Influence of cyclic thermal treatment near the first order phase transition on the supramolecular structure of C60

We have studied the modification of supramolecular structure of fullerene (precipitated from supersaturated solution) subjected by cyclic thermal treatment. The investigation of supramolecular structure of C60 crystals was performed by neutron diffraction and small angle scattering at different stages of cyclic thermal treatment. The characteristic domain size inside the crystallites (from the diffraction peaks broadening obtained) was D∝30-50 nm corresponding to the correlation radius of inhomogeneities Rc∼D obtained from the small angle scattering measurements. Using the SANS measurements we found also small inhomogeneities with radius of rc∝3-4 nm forming structures at the crystal surface with the characteristic period of ∝2rc sim10 nm. The cyclic thermal treatment of sample reduced the concentration of large defects for ∝6% vol. and the fragmentation of surface structures at the scale ∝10 nm. We have analysed the changing of surface structure, applying a model for small angle scattering intensity I=I0/(1+Rc2q2)β/2, where the β parameter yields the fractal dimension Ds=6-β of the surface. (orig.)