1
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He X, Ghosh M, Yang DS. Impacts of hot electron diffusion, electron-phonon coupling, and surface atoms on metal surface dynamics revealed by reflection ultrafast electron diffraction. J Chem Phys 2024; 160:224701. [PMID: 38856064 DOI: 10.1063/5.0205948] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2024] [Accepted: 05/27/2024] [Indexed: 06/11/2024] Open
Abstract
Metals exhibit nonequilibrium electron and lattice subsystems at transient times following femtosecond laser excitation. In the past four decades, various optical spectroscopy and time-resolved diffraction methods have been used to study electron-phonon coupling and the effects of underlying dynamical processes. Here, we take advantage of the surface specificity of reflection ultrafast electron diffraction (UED) to examine the structural dynamics of photoexcited metal surfaces, which are apparently slower in recovery than predicted by thermal diffusion from the profile of absorbed energy. Fast diffusion of hot electrons is found to critically reduce surface excitation and affect the temporal dependence of the increased atomic motions on not only the ultrashort but also sub-nanosecond times. Whereas the two-temperature model with the accepted physical constants of platinum can reproduce the observed surface lattice dynamics, gold is found to exhibit appreciably larger-than-expected dynamic vibrational amplitudes of surface atoms while keeping the commonly used electron-phonon coupling constant. Such surface behavioral difference at transient times can be understood in the context of the different strengths of binding to surface atoms for the two metals. In addition, with the quantitative agreements between diffraction and theoretical results, we provide convincing evidence that surface structural dynamics can be reliably obtained by reflection UED even in the presence of laser-induced transient electric fields.
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Affiliation(s)
- Xing He
- Department of Chemistry, University of Houston, Houston, Texas 77204, USA
| | - Mithun Ghosh
- Department of Chemistry, University of Houston, Houston, Texas 77204, USA
| | - Ding-Shyue Yang
- Department of Chemistry, University of Houston, Houston, Texas 77204, USA
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2
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Horn-von Hoegen M. Structural dynamics at surfaces by ultrafast reflection high-energy electron diffraction. STRUCTURAL DYNAMICS (MELVILLE, N.Y.) 2024; 11:021301. [PMID: 38495951 PMCID: PMC10942804 DOI: 10.1063/4.0000234] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/08/2023] [Accepted: 02/13/2024] [Indexed: 03/19/2024]
Abstract
Many fundamental processes of structural changes at surfaces occur on a pico- or femtosecond timescale. In order to study such ultrafast processes, we have combined modern surface science techniques with fs-laser pulses in a pump-probe scheme. Grazing incidence of the electrons ensures surface sensitivity in ultrafast reflection high-energy electron diffraction (URHEED). Utilizing the Debye-Waller effect, we studied the nanoscale heat transport from an ultrathin film through a hetero-interface or the damping of vibrational excitations in monolayer adsorbate systems on the lower ps-timescale. By means of spot profile analysis, the different cooling rates of epitaxial Ge nanostructures of different size and strain state were determined. The excitation and relaxation dynamics of a driven phase transition far away from thermal equilibrium is demonstrated using the In-induced (8 × 2) reconstruction on Si(111). This Peierls-distorted surface charge density wave system exhibits a discontinuous phase transition of first order at 130 K from a (8 × 2) insulating ground state to (4 × 1) metallic excited state. Upon excitation by a fs-laser pulse, this structural phase transition is non-thermally driven in only 700 fs into the excited state. A small barrier of 40 meV hinders the immediate recovery of the ground state, and the system is found in a metastable supercooled state for up to few nanoseconds.
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Affiliation(s)
- Michael Horn-von Hoegen
- Department of Physics and Center for Nanointegration CENIDE, University of Duisburg-Essen, Lotharstrasse. 1, 47057 Duisburg, Germany
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3
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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.
