Illinois 60637, United States
- Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, United States
| | - Jacob S Higgins
- Department of Chemistry, The University of Chicago, Chicago, Illinois 60637, United States
- James Franck Institute, The University of Chicago, Chicago, Illinois 60637, United States
- Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, United States
| | - Jiwoong Park
- Department of Chemistry, The University of Chicago, Chicago, Illinois 60637, United States
- James Franck Institute, The University of Chicago, Chicago, Illinois 60637, United States
- Pritzker School of Molecular Engineering, The University of Chicago, Chicago, Illinois 60637, United States
| | - Gregory S Engel
- Department of Chemistry, The University of Chicago, Chicago, Illinois 60637, United States
- James Franck Institute, The University of Chicago, Chicago, Illinois 60637, United States
- Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, United States
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Park S, Mutz N, Kovalenko SA, Schultz T, Shin D, Aljarb A, Li L, Tung V, Amsalem P, List‐Kratochvil EJW, Stähler J, Xu X, Blumstengel S, Koch N. Type-I Energy Level Alignment at the PTCDA-Monolayer MoS 2 Interface Promotes Resonance Energy Transfer and Luminescence Enhancement. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2021; 8:2100215. [PMID: 34194946 PMCID: PMC8224443 DOI: 10.1002/advs.202100215] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/18/2021] [Revised: 02/24/2021] [Indexed: 06/13/2023]
Abstract
Van der Waals heterostructures consisting of 2D semiconductors and conjugated molecules are of increasing interest because of the prospect of a synergistic enhancement of (opto)electronic properties. In particular, perylenetetracarboxylic dianhydride (PTCDA) on monolayer (ML)-MoS2 has been identified as promising candidate and a staggered type-II energy level alignment and excited state interfacial charge transfer have been proposed. In contrast, it is here found with inverse and direct angle resolved photoelectron spectroscopy that PTCDA/ML-MoS2 supported by insulating sapphire exhibits a straddling type-I level alignment, with PTCDA having the wider energy gap. Photoluminescence (PL) and sub-picosecond transient absorption measurements reveal that resonance energy transfer, i.e., electron-hole pair (exciton) transfer, from PTCDA to ML-MoS2 occurs on a sub-picosecond time scale. This gives rise to an enhanced PL yield from ML-MoS2 in the heterostructure and an according overall modulation of the photoresponse. These results underpin the importance of a precise knowledge of the interfacial electronic structure in order to understand excited state dynamics and to devise reliable design strategies for optimized optoelectronic functionality in van der Waals heterostructures.
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Affiliation(s)
- Soohyung Park
- Advanced Analysis CenterKorea Institute of Science and Technology (KIST)Seoul02792South Korea
| | - Niklas Mutz
- Humboldt‐Universität zu BerlinInstitut für Physik & IRIS AdlershofBerlin12489Germany
| | | | - Thorsten Schultz
- Humboldt‐Universität zu BerlinInstitut für Physik & IRIS AdlershofBerlin12489Germany
- Helmholtz‐Zentrum für Materialien und Energie GmbHBerlin12489Germany
| | - Dongguen Shin
- Humboldt‐Universität zu BerlinInstitut für Physik & IRIS AdlershofBerlin12489Germany
| | - Areej Aljarb
- Physical Sciences and EngineeringKing Abdullah University of Science and TechnologyThuwal23955‐6900Saudi Arabia
| | - Lain‐Jong Li
- Department of Mechanical EngineeringThe University of Hong KongPokfulam RoadHong Kong
| | - Vincent Tung
- Physical Sciences and EngineeringKing Abdullah University of Science and TechnologyThuwal23955‐6900Saudi Arabia
| | - Patrick Amsalem
- Humboldt‐Universität zu BerlinInstitut für Physik & IRIS AdlershofBerlin12489Germany
| | - Emil J. W. List‐Kratochvil
- Humboldt‐Universität zu BerlinInstitut für Physik & IRIS AdlershofBerlin12489Germany
- Humboldt‐Universität zu BerlinInstitut für ChemieBerlin12489Germany
- Helmholtz‐Zentrum für Materialien und Energie GmbHBerlin12489Germany
| | - Julia Stähler
- Humboldt‐Universität zu BerlinInstitut für ChemieBerlin12489Germany
| | - Xiaomin Xu
- Shenzhen Geim Graphene CenterTsinghua‐Berkeley Shenzhen InstituteTsinghua UniversityShenzhen518055China
| | - Sylke Blumstengel
- Humboldt‐Universität zu BerlinInstitut für Physik & IRIS AdlershofBerlin12489Germany
- Humboldt‐Universität zu BerlinInstitut für ChemieBerlin12489Germany
| | - Norbert Koch
- Humboldt‐Universität zu BerlinInstitut für Physik & IRIS AdlershofBerlin12489Germany
- Helmholtz‐Zentrum für Materialien und Energie GmbHBerlin12489Germany
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34
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Zhao C, Tao W, Chen Z, Zhou H, Zhang C, Lin J, Zhu H. Ultrafast Electron Transfer with Long-Lived Charge Separation and Spin Polarization in WSe 2/C 60 Heterojunction. J Phys Chem Lett 2021; 12:3691-3697. [PMID: 33829780 DOI: 10.1021/acs.jpclett.1c00848] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
The strong excitonic effect in monolayer transition-metal dichalcogenides (TMDs) endows them with intriguing optoelectronic properties but also short-lived population and valley polarization. Exciton dissociation by interfacial charge transfer has been shown as an effective approach to prolonging excited-state lifetimes. Herein, by ultrafast spectroscopy and building-block molecule C60, we investigated exciton and valley polarization dynamics in the prototypical WSe2/C60 inorganic-organic hybrid. We show that excitons in WSe2 can be dissociated through ultrafast (∼1 ps) electron transfer to C60, with nanosecond charge separation due to thermally activated electron diffusion in C60 film. Because of suppressed electron-hole exchange interaction after electron transfer, hole in WSe2 exhibits a spin/valley polarization lifetime of ∼60 ps at room temperature, more than 2 orders of magnitude longer than that in WSe2 monolayer. This study suggests exciton dissociation as a general approach to suppress electron-hole interaction and prolong the charge/spin/valley lifetime in TMDs.
