Nanosprings

The transition from linear to helical growth of amorphous boron carbide nanowires has been examined with high-resolution transmission electron microscopy. Based on the observed changes of the iron catalyst at the transition point from linear to helical growth, a model of helical growth of solid nanowires has been developed based on the work of adhesion of the metallic catalyst to the tip of the nanowire. This model demonstrates that contact angle anisotropy at the catalyst/wire interface drives helical growth. The anisotropy is introduced when the radius of the droplet (R) exceeds the radius of the nanowire (ρ), and the center of mass of the metal droplet is displaced laterally from the central axis of the nanowire.