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Rasheed A. Self-assembly of nickel icosahedrons and truncated octahedral nanocrystals on a SrTiO3 (111) support. Microscopy (Oxf) 2021; 70:e1-e5. [PMID: 33372677 DOI: 10.1093/jmicro/dfaa078] [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: 10/10/2020] [Accepted: 12/28/2020] [Indexed: 11/14/2022] Open
Abstract
Nickel nanocrystals have received much attention for their ferromagnetic properties. The crystal properties are strongly dependent on their facets and therefore detailed study of their morphology, facets and orientation is critical for magnetic applications. In this work, equilibrium crystal shapes of self-assembled nickel nanocrystals on the (111) termination of strontium titanate (SrTiO3) at room temperature and under ultra-high vacuum (UHV) conditions have been investigated using scanning tunneling microscope. SrTiO3 (111) substrate was sputtered (0.5 keV, 2.5 µA, 10 min) and annealed (900°C, 1 h) under UHV conditions. Three different periodicities were observed: 2.21 ± 0.01 nm corresponding to (4 × 4) reconstruction, 3.31 ± 0.02 nm corresponding to (6 × 6) reconstruction and 2.85 ± 0.05 nm, rotated at 30° with respect to (4 × 4) reconstruction, corresponding to (3√3 × 3√3)R30° reconstruction. Nickel (∼1 ml) was deposited using an e-beam evaporator on the substrate preheated to 320°C and the sample was post-annealed multiple times. Nickel took platonic shapes of supported icosahedron comprising of (111) facets and truncated octahedron comprising of (001) and (111) facets. Based on surface energy ratios of truncated octahedrons at equilibrium, the work of adhesion was calculated to be 3.889 ± 0.167 J/m2.
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Affiliation(s)
- Atif Rasheed
- Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, United Kingdom
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52
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Tyukalova E, Vimal Vas J, Ignatans R, Mueller AD, Medwal R, Imamura M, Asada H, Fukuma Y, Rawat RS, Tileli V, Duchamp M. Challenges and Applications to Operando and In Situ TEM Imaging and Spectroscopic Capabilities in a Cryogenic Temperature Range. Acc Chem Res 2021; 54:3125-3135. [PMID: 34339603 DOI: 10.1021/acs.accounts.1c00078] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
ConspectusIn this Account, we describe the challenges and promising applications of transmission electron microscopy (TEM) imaging and spectroscopy at cryogenic temperatures. Our work focuses on two areas of application: the delay of electron-beam-induced degradation and following low-temperature phenomena in a continuous and variable temperature range. For the former, we present a study of LiMn1.5Ni0.5O4 lithium ion battery cathode material that undergoes electron beam-induced degradation when studied at room temperature by TEM. Cryogenic imaging reveals the true structure of LiMn1.5Ni0.5O4 nanoparticles in their discharged state. Improved stability under electron beam irradiation was confirmed by following the evolution of the O K-edge fine structure by electron energy-loss spectroscopy. Our results demonstrate that the effect of radiation damage on discharged LiMn1.5Ni0.5O4 was previously underestimated and that atomic-resolution imaging at cryogenic temperature has a potential to be generalized to most of the Li-based materials and beyond. For the latter, we present two studies in the imaging of low-temperature phenomena on the local scale, namely, the evolution of ferroelectric and ferromagnetic domains walls, in BaTiO3 and Y3Fe5O12 systems, respectively, in a continuous and variable temperature range. Continuous imaging of the phase transition in BaTiO3, a prototypical ferroelectric system, from the low-temperature orthorhombic phase continuously up to the centrosymmetric high-temperature phase is shown to be possible inside a TEM. Similarly, the propagation of domain walls in Y3Fe5O12, a magnetic insulator, is studied from ∼120 to ∼400 K and combined with the application of a magnetic field and electrical current pulses to mimic the operando conditions as in domain wall memory and logic devices for information technology. Such studies are promising for studying the pinning of the ferroelectric and magnetic domains versus temperature, spin-polarized current, and externally applied magnetic field to better manipulate the domain walls. The capability of combining operando TEM stimuli such as current, voltage, and/or magnetic field with in situ TEM imaging in a continuous cryogenic temperature range will allow the uncovering of fundamental phenomena on the nanometer scale. These studies were made possible using a MEMS-based TEM holder that allowed an electron-transparent sample to be transferred and electrically contacted on a MEMS chip. The six-contact double-tilt holder allows the alignment of the specimen into its zone axis while simultaneously using four electrical contacts to regulate the temperature and two contacts to apply the electrical stimuli, i.e., operando TEM imaging. This Account leads to the demonstration of (i) the high-resolution imaging and spectroscopy of nanoparticles oriented in the desired [110] zone-axis direction at cryogenic temperatures to mitigate the electron beam degradation, (ii) imaging of low-temperature transitions with accurate and continuous control of the temperature that allowed single-frame observation of the presence of both the orthorhombic and tetragonal phases in the BaTiO3 system, and (iii) magnetic domain wall propagation as a function of temperature, magnetic field, and current pulses (100 ns with a 100 kHz repetition rate) in the Y3Fe5O12 system.
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Affiliation(s)
| | | | - Reinis Ignatans
- Institute of Materials, École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland
| | | | | | - Masaaki Imamura
- Department of Electrical Engineering, Fukuoka Institute of Technology, Fukuoka 811-0295, Japan
| | - Hironori Asada
- Graduate School of Sciences and Technology for Innovation, Yamaguchi University, Ube 755-8611, Japan
| | - Yasuhiro Fukuma
- Department of Physics and Information Technology, Kyushu Institute of Technology, Iizuka 820-8502, Japan
- Research Center for Neuromorphic AI Hardwares, Kyushu Institute of Technology, Kitakyushu 808-0196, Japan
| | | | - Vasiliki Tileli
- Institute of Materials, École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland
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Kaspar TC, Spurgeon SR, Matthews BE, Bowden ME, Heald SM, Wang L, Kelley R, Paudel R, Isaacs-Smith T, Comes RB, Yin X, Tang CS, Wee ATS, Chambers SA. Incorporation of Ti in epitaxial Fe 2TiO 4thin films. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2021; 33:314004. [PMID: 34038894 DOI: 10.1088/1361-648x/ac0571] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/25/2021] [Accepted: 05/26/2021] [Indexed: 06/12/2023]
Abstract
The titanomagnetites (Fe2-xTixO4,x⩽ 1) are a family of reducible spinel-structure oxides of interest for their favorable magnetic, catalytic, and electrical transport properties. To understand the stability of the system during low temperature deposition, epitaxial thin films of Fe2TiO4were deposited by molecular beam epitaxy (MBE) on MgO(001) at 250-375 °C. The homogeneous incorporation of Ti, Fe valence state, and film morphology were all found to be strongly dependent on the oxidation conditions at the low substrate temperatures employed. More oxidizing conditions led to phase separation into epitaxial, faceted Fe3O4and rutile TiO2. Less oxidizing conditions resulted in polycrystalline films that exhibited Ti segregation to the film surface, as well as mixed Fe valence (Fe3+, Fe2+, Fe0). A narrow window of intermediate oxygen partial pressure during deposition yielded nearly homogeneous Ti incorporation and a large fraction of Fe2+. However, these films were poorly crystallized, and no occupation of tetrahedral sites in the spinel lattice by Fe2+was detected by x-ray magnetic circular dichroism at the Fe L-edge. After vacuum annealing, a small fraction of Fe2+was found to occupy tetrahedral sites. Comparison of these results with previous work suggests that the low temperature deposition conditions imposed by use of MgO substrates limits the incorporation of Ti into the spinel lattice. This work suggests a path towards obtaining stoichiometric, well-crystallized Fe2TiO4by MBE by utilizing high substrate temperature and low oxygen partial pressure during deposition on thermally stable substrates.
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Affiliation(s)
- Tiffany C Kaspar
- Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, WA, United States of America
| | - Steven R Spurgeon
- Energy and Environment Directorate, Pacific Northwest National Laboratory, Richland, WA, United States of America
| | - Bethany E Matthews
- Energy and Environment Directorate, Pacific Northwest National Laboratory, Richland, WA, United States of America
| | - Mark E Bowden
- Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA, United States of America
| | - Steve M Heald
- Advanced Photon Source, Argonne National Laboratory, Argonne, IL, United States of America
| | - Le Wang
- Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, WA, United States of America
| | - Ron Kelley
- ThermoFisher Scientific, Hillsboro, OR, United States of America
| | - Rajendra Paudel
- Department of Physics, Auburn University, Auburn, AL, United States of America
| | - Tamara Isaacs-Smith
- Department of Physics, Auburn University, Auburn, AL, United States of America
| | - Ryan B Comes
- Department of Physics, Auburn University, Auburn, AL, United States of America
| | - Xinmao Yin
- Singapore Synchrotron Light Source, National University of Singapore, Singapore
- Department of Physics, Faculty of Science, National University of Singapore, Singapore
| | - Chi Sin Tang
- Singapore Synchrotron Light Source, National University of Singapore, Singapore
- Department of Physics, Faculty of Science, National University of Singapore, Singapore
| | - Andrew T S Wee
- Department of Physics, Faculty of Science, National University of Singapore, Singapore
| | - Scott A Chambers
- Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, WA, United States of America
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54
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Identification and correction of temporal and spatial distortions in scanning transmission electron microscopy. Ultramicroscopy 2021; 229:113337. [PMID: 34298205 DOI: 10.1016/j.ultramic.2021.113337] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2020] [Revised: 06/03/2021] [Accepted: 06/09/2021] [Indexed: 11/23/2022]
Abstract
Scanning transmission electron microscopy (STEM) has become the technique of choice for quantitative characterization of atomic structure of materials, where the minute displacements of atomic columns from high-symmetry positions can be used to map strain, polarization, octahedra tilts, and other physical and chemical order parameter fields. The latter can be used as inputs into mesoscopic and atomistic models, providing insight into the correlative relationships and generative physics of materials on the atomic level. However, these quantitative applications of STEM necessitate understanding the microscope induced image distortions and developing the pathways to compensate them both as part of a rapid calibration procedure for in situ imaging, and the post-experimental data analysis stage. Here, we explore the spatiotemporal structure of the microscopic distortions in STEM using multivariate analysis of the atomic trajectories in the image stacks. Based on the behavior of principal component analysis (PCA), we develop the Gaussian process (GP)-based regression method for quantification of the distortion function. The limitations of such an approach and possible strategies for implementation as a part of in-line data acquisition in STEM are discussed. The analysis workflow is summarized in a Jupyter notebook that can be used to retrace the analysis and analyze the reader's data.
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Couillard M. Micrometre-scale strain mapping of transistor arrays extracted from undersampled atomic-resolution images. Micron 2021; 148:103100. [PMID: 34144297 DOI: 10.1016/j.micron.2021.103100] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2021] [Revised: 05/17/2021] [Accepted: 06/03/2021] [Indexed: 11/25/2022]
Abstract
Strain maps extracted from atomic resolution images have the ultimate spatial resolution, but have a field of view limited by the sampling necessary to resolve atomic lattices. This has typically confined strain maps to dimensions less than ∼100 nanometers. To extend the field of view beyond this limit, we apply a modified geometric phase analysis to undersampled images of atomic lattices (i.e. with a pixel size too large to resolve atomic lattices). To reduce the effects of environmental and instrumental instabilities, the images were obtained by aligning series of rapid annular dark field scanning transmission electron microscopy acquisitions. We demonstrate that for undersampled images, a geometric phase analysis can still be performed on aliased frequencies and, as long as the appropriate scaling matrix is applied, provide accurate atomic displacement measurements at large scale. Experimental challenges related to the increased effects of scanning errors as the magnification is lowered are examined. Although such errors are found to significantly reduce geometric phase signals, it was still possible to produce strain maps for arrays of up to sixteen 20nm-technology transistors, corresponding to a field of view exceeding one micrometer.
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Affiliation(s)
- Martin Couillard
- National Research Council Canada, Energy, Mining and Environment Research Centre, 1200 Montreal Road, Ottawa, ON, K1A OR6, Canada.
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56
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Ishikawa R, Tanaka R, Kawahara K, Shibata N, Ikuhara Y. Atomic-Resolution Topographic Imaging of Crystal Surfaces. ACS NANO 2021; 15:9186-9193. [PMID: 33983030 DOI: 10.1021/acsnano.1c02907] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
The surface of metal oxides is of technological importance and is extensively used as a substrate for various electronic and chemical applications. A real surface, however, is not a perfectly well-defined and clean surface, but rather contains a diverse class of atomistic defects. Here, we show the direct determination of the 3D surface atomic structure of SrTiO3 (001) including termination layers and atomistic defects such as vacancies, adatoms, ledges, kinks, and their complex combinations, by using depth sectioning of atomic-resolution annular dark-field scanning transmission electron microscopy (ADF STEM). To overcome the poor depth resolution in STEM, we statistically analyze the column by column depth profiles of ADF STEM images with a Bayesian framework fitting algorithm, and we achieve depth resolution at the entrance surface of ±0.9 Å for 1518 individual atomic columns. The present atomic-resolution 3D electron microscopy at the surface will provide fertile ground especially in surface science.
