Anharmonicity of graphite from UV Raman spectroscopy to 2700 K

First-order Raman spectra of pyrolytic graphite (PG) and highly oriented pyrolytic graphite (HOPG) were recorded in situ up to 2670 K and 2491 K, respectively, using a development of wire-loop heating cell technique attached to a UV-Raman spectrometer (244 nm). Raman shift of the E2g in-plane stretching mode of graphite (G band) is used to discuss the anharmonicity by a comparison with calculations in the density-functional theory (DFT). High temperature Raman shifts are well described by anharmonic DFT calculations [1] up to 900 K. Anharmonicity is also determined from the temperature dependence of the Raman linewidth. The quartic term of phonon–phonon scattering process dominates at high temperature with respect to electron–phonon coupling that causes a slight decrease of linewidth with increasing temperature below 1000 K. The G band position is determined with a good reproducibility to 2700 K and can be used as a thermometer for in situ studies. Deep UV-Raman proves a viable solution for expanding significantly the temperature range for studying in situ vibrational properties of condensed matter, and particularly the monitoring of carbon-based material processing.