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Affiliation(s)
- Chang Zhao
- State Key Laboratory of Modern Optical Instrumentation, Key Laboratory of Excited-State Materials of Zhejiang Province, Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang, China
| | - Weijian Tao
- State Key Laboratory of Modern Optical Instrumentation, Key Laboratory of Excited-State Materials of Zhejiang Province, Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang, China
| | - Zeng Chen
- State Key Laboratory of Modern Optical Instrumentation, Key Laboratory of Excited-State Materials of Zhejiang Province, Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang, China
| | - Hongzhi Zhou
- State Key Laboratory of Modern Optical Instrumentation, Key Laboratory of Excited-State Materials of Zhejiang Province, Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang, China
| | - Chi Zhang
- State Key Laboratory of Modern Optical Instrumentation, Key Laboratory of Excited-State Materials of Zhejiang Province, Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang, China
| | - Junyi Lin
- State Key Laboratory of Modern Optical Instrumentation, Key Laboratory of Excited-State Materials of Zhejiang Province, Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang, China
| | - Haiming Zhu
- State Key Laboratory of Modern Optical Instrumentation, Key Laboratory of Excited-State Materials of Zhejiang Province, Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang, China
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35
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Li Y, Chen Y, Zhou H, Zhu H. Transient Optical Modulation of Two-Dimensional Materials by Excitons at Ultimate Proximity. ACS NANO 2021; 15:5495-5501. [PMID: 33689306 DOI: 10.1021/acsnano.1c00243] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Controlling the optical response of two-dimensional (2D) layered materials is critical for their optoelectronic and photonic applications. Current transient optical modulation of 2D semiconductors is mainly based on the band filling effect, which requires internal exciton/charge occupation from photoexcitation or charge injection. However, 2D atomically thin layers exhibit a strong excitonic effect and environmental sensitivity, offering exciting opportunities to engineer their optical properties through an external dielectric or electronic environment. Here, using femtosecond transient absorption spectroscopy as a tool and transition-metal dichalcogenide (TMD) van der Waals heterostructures with type I band alignment, we show the transient absorption modulation of the TMD layer by excitons at ultimate proximity without direct photoexcitation or exciton/charge occupation. Further layer-dependent study indicates the presence of excitons reduces the exciton oscillator strength in adjacent layers through the electric field effect because of environmental sensitivity and proximity of 2D materials. This result demonstrates the transient optical modulation with decoupled light absorption and modulation components and suggests an alternative approach to control the optical response of 2D materials for optoelectronic and photonic applications.
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Affiliation(s)
- Yujie Li
- State Key Laboratory of Modern Optical Instrumentation, Key Laboratory of Excited-State Materials of Zhejiang Province, Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang 310027, China
| | - Yuzhong Chen
- State Key Laboratory of Modern Optical Instrumentation, Key Laboratory of Excited-State Materials of Zhejiang Province, Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang 310027, China
| | - Hongzhi Zhou
- State Key Laboratory of Modern Optical Instrumentation, Key Laboratory of Excited-State Materials of Zhejiang Province, Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang 310027, China
| | - Haiming Zhu
- State Key Laboratory of Modern Optical Instrumentation, Key Laboratory of Excited-State Materials of Zhejiang Province, Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang 310027, China
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36
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Zhou Q, Zhou H, Tao W, Zheng Y, Chen Y, Zhu H. Highly Efficient Multiple Exciton Generation and Harvesting in Few-Layer Black Phosphorus and Heterostructure. NANO LETTERS 2020; 20:8212-8219. [PMID: 33044075 DOI: 10.1021/acs.nanolett.0c03328] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Multiple exciton generation (MEG) in semiconductors that yields two or more excitons by absorbing one high-energy photon has been proposed to break the Shockley-Queisser limit and boost photon-to-electron conversion efficiency. However, MEG performance in conventional bulk semiconductors or later colloidal nanocrystals is far from satisfactory. Here, we report efficient MEG in few-layer black phosphorus (BP), a direct narrow bandgap two-dimensional (2D) semiconductor with layer-tunable properties. MEG performance improves with decreasing layer number and reaches 2.09Eg threshold and 93% efficiency for two-layer BP, approaching energy conservation limit. The enhanced MEG can be attributed to strong Coulomb interaction and high density of states in 2D materials. Furthermore, MEG of BP shows negligible degradation in vertical heterostructure and multielectron can be extracted by interfacial transfer with near unity yield. These results suggest 2D semiconductors as an ideal system for next generation highly efficient light emission and charge transfer devices.
