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Ali H, Rusz J, Bürgler DE, Adam R, Schneider CM, Tai CW, Thersleff T. Noise-dependent bias in quantitative STEM-EMCD experiments revealed by bootstrapping. Ultramicroscopy 2024; 257:113891. [PMID: 38043363 DOI: 10.1016/j.ultramic.2023.113891] [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: 07/07/2023] [Revised: 11/13/2023] [Accepted: 11/23/2023] [Indexed: 12/05/2023]
Abstract
Electron magnetic circular dichroism (EMCD) is a powerful technique for estimating element-specific magnetic moments of materials on nanoscale with the potential to reach atomic resolution in transmission electron microscopes. However, the fundamentally weak EMCD signal strength complicates quantification of magnetic moments, as this requires very high precision, especially in the denominator of the sum rules. Here, we employ a statistical resampling technique known as bootstrapping to an experimental EMCD dataset to produce an empirical estimate of the noise-dependent error distribution resulting from application of EMCD sum rules to bcc iron in a 3-beam orientation. We observe clear experimental evidence that noisy EMCD signals preferentially bias the estimation of magnetic moments, further supporting this with error distributions produced by Monte-Carlo simulations. Finally, we propose guidelines for the recognition and minimization of this bias in the estimation of magnetic moments.
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Affiliation(s)
- Hasan Ali
- Department of Materials Science and Engineering, Uppsala University, Box 534, Uppsala 751 21, Sweden; Department of Materials and Environmental Chemistry, Stockholm University, Stockholm 106 91, Sweden; Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons, Forschungszentrum Jülich, Jülich 52425, Germany.
| | - Jan Rusz
- Department of Physics and Astronomy, Uppsala University, Box 516, Uppsala 751 20, Sweden
| | - Daniel E Bürgler
- Peter Grünberg Institut, Forschungszentrum Jülich GmbH, Jülich D-52425, Germany
| | - Roman Adam
- Peter Grünberg Institut, Forschungszentrum Jülich GmbH, Jülich D-52425, Germany
| | - Claus M Schneider
- Peter Grünberg Institut, Forschungszentrum Jülich GmbH, Jülich D-52425, Germany
| | - Cheuk-Wai Tai
- Department of Materials and Environmental Chemistry, Stockholm University, Stockholm 106 91, Sweden
| | - Thomas Thersleff
- Department of Materials and Environmental Chemistry, Stockholm University, Stockholm 106 91, Sweden
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Ali H, Sathyanath SKM, Tai CW, Rusz J, Uusimaki T, Hjörvarsson B, Thersleff T, Leifer K. Single scan STEM-EMCD in 3-beam orientation using a quadruple aperture. Ultramicroscopy 2023; 251:113760. [PMID: 37285614 DOI: 10.1016/j.ultramic.2023.113760] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2022] [Revised: 03/06/2023] [Accepted: 05/13/2023] [Indexed: 06/09/2023]
Abstract
The need to acquire multiple angle-resolved electron energy loss spectra (EELS) is one of the several critical challenges associated with electron magnetic circular dichroism (EMCD) experiments. If the experiments are performed by scanning a nanometer to atomic-sized electron probe on a specific region of a sample, the precision of the local magnetic information extracted from such data highly depends on the accuracy of the spatial registration between multiple scans. For an EMCD experiment in a 3-beam orientation, this means that the same specimen area must be scanned four times while keeping all the experimental conditions same. This is a non-trivial task as there is a high chance of morphological and chemical modification as well as non-systematic local orientation variations of the crystal between the different scans due to beam damage, contamination and spatial drift. In this work, we employ a custom-made quadruple aperture to acquire the four EELS spectra needed for the EMCD analysis in a single electron beam scan, thus removing the above-mentioned complexities. We demonstrate a quantitative EMCD result for a beam convergence angle corresponding to sub-nm probe size and compare the EMCD results for different detector geometries.