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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
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4
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Zong A, Zhang Q, Zhou F, Su Y, Hwangbo K, Shen X, Jiang Q, Liu H, Gage TE, Walko DA, Kozina ME, Luo D, Reid AH, Yang J, Park S, Lapidus SH, Chu JH, Arslan I, Wang X, Xiao D, Xu X, Gedik N, Wen H. Spin-mediated shear oscillators in a van der Waals antiferromagnet. Nature 2023; 620:988-993. [PMID: 37532936 DOI: 10.1038/s41586-023-06279-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2022] [Accepted: 06/02/2023] [Indexed: 08/04/2023]
Abstract
Understanding how microscopic spin configuration gives rise to exotic properties at the macroscopic length scale has long been pursued in magnetic materials1-5. One seminal example is the Einstein-de Haas effect in ferromagnets1,6,7, in which angular momentum of spins can be converted into mechanical rotation of an entire object. However, for antiferromagnets without net magnetic moment, how spin ordering couples to macroscopic movement remains elusive. Here we observed a seesaw-like rotation of reciprocal lattice peaks of an antiferromagnetic nanolayer film, whose gigahertz structural resonance exhibits more than an order-of-magnitude amplification after cooling below the Néel temperature. Using a suite of ultrafast diffraction and microscopy techniques, we directly visualize this spin-driven rotation in reciprocal space at the nanoscale. This motion corresponds to interlayer shear in real space, in which individual micro-patches of the film behave as coherent oscillators that are phase-locked and shear along the same in-plane axis. Using time-resolved optical polarimetry, we further show that the enhanced mechanical response strongly correlates with ultrafast demagnetization, which releases elastic energy stored in local strain gradients to drive the oscillators. Our work not only offers the first microscopic view of spin-mediated mechanical motion of an antiferromagnet but it also identifies a new route towards realizing high-frequency resonators8,9 up to the millimetre band, so the capability of controlling magnetic states on the ultrafast timescale10-13 can be readily transferred to engineering the mechanical properties of nanodevices.
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Affiliation(s)
- Alfred Zong
- Department of Chemistry, University of California, Berkeley, Berkeley, CA, USA
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Qi Zhang
- Department of Physics, University of Washington, Seattle, WA, USA
- Advanced Photon Source, Argonne National Laboratory, Lemont, IL, USA
- Department of Physics, Nanjing University, Nanjing, China
| | - Faran Zhou
- Advanced Photon Source, Argonne National Laboratory, Lemont, IL, USA
| | - Yifan Su
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Kyle Hwangbo
- Department of Physics, University of Washington, Seattle, WA, USA
| | - Xiaozhe Shen
- SLAC National Accelerator Laboratory, Menlo Park, CA, USA
| | - Qianni Jiang
- Department of Physics, University of Washington, Seattle, WA, USA
| | - Haihua Liu
- Center for Nanoscale Materials, Argonne National Laboratory, Lemont, IL, USA
| | - Thomas E Gage
- Center for Nanoscale Materials, Argonne National Laboratory, Lemont, IL, USA
| | - Donald A Walko
- Advanced Photon Source, Argonne National Laboratory, Lemont, IL, USA
| | | | - Duan Luo
- SLAC National Accelerator Laboratory, Menlo Park, CA, USA
| | | | - Jie Yang
- SLAC National Accelerator Laboratory, Menlo Park, CA, USA
| | - Suji Park
- SLAC National Accelerator Laboratory, Menlo Park, CA, USA
- Department of Materials Science and Engineering, Stanford University, Stanford, CA, USA
- Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, NY, USA
| | - Saul H Lapidus
- Advanced Photon Source, Argonne National Laboratory, Lemont, IL, USA
| | - Jiun-Haw Chu
- Department of Physics, University of Washington, Seattle, WA, USA
| | - Ilke Arslan
- Center for Nanoscale Materials, Argonne National Laboratory, Lemont, IL, USA
| | - Xijie Wang
- SLAC National Accelerator Laboratory, Menlo Park, CA, USA
| | - Di Xiao
- Department of Physics, University of Washington, Seattle, WA, USA
- Department of Materials Science and Engineering, University of Washington, Seattle, WA, USA
- Physical Sciences Division, Pacific Northwest National Laboratory, Richland, WA, USA
| | - Xiaodong Xu
- Department of Physics, University of Washington, Seattle, WA, USA.
- Department of Materials Science and Engineering, University of Washington, Seattle, WA, USA.
| | - Nuh Gedik
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA.
| | - Haidan Wen
- Advanced Photon Source, Argonne National Laboratory, Lemont, IL, USA.
- Materials Science Division, Argonne National Laboratory, Lemont, IL, USA.
