Phase transitions in shocked amorphous silicon

Crystalline silicon exhibits a complex phase diagram with numerous stable and metastable phases, some of which are recoverable under ambient conditions. Amorphous silicon (a-Si), a kinetically trapped metastable state, offers potential for discovering new metastable states and crystallizing thermodynamically stable structures. Compared to its crystalline counterparts, an a-Si precursor facilitates phase transformations by lowering the kinetic barriers associated with reconstructive phase transitions. We explore the structural evolution of a-Si under dynamic shock compression using quantum-accurate, large-scale molecular dynamics simulations on exascale supercomputers with a machine-learning interatomic potential. Our simulations support shock compression experiments at the European X-Ray Free Electron Laser facility by providing atomic-scale interpretation of experimental results.