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Influence of non-dipole trnasitions on the extraction of EMCD
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
2019 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

ELNES-spectra of the L3 and L2-edge of bcc-iron are simulated using a Bloch wave method for the calculation of the DDSCS within a 1st-order Born approximation of the inelastic electron scattering process in order to study the influence of non-dipole terms on the EMCD-signal. The necessary electronic structure information is obtained from a DFT-calculation using WIEN2k.Two different different ways of extracting the EMCD-signal are considered: the pEMCD-signal, which is extracted from the pure imaginary part of the MDFF, and the eEMCD-signal, extracted via an EMCD difference method.A non-negligible contribution of the 13 cross term to the eEMCD-signal is found. Furthermore it is shown that the double difference method and the single left-right difference method cancel out the contributions of the 01-term to the eEMCD-signal. The pEMCD-signal is found to be influenced by non-dipole terms only for large scattering angles. Conclusive quantitative results on the influence of non-dipole contributions to the eEMCD-signal remain to be found, however, since it is uncovered that the eEMCD-signal is strongly disturbed by the choice of the post-edge normalization range due to the inaccurate description of the post-edge region in the present simulation. Furthermore a not anticipated "apparent anisotropy" of the real part of the MDFF is found, whose cause is presently unknown.As a byproduct of these investigations deeper insight is gained on a reason, why the double difference method is superior to the other extraction methods. It practically eliminates the effect of non-dipole terms 01 and 12.Lastly two effects are encountered that might pave the way to a deeper understanding of why the L2-edge is experimentally often observed to be weakened or suppressed relative to the L3-edge in comparison with simulations.

Place, publisher, year, edition, pages
2019. , p. 66
Series
FYSAST ; FYSMAS1084
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:uu:diva-373757OAI: oai:DiVA.org:uu-373757DiVA, id: diva2:1279442
Educational program
Master Programme in Physics
Presentation
2018-12-13, Ångströmlaboratoriet, Fakultetsrummet Å1203, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Supervisors
Examiners
Available from: 2019-02-04 Created: 2019-01-16 Last updated: 2019-02-04Bibliographically approved

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