UV Raman of pyrocarbons, interests in the deconvolution of visible Raman spectra

This work is focused on the comparison of the first order Raman features of pyrocarbons, recorded with both UV (325 nm) and visible (632.8 nm) excitations. The analysis of the UV spectra is easier, and helpful for the understanding of the spectra recorded with a 632.8 nm wavelength. Several main results arise. Firstly, as expected, the frequency of the disorder induced D mode is shifted to higher frequency and its intensity strongly decreases with increasing laser energy. Secondly, the frequency and FWHM of the E2g mode determined from a graphitized pyrocarbon are identical for both exciting wavelengths. Accordingly, for each as-deposited pyrocarbon, the UV spectral parameters of the E2g mode were used to fit their corresponding spectrum recorded with the 632.8 nm wavelength. The results suggest the presence of a rather intense disorder D ’ mode in the visible spectra of the as-deposited pyrocarbons. The lack of the D’ component in the fitting procedure indeed leads to a misfit of the frequency of the E2g mode. Thirdly, the out-of-plane ("B2g " or "A2u") mode is observed at the same frequency (867 cm-1) with both the UV and visible wavelengths. Contrary to the D mode, this feature shows no resonant origin