1
|
Stöger-Pollach M, Ederer M. Experimental evidence of magnetism in a 2D electron gas at the CoO/Co 3O 4 interface by employing EMCD. Micron 2024; 185:103687. [PMID: 39053049 DOI: 10.1016/j.micron.2024.103687] [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: 03/19/2024] [Revised: 06/25/2024] [Accepted: 06/26/2024] [Indexed: 07/27/2024]
Abstract
In the present study we investigate the CoO/Co3O4 interface in order to determine its intriguing magnetic behavior, which can be utilized for tailoring magnetic properties, enabling spin transport, enhancing magnetic coupling, tuning device functionalities, and realizing miniaturized magnetic devices for various technological applications. We decipher the magnetic properties of the CoO/Co3O4 interface from first principles calculations using Wien2k and probe them experimentally by employing electron energy-loss magnetic chiral dichroism (EMCD), which is an electron-energy loss spectrometry (EELS) based technique in the transmission electron microscope (TEM). Both, theory and experiment, are in perfect agreement and result in a ferromagnetic 2D-electron gas of 5Å thickness directly at the interface.
Collapse
Affiliation(s)
- Michael Stöger-Pollach
- University Service Center for Transmission Electron Microscopy (USTEM), Technische Universität Wien, Wiedner Hauptstraße 8-10, Wien 1040, Austria; Institute of Solid State Physics, Technische Universität Wien, Wiedner Hauptstraße 8-10, Wien 1040, Austria.
| | - Manuel Ederer
- University Service Center for Transmission Electron Microscopy (USTEM), Technische Universität Wien, Wiedner Hauptstraße 8-10, Wien 1040, Austria; Institute of Solid State Physics, Technische Universität Wien, Wiedner Hauptstraße 8-10, Wien 1040, Austria
| |
Collapse
|
2
|
Del-Pozo-Bueno D, Kepaptsoglou D, Ramasse QM, Peiró F, Estradé S. Machine Learning Data Augmentation Strategy for Electron Energy Loss Spectroscopy: Generative Adversarial Networks. MICROSCOPY AND MICROANALYSIS : THE OFFICIAL JOURNAL OF MICROSCOPY SOCIETY OF AMERICA, MICROBEAM ANALYSIS SOCIETY, MICROSCOPICAL SOCIETY OF CANADA 2024; 30:278-293. [PMID: 38684097 DOI: 10.1093/mam/ozae014] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/29/2023] [Revised: 08/01/2023] [Accepted: 02/12/2024] [Indexed: 05/02/2024]
Abstract
Recent advances in machine learning (ML) have highlighted a novel challenge concerning the quality and quantity of data required to effectively train algorithms in supervised ML procedures. This article introduces a data augmentation (DA) strategy for electron energy loss spectroscopy (EELS) data, employing generative adversarial networks (GANs). We present an innovative approach, called the data augmentation generative adversarial network (DAG), which facilitates data generation from a very limited number of spectra, around 100. Throughout this study, we explore the optimal configuration for GANs to produce realistic spectra. Notably, our DAG generates realistic spectra, and the spectra produced by the generator are successfully used in real-world applications to train classifiers based on artificial neural networks (ANNs) and support vector machines (SVMs) that have been successful in classifying experimental EEL spectra.
Collapse
Affiliation(s)
- Daniel Del-Pozo-Bueno
- LENS-MIND, Departament d'Enginyeria Electrònica i Biomèdica, Universitat de Barcelona, 1-11 Martí i Franquès, 08028 Barcelona, Spain
- Institute of Nanoscience and Nanotechnology (IN2UB), Universitat de Barcelona, 1-11 Martí i Franquès, 08028 Barcelona, Spain
| | - Demie Kepaptsoglou
- SuperSTEM Laboratory, Sci-Tech Daresbury Campus, Keckwick Lane, Daresbury WA4 4AD, UK
- School of Physics, Engineering and Technology, University of York, Newton way, YO10 5DD Heslington, UK
| | - Quentin M Ramasse
- SuperSTEM Laboratory, Sci-Tech Daresbury Campus, Keckwick Lane, Daresbury WA4 4AD, UK
- Schools of Chemical and Process Engineering & Physics and Astronomy, Woodhouse Lane, University of Leeds, LS2 9JT Leeds, UK
| | - Francesca Peiró
- LENS-MIND, Departament d'Enginyeria Electrònica i Biomèdica, Universitat de Barcelona, 1-11 Martí i Franquès, 08028 Barcelona, Spain
- Institute of Nanoscience and Nanotechnology (IN2UB), Universitat de Barcelona, 1-11 Martí i Franquès, 08028 Barcelona, Spain
| | - Sònia Estradé
- LENS-MIND, Departament d'Enginyeria Electrònica i Biomèdica, Universitat de Barcelona, 1-11 Martí i Franquès, 08028 Barcelona, Spain
- Institute of Nanoscience and Nanotechnology (IN2UB), Universitat de Barcelona, 1-11 Martí i Franquès, 08028 Barcelona, Spain
| |
Collapse
|
3
|
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.
