Circular dichroism in hard X-ray photoelectron diffraction observed by time-of-flight momentum microscopy

O Tkach; T-P Vo; O Fedchenko; K Medjanik; Y Lytvynenko; S Babenkov; D Vasilyev; Q L Nguyen; T R F Peixoto; A Gloskowskii; C Schlueter; S Chernov; M Hoesch; D Kutnyakhov; M Scholz; L Wenthaus; N Wind; S Marotzke; A Winkelmann; K Rossnagel; J Minár; H-J Elmers; G Schönhense

doi:10.1016/j.ultramic.2023.113750

Circular dichroism in hard X-ray photoelectron diffraction observed by time-of-flight momentum microscopy

Ultramicroscopy. 2023 Aug:250:113750. doi: 10.1016/j.ultramic.2023.113750. Epub 2023 May 6.

Authors

O Tkach¹, T-P Vo², O Fedchenko³, K Medjanik³, Y Lytvynenko⁴, S Babenkov³, D Vasilyev³, Q L Nguyen⁵, T R F Peixoto⁶, A Gloskowskii⁶, C Schlueter⁶, S Chernov⁶, M Hoesch⁶, D Kutnyakhov⁶, M Scholz⁶, L Wenthaus⁶, N Wind⁷, S Marotzke⁸, A Winkelmann⁹, K Rossnagel⁸, J Minár², H-J Elmers³, G Schönhense³

Affiliations

¹ Johannes Gutenberg-Universität, Institut für Physik, 55128 Mainz, Germany; Sumy State University, Rymskogo-Korsakova 2, 40007 Sumy, Ukraine. Electronic address: tkachole@uni-mainz.de.
² New Technologies - Research Centre, Univ. of West Bohemia, 30100 Pilsen, Czech Republic.
³ Johannes Gutenberg-Universität, Institut für Physik, 55128 Mainz, Germany.
⁴ Johannes Gutenberg-Universität, Institut für Physik, 55128 Mainz, Germany; Institute of Magnetism of the NAS of Ukraine and MES of Ukraine, 03142 Kyiv, Ukraine.
⁵ Linac Coherent Light Source, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA.
⁶ Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany.
⁷ Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany; Institut für Experimentalphysik, Universität Hamburg, 22761 Hamburg, Germany.
⁸ Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany; Institut für Experimentelle und Angewandte Physik, Christian-Albrechts-Universität zu Kiel, 24098 Kiel, Germany.
⁹ Academic Centre for Materials and Nanotechn., Univ. of Science and Technology, Kraków, Poland.

PMID: 37178606
DOI: 10.1016/j.ultramic.2023.113750

Abstract

X-ray photoelectron diffraction (XPD) is a powerful technique that yields detailed structural information of solids and thin films that complements electronic structure measurements. Among the strongholds of XPD we can identify dopant sites, track structural phase transitions, and perform holographic reconstruction. High-resolution imaging of k_ll-distributions (momentum microscopy) presents a new approach to core-level photoemission. It yields full-field k_x-k_y XPD patterns with unprecedented acquisition speed and richness in details. Here, we show that beyond the pure diffraction information, XPD patterns exhibit pronounced circular dichroism in the angular distribution (CDAD) with asymmetries up to 80%, alongside with rapid variations on a small k_ll-scale (0.1 Å^-1). Measurements with circularly-polarized hard X-rays (hν = 6 keV) for a number of core levels, including Si, Ge, Mo and W, prove that core-level CDAD is a general phenomenon that is independent of atomic number. The fine structure in CDAD is more pronounced compared to the corresponding intensity patterns. Additionally, they obey the same symmetry rules as found for atomic and molecular species, and valence bands. The CD is antisymmetric with respect to the mirror planes of the crystal, whose signatures are sharp zero lines. Calculations using both the Bloch-wave approach and one-step photoemission reveal the origin of the fine structure that represents the signature of Kikuchi diffraction. To disentangle the roles of photoexcitation and diffraction, XPD has been implemented into the Munich SPRKKR package to unify the one-step model of photoemission and multiple scattering theory.