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Affiliation(s)
- Ryo Ishikawa
- Institute of Engineering Innovation, University of Tokyo, Bunkyo, Tokyo 113-8656, Japan
- PRESTO, Japan Science and Technology Agency, Kawaguchi, Saitama 332-0012, Japan
| | - Riku Tanaka
- Institute of Engineering Innovation, University of Tokyo, Bunkyo, Tokyo 113-8656, Japan
| | - Kazuaki Kawahara
- Institute of Engineering Innovation, University of Tokyo, Bunkyo, Tokyo 113-8656, Japan
| | - Naoya Shibata
- Institute of Engineering Innovation, University of Tokyo, Bunkyo, Tokyo 113-8656, Japan
- Nanostructures Research Laboratory, Japan Fine Ceramics Center, Nagoya, Aichi 456-8587, Japan
| | - Yuichi Ikuhara
- Institute of Engineering Innovation, University of Tokyo, Bunkyo, Tokyo 113-8656, Japan
- Nanostructures Research Laboratory, Japan Fine Ceramics Center, Nagoya, Aichi 456-8587, Japan
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57
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MacArthur KE, Clement A, Heggen M, Dunin-Borkowski RE. Combining quantitative ADF STEM with SiN x membrane-based MEMS devices: A simulation study with Pt nanoparticles. Ultramicroscopy 2021; 231:113270. [PMID: 33888359 DOI: 10.1016/j.ultramic.2021.113270] [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: 09/08/2020] [Revised: 03/24/2021] [Accepted: 04/05/2021] [Indexed: 11/26/2022]
Abstract
Computer simulations are used to assess the influence of a 20-nm-thick SiNx membrane on the quantification of atomic-resolution annular dark-field (ADF) scanning transmission electron microscopy images of Pt nanoparticles. The discussions include the effect of different nanoparticle/membrane arrangements, accelerating voltage, nanoparticle thickness and the presence of adjacent atomic columns on the accuracy with which the number of Pt atoms in each atom column can be counted. The results, which are based on the use of ADF scattering cross-sections, show that an accuracy of better than a single atom is attainable at 200 and 300 kV. At 80kV, the scattering in a typical SiNx membrane is sufficiently strong that the best possible atom counting accuracy is reduced to +/- 2 atoms. The implications of the work for quantitative studies of Pt nanoparticles imaged through SiNx membranes are discussed.
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Affiliation(s)
- Katherine E MacArthur
- Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons and Peter Grünberg Institute, Forschungszentrum Jülich, 52425 Jülich, Germany.
| | - Antoine Clement
- Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons and Peter Grünberg Institute, Forschungszentrum Jülich, 52425 Jülich, Germany; Ecole Nationale Supérieure des Mines de Nancy, Campus Artem, BP 14234, 92 rue du Sergent Blandan, 54042 Nancy cedex, France
| | - Marc Heggen
- Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons and Peter Grünberg Institute, Forschungszentrum Jülich, 52425 Jülich, Germany
| | - Rafal E Dunin-Borkowski
- Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons and Peter Grünberg Institute, Forschungszentrum Jülich, 52425 Jülich, Germany
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58
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Real-space observation of ferroelectrically induced magnetic spin crystal in SrRuO 3. Nat Commun 2021; 12:2007. [PMID: 33790268 PMCID: PMC8012650 DOI: 10.1038/s41467-021-22165-5] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2020] [Accepted: 03/04/2021] [Indexed: 11/25/2022] Open
Abstract
Unusual features in the Hall Resistivity of thin film systems are frequently associated with whirling spin textures such as Skyrmions. A host of recent investigations of Hall Hysteresis loops in SrRuO3 heterostructures have provided conflicting evidence for different causes for such features. We have constructed an SrRuO3-PbTiO3 (Ferromagnetic – Ferroelectric) bilayer that exhibits features in the Hall Hysteresis previously attributed to a Topological Hall Effect, and Skyrmions. Here we show field dependent Magnetic Force Microscopy measurements throughout the key fields where the ‘THE’ presents, revealing the emergence to two periodic, chiral spin textures. The zero-field cycloidal phase, which then transforms into a ‘double-q’ incommensurate spin crystal appears over the appearance of the ‘Topological-like’ Hall effect region, and develop into a ferromagnetic switching regime as the sample reaches saturation, and the ‘Topological-like’ response diminishes. Scanning Tunnelling Electron Microscopy and Density Functional Theory is used to observe and analyse surface inversion symmetry breaking and confirm the role of an interfacial Dzyaloshinskii–Moriya interaction at the heart of the system. There is an ongoing debate in the origin of unusual bumps in the resistive Hall measurements in SrRuO3 systems. Here, the authors analyze surface inversion symmetry breaking and confirm the role of an interfacial Dzyaloshinskii–Moriya interaction at the heart of the system, revealing a magnetic spin crystal emergent across the unusual bumps.
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59
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Zhang C, Feng J, Yankovich AB, Kvit A, Berkels B, Voyles PM. Optimizing Nonrigid Registration for Scanning Transmission Electron Microscopy Image Series. MICROSCOPY AND MICROANALYSIS : THE OFFICIAL JOURNAL OF MICROSCOPY SOCIETY OF AMERICA, MICROBEAM ANALYSIS SOCIETY, MICROSCOPICAL SOCIETY OF CANADA 2021; 27:90-98. [PMID: 33222719 DOI: 10.1017/s1431927620024708] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Achieving sub-picometer precision measurements of atomic column positions in high-resolution scanning transmission electron microscope images using nonrigid registration (NRR) and averaging of image series requires careful optimization of experimental conditions and the parameters of the registration algorithm. On experimental data from SrTiO3 [100], sub-pm precision requires alignment of the sample to the zone axis to within 1 mrad tilt and sample drift of less than 1 nm/min. At fixed total electron dose for the series, precision in the fast scan direction improves with shorter pixel dwell time to the limit of our microscope hardware, but the best precision along the slow scan direction occurs at 6 μs/px dwell time. Within the NRR algorithm, the “smoothness factor” that penalizes large estimated shifts is the most important parameter for sub-pm precision, but in general, the precision of NRR images is robust over a wide range of parameters.
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Affiliation(s)
- Chenyu Zhang
- Department of Materials Science and Engineering, University of Wisconsin - Madison, 1509 University Avenue, Madison, WI53706, USA
| | - Jie Feng
- Department of Materials Science and Engineering, University of Wisconsin - Madison, 1509 University Avenue, Madison, WI53706, USA
| | - Andrew B Yankovich
- Department of Materials Science and Engineering, University of Wisconsin - Madison, 1509 University Avenue, Madison, WI53706, USA
| | - Alexander Kvit
- Department of Materials Science and Engineering, University of Wisconsin - Madison, 1509 University Avenue, Madison, WI53706, USA
| | - Benjamin Berkels
- Aachen Institute for Advanced Study in Computational Engineering Science, RWTH Aachen University, Schinkelstr. 2, 52056Aachen, Germany
| | - Paul M Voyles
- Department of Materials Science and Engineering, University of Wisconsin - Madison, 1509 University Avenue, Madison, WI53706, USA
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60
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Mullarkey T, Downing C, Jones L. Development of a Practicable Digital Pulse Read-Out for Dark-Field STEM. MICROSCOPY AND MICROANALYSIS : THE OFFICIAL JOURNAL OF MICROSCOPY SOCIETY OF AMERICA, MICROBEAM ANALYSIS SOCIETY, MICROSCOPICAL SOCIETY OF CANADA 2021; 27:99-108. [PMID: 33334386 DOI: 10.1017/s1431927620024721] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
When characterizing beam-sensitive materials in the scanning transmission electron microscope (STEM), low-dose techniques are essential for the reliable observation of samples in their true state. A simple route to minimize both the total electron-dose and the dose-rate is to reduce the electron beam-current and/or raster the probe at higher speeds. At the limit of these settings, and with current detectors, the resulting images suffer from unacceptable artifacts, including signal-streaking, detector-afterglow, and poor signal-to-noise ratios (SNRs). In this article, we present an alternative approach to capture dark-field STEM images by pulse-counting individual electrons as they are scattered to the annular dark-field (ADF) detector. Digital images formed in this way are immune from analog artifacts of streaking or afterglow and allow clean, high-SNR images to be obtained even at low beam-currents. We present results from both a ThermoFisher FEI Titan G2 operated at 300 kV and a Nion UltraSTEM200 operated at 200 kV, and compare the images to conventional analog recordings. ADF data are compared with analog counterparts for each instrument, a digital detector-response scan is performed on the Titan, and the overall rastering efficiency is evaluated for various scanning parameters.
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Affiliation(s)
- Tiarnan Mullarkey
- School of Physics, Trinity College Dublin, Dublin 2, Ireland
- Centre for Doctoral Training in the Advanced Characterisation of Materials, AMBER Centre, Dublin 2, Ireland
| | - Clive Downing
- Advanced Microscopy Laboratory, Centre for Research on Adaptive Nanostructures and Nanodevices (CRANN), Dublin 2, Ireland
| | - Lewys Jones
- School of Physics, Trinity College Dublin, Dublin 2, Ireland
- Advanced Microscopy Laboratory, Centre for Research on Adaptive Nanostructures and Nanodevices (CRANN), Dublin 2, Ireland
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61
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Liu P, Arslan Irmak E, De Backer A, De Wael A, Lobato I, Béché A, Van Aert S, Bals S. Three-dimensional atomic structure of supported Au nanoparticles at high temperature. NANOSCALE 2021; 13:1770-1776. [PMID: 33432963 DOI: 10.1039/d0nr08664a] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Au nanoparticles (NPs) deposited on CeO2 are extensively used as thermal catalysts since the morphology of the NPs is expected to be stable at elevated temperatures. Although it is well known that the activity of Au NPs depends on their size and surface structure, their three-dimensional (3D) structure at the atomic scale has not been completely characterized as a function of temperature. In this paper, we overcome the limitations of conventional electron tomography by combining atom counting applied to aberration-corrected scanning transmission electron microscopy images and molecular dynamics relaxation. In this manner, we are able to perform an atomic resolution 3D investigation of supported Au NPs. Our results enable us to characterize the 3D equilibrium structure of single NPs as a function of temperature. Moreover, the dynamic 3D structural evolution of the NPs at high temperatures, including surface layer jumping and crystalline transformations, has been studied.
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Affiliation(s)
- Pei Liu
- Electron Microscopy for Materials Science (EMAT), University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium.
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Evaluation of the Nanodomain Structure in In-Zn-O Transparent Conductors. NANOMATERIALS 2021; 11:nano11010198. [PMID: 33466848 PMCID: PMC7830485 DOI: 10.3390/nano11010198] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/21/2020] [Revised: 01/07/2021] [Accepted: 01/09/2021] [Indexed: 11/17/2022]
Abstract
The optimization of novel transparent conductive oxides (TCOs) implies a better understanding of the role that the dopant plays on the optoelectronic properties of these materials. In this work, we perform a systematic study of the homologous series ZnkIn2Ok+3 (IZO) by characterizing the specific location of indium in the structure that leads to a nanodomain framework to release structural strain. Through a systematic study of different terms of the series, we have been able to observe the influence of the k value in the nano-structural features of this homologous series. The stabilization and visualization of the structural modulation as a function of k is discussed, even in the lowest term of the series (k = 3). The strain fields and atomic displacements in the wurtzite structure as a consequence of the introduction of In3+ are evaluated.
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63
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Pokle A, Ahmed S, Schweidler S, Bianchini M, Brezesinski T, Beyer A, Janek J, Volz K. In Situ Monitoring of Thermally Induced Effects in Nickel-Rich Layered Oxide Cathode Materials at the Atomic Level. ACS APPLIED MATERIALS & INTERFACES 2020; 12:57047-57054. [PMID: 33296166 DOI: 10.1021/acsami.0c16685] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
The thermal stability of cathode active materials (CAMs) is of major importance for the safety of lithium-ion batteries (LIBs). A thorough understanding of how commercially viable layered oxide CAMs behave at the atomic length scale upon heating is indispensable for the further development of LIBs. Here, structural changes of Li(Ni0.85Co0.15Mn0.05)O2 (NCM851005) at elevated temperatures are studied by in situ aberration-corrected scanning transmission electron microscopy (AC-STEM). Heating NCM851005 inside the microscope under vacuum conditions enables us to observe phase transitions and other structural changes at high spatial resolutions. This has been primarily possible by establishing low-dose electron beam conditions in STEM. Specific focus is put on the evolution of inherent nanopore defects found in the primary grains, which are believed to play an important role in LIB degradation. The onset temperature of structural changes is found to be ∼175 °C, resulting in phase transformation from a layered to a rock-salt-like structure, especially at the internal interfaces, and increasing intragrain inhomogeneity. The reducing environment and heat application lead to the formation and subsequent densification of {003}- and {014}-type facets. In the light of these results, postsynthesis electrode drying processes applied under reducing environment and heat, for example, in the preparation of solid-state batteries, should be re-examined carefully.
