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Li A, Zeiger PM, He Z, Xu M, Pennycook SJ, Rusz J, Zhou W. Systematic Absences of Optical Phonon Modes in Phonon Dispersion Measured by Electron Microscopy. PHYSICAL REVIEW LETTERS 2024; 133:046101. [PMID: 39121401 DOI: 10.1103/physrevlett.133.046101] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/23/2024] [Accepted: 06/10/2024] [Indexed: 08/11/2024]
Abstract
Phonon dispersion relations are widely used to elucidate the vibrational properties of materials. As an emerging technique, momentum-resolved vibrational spectroscopy in scanning transmission electron microscopy offers an unparalleled approach to explore q-dependent phonon behavior at local structures. In this study, we systematically investigate the phonon dispersion of monolayer graphene across several Brillouin zones (BZs) using momentum-resolved vibrational spectroscopy and find that the optical phonon signals vanish at the Γ points with indices (hk0) satisfying h+2k=3n (n denoted integers). Theoretical analysis reveals that the observed phenomena arise from the complete destructive interference of the scattered waves from different basis atoms. This observation, corroborated by the study of diamond, should be a general characteristic of materials composed of symmetrically equivalent pairs of the same elements. Moreover, our results emphasize the importance of multiple scattering in interpreting the vibrational signals in bulk materials. We demonstrate that the systematic absences and dynamic effects, which have not been much appreciated before, offer new insights into the experimental assessment of local vibrational properties of materials.
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2
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Urbieta M, Barbry M, Koval P, Rivacoba A, Sánchez-Portal D, Aizpurua J, Zabala N. Footprints of atomic-scale features in plasmonic nanoparticles as revealed by electron energy loss spectroscopy. Phys Chem Chem Phys 2024; 26:14991-15004. [PMID: 38741574 DOI: 10.1039/d4cp01034e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/16/2024]
Abstract
We present a first-principles theoretical study of the atomistic footprints in the valence electron energy loss spectroscopy (EELS) of nanometer-size metallic particles. Charge density maps of excited plasmons and EEL spectra for specific electron paths through a nanoparticle (Na380 atom cluster) are modeled using ab initio calculations within time-dependent density functional theory. Our findings unveil the atomic-scale sensitivity of EELS within this low-energy spectral range. Whereas localized surface plasmons (LSPs) are particularly sensitive to the atomistic structure of the surface probed by the electron beam, confined bulk plasmons (CBPs) reveal quantum size effects within the nanoparticle's volume. Moreover, we prove that classical local dielectric theories mimicking the atomistic structure of the nanoparticles reproduce the LSP trends observed in quantum calculations, but fall short in describing the CBP behavior observed under different electron trajectories.
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Affiliation(s)
- Mattin Urbieta
- Matematika Aplikatua Saila, Gipuzkoako Ingeniaritza Eskola (Eibarko Atala), University of the Basque Country UPV/EHU, 20018 Eibar, Spain.
- Centro de Física de Materiales CSIC - UPV/EHU, Paseo Manuel de Lardizabal 5, Donostia-San Sebastian, Gipuzkoa 20018, Spain
- Donostia International Physics Center (DIPC), Paseo Manuel de Lardizabal 4, Donostia-San Sebastian, Gipuzkoa 20018, Spain
| | - Marc Barbry
- Centro de Física de Materiales CSIC - UPV/EHU, Paseo Manuel de Lardizabal 5, Donostia-San Sebastian, Gipuzkoa 20018, Spain
- Donostia International Physics Center (DIPC), Paseo Manuel de Lardizabal 4, Donostia-San Sebastian, Gipuzkoa 20018, Spain
| | - Peter Koval
- Simune Atomistics S.L., Avenida de Tolosa 76, Donostia-San Sebastian 20018, Spain
| | - Alberto Rivacoba
- Donostia International Physics Center (DIPC), Paseo Manuel de Lardizabal 4, Donostia-San Sebastian, Gipuzkoa 20018, Spain
| | - Daniel Sánchez-Portal
- Centro de Física de Materiales CSIC - UPV/EHU, Paseo Manuel de Lardizabal 5, Donostia-San Sebastian, Gipuzkoa 20018, Spain
- Donostia International Physics Center (DIPC), Paseo Manuel de Lardizabal 4, Donostia-San Sebastian, Gipuzkoa 20018, Spain
| | - Javier Aizpurua
- Donostia International Physics Center (DIPC), Paseo Manuel de Lardizabal 4, Donostia-San Sebastian, Gipuzkoa 20018, Spain
- Department of Electricity and Electronics, FCT-ZTF, University of the Basque Country (UPV/EHU), Barrio Sarriena z/g, Leioa, Bizkaia 48940, Spain.
