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ERC

NanoSurfs Report Summary

Project ID: 615233
Funded under: FP7-IDEAS-ERC
Country: Germany

Mid-Term Report Summary - NANOSURFS (Nanostructured Surfaces: Molecular Functionality on advanced sp2-bonded substrates)

The primary goal of the NanoSurfs project is to engineer molecular properties by combining suitable molecular units with two-dimensional materials, namely sp2-bonded substrates. Hereby, we focus on molecular functionalities as switching, ligation of gases, reactivity, charge transfer and self-assembly into supramolecular architectures. On the one hand, we grow well-defined, nanostructured sp2 monolayers as boron nitride (BN) or graphene on suitable supports by scalable processes like chemical vapour deposition (CVD). On the other hand, we study and control individual functional molecules and their assembly on these advanced supports in exquisite detail by molecular-level scanning tunnelling microscopy, spectroscopy as well as frequency-modulated atomic force microscopy. The insight gained by these studies featuring a comprehensive characterization of molecular nanostructures on the atomic level is used to deliberately tailor the molecule / sp2 / support interfaces to achieve heterostructures with targeted properties. In addition, space-averaging methods as lab- or synchrotron-based x-ray spectroscopy techniques yielded complementary information on electronic, chemical and structural aspects of our systems.
We achieved the formation of atomically-defined boron nitride and graphene layers on rather inert metallic supports like silver single crystals or films, thus systematically extending the library of known sp2 / metal systems. To this end, we developed and refined preparation protocols covering atomic deposition, ion-gun assisted CVD, and intercalation of metals. The resulting interfaces were comprehensively characterized both by complementary experimental techniques and computational modelling. These comparative studies revealed for example how the work function and electronic corrugation of a BN terminated surface can be controlled, thus providing tailored supports for molecular adsorbates.
We made significant progress regarding the self-assembly of molecular nanostructures on BN on copper platforms. Two-dimensional nanoporous metal-organic networks featuring Co centres in distinct environments were assembled from novel carbonitrile-functionalized porphyrin molecules. Furthermore, we demonstrated for the first time an in situ metallation of tetrypyrrole macrocycles with deposited metal atoms directly on an sp2 sheet. Highly ordered oligophenylene monolayers reveal a spatially modulated conductance at the nanometre-scale. Moreover, conductance variations at the molecular level are resolved and assigned to the excitation of vibrational modes of the oligophenylene. The functionalization of pyrenes – photoactive polycyclic aromatic hydrocarbons – with pyridyl moieties in distinct positions was used to assemble supramolecular arrays electronically decoupled from the underlying copper support by the BN spacer. These examples highlight properties that could not be achieved by the respective molecular systems coupled directly to a metallic surface.
Novel, stable sp2 / tetrapyrrole hybrid structures could be achieved by covalently attaching porphines to the edges of graphene flakes grown on a silver platform employing an on-surface reaction only yielding hydrogen as byproduct. The resulting interfacial bonding motifs – featuring up to four additional C-C bonds – were resolved by frequency-modulated atomic force microscopy, whereas scanning tunneling microscopy and spectroscopy was employed to characterize the electronic structure near the Fermi level. We notably demonstrated that metallation and ligation reactions characteristic for macrocyclic compounds persist in the hybrid structure, thus opening up pathways to engineer properties of the system that are relevant in view of potential applications in heterogenous catalysis and optoelectronics.

Reported by

TECHNISCHE UNIVERSITAET MUENCHEN
Germany
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