C₆₀ molecule

Fullerenes are a new family of carbon besides diamond and graphite. In fullerenes the planar structure of graphite is converted into quasi-icosahedral cages by 12 pentagonal "defects". Such an extremely stable cage is the C₆₀ molecule, which copies the pattern of a soccer ball. Researchers have been looking for ways to use the soccer-ball-shaped molecules of pure carbon known as fullerenes (or buckyballs) since they were first synthesized, more than a decade ago. But the solid materials they form are often weak and easily degraded because the individual spheres hold to their neighbors through weak van der Waals forces, rather than forming sturdy bonds. Addition of nitrogen into the graphitic sheets makes it favourable to form pentagons and induce curvature of the sheets. Therefore the fullerene structure can be synthesised at lower temperatures. The fullerene-like shells can grow in an encapsulated manner forming so called nano-onions. The incorporated nitrogen also helps to strengthen the material by allowing the spheres to form tight covalent bonds between each other. The onions were identified by TEM and analyzed by EELS. Each "onion" was a few nanometers across and contained a core of C₄₈N₁₂ a new aza-fullerene. The onions seem to be strongly bonded to each other, based on structural calculations and mechanical tests. The mechanical properties were characterized by nanoindentation using a sharp diamond-tipped probe. According to the mechanical tests, the material is fracture tough due to its extreme elasticity making the material good for protective coatings on hard disks, bearings and medical implants. The material holds the potential in other applications as well, such as solid lubricants or electron emitters in flat panel displays.