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5
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Hanisch-Blicharski A, Tinnemann V, Wall S, Thiemann F, Groven T, Fortmann J, Tajik M, Brand C, Frost BO, von Hoegen A, Hoegen MHV. Violation of Boltzmann Equipartition Theorem in Angular Phonon Phase Space Slows down Nanoscale Heat Transfer in Ultrathin Heterofilms. NANO LETTERS 2021; 21:7145-7151. [PMID: 34407373 DOI: 10.1021/acs.nanolett.1c01665] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Heat transfer through heterointerfaces is intrinsically hampered by a thermal boundary resistance originating from the discontinuity of the elastic properties. Here, we show that with shrinking dimensions the heat flow from an ultrathin epitaxial film through atomically flat interfaces into a single crystalline substrate is significantly reduced due to violation of Boltzmann equipartition theorem in the angular phonon phase space. For films thinner than the phonons mean free path, we find phonons trapped in the film by total internal reflection, thus suppressing heat transfer. Repopulation of those phonon states, which can escape the film through the interface by transmission and refraction, becomes the bottleneck for cooling. The resulting nonequipartition in the angular phonon phase space slows down the cooling by more than a factor of 2 compared to films governed by phonons diffuse scattering. These allow tailoring of the thermal interface conductance via manipulation of the interface.
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Affiliation(s)
| | - Verena Tinnemann
- Faculty of Physics, University of Duisburg-Essen, Lotharstraße 1, 47057 Duisburg, Germany
| | - Simone Wall
- Faculty of Physics, University of Duisburg-Essen, Lotharstraße 1, 47057 Duisburg, Germany
| | - Fabian Thiemann
- Faculty of Physics, University of Duisburg-Essen, Lotharstraße 1, 47057 Duisburg, Germany
| | - Thorben Groven
- Faculty of Physics, University of Duisburg-Essen, Lotharstraße 1, 47057 Duisburg, Germany
| | - Jonas Fortmann
- Faculty of Physics, University of Duisburg-Essen, Lotharstraße 1, 47057 Duisburg, Germany
| | - Mohammad Tajik
- Faculty of Physics, University of Duisburg-Essen, Lotharstraße 1, 47057 Duisburg, Germany
| | - Christian Brand
- Faculty of Physics, University of Duisburg-Essen, Lotharstraße 1, 47057 Duisburg, Germany
| | - Bengt-Olaf Frost
- Faculty of Physics, University of Duisburg-Essen, Lotharstraße 1, 47057 Duisburg, Germany
| | - Alexander von Hoegen
- Max Planck Institute for the Structure and Dynamics of Matter, CFEL, Luruper Chaussee 149, 22761 Hamburg, Germany
| | - Michael Horn-von Hoegen
- Faculty of Physics, University of Duisburg-Essen, Lotharstraße 1, 47057 Duisburg, Germany
- Center for Nanointegration (CENIDE), Carl-Benz-Straße 201, 47057 Duisburg, Germany
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6
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Ji S, Grånäs O, Weissenrieder J. Manipulation of Stacking Order in Td-WTe 2 by Ultrafast Optical Excitation. ACS NANO 2021; 15:8826-8835. [PMID: 33913693 PMCID: PMC8291768 DOI: 10.1021/acsnano.1c01301] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/10/2021] [Accepted: 04/27/2021] [Indexed: 06/12/2023]
Abstract
Subtle changes in stacking order of layered transition metal dichalcogenides may have profound influence on the electronic and optical properties. The intriguing electronic properties of Td-WTe2 can be traced to the break of inversion symmetry resulting from the ground-state stacking sequence. Strategies for perturbation of the stacking order are actively pursued for intentional tuning of material properties, where optical excitation is of specific interest since it holds the potential for integration of ultrafast switches in future device designs. Here we investigate the structural response in Td-WTe2 following ultrafast photoexcitation by time-resolved electron diffraction. A 0.23 THz shear phonon, involving layer displacement along the b axis, was excited by a 515 nm laser pulse. Pump fluences in excess of a threshold of ∼1 mJ/cm2 result in formation, with an ∼5 ps time constant, of a new stacking order by layer displacement along the b axis in the direction toward the centrosymmetric 1T* phase. The shear displacement of the layers increases with pump fluence until saturation at ∼8 pm. We demonstrate that the excitation of the shear phonon and the stabilization of the metastable phase are decoupled when using an optical pump as evidenced by observation of a transition also in samples with a pinned shear phonon. The results are compared to dynamic first-principles simulations and the transition is interpreted in terms of a mechanism where transient local disorder is prominent before settling at the atomic positions of the metastable phase. This interpretation is corroborated by results from diffuse scattering. The correlation between excitation of intralayer vibrations and interlayer interaction demonstrates the importance of including both short- and long-range interactions in an accurate description of how optical fields can be employed to manipulate the stacking order in 2-dimensional transition metal dichalcogenides.