Collapse
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
| |
Collapse
|
4
|
Del-Pozo-Bueno D, Kepaptsoglou D, Peiró F, Estradé S. Comparative of machine learning classification strategies for electron energy loss spectroscopy: Support vector machines and artificial neural networks. Ultramicroscopy 2023; 253:113828. [PMID: 37556961 DOI: 10.1016/j.ultramic.2023.113828] [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: 04/25/2023] [Revised: 07/26/2023] [Accepted: 08/02/2023] [Indexed: 08/11/2023]
Abstract
Machine Learning (ML) strategies applied to Scanning and conventional Transmission Electron Microscopy have become a valuable tool for analyzing the large volumes of data generated by various S/TEM techniques. In this work, we focus on Electron Energy Loss Spectroscopy (EELS) and study two ML techniques for classifying spectra in detail: Support Vector Machines (SVM) and Artificial Neural Networks (ANN). Firstly, we systematically analyze the optimal configurations and architectures for ANN classifiers using random search and the tree-structured Parzen estimator methods. Secondly, a new kernel strategy is introduced for the soft-margin SVMs, the cosine kernel, which offers a significant advantage over the previously studied kernels and other ML classification strategies. This kernel allows us to bypass the normalization of EEL spectra, achieving accurate classification. This result is highly relevant for the EELS community since we also assess the impact of common normalization techniques on our spectra using Uniform Manifold Approximation and Projection (UMAP), revealing a strong bias introduced in the spectra once normalized. In order to evaluate and study both classification strategies, we focus on determining the oxidation state of transition metals through their EEL spectra, examining which feature is more suitable for oxidation state classification: the oxygen K peak or the transition metal white lines. Subsequently, we compare the resistance to energy loss shifts for both classifiers and present a strategy to improve their resistance. The results of this study suggest the use of soft-margin SVMs for simpler EELS classification tasks with a limited number of spectra, as they provide performance comparable to ANNs while requiring lower computational resources and reduced training times. Conversely, ANNs are better suited for handling complex classification problems with extensive training data.
Collapse
Affiliation(s)
- Daniel Del-Pozo-Bueno
- Departament d'Enginyeria Electrònica i Biomèdica, LENS-MIND, Universitat de Barcelona, Barcelona 08028, Spain; Institute of Nanoscience and Nanotechnology (IN2UB), Universitat de Barcelona, Barcelona 08028, Spain.
| | - Demie Kepaptsoglou
- SuperSTEM, Sci-Tech Daresbury Campus, Daresbury WA4 4AD, UK; School of Physics, Engineering and Technology, University of York, Heslington YO10 5DD, UK
| | - Francesca Peiró
- Departament d'Enginyeria Electrònica i Biomèdica, LENS-MIND, Universitat de Barcelona, Barcelona 08028, Spain; Institute of Nanoscience and Nanotechnology (IN2UB), Universitat de Barcelona, Barcelona 08028, Spain
| | - Sònia Estradé
- Departament d'Enginyeria Electrònica i Biomèdica, LENS-MIND, Universitat de Barcelona, Barcelona 08028, Spain; Institute of Nanoscience and Nanotechnology (IN2UB), Universitat de Barcelona, Barcelona 08028, Spain
| |
Collapse
|
5
|
Golosovsky IV, Kibalin IA, Gukasov A, Roca AG, López-Ortega A, Estrader M, Vasilakaki M, Trohidou KN, Hansen TC, Puente-Orench I, Lelièvre-Berna E, Nogués J. Elucidating Individual Magnetic Contributions in Bi-Magnetic Fe 3 O 4 /Mn 3 O 4 Core/Shell Nanoparticles by Polarized Powder Neutron Diffraction. SMALL METHODS 2023; 7:e2201725. [PMID: 37391272 DOI: 10.1002/smtd.202201725] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/31/2022] [Revised: 05/10/2023] [Indexed: 07/02/2023]
Abstract
Heterogeneous bi-magnetic nanostructured systems have had a sustained interest during the last decades owing to their unique magnetic properties and the wide range of derived potential applications. However, elucidating the details of their magnetic properties can be rather complex. Here, a comprehensive study of Fe3 O4 /Mn3 O4 core/shell nanoparticles using polarized neutron powder diffraction, which allows disentangling the magnetic contributions of each of the components, is presented. The results show that while at low fields the Fe3 O4 and Mn3 O4 magnetic moments averaged over the unit cell are antiferromagnetically coupled, at high fields, they orient parallel to each other. This magnetic reorientation of the Mn3 O4 shell moments is associated with a gradual evolution with the applied field of the local magnetic susceptibility from anisotropic to isotropic. Additionally, the magnetic coherence length of the Fe3 O4 cores shows some unusual field dependence due to the competition between the antiferromagnetic interface interaction and the Zeeman energies. The results demonstrate the great potential of the quantitative analysis of polarized neutron powder diffraction for the study of complex multiphase magnetic materials.