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Affiliation(s)
- Hasan Ali
- Department of Materials and Environmental Chemistry, Stockholm University, 106 91 Stockholm, Sweden; Department of Materials Science and Engineering, Uppsala University, Box 534, 75121, Uppsala, Sweden.
| | | | - Cheuk-Wai Tai
- Department of Materials and Environmental Chemistry, Stockholm University, 106 91 Stockholm, Sweden
| | - Jan Rusz
- Department of Physics and Astronomy, Uppsala University, Box 516, 751 20 Uppsala, Sweden
| | - Toni Uusimaki
- Department of Materials and Environmental Chemistry, Stockholm University, 106 91 Stockholm, Sweden
| | - Björgvin Hjörvarsson
- Department of Physics and Astronomy, Uppsala University, Box 516, 751 20 Uppsala, Sweden
| | - Thomas Thersleff
- Department of Materials and Environmental Chemistry, Stockholm University, 106 91 Stockholm, Sweden
| | - Klaus Leifer
- Department of Materials Science and Engineering, Uppsala University, Box 534, 75121, Uppsala, Sweden
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Song D, Zheng F, Dunin-Borkowski RE. Prospect for measuring two-dimensional van der Waals magnets by electron magnetic chiral dichroism. Ultramicroscopy 2022; 234:113476. [PMID: 35114564 DOI: 10.1016/j.ultramic.2022.113476] [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: 11/01/2021] [Revised: 01/13/2022] [Accepted: 01/24/2022] [Indexed: 10/19/2022]
Abstract
Two-dimensional (2D) van der Waals magnets have drawn considerable attention in recent years triggered by the huge interest in novel magnetism and spintronic devices. Magnetic measurement of 2D van der Waals (vdW) magnets is crucial to understand the physical origin of magnetism in 2D limits. Therefore, advanced magnetic characterization techniques are highly required. However, only a limited number of such techniques are available due to the extremely small volume of 2D vdW magnets. Here, we introduce the electron magnetic chiral dichroism (EMCD) technique in transmission electron microscope (TEM) to measure 2D vdW crystals. In comparison with some other already-employed techniques in 2D magnets, EMCD is able to quantitatively measure magnetic parameters in three orthogonal directions at nanometer or even at atomic scale. We then perform EMCD simulations on several typical 2D vdW magnets with respect to the accelerating voltage, the number of atomic layers and beam tilt under zone axial orientation. The intensity and distribution of EMCD signals in three orthogonal directions are given in the diffraction plane, thereby providing an optimized design to achieve EMCD measurements. Finally, we discuss the signal-to-noise-ratio and required electron dose in order to obtain a measurable EMCD signal for 2D vdW magnets. Our results provide a feasibility analysis and guideline to measure 2D vdW magnets in future experiments.
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Affiliation(s)
- Dongsheng Song
- Information Materials and Intelligent Sensing Laboratory of Anhui Province, Key Laboratory of Structure and Functional Regulation of Hybrid Materials of Ministry of Education, Institutes of Physical Science and Information Technology, Anhui University, Hefei 230601, China; Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons and Peter Grünberg Institute, Forschungszentrum Jülich, Jülich 52425, Germany.
| | - Fengshan Zheng
- Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons and Peter Grünberg Institute, Forschungszentrum Jülich, Jülich 52425, Germany
| | - Rafal E Dunin-Borkowski
- Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons and Peter Grünberg Institute, Forschungszentrum Jülich, Jülich 52425, Germany
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Song D, Dunin-Borkowski RE. Three-Dimensional Measurement of Magnetic Moment Vectors Using Electron Magnetic Chiral Dichroism at Atomic Scale. PHYSICAL REVIEW LETTERS 2021; 127:087202. [PMID: 34477412 DOI: 10.1103/physrevlett.127.087202] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/23/2021] [Accepted: 07/29/2021] [Indexed: 06/13/2023]
Abstract
Here we have developed an approach of three-dimensional (3D) measurement of magnetic moment vectors in three Cartesian directions using electron magnetic chiral dichroism (EMCD) at atomic scale. Utilizing a subangstrom convergent electron beam in the scanning transmission electron microscopy (STEM), beam-position-dependent chiral electron energy-loss spectra (EELS), carrying the EMCD signals referring to magnetization in three Cartesian directions, can be obtained during the scanning across the atomic planes. The atomic resolution EMCD signals from all of three directions can be separately obtained simply by moving the EELS detector. Moreover, the EMCD signals can be remarkably enhanced using a defocused electron beam, relieving the issues of low signal intensity and signal-to-noise-ratio especially at atomic resolution. Our proposed method is compatible with the setup of the widely used atomic resolution STEM-EELS technique and provides a straightforward way to achieve 3D magnetic measurement at atomic scale on newly developing magnetic-field-free TEM.
