1
|
Dihingia N, Vázquez-Lizardi GA, Wu RJ, Reifsnyder Hickey D. Quantifying the thickness of WTe2 using atomic-resolution STEM simulations and supervised machine learning. J Chem Phys 2024; 160:091101. [PMID: 38436439 DOI: 10.1063/5.0188928] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2023] [Accepted: 02/09/2024] [Indexed: 03/05/2024] Open
Abstract
For two-dimensional (2D) materials, the exact thickness of the material often dictates its physical and chemical properties. The 2D quantum material WTe2 possesses properties that vary significantly from a single layer to multiple layers, yet it has a complicated crystal structure that makes it difficult to differentiate thicknesses in atomic-resolution images. Furthermore, its air sensitivity and susceptibility to electron beam-induced damage heighten the need for direct ways to determine the thickness and atomic structure without acquiring multiple measurements or transferring samples in ambient atmosphere. Here, we demonstrate a new method to identify the thickness up to ten van der Waals layers in Td-WTe2 using atomic-resolution high-angle annular dark-field scanning transmission electron microscopy image simulation. Our approach is based on analyzing the intensity line profiles of overlapping atomic columns and building a standard neural network model from the line profile features. We observe that it is possible to clearly distinguish between even and odd thicknesses (up to seven layers), without using machine learning, by comparing the deconvoluted peak intensity ratios or the area ratios. The standard neural network model trained on the line profile features allows thicknesses to be distinguished up to ten layers and exhibits an accuracy of up to 94% in the presence of Gaussian and Poisson noise. This method efficiently quantifies thicknesses in Td-WTe2, can be extended to related 2D materials, and provides a pathway to characterize precise atomic structures, including local thickness variations and atomic defects, for few-layer 2D materials with overlapping atomic column positions.
Collapse
Affiliation(s)
- Nikalabh Dihingia
- Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
| | - Gabriel A Vázquez-Lizardi
- Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
| | - Ryan J Wu
- Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
| | - Danielle Reifsnyder Hickey
- Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
- Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
- Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
| |
Collapse
|
2
|
Fox C, Mao Y, Zhang X, Wang Y, Xiao J. Stacking Order Engineering of Two-Dimensional Materials and Device Applications. Chem Rev 2024; 124:1862-1898. [PMID: 38150266 DOI: 10.1021/acs.chemrev.3c00618] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2023]
Abstract
Stacking orders in 2D van der Waals (vdW) materials dictate the relative sliding (lateral displacement) and twisting (rotation) between atomically thin layers. By altering the stacking order, many new ferroic, strongly correlated and topological orderings emerge with exotic electrical, optical and magnetic properties. Thanks to the weak vdW interlayer bonding, such highly flexible and energy-efficient stacking order engineering has transformed the design of quantum properties in 2D vdW materials, unleashing the potential for miniaturized high-performance device applications in electronics, spintronics, photonics, and surface chemistry. This Review provides a comprehensive overview of stacking order engineering in 2D vdW materials and their device applications, ranging from the typical fabrication and characterization methods to the novel physical properties and the emergent slidetronics and twistronics device prototyping. The main emphasis is on the critical role of stacking orders affecting the interlayer charge transfer, orbital coupling and flat band formation for the design of innovative materials with on-demand quantum properties and surface potentials. By demonstrating a correlation between the stacking configurations and device functionality, we highlight their implications for next-generation electronic, photonic and chemical energy conversion devices. We conclude with our perspective of this exciting field including challenges and opportunities for future stacking order engineering research.
