Nucleation and growth of PbS nanocrystals and simulation of X-ray diffraction patterns

Ultrasmall particles of lead sulfide were synthesized from lead ions and long-chain thiols in a non-aqueous medium. The growth of nanocrystals with the macroscopic rocksalt lattice (up to size > 10 nm) proceeds through several steps: Pb-thiolate complexes with no solid phase, small nuclei at the beginning of crystal lattice formation, and nanometer particles with a bulk-like structure. This process is studied by X-ray diffraction (XRD), scanning tunneling microscopy (STM), and atomic force microscopy (AFM). XRD patterns are simulated with sufficiently good fit to the experiment for rocksalt-type model lattices including 27, 75, 125, and 729 atoms. Lead sulfide particles formed at the different steps show the pronounced quantum-size effect in optical spectra, They can be precipitated from colloids in the form of a stable solid phase. (C) 1998 Published by Elsevier Science B.V. All rights reserved.