Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 114, Issue 37, Pages 9791-9796Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1708853114
Keywords
amorphization; laser shock; nanocrystallization; germanium; gradient materials
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Funding
- Office of Basic Energy Science, US Department of Energy
- University of California (UC) Research Laboratories [09-LR-06-118456-MEYM]
- National Nuclear Security Administration [DE-NA0002930]
- UC Office of the President Laboratory Fees Research Program [LFR-17-449059]
- US Department of Energy [DE-AC52-07NA27344]
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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.
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