User Community Science: Soft decoupling of organic molecules on metal
The illustration shows how iodine (purple) is embedded between the organic layer and the metal, thus reducing adhesion. © IFM, University of Linköping
An international team has discovered an elegant way to decouple organic nanosheets grown on metal surfaces. After iodine intercalation, measurements at the synchrotron source BESSY II of Helmholtz-Zentrum Berlin (HZB) showed that a network of organic molecules behaved almost as it was free-standing. The strong influence of the metal on the network was reduced. This opens up new ways to transfer organic nanostructures from metal surfaces onto more suitable substrates for molecular electronics. The results have been published in “Angewandte Chemie”.
Specific organic molecules – typically on reactive metallic surfaces – can interlink via chemical bond formation into extended nanostructures. Highly stable two-dimensional molecular networks can be grown in this manner. However, these networks then adhere to the metallic support, which also strongly influences their properties. To make use of these kinds of organic networks in molecular electronics, for instance, the metal would have to be laboriously removed.
Iodine vapour reduces adhesion
Now a team headed by Markus Lackinger at the Technische Universität München and the Deutsches Museum together with partners at other universities in Germany and Sweden have discovered an elegant way to reduce the adhesion between the network and the metal. They simply exposed the networks bound to the metal to iodine vapour. “After the networks had been synthesized on a silver surface, we used iodine vapour. We hoped iodine would embed between the organic layer and the metal”, explains Lackinger. To do this, they investigated a nanosheet consisting of interlinked phenyl rings (polyphenylene) on a silver surface. The iodine actually migrated beneath the interlinked phenyl rings to form an atomically thin interlayer on the metal surface. After the intercalation of the iodine, measurements at BESSY II proved that the molecular network behaved almost as if it was detached. The strong influence of the metal was reduced.
Application: New transfer techniques
These results could be advantageous for future applications. “Molecular nanosheets do not grow on any surface. For this reason, we have to develop transfer techniques. Then we could fabricate the networks on metal surfaces and subsequently transfer them over to other surfaces that are more suitable for molecular electronics. Being able to mitigate the adhesion with an iodine interlayer is possibly a first step in this direction”, explains Lackinger.
Publication: Post-Synthetic Decoupling of On-Surface Synthesized Covalent Nanostructures from Ag(111), Atena Rastgoo-Lahrood, Jonas Björk, Matthias Lischka, Johanna Eichhorn, Stephan Kloft, Massimo Fritton, Thomas Strunskus, Debabrata Samanta, Michael Schmittel, Wolfgang M. Heckl, Markus Lackinger, Angew. Chem. Int. Ed.. doi: 10.1002/anie.201600684
- Battery research with the HZB X-ray microscopeNew cathode materials are being developed to further increase the capacity of lithium batteries. Multilayer lithium-rich transition metal oxides (LRTMOs) offer particularly high energy density. However, their capacity decreases with each charging cycle due to structural and chemical changes. Using X-ray methods at BESSY II, teams from several Chinese research institutions have now investigated these changes for the first time with highest precision: at the unique X-ray microscope, they were able to observe morphological and structural developments on the nanometre scale and also clarify chemical changes.
- BESSY II: New procedure for better thermoplasticsBio-based thermoplastics are produced from renewable organic materials and can be recycled after use. Their resilience can be improved by blending bio-based thermoplastics with other thermoplastics. However, the interface between the materials in these blends sometimes requires enhancement to achieve optimal properties. A team from the Eindhoven University of Technology in the Netherlands has now investigated at BESSY II how a new process enables thermoplastic blends with a high interfacial strength to be made from two base materials: Images taken at the new nano station of the IRIS beamline showed that nanocrystalline layers form during the process, which increase material performance.
- Hydrogen: Breakthrough in alkaline membrane electrolysersA team from the Technical University of Berlin, HZB, IMTEK (University of Freiburg) and Siemens Energy has developed a highly efficient alkaline membrane electrolyser that approaches the performance of established PEM electrolysers. What makes this achievement remarkable is the use of inexpensive nickel compounds for the anode catalyst, replacing costly and rare iridium. At BESSY II, the team was able to elucidate the catalytic processes in detail using operando measurements, and a theory team (USA, Singapore) provided a consistent molecular description. In Freiburg, prototype cells were built using a new coating process and tested in operation. The results have been published in the prestigious journal Nature Catalysis.