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Regensburg 2022 – scientific programme

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O: Fachverband Oberflächenphysik

O 9: Ultrafast Electron Dynamics at Surfaces and Interfaces 2

O 9.6: Talk

Monday, September 5, 2022, 16:15–16:30, H3

Influence of carbon buffer layer on non-equilibrium carrier dynamics of epitaxial graphene and WS2/graphene heterostructures — •Lukas Bruckmeier1, Niklas Hofmann1, Leonard Weigl1, Johannes Gradl1, Neeraj Mishra2,3, Stiven Forti2, Camilla Coletti2,3, and Isabella Gierz11Faculty for Physics, University of Regensburg, Regensburg, Germany — 2Center for Nanotechnology Innovation@NEST, Istituto Italiano di Tecnologia, Pisa, Italy — 3Graphene Labs, Istituto Italiano di Tecnologia, Genova, Italy

The non-equilibrium photocarrier dynamics of epitaxial graphene on SiC(0001) have been studied in detail in the past. The fact that the graphene layer rests on a second two-dimensional carbon buffer layer (BL) - the well-known (6√3×6√3)R30 reconstruction - was believed to be of minor importance for the interpretation of the time-resolved data. We use time- and angle-resolved photoemission spectroscopy to show that photoexcitation of the graphene/BL heterostructure is followed by a short-lived transient decrease in binding energy of the Dirac cone indicating a transient charging of the graphene layer with excess electrons. We attribute the transient n-doping of the graphene layer to the resonant excitation of a direct electronic transition between the non-dispersive states of the BL located 0.5eV below the Fermi level and the Dirac cone. We further show that this direct electronic transition affects the charge transfer dynamics in epitaxial WS2/graphene/BL heterostructures.

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