  A model for the formation of carbon nanotubes (CNTs) and layered graphene in
an arc discharge method is developed on the basis of observed erosion of
graphite anode under various experimental conditions and analyses of the
morphology of the eroded anode-surface, concerned cathode deposits and their
constituents. It is predicted that, cold thermal shock, triggered by the rapid
movement of the anode-spot, leads to crack microbranching at some selected
locations on the anode-surface. These crack-microbranches cleave and fragment
the basal planes of pairs of adjacent crystallites into curved graphitic
nanoribbons with minimum two basal planes. These nanoribbons further react
chemically with the C2 and C3 precursors present in the dusty carbon plasma and
evolve either in the form of CNT or layered-graphene, depending on the
viscosity and composition of the gaseous environment they are exposed to, just
after getting detached from the anode.
