Nucleation and growth of CdS nanoparticles observed by ultrafast SAXS
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Nucleation and growth of CdS nanoparticles observed by ultrafast SAXS A. Schiener1, T. Wlochowitz1, S. Gerth1, T. Unruh1, A. Rempel2, H. Amenitsch3 and A. Magerl1 1 Chair for Crystallography and Structural Physics, University of Erlangen-Nürnberg, Staudtstraße 3, D-91034 Erlangen, Germany 2 Institute of Solid State Chemistry, Ural Branch of the Russian Academy of Sciences, 620990 Ekaterinburg, Russia 3 Institute of Biophysics and Nanosystems Research, Austrian Academy of Sciences, A-8042 Graz, Austria ABSTRACT Aqueous solutions containing Cd2+ and S2- ions have been brought together in a T-mixer, and the formation of CdS nanoparticles has been monitored by ultrafast X-ray small angle scattering down to 0.2 ms. While no particle formation is observed for a laminar flow, their growth can be followed in-situ for conditions of turbulent flow. INTRODUCTION Although strong research activities are dedicated at present to the synthesis and use of nanoparticles [1, 2] very little is known about their nucleation and growth process [3]. This holds in particular for rapid synthesis conditions as expected in case of II-VI quantum dots like cadmium sulfide (CdS) from solutions with high supersaturation. Stabilizers like organic ligands or surfactants may play a fundamental role in the reaction mechanism and also in the reaction rate. In general the growth conditions are crucial for tailoring particle size and size distribution. The better understanding of the early stages of particle formation appears to be indispensable to gain the efficiency of industrial particle fabrication [3]. To access the early stages of particle nucleation and crystal growth of II-VI nanoparticles we have performed ultrafast Small Angle X-ray Scattering (SAXS) experiments with a T-mixer reaching the 200 µs time scale. The experiments were conducted with both laminar and turbulent flows and we show that the flow conditions have a striking influence on the reaction rates [3, 4]. CdS nanoparticles have first been synthesized by Kaito in 1976 [6]. Since then many different synthesis routes have been developed [5, 7, 8, 9, 10]. Lately, our research group has been focused on a particular promising synthesis route to produce stable nanoparticles by a chemical bath reaction in aqueous media discovered by N. S. Kozhevnikova et al. in 2009 [11]. The present work is an attempt to analyze the early stages of the growth process of CdS particles through in-situ SAXS measurements at the beamline BL 5.2 L at the synchrotron ELETTRA [12]. The mixing of the two reagents CdCl2 and Na2S including in some cases an admixture of EDTA as a stabilizer was carried out in a micro T-mixer which allowed for a time resolution below the millisecond range. EXPERIMENT Synthesis route of CdS in aqueous solution
Mixing of aqueous solutions of sodium sulfide (Na2S) and of cadmium chloride (CdCl2) with C10H14N2O8Na2 (disodiumethylen-diamintetraacetate, Na2H2-EDTA or Na2H2Y) leads to the formation of stable CdS nanoparticles [11]. In this process EDTA in solution may be used to prevent par
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