Dynamics of VLS-Grown\nSi Nanowires: Insights from\nMolecular Dynamics Simulations on Facet Evolution, Twinning, Nucleation,\nand Impurity Dynamics

A clear understanding\nof the mechanisms governing the growth of\nnanowires is crucial to achieving control over their structures and\nproperties. Here, we employ molecular dynamics (MD) simulations to\ninvestigate several important phenomena in Au-catalyzed Si nanowires\n(SiNWs) grown via the vapor–liquid–solid method. MD\nsimulation serves as a complementary tool for uncovering the mechanisms\nof nanowire growth at temporal and spatial scales that current experimental\ntechniques cannot achieve. After verifying the trend in the phase\ndiagram and the preferred growth direction, we present detailed atomistic\ninsights into the growth mechanisms, including truncation, twinning,\nnucleation processes, and the dynamics of Au impurities. Our study\nreveals that nucleation of truncating nanowires occurs at the edge\nof the main facet where it meets the {111} truncating edge, which\ntends to have a large truncating area and thus attributes to an asymmetric\nwetting appearance on the side walls. Observed twinning phenomena\nconfirm the nucleation point as twinning changes the location of {111}\ntruncating edges, subsequently altering the nucleation site. Additionally,\nwe explore the early stage of growth and observe tapering facilitated\nby changes in the contact angle during the growth, independent of\nsurface diffusion. The “crawling” mechanism is also\nelucidated through atomistic details. Furthermore, investigations\ninto Au impurity incorporation in SiNWs reveal their predominant presence\nwithin the bottom layer of each Si bilayer. Their transient incorporation\nat the SiNW’s top surface at the liquid–solid interface,\nfollowed by rapid dissolution into the liquid phase, highlights the\ndynamic nature of impurity interactions during the growth process.\nThese findings could provide insights into other types of nanowires\ngrown via the vapor–liquid–solid method.