Department Physik, Universität Siegen, 57068 Siegen, Germany
03.10.2019. u 15:00h
IF - predavaonica u zgradi Mladen Paić
Two-dimensional materials like graphene (gr) and hexagonal boron nitride (hBN) can be epitaxially grown on transition metal surfaces as Ir(111) in high structural quality. The exact geometry is determined using scanning tunneling microscopy (STM) in-plane and x-ray standing waves (XSW) out of plane and compared to results from density functional theory (DFT). We find a delicate interplay between physisorption and chemisorption due to the inherent lattice mismatch which leads to superperiodic structures. These moiré patterns induce changes in the electronic structure and can serve as templates for the adsorption of atoms and molecules.
Significant modifications arise upon intercalation of alkali metals between the ultrathin epitaxial layers and their substrate. For both hBN/Ir(111) and gr/Ir(111) we find that intercalation removes the residual interaction with the substrate and in consequence irons out the corrugation of the 2D materials. Here, Li intercalation is most efficient as already small coverages lead to full decoupling. In addition, graphene is strongly doped by the charge transfer from the alkali atoms. In the case of hBN, intercalated Cs leads to a surface dipole which in turn strongly shifts the π-bands, a step towards the experimental determination of the band gap of hBN.