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Dresden 2017 – scientific programme

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O: Fachverband Oberflächenphysik

O 86: Graphene: Electronic Properties, Structure and Substrate Interaction I

O 86.4: Talk

Thursday, March 23, 2017, 11:15–11:30, WIL A317

Observation of photoemission "dark lines" for Ir(111) and graphene/Ir(111) via high-resolution ToF k-microscopy — •Anna Zaporozhchenko-Zymaková1,2, Dmytro Kutnyakhov1,3, Katerina Medjanik1, Christian Tusche4, Olena Fedchenko1, Sergey Chernov1, Martin Ellguth1, Sergej A. Nepijko1, Hans-Joachim Elmers1,2, and Gerd Schönhense1,21Inst. für Physik, Univ. Mainz — 2MAINZ graduate school — 3DESY, Hamburg — 4PGI-6, Forschungszentrum Jülich

ToF k-microscopy [1,2] has been used to analyze emergent photoelectron diffraction effects for UHV/Ir(111) and graphene/Ir(111). We observed a regular pattern of dark lines with circular shape and six-fold symmetry that have been overlooked in previous experiments. Quantitative evaluation along with a model calculation reveals that electrons initially located within the first Brillouin zone can with finite probability be scattered by a reciprocal lattice vector into a state that propagates parallel to the surface. Such electrons vanish due to inelastic scattering events in the vicinity of the surface. This leads to a reduced intensity observed as dark lines. The relevant reciprocal lattice vector corresponds to the lattice of the topmost layer (in our case Ir or graphene). The dark lines appear in a certain photon energy range satisfying the congruence of lattice constant and wavelength. The parallel momentum of the dark lines decreases with increasing photon energy in agreement with the model. The effect has been observed with both p- and s-polarized light at BESSY II (10m NIM). [1] Chernov et al., Ultramic. 159, 453 (2015); [2] Tusche et al., APL 108, 261602 (2016).

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