Electrical, optical and mechanical properties of inorganic nanostructures have strong relationships with their morphologies. For example, one-dimensional (1D) nanomaterials such as carbon nanotubes, ZnO nanowires, TiO2 nanotubes possess novel properties that have applications in nanoelectronics, nanophotonics, renewable energy, and chemical and biological sensing. Hierarchical 1D nanostructures with increasing structural complexity that extend into 3D, such as in these pine tree nanowires, can potentially increase these functionalities and enhance applications such as solar energy conversion and 3-D nanoelectronics. Many branched hierarchical nanostructures have been synthesized and their properties have been studied. Examples include hyperbranched PbS/PbSe for potential solar energy applications and chiral mesoporous silicas as catalysis and separation media. Understanding the underlying growth mechanisms of these materials is important for manipulating their architectures and therefore controlling their properties. This project will focus on probing kinetic and thermodynamic mechanisms of branched nanocrystal nucleation and growth at the atomic level via in situ TEM. Specifically, we will investigate PdS/PdSe hyperbranched nanostructure growth, which proceeds via a vapor-liquid-solid (VLS) mechanism at elevated temperatures of 450ºC to 650ºC.