Transitional behaviour in the transformation from active end planes to stable loops caused by annealing

Here we investigate the stabilization process on the active outer/inner surfaces (or the end plane of a graphene sheet) for shortened cup-stacked-type carbon nanotubes caused by annealing, utilizing both analytic and electrochemical techniques. The suggested schematic procedure for loop formation is as follows: (a) formation of single-type loops between neighbouring truncated conical graphene layers at 900–1200 °C through a zipping mechanism after the evolution of hydrogen gas; (b) the transition from single- to multi-type loops above 1500 °C accompanying a decrease in specific surface area.