In situ investigation of two-step nucleation and growth of CdS nanoparticles from solution

We report on a combined ultra-fast in situ SAXS and WAXS study along a free-jet providing insight into the evolution of the morphology and crystalline structure of CdS quantum dots in the very early stage of nucleation between 100 μs and 2.5 ms with a time resolution down to 10 μs. Accessing this yet unexplored time regime provides direct evidence of a two-step mechanism via formation of prenucleation clusters followed by nanoparticle nucleation from coalescing precursors. Using ab initio calculations, the latter species is identified as Cd 13 S 4 (SH) 18 clusters, the stability of which results from a compact surface and inner structure. We report on an ultra-fast in situ SAXS and WAXS study along a free-jet. A two-step nucleation mechanism for CdS is observed and supported by ab initio calculations.