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Affiliation(s)
- Anuj Pokle
- Materials Science Center (WZMW) and Department of Physics, Philipps-University Marburg, Hans-Meerwein -Str.6, 35032, Marburg, Germany
| | - Shamail Ahmed
- Materials Science Center (WZMW) and Department of Physics, Philipps-University Marburg, Hans-Meerwein -Str.6, 35032, Marburg, Germany
| | - Simon Schweidler
- Battery and Electrochemistry Laboratory, Institute of Nanotechnology, Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany
| | - Matteo Bianchini
- Battery and Electrochemistry Laboratory, Institute of Nanotechnology, Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany
- BASF SE, Carl-Bosch-Strasse 38, 67056 Ludwigshafen, Germany
| | - Torsten Brezesinski
- Battery and Electrochemistry Laboratory, Institute of Nanotechnology, Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany
| | - Andreas Beyer
- Materials Science Center (WZMW) and Department of Physics, Philipps-University Marburg, Hans-Meerwein -Str.6, 35032, Marburg, Germany
| | - Jürgen Janek
- Battery and Electrochemistry Laboratory, Institute of Nanotechnology, Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany
- Institute of Physical Chemistry & Center for Materials Research, Justus-Liebig-University, Heinrich-Buff-Ring 17, 35392 Giessen, Germany
| | - Kerstin Volz
- Materials Science Center (WZMW) and Department of Physics, Philipps-University Marburg, Hans-Meerwein -Str.6, 35032, Marburg, Germany
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64
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Tong VS, Ben Britton T. TrueEBSD: Correcting spatial distortions in electron backscatter diffraction maps. Ultramicroscopy 2020; 221:113130. [PMID: 33290982 DOI: 10.1016/j.ultramic.2020.113130] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2019] [Revised: 08/28/2020] [Accepted: 10/01/2020] [Indexed: 11/19/2022]
Abstract
Electron backscatter diffraction (EBSD) in the scanning electron microscope is routinely used for microstructural characterisation of polycrystalline materials. Maps of EBSD data are typically acquired at high stage tilt and slow scan speed, leading to tilt and drift distortions that obscure or distort features in the final microstructure map. In this paper, we describe TrueEBSD, an automatic postprocessing procedure for distortion correction with pixel-scale precision. Intermediate images are used to separate tilt and drift distortion components and fit each to a physically-informed distortion model. We demonstrate TrueEBSD on three case studies (titanium, zirconium and hydride containing Zr), where distortion removal has enabled characterisation of otherwise inaccessible microstructural features.
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Affiliation(s)
- Vivian S Tong
- Department of Materials, Imperial College London, Exhibition Road, London, SW7 2AZ, United Kingdom
| | - T Ben Britton
- Department of Materials, Imperial College London, Exhibition Road, London, SW7 2AZ, United Kingdom.
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65
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Abstract
Formation of highly symmetric skeletal elements in demosponges, called spicules, follows a unique biomineralization mechanism in which polycondensation of an inherently disordered amorphous silica is guided by a highly ordered proteinaceous scaffold, the axial filament. The enzymatically active proteins, silicateins, are assembled into a slender hybrid silica/protein crystalline superstructure that directs the morphogenesis of the spicules. Furthermore, silicateins are known to catalyze the formation of a large variety of other technologically relevant organic and inorganic materials. However, despite the biological and biotechnological importance of this macromolecule, its tertiary structure was never determined. Here we report the atomic structure of silicatein and the entire mineral/organic hybrid assembly with a resolution of 2.4 Å. In this work, the serial X-ray crystallography method was successfully adopted to probe the 2-µm-thick filaments in situ, being embedded inside the skeletal elements. In combination with imaging and chemical analysis using high-resolution transmission electron microscopy, we provide detailed information on the enzymatic activity of silicatein, its crystallization, and the emergence of a functional three-dimensional silica/protein superstructure in vivo. Ultimately, we describe a naturally occurring mineral/protein crystalline assembly at atomic resolution.
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66
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In-situ monitoring of interface proximity effects in ultrathin ferroelectrics. Nat Commun 2020; 11:5815. [PMID: 33199714 PMCID: PMC7669862 DOI: 10.1038/s41467-020-19635-7] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2020] [Accepted: 10/25/2020] [Indexed: 01/28/2023] Open
Abstract
The development of energy-efficient nanoelectronics based on ferroelectrics is hampered by a notorious polarization loss in the ultrathin regime caused by the unscreened polar discontinuity at the interfaces. So far, engineering charge screening at either the bottom or the top interface has been used to optimize the polarization state. Yet, it is expected that the combined effect of both interfaces determines the final polarization state; in fact the more so the thinner a film is. The competition and cooperation between interfaces have, however, remained unexplored so far. Taking PbTiO3 as a model system, we observe drastic differences between the influence of a single interface and the competition and cooperation of two interfaces. We investigate the impact of these configurations on the PbTiO3 polarization when the interfaces are in close proximity, during thin-film synthesis in the ultrathin limit. By tailoring the interface chemistry towards a cooperative configuration, we stabilize a robust polarization state with giant polarization enhancement. Interface cooperation hence constitutes a powerful route for engineering the polarization in thin-film ferroelectrics towards improved integrability for oxide electronics in reduced dimension. How to maintain a robust polarization in ferroelectrics despite its inherent suppression when going to the thin-film limit is a long-standing issue. Here, the authors propose the concept of competitive and cooperative interfaces and establish robust polarization states in the ultrathin regime.
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67
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Ellaby T, Varambhia A, Luo X, Briquet L, Sarwar M, Ozkaya D, Thompsett D, Nellist PD, Skylaris CK. Strain effects in core-shell PtCo nanoparticles: a comparison of experimental observations and computational modelling. Phys Chem Chem Phys 2020; 22:24784-24795. [PMID: 33107513 DOI: 10.1039/d0cp04318d] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Strain in Pt nanoalloys induced by the secondary metal has long been suggested as a major contributor to the modification of catalytic properties. Here, we investigate strain in PtCo nanoparticles using a combination of computational modelling and microscopy experiments. We have used a combination of molecular dynamics (MD) and large-scale density functional theory (DFT) for our models, alongside experimental work using annular dark field scanning transmission electron microscopy (ADF-STEM). We have performed extensive validation of the interatomic potential against DFT using a Pt568Co18 nanoparticle. Modelling gives access to 3 dimensional structures that can be compared to the 2D ADF-STEM images, which we use to build an understanding of nanoparticle structure and composition. Strain has been measured for PtCo and pure Pt nanoparticles, with MD annealed models compared to ADF-STEM images. Our analysis was performed on a layer by layer basis, where distinct trends between the Pt and PtCo alloy nanoparticles are observed. To our knowledge, we show for the first time a way in which detailed atomistic simulations can be used to augment and help interpret the results of ADF-STEM strain mapping experiments, which will enhance their use in characterisation towards the development of improved catalysts.
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Affiliation(s)
- Tom Ellaby
- Department of Chemistry, University of Southampton, Southampton, UK.
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68
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Evans DM, Holstad TS, Mosberg AB, Småbråten DR, Vullum PE, Dadlani AL, Shapovalov K, Yan Z, Bourret E, Gao D, Akola J, Torgersen J, van Helvoort ATJ, Selbach SM, Meier D. Conductivity control via minimally invasive anti-Frenkel defects in a functional oxide. NATURE MATERIALS 2020; 19:1195-1200. [PMID: 32807925 DOI: 10.1038/s41563-020-0765-x] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/20/2019] [Accepted: 07/10/2020] [Indexed: 06/11/2023]
Abstract
Utilizing quantum effects in complex oxides, such as magnetism, multiferroicity and superconductivity, requires atomic-level control of the material's structure and composition. In contrast, the continuous conductivity changes that enable artificial oxide-based synapses and multiconfigurational devices are driven by redox reactions and domain reconfigurations, which entail long-range ionic migration and changes in stoichiometry or structure. Although both concepts hold great technological potential, combined applications seem difficult due to the mutually exclusive requirements. Here we demonstrate a route to overcome this limitation by controlling the conductivity in the functional oxide hexagonal Er(Mn,Ti)O3 by using conductive atomic force microscopy to generate electric-field induced anti-Frenkel defects, that is, charge-neutral interstitial-vacancy pairs. These defects are generated with nanoscale spatial precision to locally enhance the electronic hopping conductivity by orders of magnitude without disturbing the ferroelectric order. We explain the non-volatile effects using density functional theory and discuss its universality, suggesting an alternative dimension to functional oxides and the development of multifunctional devices for next-generation nanotechnology.
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Affiliation(s)
- Donald M Evans
- Department of Materials Science and Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, Norway.
| | - Theodor S Holstad
- Department of Materials Science and Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, Norway
| | - Aleksander B Mosberg
- Department of Physics, Norwegian University of Science and Technology (NTNU), Trondheim, Norway
| | - Didrik R Småbråten
- Department of Materials Science and Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, Norway
| | | | - Anup L Dadlani
- Department of Mechanical and Industrial Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, Norway
| | - Konstantin Shapovalov
- Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Campus UAB, Bellaterra, Spain
| | - Zewu Yan
- Department of Physics, ETH Zurich, Zürich, Switzerland
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Edith Bourret
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - David Gao
- Department of Physics, Norwegian University of Science and Technology (NTNU), Trondheim, Norway
- Nanolayers Research Computing Ltd, London, UK
| | - Jaakko Akola
- Department of Physics, Norwegian University of Science and Technology (NTNU), Trondheim, Norway
- Computational Physics Laboratory, Tampere University, Tampere, Finland
| | - Jan Torgersen
- Department of Mechanical and Industrial Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, Norway
| | | | - Sverre M Selbach
- Department of Materials Science and Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, Norway
| | - Dennis Meier
- Department of Materials Science and Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, Norway.
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69
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Domínguez C, Georgescu AB, Mundet B, Zhang Y, Fowlie J, Mercy A, Waelchli A, Catalano S, Alexander DTL, Ghosez P, Georges A, Millis AJ, Gibert M, Triscone JM. Length scales of interfacial coupling between metal and insulator phases in oxides. NATURE MATERIALS 2020; 19:1182-1187. [PMID: 32778815 DOI: 10.1038/s41563-020-0757-x] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/18/2019] [Accepted: 07/02/2020] [Indexed: 06/11/2023]
Abstract
Controlling phase transitions in transition metal oxides remains a central feature of both technological and fundamental scientific relevance. A well-known example is the metal-insulator transition, which has been shown to be highly controllable. However, the length scale over which these phases can be established is not yet well understood. To gain insight into this issue, we atomically engineered an artificially phase-separated system through fabricating epitaxial superlattices that consist of SmNiO3 and NdNiO3, two materials that undergo a metal-to-insulator transition at different temperatures. We demonstrate that the length scale of the interfacial coupling between metal and insulator phases is determined by balancing the energy cost of the boundary between a metal and an insulator and the bulk phase energies. Notably, we show that the length scale of this effect exceeds that of the physical coupling of structural motifs, which introduces a new framework for interface-engineering properties at temperatures against the bulk energetics.
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Affiliation(s)
- Claribel Domínguez
- Department of Quantum Matter Physics, University of Geneva, Geneva, Switzerland.
| | | | - Bernat Mundet
- Department of Quantum Matter Physics, University of Geneva, Geneva, Switzerland
- Electron Spectrometry and Microscopy Laboratory (LSME), Institute of Physics (IPHYS), École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
| | - Yajun Zhang
- Theoretical Materials Physics, CESAM, University of Liège, Liège, Belgium
| | - Jennifer Fowlie
- Department of Quantum Matter Physics, University of Geneva, Geneva, Switzerland
| | - Alain Mercy
- Theoretical Materials Physics, CESAM, University of Liège, Liège, Belgium
| | - Adrien Waelchli
- Department of Quantum Matter Physics, University of Geneva, Geneva, Switzerland
| | - Sara Catalano
- Department of Quantum Matter Physics, University of Geneva, Geneva, Switzerland
| | - Duncan T L Alexander
- Electron Spectrometry and Microscopy Laboratory (LSME), Institute of Physics (IPHYS), École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
| | - Philippe Ghosez
- Theoretical Materials Physics, CESAM, University of Liège, Liège, Belgium
| | - Antoine Georges
- Department of Quantum Matter Physics, University of Geneva, Geneva, Switzerland
- Center for Computational Quantum Physics, Flatiron Institute, New York, NY, USA
- Collège de France, Paris, France
- Centre de Physique Théorique (CPHT), CNRS, Institut Polytechnique de Paris, Paris, France
| | - Andrew J Millis
- Center for Computational Quantum Physics, Flatiron Institute, New York, NY, USA
- Department of Physics, Columbia University, New York, NY, USA
| | - Marta Gibert
- Physik-Institut, University of Zurich, Zurich, Switzerland
| | - Jean-Marc Triscone
- Department of Quantum Matter Physics, University of Geneva, Geneva, Switzerland
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70
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Milagres de Oliveira T, Albrecht W, González-Rubio G, Altantzis T, Lobato Hoyos IP, Béché A, Van Aert S, Guerrero-Martínez A, Liz-Marzán LM, Bals S. 3D Characterization and Plasmon Mapping of Gold Nanorods Welded by Femtosecond Laser Irradiation. ACS NANO 2020; 14:12558-12570. [PMID: 32790321 DOI: 10.1021/acsnano.0c02610] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Ultrafast laser irradiation can induce morphological and structural changes in plasmonic nanoparticles. Gold nanorods (Au NRs), in particular, can be welded together upon irradiation with femtosecond laser pulses, leading to dimers and trimers through the formation of necks between individual nanorods. We used electron tomography to determine the 3D (atomic) structure at such necks for representative welding geometries and to characterize the induced defects. The spatial distribution of localized surface plasmon modes for different welding configurations was assessed by electron energy loss spectroscopy. Additionally, we were able to directly compare the plasmon line width of single-crystalline and welded Au NRs with single defects at the same resonance energy, thus making a direct link between the structural and plasmonic properties. In this manner, we show that the occurrence of (single) defects results in significant plasmon broadening.