Collapse
Affiliation(s)
- I V Golosovsky
- National Research Center "Kurchatov Institute", B. P. Konstantinov Petersburg Nuclear Physics Institute, Gatchina, 188300, Russia
| | - I A Kibalin
- Laboratoire Léon Brillouin, CEA-CNRS, CE-Saclay, Gif-sur-Yvette, 91191, France
| | - A Gukasov
- Laboratoire Léon Brillouin, CEA-CNRS, CE-Saclay, Gif-sur-Yvette, 91191, France
| | - A G Roca
- Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and BIST, Campus UAB, Bellaterra, Barcelona, 08193, Spain
| | - A López-Ortega
- Departamento de Ciencias, Universidad Pública de Navarra, Pamplona, 31006, Spain
- Institute for Advanced Materials and Mathematics INAMAT2, Universidad Pública de Navarra, Pamplona, 31006, Spain
| | - M Estrader
- Departament de Química Inorgànica i Orgànica, carrer Martí i Franqués 1-11, Universitat de Barcelona, Barcelona, 08028, Spain
- Institut de Nanociència i Nanotecnologia IN2UB, carrer Martí i Franqués 1-11, Universitat de Barcelona, Barcelona, 08028, Spain
| | - M Vasilakaki
- Institute of Nanoscience and Nanotechnology, NCSR "Demokritos", 153 10, Agia Paraskevi, Attiki, 15310, Greece
| | - K N Trohidou
- Institute of Nanoscience and Nanotechnology, NCSR "Demokritos", 153 10, Agia Paraskevi, Attiki, 15310, Greece
| | - T C Hansen
- Institut Laue Langevin, 71 avenue des Martyrs, Grenoble, 38000, France
| | - I Puente-Orench
- Institut Laue Langevin, 71 avenue des Martyrs, Grenoble, 38000, France
- Instituto de NanoCiencia y Materiales de Aragón, Zaragoza, 50009, Spain
| | - E Lelièvre-Berna
- Institut Laue Langevin, 71 avenue des Martyrs, Grenoble, 38000, France
| | - J Nogués
- Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and BIST, Campus UAB, Bellaterra, Barcelona, 08193, Spain
- ICREA, Barcelona, 08010, Spain
| |
Collapse
|
6
|
Lavorato GC, de Almeida AA, Vericat C, Fonticelli MH. Redox phase transformations in magnetite nanoparticles: impact on their composition, structure and biomedical applications. NANOTECHNOLOGY 2023; 34:192001. [PMID: 36825776 DOI: 10.1088/1361-6528/acb943] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/08/2022] [Accepted: 02/06/2023] [Indexed: 06/18/2023]
Abstract
Magnetite nanoparticles (NPs) are one of the most investigated nanomaterials so far and modern synthesis methods currently provide an exceptional control of their size, shape, crystallinity and surface functionalization. These advances have enabled their use in different fields ranging from environmental applications to biomedicine. However, several studies have shown that the precise composition and crystal structure of magnetite NPs depend on their redox phase transformations, which have a profound impact on their physicochemical properties and, ultimately, on their technological applications. Although the physical mechanisms behind such chemical transformations in bulk materials have been known for a long time, experiments on NPs with large surface-to-volume ratios have revealed intriguing results. This article is focused on reviewing the current status of the field. Following an introduction on the fundamental properties of magnetite and other related iron oxides (including maghemite and wüstite), some basic concepts on the chemical routes to prepare iron oxide nanomaterials are presented. The key experimental techniques available to study phase transformations in iron oxides, their advantages and drawbacks to the study of nanomaterials are then discussed. The major section of this work is devoted to the topotactic oxidation of magnetite NPs and, in this regard, the cation diffusion model that accounts for the experimental results on the kinetics of the process is critically examined. Since many synthesis routes rely on the formation of monodisperse magnetite NPs via oxidation of wüstite counterparts, the modulation of their physical properties by crystal defects arising from the oxidation process is also described. Finally, the importance of a precise control of the composition and structure of magnetite-based NPs is discussed and its role in their biomedical applications is highlighted.
Collapse
Affiliation(s)
- Gabriel C Lavorato
- Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA), Facultad de Ciencias Exactas, Universidad Nacional de La Plata, C. C. 16, Suc. 4, 1900 La Plata, Argentina
| | - Adriele A de Almeida
- Instituto de Física 'Gleb Wataghin' (IFGW), Universidade Estadual de Campinas-UNICAMP, R. Sérgio Buarque de Holanda, 777-CEP: 13083-859, Campinas - SP, Brazil
| | - Carolina Vericat
- Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA), Facultad de Ciencias Exactas, Universidad Nacional de La Plata, C. C. 16, Suc. 4, 1900 La Plata, Argentina
| | - Mariano H Fonticelli
- Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA), Facultad de Ciencias Exactas, Universidad Nacional de La Plata, C. C. 16, Suc. 4, 1900 La Plata, Argentina
| |
Collapse
|