J. Maniks

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

Abstract 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.

Atmosphere-induced change of microhardness and plasticity of C60 single crystals and polycrystalline films

Abstract The effect of air exposure and visible light illumination on the microhardness, plasticity and dislocation mobility in the C60 single crystals was investigated. Microhardness values for defined structural states of the fullerene (pristine, oxygen-intercalated, photo-oxidized) are reported. It has been shown that oxygen intercalation in the fullerene lattice during air-aging in the dark results in the suppression of dislocation mobility. However, only a slight increase in the hardness of oxygenated samples was observed. A remarkable increase in the hardness and decrease in the plasticity of the C60 crystals under illumination-assisted air exposure was noted. Photochemical transformation was found to be localized in the nearsurface layer of 1–5 μm. The data on the recovery of the micromechanical properties of the photo-oxidized surface layer under heating in air are presented.

Temperature Dependence of the Microhardness and Dislocation Mobility in the Near-Surface Layer of C60 Crystals

Abstract Temperature dependence of the Vickers microhardness and dislocation mobility of as grown and aged in air C60 single crystals in the range of 300-550K has been investigated. An anomalous change of the hardness in the near-surface layer of C60crystals around 470K is observed which is explained by the phase transition from an oxygen-intercalated to an oxidised structure. the growth of the oxide film on heating the crystals in air at temperatures higher than 470K is detected, and hardness of 280 MPa of the oxide film is measured. the stress-promoted oxidation of fullerite in the local zones of indentation at 390-470K is discovered. It has been found that ageing of the crystals in air reduce the temperature of the stress-promoted oxidation.

Photoinduced hardening and reduction of dislocation mobility in C60 single crystals: The wavelength dependence

An increase of the microhardness and decrease of the dislocation mobility in C60 single crystals after light-irradiation in the wavelength range of 150–900nm in air has been observed giving evidence for photo-induced change in bonding. Efficiency of C60 phototransformation was found to increase with decreasing the wavelength.

Adhesion and Strength Properties of C60 Films on Silicon Substrates

Abstract Direct pull tests were used to examine the adhesion and rupture strength of C60 films on a silicon substrate. The measured strength values were in the range of 3.5-15 MPa depending on deposition conditions. The cohesive fracture inside the fullerite film due to strong bonding at the film/substrate interface was predominantly observed. Comparison of the rupture strength and microhardness is made. The results show that adherence of C60 film to a silicon substrate is high enough for various technological applications.

Photo‐Induced Polymerization and Stress Effects in Fullerite C60

Abstract Modifications of the structure and hardness of fullerite C60 crystals under stresses generated during photo‐induced polymerization are investigated.

The illumination-time and wavelength dependences of photoinduced hardening of C60 crystals

The fullerite photopolymerization in air in the wavelength range 350–900 nm was investigated using microhardness and dislocation mobility methods. The photoinduced effects of the hardening and reduction of a dislocation mobility were found to increase linearly with increasing photon energy. The existence of two phototransformed states is supposed from the kinetics data on photoinduced hardening.