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Affiliation(s)
- Thaís Milagres de Oliveira
- EMAT, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
- NANOlab Center of Excellence, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
| | - Wiebke Albrecht
- EMAT, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
- NANOlab Center of Excellence, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
| | - Guillermo González-Rubio
- CIC biomaGUNE, Basque Research and Technology Alliance (BRTA), Paseo de Miramón 182, 20014 Donostia-San Sebastián, Spain
- Departamento de Química Física, Universidad Complutense de Madrid, Avenida Complutense s/n, 28040 Madrid, Spain
| | - Thomas Altantzis
- EMAT, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
- NANOlab Center of Excellence, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
| | - Ivan Pedro Lobato Hoyos
- EMAT, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
- NANOlab Center of Excellence, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
| | - Armand Béché
- EMAT, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
- NANOlab Center of Excellence, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
| | - Sandra Van Aert
- EMAT, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
- NANOlab Center of Excellence, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
| | - Andrés Guerrero-Martínez
- Departamento de Química Física, Universidad Complutense de Madrid, Avenida Complutense s/n, 28040 Madrid, Spain
| | - Luis M Liz-Marzán
- CIC biomaGUNE, Basque Research and Technology Alliance (BRTA), Paseo de Miramón 182, 20014 Donostia-San Sebastián, Spain
- CIBER de Bioingeniería, Biomateriales y Nanomedicina (CIBER-BBN), Paseo de Miramón 182, 20014 Donostia-San Sebastián, Spain
- Ikerbasque (Basque Foundation for Science), 48013 Bilbao, Spain
| | - Sara Bals
- EMAT, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
- NANOlab Center of Excellence, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
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71
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Wu Y, Fang Y, Fan Z, Wang C, Liu C. An automated vertical drift correction algorithm for AFM images based on morphology prediction. Micron 2020; 140:102950. [PMID: 33096453 DOI: 10.1016/j.micron.2020.102950] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2020] [Revised: 09/08/2020] [Accepted: 09/08/2020] [Indexed: 11/18/2022]
Abstract
The atomic force microscope (AFM) has become a powerful tool in many fields. However, environmental noise and other disturbances are very likely to cause the AFM probe to vibrate, which lead to vertical drift in AFM imaging and limit its further application. Therefore, to correct image distortion caused by vertical drift, a morphology prediction based image correction algorithm is proposed in this paper. Specifically, a Gaussian-Hann filter is first designed for distorted AFM images, based on which, an adaptive image binarization algorithm is developed to achieve accurate object detection and background extraction. Furthermore, an advanced morphology prediction algorithm, consisting of morphological approximation prediction and morphological detail prediction, is proposed to correct image distortion by using the extracted substrate of a sample image. Approximate morphology is generated by an improved weighted fusion autoregressive model, and morphological detail is obtained by energy analysis based on discrete wavelet transform. Experimental and application results are presented to illustrate that the proposed algorithm is able to effectively eliminate vertical drift of AFM images.
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Affiliation(s)
- Yinan Wu
- Institute of Robotics and Automatic Information System, College of Artificial Intelligence, Nankai University, Tianjin, China; Tianjin Key Laboratory of Intelligent Robotics, Nankai University, Tianjin, China
| | - Yongchun Fang
- Institute of Robotics and Automatic Information System, College of Artificial Intelligence, Nankai University, Tianjin, China; Tianjin Key Laboratory of Intelligent Robotics, Nankai University, Tianjin, China.
| | - Zhi Fan
- Institute of Robotics and Automatic Information System, College of Artificial Intelligence, Nankai University, Tianjin, China; Tianjin Key Laboratory of Intelligent Robotics, Nankai University, Tianjin, China
| | - Chao Wang
- Institute of Robotics and Automatic Information System, College of Artificial Intelligence, Nankai University, Tianjin, China; Tianjin Key Laboratory of Intelligent Robotics, Nankai University, Tianjin, China
| | - Cunhuan Liu
- Institute of Robotics and Automatic Information System, College of Artificial Intelligence, Nankai University, Tianjin, China; Tianjin Key Laboratory of Intelligent Robotics, Nankai University, Tianjin, China
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72
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De Wael A, De Backer A, Van Aert S. Hidden Markov model for atom-counting from sequential ADF STEM images: Methodology, possibilities and limitations. Ultramicroscopy 2020; 219:113131. [PMID: 33091707 DOI: 10.1016/j.ultramic.2020.113131] [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: 07/31/2020] [Revised: 09/30/2020] [Accepted: 10/01/2020] [Indexed: 10/23/2022]
Abstract
We present a quantitative method which allows us to reliably measure dynamic changes in the atomic structure of monatomic crystalline nanomaterials from a time series of atomic resolution annular dark field scanning transmission electron microscopy images. The approach is based on the so-called hidden Markov model and estimates the number of atoms in each atomic column of the nanomaterial in each frame of the time series. We discuss the origin of the improved performance for time series atom-counting as compared to the current state-of-the-art atom-counting procedures, and show that the so-called transition probabilities that describe the probability for an atomic column to lose or gain one or more atoms from frame to frame are particularly important. Using these transition probabilities, we show that the method can also be used to estimate the probability and cross section related to structural changes. Furthermore, we explore the possibilities for applying the method to time series recorded under variable environmental conditions. The method is shown to be promising for a reliable quantitative analysis of dynamic processes such as surface diffusion, adatom dynamics, beam effects, or in situ experiments.
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Affiliation(s)
- Annelies De Wael
- EMAT, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium; NANOlab Center of Excellence, University of Antwerp, Belgium
| | - Annick De Backer
- EMAT, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium; NANOlab Center of Excellence, University of Antwerp, Belgium
| | - Sandra Van Aert
- EMAT, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium; NANOlab Center of Excellence, University of Antwerp, Belgium.
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73
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Popel AJ, Spurgeon SR, Matthews B, Olszta MJ, Tan BT, Gouder T, Eloirdi R, Buck EC, Farnan I. An Atomic-Scale Understanding of UO 2 Surface Evolution during Anoxic Dissolution. ACS APPLIED MATERIALS & INTERFACES 2020; 12:39781-39786. [PMID: 32805849 DOI: 10.1021/acsami.0c09611] [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
Our present understanding of surface dissolution of nuclear fuels such as uranium dioxide (UO2) is limited by the use of nonlocal characterization techniques. Here we discuss the use of state-of-the-art scanning transmission electron microscopy (STEM) to reveal atomic-scale changes occurring to a UO2 thin film subjected to anoxic dissolution in deionized water. No amorphization of the UO2 film surface during dissolution is observed, and dissolution occurs preferentially at surface reactive sites that present as surface pits which increase in size as the dissolution proceeds. Using a combination of STEM imaging modes, energy-dispersive X-ray spectroscopy (STEM-EDS), and electron energy loss spectroscopy (STEM-EELS), we investigate structural defects and oxygen passivation of the surface that originates from the filling of the octahedral interstitial site in the center of the unit cells and its associated lattice contraction. Taken together, our results reveal complex pathways for both the dissolution and infiltration of solutions into UO2 surfaces.
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Affiliation(s)
- Aleksej J Popel
- Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, United Kingdom
| | - Steven R Spurgeon
- Energy and Environment Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
| | - Bethany Matthews
- Energy and Environment Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
| | - Matthew J Olszta
- Energy and Environment Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
| | - Beng Thye Tan
- Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, United Kingdom
| | - Thomas Gouder
- European Commission, Joint Research Centre, Directorate for Nuclear Safety and Security, Postfach 2340, DE-76215 Karlsruhe, Germany
| | - Rachel Eloirdi
- European Commission, Joint Research Centre, Directorate for Nuclear Safety and Security, Postfach 2340, DE-76215 Karlsruhe, Germany
| | - Edgar C Buck
- Energy and Environment Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
| | - Ian Farnan
- Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, United Kingdom
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74
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Zamani M, Imbalzano G, Tappy N, Alexander DTL, Martí-Sánchez S, Ghisalberti L, Ramasse QM, Friedl M, Tütüncüoglu G, Francaviglia L, Bienvenue S, Hébert C, Arbiol J, Ceriotti M, Fontcuberta I Morral A. 3D Ordering at the Liquid-Solid Polar Interface of Nanowires. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2020; 32:e2001030. [PMID: 32762011 DOI: 10.1002/adma.202001030] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/13/2020] [Revised: 06/29/2020] [Indexed: 06/11/2023]
Abstract
The nature of the liquid-solid interface determines the characteristics of a variety of physical phenomena, including catalysis, electrochemistry, lubrication, and crystal growth. Most of the established models for crystal growth are based on macroscopic thermodynamics, neglecting the atomistic nature of the liquid-solid interface. Here, experimental observations and molecular dynamics simulations are employed to identify the 3D nature of an atomic-scale ordering of liquid Ga in contact with solid GaAs in a nanowire growth configuration. An interplay between the liquid ordering and the formation of a new bilayer is revealed, which, contrary to the established theories, suggests that the preference for a certain polarity and polytypism is influenced by the atomic structure of the interface. The conclusions of this work open new avenues for the understanding of crystal growth, as well as other processes and systems involving a liquid-solid interface.
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Affiliation(s)
- Mahdi Zamani
- Laboratory of Semiconductor Materials, Institute of Materials, Faculty of Engineering, École Polytechnique Fédérale de Lausanne, EPFL, Lausanne, 1015, Switzerland
| | - Giulio Imbalzano
- Laboratory of Computational Science and Modeling, Institute of Materials, Faculty of Engineering, École Polytechnique Fédérale de Lausanne, EPFL, Lausanne, 1015, Switzerland
| | - Nicolas Tappy
- Laboratory of Semiconductor Materials, Institute of Materials, Faculty of Engineering, École Polytechnique Fédérale de Lausanne, EPFL, Lausanne, 1015, Switzerland
| | - Duncan T L Alexander
- Electron Spectrometry and Microscopy Laboratory, Institute of Physics, Faculty of Basic Sciences, École Polytechnique Fédérale de Lausanne, EPFL, Lausanne, 1015, Switzerland
- Interdisciplinary Centre for Electron Microscopy (CIME), École Polytechnique Fédérale de Lausanne, EPFL, Lausanne, 1015, Switzerland
| | - Sara Martí-Sánchez
- Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and BIST, Campus UAB, Bellaterra, Barcelona, Catalonia, 08193, Spain
| | - Lea Ghisalberti
- Laboratory of Semiconductor Materials, Institute of Materials, Faculty of Engineering, École Polytechnique Fédérale de Lausanne, EPFL, Lausanne, 1015, Switzerland
| | - Quentin M Ramasse
- SuperSTEM Laboratory, SciTech Daresbury Campus, Keckwick Lane, Daresbury, WA4 4AD, UK
- School of Chemical and Process Engineering and School of Physics and Astronomy, University of Leeds, Leeds, LS2 9JT, UK
| | - Martin Friedl
- Laboratory of Semiconductor Materials, Institute of Materials, Faculty of Engineering, École Polytechnique Fédérale de Lausanne, EPFL, Lausanne, 1015, Switzerland
| | - Gözde Tütüncüoglu
- Laboratory of Semiconductor Materials, Institute of Materials, Faculty of Engineering, École Polytechnique Fédérale de Lausanne, EPFL, Lausanne, 1015, Switzerland
| | - Luca Francaviglia
- Laboratory of Semiconductor Materials, Institute of Materials, Faculty of Engineering, École Polytechnique Fédérale de Lausanne, EPFL, Lausanne, 1015, Switzerland
| | - Sebastien Bienvenue
- Laboratory of Computational Science and Modeling, Institute of Materials, Faculty of Engineering, École Polytechnique Fédérale de Lausanne, EPFL, Lausanne, 1015, Switzerland
| | - Cécile Hébert
- Electron Spectrometry and Microscopy Laboratory, Institute of Physics, Faculty of Basic Sciences, École Polytechnique Fédérale de Lausanne, EPFL, Lausanne, 1015, Switzerland
- Institute of Materials, Faculty of Engineering, École Polytechnique Fédérale de Lausanne, EPFL, Lausanne, 1015, Switzerland
| | - Jordi Arbiol
- Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and BIST, Campus UAB, Bellaterra, Barcelona, Catalonia, 08193, Spain
- ICREA, Pg. Lluís Companys 23, Barcelona, Catalonia, 08010, Spain
| | - Michele Ceriotti
- Laboratory of Computational Science and Modeling, Institute of Materials, Faculty of Engineering, École Polytechnique Fédérale de Lausanne, EPFL, Lausanne, 1015, Switzerland
| | - Anna Fontcuberta I Morral
- Laboratory of Semiconductor Materials, Institute of Materials, Faculty of Engineering, École Polytechnique Fédérale de Lausanne, EPFL, Lausanne, 1015, Switzerland
- Institute of Physics, Faculty of Basic Sciences, École Polytechnique Fédérale de Lausanne, EPFL, Lausanne, 1015, Switzerland
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75
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CHRISTIANSEN E, RINGDALEN I, BJØRGE R, MARIOARA C, HOLMESTAD R. Multislice image simulations of sheared needle‐like precipitates in an Al‐Mg‐Si alloy. J Microsc 2020; 279:265-273. [DOI: 10.1111/jmi.12901] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2019] [Revised: 03/16/2020] [Accepted: 05/08/2020] [Indexed: 11/29/2022]
Affiliation(s)
- E. CHRISTIANSEN
- Centre for Advanced Structural Analysis (CASA)NTNU – Norwegian University of Science and TechnologyTrondheim Norway
- Department of PhysicsFaculty of Natural Sciences, NTNUHøgskoleringen 5 Trondheim 4791 Norway
| | - I.G. RINGDALEN
- Materials and NanotechnologySINTEF IndustryTrondheim 7465 Norway
| | - R. BJØRGE
- Materials and NanotechnologySINTEF IndustryTrondheim 7465 Norway
| | - C.D. MARIOARA
- Centre for Advanced Structural Analysis (CASA)NTNU – Norwegian University of Science and TechnologyTrondheim Norway
- Materials and NanotechnologySINTEF IndustryTrondheim 7465 Norway
| | - R. HOLMESTAD
- Centre for Advanced Structural Analysis (CASA)NTNU – Norwegian University of Science and TechnologyTrondheim Norway
- Department of PhysicsFaculty of Natural Sciences, NTNUHøgskoleringen 5 Trondheim 4791 Norway
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76
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Evaluation of different rectangular scan strategies for STEM imaging. Ultramicroscopy 2020; 215:113021. [PMID: 32485392 DOI: 10.1016/j.ultramic.2020.113021] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2020] [Revised: 05/03/2020] [Accepted: 05/07/2020] [Indexed: 11/24/2022]
Abstract
STEM imaging is typically performed by raster scanning a focused electron probe over a sample. Here we investigate and compare three different scan patterns, making use of a programmable scan engine that allows to arbitrarily set the sequence of probe positions that are consecutively visited on the sample. We compare the typical raster scan with a so-called 'snake' pattern where the scan direction is reversed after each row and a novel Hilbert scan pattern that changes scan direction rapidly and provides an homogeneous treatment of both scan directions. We experimentally evaluate the imaging performance on a single crystal test sample by varying dwell time and evaluating behaviour with respect to sample drift. We demonstrate the ability of the Hilbert scan pattern to more faithfully represent the high frequency content of the image in the presence of sample drift. It is also shown that Hilbert scanning provides reduced bias when measuring lattice parameters from the obtained scanned images while maintaining similar precision in both scan directions which is especially important when e.g. performing strain analysis. Compared to raster scanning with flyback correction, both snake and Hilbert scanning benefit from dose reduction as only small probe movement steps occur.
