Cross-Linked Nano-onions of Carbon Nitride in the Solid Phase: Existence of a Novel $C_{48}{N}_{12}$ Aza-Fullerene

We report a new fullerenelike material consisting of cross-linked nano-onions of C and N. Growth of the onion shells takes place atom by atom on a substrate surface and yields thin solid films during magnetron sputter deposition. Electron microscopy and energy loss spectroscopy show that the core shell contains up to $20\mathrm{at}.\mathrm{}\%$ N corresponding to ${\mathrm{C}}_{48}{\mathrm{N}}_{12}$ aza-fullerene composition. Nanoindentation of this nanostructured material gives high resilience with hardness 7 GPa, Young's modulus 37 GPa, and complete elastic recovery after loading with 0.5 mN to a depth of 75 nm. Total energy calculations show the stability of ${\mathrm{C}}_{60-2n}{\mathrm{N}}_{2n}$ aza-fullerenes and suggest the existence of a novel ${\mathrm{C}}_{48}{\mathrm{N}}_{12}$ molecule.