Preprint FZJ-2025-02297

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Solving the Phase Problem of Diffraction:X-ray Standing Waves Imaging on Bismuthene/SiC(0001)

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2025

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Abstract: The phase retrieval problem is a fundamental shortcoming of all diffraction-based methods, arising from theinability to measure the phase of scattered waves. The (normal incidence) X-ray standing wave (NIXSW) techniquecircumvents this issue by introducing a (Bragg-generated) X-ray standing wave field throughout the sample, rela-tive to which any atomic species can be localized by probing its fluorescence or photoelectron yield. In essence,in a single measurement the complex scattering factor (i.e., its amplitude and phase) corresponding to the usedBragg reflection is determined. Performing this for multiple Bragg reflections enables one to reconstruct the scat-tering density of the sample in three dimensions, straightforwardly as the Fourier sum of all measured (complex)scattering factors. Here, we utilize this technique to reveal the structural key features involved in the formation ofthe quantum spin Hall insulator bismuthene on silicon carbide. In this prominent example, the two-dimensional Bilayer is confined between a 4H-SiC substrate crystal and an epitaxial graphene layer. The key finding is a changein the adsorption site of the Bi atoms underneath the graphene upon hydrogenation, caused by the H-saturation ofone (out of three) Si dangling bonds per unit cell. This structural change, clearly revealed by our NIXSW imagingexperiment, is the key feature leading to the formation of the characteristic band structure of the 2D bismuthenehoneycomb.


Contributing Institute(s):
  1. Quantum Nanoscience (PGI-3)
Research Program(s):
  1. 5213 - Quantum Nanoscience (POF4-521) (POF4-521)
  2. SFB 1083 A12 - Struktur und Anregungen von hetero-epitaktischen Schichtsystemen aus schwach wechselwirkenden 2D-Materialien und molekularen Schichten (A12) (385975694) (385975694)

Appears in the scientific report 2025
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 Datensatz erzeugt am 2025-04-16, letzte Änderung am 2025-04-23



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