Graphite evaporation by DC arc discharge in rarefied hydrogen gas forms three types of carbon allotropes on the cathode surface as carbonaceous deposit. Typical one is multiwalled carbon nanotubes (MWNTs) found in the central region of the cathode deposit. Other carbon allotropes are carbonaceous hard outer shell and petal-like graphene sheets. As-grown MWNTs could be easily purified by removing few co-existing carbon nanoparticles with the use of thermal etching in air. The X-ray diffraction patterns of purified MWNTs were similar to those of graphene sheetsand those of the outer shell and the raw graphite rod bore a resemblance to each other. In Raman spectra of purified MWNTs, downshift more than 10cm-1 was observed for the first order Raman-allowed phonon mode. Particular new peaks of Raman spectra for purified MWNTs were also observed.
Keywords: multiwalled carbon nanotubes, graphene sheets, hydrogen arc discharge, SEM, XRD, Raman spectra
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