Raman Spectra for Characterization of Onion-Like Carbon

In this work the Raman spectroscopy abilities for diagnostics of carbon onions synthesized from nanodiamonds have been analyzed. Several series of nanodiamonds transformed into onion-like carbon by heating at 1000-1900 K in vacuum were characterized with Raman spectroscopy. A high resolution transmission electron microscopy (HRTEM) was used to estimate the average size of nanodiamonds in the series synthesized by different methods. Each series consisted of a pristine nanodiamond powder and materials appeared after its heat treatment at different temperatures in vacuum. The changes corresponding to the nanodiamond crystal transformation into the onion-like carbon (via the stage of diamond cores enveloped by a few layer graphene) have been revealed in Raman spectra. The basic attention has been paid to behavior of D (disorder-induced), G (graphite) and 2D (two-phonon scattering)-bands in the Raman spectra.