Web Release Date: March 26,
Threshold Size for Ambient Metastability of Rocksalt CdSe Nanocrystals
Department of Chemistry, University of California, Berkeley, California 94720, and Materials Science Division, Lawrence Berkeley National Laboratory, University of California, Berkeley, California 94720
Received: October 12, 2001
In Final Form: January 3, 2002
Abstract:
We show that metastable rocksalt CdSe nanocrystals can persist at ambient pressure depending on the physical size of the particle. The size-dependence of the hysteresis loop was measured for the solid-solid transition in CdSe nanocrystals, between four- and six-coordinate structures. A systematic shift of the entire hysteresis loop to lower pressure results in a threshold size of ~11 nm for ambient metastability of the six-coordinate rocksalt structure. Smaller nanocrystals transform back to the four-coordinate structure as occurs in the CdSe bulk solid. Surface energy contributions are used to explain the shift. The results have important implications for the optimum synthesis of metastable nanocrystal solids under ambient conditions.
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