Raman spectroscopy measurements on carbon(60) compressed under high pressures.

摘要

The vibrational properties of Fullerene C60 under high pressures at room temperature were studied by Raman spectroscopy.; The Raman spectrum of pristine C60 at ambient conditions was measured which is in agreement with published data. The effect of laser power on the Raman shifts of C60 was studied and the downshifts of the Raman modes of C60 indicated the occurrence of photopolymerization under high laser power and care was taken to minimize this photopolymerization effect in our experiments.; The Raman spectra taken under non-hydrostatic pressure indicated that the Raman shifts of the Ag(2) band do not follow the linearity between 4 and 8.28 GPa; a turnaround at about 7.26 GPa was observed. By using a 16:3:1 methanol-ethanol-water mixture (MEW) as the pressure transmitting medium, C60 was compressed up to 31.1 GPa under almost hydrostatic pressure. The pressure dependence of the Ag(2) mode is qualitatively similar. However, the range of the linear behavior and the turnaround pressure are different. A major change in the shape of the Raman spectrum occurs at around 14.7 GPa and 27 GPa. All these changes in Raman spectra indicate the occurrence of structural phase transitions in the material. There are hardly any changes in the frequencies of Raman modes of the material compressed under 31.1 GPa and the recovered phase upon release of pressure down to ambient. Comparing the pressure-induced phases for non-HPHT C60 samples and HPHT C60 samples, it is found that the phase transitions occur at different pressures and the final high-pressure phases are different. This indicates that the sample preparation details have significant influence on the phase transformations of the material at very high pressures (≥20GPa).; The Raman spectra of 16:3:1 methanol-ethanol-water mixture (MEW) as the pressure-transmitting medium as well as their components were measured under ambient conditions. The Raman spectra for wavenumbers in the range 1400--1600 cm-1 for MEW as function of pressure up to 6.2GPa at room temperature were measured. The pressure dependences of the wavenumber, FWHM and relative intensity of the Raman bands of MEW are demonstrated. By constraining the Raman shifts of the two bands of MEW and their relative intensities, the pressure dependence of Raman shifts of Ag(2) mode of C 60 using the pressure transmitting medium was reanalyzed. The MEW do have significant influence on the Raman shifts of Ag(2) mode of C60 However, there are still unknown factors which need further investigation.