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Affiliation(s)
- Dongsheng Song
- Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons and Peter Grünberg Institute, Forschungszentrum Jülich, 52425 Jülich, Germany
- Information Materials and Intelligent Sensing Laboratory of Anhui Province, Key Laboratory of Structure and Functional Regulation of Hybrid Materials of Ministry of Education, Institutes of Physical Science and Information Technology, Anhui University, Hefei 230601, China
| | - 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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Ali H, Rusz J, Warnatz T, Hjörvarsson B, Leifer K. Simultaneous mapping of EMCD signals and crystal orientations in a transmission electron microscope. Sci Rep 2021; 11:2180. [PMID: 33500427 PMCID: PMC7838276 DOI: 10.1038/s41598-021-81071-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2020] [Accepted: 12/17/2020] [Indexed: 11/09/2022] Open
Abstract
When magnetic properties are analysed in a transmission electron microscope using the technique of electron magnetic circular dichroism (EMCD), one of the critical parameters is the sample orientation. Since small orientation changes can have a strong impact on the measurement of the EMCD signal and such measurements need two separate measurements of conjugate EELS spectra, it is experimentally non-trivial to measure the EMCD signal as a function of sample orientation. Here, we have developed a methodology to simultaneously map the quantitative EMCD signals and the local orientation of the crystal. We analyse, both experimentally and by simulations, how the measured magnetic signals evolve with a change in the crystal tilt. Based on this analysis, we establish an accurate relationship between the crystal orientations and the EMCD signals. Our results demonstrate that a small variation in crystal tilt can significantly alter the strength of the EMCD signal. From an optimisation of the crystal orientation, we obtain quantitative EMCD measurements.
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Affiliation(s)
- Hasan Ali
- Applied Materials Science, Department of Materials Science and Engineering, Uppsala University, Box 534, 75121, Uppsala, Sweden.,Department of Electrical Engineering, Mirpur University of Science and Technology (MUST), Mirpur, 10250, AJK, Pakistan.,Department of Materials and Environmental Chemistry, Stockholm University, 10691, Stockholm, Sweden
| | - Jan Rusz
- Department of Physics and Astronomy, Uppsala University, Box 516, 75120, Uppsala, Sweden
| | - Tobias Warnatz
- Department of Physics and Astronomy, Uppsala University, Box 516, 75120, Uppsala, Sweden
| | - Björgvin Hjörvarsson
- Department of Physics and Astronomy, Uppsala University, Box 516, 75120, Uppsala, Sweden
| | - Klaus Leifer
- Applied Materials Science, Department of Materials Science and Engineering, Uppsala University, Box 534, 75121, Uppsala, Sweden.
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Thersleff T, Budnyk S, Drangai L, Slabon A. Dissecting complex nanoparticle heterostructures via multimodal data fusion with aberration-corrected STEM spectroscopy. Ultramicroscopy 2020; 219:113116. [PMID: 33032159 DOI: 10.1016/j.ultramic.2020.113116] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2020] [Revised: 08/12/2020] [Accepted: 09/13/2020] [Indexed: 01/25/2023]
Abstract
With nanostructured materials such as catalytic heterostructures projected to play a critical role in applications ranging from water splitting to energy harvesting, tailoring their properties to specific tasks requires an increasingly comprehensive characterization of their local chemical and electronic landscape. Although aberration-corrected electron spectroscopy currently provides sufficient spatial resolution to study this space, an approach to concurrently dissect both the electronic structure and full composition of buried metal/oxide interfaces remains a considerable challenge. In this manuscript, we outline a statistical methodology to jointly analyze simultaneously-acquired STEM EELS and EDX datasets by fusing them along their shared spatial factors. We show how this procedure can be used to derive a rich descriptive model for estimating both transition metal valency and full chemical composition from encapsulated morphologies such as core-shell nanoparticles. We demonstrate this on a heterogeneous Co-P thin film catalyst, concluding that this system is best described as a multi-shell phosphide structure with a P-doped metallic Co core.
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Affiliation(s)
- Thomas Thersleff
- Stockholm University, Department of Materials and Environmental Chemistry, Stockholm 10691, Sweden.
| | - Serhiy Budnyk
- Austrian Centre of Competence for Tribology, AC2T research GmbH, Viktor-Kaplan-Straße 2, Wr. Neustadt, 2700, Austria
| | - Larissa Drangai
- Austrian Centre of Competence for Tribology, AC2T research GmbH, Viktor-Kaplan-Straße 2, Wr. Neustadt, 2700, Austria
| | - Adam Slabon
- Stockholm University, Department of Materials and Environmental Chemistry, Stockholm 10691, Sweden
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