期刊
NANO LETTERS
卷 17, 期 9, 页码 5314-5320出版社
AMER CHEMICAL SOC
DOI: 10.1021/acs.nanolett.7b01705
关键词
Nanociystals; transient diffraction; melting multiexciton; molecular dynamics; phonon
类别
资金
- Ultrafast Initiative of the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, through Argonne National Laboratory [DE-AC02-06CH11357]
- Joseph J. Katz Postdoctoral Fellowship at ANL
- U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences [DE-AC02-06CH11357]
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 similar to 15 electronhole 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. 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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