Berlin 2024 – scientific programme

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O: Fachverband Oberflächenphysik

O 26: Focus Session: Spin Phenomena in Chiral Molecular Systems I (joint session O/TT)

O 26.4: Talk

Tuesday, March 19, 2024, 12:00–12:15, MA 141

Spin-Resolved Photoemission Studies of Heptahelicene and Tetrapyrrole (Sub-)Monolayers — •Paul V. Möllers¹, Bianca C. Baciu², Rafael Rodriguez³, Johannes Seibel⁴, Adrian J. Urban⁵, Albert Guijarro², Jeanne Crassous³, Karl-Heinz Ernst⁴, Hiroshi M. Yamamoto⁵, and Helmut Zacharias¹ — ¹Center for Soft Nanoscience (SoN), Univ. Münster, Germany — ²Inst. Universitario de Síntesis Orgánica, Univ. de Alicante, Spain — ³Univ. of Rennes, CNRS, Inst. des Sciences Chimiques de Rennes (ISCR), France — ⁴Eidgenössische Materialprüfungs- und Forschungsanstalt (EMPA), Swiss Federal Laboratories for Materials Science and Technology, Switzerland — ⁵Inst. for Molecular Science, Research Center of Integrative Molecular Systems, Japan

We present recent results of spin-resolved photoemission studies [1] performed with layers of dithia-heptahelicene molecules [2]. A photoelectron spin polarization (SP) of more than |P| = 30% was measured at full monolayer (ML) coverage. The SP was furthermore measured at varying submonolayer coverages to probe the role of cooperative effects in its emergence. Indeed, a sharp, nonlinear increase of the SP was found at high surface coverages above 80% of a ML. We interpret this behavior not as a direct effect of intermolecular interactions on CISS, but argue that it is mediated through a phase transition in the molecular ordering within the ML. Similar measurements were performed with layers of helical tetrapyrrole complexes. [1] Möllers et al., Isr. J. Chem. 2022, 62, e202200062 [2] Baciu et al., Nanoscale Adv. 2020, 2, 1921 [3] Urban et al., Chem. Eur. J. 2023, 29, e202300940

Keywords: CISS; helicene; photoemission; Mott; monolayer