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74 Graphene – Synthesis, Characterization, Properties and Applications spectroscopy for reasons not established yet. The 1,600 cm-1 phonon frequency assigned to the perfect graphite’s aromatic carbon ring is confirmed by FTIR as previously seen in Raman spectroscopy. The group of absorption peaks from 3,000 to 3,550 cm-1 have previously been assigned to OH bonds which suggest that some terminal oxygen atoms in the WO3 structure are not only bonded to the carbon aromatic rings but also to hydrogen. No C–H bonds were found by FTIR. Raman spectroscopy of these structures supports the fact that there exists mixed valence of V4+ (signified by the 300 cm-1 phonon which is an undertone of the main 600 cm-1 peak which in these samples is masked by the strong Si–Si background noise from the substrate at 520 cm-1) and V5+ from 930–970 cm-1. The peak at 1,120 cm-1 suggests the presence of C–C bonds in the VO2/V2O5 structure. As opposed to the carbon modified WO3 nano-platelets which showed aromatic carbon apart from C–C bonds, Raman spectroscopy showed no aromatic rings in VO2/V2O5 triangular envelopes. 4. Possible mechanism of formation of the triangular envelopes made out of graphene sheets and VOx inorganic fullerenes Since the discovery of carbon nano-tube structure in the early 1980s, Tenne and co-workers also reported similar structures in WSe2 and MoS2 [46]. The argument was that metal chalcogenides and oxides are also capable of arranging their unit cells in a hexagonal close packing as in carbon, thereby forming a layer of atoms whose edges leave dangling bonds. These bonds cause intense attractive forces which compel the layer to fold on itself into various shapes such as tubes, scrolls and rods. Formation of fullerenes is due to defects which are found to be pentagonal, rectangular and triangular bonds, which are possible in all transition metal compounds. Different processes of formation of, for instance, V2O5 capsules [47, 48] have led authors to suggest various mechanisms. We suggest that the formation of our triangular envelopes/capsules starts with the formation of closely packed hexagonal 2-D layers when the VOx is subjected to the laser beam. This assumption is based on the known experimental and theoretical facts from computer modelling that V2O5 is capable of wrapping into V2O5 nano-tubes [49] either as a zig–zag framework or in an arm chair structure [50]. It is also known that a mixture of V4+ and V5+ in (VIVO) [VVO4].0.5[C3N2H12] can lead to a layered structure [51]. The organic layer intercalates the inorganic counterpart with the latter containing square pyramids formed by V4+ ions and tetrahedral pyramids formed by V5+ ions. On this layer are randomly scattered fullerenes of the same material which have self-assembled under the same laser beam. These fullerenes together with dangling bonds on the layer periphery exert intense attractive forces which cause the layer to fold on itself in a certain pattern. A schematic cartoon of the possible formation of the VO2/V2O5 triangular envelops that encapsulate the VO2/V2O5 QDs and the VO2/V2O5 fullerenes are shown in Fig. 7. A hexagonal packing in a zig–zag fashion ends up having arm-chair structure dangling bonds in the periphery of the hexagon. The dangling bonds and the van der Waal’s forces from the particles sitting on the surface compel this sheeting to wrap on itself from a hexagon, through intermediate stages, into a triangular envelope. The foldings are along arm-chair structure on two sides of the triangle AEC (sides AC and EC in Fig. 16 (a)) and along a zig–zag structure on the third side of the triangle (side AE).PDF Image | GRAPHENE SYNTHESIS CHARACTERIZATION PROPERTIES
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