An international research team led by NIMS and Osaka University has succeeded in directly attaching bromine atoms and fullerene molecules to specific sites on a target molecule using the probe of a scanning probe microscope. This technique allows us to synthesis functional carbon nanostructures, which is usually challenging through conventional reaction in solution. These nanostructures may have excellent electrical properties and are beneficial for the development of new nanoelectronic devices.

The resolution of scanning probe microscopy has significantly improved, enabling direct observation of inner structures of individual molecules adsorbed on surfaces. Furthermore, it became possible to modify molecular structures by removing specific atoms from them using the probe of a scanning probe microscope. These technical advances have attracted interests of researchers towards achieving novel compounds in a bottom-up approach—creation of desirable materials by manipulating single molecules. Highly electrically conductive carbon nanostructures, including graphene, are particularly promising as electronic materials and have been functionalized by integrating non-carbon atoms into them. However, efforts to directly attach non-carbon atoms and additional molecules to specific sites on carbon nanostructures through addition reactions had been unsuccessful.

This research team recently synthesized uniquely structured three-dimensional graphene nanoribbons (GNRs) and succeeded in replacing specific bromine atoms protruding from the GNR surface with fullerene molecules. The 3D GNRs were synthesized by heating precursor molecules on metal surfaces and allowing them to undergo polymerization reactions. The removal of protruding bromine atoms produces unstable radical species and immediately reacts with other molecules in solution. However, the unstable condition can be kept if the detachement reaction is induced in an extreme environment (i.e., extreme low temperature and ultra-high vacuum). The team then attached a bromine atom or a fullerene molecule to the tip apex of the probe and directly transferred it to the reactive target site on the GNR, namely the addition reaction. This is the first demonstration to functionalize the GNRs with another molecule by the local probe.

This technique allows us to modify graphene nanostructure with high-precision modification and may facilitate the development of electronic devices with new functions.

This project was carried out by an international joint research team led by Shigeki Kawai (Principal Researcher, Nano Functionality Integration Group, International Center for Materials Nanoarchitectonics, NIMS), Takashi Kubo (Professor, Department of Chemistry, Graduate School of Science, Osaka University), Adam Foster (Professor, Aalto University, Finland) and Ernst Meyer (Professor, University of Basel, Switzerland).
This work was supported by the MEXT Grant-in-Aid for Scientific Research (grant numbers 19H00856 and 18K19004) and the NIMS Joint Research Hub Program.
This research was published in Science Advances, an open-access scientific journal, at 2:00 pm on February 28, 2020, Eastern Standard Time (at 4:00 am on February 29, Japan Time).