PRODUCTION AND APPLICATIONS OF GRAPHENE AND ITS COMPOSITES

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PRODUCTION AND APPLICATIONS OF GRAPHENE AND ITS COMPOSITES ( production-and-applications-graphene-and-its-composites )

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Chapter 3 – Raman Spectroscopy of Graphene and Graphene-based Strain Sensors Moreover, the LPE graphene mostly contains a D band (in bulk measurement), and the 𝐼𝐷⁄𝐼𝐺 ratio are often related to edges produced due to the LPE process. The Coleman group, who carried out extensive study59-63, 77 on sonication-assisted production of graphene, have shown that sonication does not produce any body defects apart from edges. Assuming the flakes are rectangular, they have probed the edge-length-to-flake- area ratio, 〈𝑤〉−1 + 〈𝐿〉−1, with the 〈𝐼𝐷⁄𝐼𝐺〉 ratio and showed that they scale linearly (Figure 3.7a), suggesting the increase in 𝐼𝐷 is mainly due to the formation of new edges.3 Figure 3.7: a) 〈𝐼𝐷⁄𝐼𝐺〉 ratio vs〈𝑤〉−1 + 〈𝐿〉−1 for NMP-sonicated graphene (36-192 hr sonication, 500-4000 rpm centrifugation). The straight line in this plot represent that the formation of new edges are responsible for increase in 𝐼𝐷⁄𝐼𝐺 ratio. The straight line also coincides with the starting graphite,(𝐼𝐷⁄𝐼𝐺)𝑝𝑜𝑤𝑑𝑒𝑟.59 b) 𝐼𝐷⁄𝐼𝐺 as a function of FWHM(G) for 120 min NMP-sonicated graphene showing a positive linear correlation. Upon annealing, effectively healing the basal plane defects, the correlation is lost.76 On the contrary, Bracamonte et al. reported that sonication of graphite to produce graphene induce basal plane defects by probing the relationship between the 〈𝐼𝐷⁄𝐼𝐺〉 ratio to FWHM(G).76 As mentioned in the previous section, FWHM(G) doesn’t increase upon introducing edges whereas it increases with bulk disorder. They have found that shorter sonication times doesn’t have any correlation between 𝐼𝐷⁄𝐼𝐺 ratio to FWHM(G), whereas it positively correlates for longer sonication times. Moreover, upon annealing the sample, thereby healing the body defects, they observed loss of correlation (Figure 3.7b), suggesting perhaps sonication does introduce basal plane defects such as topological defects (like pentagon-heptagon pairs).76 These studies on LPE graphene using Raman spectroscopy show its significance in deriving wealth of information. 79

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