Dynamics of VLS-Grown Si Nanowires: Insights from Molecular Dynamics Simulations on Facet Evolution, Twinning, Nucleation, and Impurity Dynamics

A clear understanding of the mechanisms governing the growth of nanowires is crucial to achieving control over their structures and properties. Here, we employ molecular dynamics (MD) simulations to investigate several important phenomena in Au-catalyzed Si nanowires (SiNWs) grown via the vapor-liquid-solid method. MD simulation serves as a complementary tool for uncovering the mechanisms of nanowire growth at temporal and spatial scales that current experimental techniques cannot achieve. After verifying the trend in the phase diagram and the preferred growth direction, we present detailed atomistic insights into the growth mechanisms, including truncation, twinning, nucleation processes, and the dynamics of Au impurities. Our study reveals that nucleation of truncating nanowires occurs at the edge of the main facet where it meets the {111} truncating edge, which tends to have a large truncating area and thus attributes to an asymmetric wetting appearance on the side walls. Observed twinning phenomena confirm the nucleation point as twinning changes the location of {111} truncating edges, subsequently altering the nucleation site. Additionally, we explore the early stage of growth and observe tapering facilitated by changes in the contact angle during the growth, independent of surface diffusion. The "crawling" mechanism is also elucidated through atomistic details. Furthermore, investigations into Au impurity incorporation in SiNWs reveal their predominant presence within the bottom layer of each Si bilayer. Their transient incorporation at the SiNW's top surface at the liquid-solid interface, followed by rapid dissolution into the liquid phase, highlights the dynamic nature of impurity interactions during the growth process. These findings could provide insights into other types of nanowires grown via the vapor-liquid-solid method.