Hard elastic carbon thin films from linking of carbon nanoparticles

HARD carbon thin films find many technological applications—as protective or biocompatible coatings, for instance. A very hard and elastic form of carbon nitride, in which curved graphene sheets are interlinked owing to the presence of small amounts of nitrogen, has recently been reported1. The hardness of these films is thought to arise from the presence of sp3-like bonds that introduce curvature into and bind together the sp2-bonded graphitic planes, rather as they do in hard, highly tetrahedrally bonded amorphous carbon films2–4. Here we show that hard, elastic thin films of pure carbon can be created by depositing closed, hollow graphitic carbon nanoparticles—nanotubes5 and carbon onions6—onto a substrate at high velocity. The particles are apparently disrupted on impact, causing them to link up. Electron-energy-loss spectra reveal a reduction in π (sp2) bonding in the intersecting regions of the nanoparticles, supporting the idea that they are covalently linked by tetrahedral sp3 bonds.