  Colloidal lead sulfide is a versatile material with great opportunities to
tune the bandgap by electronic confinement and to adapt the optical and
electrical properties to the target application. We present a new and simple
synthetic route to control size and shape of PbS nanoparticles. Increasing
concentrations of explicitly added acetic acid are used to tune the shape of
PbS nanoparticles from quasi-spherical particles via octahedrons to six-armed
stars. The presence of acetate changes the intrinsic surface energies of the
different crystal facets and enables the growth along the <100> direction.
Furthermore, the presence of 1,2-dichloroethane alters the reaction kinetics,
which results in smaller nanoparticles with a narrower size distribution.
