Pressure and shear-induced amorphization of silicon

Abstract

Here we report that high-power, pulsed, laser-driven shock compression of monocrystalline silicon produces directional amorphization, revealed by high-resolution transmission electron microscopy and confirmed by molecular dynamics simulations. Shear-induced lattice defects (stacking faults and twins) on crystallographic slip planes play a crucial role in the onset of amorphization. The typical high-pressure solid-solid phase transitions of silicon are not observed whereas the high shear stresses are relaxed by localized dislocation motion/interactions and eventually by directional amorphization, which occurs below the critical hydrostatic pressure for melting of silicon in shock compression. It is therefore proposed that the combined effects of hydrostatic and shear stresses lead to directional amorphization.

Real-Time Examination of Atomistic Mechanisms during Shock-Induced Structural Transformation in Silicon

“…However, the MD simulations [2,36,37] predicted a peak state which was in a mixed phase rather than the completely transformed material. Additionally, the high pressure structure determined from MD simulations for shocked Si(100) was identified as Imma [2] or amorphous [23]. These findings from the MD simulations are contradicted by our experimental results.…”

“…Thus, we conclude that shocked Si (26 GPa impact stress followed by partial stress release to 19 GPa) remains crystalline rather than amorphous (as recently suggested in Ref. 23) and transforms to a randomly oriented polycrystalline simple hexagonal structure.…”

“…Recent molecular dynamics (MD) simulations for germanium [36] and silicon [2,23,37] shocked along [100] cd have suggested that the transformation mechanisms for structural changes between the cd silicon and the β-Sn, Imma and sh structures are more complex than commonly assumed [12,14,15,18,[30][31][32][33][34][35]. An interesting finding of the MD simulations was that the transformations occurred along shear bands [2,36,37] which were attributed to planar stacking faults [36,37].…”

“…Analysis of transmitted wave profiles in shocked single crystal silicon has indicated -through density determinationthat a phase transformation begins around 13 GPa [20][21][22] and that above 16 GPa the density of shocked silicon is consistent with the density of one of the high-pressure crystalline structures observed under static compression [22]. However, recent post-mortem analysis of recovered laser shocked Si(100) suggested that amorphization rather than transformation to a high-pressure crystalline structure occurs during shock-compression of Si(100) [23]. Additionally, previous XRD measurements on laser-shocked single crystal silicon with reported stresses greater than the phase transformation stress did not find evidence for any of the high-pressure silicon structures found under static compression [24,25].…”

Generating gradient germanium nanostructures by shock-induced amorphization and crystallization

“…The short duration of the stress pulse and impedancematched encapsulation preserves the integrity of the target by suppressing the full development of cracks and enables postshock microstructure characterization. Using this methodology, we have previously reported shock-induced amorphization in silicon (18) and boron carbide (19). Before that, Jeanloz et al (20) discovered this phenomenon in olivine (iron/magnesium silicate) subjected to shock compression.…”