Buckyball sandwiches under high temperatures and pressures

We employ atomistic machine-learning simulations to explore the atomic structures resulting from buckyball-graphene sandwich systems, where ${\mathrm{C}}_{60}$ molecules are confined between graphene layers under high temperature and pressure. We find that, depending on the thermodynamic conditions, ${\mathrm{C}}_{60}$ molecules can transform into dimers, trimers, and fullerene peanuts, as well as collapse into two- and three-dimensional amorphous condensed phases, including amorphous graphene and amorphous diamond. All of these forms have different electronic properties. Notably, the graphene layers maintain their structural integrity well with minimal changes, collapsing only under the most extreme conditions explored. Our study provides a unified framework for understanding the atomistic properties of fullerene-derived nanomaterials consistent with experiments and their dependence on the synthesis conditions. These findings suggest that graphene could function as an effective nanoscale ``reactor'' to synthesize novel carbon-based materials with diverse properties using ${\mathrm{C}}_{60}$ as a precursor.