- Ikerbasque, Basque Foundation for Science, Bilbao, Bizkaia 48011, Spain
| | - Nerea Zabala
- Centro de Física de Materiales CSIC - UPV/EHU, Paseo Manuel de Lardizabal 5, Donostia-San Sebastian, Gipuzkoa 20018, Spain
- Donostia International Physics Center (DIPC), Paseo Manuel de Lardizabal 4, Donostia-San Sebastian, Gipuzkoa 20018, Spain
- Department of Electricity and Electronics, FCT-ZTF, University of the Basque Country (UPV/EHU), Barrio Sarriena z/g, Leioa, Bizkaia 48940, Spain.
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Yan J, Shi R, Wei J, Li Y, Qi R, Wu M, Li X, Feng B, Gao P, Shibata N, Ikuhara Y. Nanoscale Localized Phonons at Al 2O 3 Grain Boundaries. NANO LETTERS 2024; 24:3323-3330. [PMID: 38466652 DOI: 10.1021/acs.nanolett.3c04149] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/13/2024]
Abstract
Nanoscale defects like grain boundaries (GBs) would introduce local phonon modes and affect the bulk materials' thermal, electrical, optical, and mechanical properties. It is highly desirable to correlate the phonon modes and atomic arrangements for individual defects to precisely understand the structure-property relation. Here we investigated the localized phonon modes of Al2O3 GBs by combination of the vibrational electron energy loss spectroscopy (EELS) in scanning transmission electron microscope and density functional perturbation theory (DFPT). The differences between GB and bulk obtained from the vibrational EELS show that the GB exhibited more active vibration at the energy range of <50 meV and >80 meV, and further DFPT results proved the wide distribution of bond lengths at GB are the main factor for the emergence of local phonon modes. This research provides insights into the phonon-defect relation and would be of importance in the design and application of polycrystalline materials.
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Affiliation(s)
- Jingyuan Yan
- Institute of Engineering Innovation, The University of Tokyo, Tokyo 113-8656, Japan
- Electron Microscopy Laboratory, School of Physics, Peking University, Beijing 100871, China
| | - Ruochen Shi
- Electron Microscopy Laboratory, School of Physics, Peking University, Beijing 100871, China
- International Center for Quantum Materials, Peking University, Beijing 100871, China
| | - Jiake Wei
- Institute of Engineering Innovation, The University of Tokyo, Tokyo 113-8656, Japan
- State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China
| | - Yuehui Li
- Electron Microscopy Laboratory, School of Physics, Peking University, Beijing 100871, China
- International Center for Quantum Materials, Peking University, Beijing 100871, China
| | - Ruishi Qi
- Electron Microscopy Laboratory, School of Physics, Peking University, Beijing 100871, China
- International Center for Quantum Materials, Peking University, Beijing 100871, China
- Department of Physics, University of California at Berkeley, Berkeley 94720, California, United States
| | - Mei Wu
- Electron Microscopy Laboratory, School of Physics, Peking University, Beijing 100871, China
- International Center for Quantum Materials, Peking University, Beijing 100871, China
| | - Xiaomei Li
- Electron Microscopy Laboratory, School of Physics, Peking University, Beijing 100871, China
- School of Integrated Circuits, East China Normal University, Shanghai 200241, China
| | - Bin Feng