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Affiliation(s)
- Qiaohui Zhou
- State Key Laboratory of Modern Optical Instrumentation, Centre for Chemistry of High-Performance and Novel Materials, Department of Chemistry, Zhejiang University, Hangzhou 310027, Zhejiang China
| | - Hongzhi Zhou
- State Key Laboratory of Modern Optical Instrumentation, Centre for Chemistry of High-Performance and Novel Materials, Department of Chemistry, Zhejiang University, Hangzhou 310027, Zhejiang China
| | - Weijian Tao
- State Key Laboratory of Modern Optical Instrumentation, Centre for Chemistry of High-Performance and Novel Materials, Department of Chemistry, Zhejiang University, Hangzhou 310027, Zhejiang China
| | - Yizhen Zheng
- State Key Laboratory of Modern Optical Instrumentation, Centre for Chemistry of High-Performance and Novel Materials, Department of Chemistry, Zhejiang University, Hangzhou 310027, Zhejiang China
| | - Yuzhong Chen
- State Key Laboratory of Modern Optical Instrumentation, Centre for Chemistry of High-Performance and Novel Materials, Department of Chemistry, Zhejiang University, Hangzhou 310027, Zhejiang China
| | - Haiming Zhu
- State Key Laboratory of Modern Optical Instrumentation, Centre for Chemistry of High-Performance and Novel Materials, Department of Chemistry, Zhejiang University, Hangzhou 310027, Zhejiang China
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37
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The ultrafast onset of exciton formation in 2D semiconductors. Nat Commun 2020; 11:5277. [PMID: 33077721 PMCID: PMC7572483 DOI: 10.1038/s41467-020-18835-5] [Citation(s) in RCA: 27] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2020] [Accepted: 09/03/2020] [Indexed: 11/24/2022] Open
Abstract
The equilibrium and non-equilibrium optical properties of single-layer transition metal dichalcogenides (TMDs) are determined by strongly bound excitons. Exciton relaxation dynamics in TMDs have been extensively studied by time-domain optical spectroscopies. However, the formation dynamics of excitons following non-resonant photoexcitation of free electron-hole pairs have been challenging to directly probe because of their inherently fast timescales. Here, we use extremely short optical pulses to non-resonantly excite an electron-hole plasma and show the formation of two-dimensional excitons in single-layer MoS2 on the timescale of 30 fs via the induced changes to photo-absorption. These formation dynamics are significantly faster than in conventional 2D quantum wells and are attributed to the intense Coulombic interactions present in 2D TMDs. A theoretical model of a coherent polarization that dephases and relaxes to an incoherent exciton population reproduces the experimental dynamics on the sub-100-fs timescale and sheds light into the underlying mechanism of how the lowest-energy excitons, which are the most important for optoelectronic applications, form from higher-energy excitations. Importantly, a phonon-mediated exciton cascade from higher energy states to the ground excitonic state is found to be the rate-limiting process. These results set an ultimate timescale of the exciton formation in TMDs and elucidate the exceptionally fast physical mechanism behind this process. The formation dynamics of excitons in 2D transition metal dichalcogenides are challenging to probe directly because of their inherently fast timescales. Here, the authors use extremely short optical pulses to excite an electron-hole plasma, and show the formation of 2D excitons in MoS2 on the timescale of 30 fs.