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77
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Campanini M, Gradauskaite E, Trassin M, Yi D, Yu P, Ramesh R, Erni R, Rossell MD. Imaging and quantification of charged domain walls in BiFeO 3. NANOSCALE 2020; 12:9186-9193. [PMID: 32297890 DOI: 10.1039/d0nr01258k] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
Charged domain walls in ferroelectrics hold great promise for the design of novel electronic devices due to their enhanced local conductivity. In fact, charged domain walls show unique properties including the possibility of being created, moved and erased by an applied voltage. Here, we demonstrate that the charged domain walls are constituted by a core region where most of the screening charge is localized and such charge accumulation is responsible for their enhanced conductivity. In particular, the link between the local structural distortions and charge screening phenomena in 109° tail-to-tail domain walls of BiFeO3 is elucidated by a series of multiscale analysis performed by means of scanning probe techniques, including conductive atomic force microscopy (cAFM) and atomic resolution differential phase contrast scanning transmission electron microscopy (DPC-STEM). The results prove that an accumulation of oxygen vacancies occurs at the tail-to-tail domain walls as the leading charge screening process. This work constitutes a new insight in understanding the behavior of such complex systems and lays down the fundaments for their implementation into novel nanoelectronic devices.
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Affiliation(s)
- Marco Campanini
- Electron Microscopy Center, Empa, Swiss Federal Laboratories for Materials Science and Technology, Ueberlandstr. 129, 8600 Dübendorf, Switzerland.
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78
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De Wael A, De Backer A, Jones L, Varambhia A, Nellist PD, Van Aert S. Measuring Dynamic Structural Changes of Nanoparticles at the Atomic Scale Using Scanning Transmission Electron Microscopy. PHYSICAL REVIEW LETTERS 2020; 124:106105. [PMID: 32216442 DOI: 10.1103/physrevlett.124.106105] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/17/2019] [Accepted: 01/30/2020] [Indexed: 06/10/2023]
Abstract
We propose a new method to measure atomic scale dynamics of nanoparticles from experimental high-resolution annular dark field scanning transmission electron microscopy images. By using the so-called hidden Markov model, which explicitly models the possibility of structural changes, the number of atoms in each atomic column can be quantified over time. This newly proposed method outperforms the current atom-counting procedure and enables the determination of the probabilities and cross sections for surface diffusion. This method is therefore of great importance for revealing and quantifying the atomic structure when it evolves over time via adatom dynamics, surface diffusion, beam effects, or during in situ experiments.
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Affiliation(s)
- Annelies De Wael
- EMAT, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium
- NANOlab Center of Excellence, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium
| | - Annick De Backer
- EMAT, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium
- NANOlab Center of Excellence, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium
| | - Lewys Jones
- Department of Materials, University of Oxford, Parks Road, OX1 3PH Oxford, United Kingdom
- Advanced Microscopy Laboratory, Centre for Research on Adaptive Nanostructures and Nanodevices (CRANN), Dublin 2, Ireland
- School of Physics, Trinity College Dublin, The University of Dublin, Dublin 2, Ireland
| | - Aakash Varambhia
- Department of Materials, University of Oxford, Parks Road, OX1 3PH Oxford, United Kingdom
| | - Peter D Nellist
- Department of Materials, University of Oxford, Parks Road, OX1 3PH Oxford, United Kingdom
| | - Sandra Van Aert
- EMAT, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium
- NANOlab Center of Excellence, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium
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79
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Winkler F, Barthel J, Dunin-Borkowski RE, Müller-Caspary K. Direct measurement of electrostatic potentials at the atomic scale: A conceptual comparison between electron holography and scanning transmission electron microscopy. Ultramicroscopy 2020; 210:112926. [PMID: 31955112 DOI: 10.1016/j.ultramic.2019.112926] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2019] [Revised: 12/18/2019] [Accepted: 12/28/2019] [Indexed: 10/25/2022]
Abstract
Off-axis electron holography and first moment STEM are sensitive to electromagnetic potentials or fields, respectively. In this work, we investigate in what sense the results obtained from both techniques are equivalent and work out the major differences. The analysis is focused on electrostatic (Coulomb) potentials at atomic spatial resolution. It is shown that the probe-forming/objective aperture strongly affects the reconstructed electrostatic potentials and that, as a result of the different illumination setups, dynamical diffraction effects show a specific response with increasing specimen thickness. It is shown that thermal diffuse scattering is negligible for a wide range of specimen thicknesses, when evaluating the first moment of diffraction patterns.
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80
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Campanini M, Erni R, Rossell MD. Probing local order in multiferroics by transmission electron microscopy. PHYSICAL SCIENCES REVIEWS 2020. [DOI: 10.1515/psr-2019-0068] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Abstract
The ongoing trend toward miniaturization has led to an increased interest in the magnetoelectric effect, which could yield entirely new device concepts, such as electric field-controlled magnetic data storage. As a result, much work is being devoted to developing new robust room temperature (RT) multiferroic materials that combine ferromagnetism and ferroelectricity. However, the development of new multiferroic devices has proved unexpectedly challenging. Thus, a better understanding of the properties of multiferroic thin films and the relation with their microstructure is required to help drive multiferroic devices toward technological application. This review covers in a concise manner advanced analytical imaging methods based on (scanning) transmission electron microscopy which can potentially be used to characterize complex multiferroic materials. It consists of a first broad introduction to the topic followed by a section describing the so-called phase-contrast methods, which can be used to map the polar and magnetic order in magnetoelectric multiferroics at different spatial length scales down to atomic resolution. Section 3 is devoted to electron nanodiffraction methods. These methods allow measuring local strains, identifying crystal defects and determining crystal structures, and thus offer important possibilities for the detailed structural characterization of multiferroics in the ultrathin regime or inserted in multilayers or superlattice architectures. Thereafter, in Section 4, methods are discussed which allow for analyzing local strain, whereas in Section 5 methods are addressed which allow for measuring local polarization effects on a length scale of individual unit cells. Here, it is shown that the ferroelectric polarization can be indirectly determined from the atomic displacements measured in atomic resolution images. Finally, a brief outlook is given on newly established methods to probe the behavior of ferroelectric and magnetic domains and nanostructures during in situ heating/electrical biasing experiments. These in situ methods are just about at the launch of becoming increasingly popular, particularly in the field of magnetoelectric multiferroics, and shall contribute significantly to understanding the relationship between the domain dynamics of multiferroics and the specific microstructure of the films providing important guidance to design new devices and to predict and mitigate failures.
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81
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Chen P, Murugappan K, Castell MR. Shapes of epitaxial gold nanocrystals on SrTiO3 substrates. Phys Chem Chem Phys 2020; 22:4416-4428. [DOI: 10.1039/c9cp06801e] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Morphological control of gold nanocrystals is important as their catalytic and optical properties are highly shape dependent.
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Affiliation(s)
- Peiyu Chen
- Department of Materials
- University of Oxford
- Parks Road
- Oxford
- UK
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82
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House RA, Maitra U, Pérez-Osorio MA, Lozano JG, Jin L, Somerville JW, Duda LC, Nag A, Walters A, Zhou KJ, Roberts MR, Bruce PG. Superstructure control of first-cycle voltage hysteresis in oxygen-redox cathodes. Nature 2019; 577:502-508. [DOI: 10.1038/s41586-019-1854-3] [Citation(s) in RCA: 266] [Impact Index Per Article: 53.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2019] [Accepted: 10/01/2019] [Indexed: 11/09/2022]
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83
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Nordlander J, Campanini M, Rossell MD, Erni R, Meier QN, Cano A, Spaldin NA, Fiebig M, Trassin M. The ultrathin limit of improper ferroelectricity. Nat Commun 2019; 10:5591. [PMID: 31811133 PMCID: PMC6897979 DOI: 10.1038/s41467-019-13474-x] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2019] [Accepted: 11/08/2019] [Indexed: 11/25/2022] Open
Abstract
The secondary nature of polarization in improper ferroelectrics promotes functional properties beyond those of conventional ferroelectrics. In technologically relevant ultrathin films, however, the improper ferroelectric behavior remains largely unexplored. Here, we probe the emergence of the coupled improper polarization and primary distortive order parameter in thin films of hexagonal YMnO3. Combining state-of-the-art in situ characterization techniques separately addressing the improper ferroelectric state and its distortive driving force, we reveal a pronounced thickness dependence of the improper polarization, which we show to originate from the strong modification of the primary order at epitaxial interfaces. Nanoscale confinement effects on the primary order parameter reduce the temperature of the phase transition, which we exploit to visualize its order-disorder character with atomic resolution. Our results advance the understanding of the evolution of improper ferroelectricity within the confinement of ultrathin films, which is essential for their successful implementation in nanoscale applications. Evolution of improper ferroelectricity within the confinement of ultrathin films is essential for their successful implementation in nanoscale applications. Here, the authors show thickness dependence of the improper polarization originating from the strong modification of the primary order at epitaxial interfaces.
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Affiliation(s)
- J Nordlander
- Department of Materials, ETH Zurich, 8093, Zurich, Switzerland.
| | - M Campanini
- Electron Microscopy Center, Empa, 8600, Dübendorf, Switzerland
| | - M D Rossell
- Electron Microscopy Center, Empa, 8600, Dübendorf, Switzerland
| | - R Erni
- Electron Microscopy Center, Empa, 8600, Dübendorf, Switzerland
| | - Q N Meier
- Department of Materials, ETH Zurich, 8093, Zurich, Switzerland
| | - A Cano
- Department of Materials, ETH Zurich, 8093, Zurich, Switzerland.,Institut Néel, CNRS, 38042, Grenoble, France
| | - N A Spaldin
- Department of Materials, ETH Zurich, 8093, Zurich, Switzerland
| | - M Fiebig
- Department of Materials, ETH Zurich, 8093, Zurich, Switzerland
| | - M Trassin
- Department of Materials, ETH Zurich, 8093, Zurich, Switzerland.
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84
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Chen T, Ellis I, Hooper TJN, Liberti E, Ye L, Lo BTW, O'Leary C, Sheader AA, Martinez GT, Jones L, Ho PL, Zhao P, Cookson J, Bishop PT, Chater P, Hanna JV, Nellist P, Tsang SCE. Interstitial Boron Atoms in the Palladium Lattice of an Industrial Type of Nanocatalyst: Properties and Structural Modifications. J Am Chem Soc 2019; 141:19616-19624. [PMID: 31747756 DOI: 10.1021/jacs.9b06120] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
It is well-established that the inclusion of small atomic species such as boron (B) in powder metal catalysts can subtly modify catalytic properties, and the associated changes in the metal lattice imply that the B atoms are located in the interstitial sites. However, there is no compelling evidence for the occurrence of interstitial B atoms, and there is a concomitant lack of detailed structural information describing the nature of this occupancy and its effects on the metal host. In this work, we use an innovative combination of high-resolution 11B magic-angle-spinning (MAS) and 105Pd static solid-state NMR nuclear magnetic resonance (NMR), synchrotron X-ray diffraction (SXRD), in situ X-ray pair distribution function (XPDF), scanning transmission electron microscopy-annular dark field imaging (STEM-ADF), electron ptychography, and electron energy loss spectroscopy (EELS) to investigate the B atom positions, properties, and structural modifications to the palladium lattice of an industrial type interstitial boron doped palladium nanoparticle catalyst system (Pd-intB/C NPs). In this study, we report that upon B incorporation into the Pd lattice, the overall face centered cubic (FCC) lattice is maintained; however, short-range disorder is introduced. The 105Pd static solid-state NMR illustrates how different types (and levels) of structural strain and disorder are introduced in the nanoparticle history. These structural distortions can lead to the appearance of small amounts of local hexagonal close packed (HCP) structured material in localized regions. The short-range lattice tailoring of the Pd framework to accommodate interstitial B dopants in the octahedral sites of the distorted FCC structure can be imaged by electron ptychography. This study describes new toolsets that enable the characterization of industrial metal nanocatalysts across length scales from macro- to microanalysis, which gives important guidance to the structure-activity relationship of the system.
