Multiscale simulations of carbon nanotube nucleation and growth: mesoscopic continuum calculations

As part of a focused computational effort on the multiscale simulations of carbon nanotube nucleation and growth, we have developed computer programs for coupled heat and mass flow in one and two dimensions. In the tip-growth mode, the sample is divided into three main regions, each of which can be further subdivided as required. In region 1, carbon is supplied to the catalytic particle from an ambient gas of carbon-containing compounds. The chemistry and thermodynamics of the decomposition of these compounds can be included in region 1, but the capability has not yet been implemented. The carbon diffuses through the catalytic particle in region 2 under concentration and temperature gradients and with a diffusion coefficient that can depend on both concentration and temperature. Region 3 consists of the interfacial region between the catalytic particle and the growing nanotube. Results to date demonstrate the key roles played by the size and shape of the catalytic particle in conjunction with the concentration and temperature gradients at the gas/solid interface and in region 2. Results also suggest how the growth of a single wall may interfere with, but not necessarily prevent, the growth of additional walls in a multi-walled nanotube. Again, the carbon concentration profile in the catalytic particle at the different growth sites is a key factor.