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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