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On the graphitization nature of oxides for the formation of carbon nanostructures

Abstract:

The graphitization role of various oxides such as silica, alumina, magnesium oxide and zirconia under typical carbon nanotube CVD synthesis conditions were analyzed. Thin films of SiO2 and SiO 2/Al203 on Si substrates were also used. All powders, upon removal from the reactor, were black in color, hinting at carbon formation. Transmission electron microscopy (TEM) studies of the material showed the oxide crystals to be coated with a few layers of material with a spacing around 0.34-0.36 nm, which is the typical graphene spacing found in graphitic nanostructures. The change of carbon feedstock, oxide, crystal size, or increasing the reaction time did not alter the number of graphitic walls. No observations of carbon formation on single-crystal substrates were reported. Results show that carbon nanotube growth may occur via the oxide support, such that the root of a carbon nanotube lies at the interface of the metal catalyst/support.