Abstract
Gradient nanostructures are attracting considerable interest due to their potential to obtain superior structural and functional properties of materials. Applying powerful laser-driven shocks (stresses of up to one-third million atmospheres, or 33 gigapascals) to germanium, we report here a complex gradient nanostructure consisting of, near the surface, nanocrystals with high density of nanotwins. Beyond there, the structure exhibits arrays of amorphous bands which are preceded by planar defects such as stacking faults generated by partial dislocations. At a lower shock stress, the surface region of the recovered target is completely amorphous. We propose that germanium undergoes amorphization above a threshold stress and that the deformation-generated heat leads to nanocrystallization. These experiments are corroborated by molecular dynamics simulations which show that supersonic partial dislocation bursts play a role in triggering the crystalline-to-amorphous transition.
Original language | English |
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Pages (from-to) | 9791-9796 |
Number of pages | 6 |
Journal | Proceedings of the National Academy of Sciences of the United States of America |
Volume | 114 |
Issue number | 37 |
DOIs | |
State | Published - Sep 12 2017 |
Funding
ACKNOWLEDGMENTS. The enthusiastic help by Dorothy Coffey is deeply acknowledged. We acknowledge the highly professional support team of the Omega Laser Facility in the Laboratory of Laser Energetics, University of Rochester. Electron microscopy was conducted at the Center for Nanophase Materials Science (CNMS) User Facility, Oak Ridge National Laboratory, which is sponsored by the Office of Basic Energy Science, US Department of Energy. This research is funded by a University of California (UC) Research Laboratories Grant (09-LR-06-118456-MEYM), a National Nuclear Security Administration Grant (DE-NA0002930), and the UC Office of the President Laboratory Fees Research Program (LFR-17-449059). B.A.R. and C.E.W. also acknowledge the support of a US Department of Energy Grant (DE-AC52-07NA27344).
Keywords
- Amorphization
- Germanium
- Gradient materials
- Laser shock
- Nanocrystallization