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Despite broad interest in colloidal lead halide perovskite nanocrystals (LHP NCs), their intrinsic fast growth has prevented controlled synthesis of small, monodisperse crystals and insights into the reaction mechanism. Recently, a much slower synthesis of LHP NCs with extreme size control has been reported, based on diluted TOPO/PbBr2 precursors and a diisooctylphosphinate capping ligand. We report new insights into the nucleation, growth, and self-assembly in this reaction, obtained by in situ synchrotron-based small-angle X-ray scattering and optical absorption spectroscopy. We show that dispersed 3 nm Cs[PbBr3] agglomerates are the key intermediate species: first, they slowly nucleate into crystals, and then they release Cs[PbBr3] monomers for further growth of the crystals. We show the merits of a low Cs[PbBr3] monomer concentration for the reaction based on oleate ligands. We also examine the spontaneous superlattice formation mechanism occurring when the growing nanocrystals in the solvent reach a critical size of 11.6 nm.

We present a detailed powder X-ray diffraction (p-XRD) and transmission electron microscopy (TEM) study to explore the structural properties of CdS, CdSe, and CdTe semiconductor nanowires (NWs) grown by the solution-liquid-solid (SLS) method. The SLS method yields easily dispersible NWs with a controllable diameter and polytypic crystal structure. The different samples exhibit different wurtzite (WZ) and zincblende (ZB) fractions, which are investigated by high-resolution TEM of selected wires with distinct crystallographic orientations, and also by p-XRD of a large amount of NWs. In combination with atomistic models containing up to one million atoms, we calculate diffraction patterns based on the kinematic theory of diffraction. We show that the ZB-rate in WZ-rich NWs can be directly determined from relative reflex intensities in the experimental p-XRD data.

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