Phase-transformation-mediated plastic deformation of monocrystalline silicon under cyclic nanoindentation

The high-pressure phase transformation behavior of monocrystalline silicon is extensively investigated, with the resulting amorphous phase enabling plastic processing. However, the microscopic mechanisms of its plastic deformation under cyclic loading remain poorly understood. Through systematic cyclic nanoindentation experiments, we find that cyclic loading raises the critical load for the transition from Si-II phase to Si-III/XII phases, thereby promoting continuous amorphous phase accumulation in the indentation zone. This shift in the phase transformation pathway leads to an increase in free volume within the amorphous phase, facilitating the formation of shear bands and enabling coordinated shear deformation. Ultimately, the rearrangement of atomic bonding induces pronounced plastic flow beneath the indenter. Our work reveals an amorphous-phase-mediated plastic deformation mechanism in monocrystalline silicon under cyclic loading, linking microscopic phase evolution to macroscopic deformation, and offers a theoretical basis for understanding its plastic behavior in ultra-precision machining.