Atmosphere-Induced Effect in Microhardness, Dislocation Mobility and Plasticity of C60 and Graphite Crystals

Formation of hard, brittle and toluene-insoluble near-surface layer (∼0.3 μm) of C₆₀ crystals under atmospheric exposure was observed. Similar atmosphere-induced effect was found for graphite crystals and might also be expected for other molecular solids. Data on ageing kinetics of C₆₀ and graphite crystals are presented. Variation of hardness with indentation depth can be described by the microhardness model for bilayer medium with different mechanical properties. Specific feature of C₆₀ and graphite crystals is that no size effect appears in the intrinsic microhardness and dislocation mobility characteristics in the indentation depth range of 0.6-4μm.