Regensburg 2025 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 29: 2D Materials: Electronic Structure and Exitations II (joint session O/HL/TT)
TT 29.1: Vortrag
Mittwoch, 19. März 2025, 10:30–10:45, H11
The Bell-Shaped Component in Diffraction from 2D Materials — •Birk Finke1, Christian Brand1, Karim Omambac1,2, Pascal Dreher1, Hannah Kohler1, Frank-J. Meyer zu Heringdorf1,3,4, and Michael Horn-von Hoegen1,3 — 1Universität Duisburg-Essen — 2Polytechnique Montréal Canada — 3Center for Nanointegration Duisburg-Essen — 4Interdisciplinary Center for Analytics on the Nanoscale
In 2D materials, the formation of moiré superlattices with graphene or hBN on crystalline surfaces alters electronic, vibrational, and chemical properties. Here we analysed an unusual broad diffraction background observed in low energy electron diffraction from 2D material systems, which is called the bell-shaped component (BSC). Employing SPA-LEED, LEEM, and µ-LEED we propose the origin to be the inelastic scattering of the low energy electrons at the vertically polarized ZA-phonons of the weakly bound graphene and hBN layers on Ir(111) and SiC(0001). For these systems the ZA-phonon branch exhibits a parabolic dispersion with a finite phonon frequency of a few meV at the Γ point. This results in a high phonon density at low energy, but high momentum causing the strong intensity of the BSC in diffraction. In the framework of kinematic scattering theory, we performed simulations of the inelastic diffuse scattering which quantitively confirm our proposal.
Keywords: Graphene; Diffraction; Phonon