Ostwald鈥檚 Rule of Stages and Its Role in CdSe Quantum Dot Crystallization

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• 作者：Aaron L. Washington ; II ; Megan E. Foley ; Soshan Cheong ; Lieth Quffa ; Christopher J. Breshike ; John Watt ; Richard D. Tilley ; Geoffrey F. Strouse
• 刊名：The Journal of the American Chemical Society
• 出版年：2012
• 出版时间：October 17, 2012
• 年：2012
• 卷：134
• 期：41
• 页码：17046-17052
• 全文大小：454K
• 年卷期：v.134,no.41(October 17, 2012)
• ISSN：1520-5126

文摘

A century ago Ostwald described the 鈥淩ule of Stages鈥?after deducing that crystal formation must occur through a series of intermediate crystallographic phases prior to formation of the final thermodynamically stable structure. Direct evidence of the Rule of Stages is lacking, and the theory has not been implemented to allow isolation of a selected structural phase. Here we report the role of Ostwald鈥檚 Rule of Stages in the growth of CdSe quantum dots (QDs) from molecular precursors in the presence of hexadecylamine. It is observed that, by controlling the rate of growth through the reaction stoichiometry and therefore the probability of ion-packing errors in the growing QD, the initially formed zinc blende (ZB) critical nuclei representing the kinetic phase can be maintained at sizes >14 nm in diameter without phase transformation to the thermodynamic wurtzite (WZ) structure. An intermediate pseudo-ZB structure is observed to appear at intermediate reaction conditions, as predicted by Ostwald. The ZB and pseudo-ZB structures convert to the WZ lattice above a critical melting temperature. This study validates Ostwald鈥檚 Rule of Stages and provides a phase diagram for growth of CdSe QDs exhibiting a specific crystallographic motif.