Regensburg 2019 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 9: Instrumentation Micro-/Nano-Analysis and Lithography/Structuring: Invited Talk Leo Gross (joint session KFM/DS/O)

O 9.3: Vortrag

Montag, 1. April 2019, 15:50–16:10, PHY 5.0.21

Hard X-ray Photoelectron Diffraction in Graphite — •Olena Fedchenko¹, Sergey Chernov¹, Katerina Medjanik¹, Sergey Babenkov¹, Dmitry Vasilyev¹, Aimo Winkelmann², Hans-Joachim Elmers¹, and Gerd Schönhense¹ — ¹JGU, Institut für Physik, Mainz — ²Laser Zentrum, Hannover

A new high-energy momentum microscope (kinetic energies up to >7 keV) allows full-field imaging of the (k_x-k_y) photoelectron distribution with a large field of view (up to 20 Å⁻¹ dia.) in momentum space and ToF energy recording. Avoiding symmetry-varying rotation of sample and/or analyser, "full-field k-imaging" provides an ideal means for X-ray photoelectron diffraction (XPD) studies. High-resolution (< 0.1^∘) diffractograms can be recorded within minutes thanks to the high brilliance of beamline P22 at PETRA III [1]. We present an XPD study for electrons from the C 1s core level in graphite in a wide energy range from 2840 to 7283 eV. Fine details in the diffractograms reflect the large number of scatterers (10⁵-10⁶) due to the large inelastic mean free path. A calculation based on the Bloch wave approach to electron diffraction by lattice planes [2] shows excellent agreement. The short photoelectron wavelength (10% of the interatomic distance) "amplifies" phase differences and turns hard X-ray XPD into a very sensitive structural tool. The results are important for valence band XPD [3].

[1] C. Schlueter et al., Synchr. Radiation News 31, 29 (2018); [2] A. Winkelmann et al., New J. of Phys. 10, 113002 (2008); [3] G. Schönhense et al., arXiv 1806.05871 (2018).