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Title: Transient Melting and Recrystallization of Semiconductor Nanocrystals Under Multiple Electron–Hole Pair Excitation

Ultrafast optical pump, X-ray diffraction probe experiments were performed on CdSe nanocrystal (NC) colloidal dispersions as functions of particle size, polytype, and pump fluence. Bragg peak shifts related to heating and peak amplitude reduction associated with lattice disordering are observed. For smaller NCs, melting initiates upon absorption of as few as ~15 electron–hole pair excitations per NC on average (0.89 excitations/nm3 for a 1.5 nm radius) with roughly the same excitation density inducing melting for all examined NCs. Diffraction intensity recovery kinetics, attributable to recrystallization, occur over hundreds of picoseconds with slower recoveries for larger particles. Zincblende and wurtzite NCs revert to initial structures following intense photoexcitation suggesting melting occurs primarily at the surface, as supported by simulations. Electronic structure calculations relate significant band gap narrowing with decreased crystallinity. These findings reflect the need to consider the physical stability of nanomaterials and related electronic impacts in high intensity excitation applications such as lasing and solid-state lighting.
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  1. Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States
Publication Date:
Grant/Contract Number:
Published Article
Journal Name:
Nano Letters
Additional Journal Information:
Journal Volume: 17; Journal Issue: 9; Journal ID: ISSN 1530-6984
American Chemical Society
Research Org:
Northwestern Univ., Evanston, IL (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
melting; molecular dynamics; multiexciton; Nanocrystals; phonon; transient diffraction
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1414909