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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 relate heating and peak amplitude reduction confers lattice disordering. For smaller NCs, melting initiates upon absorption of as few as ~15 electron-hole pair excitations per NC on average (0.89 excitations/nm 3 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. Here, 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.
Authors:
 [1] ;  [1] ; ORCiD logo [2] ;  [2] ;  [1] ;  [2] ;  [1] ;  [1] ;  [1] ; ORCiD logo [1] ;  [3] ; ORCiD logo [3]
  1. Northwestern Univ., Evanston, IL (United States)
  2. Argonne National Lab. (ANL), Lemont, IL (United States)
  3. Northwestern Univ., Evanston, IL (United States); Argonne National Lab. (ANL), Lemont, IL (United States)
Publication Date:
Grant/Contract Number:
AC02-06CH11357
Type:
Published Article
Journal Name:
Nano Letters
Additional Journal Information:
Journal Volume: 17; Journal Issue: 9; Journal ID: ISSN 1530-6984
Publisher:
American Chemical Society
Research Org:
Argonne National Lab. (ANL), Argonne, IL (United States); Northwestern Univ., Evanston, IL (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
77 NANOSCIENCE AND NANOTECHNOLOGY; 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; melting; molecular dynamics; multiexciton; Nanocrystals; phonon; transient diffraction
OSTI Identifier:
1374084
Alternate Identifier(s):
OSTI ID: 1405316; OSTI ID: 1414909