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38
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Li Y, Zhou H, Chen Y, Zhao Y, Zhu H. Efficient hot-electron extraction in two-dimensional semiconductor heterostructures by ultrafast resonant transfer. J Chem Phys 2020; 153:044705. [PMID: 32752698 DOI: 10.1063/5.0018072] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Energy loss from hot-carrier cooling sets the thermodynamic limit for the photon-to-power conversion efficiency in optoelectronic applications. Efficient hot-electron extraction before cooling could reduce the energy loss and leads to efficient next generation devices, which, unfortunately, is challenging to achieve in conventional semiconductors. In this work, we explore hot-electron transfer in two-dimensional (2D) layered semiconductor heterostructures, which have shown great potential for exploring new physics and optoelectronic applications. Using broadband micro-area ultrafast spectroscopy, we firmly established a type I band alignment in the WS2-MoTe2 heterostructure and ultrafast (∼60 fs) hot-electron transfer from photoexcited MoTe2 to WS2. The hot-electron transfer efficiency increases with excitation energy or excess energy as a result of a more favorable continuous competition between resonant electron transfer and cooling, reaching 90% for hot electrons with 0.3 eV excess energy. This study reveals exciting opportunities of designing extremely thin absorber and hot-carrier devices using 2D semiconductors and also sheds important light on the photoinduced interfacial process including charge transfer and generation in 2D heterostructures and optoelectronic devices.
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Affiliation(s)
- Yujie Li
- Centre for Chemistry of High-Performance & Novel Materials, Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang 310027, China
| | - Hongzhi Zhou
- Centre for Chemistry of High-Performance & Novel Materials, Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang 310027, China
| | - Yuzhong Chen
- Centre for Chemistry of High-Performance & Novel Materials, Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang 310027, China
| | - Yida Zhao
- Centre for Chemistry of High-Performance & Novel Materials, Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang 310027, China
| | - Haiming Zhu
- Centre for Chemistry of High-Performance & Novel Materials, Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang 310027, China
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39
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Shi J, Baldini E, Latini S, Sato SA, Zhang Y, Pein BC, Shen PC, Kong J, Rubio A, Gedik N, Nelson KA. Room Temperature Terahertz Electroabsorption Modulation by Excitons in Monolayer Transition Metal Dichalcogenides. NANO LETTERS 2020; 20:5214-5220. [PMID: 32539410 DOI: 10.1021/acs.nanolett.0c01134] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
The interaction between off-resonant laser pulses and excitons in monolayer transition metal dichalcogenides is attracting increasing interest as a route for the valley-selective coherent control of the exciton properties. Here, we extend the classification of the known off-resonant phenomena by unveiling the impact of a strong THz field on the excitonic resonances of monolayer MoS2. We observe that the THz pump pulse causes a selective modification of the coherence lifetime of the excitons, while keeping their oscillator strength and peak energy unchanged. We rationalize these results theoretically by invoking a hitherto unobserved manifestation of the Franz-Keldysh effect on an exciton resonance. As the modulation depth of the optical absorption reaches values as large as 0.05 dB/nm at room temperature, our findings open the way to the use of semiconducting transition metal dichalcogenides as compact and efficient platforms for high-speed electroabsorption devices.
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Affiliation(s)
- Jiaojian Shi
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Edoardo Baldini
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Simone Latini
- Max Planck Institute for the Structure and Dynamics of Matter, Center for Free Electron Laser Science, 22761 Hamburg, Germany
| | - Shunsuke A Sato
- Max Planck Institute for the Structure and Dynamics of Matter, Center for Free Electron Laser Science, 22761 Hamburg, Germany
- Center for Computational Sciences, University of Tsukuba, Tsukuba 305-8577, Japan
| | - Yaqing Zhang
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Brandt C Pein
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Pin-Chun Shen
- Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Jing Kong
- Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Angel Rubio
- Max Planck Institute for the Structure and Dynamics of Matter, Center for Free Electron Laser Science, 22761 Hamburg, Germany
- Nano-Bio Spectroscopy Group, Departamento de Fisica de Materiales, Universidad del País Vasco, 20018 San Sebastían, Spain
- Center for Computational Quantum Physics, Simons Foundation Flatiron Institute, New York, New York 10010, United States
| | - Nuh Gedik
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Keith A Nelson
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
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40
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Katsch F, Selig M, Knorr A. Exciton-Scattering-Induced Dephasing in Two-Dimensional Semiconductors. PHYSICAL REVIEW LETTERS 2020; 124:257402. [PMID: 32639791 DOI: 10.1103/physrevlett.124.257402] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/16/2019] [Revised: 01/25/2020] [Accepted: 06/01/2020] [Indexed: 05/13/2023]
Abstract
Enhanced Coulomb interactions in monolayer transition metal dichalcogenides cause tightly bound electron-hole pairs (excitons) that dominate their linear and nonlinear optical response. The latter includes bleaching, energy renormalizations, and higher-order Coulomb correlation effects like biexcitons and excitation-induced dephasing. While the first three are extensively studied, no theoretical footing for excitation-induced dephasing in exciton-dominated semiconductors is available so far. In this Letter, we present microscopic calculations based on excitonic Heisenberg equations of motion and identify the coupling of optically pumped excitons to exciton-exciton scattering continua as the leading mechanism responsible for an optical-power-dependent linewidth broadening (excitation-induced dephasing) and sideband formation. Performing time-, momentum-, and energy-resolved simulations, we quantitatively evaluate the exciton-induced dephasing for the most common monolayer transition metal dichalcogenides and find an excellent agreement with recent experiments.
