RAMAN-SCATTERING OF SOLUTION-GROWN AND VACUUM-DEPOSITED C-60 CRYSTALS

Raman spectra of solution-grown C-60 crystals and evaporated films of C-60 were measured by near-infrared laser excitation and compared with spectra of a sublimation-grown C-60 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 C-60. The broadening in the solution-grown crystals was reduced by heat treatment after growth. A reduction in bandwidth was also found for C-60 films evaporated at an elevated substrate temperature. Comparison of the Raman spectra of solid C-60 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 C-60 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 C-60 solids containing residual solvent molecules or defects.