Raman scattering of solution-grown and vacuum-deposited C60 crystals

Raman spectra of solution-grown C60 crystals and evaporated films of C60 were measured by near-infrared laser excitation and compared with spectra of a sublimation-grown C60 crystal. Carbon disulfide and toluene were used as solutions. Broadening of the intramolecular Raman bands was observed in the solution-grown crystals and evaporated films of C60. The broadening in the solution-grown crystals was reduced by heat treatment after growth. A reduction in bandwidth was also found for C60 films evaporated at an elevated substrate temperature. Comparison of the Raman spectra of solid C60 prepared under different conditions shows that random distribution of solvent molecules in solution-grown crystals and structural disorder in evaporated films perturb force fields in solid C60 and bring about inhomogeneous broadening of the intramolecular vibrational bands. It is found that the effect of the phase transition on the Raman spectra is obscured in C60 solids containing residual solvent molecules or defects.