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Affiliation(s)
- Tianyi Chen
- Wolfson Catalysis Center, Department of Chemistry , University of Oxford , Oxford OX1 3QR , United Kingdom.,Department of Materials , University of Oxford , Oxford OX1 3PH , United Kingdom
| | - Ieuan Ellis
- Wolfson Catalysis Center, Department of Chemistry , University of Oxford , Oxford OX1 3QR , United Kingdom.,Johnson Matthey , Blount's Court, Sonning Common , Reading RG4 9NH , United Kingdom
| | - Thomas J N Hooper
- Department of Physics , University of Warwick , Coventry CV4 7AL , United Kingdom
| | - Emanuela Liberti
- Department of Materials , University of Oxford , Oxford OX1 3PH , United Kingdom
| | - Lin Ye
- Wolfson Catalysis Center, Department of Chemistry , University of Oxford , Oxford OX1 3QR , United Kingdom
| | - Benedict T W Lo
- Wolfson Catalysis Center, Department of Chemistry , University of Oxford , Oxford OX1 3QR , United Kingdom
| | - Colum O'Leary
- Department of Materials , University of Oxford , Oxford OX1 3PH , United Kingdom
| | - Alexandra A Sheader
- Department of Materials , University of Oxford , Oxford OX1 3PH , United Kingdom
| | - Gerardo T Martinez
- Department of Materials , University of Oxford , Oxford OX1 3PH , United Kingdom
| | - Lewys Jones
- Department of Materials , University of Oxford , Oxford OX1 3PH , United Kingdom
| | - Ping-Luen Ho
- Wolfson Catalysis Center, Department of Chemistry , University of Oxford , Oxford OX1 3QR , United Kingdom.,Department of Materials , University of Oxford , Oxford OX1 3PH , United Kingdom
| | - Pu Zhao
- Wolfson Catalysis Center, Department of Chemistry , University of Oxford , Oxford OX1 3QR , United Kingdom
| | - James Cookson
- Johnson Matthey , Blount's Court, Sonning Common , Reading RG4 9NH , United Kingdom
| | - Peter T Bishop
- Johnson Matthey , Blount's Court, Sonning Common , Reading RG4 9NH , United Kingdom
| | - Philip Chater
- Diamond Light Source Ltd. , Harwell Science and Innovation Campus, Didcot, Oxfordshire OX11 0DE , United Kingdom
| | - John V Hanna
- Department of Physics , University of Warwick , Coventry CV4 7AL , United Kingdom
| | - Peter Nellist
- Department of Materials , University of Oxford , Oxford OX1 3PH , United Kingdom
| | - Shik Chi Edman Tsang
- Wolfson Catalysis Center, Department of Chemistry , University of Oxford , Oxford OX1 3QR , United Kingdom
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85
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Bárcena-González G, Guerrero-Lebrero MP, Guerrero E, Yañez A, Nuñez-Moraleda B, Kepaptsoglou D, Lazarov VK, Galindo PL. HAADF-STEM Image Resolution Enhancement Using High-Quality Image Reconstruction Techniques: Case of the Fe 3O 4(111) Surface. MICROSCOPY AND MICROANALYSIS : THE OFFICIAL JOURNAL OF MICROSCOPY SOCIETY OF AMERICA, MICROBEAM ANALYSIS SOCIETY, MICROSCOPICAL SOCIETY OF CANADA 2019; 25:1297-1303. [PMID: 31407642 DOI: 10.1017/s1431927619014788] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
From simple averaging to more sophisticated registration and restoration strategies, such as super-resolution (SR), there exist different computational techniques that use a series of images of the same object to generate enhanced images where noise and other distortions have been reduced. In this work, we provide qualitative and quantitative measurements of this enhancement for high-angle annular dark-field scanning transmission electron microscopy imaging. These images are compared in two ways, qualitatively through visual inspection in real and reciprocal space, and quantitatively, through the calculation of objective measurements, such as signal-to-noise ratio and atom column roundness. Results show that these techniques improve the quality of the images. In this paper, we use an SR methodology that allows us to take advantage of the information present in the image frames and to reliably facilitate the analysis of more difficult regions of interest in experimental images, such as surfaces and interfaces. By acquiring a series of cross-sectional experimental images of magnetite (Fe3O4) thin films (111), we have generated interpolated images using averaging and SR, and reconstructed the atomic structure of the very top surface layer that consists of a full monolayer of Fe, with topmost Fe atoms in tetrahedrally coordinated sites.
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Affiliation(s)
- G Bárcena-González
- Department of Computer Science and Engineering, Universidad de Cádiz, 11510 Puerto Real, Spain
| | - M P Guerrero-Lebrero
- Department of Computer Science and Engineering, Universidad de Cádiz, 11510 Puerto Real, Spain
| | - E Guerrero
- Department of Computer Science and Engineering, Universidad de Cádiz, 11510 Puerto Real, Spain
| | - A Yañez
- Department of Computer Science and Engineering, Universidad de Cádiz, 11510 Puerto Real, Spain
| | - B Nuñez-Moraleda
- Department of Computer Science and Engineering, Universidad de Cádiz, 11510 Puerto Real, Spain
| | - D Kepaptsoglou
- Department of Physics, University of York, Heslington, York, UK
- SuperSTEM Laboratory, SciTech Daresbury Campus, Daresbury WA4 4AD, UK
| | - V K Lazarov
- Department of Physics, University of York, Heslington, York, UK
| | - P L Galindo
- Department of Computer Science and Engineering, Universidad de Cádiz, 11510 Puerto Real, Spain
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86
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Christiansen E, Marioara CD, Holmedal B, Hopperstad OS, Holmestad R. Nano-scale characterisation of sheared β" precipitates in a deformed Al-Mg-Si alloy. Sci Rep 2019; 9:17446. [PMID: 31767885 PMCID: PMC6877512 DOI: 10.1038/s41598-019-53772-4] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2019] [Accepted: 11/05/2019] [Indexed: 11/18/2022] Open
Abstract
This paper compares the nano-scale structure of β" precipitates in a peak-aged Al-Mg-Si alloy before and after deformation. Three complementary advanced transmission electron microscopy techniques are used to reveal the structures and elucidate the interaction between dislocations and β" precipitates. We show that the needle-like and semi-coherent β" precipitates are sheared several times on different planes by dislocations during deformation, with no indications that they are bypassed or looped. Our results show that dislocations cut through precipitates and leave behind planar defects lying on planes inclined to 〈100〉 directions inside the precipitates. The results also indicate that precipitates are sheared in single steps, and the implication of this observation is discussed in terms of slip behaviour.
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Affiliation(s)
- Emil Christiansen
- Centre for Advanced Structural Analysis (CASA), NTNU - Norwegian University of Science and Technology, Trondheim, N-7491, Norway.
- Department of Physics, Faculty of Natural Sciences, NTNU, Trondheim, N-7491, Norway.
| | - Calin Daniel Marioara
- Centre for Advanced Structural Analysis (CASA), NTNU - Norwegian University of Science and Technology, Trondheim, N-7491, Norway
- Materials and Nanotechnology, SINTEF Industry, Trondheim, N-7465, Norway
| | - Bjørn Holmedal
- Centre for Advanced Structural Analysis (CASA), NTNU - Norwegian University of Science and Technology, Trondheim, N-7491, Norway
- Department of Materials Science and Engineering, Faculty of Natural Sciences, NTNU, Trondheim, N-7491, Norway
| | - Odd Sture Hopperstad
- Centre for Advanced Structural Analysis (CASA), NTNU - Norwegian University of Science and Technology, Trondheim, N-7491, Norway
- Department of Structural Engineering, Faculty of Engineering, NTNU, Trondheim, N-7491, Norway
| | - Randi Holmestad
- Centre for Advanced Structural Analysis (CASA), NTNU - Norwegian University of Science and Technology, Trondheim, N-7491, Norway
- Department of Physics, Faculty of Natural Sciences, NTNU, Trondheim, N-7491, Norway
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87
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Liberti E, Lozano JG, Pérez Osorio MA, Roberts MR, Bruce PG, Kirkland AI. Quantifying oxygen distortions in lithium-rich transition-metal-oxide cathodes using ABF STEM. Ultramicroscopy 2019; 210:112914. [PMID: 31811959 DOI: 10.1016/j.ultramic.2019.112914] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2019] [Revised: 11/11/2019] [Accepted: 11/22/2019] [Indexed: 11/26/2022]
Abstract
Lithium-rich cathodes can store excess charge beyond the transition metal redox capacity by participation of oxygen in reversible anionic redox reactions. Although these processes are crucial for achieving high energy densities, their structural origins are not yet fully understood. Here, we explore the use of annular bright-field (ABF) imaging in scanning transmission electron microscopy (STEM) to measure oxygen distortions in charged Li1.2Ni0.2Mn0.6O2. We show that ABF STEM data can provide positional accuracies below 20 pm but this is restricted to cases where no specimen mistilt is present, and only for a range of thicknesses above 3.5 nm. The reliability of these measurements is compromised even when the experimental and post-processing designs are optimised for accuracy and precision, indicating that extreme care must be taken when attempting to quantify distortions in these materials.
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Affiliation(s)
- E Liberti
- Department of Materials, University of Oxford, Parks Road OX1 3PH, UK.
| | - J G Lozano
- Department of Materials, University of Oxford, Parks Road OX1 3PH, UK
| | - M A Pérez Osorio
- Department of Materials, University of Oxford, Parks Road OX1 3PH, UK
| | - M R Roberts
- Department of Materials, University of Oxford, Parks Road OX1 3PH, UK
| | - P G Bruce
- Department of Materials, University of Oxford, Parks Road OX1 3PH, UK
| | - A I Kirkland
- Department of Materials, University of Oxford, Parks Road OX1 3PH, UK
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88
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Ahmed S, Pokle A, Schweidler S, Beyer A, Bianchini M, Walther F, Mazilkin A, Hartmann P, Brezesinski T, Janek J, Volz K. The Role of Intragranular Nanopores in Capacity Fade of Nickel-Rich Layered Li(Ni 1-x-yCo xMn y)O 2 Cathode Materials. ACS NANO 2019; 13:10694-10704. [PMID: 31480835 DOI: 10.1021/acsnano.9b05047] [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
Ni-rich layered LiNi1-x-yCoxMnyO2 (NCM, x + y ≤ 0.2) is an intensively studied class of cathode active materials for lithium-ion batteries, offering the advantage of high specific capacities. However, their reactivity is also one of the major issues limiting the lifetime of the batteries. NCM degradation, in literature, is mostly explained both by disintegration of secondary particles (large anisotropic volume changes during lithiation/delithiation) and by formation of rock-salt like phases at the grain surfaces at high potential with related oxygen loss. Here, we report the presence of intragranular nanopores in Li1+x(Ni0.85Co0.1Mn0.05)1-xO2 (NCM851005) and track their morphological evolution from pristine to cycled material (200 and 500 cycles) using aberration-corrected scanning transmission electron microscopy (STEM), electron energy loss spectroscopy, energy dispersive X-ray spectroscopy, and time-of-flight secondary ion mass spectrometry. Pores are already found in the primary particles of pristine material. Any potential effect of TEM sample preparation on the formation of nanopores is ruled out by performing thickness series measurements on the lamellae produced by focused ion beam milling. The presence of nanopores in pristine NCM851005 is in sharp contrast to previously observed pore formation during electrochemical cycling or heating. The intragranular pores have a diameter in the range between 10 and 50 nm with a distinct morphology that changes during cycling operation. A rock-salt like region is observed at the pore boundaries even in pristine material, and these regions grow with prolonged cycling. It is suggested that the presence of nanopores strongly affects the degradation of high-Ni NCM, as the pore surfaces apparently increase (i) oxygen loss, (ii) formation of rock-salt regions, and (iii) strain-induced effects within the primary grains. High-resolution STEM demonstrates that nanopores are a source of intragranular cracking during cycling.
