Fullerene-like alloyed carbon films

The synthesis, structure and properties of fullerene-like alloyed carbon films are reviewed. The term fullerene-like describes extended structures consisting of curved basal planes, which are stacked perpendicular to the basal planes. Fullerene-like structures can be observed in layered materials like graphitic carbon, carbon nitride, hexagonal boron nitride or tungsten disulfide. They can be characterized by extension, curvature and cross-linking of basal planes. Their structure results in an exceptional combination of mechanical properties such as high hardness, high elastic recovery, high wear resistance and low coefficient of friction.

In carbon based fullerene-like structures, these properties result from stiff (sigma pi)-bonds within the basal graphitic planes, fullerene-like structure assuring the presence of their 3D network due to the curvature and cross-linking. The fullerene-like structure of pure carbon can be further stabilized by alloying with nitrogen. Different nitrogen incorporation routes result in different local carbon-nitrogen bonding arrangements which then determine the extension, curvature and cross-linking of basal planes. Since both elements – carbon and nitrogen – can form sp1, sp2 and sp3 bonds, the nanostructure is determined by the relative concentration of local chemical environments such as nitrile-like, pyridine-like or graphite-substitutional. The former two configurations are terminating, thus hindering the extension of basal planes The latter induces buckling in the planes due to stabilization of pentagon rings or due to the difference between C-N and C-C bonds which locally shrinks the network.

An alternative way to produce fullerene-like structures is carbon alloying with metallic elements. The metal atoms segregate into the nanoparticles which act as catalytic sites for the six-fold-ring clustering of carbon atoms. Different metal incorporation routes determine the shape of metal nanoparticles ranging from completely spherical to nanorod-like. This significantly affects the graphitization of carbon as the so-formed graphitic planes follow the boundaries of the metal nanoparticles resulting in partially wrapped metal nanocolumns or completely encapsulated metal nanoparticles. These fullerene-like nanostructures might be used for applications as low-friction, self-lubrication, wear resistant coatings, as 2D network of tunnel junctions, as nanocontainers for foreign materials, or for encapsulation of ferromagnetic nanoparticles in non-magnetic media.