- Institute of Engineering Innovation, The University of Tokyo, Tokyo 113-8656, Japan
- PRESTO, Japan Science and Technology Agency, Kawaguchi 332-0012, Japan
| | - Peng Gao
- Electron Microscopy Laboratory, School of Physics, Peking University, Beijing 100871, China
- International Center for Quantum Materials, Peking University, Beijing 100871, China
- Interdisciplinary Institute of Light-Element Quantum Materials and Research Center for Light-Element Advanced Materials, Peking University, Beijing 100871, China
| | - Naoya Shibata
- Institute of Engineering Innovation, The University of Tokyo, Tokyo 113-8656, Japan
- Nanostructures Research Laboratory, Japan Fine Ceramics Center, Nagoya 456-8587, Japan
| | - Yuichi Ikuhara
- Institute of Engineering Innovation, The University of Tokyo, Tokyo 113-8656, Japan
- Nanostructures Research Laboratory, Japan Fine Ceramics Center, Nagoya 456-8587, Japan
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4
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Zeiger PM, Barthel J, Allen LJ, Rusz J. Simulations of Phonon Spectroscopy in the Impact Scattering Regime - Advances and Applications. MICROSCOPY AND MICROANALYSIS : THE OFFICIAL JOURNAL OF MICROSCOPY SOCIETY OF AMERICA, MICROBEAM ANALYSIS SOCIETY, MICROSCOPICAL SOCIETY OF CANADA 2023; 29:628-629. [PMID: 37613084 DOI: 10.1093/micmic/ozad067.306] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/25/2023]
Affiliation(s)
- Paul M Zeiger
- Uppsala University, Department of Physics and Astronomy, Uppsala, Sweden
| | - Juri Barthel
- RWTH Aachen University, Central Facility for Electron Microscopy, Aachen, Germany
- Forschungszentrum Jülich GmbH, Ernst Ruska-Centre (ER-C 2), Jülich, Germany
| | - Leslie J Allen
- University of Melbourne, School of Physics, Victoria, Australia
| | - Ján Rusz
- Uppsala University, Department of Physics and Astronomy, Uppsala, Sweden
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5
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Hoglund ER, Bao DL, O'Hara A, Pfeifer TW, Hoque MSB, Makarem S, Howe JM, Pantelides ST, Hopkins PE, Hachtel JA. Direct Visualization of Localized Vibrations at Complex Grain Boundaries. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2023; 35:e2208920. [PMID: 36634374 DOI: 10.1002/adma.202208920] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/27/2022] [Revised: 11/25/2022] [Indexed: 06/17/2023]
Abstract
Grain boundaries (GBs) are a prolific microstructural feature that dominates the functionality of a wide class of materials. The functionality at a GB results from the unique atomic arrangements, different from those in the grain, that have driven extensive experimental and theoretical studies correlating atomic-scale GB structures to macroscopic electronic, infrared optical, and thermal properties. In this work, a SrTiO3 GB is examined using atomic-resolution aberration-corrected scanning transmission electron microscopy and ultrahigh-energy-resolution monochromated electron energy-loss spectroscopy, in conjunction with density functional theory. This combination enables the correlation of the GB structure, nonstoichiometry, and chemical bonding with a redistribution of vibrational states within the GB dislocation cores. The new experimental access to localized GB vibrations provides a direct route to quantifying the impact of individual boundaries on macroscopic properties.