Collapse
Affiliation(s)
- Carter Fox
- Department of Materials Science and Engineering, University of Wisconsin─Madison, Madison, Wisconsin 53706, United States
- Department of Physics, University of Wisconsin─Madison, Madison, Wisconsin 53706, United States
| | - Yulu Mao
- Department of Electrical and Computer Engineering, University of Wisconsin─Madison, Madison, Wisconsin 53706, United States
| | - Xiang Zhang
- Faculty of Science, University of Hong Kong, Hong Kong, China
- Faculty of Engineering, University of Hong Kong, Hong Kong, China
| | - Ying Wang
- Department of Materials Science and Engineering, University of Wisconsin─Madison, Madison, Wisconsin 53706, United States
- Department of Physics, University of Wisconsin─Madison, Madison, Wisconsin 53706, United States
- Department of Electrical and Computer Engineering, University of Wisconsin─Madison, Madison, Wisconsin 53706, United States
| | - Jun Xiao
- Department of Materials Science and Engineering, University of Wisconsin─Madison, Madison, Wisconsin 53706, United States
- Department of Physics, University of Wisconsin─Madison, Madison, Wisconsin 53706, United States
| |
Collapse
|
3
|
Prasad AK, Šebesta J, Esteban-Puyuelo R, Maldonado P, Ji S, Sanyal B, Grånäs O, Weissenrieder J. Nonequilibrium Phonon Dynamics and Its Impact on the Thermal Conductivity of the Benchmark Thermoelectric Material SnSe. ACS NANO 2023; 17:21006-21017. [PMID: 37862596 PMCID: PMC10655201 DOI: 10.1021/acsnano.3c03827] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/22/2023]
Abstract
Thermoelectric materials play a vital role in the pursuit of a sustainable energy system by allowing the conversion of waste heat to electric energy. Low thermal conductivity is essential to achieving high-efficiency conversion. The conductivity depends on an interplay between the phononic and electronic properties of the nonequilibrium state. Therefore, obtaining a comprehensive understanding of nonequilibrium dynamics of the electronic and phononic subsystems as well as their interactions is key for unlocking the microscopic mechanisms that ultimately govern thermal conductivity. A benchmark material that exhibits ultralow thermal conductivity is SnSe. We study the nonequilibrium phonon dynamics induced by an excited electron population using a framework combining ultrafast electron diffuse scattering and nonequilibrium kinetic theory. This in-depth approach provides a fundamental understanding of energy transfer in the spatiotemporal domain. Our analysis explains the dynamics leading to the observed low thermal conductivity, which we attribute to a mode-dependent tendency to nonconservative phonon scattering. The results offer a penetrating perspective on energy transport in condensed matter with far-reaching implications for rational design of advanced materials with tailored thermal properties.
Collapse
Affiliation(s)
- Amit Kumar Prasad
- Materials and Nano Physics, School of Engineering Sciences, KTH Royal Institute of Technology, SE-100 44 Stockholm, Sweden
| | - Jakub Šebesta
- Materials Theory, Department of Physics and Astronomy, Uppsala University, Box 516, 751 20 Uppsala, Sweden
| | - Raquel Esteban-Puyuelo
- Materials Theory, Department of Physics and Astronomy, Uppsala University, Box 516, 751 20 Uppsala, Sweden
| | - Pablo Maldonado
- Materials Theory, Department of Physics and Astronomy, Uppsala University, Box 516, 751 20 Uppsala, Sweden
| | - Shaozheng Ji
- Materials and Nano Physics, School of Engineering Sciences, KTH Royal Institute of Technology, SE-100 44 Stockholm, Sweden
| | - Biplab Sanyal
- Materials Theory, Department of Physics and Astronomy, Uppsala University, Box 516, 751 20 Uppsala, Sweden
| | - Oscar Grånäs
- Materials Theory, Department of Physics and Astronomy, Uppsala University, Box 516, 751 20 Uppsala, Sweden
| | - Jonas Weissenrieder
- Materials and Nano Physics, School of Engineering Sciences, KTH Royal Institute of Technology, SE-100 44 Stockholm, Sweden
| |
Collapse
|
4
|
Wang C, Liu X, Chen Q, Chen D, Wang Y, Meng S. Coherent-Phonon-Driven Intervalley Scattering and Rabi Oscillation in Multivalley 2D Materials. PHYSICAL REVIEW LETTERS 2023; 131:066401. [PMID: 37625067 DOI: 10.1103/physrevlett.131.066401] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/22/2022] [Revised: 05/15/2023] [Accepted: 06/29/2023] [Indexed: 08/27/2023]
Abstract
Resolving the complete electron scattering dynamics mediated by coherent phonons is crucial for understanding electron-phonon couplings beyond equilibrium. Here we present a time-resolved theoretical investigation on strongly coupled ultrafast electron and phonon dynamics in monolayer WSe_{2}, with a focus on the intervalley scattering from the optically "bright" K state to "dark" Q state. We find that the strong coherent lattice vibration along the longitudinal acoustic phonon mode [LA(M)] can drastically promote K-to-Q transition on a timescale of ∼400 fs, comparable with previous experimental observation on thermal-phonon-mediated electron dynamics. Further, this coherent-phonon-driven intervalley scattering occurs in an unconventional steplike manner and further induces an electronic Rabi oscillation. By constructing a two-level model and quantitatively comparing with ab initio dynamic simulations, we uncover the critical role of nonadiabatic coupling effects. Finally, a new strategy is proposed to effectively tune the intervalley scattering rates by varying the coherent phonon amplitude, which could be realized via light-induced nonlinear phononics that we hope will spark experimental investigation.
