Graphitization Mechanism during the Carbon-Nanotube Formation Based on the In-Situ HRTEM Observation

Abstract

The mechanism of the carbon nanotube (CNT) formation and its graphitization has not been well understood and is still under controversy. The authors have been studying a new process to form CNTs, where polyynecontaining carbons are heated and irradiated by an electron beam in a transmission electron microscope (TEM). The technique is compatible to an in-situ observation and was applied to a high-resolution TEM (HRTEM) to elucidate the graphitization mechanism. The observation shows that micro-graphenes exist from the beginning of the formation process and develop to form highly ordered graphene layers through fusion and rearrangement of the premature layers, accompanied by evaporation of micro-graphenes. The CNT formation mechanism focusing on its graphitization is presented and discussed.

In situ synthesis of carbon nanotubes decorated with palladium nanoparticles using arc-discharge in solution method

“…Such defects could initiate an inner cap with time. The scroll mechanism can form a convoluted multiwalled CNT which could eventually transform to a concentric multiwalled CNT by the process of rearrangement of carbon atoms as suggested by Yasuda et al 44 Figure 13(c) shows the same numbers of walls in the two sides of a CNT which may support the scroll mechanism. The formation of a cap on the CNT was possibly from the systematic deposition of atomic carbon produced during the arc-discharge process.…”

Elastic modulus of multi-walled carbon nanotubes produced by catalytic chemical vapour deposition

“…High-resolution TEM studies of MWCNTs irradiated by a large flux of electrons show possible pathways for improvements in the wall structure when there is sufficient energy: fusion of the round-shaped graphene into the walls or rearrangement of the graphene layers [37].…”

Ecofriendly synthesis of MWCNTs by electric arc in aqueous medium: Comparative study of 6B pencil and mineral graphite

“…The higher the G' band intensity compared to the D and G bands, the higher the MWCNTs purity, which translated to less amorphous carbon and defects 37 . MWCNTs quality can also be determined using the ( I D / I G ) ratio which is related to the carbon graphitization degree 39 . The lower the ratio, the higher the graphitization degree, and the higher the quality of MWCNTs present in the sample 38 .…”