Atomistic deformation mechanism of silicon under laser-driven shock compression

TL;DR

This study uses ultrafast x-ray diffraction to reveal the inelastic shear release mechanism in silicon under laser-driven shock compression, resolving decades-long debates and demonstrating strain rate-dependent deformation in a non-metallic material.

Contribution

First direct, time-resolved evidence of inelastic shear release in silicon during shock compression at ultra-high strain rates.

Findings

Silicon deforms via inelastic shear release during shock compression.

Deformation mechanisms depend on strain rate.

Provides direct experimental proof supporting theoretical predictions.

Abstract

Silicon (Si) is one of the most abundant elements on Earth, and it is the most important and widely used semiconductor, constituting the basis of modern electronic devices. Despite extensive study, some properties of Si remain elusive. For example, the behaviour of Si under high pressure, in particular at the ultra-high strain rates characteristic of dynamic compression, has been a matter of debate for decades. A detailed understanding of how Si deforms is crucial for a variety of fields, ranging from planetary science to materials design. Simulations suggest that in Si the shear stress generated during shock compression is released inelastically, i.e., via a high-pressure phase transition, challenging the classical picture of relaxation via defect-mediated plasticity. However, experiments at the short timescales characteristic of shock compression are challenging, and direct evidence supporting either deformation mechanism remain elusive. Here, we use sub-picosecond, highly-monochromatic x-ray diffraction to study (100)-oriented single-crystal Si under laser-driven shock compression. We provide the first unambiguous, time-resolved picture of Si deformation at ultra-high strain rates, demonstrating the predicted inelastic shear release. Our results resolve the longstanding controversy on silicon deformation under dynamic compression, and provide direct proof of strain rate-dependent deformation mechanisms in a non-metallic system, which is key for the study of planetary-relevant materials.