Dresden 2017 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 66: Graphene: Electronic Properties, Structure and Substrate Interaction I (joint session DY, DS, HL, MA, O, TT, organized by O)

TT 66.4: 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-Zymaková^1,2, Dmytro Kutnyakhov^1,3, Katerina Medjanik¹, Christian Tusche⁴, Olena Fedchenko¹, Sergey Chernov¹, Martin Ellguth¹, Sergej A. Nepijko¹, Hans-Joachim Elmers^1,2, and Gerd Schönhense^1,2 — ¹Inst. 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).