Instabilities in carbon nanocone stacks

Abstract

Possessing remarkable electronic, mechanical and optical properties, pristine single-walled carbon nanocones (CNCs) are envisioned here to be pulled-out co-axially from a nanocone stack. The process is simulated using molecular mechanics (MM) and dynamics (MD) employing MM3 and REBO + LJ potentials, respectively. During pulling-out, rim of the lowermost cone is constrained while the tip of the outermost cone is displaced axially from its equilibrium, quasi-statically in case of MM and by prescribing velocity of 0.1 Å/pico-sec in case of MD. During pulling-out, at a critical distance, the top cone abruptly breaks the axial symmetry with its wall deforming considerably outward. The source of this instability is building-up of compressive circumferential strain in the wall with increasing displacement; a competition between stretching and van der Waal's energy terms of the system. Interestingly, during reversal of the pulling-out process, the system is found to trace a different equilibrium path. Further, in a few-walled CNCs if the tip of the top-most cone is compressed from its equilibrium position, the stack inverts completely by breaking axial symmetry aided by snap-through buckling in segments of the periphery. Irrespective of apex angle, hydrogen passivation, temperature and potential used, the aforementioned observations are found to be intrinsic to the system.