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Affiliation(s)
- Florian Katsch
- Institut für Theoretische Physik, Nichtlineare Optik und Quantenelektronik, Technische Universität Berlin, 10623 Berlin, Germany
| | - Malte Selig
- Institut für Theoretische Physik, Nichtlineare Optik und Quantenelektronik, Technische Universität Berlin, 10623 Berlin, Germany
| | - Andreas Knorr
- Institut für Theoretische Physik, Nichtlineare Optik und Quantenelektronik, Technische Universität Berlin, 10623 Berlin, Germany
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41
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Zhou H, Zhao Y, Tao W, Li Y, Zhou Q, Zhu H. Controlling Exciton and Valley Dynamics in Two-Dimensional Heterostructures with Atomically Precise Interlayer Proximity. ACS NANO 2020; 14:4618-4625. [PMID: 32181635 DOI: 10.1021/acsnano.0c00218] [Citation(s) in RCA: 28] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
Two-dimensional (2D) materials and heterostructures with strong excitonic effect and spin/valley properties have emerged as an exciting platform for optoelectronic and spin/valleytronic applications. There, precise control of the exciton transformation process (including intralayer to interlayer exciton transition and recombination) and valley polarization process via structural tuning is crucial but remains largely unexplored. Here, using hexagonal boron nitride (BN) as an intermediate layer, we show the fine-tuning of exciton and valley dynamics in 2D heterostructures with atomic precision. Both interfacial electron and hole transfer rates decrease exponentially with increasing BN thickness, which can be well-described with quantum tunneling model. The increased spatial separation with BN intercalation weakens the electron-hole Coulomb interaction and significantly prolongs the interlayer exciton population and valley polarization lifetimes in van der Waals (vdW) heterostructures. For example, WSe2/WS2 heterostructures with monolayer BN intercalation exhibit a hole valley polarization lifetime of ∼60 ps at room temperature, which is approximately threefold and 3 orders of magnitude longer than that in WSe2/WS2 heterobilayer without BN and WSe2 monolayer, respectively. Considering a large family of layered materials, this study suggests a general approach to tailor and optimize exciton and valley properties in vdW heterostructures with atomic precision.
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Affiliation(s)
- Hongzhi Zhou
- Centre for Chemistry of High-Performance & Novel Materials, Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang 310027, China
| | - Yida Zhao
- Centre for Chemistry of High-Performance & Novel Materials, Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang 310027, China
| | - Weijian Tao
- Centre for Chemistry of High-Performance & Novel Materials, Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang 310027, China
| | - Yujie Li
- Centre for Chemistry of High-Performance & Novel Materials, Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang 310027, China
| | - Qiaohui Zhou
- Centre for Chemistry of High-Performance & Novel Materials, Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang 310027, China
| | - Haiming Zhu
- Centre for Chemistry of High-Performance & Novel Materials, Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang 310027, China
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42
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Dal Conte S, Trovatello C, Gadermaier C, Cerullo G. Ultrafast Photophysics of 2D Semiconductors and Related Heterostructures. TRENDS IN CHEMISTRY 2020. [DOI: 10.1016/j.trechm.2019.07.007] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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43
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Ling J, Miao X, Sun Y, Feng Y, Zhang L, Sun Z, Ji M. Vibrational Imaging and Quantification of Two-Dimensional Hexagonal Boron Nitride with Stimulated Raman Scattering. ACS NANO 2019; 13:14033-14040. [PMID: 31725258 DOI: 10.1021/acsnano.9b06337] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Hexagonal boron nitride (h-BN) is an important member of two-dimensional (2D) materials with a large direct bandgap, and has attracted growing interest in ultraviolet optoelectronics and nanoelectronics. Compared with graphene and graphite, h-BN has weak Raman effect because of the far off-resonance excitation; hence, it is difficult to exploit Raman spectroscopy to characterize important properties of 2D h-BN, such as thickness, doping, and strain effects. Here, we applied stimulated Raman scattering (SRS) to enhance the sensitivity of the E2g Raman mode of h-BN. We showed that SRS microscopy achieves rapid high resolution imaging of h-BN with a pixel dwell time 4 orders of magnitude smaller than conventional spontaneous Raman microscopy. Moreover, the near-perfect linear dependence of signal intensity on h-BN thickness and isotropic polarization dependence allow convenient determination of the flake thickness with SRS imaging. Our results indicated that SRS microscopy provides a promising tool for high-speed quantification of h-BN and holds the potential for vibrational imaging of 2D materials.
