Amorphization and nanocrystallization of silicon under shock compression
S Zhao and EN Hahn and B Kad and BA Remington and CE Wehrenberg and EM Bringa and MA Meyers, ACTA MATERIALIA, 103, 519-533 (2016).
High-power, short-duration, laser-driven, shock compression and recovery experiments on 001 silicon unveiled remarkable structural changes above a pressure threshold. Two distinct amorphous regions were identified: (a) a bulk amorphous layer close to the surface and (b) amorphous bands initially aligned with (111) slip planes. Further increase of the laser energy leads to the re-crystallization of amorphous silicon into nanocrystals with high concentration of nano- twins. This amorphization is produced by the combined effect of high magnitude hydrostatic and shear stresses under dynamic shock compression. Shockinduced defects play a very important role in the onset of amorphization. Calculations of the free energy changes with pressure and shear, using the Patel-Cohen methodology, are in agreement with the experimental results. Molecular dynamics simulation corroborates the amorphization, showing that it is initiated by the nucleation and propagation of partial dislocations. The nucleation of amorphization is analyzed qualitatively by classical nucleation theory. (c) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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