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Affiliation(s)
- Eric R Hoglund
- Department of Materials Science and Engineering, University of Virginia, Charlottesville, VA, 22904, USA
| | - De-Liang Bao
- Department of Physics and Astronomy, Vanderbilt University, Nashville, TN, 37235, USA
| | - Andrew O'Hara
- Department of Physics and Astronomy, Vanderbilt University, Nashville, TN, 37235, USA
| | - Thomas W Pfeifer
- Department of Mechanical and Aerospace Engineering, University of Virginia, Charlottesville, VA, 22904, USA
| | - Md Shafkat Bin Hoque
- Department of Mechanical and Aerospace Engineering, University of Virginia, Charlottesville, VA, 22904, USA
| | - Sara Makarem
- Department of Materials Science and Engineering, University of Virginia, Charlottesville, VA, 22904, USA
| | - James M Howe
- Department of Materials Science and Engineering, University of Virginia, Charlottesville, VA, 22904, USA
| | - Sokrates T Pantelides
- Department of Physics and Astronomy, Vanderbilt University, Nashville, TN, 37235, USA
| | - Patrick E Hopkins
- Department of Mechanical and Aerospace Engineering, University of Virginia, Charlottesville, VA, 22904, USA
| | - Jordan A Hachtel
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN, 37830, USA
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6
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Chen X, Kim DS, LeBeau JM. A comparison of molecular dynamics potentials used to account for thermal diffuse scattering in multislice simulations. Ultramicroscopy 2023; 244:113644. [PMID: 36410085 DOI: 10.1016/j.ultramic.2022.113644] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2022] [Revised: 08/31/2022] [Accepted: 11/12/2022] [Indexed: 11/18/2022]
Abstract
Here we investigate electron scattering simulations with thermal displacements incorporated using molecular dynamics potentials. Specifically, we explore the sensitivity of electron scattering to the phonon band structure, or more explicitly interatomic forces. Silicon serves as the model material where we introduce thermal atomic displacements via empirical and machine-learned molecular dynamics interatomic potentials and compare them to finite-temperature density functional theory interatomic forces. We demonstrate that when molecular dynamics potentials do not sufficiently reproduce the correct phonon band structure, significant errors in the simulated diffraction and image intensities can occur. Moreover, for Si, we find that multislice simulations using machine-learned interatomic potentials are more accurate than empirical ones. In addition to the selected atomic potential, we demonstrate that the sensitivity to the phonon band structure also depends on the crystal zone axis, which can be used to enhance sensitivity to thermal displacements. Finally, we provide a sensitivity analysis with angle-resolved scanning transmission electron microscopy (STEM) to enhance image sensitivity to the details of the phonon band structure.
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Affiliation(s)
- Xi Chen
- Department of Materials Science & Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, United States of America
| | - Dennis S Kim
- Department of Materials Science & Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, United States of America
| | - James M LeBeau
- Department of Materials Science & Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, United States of America.
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7
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Rez P, Boland T, Elsässer C, Singh A. Localized Phonon Densities of States at Grain Boundaries in Silicon. MICROSCOPY AND MICROANALYSIS : THE OFFICIAL JOURNAL OF MICROSCOPY SOCIETY OF AMERICA, MICROBEAM ANALYSIS SOCIETY, MICROSCOPICAL SOCIETY OF CANADA 2022; 28:1-8. [PMID: 35293309 DOI: 10.1017/s143192762200040x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Since it is now possible to record vibrational spectra at nanometer scales in the electron microscope, it is of interest to explore whether extended defects in crystals such as dislocations or grain boundaries will result in measurable changes of the phonon densities of states (dos) that are reflected in the spectra. Phonon densities of states were calculated for a set of high angle grain boundaries in silicon. The boundaries are modeled by supercells with up to 160 atoms, and the vibrational densities of states were calculated by taking the Fourier transform of the velocity–velocity autocorrelation function from molecular dynamics simulations with larger supercells doubled in all three directions. In selected cases, the results were checked on the original supercells by comparison with the densities of states obtained by diagonalizing the dynamical matrix calculated using density functional theory. Near the core of the grain boundary, the height of the optic phonon peak in the dos at 60 meV was suppressed relative to features due to acoustic phonons that are largely unchanged relative to their bulk values. This can be attributed to the variation in the strength of bonds in grain boundary core regions where there is a range of bond lengths.
