Induced branching in confined PbSe nanowires

The synthesis of narrow diameter (< 10 nm) straight and branched PbSe nanowires (NWs) using a seeded solution approach is described. Solution-based PbSe NWs are obtained by injecting a solution consisting of trioctylphosphine selenide (TOPSe) and Au/Bi core/shell nanoparticles (NPs) into a mixture composed primarily of a mild coordinating solvent, a fatty acid, and a Ph precursor at moderate temperatures. The resulting NWs have diameters between 5 and 10 nm and lengths ranging from 1 to 5 mu m. High-resolution transmission electron microscopy (TEM) reveals that the NWs exhibit a high degree of crystallinity and grow along the 100) directions of the lattice. By varying the initial reaction conditions, in particular the Pb to Se precursor ratio, branched NWs can be obtained. The growth mechanism appears similar to the case of analogous (branched) CdSe NWs, although the underlying rock salt structure of PbSe leads to right angles and t-shapes as opposed to CdSe, where v-shape, y-shape, and tripod morphologies are observed due to its underlying zinc blende and wurtzite lattices. In addition, "mergedy" NWs and higher order structures exhibiting multiple branching points are observed. Both straight and branched NWs have radii well below the bulk exciton Bohr radius of PbSe (46 nm), opening up opportunities for interesting optical and electrical studies of strong confinement in this system. The current investigation also sheds additional light on the mechanism behind self-induced branching in one-dimensional (1D) nanowires.