Graphene characterization

In conclusion, in this Chapter I have shown that Raman spectroscopy is a powerful, fast, non-destructive tool for graphene characterization. 

There is an infinite number of possible atomic structures of graphene tubules. Each structure is characterized by its diameter and the helical arrangement of the carbon hexagons. Presumably, only single-shell tubes with small diameters of about 10 A are formed and tubes with larger diameters are multishell tubes. 

Since their first discovery by Iijima in 1991 [1], carbon nanotubes have attracted a great deal of interest due to their very exciting properties. Their structure is characterized by cylindrically shaped enclosed graphene layers that can form co-axially stacked multi-wall nanotubes (MWNTs) or single-walled nanotubes (SWNTs). Like in graphite, carbon atoms are strongly bonded to each other in the curved honeycomb network but have much weaker Van der Waals-type interaction with carbons belonging to... 

The structure of SWCNTs is characterized by the concept of chirality, which essentially describes the way the graphene layer is wrapped and is represented by a pair of indices (n, m). The integers n and m denote the number of unit vectors (a a2) along the two directions in the hexagonal crystal lattice of graphene that result in the chiral vector C (Fig. 1.1) ... 

The characterization of graphene often involves several techniques in conjunction in order to build up a complete picture of the material. The techniques typically include electron microscopy, Raman spectroscopy, X-ray photo-emission spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR) and thermal-gravimetric analysis (TGA). 

While electron microscopy is an invaluable tool for characterization of graphene, it is a costly and often time-consuming technique. In contrast, Raman spectroscopy is a quick and easy method to obtain a wide range of properties of graphene, including flake size, layer number, defect density, and doping levels amongst others [118]. 

C.-Y. Su, Y. Xu, W. Zhang, J. Zhao, X. Tang, C.-H. Tsai, et al., Electrical and spectroscopic characterizations of ultra-large reduced graphene oxide monolayers, Chemistry of Materials, 21 (2009) 5674-5680. 

R.S. Weatherup, B.C. Bayer, R. Blume, C. Ducati, C. Baehtz, R. Schlogl, et al., In situ characterization of alloy catalysts for low-temperature graphene growth, Nano Letters, 11 (2011) 4154-4160. 

Characterization of graphene films and transistors grown on sapphire by metal-free chemical vapor deposition, ACS Nano, 5 (2011) 8062-8069. 

Nanocarbon structures such as fullerenes, carbon nanotubes and graphene, are characterized by their weak interphase interaction with host matrices (polymer, ceramic, metals) when fabricating composites [99,100]. In addition to their characteristic high surface area and high chemical inertness, this fact turns these carbon nanostructures into materials that are very difficult to disperse in a given matrix. However, uniform dispersion and improved nanotube/matrix interactions are necessary to increase the mechanical, physical and chemical properties as well as biocompatibility of the composites [101,102]. 

Fan, L., et al., Ferrocene functionalized graphene preparation, characterization and efficient electron transfer toward sensors ofH202. Journal of Materials Chemistry, 2012. 22(13) ... 

Tu, X., et ah, One-pot synthesis, characterization, and enhanced photocatalytic activity of a BiOBr-graphene composite. Chemistry - A European Journal, 2012.18(45) p. 14359-14366. 

Materials should be characterized and described in as many details as possible, because the nanotube toxicity can depend on by-products of their synthesis as well as on their design. It would be desirable to provide at least information on their composition (including metals and heteroatoms, which are present in a quantity higher than 0.1%), detailed description of morphology, data on surface chemistry, crystallinity, and spatial organization of graphene planes ... 

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