C60 fullerene molecules are usually encapsulated before studying their dynamical properties and mutual bonding by means of electron microscopy. For this aim, a successful strategy is the use of carbon nanotubes to wrap buckyball molecules in a peapod-like configuration. Among the several advantages of this approach — such as the high localization accuracy — a clear drawback is the constraint along one single spatial dimension. In fact, free fullerene molecules on surfaces can self-assemble in two-dimensional configurations.
Now Mirzayev, Mustonen and colleagues report on the encapsulation of C60 molecules in two monolayer graphene sheets at room temperature. Within these suspended hybrid structures, which are visualized by means of high-resolution scanning tunnelling electron microscopy, the researchers observe wide areas where the buckyballs are arranged in a stable single-layer hexagonal close packed lattice. Still, isolated buckyballs rotate steadily while diffusive effects are observed at the lattice edges.
Aside from maintaining a stable spatial configuration, graphene offers an effective protecting layer against the possible modifications induced by the electron beam in the molecules. Yet, the researchers observe beam-induced knock-on damage and the generation of intermolecular bonds. They also report that high degrees of dimerization suppress the tendency for the single molecules to rotate freely — peanut-like clusters tend to rotate around their joint axis, while triangular clusters do not rotate at all.
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Prando, G. Graphene-packed fullerene. Nature Nanotech (2017). https://doi.org/10.1038/nnano.2017.144