The elastic free energy of carbon nanotubes grown by iron-catalyzed decomposition of acetylene is introduced to describe the possible tubular shapes. The equilibrium shape equation can be obtained by the first variation of the elastic free energy of the slightly distorted tube. The model is consistent with both stable and metastable shapes observed in our experiments. The results are due to the fluctuation of growth conditions, such as the pressure, temperature, and composition of the vapor. © 1996 The American Physical Society.

• Received 9 July 1996

DOI:https://doi.org/10.1103/PhysRevB.54.16436