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Molecular Engineering at Surfaces
Surface-supported supramolecular networks

The exploitation of non-covalent interactions between molecules to form extended regular assemblies is a concept that has been used in supra-molecular chemistry for nearly half a century and that has been brought to surfaces in the last decade. The structure of complex molecular lattices, which can form on atomically flat surfaces, is dictated by the delicate balance of inter molecular and surface-molecule interactions.

In this research field we have very intensively investigated how the molecular assemblies can be guided by specific molecule-substrate interaction. In this respect we have studied in great detail the processes leading to site specific adsorption on vicinal surfaces, surfaces showing large scale reconstructions and strain-relieve networks. By intimate comparison of ab initio simulations and experiments we could elucidate the prominent role of variations of the surface potential for the site specific molecule adsorption of our template surfaces. The design of molecular recognition patterns to achieve rationally designed molecular networks is a further topic of interest also in view of using novel molecular interaction mechanisms, such as p-p  interaction in contorted hexa-peri-benzo-corone (HBC). Also the question of the electronic coupling in non-covalently bonded molecular networks is of great importance to us. Generally the understanding and control of surface supported supra-molecular structures is the corner stone of our general bottom-up strategy to synthesize novel low-dimensional organic materials.

Surface-programmed covalent coupling and network formation

Whereas the weakly bonded supra-molecular networks are of great scientific interest, as they allow detailed research on intermolecular recognition patterns with many parallels to biological systems, the bottom-up fabrication of novel technological materials will also require as crucial step the covalent coupling of the molecular precursors. In this regard we follow a rigorous strategy of exploring surface supported/mediated covalent coupling reactions.

Recently, we have developed a novel bottom-up approach using covalent interactions to fabricate thermally stable and chemically inert molecular architectures such as low-dimensional polyimides, porous graphene or graphene nanoribbons. The possibility to confine chemical synthesis to two dimensions has paved the road for the design and fabrication of novel, low-dimensional materials which are otherwise not accessible via traditional solution-based chemical routes. As examples of this route we can mention the Ullmann-type coupling and the cyclo-dehydrogenation reaction, which are both crucial steps in our synthesis of nano graphene structures. It is our dual aim to use surface-programmed reactions for synthesis of novel materials and at the same time gain a fundamental understanding of the process involved in these coupling reactions. We achieve this insight by extensive ab initio simulations and dedicated experiments, such as the detailed investigation of STM tip induced reaction pathways. Extending the library of reaction schemes will thus be the main task for the future, which will then allow for increased complexity in fabricated structures by introducing multistep synthesis protocols.

Functional organic monolayers

In the design and fabrication of novel low-dimensional organic materials we always strive to achieve novel functionalities. The electronic properties and functionalities are certainly very prominent here, but by no means exclusive. We also investigate host-guest recognition, enhanced gas absorption or selective gas permeability.

By the covalent coupling of cyclo-hexa-m-phenylene (CHP) we achieved the synthesis of an extraordinary modification of graphene namely porous graphene. This novel two-dimensional crystal exhibits a honeycomb lattice just like ordinary graphene, but the fundamental building unit is not a carbon atom but a benzene ring. This modification has profound implications on the electronic structure, whereas graphene is a semi-metal, our porous graphene is a semi-conductor with a significantly large gap. Furthermore the pores allow highly specific gas permeation. Atomistic simulation showed a permeability of H through the CHP derived porous graphene which is at least 5 orders of magnitude higher than for O2 or CO2 showing the potential of this material for gas purification e.g. in fuel cell applications. In a different project we studied experimentally as well as theoretically the methane adsorption at surface supported sumanene monolayers. Here we could show that single methane molecules are trapped in the concave bowl of the sumanene. The fundamental understanding of the adsorption of methane at curved graphitic surfaces is of high technological relevance for the development of low pressure natural gas storage tanks.

ADDRESS

nanotech@surfaces Laboratory

Empa, Swiss Federal Laboratories for

Materials Science & Technology

Ueberlandstrasse 129

8600 Duebendorf

Switzerland

How to find us :

printable map, interactive map

 

CONTACT

Prof. Dr. Roman Fasel, Head of Laboratory

Dr. Oliver Gröning, Deputy head

Ms. Christine Tran, Head assistant

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