Raman scattering study of highly fluorinated graphite

Raman spectra of highly fluorinated C_xF samples (1 < x < 2) prepared at room temperature and 515°C were measured. C_xF samples prepared at room temperature exhibited two Raman bands at 1593-1583 and 1555-1542 cm^-1. Graphite samples fluorinated at 515°C for 1 and 2 min also gave similar bands at 1581-1580 and 1550-1538 cm^-1. However, graphite samples fluorinated from 15 min to 10 h at 515°C no longer showed such spectra. The Raman peaks shifted to lower frequencies with increasing fluorine concentration in C_xF. This trend is due to the weakening of the C-C bonds of the graphene layers. Observation of both kinds of Raman bands suggests the coexistence of two highly fluorinated phases, C₂F and C₁F, in the samples. The process of formation of graphite fluoride is discussed on the basis of the Raman spectra of C_xF samples obtained at 515°C.