The intrinsic temperature effect of the Raman spectra of graphite

The Raman spectra of ion-implanted highly oriented pyrolytic graphite (HOPG) are reported, in which an additional mode at $\text{1083\hspace{0.05em}}{\mathrm{cm}}^{\mathrm{-1}}$ and three doublet structures in the positions of $\text{∼1350,}$ $\text{∼2450,}$ and $\text{∼2710\hspace{0.05em}}{\mathrm{cm}}^{\mathrm{-1}}$ are revealed. Noticeable frequency shifts are observed for all the Raman bands between the spectra excited with different laser powers, which are interpreted as the pure temperature effect and a downshift in the C–C stretching frequency induced by the thermal expansion. Moreover, the pure temperature effect ${\mathrm{(d\omega /dT)}}_V$ without anharmonic contribution is achieved in pristine HOPG. The results suggest that the pure temperature effect without anharmonic contribution plays an important role in the frequency shifts with temperature.