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44
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Panna D, Balasubramanian K, Khatei J, Rybak L, Slobodkin Y, Steinberg H, Hayat A. Observation of 2D semiconductor P-type dark-exciton lifetime using two-photon ultrafast spectroscopy. OPTICS EXPRESS 2019; 27:33427-33435. [PMID: 31878412 DOI: 10.1364/oe.27.033427] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/06/2019] [Accepted: 09/21/2019] [Indexed: 06/10/2023]
Abstract
We report direct measurements of intrinsic lifetimes of P-type dark-excitons in MoS2 monolayers. Using sub-gap excitation, we demonstrate two-photon excited direct population of P-type dark excitons, observe their scattering to bright states and decay with femtosecond resolution. In contrast to one-photon excitation schemes, non-monotonic density variation in bright exciton population observed under two-photon excitation shows the indirect nature of its population and competing decay pathways. Detailed modeling of different recombination pathways of bright and dark excitons allows experimental measurement of 2P dark → 1S bright exciton scattering rates. These insights into the dark states in a MoS2 monolayer pave the way for novel devices such as quantum memories and computing.
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45
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Han S, Boguschewski C, Gao Y, Xiao L, Zhu J, van Loosdrecht PHM. Incoherent phonon population and exciton-exciton annihilation dynamics in monolayer WS 2 revealed by time-resolved Resonance Raman scattering. OPTICS EXPRESS 2019; 27:29949-29961. [PMID: 31684250 DOI: 10.1364/oe.27.029949] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/04/2019] [Accepted: 08/18/2019] [Indexed: 06/10/2023]
Abstract
Atomically thin layer transition metal dichalcogenides have been intensively investigated for their rich optical properties and potential applications on nano-electronics. In this work, we study the incoherent phonon and exciton population dynamics in monolayer WS2 by time-resolved Resonance Raman scattering spectroscopy. Upon excitation of the exciton transition, both Stokes and anti-Stokes scattering strength of the optical and the longitudinal acoustic two phonon modes exhibit large reduction. Based on the assumption of quasi-equilibrium distribution, the hidden phonon population dynamics is retrieved, which shows an instant build-up and a relaxation lifetime of ∼4 ps at the exciton density ∼1012cm-2. A phonon temperature rises of ∼20 K was identified due to the exciton excitation and relaxation. The exciton relaxation dynamics extracted from the transient vibrational Raman response shows strong excitation density dependence, signaling an important bi-molecular contribution to the decay. These results provide significant knowledge on the thermal dynamics after optical excitation, enhance the understanding of the fundamental exciton dynamics in two-dimensional transition metal materials, and demonstrate that time-resolved Resonance Raman scattering spectroscopy is a powerful method for exploring quasi-particle dynamics in optical materials.
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46
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Fan P, Zheng B, Sun X, Zheng W, Xu Z, Ge C, Liu Y, Zhuang X, Li D, Wang X, Zhu X, Jiang Y, Pan A. Trion-Induced Distinct Transient Behavior and Stokes Shift in WS 2 Monolayers. J Phys Chem Lett 2019; 10:3763-3772. [PMID: 31244271 DOI: 10.1021/acs.jpclett.9b01422] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Understanding the excitonic behavior in two-dimensional transition-metal dichalcogenides (2D TMDs) is of both fundamental interest and critical importance for optoelectronic applications. Here, we investigate the transient excitonic behavior and Stokes shift in WS2 monolayers on both sapphire and glass substrates. Trion formation was confirmed as the origin of the distinct photoluminescence (PL) emission and Stokes shift in WS2 monolayers. Moreover, the transient studies demonstrate faster recombination of both the exciton and the short-lived trion on the glass substrate as compared to that on the sapphire substrate, owing to the heavier n-doping and greater number of defects introduced by the glass substrate. In addition, a long-lived trion species attributed to the intervalley triplet trion was observed on the glass substrate, with a lifetime on the nanosecond time scale. These findings offer a comprehensive understanding of the excitonic behavior and Stokes shift in WS2 monolayers and will lay the foundation for further fundamental investigations in the field.
