Enhanced densification under shock compression in porous silicon

Abstract

Under shock compression, most porous materials exhibit lower densities for a given pressure than that of a full-dense sample of the same material. However, some porous materials exhibit an anomalous, or enhanced, densification under shock compression. We demonstrate a molecular mechanism that drives this behavior. We also present evidence from atomistic simulation that pure silicon belongs to this anomalous class of materials. Atomistic simulations indicate that local shear strain in the neighborhood of collapsing pores nucleates a local solid-solid phase transformation even when bulk pressures are below the thermodynamic phase transformation pressure. This metastable, local, and partial, solid-solid phase transformation, which accounts for the enhanced densification in silicon, is driven by the local stress state near the void, not equilibrium thermodynamics. This mechanism may also explain the phenomenon in other covalently bonded materials.

Amorphization and nanocrystallization of silicon under shock compression

“…Our simulations are carried out with the MOD interatomic potential [33], which predicts a melting T of 1680 K at P=0 GPa. Simulations by Lane and coworkers [36]…”

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

“…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].…”

“…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]. 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].…”

Supersonic Dislocation Bursts in Silicon

“…Regarding silicon, there are several shock experiments at applicable strain rates 2 12 13 14 in addition to multiple MD simulations 2 13 14 15 16 . Notably, Smith et al 17 used laser-driven shocks to measure the elastic limit as a function of strain rate.…”