Catalyst-particle configurations: From nanowires to carbon nanotubes

Surface-energy minimization is used to study capillary effects that determine the stable configurations of (liquid or solid) particles atop tubes or wires. The results give allowable ranges for the volume (Vc) of the particles as a function of the inner and outer radii of the tubes, RI and Ro, respectively. When RI/Ro=0, the object is a nanowire. When RI/Ro=1, it is a single-wall carbon nanotube. When 0<RI/Ro<1, it can be thought of as a multiwall carbon nanotube. Moreover, the transition paths among different configurations are studied. These results suggest possible mechanisms for the reshaping of the "pear-like" catalyst particles in carbon nanotubes that oscillate across local energy-maximum points with respect to the position of the lower interface in the inner wall.