PNNL

Abstract

Vapor-liquid-solid (VLS) method is vastly employed to grow hierarchical structures with unique properties. However, key questions remain, such as what controls the branch density and how the growth rate is correlated to the catalyst droplet size. Here, PbSe is employed as a model system and an in-depth understanding of the kinetics of the nucleation, growth, and subsequent coalescence processes of Bi liquid catalyst droplets is provided by direct observation of PbSe branched wire growth in an environmental transmission electron microscope. This brings a kinetic control of the branch density by varying the parameters, such as temperature. The dependence of wire growth rate on the catalyst droplet size is revealed unambiguously, i.e., the smaller the catalyst size the larger wire VLS growth rate, because the increased chemical potential from the smaller radius of curvature leads to a reduced solubility of precursors in catalyst droplets, an increase in the supersaturation, and a subsequent increase in the wire growth rate. These results extend the fundamental understanding of the VLS growth mechanism of branched structures and benefit the structure design of hierarchical materials with tailored properties.