Raman spectroscopy of closed-shell carbon particles

Raman spectra of annealed carbon soot reveal strong structural changes. Downshifts of the graphite-like phonon bands to lower energies after annealing are suggested to be related to strained or curved graphitic planes. The effect of curvature on the energy of the in-plane optical phonon mode is quantitatively estimated by applying the semi-empirical interatomic Tersoff potential. A weighted average curvature corresponding to a bond bending of 2.1[o] is deduced for spherical shells with 20.6 Å radius. These findings are consistent with high-resolution electron microscopy images which reveal closed-shell carbon particles in the same size range