Triangular PbS nano-pyramids, square nanoplates, and nanorods formed at the air/water interface

PbS nanocrystals with different shapes were synthesized at the air/PbCl2 aqueous solution interface via reaction between Pb2+ and H2S gas under poly(9-vinylcarbazole) (PVK) thin films and characterized by transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), electron diffractometry (ED), scanning electron microscopy (SEM), and UV-vis spectroscopy. It was found that the shapes of the nanocrystals depend on the experimental conditions, such as temperature, subphase concentration, and H2S amount. Triangular nanopyramids and nanoplates/nanorods were formed at ca. 20 and 30 degrees C, respectively. The (111) plane of the nanopyramid is parallel to the water surface, and the other three sides are (100), (010), and (001) faces, respectively. For the rectangular nanoplates and nanorods, the (001) planes are parallel to the water surface. The formation of the nanopyramids should be related to lattice matching between the two-dimensional arrays of nitrogen atoms in PVK Langmuir monolayers at 20 degrees C with the (111) crystal face of PbS, while the formation of nanoplates and nanorods at 30 degrees C would be ascribed to the variation of the Langmuir monolayer structure. In addition, the shapes of nanoplates/nanorods changed with the subphase concentrations and H2S Volumes.