期刊
ACS NANO
卷 13, 期 10, 页码 11623-11631出版社
AMER CHEMICAL SOC
DOI: 10.1021/acsnano.9b05466
关键词
BN nanotubes; nonthermal transient; ultrafast structural dynamics; bandgap renormalization; ultrafast transmission electron microscopy
类别
资金
- National Key Research and Development Program of China [2016YEA0300303, 2017YFA0504703, 2017YEA0302904, 2017YFA0303000]
- National Basic Research Program of China [2015CB921304]
- National Natural Science Foundation of China [11774391, 11774403, 11804381]
- Chinese Academy of Sciences [XDB25000000, XDB07020000]
- Scientific Instrument Developing Project of the Chinese Academy of Sciences [ZDKYYQ20170002]
- Postdoctoral Innovation Talent Support Program of China [BX20180351]
Structural dynamics and changes in electronic structures driven by photoexcited carriers are critical issues in both semiconducting and optoelectronic nanodevices. Herein, a phase diagram for the transient states and relevant dynamic processes in multiwalled boron nitride nanotubes (BNNTs) has been extensively studied for a full reversible cycle after a fs-laser excitation in ultrafast TEMs, and the significant structural features and evolution of electronic natures have been investigated using pulsed electron diffraction and femtosecond-resolved electron energy-loss spectroscopy (EELS). It is revealed that nonthermal anisotropic alterations of the lattice apparently precede the phonon-driven thermal transients along the radial and axial directions. Ab initio calculations support these findings and show that electrons excited from the pi to pi* orbitals in the BN nanotubes weaken the intralayer bonds while strengthening the interlayer bonds along the radial direction. Importantly, time-resolved EELS measurements show contraction of the energy bandgap after fs-laser excitation associated with nonthermal structural transients. This fact verifies that laser-induced bandgap renormalization in semiconductors can essentially be correlated with both the rapid processes of excited carriers and nonthermal lattice evolution.
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