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Affiliation(s)
- Shamail Ahmed
- Materials Science Centre and Faculty of Physics , Philipps University Marburg , Hans-Meerwein-Strasse 6 , 35043 Marburg , Germany
| | - Anuj Pokle
- Materials Science Centre and Faculty of Physics , Philipps University Marburg , Hans-Meerwein-Strasse 6 , 35043 Marburg , Germany
| | - Simon Schweidler
- Battery and Electrochemistry Laboratory, Institute of Nanotechnology , Karlsruhe Institute of Technology (KIT) , Hermann-von-Helmholtz-Platz 1 , 76344 Eggenstein-Leopoldshafen , Germany
| | - Andreas Beyer
- Materials Science Centre and Faculty of Physics , Philipps University Marburg , Hans-Meerwein-Strasse 6 , 35043 Marburg , Germany
| | - Matteo Bianchini
- Battery and Electrochemistry Laboratory, Institute of Nanotechnology , Karlsruhe Institute of Technology (KIT) , Hermann-von-Helmholtz-Platz 1 , 76344 Eggenstein-Leopoldshafen , Germany
| | - Felix Walther
- Institute of Physical Chemistry and Center for Materials Research , Justus-Liebig-University , Heinrich-Buff-Ring 17 , 35392 Giessen , Germany
| | - Andrey Mazilkin
- Battery and Electrochemistry Laboratory, Institute of Nanotechnology , Karlsruhe Institute of Technology (KIT) , Hermann-von-Helmholtz-Platz 1 , 76344 Eggenstein-Leopoldshafen , Germany
- Karlsruhe Nano Micro Facility, Karlsruhe Institute of Technology (KIT) , Hermann-von-Helmholtz-Platz 1 , 76344 Eggenstein-Leopoldshafen , Germany
| | - Pascal Hartmann
- Battery and Electrochemistry Laboratory, Institute of Nanotechnology , Karlsruhe Institute of Technology (KIT) , Hermann-von-Helmholtz-Platz 1 , 76344 Eggenstein-Leopoldshafen , Germany
- BASF SE , Carl-Bosch-Strasse 38 , 67056 Ludwigshafen , Germany
| | - Torsten Brezesinski
- Battery and Electrochemistry Laboratory, Institute of Nanotechnology , Karlsruhe Institute of Technology (KIT) , Hermann-von-Helmholtz-Platz 1 , 76344 Eggenstein-Leopoldshafen , Germany
| | - Jürgen Janek
- Battery and Electrochemistry Laboratory, Institute of Nanotechnology , Karlsruhe Institute of Technology (KIT) , Hermann-von-Helmholtz-Platz 1 , 76344 Eggenstein-Leopoldshafen , Germany
- Institute of Physical Chemistry and Center for Materials Research , Justus-Liebig-University , Heinrich-Buff-Ring 17 , 35392 Giessen , Germany
| | - Kerstin Volz
- Materials Science Centre and Faculty of Physics , Philipps University Marburg , Hans-Meerwein-Strasse 6 , 35043 Marburg , Germany
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89
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Drzeżdżon J, Jacewicz D, Sielicka A, Chmurzyński L. A review of new approaches to analytical methods to determine the structure and morphology of polymers. Trends Analyt Chem 2019. [DOI: 10.1016/j.trac.2019.06.013] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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90
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Haruta M, Fujiyoshi Y, Nemoto T, Ishizuka A, Ishizuka K, Kurata H. Extremely low count detection for EELS spectrum imaging by reducing CCD read-out noise. Ultramicroscopy 2019; 207:112827. [PMID: 31445356 DOI: 10.1016/j.ultramic.2019.112827] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2019] [Revised: 08/06/2019] [Accepted: 08/12/2019] [Indexed: 10/26/2022]
Abstract
Extremely low count detection for EELS spectrum imaging is required to overcome problems with electron irradiation and widen the range of available applications. We have made a systematic statistical study of the reduction of CCD noise for EELS. We propose a calculation method to estimate the properties of noise and a procedure to reduce it. Since the dominant noise is a practically random component, it can be reduced by subtracting the population mean of the dark reference and a summation over an appropriate number of spectra, depending on the standard deviation of the noise. A gain-averaging method can further improve the signal-to-noise (SN) ratio. It is thereby demonstrated that a high-SN spectrum can be obtained even for a single-count core-loss signal. The present method would be useful for measuring low signal spectrum such as monochromated spectra and for radiation sensitive materials.
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Affiliation(s)
- Mitsutaka Haruta
- Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan.
| | - Yoshifumi Fujiyoshi
- Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan
| | - Takashi Nemoto
- Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan
| | - Akimitsu Ishizuka
- HREM Research Inc., 14-48 Matsukazedai, Higashimatsuyama, Saitama 355-0055, Japan
| | - Kazuo Ishizuka
- HREM Research Inc., 14-48 Matsukazedai, Higashimatsuyama, Saitama 355-0055, Japan
| | - Hiroki Kurata
- Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan
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91
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Lotnyk A, Dankwort T, Hilmi I, Kienle L, Rauschenbach B. In situ observations of the reversible vacancy ordering process in van der Waals-bonded Ge-Sb-Te thin films and GeTe-Sb 2Te 3 superlattices. NANOSCALE 2019; 11:10838-10845. [PMID: 31135011 DOI: 10.1039/c9nr02112d] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
Chalcogenide-based thin films are employed in data storage and memory technology whereas van der Waals-bonded layered chalcogenide heterostructures are considered to be a main contender for memory devices with low power consumption. The reduction of switching energy is due to the lowering of entropic losses governed by the restricted motion of atoms in one dimension within the crystalline states. The investigations of switching mechanisms in such superlattices have recently attracted much attention and the proposed models are still under debate. This is partially due to the lack of direct observation of atomic scale processes, which might occur in these chalcogenide systems. This work reports direct, nanoscale observations of the order-disorder processes in van der Waals bonded Ge-Sb-Te thin films and GeTe-Sb2Te3-based superlattices using in situ experiments inside an aberration-corrected transmission electron microscope. The findings reveal a reversible self-assembled reconfiguration of the structural order in these materials. This process is associated with the ordering of randomly distributed vacancies within the studied materials into ordered vacancy layers and with readjustment of the lattice plane distances within the newly formed layered structures, indicating the high flexibility of these layered chalcogenide-based systems. Thus, the ordering process results in the formation of vacancy-bonded building blocks intercalated within van der Waals-bonded units. Moreover, vacancy-bonded building blocks can be reconfigured to the initial structure under the influence of an electron beam, while in situ exposure of the recovered layers to a targeted electron beam leads to the reverse process. Overall, the outcomes provide new insights into local structure and switching mechanism in chalcogenide superlattices.
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Affiliation(s)
- Andriy Lotnyk
- Leibniz Institute of Surface Engineering (IOM), Permoserstr. 15, 04318, Leipzig, Germany.
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92
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Roslova M, Hunger J, Bastien G, Pohl D, Haghighi HM, Wolter AUB, Isaeva A, Schwarz U, Rellinghaus B, Nielsch K, Büchner B, Doert T. Detuning the Honeycomb of the α-RuCl 3 Kitaev Lattice: A Case of Cr 3+ Dopant. Inorg Chem 2019; 58:6659-6668. [PMID: 31045349 DOI: 10.1021/acs.inorgchem.8b03545] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Fine-tuning chemistry by doping with transition metals enables new perspectives for exploring Kitaev physics on a two-dimensional (2D) honeycomb lattice of α-RuCl3, which is promising in the field of quantum information protection and quantum computation. The key parameters to vary by doping are both Heisenberg and Kitaev components of the nearest-neighbor exchange interaction between the Jeff = 1/2 Ru3+ spins, depending strongly on the peculiarities of the crystal structure. Here, we present crystal growth by chemical vapor transport and structure elucidation of a solid solution series Ru1- xCr xCl3 (0 ≤ x ≤ 1), with Cr3+ ions coupled to the Ru3+ Kitaev host. The Cr3+ substitution preserves the honeycomb type lattice of α-RuCl3 and creates mixed occupancy of Ru/Cr sites without cationic order within the layers as confirmed by single-crystal X-ray diffraction and transmission electron microscopy investigations. In contrast to high-quality single crystals of α-RuCl3 with ABAB-stacked layers, the ternary compounds demonstrate a significant stacking disorder along the c-axis direction as evidenced by X-ray diffraction and high resolution scanning transmission electron microscopy (HR-STEM). Raman spectra of substituted samples are in line with the symmetry conservation of the parent lattice upon chromium doping. At the same time, our magnetic susceptibility data indicate that the Kitaev physics of α-RuCl3 is increasingly suppressed by the dominant spin-only driven magnetism of Cr3+ ( S = 3/2) in Ru1- xCr xCl3.
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Affiliation(s)
- Maria Roslova
- Faculty of Chemistry and Food Chemistry , Technische Universität Dresden , 01062 Dresden , Germany
| | - Jens Hunger
- Faculty of Chemistry and Food Chemistry , Technische Universität Dresden , 01062 Dresden , Germany
| | - Gaël Bastien
- Institute for Solid State and Materials Research (IFW) Dresden , 01171 Dresden , Germany
| | - Darius Pohl
- Institute for Solid State and Materials Research (IFW) Dresden , 01171 Dresden , Germany.,Dresden Center for Nanoanalysis, cfaed , Technische Universität Dresden , 01062 Dresden , Germany
| | - Hossein M Haghighi
- Institute for Solid State and Materials Research (IFW) Dresden , 01171 Dresden , Germany
| | - Anja U B Wolter
- Institute for Solid State and Materials Research (IFW) Dresden , 01171 Dresden , Germany
| | - Anna Isaeva
- Faculty of Chemistry and Food Chemistry , Technische Universität Dresden , 01062 Dresden , Germany
| | - Ulrich Schwarz
- Max Planck Institute for Chemical Physics of Solids , 01187 Dresden , Germany
| | - Bernd Rellinghaus
- Dresden Center for Nanoanalysis, cfaed , Technische Universität Dresden , 01062 Dresden , Germany
| | - Kornelius Nielsch
- Institute for Solid State and Materials Research (IFW) Dresden , 01171 Dresden , Germany
| | - Bernd Büchner
- Institute for Solid State and Materials Research (IFW) Dresden , 01171 Dresden , Germany
| | - Thomas Doert
- Faculty of Chemistry and Food Chemistry , Technische Universität Dresden , 01062 Dresden , Germany
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93
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Composition determination of semiconductor alloys towards atomic accuracy by HAADF-STEM. Ultramicroscopy 2019; 200:84-96. [PMID: 30844539 DOI: 10.1016/j.ultramic.2019.02.009] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2018] [Revised: 12/21/2018] [Accepted: 02/12/2019] [Indexed: 11/23/2022]
Abstract
This paper presents a comprehensive investigation of an extended method to determine composition of materials by scanning transmission electron microscopy (STEM) high angle annular darkfield (HAADF) images and using complementary multislice simulations. The main point is to understand the theoretical capabilities of the algorithm and address the intrinsic limitations of using STEM HAADF intensities for composition determination. A special focus is the potential of the method regarding single-atom accuracy. All-important experimental parameters are included into the multislice simulations to ensure the best possible fit between simulation and experiment. To demonstrate the capabilities of the extended method, results for three different technical important semiconductor samples are presented. Overall the method shows a high lateral resolution combined with a high accuracy towards single-atom accuracy.
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94
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Piché D, Tavernaro I, Fleddermann J, Lozano JG, Varambhia A, Maguire ML, Koch M, Ukai T, Hernández Rodríguez AJ, Jones L, Dillon F, Reyes Molina I, Mitzutani M, González Dalmau ER, Maekawa T, Nellist PD, Kraegeloh A, Grobert N. Targeted T 1 Magnetic Resonance Imaging Contrast Enhancement with Extraordinarily Small CoFe 2O 4 Nanoparticles. ACS APPLIED MATERIALS & INTERFACES 2019; 11:6724-6740. [PMID: 30688055 PMCID: PMC6385080 DOI: 10.1021/acsami.8b17162] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/03/2018] [Accepted: 01/28/2019] [Indexed: 06/09/2023]
Abstract
Extraordinarily small (2.4 nm) cobalt ferrite nanoparticles (ESCIoNs) were synthesized by a one-pot thermal decomposition approach to study their potential as magnetic resonance imaging (MRI) contrast agents. Fine size control was achieved using oleylamine alone, and annular dark-field scanning transmission electron microscopy revealed highly crystalline cubic spinel particles with atomic resolution. Ligand exchange with dimercaptosuccinic acid rendered the particles stable in physiological conditions with a hydrodynamic diameter of 12 nm. The particles displayed superparamagnetic properties and a low r2/ r1 ratio suitable for a T1 contrast agent. The particles were functionalized with bile acid, which improved biocompatibility by significant reduction of reactive oxygen species generation and is a first step toward liver-targeted T1 MRI. Our study demonstrates the potential of ESCIoNs as T1 MRI contrast agents.
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Affiliation(s)
- Dominique Piché
- Materials
Department, University of Oxford, Parks Road, Oxford OX1 3PH, England
| | - Isabella Tavernaro
- INM
- Leibniz Institute for New Materials, Campus D2 2, 66123 Saarbrücken, Germany
| | - Jana Fleddermann
- INM
- Leibniz Institute for New Materials, Campus D2 2, 66123 Saarbrücken, Germany
| | - Juan G. Lozano
- Materials
Department, University of Oxford, Parks Road, Oxford OX1 3PH, England
| | - Aakash Varambhia
- Materials
Department, University of Oxford, Parks Road, Oxford OX1 3PH, England
| | - Mahon L. Maguire
- British
Heart Foundation Experimental Magnetic Resonance Unit, Wellcome Trust Centre for Human Genetics, Roosevelt Drive, Oxford OX3 7BN, England
| | - Marcus Koch
- INM
- Leibniz Institute for New Materials, Campus D2 2, 66123 Saarbrücken, Germany
| | - Tomofumi Ukai
- Bio-Nano
Electronics Research Centre, Toyo University, 2100, Kujirai, Kawagoe, Saitama 350-8585, Japan
| | - Armando J. Hernández Rodríguez
- Departamento
de Imágenes por Resonancia Magnética, Cuban Neurosciences Center, Street 190 e/25 and 27, Cubanacan
Playa, Havana CP 11600, Cuba
| | - Lewys Jones
- Advanced
Microscopy Laboratory, Centre for Research
on Adaptive Nanostructures and Nanodevices (CRANN), Dublin 2, Ireland
- School of
Physics, Trinity College Dublin, Dublin 2, Ireland
| | - Frank Dillon
- Materials
Department, University of Oxford, Parks Road, Oxford OX1 3PH, England
| | - Israel Reyes Molina
- Departamento
de Imágenes por Resonancia Magnética, Cuban Neurosciences Center, Street 190 e/25 and 27, Cubanacan
Playa, Havana CP 11600, Cuba
| | - Mai Mitzutani
- Materials
Department, University of Oxford, Parks Road, Oxford OX1 3PH, England
- Department
of Material Science and Engineering, Tokyo
Institute of Technology, S8-25, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8552, Japan
| | - Evelio R. González Dalmau
- Departamento
de Imágenes por Resonancia Magnética, Cuban Neurosciences Center, Street 190 e/25 and 27, Cubanacan
Playa, Havana CP 11600, Cuba
| | - Toru Maekawa
- Bio-Nano
Electronics Research Centre, Toyo University, 2100, Kujirai, Kawagoe, Saitama 350-8585, Japan
| | - Peter D. Nellist
- Materials
Department, University of Oxford, Parks Road, Oxford OX1 3PH, England
| | - Annette Kraegeloh
- INM
- Leibniz Institute for New Materials, Campus D2 2, 66123 Saarbrücken, Germany
| | - Nicole Grobert
- Materials
Department, University of Oxford, Parks Road, Oxford OX1 3PH, England
- Williams Advanced Engineering, Grove, Oxfordshire, OX12
0DQ, England
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95
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Van Aert S, De Backer A, Jones L, Martinez GT, Béché A, Nellist PD. Control of Knock-On Damage for 3D Atomic Scale Quantification of Nanostructures: Making Every Electron Count in Scanning Transmission Electron Microscopy. PHYSICAL REVIEW LETTERS 2019; 122:066101. [PMID: 30822049 DOI: 10.1103/physrevlett.122.066101] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/13/2018] [Revised: 01/14/2019] [Indexed: 06/09/2023]
Abstract
Understanding nanostructures down to the atomic level is the key to optimizing the design of advanced materials with revolutionary novel properties. This requires characterization methods capable of quantifying the three-dimensional (3D) atomic structure with the highest possible precision. A successful approach to reach this goal is to count the number of atoms in each atomic column from 2D annular dark field scanning transmission electron microscopy images. To count atoms with single atom sensitivity, a minimum electron dose has been shown to be necessary, while on the other hand beam damage, induced by the high energy electrons, puts a limit on the tolerable dose. An important challenge is therefore to develop experimental strategies to optimize the electron dose by balancing atom-counting fidelity vs the risk of knock-on damage. To achieve this goal, a statistical framework combined with physics-based modeling of the dose-dependent processes is here proposed and experimentally verified. This model enables an investigator to theoretically predict, in advance of an experimental measurement, the optimal electron dose resulting in an unambiguous quantification of nanostructures in their native state with the highest attainable precision.
