PbSe nanocrystal shape development: Oriented attachment at mild conditions and microwave assisted growth of nanocubes

PbSe nanocrystals have been synthesized by conventional hot injection process and also using microwave technique. For PbSe nanocrystals obtained via hot injection process at 160°C, the quality of the interface between the isolated and purified nanocrystals, after removal of capping ligands, strongly depends on the structure and stoichiometry of the surface. High resolution transmission electron microscopy has been used to investigate the interface between size selected PbSe nanocrystals. Oriented attachment of nanocrystals is achieved by protonation of oleate capping ligands using wet methanol and subsequent solvent evaporation. The removal of oleate from the surface is monitored using infrared spectroscopy. The attachment between preformed PbSe NCs has taken place exclusively through the {100} facets of the rock-salt lattice. In contrast to other related observations, it is found that nanocrystals can also attach through adjacent {100} facets. We have also studied the shape evolution of cubic PbSe NCs during microwave synthesis using transmission electron microscopy. The formation of PbSe nanocubes is attributed to the higher growth rate in the {111} direction compared to that in the {100} direction.