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Localization of magnetic circular dichroic spectra in transmission electron microscopy experiments with atomic plane resolution
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.ORCID iD: 0000-0002-0074-1349
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
Nagoya Univ, Inst Mat & Syst Sustainabil, Adv Measurement Technol Ctr, Electron Nanoscopy Sect,Chikusa Ku, Furo Cho, Nagoya, Aichi 4648603, Japan..
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences. Stockholm Univ, Dept Mat & Environm Chem, Svante Arrhenius Vag 16C, S-10691 Stockholm, Sweden..
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2017 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, no 17, article id 174412Article in journal (Refereed) Published
Abstract [en]

Inelastic electron scattering is a consequence of mostly Coulomb interaction between electrons in the sample and electron beam and, as such, it is a nonlocal event. In atomic resolution experiments, it thus opens the following question: How far is the origin of the inelastic scattering signal that is observed when the electron beam is passing nearby an atomic column or plane? We analyze computationally the delocalization of the magnetic signal in electron magnetic circular dichroism (EMCD) experiments in the so-called three-beam orientation, allowing one to image individual atomic planes. We compare the classical EMCD setup using the double-difference procedure (DD-EMCD) to a recently introduced atomic plane resolution EMCD (APR-EMCD) geometry, assuming the same probe size. We observe a strong localization of the EMCD signal to the closest atomic plane, confirming the potential of EMCD to study an evolution of magnetic properties near surfaces or interfaces with atomic plane resolution. The localization of the EMCD signal is remarkably higher than the localization of the nonmagnetic component of the inelastic scattering cross section. We also analyze double-channeling effects and find them particularly strong for the DD-EMCD method, while for APR-EMCD they appear to be minor. The DD-EMCD signal, on the other hand, appears to be more robust with respect to sample thickness than that of the APR-EMCD.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC , 2017. Vol. 95, no 17, article id 174412
National Category
Physical Sciences Engineering and Technology
Identifiers
URN: urn:nbn:se:uu:diva-325336DOI: 10.1103/PhysRevB.95.174412ISI: 000401223700004OAI: oai:DiVA.org:uu-325336DiVA, id: diva2:1118234
Funder
Swedish Research CouncilGöran Gustafsson Foundation for Research in Natural Sciences and Medicine
Available from: 2017-06-30 Created: 2017-06-30 Last updated: 2018-04-11Bibliographically approved
In thesis
1. Signal Processing Tools for Electron Microscopy
Open this publication in new window or tab >>Signal Processing Tools for Electron Microscopy
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The detection of weak signals in noisy data is a problem which occurs across various disciplines. Here, the signal of interest is the spectral signature of the electron magnetic chiral dichroism (EMCD) effect. In principle, EMCD allows for the measurement of local magnetic structures in the electron microscope, its spatial resolution, versatility and low hardware requirements giving it an eminent position among competing measurement techniques. However, experimental shortcomings as well as intrinsically low signal to noise ratio render its measurement challenging to the present day.   

This thesis explores how posterior data processing may aid the analysis of various data from the electron microscope. Following a brief introduction to different signals arising in the microscope and a yet briefer survey of the state of the art of EMCD measurements, noise removal strategies are presented. Afterwards, gears are shifted to discuss the separation of mixed signals into their physically meaningful source components based on their assumed mathematical characteristics, so called blind source separation (BSS).    

A data processing workflow for detecting weak signals in noisy spectra is derived from these considerations, ultimately culminating in several demonstrations of the extraction of EMCD signals. While the focus of the thesis does lie on data processing strategies for EMCD detection, the approaches presented here are similarly applicable in other situations. Related topics such as the general analysis of hyperspectral images using BSS methods or the fast analysis of large data sets are also discussed.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2018. p. 60
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1672
National Category
Physical Sciences Computer Sciences Other Mathematics
Identifiers
urn:nbn:se:uu:diva-348264 (URN)978-91-513-0345-1 (ISBN)
Public defence
2018-06-12, Å2001, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:00 (English)
Opponent
Supervisors
Available from: 2018-05-18 Created: 2018-04-11 Last updated: 2018-05-18

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Rusz, JanSpiegelberg, JakobLeifer, KlausOppeneer, Peter M.

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