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Affiliation(s)
- Sandra Van Aert
- EMAT, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium
| | - Annick De Backer
- EMAT, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium
| | - Lewys Jones
- Department of Materials, University of Oxford, 16 Parks Road, Oxford OX1 3PH, United Kingdom
- Advanced Microscopy Laboratory, Centre for Research on Adaptive Nanostructures and Nanodevices (CRANN), Dublin 2, Ireland
- School of Physics, Trinity College Dublin, The University of Dublin, Dublin 2, Ireland
| | - Gerardo T Martinez
- EMAT, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium
- Department of Materials, University of Oxford, 16 Parks Road, Oxford OX1 3PH, United Kingdom
| | - Armand Béché
- EMAT, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium
| | - Peter D Nellist
- Department of Materials, University of Oxford, 16 Parks Road, Oxford OX1 3PH, United Kingdom
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96
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Wang S, Hu X, Goniakowski J, Noguera C, Castell MR. Influence of the support on stabilizing local defects in strained monolayer oxide films. NANOSCALE 2019; 11:2412-2422. [PMID: 30667032 DOI: 10.1039/c8nr08606k] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Two-dimensional materials with a honeycomb lattice, such as graphene and hexagonal boron nitride, often contain local defects in which the hexagonal elements are replaced by four-, five-, seven-, and eight-membered rings. An example is the Stone-Wales (S-W) defect, where a bond rotation causes four hexagons to be transformed into a cluster of two pentagons and two heptagons. A further series of similar defects incorporating divacancies results in larger structures of non-hexagonal elements. In this paper, we use scanning tunneling microscopy (STM) and density functional theory (DFT) modeling to investigate the structure and energetics of S-W and divacancy defects in a honeycomb (2 × 2) Ti2O3 monolayer grown on an Au(111) substrate. The epitaxial rumpled Ti2O3 monolayer is pseudomorphic and in a state of elastic compression. As a consequence, divacancy defects, which induce tension in freestanding films, relieve the compression in the epitaxial Ti2O3 monolayer and therefore have significantly lower energies when compared with their freestanding counterparts. We find that at the divacancy defect sites there is a local reduction of the charge transfer between the film and the substrate, the rumpling is reduced, and the film has an increased separation from the substrate. Our results demonstrate the capacity of the substrate to significantly influence the energetics, and hence favor vacancy-type defects, in compressively strained 2D materials. This approach could be applied more broadly, for example to tensile monolayers, where vacancy-type defects would be rare and interstitial-type defects might be favored.
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Affiliation(s)
- Shuqiu Wang
- Department of Materials, University of Oxford, Parks Road, Oxford, OX1 3PH, UK.
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97
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Berkels B, Liebscher CH. Joint non-rigid image registration and reconstruction for quantitative atomic resolution scanning transmission electron microscopy. Ultramicroscopy 2019; 198:49-57. [PMID: 30641407 DOI: 10.1016/j.ultramic.2018.12.016] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2018] [Revised: 12/19/2018] [Accepted: 12/23/2018] [Indexed: 11/29/2022]
Abstract
Aberration corrected scanning transmission electron microscopes (STEM) enable to determine local strain fields, composition and bonding states at atomic resolution. The precision to locate atomic columns is often obstructed by scan artifacts limiting the quantitative interpretation of STEM datasets. Here, a novel bias-corrected non-rigid registration approach is presented that compensates for fast and slow scan artifacts in STEM image series. The bias-correction is responsible for the correction of the slow scan artifacts and based on a explicit coupling of the deformations of the individual images in a series via a minimization of the average deformation. This allows to reduce fast scan noise in an image series and slow scan distortions simultaneously. The novel approach is tested on synthetic and experimental images and its implication on atomic resolution strain and elemental mapping is discussed.
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98
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Altantzis T, Lobato I, De Backer A, Béché A, Zhang Y, Basak S, Porcu M, Xu Q, Sánchez-Iglesias A, Liz-Marzán LM, Van Tendeloo G, Van Aert S, Bals S. Three-Dimensional Quantification of the Facet Evolution of Pt Nanoparticles in a Variable Gaseous Environment. NANO LETTERS 2019; 19:477-481. [PMID: 30540912 PMCID: PMC6437648 DOI: 10.1021/acs.nanolett.8b04303] [Citation(s) in RCA: 34] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
Pt nanoparticles play an essential role in a wide variety of catalytic reactions. The activity of the particles strongly depends on their three-dimensional (3D) structure and exposed facets, as well as on the reactive environment. High-resolution electron microscopy has often been used to characterize nanoparticle catalysts but unfortunately most observations so far have been either performed in vacuum and/or using conventional (2D) in situ microscopy. The latter however does not provide direct 3D morphological information. We have implemented a quantitative methodology to measure variations of the 3D atomic structure of nanoparticles under the flow of a selected gas. We were thereby able to quantify refaceting of Pt nanoparticles with atomic resolution during various oxidation-reduction cycles. In a H2 environment, a more faceted surface morphology of the particles was observed with {100} and {111} planes being dominant. On the other hand, in O2 the percentage of {100} and {111} facets decreased and a significant increase of higher order facets was found, resulting in a more rounded morphology. This methodology opens up new opportunities toward in situ characterization of catalytic nanoparticles because for the first time it enables one to directly measure 3D morphology variations at the atomic scale in a specific gaseous reaction environment.
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Affiliation(s)
- Thomas Altantzis
- Electron
Microscopy for Materials Research (EMAT), University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium
| | - Ivan Lobato
- Electron
Microscopy for Materials Research (EMAT), University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium
| | - Annick De Backer
- Electron
Microscopy for Materials Research (EMAT), University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium
| | - Armand Béché
- Electron
Microscopy for Materials Research (EMAT), University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium
| | - Yang Zhang
- Electron
Microscopy for Materials Research (EMAT), University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium
| | - Shibabrata Basak
- DENSsolutions, Informaticalaan 12, Delft, 2628ZD, The Netherlands
| | - Mauro Porcu
- DENSsolutions, Informaticalaan 12, Delft, 2628ZD, The Netherlands
| | - Qiang Xu
- DENSsolutions, Informaticalaan 12, Delft, 2628ZD, The Netherlands
| | - Ana Sánchez-Iglesias
- Bionanoplasmonics
Laboratory, CIC biomaGUNE, Paseo de Miramón 182, 20014 Donostia - San Sebastian, Spain
| | - Luis M. Liz-Marzán
- Bionanoplasmonics
Laboratory, CIC biomaGUNE, Paseo de Miramón 182, 20014 Donostia - San Sebastian, Spain
- Ikerbasque,
Basque Foundation for Science, 48013 Bilbao, Spain
| | - Gustaaf Van Tendeloo
- Electron
Microscopy for Materials Research (EMAT), University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium
| | - Sandra Van Aert
- Electron
Microscopy for Materials Research (EMAT), University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium
| | - Sara Bals
- Electron
Microscopy for Materials Research (EMAT), University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium
- E-mail:
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99
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Campanini M, Nasi L, Fabbrici S, Casoli F, Celegato F, Barrera G, Chiesi V, Bedogni E, Magén C, Grillo V, Bertoni G, Righi L, Tiberto P, Albertini F. Magnetic Shape Memory Turns to Nano: Microstructure Controlled Actuation of Free-Standing Nanodisks. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2018; 14:e1803027. [PMID: 30294862 DOI: 10.1002/smll.201803027] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/31/2018] [Revised: 09/12/2018] [Indexed: 06/08/2023]
Abstract
Magnetic shape memory materials hold a great promise for next-generation actuation devices and systems for energy conversion, thanks to the intimate coupling between structure and magnetism in their martensitic phase. Here novel magnetic shape memory free-standing nanodisks are proposed, proving that the lack of the substrate constrains enables the exploitation of new microstructure-controlled actuation mechanisms by the combined application of different stimuli-i.e., temperature and magnetic field. The results show that a reversible areal strain (up to 5.5%) can be achieved and tuned in intensity and sign (i.e., areal contraction or expansion) by the application of a magnetic field. The mechanisms at the basis of the actuation are investigated by experiments performed at different length scales and directly visualized by several electron microscopy techniques, including electron holography, showing that thermo/magnetomechanical properties can be optimized by engineering the martensitic microstructure through epitaxial growth and lateral confinement. These findings represent a step forward toward the development of a new class of temperature-field controlled nanoactuators and smart nanomaterials.
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Affiliation(s)
- Marco Campanini
- IMEM-CNR, Parco Area delle Scienze 37/A, 43124, Parma, Italy
- Empa, Ueberlandstrasse 129, 8600, Dübendorf, Switzerland
| | - Lucia Nasi
- IMEM-CNR, Parco Area delle Scienze 37/A, 43124, Parma, Italy
| | - Simone Fabbrici
- IMEM-CNR, Parco Area delle Scienze 37/A, 43124, Parma, Italy
- MIST E-R, via P. Gobetti 101, 40129, Bologna, Italy
| | | | | | | | | | - Elena Bedogni
- Dipartimento di Scienze Chimiche, Università di Parma, 43121, Parma, Italy
| | - César Magén
- ICMA, Universidad de Zaragoza-CSIC, 50009, Zaragoza, Spain
- LMA, Instituto de Nanociencia de Aragón, Universidad de Zaragoza, 50018, Zaragoza, Spain
| | - Vincenzo Grillo
- IMEM-CNR, Parco Area delle Scienze 37/A, 43124, Parma, Italy
- S3-CNR, Via Campi 213A, 41125, Modena, Italy
| | - Giovanni Bertoni
- IMEM-CNR, Parco Area delle Scienze 37/A, 43124, Parma, Italy
- Istituto Italiano di Tecnologia, Via Morego 30, 16163, Genova, Italy
| | - Lara Righi
- Dipartimento di Scienze Chimiche, Università di Parma, 43121, Parma, Italy
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100
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Lozano JG, Martinez GT, Jin L, Nellist PD, Bruce PG. Low-Dose Aberration-Free Imaging of Li-Rich Cathode Materials at Various States of Charge Using Electron Ptychography. NANO LETTERS 2018; 18:6850-6855. [PMID: 30257093 DOI: 10.1021/acs.nanolett.8b02718] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Imaging the complete atomic structure of materials, including light elements, with minimal beam-induced damage of the sample is a long-standing challenge in electron microscopy. Annular bright-field scanning transmission electron microscopy is often used to image elements with low atomic numbers, but due to its low efficiency and high sensitivity to precise imaging parameters it comes at the price of potentially significant beam damage. In this paper, we show that electron ptychography is a powerful technique to retrieve reconstructed phase images that provide the full structure of beam-sensitive materials containing light and heavy elements. Due to its much higher efficiency, we can reduce the beam currents used down to the subpicoampere range. Electron ptychography also allows residual lens aberrations to be corrected at the postprocessing stage, which avoids the need for fine-tuning of the probe that would result in further beam damage and provides aberration-free reconstructed phase images. We have used electron ptychography to obtain structural information from aberration-free reconstructed phase images in the technologically relevant lithium-rich transition metal oxides at different states of charge. We can unambiguously determine the position of the lithium and oxygen atomic columns while amorphization of the surface, formation of beam-induced surface reconstruction layers, or migration of transition metals to the alkali layers are drastically reduced.
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Affiliation(s)
- Juan G Lozano
- Department of Materials , University of Oxford , Parks Road , OX1 3PH Oxford , United Kingdom
| | - Gerardo T Martinez
- Department of Materials , University of Oxford , Parks Road , OX1 3PH Oxford , United Kingdom
| | - Liyu Jin
- Department of Materials , University of Oxford , Parks Road , OX1 3PH Oxford , United Kingdom
| | - Peter D Nellist
- Department of Materials , University of Oxford , Parks Road , OX1 3PH Oxford , United Kingdom
| | - Peter G Bruce
- Department of Materials , University of Oxford , Parks Road , OX1 3PH Oxford , United Kingdom
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