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Affiliation(s)
- Peng Fan
- Key Laboratory for Micro-Nano Physics and Technology of Hunan Province, School of Physics and Electronics , Hunan University , Changsha 410082 , People's Republic of China
| | - Biyuan Zheng
- Key Laboratory for Micro-Nano Physics and Technology of Hunan Province, School of Physics and Electronics , Hunan University , Changsha 410082 , People's Republic of China
| | - Xingxia Sun
- Key Laboratory for Micro-Nano Physics and Technology of Hunan Province, College of Materials Science and Engineering , Hunan University , Changsha 410082 , People's Republic of China
| | - Weihao Zheng
- Key Laboratory for Micro-Nano Physics and Technology of Hunan Province, School of Physics and Electronics , Hunan University , Changsha 410082 , People's Republic of China
| | - Zheyuan Xu
- Key Laboratory for Micro-Nano Physics and Technology of Hunan Province, School of Physics and Electronics , Hunan University , Changsha 410082 , People's Republic of China
| | - Cuihuan Ge
- Key Laboratory for Micro-Nano Physics and Technology of Hunan Province, School of Physics and Electronics , Hunan University , Changsha 410082 , People's Republic of China
| | - Yong Liu
- Key Laboratory for Micro-Nano Physics and Technology of Hunan Province, School of Physics and Electronics , Hunan University , Changsha 410082 , People's Republic of China
| | - Xiujuan Zhuang
- Key Laboratory for Micro-Nano Physics and Technology of Hunan Province, School of Physics and Electronics , Hunan University , Changsha 410082 , People's Republic of China
| | - Dong Li
- Key Laboratory for Micro-Nano Physics and Technology of Hunan Province, College of Materials Science and Engineering , Hunan University , Changsha 410082 , People's Republic of China
| | - Xiao Wang
- Key Laboratory for Micro-Nano Physics and Technology of Hunan Province, School of Physics and Electronics , Hunan University , Changsha 410082 , People's Republic of China
| | - Xiaoli Zhu
- Key Laboratory for Micro-Nano Physics and Technology of Hunan Province, School of Physics and Electronics , Hunan University , Changsha 410082 , People's Republic of China
| | - Ying Jiang
- Key Laboratory for Micro-Nano Physics and Technology of Hunan Province, School of Physics and Electronics , Hunan University , Changsha 410082 , People's Republic of China
| | - Anlian Pan
- Key Laboratory for Micro-Nano Physics and Technology of Hunan Province, College of Materials Science and Engineering , Hunan University , Changsha 410082 , People's Republic of China
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Ye J, Li Y, Yan T, Zhai G, Zhang X. Ultrafast Dynamics of Spin Generation and Relaxation in Layered WSe 2. J Phys Chem Lett 2019; 10:2963-2970. [PMID: 31084014 DOI: 10.1021/acs.jpclett.9b01068] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
We investigated the build-up and relaxation processes of spin-polarized A- and B-exciton dynamics in monolayer, bilayer, and bulk WSe2 using helicity-resolved two-color pump-probe spectroscopy. Substantial spin polarization was confirmed in bulk crystals, though the spin polarization degree of A excitons decreased from monolayer to bulk. However, the spin polarization of A excitons almost vanished in all different layered-flakes when resonantly pumping the B-exciton transition, owing to the dominant role of interexciton transfer. When resonantly pumping the A-exciton transition, the spin polarization of the up-converted B excitons was inverted in all layers because of the efficient Dexter-like coupling and phonon-assisted scattering. The same short spin relaxation time (1.8 ± 0.2 ps) of A excitons was found for all studied flakes in the subsequent spin depolarization processes, which was ascribed to the active electron-phonon scattering resulting from the intrinsic small conduction-band spin-orbit coupling splitting in layered WSe2.
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Affiliation(s)
- Jialiang Ye
- State Key Laboratory of Superlattices and Microstructures , Institute of Semiconductors, Chinese Academy of Sciences , Beijing 100083 , P.R. China
- Center of Materials Science and Optoelectronics Engineering , University of Chinese Academy of Sciences , Beijing 100049 , P.R. China
| | - Ying Li
- State Key Laboratory of Superlattices and Microstructures , Institute of Semiconductors, Chinese Academy of Sciences , Beijing 100083 , P.R. China
- Center of Materials Science and Optoelectronics Engineering , University of Chinese Academy of Sciences , Beijing 100049 , P.R. China
| | - Tengfei Yan
- State Key Laboratory of Superlattices and Microstructures , Institute of Semiconductors, Chinese Academy of Sciences , Beijing 100083 , P.R. China
| | - Guihao Zhai
- State Key Laboratory of Superlattices and Microstructures , Institute of Semiconductors, Chinese Academy of Sciences , Beijing 100083 , P.R. China
- Center of Materials Science and Optoelectronics Engineering , University of Chinese Academy of Sciences , Beijing 100049 , P.R. China
| | - Xinhui Zhang
- State Key Laboratory of Superlattices and Microstructures , Institute of Semiconductors, Chinese Academy of Sciences , Beijing 100083 , P.R. China
- Center of Materials Science and Optoelectronics Engineering , University of Chinese Academy of Sciences , Beijing 100049 , P.R. China
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48
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Scharf B, Van Tuan D, Žutić I, Dery H. Dynamical screening in monolayer transition-metal dichalcogenides and its manifestations in the exciton spectrum. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2019; 31:203001. [PMID: 30763925 DOI: 10.1088/1361-648x/ab071f] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Monolayer transition-metal dichalcogenides (ML-TMDs) offer exciting opportunities to test the manifestations of many-body interactions through changes in the charge density. The two-dimensional character and reduced screening in ML-TMDs lead to the formation of neutral and charged excitons with binding energies orders of magnitude larger than those in conventional bulk semiconductors. Tuning the charge density by a gate voltage leads to profound changes in the optical spectra of excitons in ML-TMDs. On the one hand, the increased screening at large charge densities should result in a blueshift of the exciton spectral lines due to reduction in the binding energy. On the other hand, exchange and correlation effects that shrink the band-gap energy at elevated charge densities (band-gap renormalization) should result in a redshift of the exciton spectral lines. While these competing effects can be captured through various approximations that model long-wavelength charge excitations in the Bethe-Salpeter equation, we show that a novel coupling between excitons and shortwave charge excitations is essential to resolve several experimental puzzles. Unlike ubiquitous and well-studied plasmons, driven by collective oscillations of the background charge density in the long-wavelength limit, we discuss the emergence of shortwave plasmons that originate from the short-range Coulomb interaction through which electrons transition between the [Formula: see text] and [Formula: see text] valleys. The shortwave plasmons have a finite energy-gap because of the removal of spin-degeneracy in both the valence- and conduction-band valleys (a consequence of breaking of inversion symmetry in combination with strong spin-orbit coupling in ML-TMDs). We study the coupling between the shortwave plasmons and the neutral exciton through the self-energy of the latter. We then elucidate how this coupling as well as the spin ordering in the conduction band give rise to an experimentally observed optical sideband in electron-doped W-based MLs, conspicuously absent in electron-doped Mo-based MLs or any hole-doped ML-TMDs. While the focus of this review is on the optical manifestations of many-body effects in ML-TMDs, a systematic description of the dynamical screening and its various approximations allow one to revisit other phenomena, such as nonequilibrium transport or superconducting pairing, where the use of the Bethe-Salpeter equation or the emergence of shortwave plasmons can play an important role.
