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O: Fachverband Oberflächenphysik

O 5: Nanostructures at Surfaces I: Organics

O 5.4: Vortrag

Montag, 1. April 2019, 11:15–11:30, H15

Coverage-dependent structural transformation of cyano-functionalized porphyrin networks on Au(111) via addition of cobalt atoms — •Brian Baker, Nico Schmidt, Mihaela Enache, and Meike Stöhr — Zernike Institute for Advanced Materials, University of Groningen, Groningen, the Netherlands

The self-assembly process of a cobalt-porphyrin (Co-TCNPP) derivative containing cyanophenyl substituents at all four meso positions under ultrahigh vacuum on Au(111) was studied with room temperature scanning tunneling microscopy (STM) and low energy electron diffraction (LEED). Deposition of Co-TCNPP onto Au(111) gave rise to the formation of a close-packed H-bonded network, which was independent of coverage as revealed by STM and LEED. A coverage dependent behavior emerged upon metal-coordination with Co-atoms. At monolayer coverage, a reticulated network exhibiting a distinct four-fold Co-coordination was formed. By reducing the molecular coverage, a structural transformation took place. The four-fold Co-coordinated network was no longer an exclusive phase and coexisted with a second metal-organic coordination network (MOCN), i.e., a chevron structure stabilized by a simultaneous expression of H-bonding and three-fold Co-coordination. We attribute the coverage-dependent structural transformation to the in-plane compression pressure exerted by the molecules deposited on the surface. Therefore, a subtle interplay between the chemical nature of the building blocks and molecular coverage can steer the formation of topologically different MOCNs and opens an alternate pathway towards the fabrication of 2D networks.