Nanodiamond synthesis from adamantane by electron-beam driven C–H activation at 100 K

Diamond and adamantane (Ad) share a Td-symmetric carbon skeleton, but converting Ad to diamond has been challenging due to selective C–H bond cleavage and monomer assembly into a diamond lattice. Electron irradiation (80–200 keV) of Ad sub-microcrystals in vacuum at 100 K for tens of seconds yielded defect-free nanodiamonds (NDs) of cubic crystal structure 2–4 nm in diameter, accompanied by hydrogen gas evolution. Time-resolved transmission electron microscopy revealed the initial formation of Ad oligomers transforming into spherical NDs. A sizable kinetic isotope effect confirmed C–H cleavage as rate-determining. Other hydrocarbons failed to form NDs, underscoring the unique suitability of Ad. This approach distinctively differs from the conventional high-temperature, high-pressure approach, exemplifying the value of controlled C–H activation for diamond synthesis.