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Affiliation(s)
- Peter Rez
- Department of Physics, Arizona State University, Tempe, AZ85287-1504, USA
| | - Tara Boland
- School For Engineering of Matter Transport and Energy, Arizona State University, Tempe, AZ85287-6106, USA
| | - Christian Elsässer
- Fraunhofer Institute for Mechanics of Materials IWM, Wöhlerstraße 11, 79108Freiburg, Germany
| | - Arunima Singh
- Department of Physics, Arizona State University, Tempe, AZ85287-1504, USA
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8
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OUP accepted manuscript. Microscopy (Oxf) 2022; 71:i174-i199. [DOI: 10.1093/jmicro/dfab050] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2021] [Revised: 11/20/2021] [Accepted: 01/28/2022] [Indexed: 11/14/2022] Open
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9
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Konečná A, Iyikanat F, García de Abajo FJ. Theory of Atomic-Scale Vibrational Mapping and Isotope Identification with Electron Beams. ACS NANO 2021; 15:9890-9899. [PMID: 34006088 DOI: 10.1021/acsnano.1c01071] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Transmission electron microscopy and spectroscopy currently enable the acquisition of spatially resolved spectral information from a specimen by focusing electron beams down to a sub-angstrom spot and then analyzing the energy of the inelastically scattered electrons with few-meV energy resolution. This technique has recently been used to experimentally resolve vibrational modes in 2D materials emerging at mid-infrared frequencies. Here, on the basis of first-principles theory, we demonstrate the possibility of identifying single isotope atom impurities in a nanostructure through the trace that they leave in the spectral and spatial characteristics of the vibrational modes. Specifically, we examine a hexagonal boron nitride molecule as an example of application, in which the presence of a single isotope impurity is revealed through changes in the electron spectra, as well as in the space-, energy-, and momentum-resolved inelastic electron signal. We compare these results with conventional far-field spectroscopy, showing that electron beams offer superior spatial resolution combined with the ability to probe the complete set of vibrational modes, including those that are optically dark. Our study is relevant for the atomic-scale characterization of vibrational modes in materials of interest, including a detailed mapping of isotope distributions.
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Affiliation(s)
- Andrea Konečná
- ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, 08860 Castelldefels, Barcelona, Spain
| | - Fadil Iyikanat
- ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, 08860 Castelldefels, Barcelona, Spain
| | - F Javier García de Abajo
- ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, 08860 Castelldefels, Barcelona, Spain
- ICREA-Institució Catalana de Recerca i Estudis Avançats, Passeig Lluís Companys 23, 08010 Barcelona, Spain
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10
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Madsen J, Susi T. The abTEM code: transmission electron microscopy from first principles. OPEN RESEARCH EUROPE 2021; 1:24. [PMID: 37645137 PMCID: PMC10446032 DOI: 10.12688/openreseurope.13015.1] [Citation(s) in RCA: 45] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 05/18/2021] [Indexed: 09/27/2023]
Abstract
Simulation of transmission electron microscopy (TEM) images or diffraction patterns is often required to interpret experimental data. Since nuclear cores dominate electron scattering, the scattering potential is typically described using the independent atom model, which completely neglects valence bonding and its effect on the transmitting electrons. As instrumentation has advanced, new measurements have revealed subtle details of the scattering potential that were previously not accessible to experiment. We have created an open-source simulation code designed to meet these demands by integrating the ability to calculate the potential via density functional theory (DFT) with a flexible modular software design. abTEM can simulate most standard imaging modes and incorporates the latest algorithmic developments. The development of new techniques requires a program that is accessible to domain experts without extensive programming experience. abTEM is written purely in Python and designed for easy modification and extension. The effective use of modern open-source libraries makes the performance of abTEM highly competitive with existing optimized codes on both CPUs and GPUs and allows us to leverage an extensive ecosystem of libraries, such as the Atomic Simulation Environment and the DFT code GPAW. abTEM is designed to work in an interactive Python notebook, creating a seamless and reproducible workflow from defining an atomic structure, calculating molecular dynamics (MD) and electrostatic potentials, to the analysis of results, all in a single, easy-to-read document. This article provides ongoing documentation of abTEM development. In this first version, we show use cases for hexagonal boron nitride, where valence bonding can be detected, a 4D-STEM simulation of molybdenum disulfide including ptychographic phase reconstruction, a comparison of MD and frozen phonon modeling for convergent-beam electron diffraction of a 2.6-million-atom silicon system, and a performance comparison of our fast implementation of the PRISM algorithm for a decahedral 20000-atom gold nanoparticle.
