  The vapor-liquid-solid (VLS) method is considered a plausible technique for
synthesizing germanium (Ge) nanostructures (e.g. nanowires), which have a broad
range of applications due to their unique electronic properties and intrinsic
compatibility with silicon. However, crystallization failures and material
defects are still frequently observed in VLS processes, with insufficient
understanding of their underlying mechanisms due to instrumental limitations
for high-resolution in-situ characterizations. Employing an accurate
interatomic potential well fitted to the gold-germanium (Au-Ge) phase diagram,
we performed molecular dynamics simulations for a systematic investigation on
the Au-catalyzed growth process of Ge crystals. From the simulations,
relationships were established between the overall Ge growth rate and several
main synthesis conditions, including substrate crystallographic orientation,
temperature and Ge supersaturation in liquid. The dynamical behaviors of Ge
atoms near the liquid-solid growing interface were captured, from which the
atom surface stability and exchange rate were estimated for quantifying the
atomistic details of the growth. These interface properties were further linked
to the surface morphologies, to explain the observed orientation-dependent
growing modes. This study sheds new lights into the understanding of the VLS
growth mechanisms of Ge crystals, and provides scientific guidelines for
designing innovative synthesis methods for similar nanomaterials.
