Shape evolution of star-shaped colloidal PbSe nanocrystals

Star-shaped colloidal PbSe nanocrystals capped with oleic acid were synthesized in solution from lead oleate and trioctylphosphine selenide precursors when lead acetate trihydrate served as the lead source. The prepared nanocrystals were characterized by X-ray diffraction, transmission electron microscopy, and Fourier transform infrared spectrometer. The nanocrystals have the same cubic rock salt lattice structure as the bulk PbSe. The initial injection of trioctylphosphine selenide into hot lead oleate solution immediately results in the formation of truncated octahedron-shaped nuclei, which are terminated by {100} faces and {111} faces. The growth along <100> direction is faster than that along <111> direction, resulting in the formation of star-shaped nanocrystals. It is confirmed that acetate in the reaction mixture plays an important role in controlling the growth mechanism and the resulting shape of nanocrystals. In addition, the reaction solvent also influences the shape of nanocrystals. The Fourier transform infrared absorption spectrum of PbSe nanocrystals exhibits dramatic blue shift from the band gap of bulk PbSe.