Precursor Conversion Kinetics and the Nucleation of Cadmium Selenide Nanocrystals

The kinetics of cadmium selenide (CdSe) nanocrystal formation was studied using UV−visible absorption spectroscopy integrated with an automated, high-throughput synthesis platform. Reaction of anhydrous cadmium octadecylphosphonate (Cd-ODPA) with alkylphosphine selenides (1, tri-n-octylphosphine sel...

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Veröffentlicht in:Journal of the American Chemical Society 2010-12, Vol.132 (51), p.18206-18213
Hauptverfasser: Owen, Jonathan S, Chan, Emory M, Liu, Haitao, Alivisatos, A. Paul
Format: Artikel
Sprache:eng
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Zusammenfassung:The kinetics of cadmium selenide (CdSe) nanocrystal formation was studied using UV−visible absorption spectroscopy integrated with an automated, high-throughput synthesis platform. Reaction of anhydrous cadmium octadecylphosphonate (Cd-ODPA) with alkylphosphine selenides (1, tri-n-octylphosphine selenide; 2, di-n-butylphenylphosphine selenide; 3, n-butyldiphenylphosphine selenide) in recrystallized tri-n-octylphosphine oxide was monitored by following the absorbance of CdSe at λ = 350 nm, where the extinction coefficient is independent of size, and the disappearance of the selenium precursor using {1H}31P NMR spectroscopy. Our results indicate that precursor conversion limits the rate of nanocrystal nucleation and growth. The initial precursor conversion rate (Q o) depends linearly on [1] (Q o(1) = 3.0−36 μM/s) and decreases as the number of aryl groups bound to phosphorus increases (1 > 2 > 3). Changes to Q o influence the final number of nanocrystals and thus control particle size. Using similar methods, we show that changing [ODPA] has a negligible influence on precursor reactivity while increasing the growth rate of nuclei, thereby decreasing the final number of nanocrystals. These results are interpreted in light of a mechanism where the precursors react in an irreversible step that supplies the reaction medium with a solute form of the semiconductor.
ISSN:0002-7863
1520-5126
DOI:10.1021/ja106777j