Nanographene synthesis by manipulating a Cu tip of atomic force microscope
A group of researchers from the University of Tokyo, Osaka University, Kyoto University, and Ehime University has fabricated nanographene (or singular graphene) in reactions invoked by approaching a metal tip to a specific position of polycyclic aromatic hydrocarbons (PAHs).
Graphene consisting of a single layer of atoms arranged in a honeycomb nanostructure is in the flat PAH family and is used for solar cells, fuel cells, and organic electronics. As a method for synthesizing nanographene, there is a bottom-up approach to perform dehydrogenation from organic molecules, but it’s difficult to selectively remove hydrogens (H) from them because much energy is required to rupture a C-H bond in organic molecules. In the bottom-up approach for nanographene synthesis, dehydrogenation takes place on a metal surface such as copper (Cu), which acts as a catalyst, assisting in the separation of H from carbon (C). C atoms then land on the metal substrate and self-assemble to form the graphene layer (This process is called chemical vapor deposition (CVD)).
To rupture the C-H bond to synthesize nanographene, thermally-induced cyclodehydrogenation (CDH) on the metallic surface is effective; however, conclusive reaction mechanisms were not elucidated thoroughly.
To understand the role of metal in CDH, the researchers focused on two types of reactants to yield cyclodehydrogenated PAHs and investigated if there was a difference caused by molecular shape or other factors.
In this study, the researchers utilized a Cu tip of an STM (scanning tunneling microscope) /nc (non-contact) AFM probe as the manipulable metal surface to catalytically activate PAH-forming reactions through hydrogenation. They attempted to remove H atoms under ultrahigh vacuum (UHV) chamber. The approach of the metal tip to the H atom ruptured the C-H bond and eventually yielded the final product of the thermal reaction at the metal surface at 4.8 K (-268.35℃).
As the tip approached the reactant, the activation barrier, the minimal amount of energy necessary to launch a chemical reaction, reduced. The dehydrogenation occurs by the Cu-tip approach, which indicates the importance of contacting a metal surface to H atoms of hydrocarbon for yielding nanographene. This shows that the metal tip works as a catalyst to dissociate individual C-H bonds.
Designing organic molecules and metal catalysts for nanographene synthesis based on this group’s study results will help efficient synthesis of nanocarbon materials. It will become possible to establish ultimate bottom-up technologies to create functional nanomolecules through the development of advanced techniques to manipulate single atoms, for example, by changing tip materials or giving different stimuli.
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The article, “Manipulable Metal Catalyst for Nanographene Synthesis,” was published in Nano Letters at DOI: https://pubs.acs.org/doi/10.1021/acs.nanolett.0c03510.
Related links
Morikawa Group, Department of Precision Science and Technology, Graduate School of Engineering, Osaka University (link in Japanese)
