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Chapter 5 β Production of Few Layer Graphene in Organic Solvents to edge defects. Unlike the GO or rGO, the FWHM(D) band doesnβt show significant broadening confirming the defects are not of sp3 type.173 Similar results were observed for FLG/DMF as shown in Appendix 9.1. The position of 2D band shifts to a lower wavenumber as a function of sonication time when fitted with single Lorentzian suggesting thinner flakes remain dispersed at high centrifugation speeds. The centrifugation speed did not have any significant effect on the position of G and D band and their respective FWHM (not shown). πΌ2π·βπΌπΊ and πΌπ·βπΌπΊ ratio had similar results as seen for FLG/NMP suggesting the increase in πΌπ·βπΌπΊ ratio is mainly because of the edges. 5.2.3.2. Raman analysis to estimate flake length and access defect type Coleman et al. have shown that the sonication of graphite to produce graphene is relatively a non-destructive process, in terms of introducing any new basal plane defects, and the observed defects are predominantly due to the edges.59-63 They have probed the correlation between the πΏ of the flakes to πΌπ·βπΌπΊ ratio to confirm that sonication doesnβt introduce any basal plane defects. This procedure was followed in this present study to prove that the defects are mainly due to the edges produced by sonication process and not that of basal plane defects. As explained in the previous section, as the size of flakes decreases due to sonication process and centrifugation speeds, the density of edges under the laser spot increases resulting in an intense D band and hence πΌπ·βπΌπΊ ratio. If the variation in πΌπ·βπΌπΊ ratio with sonication time and centrifugation speed is only because of the flake size, then the πΌπ·βπΌπΊ ratio must relate to the mean length of the flake (γπΏγ) such that, 59, 61-63 πΌπ· = (πΌπ·) + π Equation 5.1 πΌπΊ πΌπΊ ππππhππ‘π γπΏγ Where, k is a constant and (πΌπ·βπΌπΊ)ππππhππ‘π is the πΌπ·βπΌπΊ ratio of starting graphite. The starting graphite powder had a (πΌπ·βπΌπΊ)ππππhππ‘π ~0.08 (Figure 5.9). Since the graphite has relatively large grain size (~ 200 ΞΌm), the ratio could not have come from edges, indicating that some basal plane defects are present in the starting graphite powder. 149PDF Image | PRODUCTION AND APPLICATIONS OF GRAPHENE AND ITS COMPOSITES
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