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

Abstract

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.

From Solute, Fluidic and Particulate Precursors to Complex Organizations of Matter

“…Mechanistic contributions of cluster species are recognized for several metals, metal oxides and semiconductors such as CdS, iridium, iron (oxyhydr) oxides, silver and titanium oxide particles . Conventionally addressed as ‘nanoclusters’, particles smaller than 2 nm typically exhibit atomic level rearrangements and distinct physical properties in relation to larger solid particles .…”

“…Hence the roughness of the free‐energy landscape for the structural dynamics of cluster populations determines their stability, short‐range order and in consequence their impact on the nucleation process (Figure ). This is evident from other instances, such as the stability of certain CdS cluster species originating from the resistance of coordination structures towards deformation during agglomeration (Figure c). Even during the synthesis of semiconductor nanoribbons, the transient existence of (CdSe) 34 clusters prior to (CdSe) 13 clusters suggest defined configurations and stabilities of distinct nanocluster populations ,…”

“… Mechanistic contributions of (a–c) solute clusters and (d‐h) liquid condensed phases in nucleation and crystallization reactions. Computer simulations of (a) the termination effects of HCO 3 − ions (dotted circle) on the growth and stability of CaCO 3 clusters, (b) the contributions of nitrate ions (dotted circle) as salt bridges between [Bi 6 O 4 (OH) 4 ](NO 3 ) 6 ] related cluster species, subsequently undergoing structural rearrangements and forming dimer species during bismuth oxide nucleation and (c) Cd 13 S 4 (SH) 18 PNCs exhibiting repulsive interactions based on thiol‐stabilized surfaces and distinct coordination structures . (d) In situ observations of LCPs as precursors for amorphous and crystalline metal particles in supersaturated Au 0 solutions .…”

Multistep Conformation Selection in Amyloid Assembly

“…13,14,16−20 This two-step nucleation 21−23 would place assembly nucleation and propagation in distinct environments and diversify assembly. 22−24 By defining the intermediates in a pH-dependent pathway, we now argue that in addition to electrochemical dynamics, 13−15 a more global consideration of β-sheet facial complementarity 11 contributes dominantly to assembly nucleation. Furthermore, template-directed propagation of the nucleus can lead to altered strand arrangements, which appear as propagation mutations.…”

A general strategy for colloidal stable ultrasmall amorphous mineral clusters in organic solvents

“…11–13 Pre-nucleation clusters have been found either experimentally or by modelling the nucleation of calcium carbonate (CaCO 3 ), 11,14 calcium phosphate, 15,16 magnetite, 17 silica, 18 amino acids, 19 quantum dots, 20,21 YVO 4 , 22 NaClO 3 , 23 1,3,5-tris(4-bromophenyl)benzene, 24 and many more. Analytical ultracentrifugation (AUC) measurements confirmed the presence of pre-nucleation clusters even in salts of simple monovalent ions like NaCl and LiI.…”