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Affiliation(s)
- Jacob Madsen
- Faculty of Physics, University of Vienna, Vienna, 1090, Austria
| | - Toma Susi
- Faculty of Physics, University of Vienna, Vienna, 1090, Austria
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11
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Madsen J, Susi T. The abTEM code: transmission electron microscopy from first principles. OPEN RESEARCH EUROPE 2021; 1:24. [PMID: 37645137 PMCID: PMC10446032 DOI: 10.12688/openreseurope.13015.2] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 05/18/2021] [Indexed: 08/31/2023]
Abstract
Simulation of transmission electron microscopy (TEM) images or diffraction patterns is often required to interpret experimental data. Since nuclear cores dominate electron scattering, the scattering potential is typically described using the independent atom model, which completely neglects valence bonding and its effect on the transmitting electrons. As instrumentation has advanced, new measurements have revealed subtle details of the scattering potential that were previously not accessible to experiment. We have created an open-source simulation code designed to meet these demands by integrating the ability to calculate the potential via density functional theory (DFT) with a flexible modular software design. abTEM can simulate most standard imaging modes and incorporates the latest algorithmic developments. The development of new techniques requires a program that is accessible to domain experts without extensive programming experience. abTEM is written purely in Python and designed for easy modification and extension. The effective use of modern open-source libraries makes the performance of abTEM highly competitive with existing optimized codes on both CPUs and GPUs and allows us to leverage an extensive ecosystem of libraries, such as the Atomic Simulation Environment and the DFT code GPAW. abTEM is designed to work in an interactive Python notebook, creating a seamless and reproducible workflow from defining an atomic structure, calculating molecular dynamics (MD) and electrostatic potentials, to the analysis of results, all in a single, easy-to-read document. This article provides ongoing documentation of abTEM development. In this first version, we show use cases for hexagonal boron nitride, where valence bonding can be detected, a 4D-STEM simulation of molybdenum disulfide including ptychographic phase reconstruction, a comparison of MD and frozen phonon modeling for convergent-beam electron diffraction of a 2.6-million-atom silicon system, and a performance comparison of our fast implementation of the PRISM algorithm for a decahedral 20000-atom gold nanoparticle.
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Affiliation(s)
- Jacob Madsen
- Faculty of Physics, University of Vienna, Vienna, 1090, Austria
| | - Toma Susi
- Faculty of Physics, University of Vienna, Vienna, 1090, Austria
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12
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ab initio description of bonding for transmission electron microscopy. Ultramicroscopy 2021; 231:113253. [PMID: 33773844 DOI: 10.1016/j.ultramic.2021.113253] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2020] [Revised: 02/12/2021] [Accepted: 02/20/2021] [Indexed: 01/10/2023]
Abstract
The simulation of transmission electron microscopy (TEM) images or diffraction patterns is often required to interpret their contrast and extract specimen features. This is especially true for high-resolution phase-contrast imaging of materials, but electron scattering simulations based on atomistic models are widely used in materials science and structural biology. Since electron scattering is dominated by the nuclear cores, the scattering potential is typically described by the widely applied independent atom model. This approximation is fast and fairly accurate, especially for scanning TEM (STEM) annular dark-field contrast, but it completely neglects valence bonding and its effect on the transmitting electrons. However, an emerging trend in electron microscopy is to use new instrumentation and methods to extract the maximum amount of information from each electron. This is evident in the increasing popularity of techniques such as 4D-STEM combined with ptychography in materials science, and cryogenic microcrystal electron diffraction in structural biology, where subtle differences in the scattering potential may be both measurable and contain additional insights. Thus, there is increasing interest in electron scattering simulations based on electrostatic potentials obtained from first principles, mainly via density functional theory, which was previously mainly required for holography. In this Review, we discuss the motivation and basis for these developments, survey the pioneering work that has been published thus far, and give our outlook for the future. We argue that a physically better justified ab initio description of the scattering potential is both useful and viable for an increasing number of systems, and we expect such simulations to steadily gain in popularity and importance.
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13
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Qi R, Li N, Du J, Shi R, Huang Y, Yang X, Liu L, Xu Z, Dai Q, Yu D, Gao P. Four-dimensional vibrational spectroscopy for nanoscale mapping of phonon dispersion in BN nanotubes. Nat Commun 2021; 12:1179. [PMID: 33608559 PMCID: PMC7896073 DOI: 10.1038/s41467-021-21452-5] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2020] [Accepted: 01/26/2021] [Indexed: 11/17/2022] Open
Abstract
Directly mapping local phonon dispersion in individual nanostructures can advance our understanding of their thermal, optical, and mechanical properties. However, this requires high detection sensitivity and combined spatial, energy and momentum resolutions, thus has been elusive. Here, we demonstrate a four-dimensional electron energy loss spectroscopy technique, and present position-dependent phonon dispersion measurements in individual boron nitride nanotubes. By scanning the electron beam in real space while monitoring both the energy loss and the momentum transfer, we are able to reveal position- and momentum-dependent lattice vibrations at nanometer scale. Our measurements show that the phonon dispersion of multi-walled nanotubes is locally close to hexagonal-boron nitride crystals. Interestingly, acoustic phonons are sensitive to defect scattering, while optical modes are insensitive to small voids. This work not only provides insights into vibrational properties of boron nitride nanotubes, but also demonstrates potential of the developed technique in nanoscale phonon dispersion measurements.