Collapse
Affiliation(s)
- Chenyu Wang
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100190, China
| | - Xinbao Liu
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100190, China
| | - Qing Chen
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100190, China
| | - Daqiang Chen
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - Yaxian Wang
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - Sheng Meng
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100190, China
- Songshan Lake Materials Laboratory, Dongguan, Guangdong 523808, China
| |
Collapse
|
5
|
Coupled ferroelectricity and superconductivity in bilayer T d-MoTe 2. Nature 2023; 613:48-52. [PMID: 36600069 DOI: 10.1038/s41586-022-05521-3] [Citation(s) in RCA: 26] [Impact Index Per Article: 26.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2022] [Accepted: 11/03/2022] [Indexed: 01/05/2023]
Abstract
Achieving electrostatic control of quantum phases is at the frontier of condensed matter research. Recent investigations have revealed superconductivity tunable by electrostatic doping in twisted graphene heterostructures and in two-dimensional semimetals such as WTe2 (refs. 1-5). Some of these systems have a polar crystal structure that gives rise to ferroelectricity, in which the interlayer polarization exhibits bistability driven by external electric fields6-8. Here we show that bilayer Td-MoTe2 simultaneously exhibits ferroelectric switching and superconductivity. Notably, a field-driven, first-order superconductor-to-normal transition is observed at its ferroelectric transition. Bilayer Td-MoTe2 also has a maximum in its superconducting transition temperature (Tc) as a function of carrier density and temperature, allowing independent control of the superconducting state as a function of both doping and polarization. We find that the maximum Tc is concomitant with compensated electron and hole carrier densities and vanishes when one of the Fermi pockets disappears with doping. We argue that this unusual polarization-sensitive two-dimensional superconductor is driven by an interband pairing interaction associated with nearly nested electron and hole Fermi pockets.
Collapse
|
6
|
Ji S, Grånäs O, Kumar Prasad A, Weissenrieder J. Influence of strain on an ultrafast phase transition. NANOSCALE 2022; 15:304-312. [PMID: 36484465 PMCID: PMC9773179 DOI: 10.1039/d2nr03395j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/20/2022] [Accepted: 12/05/2022] [Indexed: 06/17/2023]
Abstract
The flexibility of 2D materials combined with properties highly sensitive to strain makes strain engineering a promising avenue for manipulation of both structure and function. Here we investigate the influence of strain, associated with microstructural defects, on a photo-induced structural phase transition in Td-WTe2. Above threshold photoexcitation of uniform, non-strained, samples result in an orthorhombic Td to a metastable orthorhombic 1T* phase transition facilitated by shear displacements of the WTe2 layers along the b axis of the material. In samples prepared with wrinkle defects WTe2 continue its trajectory through a secondary transition that shears the unit cell along the c axis towards a metastable monoclinic 1T' phase. The time scales and microstructural evolution associated with the transition and its subsequent recovery to the 1T* phase is followed in detail by a combination of ultrafast electron diffraction and microscopy. Our findings show how local strain fields can be employed for tailoring phase change dynamics in ultrafast optically driven processes with potential applications in phase change devices.
Collapse
Affiliation(s)
- Shaozheng Ji
- Materials and Nano Physics, School of Engineering Sciences, KTH Royal Institute of Technology, SE-100 44 Stockholm, Sweden.
