A few-layer covalent network of fullerenes

E Meirzadeh and AM Evans and M Rezaee and M Milich and CJ Dionne and TP Darlington and ST Bao and AK Bartholomew and T Handa and DJ Rizzo and RA Wiscons and M Reza and A Zangiabadi and N Fardian-Melamed and AC Crowther and PJ Schuck and DN Basov and XY Zhu and A Giri and PE Hopkins and P Kim and ML Steigerwald and JJ Yang and C Nuckolls and X Roy, NATURE, 613, 71-+ (2023).

DOI: 10.1038/s41586-022-05401-w

The two natural allotropes of carbon, diamond and graphite, are extended networks of sp(3)-hybridized and sp(2)-hybridized atoms, respectively(1). By mixing different hybridizations and geometries of carbon, one could conceptually construct countless synthetic allotropes. Here we introduce graphullerene, a two-dimensional crystalline polymer of C60 that bridges the gulf between molecular and extended carbon materials. Its constituent fullerene subunits arrange hexagonally in a covalently interconnected molecular sheet. We report charge-neutral, purely carbon-based macroscopic crystals that are large enough to be mechanically exfoliated to produce molecularly thin flakes with clean interfaces-a critical requirement for the creation of heterostructures and optoelectronic devices2. The synthesis entails growing single crystals of layered polymeric (Mg4C60)(8) by chemical vapour transport and subsequently removing the magnesium with dilute acid. We explore the thermal conductivity of this material and find it to be much higher than that of molecular C-60, which is a consequence of the in-plane covalent bonding. Furthermore, imaging few-layer graphullerene flakes using transmission electron microscopy and near field nano-photoluminescence spectroscopy reveals the existence of moire-like superlattices(3). More broadly, the synthesis of extended carbon structures by polymerization of molecular precursors charts a clear path to the systematic design of materials for the construction of two-dimensional heterostructures with tunable optoelectronic properties.

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