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Affiliation(s)
- Shaozheng Ji
- Materials
and Nano Physics, School of Engineering Sciences, KTH Royal Institute of Technology, SE-100 44 Stockholm, Sweden
| | - Oscar Grånäs
- Division
for Materials Theory, Department of Physics and Astronomy, Uppsala University, SE-751 20 Uppsala, Sweden
| | - Jonas Weissenrieder
- Materials
and Nano Physics, School of Engineering Sciences, KTH Royal Institute of Technology, SE-100 44 Stockholm, Sweden
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7
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Bach N, Schäfer S. Ultrafast strain propagation and acoustic resonances in nanoscale bilayer systems. STRUCTURAL DYNAMICS (MELVILLE, N.Y.) 2021; 8:035101. [PMID: 34169119 PMCID: PMC8214470 DOI: 10.1063/4.0000079] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/21/2020] [Accepted: 04/21/2021] [Indexed: 06/13/2023]
Abstract
Ultrafast structural probing has greatly enhanced our understanding of the coupling of atomic motion to electronic and phononic degrees-of-freedom in quasi-bulk materials. In bi- and multilayer model systems, additionally, spatially inhomogeneous relaxation channels are accessible, often governed by pronounced interfacial couplings and local excitations in confined geometries. Here, we systematically explore the key dependencies of the low-frequency acoustic phonon spectrum in an elastically mismatched metal/semiconductor bilayer system optically excited by femtosecond laser pulses. We track the spatiotemporal strain wave propagation in the heterostructure employing a discrete numerical linear chain simulation and access acoustic wave reflections and interfacial couplings with a phonon mode description based on a continuum mechanics model. Due to the interplay of elastic properties and mass densities of the two materials, acoustic resonance frequencies of the heterostructure significantly differ from breathing modes in monolayer films. For large acoustic mismatch, the spatial localization of phonon eigenmodes is derived from analytical approximations and can be interpreted as harmonic oscillations in decoupled mechanical resonators.
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Affiliation(s)
- N. Bach
- Institute of Physics, University of Oldenburg, 26129 Oldenburg, Germany
| | - S. Schäfer
- Institute of Physics, University of Oldenburg, 26129 Oldenburg, Germany
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8
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Windsor YW, Zahn D, Kamrla R, Feldl J, Seiler H, Chiang CT, Ramsteiner M, Widdra W, Ernstorfer R, Rettig L. Exchange-Striction Driven Ultrafast Nonthermal Lattice Dynamics in NiO. PHYSICAL REVIEW LETTERS 2021; 126:147202. [PMID: 33891443 DOI: 10.1103/physrevlett.126.147202] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/30/2020] [Accepted: 03/03/2021] [Indexed: 06/12/2023]
Abstract
We use femtosecond electron diffraction to study ultrafast lattice dynamics in the highly correlated antiferromagnetic (AFM) semiconductor NiO. Using the scattering vector (Q) dependence of Bragg diffraction, we introduce Q-resolved effective temperatures describing the transient lattice. We identify a nonthermal lattice state with preferential displacement of O compared to Ni ions, which occurs within ∼0.3 ps and persists for 25 ps. We associate this with transient changes to the AFM exchange striction-induced lattice distortion, supported by the observation of a transient Q asymmetry of Friedel pairs. Our observation highlights the role of spin-lattice coupling in routes towards ultrafast control of spin order.
