Real-Time in Situ Probing of High-Temperature Quantum Dots Solution Synthesis

Abstract

Understanding the formation mechanism of colloidal nanocrystals is of paramount importance in order to design new nanostructures and synthesize them in a predictive fashion. However, reliable data on the pathways leading from molecular precursors to nanocrystals are not available yet. We used synchrotron-based time-resolved in situ small and wide-angle X-ray scattering to experimentally monitor the formation of CdSe quantum dots synthesized in solution through the heating up of precursors in octadecene at 240 °C. Our experiment yields a complete movie of the structure of the solution from the self-assembly of the precursors to the formation of the quantum dots. We show that the initial cadmium precursor lamellar structure melts into small micelles at 100 °C and that the first CdSe nuclei appear at 218.7 °C. The size distributions and concentration in nanocrystals are measured in a quantitative fashion as a function of time. We show that a short nucleation burst lasting 30 s is followed by a slow decrease of nanoparticle concentration. The rate-limiting process of the quantum dot formation is found to be the thermal activation of selenium.

Organic Phase Syntheses of Magnetic Nanoparticles and Their Applications

“…The method was also used to study the growth mechanism of the CdSe NPs. 103 From the NP size distribution and NP concentration data obtained, the growth of the NPs was thought to be limited by the thermal activation of the Se precursor. Using the in situ X-ray scattering, the fast nucleation and growth kinetics of Ag NPs were studied.…”

Analysis of Particle Size Distributions of Quantum Dots: From Theory to Application

“…As only one superimposed scattering curve is recorded, data interpretation is challenging and cross-validation against other, independent techniques is required. However, once established for a certain system, SAXS is a powerful technique for particle analysis (Abécassis B. et al, 2015;Caetano B.L. et al, 2010;Polte J. et al, 2010).…”

In Situ Synchrotron X‐ray Characterization Shining Light on the Nucleation and Growth Kinetics of Colloidal Nanoparticles

“…These time‐dependent parameters of CNPs are then used to fit Equation (4) or Equation (5) to determine the growth mechanism of the CNPs. These parameters can also be obtained from the Monte‐Carlo fitting of the SAXS patterns using Equation (8), where all the parameters are randomly chosen with little or no empirical knowledge . For example, Wu et al used in situ SAXS to study the synthesis of monodisperse Pd CNPs in octadecene containing Pd(acac) 2 (acac=acetylacetonate) as precursor reactant and various amounts of trioctylphosphine(TOP), oleic acid, and oleylamine as surfactant ligand .…”

“…This strategy can also be used to study the synthesis of monodisperse CNPs in the presence of a micelle phase. For example, Abécassis et al observed the melting of lamellar micelles and the following formation of small micelles (<1 nm) in the synthesis of CdSe NPs using the combined in situ SAXS and WAXS . Yi et al used in situ SAXS to reveal the role of tetraethylorthosilicate/cetyltrimethylammonium bromide (TEOS/CTAB) micelles in the synthesis of mesoporous silica NPs …”