Raman identification of onion-like carbon

In situ formation of onion-like carbon from the evaporation of ultra-dispersed nanodiamonds

“…Similarly, the full width at half maximum (FWHM) of the D band of 77 cm -1 is rather large, providing further evidence of the defective nature of the evaporated OLC particles. The centre of the 7 (broad) G band in the evaporated OLC is at 1590 cm -1 , which is identical to that observed by Obraztsova et al [21] for nanodiamond partially graphitized at 1400 K.…”

“…4, the symmetric shape of the latter suggests that any nanodiamond contribution to the Raman spectrum, if present, is extremely small. Ultra-dispersed nanodiamond samples annealed to the range of temperatures used for evaporation in this study typically form buckydiamonds with a clear contribution from nanodiamond present in the Raman spectra [21]. Only the smallest OLC particles (typically less than about 2 nm in diameter, corresponding to three to five carbon shells) formed by annealing nanodiamond at these temperatures have been observed to have diamondfree cores [21].…”

“…Nanocrystalline diamond has a relatively narrow Raman band at ~1323 cm -1 [21] and although this overlaps with the D band in the evaporated OLC sample, shown in Fig. 4, the symmetric shape of the latter suggests that any nanodiamond contribution to the Raman spectrum, if present, is extremely small.…”

“…4 and is typical of carbon nanomaterials. It was shown in an earlier Raman study by Obraztsova et al [21], that the Raman spectrum of OLC formed by annealing ND precursors possesses two distinct bands associated with 'disordered' carbon (D) and 'graphitic' carbon (G). Sano et al [22], examining OLC formed by arc-discharge under water observed more modes in addition to a G band frequency much closer to that of HOPG, which implied that onions are perfectly spherical with fewer defects.…”

“…Ultra-dispersed nanodiamond samples annealed to the range of temperatures used for evaporation in this study typically form buckydiamonds with a clear contribution from nanodiamond present in the Raman spectra [21]. Only the smallest OLC particles (typically less than about 2 nm in diameter, corresponding to three to five carbon shells) formed by annealing nanodiamond at these temperatures have been observed to have diamondfree cores [21]. Moreover, partially graphitized nanodiamond particles formed in this temperature range are often linked by extended curved graphitic layers [11].…”