Morphological Instabilities and the Dynamics of Carbon Nanotube Forest Growth

Vertically aligned carbon nanotube forests show various morphologies on both macro- and micro-scales. These morphologies are a result of growth mechanisms and interactions between nanotubes. By investigating these morphologies, we study both the growth mechanisms and the interactions. We examine forest morphologies in situ, dynamically during chemical vapor deposition growth and ex situ, post growth. In situ observations allow the separate characterization of nucleation, growth and termination phases, and the exploration of connections between morphology and growth. Forests systematically show different morphologies, ranging from uniform to cracked, delaminated, and periodically rippled. These are discussed in terms of the balance of forces within the forests including cohesion, adhesion, and stiffness. We propose a simplified model that predicts termination as a result of an imbalance in the forces present. We show that growth rate differences drive many morphological effects, and these differences originate in the nucleation phase due to gas diffusion