Tribological properties of fullerenes C60 and C70 microparticles

The frictional behaviors of fullerenes C60 and C70 were studied because they were speculated to be solid lubricants. For the sublimated pure C60 films on Si(001), a high friction coefficient (0.55–0.8) was observed under different loads and pin materials. For the C70 film, the friction coefficient showed a pin dependence, which changed from 0.5 with an Al2O3 pin to about 0.9 with a 440 stainless steel pin. The relatively high friction coefficients of C60 and C70 films were due to the tendency of the C60 and C70 particles to clump and compress into high shear strength layers rather than due to the impurities in the fullerenes. The benzene-solvated C60 · 4C6H6 and C70 · xC6H6 showed a lowered friction coefficient (0.25 for C60 · 4C6H6 and 0.3 for C 70 · xC6H6), which might result from the lowered shear strength of the hcp structure of C60 · 4C6H6 and C70 · xC6H6 molecular crystals in which the benzene molecules were intercalate