Synthesis of CdSe magic-sized nanocluster and its effect on nanocrystal preparation in a microfluidic reactor
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Asuka Tashiro Department of Chemistry and Applied Chemistry, Saga University, Honjo-machi, Saga-city, Saga 840-8502, Japan
Hiroyuki Nakamura, Masato Uehara, and Masaya Miyazaki Micro-space Chemistry Lab, National Institute of Advanced Industrial Science and Technology (AIST), Saga 841-052, Japan
Takanori Watari Department of Chemistry and Applied Chemistry, Saga University, Honjo-machi, Saga-city, Saga 840-8502, Japan
Hideaki Maedaa) Micro-space Chemistry Lab, National Institute of Advanced Industrial Science and Technology (AIST), Saga 841-052, Japan (Received April 21, 2004; accepted 29 July 2004)
CdSe magic-sized nanoclusters were synthesised at relatively low temperatures (90–150 °C) in the organometallic raw material solution by a very simple method. The variation process from nanoclusters to nanocrystals has been determined using the microreactor, and it was found that these nanoclusters could increase the CdSe nuclei number and product yield in the microfluidic reactor method. Meanwhile, the microreactor shows the advantage for studying the nanocrystal-growth process due to the precise time and temperature control and high reproducibility.
I. INTRODUCTION
The synthesis of high-quality CdSe nanocrystals has been an important topic in the field of materials chemistry in recent years due to their technical and fundamental importance. Much effort has been made to obtain better photoluminescence properties, a narrow particle size distribution, a controllable particle shape, and so forth,1–5 and it was found that all these properties of CdSe strongly depend on the kinetics of the initial nucleation and growth. As the representatives of the state of matter intermediate between molecules and crystalline solids, cluster molecules have attracted a lot of attention regarding the forming mechanism of nanoparticles and their controlled nucleation and growth. In the particular case of semiconductor materials, the small clusters themselves are of interest, given that the transport and optical behaviors vary as a function of crystallitic size. So far, in a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2004.0420 J. Mater. Res., Vol. 19, No. 11, Nov 2004
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cadmium chalcogenide semiconductors, a few remarkable cluster examples have been obtained, including Cd32S14(SC6H5)36⭈4DMF, Cd10Se4(SPh)16,6–9 in which recrystallization was usually necessary. In the conventional organometallic routine for semiconductor nanocrystals, some magic-sized nanoclusters have been reported to be found after a short time during the reaction, and they were believed to be important for controlling the nanocrystal growth.10 However, these nanoclusters were usually an intermediate state, and would quickly become regular nanocrystals as the reaction proceeded. In this communication, we will show that the magic-sized CdSe nanoclusters can simply be obtained if the raw materials used in the organometallic route were heat-treated under appropriate conditi
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