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Affiliation(s)
- Ruishi Qi
- Electron Microscopy Laboratory, School of Physics, Peking University, Beijing, China
- International Center for Quantum Materials, Peking University, Beijing, China
- Department of Physics, University of California at Berkeley, Berkeley, CA, USA
| | - Ning Li
- Electron Microscopy Laboratory, School of Physics, Peking University, Beijing, China
- International Center for Quantum Materials, Peking University, Beijing, China
- Academy for Advanced Interdisciplinary Studies, Peking University, Beijing, China
| | - Jinlong Du
- Electron Microscopy Laboratory, School of Physics, Peking University, Beijing, China
| | - Ruochen Shi
- Electron Microscopy Laboratory, School of Physics, Peking University, Beijing, China
- International Center for Quantum Materials, Peking University, Beijing, China
| | - Yang Huang
- School of Materials Science and Engineering, Hebei University of Technology, Tianjin, China
- Hebei Key Laboratory of Boron Nitride Micro and Nano Materials, Hebei University of Technology, Tianjin, China
| | - Xiaoxia Yang
- CAS Key Laboratory of Nanophotonic Materials and Devices, CAS Center for Excellence in Nanoscience, National Center for Nanoscience and Technology, Beijing, China
| | - Lei Liu
- School of Materials Science and Engineering, Peking University, Beijing, China
| | - Zhi Xu
- Songshan Lake Materials Lab, Institute of Physics, Chinese Academy of Sciences, Guangdong, China
| | - Qing Dai
- CAS Key Laboratory of Nanophotonic Materials and Devices, CAS Center for Excellence in Nanoscience, National Center for Nanoscience and Technology, Beijing, China
| | - Dapeng Yu
- Shenzhen Key Laboratory of Quantum Science and Engineering, Shenzhen, China
| | - Peng Gao
- Electron Microscopy Laboratory, School of Physics, Peking University, Beijing, China.
- International Center for Quantum Materials, Peking University, Beijing, China.
- Collaborative Innovation Center of Quantum Matter, and Beijing Key Laboratory of Quantum Devices, Beijing, China.
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14
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Rez P, Singh A. Lattice resolution of vibrational modes in the electron microscope. Ultramicroscopy 2020; 220:113162. [PMID: 33189051 DOI: 10.1016/j.ultramic.2020.113162] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2020] [Revised: 10/28/2020] [Accepted: 11/01/2020] [Indexed: 10/23/2022]
Abstract
The combination of aberration correction and ultra high energy resolution with monochromators has made it possible to record images showing lattice resolution in phonon modes, both with a displaced collection aperture and more recently with an on -axis collection aperture. In practice the objective aperture has to include Bragg reflections that correspond to the observed lattice image spacings, and the specimen has to be sufficiently thick for adequate phonon scattered intensity. There has been controversy as to whether the images with the on axis detector are really a consequence of lattice resolution in a phonon mode or just a transfer of information from an image that was formed by elastically scattered electrons. We present results of calculations based on a theory that includes the possibility of dynamical electron diffraction for both incident and scattered electrons and the full phonon dispersion relation. We show that Umklapp scattering from the second Brillouin Zone back to the first Brillouin Zone is necessary for lattice resolution with the on axis detector and that it is therefore reasonable to attribute the lattice resolution to the phonon scattering.
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Affiliation(s)
- Peter Rez
- Department of Physics, Arizona State University, Tempe, AZ 85287-1504, USA.
| | - Arunima Singh
- Department of Physics, Arizona State University, Tempe, AZ 85287-1504, USA
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