- Ultrafast Electron Microscopy Laboratory, The MOE Key Laboratory of Weak-Light Nonlinear Photonics, School of Physics, Nankai University, Tianjin 300071, China
| | - Oscar Grånäs
- Materials Theory, Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden
| | - Amit Kumar Prasad
- Materials and Nano Physics, School of Engineering Sciences, KTH Royal Institute of Technology, SE-100 44 Stockholm, Sweden.
| | - Jonas Weissenrieder
- Materials and Nano Physics, School of Engineering Sciences, KTH Royal Institute of Technology, SE-100 44 Stockholm, Sweden.
| |
Collapse
|
7
|
Qi Y, Guan M, Zahn D, Vasileiadis T, Seiler H, Windsor YW, Zhao H, Meng S, Ernstorfer R. Traversing Double-Well Potential Energy Surfaces: Photoinduced Concurrent Intralayer and Interlayer Structural Transitions in XTe 2 (X = Mo, W). ACS NANO 2022; 16:11124-11135. [PMID: 35793703 DOI: 10.1021/acsnano.2c03809] [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
The microscopic arrangement of atoms and molecules is the determining factor in how materials behave and perform; i.e., the structure determines the property, a traditional paradigm in materials science. Photoexcitation-driven manipulation of the crystal structure and associated electronic properties in quantum materials provides opportunities for the exploration of exotic physics and practical applications; however, a generalized mechanism for such symmetry engineering is absent. Here, by ultrafast electron diffraction, structure factor calculation, and TDDFT-MD simulations, we report the photoinduced concurrent intralayer and interlayer structural transitions in the Td and 1T' phases of XTe2 (X = Mo, W). We discuss the modification of multiple quantum electronic states associated with the intralayer and interlayer structural transitions, such as the topological band inversion and the higher-order topological state. The twin structures and the stacking faults in XTe2 are also identified by ultrafast structural responses. The comprehensive study of the ultrafast structural response in XTe2 suggests the traversal of all double-well potential energy surfaces (DWPES) by laser excitation, which is expected to be an intrinsic mechanism in the field of photoexcitation-driven global/local symmetry engineering and also a critical ingredient inducing the exotic properties in the non-equilibrium state in a large number of material systems.
Collapse
Affiliation(s)
- Yingpeng Qi
- Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, Berlin 14195, Germany
- Center for Ultrafast Science and Technology, School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China
| | - Mengxue Guan
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, P. R. China
| | - Daniela Zahn
- Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, Berlin 14195, Germany
| | - Thomas Vasileiadis
- Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, Berlin 14195, Germany
| | - Hélène Seiler
- Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, Berlin 14195, Germany
| | - Yoav William Windsor
- Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, Berlin 14195, Germany
| | - Hui Zhao
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, P. R. China
| | - Sheng Meng
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, P. R. China
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Ralph Ernstorfer
- Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, Berlin 14195, Germany
| |
Collapse
|
8
|
Dai Y, Zheng Q, Ziffer ME, Rhodes D, Hone J, Zhao J, Zhu X. Ultrafast Ferroelectric Ordering on the Surface of a Topological Semimetal MoTe 2. NANO LETTERS 2021; 21:9903-9908. [PMID: 34788055 DOI: 10.1021/acs.nanolett.1c02965] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Transient tuning of material properties by light usually requires intense laser fields in the nonlinear excitation regime. Here, we report ultrafast ferroelectric ordering on the surface of a paraelectric topological semimetal 1T'-MoTe2 in the linear excitation regime, with the order parameter directly proportional to the excitation intensity. The ferroelectric ordering, driven by a transient electric field created by electrons trapped ångstroms away from the surface in the image potential state (IPS), is evidenced in two-photon photoemission spectroscopy showing the energy relaxation rate proportional to IPS electron density, but with negligible change in the free-electron-like parallel dispersion. First-principles calculations reveal an improper ferroelectric ordering associated with an anharmonic interlayer shearing mode. Our findings demonstrate an ultrafast charge-based pathway for creating transient polarization orders.
Collapse
Affiliation(s)
- Yanan Dai
- Department of Chemistry, Columbia University, New York, New York 10027, United States
| | - Qijing Zheng
- Department of Physics, University of Science and Technology of China, Hefei, Anhui230026, China
| | - Mark E Ziffer
- Department of Chemistry, Columbia University, New York, New York 10027, United States
| | - Daniel Rhodes
- Department of Mechanical Engineering, Columbia University, New York, New York 10027, United States
| | - James Hone
- Department of Mechanical Engineering, Columbia University, New York, New York 10027, United States
| | - Jin Zhao
- Department of Physics, University of Science and Technology of China, Hefei, Anhui230026, China
| | - Xiaoyang Zhu
- Department of Chemistry, Columbia University, New York, New York 10027, United States
| |
Collapse
|