Nanowires (NWs) are considered as promising components of the next-generation optical and electronic devices. One commonly used method for NW synthesis is the chemical vapor deposition (CVD) by the vapor-liquid-solid (VLS) growth mechanism as shown below.
Despite decades of study on the NW and single crystal whisker VLS growth, many fundamental aspects are still not well understood due to limitations on experimental diagnostic methods. Theoretical models and computations can complement experiments to help us answer the fundamental questions.
We have been constructing both atomistic and continuum models for the gold-catalyzed VLS growth of silicon and germanium nanowires.
On the atomistic scale, we developed Au-Si and Au-Ge MEAM potentials that are fitted to ab initio data and binary phase diagrams. The following figure compares the experimental binary phase diagram and the phase diagram predicted by our Au-Si potential. Using these interatomic potentials, we perform molecular dynamics (MD) simulations to understand the atomistic mechanisms of VLS nanowire growth (a snapshot is shown below).
On the continuum scale, we developed a three-dimensional multi-phase field (MPF) model for studying the morphology changes of the nanowire and catalyst droplet during VLS growth. Of special interest is the phenomenon of growth kinking, i.e. the sudden change of growth directions. The phase field model helps us understand the mechanism of growth kinking observed in experiments and provides suggestions on how they might be avoided during growth. The following figures show kinking observed in phase field simulations and in experiments.