A Molecular Dynamics Study of the Brittle-to-Ductile Transition of Silicon Nanowires Using the MEAM Potential

Silicon nanowires (NWs) are novel nano-scale structures with a variety of potential applications such as electronic and optoelectronic devices including high-precision sensors and actuators. Recent experiments have found that Si NWs exhibit a strong size-dependent brittle-to-ductile transition (BDT) such that small-diameter Si NWs can sustain large plastic deformations at room temperature. In this study, the molecular dynamics (MD) methodology using the modified embedded atom method (MEAM) potential is employed to unveil the fundamental mechanisms governing the size-dependent BDT of Si NWs. The MD simulations mimic the uniaxial tensile test along the [110] direction on Si NWs with diameters of 2 to 7 nm at various temperatures and strain rates. The simulations test the validity of many different parameter sets of the MEAM potential for Si and the results show that only a certain type of MEAM parameter sets can reproduce the size-dependent BDT phenomenon. A subsequent systematic analysis reveals the key parameters and functional forms of MEAM that strongly affect this observation. This study also discusses the connection between the critical MEAM parameters and their physical meanings and ultimately postulates the main atomic-scale mechanisms of the BDT of Si NWs.