Synthese, strukturelle Eigenschaften und Magnetismus neuartiger graphen-basierter Materialien

• Antragsteller: Professor Dr. Clemens Laubschat
• Fachliche Zuordnung: Experimentelle Physik der kondensierten Materie ; Physikalische Chemie von Festkörpern und Oberflächen, Materialcharakterisierung
• Förderung: Förderung von 2017 bis 2022
• Projektkennung: Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 321825916

• Erstellungsjahr: 2021

Zusammenfassung der Projektergebnisse

In the present project, we have dealt with epitaxial monolayers of pristine and B-doped graphene as well as of h-BN on Co(0001) surfaces. Corresponding thin films could be prepared "in situ" by CVD and were investigated by photoemission, PED, LEED, PEEM, STM and accompanying DFT calculations. Pristine graphene/Co(0001) shows a spinpolarized "mini cone" with majority spin near the Fermi energy and a Fermi surface largely characterized by minority spin states. B-doping shifts the "mini cone" to lower binding energies and produces a triangular spin-polarized Fermi surface around the K point. h-BN behaves metal-like on Co in contrast to the well-known behaviour of a free-standing h-BN layer, with finite density of states at the Fermi energy caused by admixtures of B and N orbitals to the 3d bands of the substrate. In both B-graphene and h-BN, the boron atoms predominantly occupy hollow sites of the Co(0001) substrate and thus a well-defined carbon sublattice, leading in the case of freestanding B-graphene layers to the formation of an energy gap at the apex of the Dirac cone. Intercalation with Li caused spatial and electronic decoupling of the B-graphene layer from the substrate and demonstrated the occurrence of the energy gaps predicted by our DFT-calculations. An attempt to compensate for the strong n-doping of the layer caused by Li intercalation performing co-intercalation of oxygen failed, since oxygen leads to extraction of Li-ions from the interface and formation of Li oxides on the sample surface. In contrast, pure graphene and h-BN/Co(0001) can be well intercalated by oxygen, whereby the completeness of the achieved intercalation depends on the size of the domains and the structural quality of the Co surface. Attempts to decouple B-graphene/Co(0001) by intercalation with Au or Si resulted in unwanted changes in the B concentration in the graphene layer. Graphene-h-BN heterolayers could be synthesized by CVD using trimethylborazine, yielding perfectly ordered epitaxial layers composed of h-BN and graphene domains of different sizes linked by C-B zigzag bonds, while C-N bonds are obviously not formed. In analogy to B-graphene, spin-polarized edge states form at the boundaries, which in principle should also occur in free-standing graphene-h-BN layers, but are not spin-polarized there. The present studies were carried out in close cooperation with the research group of Prof. D. Usachov from the University of St. Petersburg and will be continued within the framework of BMBF project 05K19ODR and with the support of the DAAD excellence cluster G-RISC at the Russian-German laboratory at BESSY, Berlin. Additionally, the good cooperation with Prof. Usachov has inspired us to submit a new joint project, in which the PED techniques developed in the course of the present project are to be applied to the investigation of layered rare-earth compounds.

Projektbezogene Publikationen (Auswahl)

• “Large-Scale Sublattice Asymmetry in Pure and Boron-Doped Graphene”, Nano Letters 16, 4535 (2016)
  D.Yu. Usachov, A.V. Fedorov, O.Yu. Vilkov, A.E. Petukhov, A.G. Rybkin, A.Ernst, M.M. Otrokov, E.V. Chulkov, I.I. Ogorodnikov, M.V. Kuznetsov, L.V. Yashina, E.Yu. Kataev, A.V. Erofeevskaya, V.Yu. Voroshnin, V.K. Adamchuk, C. Laubschat, and D.V. Vyalikh
  
• “Cobalt-assisted recrystallization and alignment of pure and doped graphene” Nanoscale 10, 12123 (2018)
  D. Yu. Usachov, K.A. Bokai, D.E. Marchenko, A.V. Fedorov, V.O. Shevelev, O. Yu. Vilkov, E.Yu. Kataev, L.V. Yashina, E. Rühl, C. Laubschat and D.V. Vyalikh
  
• “Site- and spin-dependent coupling at the highly ordered h-BN/Co(0001) interface” Phys. Rev. B 98, 195438 (2018)
  D.Yu. Usachov, A.V. Tarasov, K.A. Bokai, V.O. Shevelev,O.Yu. Vilkov, A.E. Petukhov, A.G.. Rybkin, I.I. Ogorodnikov, M.V. Kuznetsov, M. Muntwiler, F. Matsui, L.V. Yashina, C. Laubschat, and D.V. Vyalikh
  
• “Spin-polarized Fermi surfaces, hole-doping and band gaps in graphene with boron impurities” Nanoscale 10 22810 (2018)
  A.V. Fedorov, L.V. Yashina, O.Yu. Vilkov, C.Laubschat, D.V. Vyalikh and D.Yu. Usachov
  
• "Decoding the structure of interfaces and impurities in 2D materials by photoelectron holography” 2D Materials 6, 045046 (2019)
  D.Y. Usachov, A.V. Tarasov, F. Matsui, M. Muntwiler, K.A. Bokai, V.O. Shevelev, O.Y. Vilkov, M.V. Kuznetsov, L.V. Yashina, C. Laubschat, ; A. Cossaro, L. Floreano, A. Verdini, and D.V. Vyalikh
  
• “Boron nitride monolayer growth on vicinal Ni(111) surfaces systematically studied with a curved crystal” 2D Mater.6 025013 (2019)
  L. Fernandez, A.A. Makarova, C. Laubschat, D.V. Vyalikh, D.Yu. Usachov, J.E. Ortega and F. Schiller
  
• “Highly Ordered and Polycrystalline Graphene on Co(0001) Intercalated by Oxygen” J. Phys. Chem C 124, 17103 (2020)
  V.O. Shevelev, K.A. Bokai, A.A. Makarova, D. Marchenko, O.Yu. Vilkov, V.Yu. Mikhailovskii, D.V. Vyalikh, and D.Yu. Usachov
  
• “Hybrid h-BN–Graphene Monolayer with B–C Boundaries on a Lattice-Matched Surface” Chem. Mater. 2020, 32, 3, 1172–1181 (2020)
  K.A. Bokai, A.V. Tarasov, V.O. Shevelev, O.Yu. Vilkov, A.A. Makarova, D. Marchenko, A.E. Petukhov, M. Muntwiler, A.V. Fedorov, V.Yu. Voroshnin, L.V. Yashina, C. Laubschat, D.V. Vyalikh, and D.Yu. Usachov