title: 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.
authors: †Laboratoire de Physique des Solides, Univ. Paris-Sud, CNRS, UMR 8502, F-91405 Orsay Cedex, France.
authors: Benjamin
authors: B
authors: Abécassis
authors: ‡LPEM, ESPCI-ParisTech, PSL Research University, CNRS UMR 8213, Sorbonne Universités, UPMC Paris 06, 10 rue Vauquelin, 75005 Paris, France.
authors: Cécile
authors: C
authors: Bouet
authors: †Laboratoire de Physique des Solides, Univ. Paris-Sud, CNRS, UMR 8502, F-91405 Orsay Cedex, France.
authors: Cyril
authors: C
authors: Garnero
authors: †Laboratoire de Physique des Solides, Univ. Paris-Sud, CNRS, UMR 8502, F-91405 Orsay Cedex, France.
authors: Doru
authors: D
authors: Constantin
authors: ‡LPEM, ESPCI-ParisTech, PSL Research University, CNRS UMR 8213, Sorbonne Universités, UPMC Paris 06, 10 rue Vauquelin, 75005 Paris, France.
authors: Nicolas
authors: N
authors: Lequeux
authors: ‡LPEM, ESPCI-ParisTech, PSL Research University, CNRS UMR 8213, Sorbonne Universités, UPMC Paris 06, 10 rue Vauquelin, 75005 Paris, France.
authors: Sandrine
authors: S
authors: Ithurria
authors: ‡LPEM, ESPCI-ParisTech, PSL Research University, CNRS UMR 8213, Sorbonne Universités, UPMC Paris 06, 10 rue Vauquelin, 75005 Paris, France.
authors: Benoit
authors: B
authors: Dubertret
authors: §National Institute for Materials Science (NIMS), 1-2-1 Sengen, 305-0047 Tsukuba, Japan.
authors: Brian Richard
authors: BR
authors: Pauw
authors: ∥ESRF - The European Synchrotron, 71 avenue des Martyrs, 38000 Grenoble, France.
authors: Diego
authors: D
authors: Pontoni
mesh_terms: D003199:Computer Systems; D003460:Crystallization / Q000379:methods*; D006358:Hot Temperature; D008422:Materials Testing / Q000379:methods*; D015336:Molecular Probe Techniques; D045663:Quantum Dots; D053838:Scattering, Small Angle; D012996:Solutions / Q000737:chemistry; D014961:X-Ray Diffraction / Q000379:methods*
chemical_list: D012996:Solutions
keywords: CdSe; SAXS; mechanism; nanoparticle; nucleation; quantum dots