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Affiliation(s)
- Y W Windsor
- Department of Physical Chemistry, Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195 Berlin, Germany
| | - D Zahn
- Department of Physical Chemistry, Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195 Berlin, Germany
| | - R Kamrla
- Institute of Physics, Martin-Luther-Universität Halle-Wittenberg, 06120 Halle, Germany
| | - J Feldl
- Paul-Drude-Institut für Festkörperelektronik, Leibniz-Institut im Forschungsverbund Berlin e.V., Hausvogteiplatz 5-7, 10117 Berlin, Germany
| | - H Seiler
- Department of Physical Chemistry, Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195 Berlin, Germany
| | - C-T Chiang
- Institute of Physics, Martin-Luther-Universität Halle-Wittenberg, 06120 Halle, Germany
| | - M Ramsteiner
- Paul-Drude-Institut für Festkörperelektronik, Leibniz-Institut im Forschungsverbund Berlin e.V., Hausvogteiplatz 5-7, 10117 Berlin, Germany
| | - W Widdra
- Institute of Physics, Martin-Luther-Universität Halle-Wittenberg, 06120 Halle, Germany
| | - R Ernstorfer
- Department of Physical Chemistry, Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195 Berlin, Germany
| | - L Rettig
- Department of Physical Chemistry, Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195 Berlin, Germany
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9
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Abstract
Time-resolved electron microscopy is based on the excitation of a sample by pulsed laser radiation and its probing by synchronized photoelectron bunches in the electron microscope column. With femtosecond lasers, if probing pulses with a small number of electrons—in the limit, single-electron wave packets—are used, the stroboscopic regime enables ultrahigh spatiotemporal resolution to be obtained, which is not restricted by the Coulomb repulsion of electrons. This review article presents the current state of the ultrafast electron microscopy (UEM) method for detecting the structural dynamics of matter in the time range from picoseconds to attoseconds. Moreover, in the imaging mode, the spatial resolution lies, at best, in the subnanometer range, which limits the range of observation of structural changes in the sample. The ultrafast electron diffraction (UED), which created the methodological basis for the development of UEM, has opened the possibility of creating molecular movies that show the behavior of the investigated quantum system in the space-time continuum with details of sub-Å spatial resolution. Therefore, this review on the development of UEM begins with a description of the main achievements of UED, which formed the basis for the creation and further development of the UEM method. A number of recent experiments are presented to illustrate the potential of the UEM method.
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10
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Tinnemann V, Streubühr C, Hafke B, Witte T, Kalus A, Hanisch-Blicharski A, Ligges M, Zhou P, von der Linde D, Bovensiepen U, Horn-von Hoegen M. Decelerated lattice excitation and absence of bulk phonon modes at surfaces: Ultra-fast electron diffraction from Bi(111) surface upon fs-laser excitation. Struct Dyn 2019; 6:065101. [PMID: 31700944 PMCID: PMC6831505 DOI: 10.1063/1.5128275] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2019] [Accepted: 10/15/2019] [Indexed: 12/30/2022] Open
Abstract
Ultrafast reflection high-energy electron diffraction is employed to follow the lattice excitation of a Bi(111) surface upon irradiation with a femtosecond laser pulse. The thermal motion of the atoms is analyzed through the Debye–Waller effect. While the Bi bulk is heated on time scales of 2 to 4 ps, we observe that the excitation of vibrational motion of the surface atoms occurs much slower with a time constant of 12 ps. This transient nonequilibrium situation is attributed to the weak coupling between bulk and surface phonon modes which hampers the energy flow between the two subsystems. From the absence of a fast component in the transient diffraction intensity, it is in addition concluded that truncated bulk phonon modes are absent at the surface.
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Affiliation(s)
- V. Tinnemann
- Department of Physics and Center for Nanointegration (CENIDE), University of Duisburg-Essen, 47048 Duisburg, Germany
| | - C. Streubühr
- Department of Physics and Center for Nanointegration (CENIDE), University of Duisburg-Essen, 47048 Duisburg, Germany
| | - B. Hafke
- Department of Physics and Center for Nanointegration (CENIDE), University of Duisburg-Essen, 47048 Duisburg, Germany
| | - T. Witte
- Department of Physics and Center for Nanointegration (CENIDE), University of Duisburg-Essen, 47048 Duisburg, Germany
| | - A. Kalus
- Department of Physics and Center for Nanointegration (CENIDE), University of Duisburg-Essen, 47048 Duisburg, Germany
| | - A. Hanisch-Blicharski
- Department of Physics and Center for Nanointegration (CENIDE), University of Duisburg-Essen, 47048 Duisburg, Germany
| | - M. Ligges
- Department of Physics and Center for Nanointegration (CENIDE), University of Duisburg-Essen, 47048 Duisburg, Germany
| | - P. Zhou
- Department of Physics and Center for Nanointegration (CENIDE), University of Duisburg-Essen, 47048 Duisburg, Germany
| | - D. von der Linde
- Department of Physics and Center for Nanointegration (CENIDE), University of Duisburg-Essen, 47048 Duisburg, Germany
| | - U. Bovensiepen
- Department of Physics and Center for Nanointegration (CENIDE), University of Duisburg-Essen, 47048 Duisburg, Germany
| | - M. Horn-von Hoegen
- Department of Physics and Center for Nanointegration (CENIDE), University of Duisburg-Essen, 47048 Duisburg, Germany
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