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Affiliation(s)
- Benedikt Scharf
- Institute for Theoretical Physics and Astrophysics, University of Würzburg, Am Hubland, 97074 Würzburg, Germany
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49
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Wu L, Chen Y, Zhou H, Zhu H. Ultrafast Energy Transfer of Both Bright and Dark Excitons in 2D van der Waals Heterostructures Beyond Dipolar Coupling. ACS NANO 2019; 13:2341-2348. [PMID: 30715845 DOI: 10.1021/acsnano.8b09059] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Two-dimensional (2D) transition-metal dichalcogenides (TMDs) have shown great potential in ultrathin and flexible optoelectronic and photonics devices. Besides emissive bright excitons, they also possess rich non-emissive dark excitons including momentum-forbidden indirect excitons and spin-forbidden triplet-like excitons, which could be dominant species under optical or electrical excitation in 2D optoelectronic and photonic devices. Efficient harvesting of both bright and dark excitons from TMDs and understanding the exciton-transfer mechanism consequently are not only of fundamental interest but also a technological challenge. Here, by combining steady-state photoluminescence spectroscopy and ultrafast transient reflectance spectroscopy, we show efficient exciton harvesting by ultrafast energy transfer in WSe2/MoTe2 van der Waals heterostructures, leading to the photoluminescence enhancement of MoTe2. The energy transfer occurs with near-unity yield and in an ultrafast (∼200 fs) manner for both bright and dark excitons, suggesting a dominant Dexter-type energy-transfer process consisting of simultaneous transfer of both electron and hole in van der Waals coupled 2D layers at ultimate proximity. This result is beyond the conventional dipole-dipole coupling mechanism typically assumed at 2D interfaces and offers a path to high speed and enhanced light harvesting and emission applications based on 2D heterostructures.
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50
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Zhou H, Zhao Y, Zhu H. Dielectric Environment-Robust Ultrafast Charge Transfer Between Two Atomic Layers. J Phys Chem Lett 2019; 10:150-155. [PMID: 30582821 DOI: 10.1021/acs.jpclett.8b03596] [Citation(s) in RCA: 29] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Understanding electron transfer across two-dimensional (2D) van der Waals (vdW) interfaces especially the effect of dielectric environment not only contributes to the rational design of high performance optoelectronic and photo/electrocatalytic devices but also unravels the nature of charge motion. Herein, we investigated the electron transfer process between two atomic thin layered materials coupled by vdW force at ultimate proximity. Despite their susceptible electronic properties, we show electron transfer at 2D vdW interface is robust and ultrafast (∼30 fs), regardless of the surrounding dielectrics and solvents. Considering the static energy landscape and dynamic nuclear rearrangements, our result suggests the electronic coupling at 2D vdW heterointerfaces is sufficiently strong such that electron transfers adiabatically in a barrierless and ultrafast manner where energetics and solvent relaxation are not that relevant. The robust ultrafast electron transfer against the variation of dielectric environment is highly encouraging for 2D optoelectronic and photo/electrocatalytic devices.
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Affiliation(s)
- Hongzhi Zhou
- Centre for Chemistry of High-Performance & Novel Materials, Department of Chemistry , Zhejiang University , Hangzhou , Zhejiang 310027 , China
| | - Yida Zhao
- Centre for Chemistry of High-Performance & Novel Materials, Department of Chemistry , Zhejiang University , Hangzhou , Zhejiang 310027 , China
| | - Haiming Zhu
- Centre for Chemistry of High-Performance & Novel Materials, Department of Chemistry , Zhejiang University , Hangzhou , Zhejiang 310027 , China
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