  We present a colloidal synthesis strategy to obtain single-crystalline PbS
nanorings. By controlling the ripening process in the presence of halide ions,
a transformation of initial PbS nanosheets to frame-like structures and finally
to nanorings was achieved. We found that the competing ligands oleic acid,
oleate and halide ions play an important role in the formation of these
nanostructures. Therefore, we propose a formation mechanism based on a
thermally induced ripening of crystal facets dependent on the surface
passivation. With this method, it became possible to synthesize colloidal
nanorings of cubic crystal phase galena PbS. The synthesis was followed via TEM
and the products are characterized by XRD, AFM and STEM tomography. Control of
the initial nanoframe morphology allows adjusting the later nanoring
dimensions.
