Molecular dynamics simulation of the uniaxial tensile test of silicon nanowires using the MEAM potential
WT Xu and WK Kim, MECHANICS OF MATERIALS, 137, UNSP 103140 (2019).
The silicon nanowire is a novel nanometer-scale structure which can be used in various electronic and optoelectronic devices. While the plastic deformation and failure mechanisms, including the brittle-to-ductile transition at room temperature, of nanowires have been studied both experimentally and theoretically, the fundamental atomic-scale mechanisms of these behaviors still remain incompletely understood. In this article we study the mechanical and failure behaviors of the 110-oriented single-crystalline silicon nanowires by performing uniaxial tensile tests using molecular dynamics simulations with three modified embedded-atom-method (MEAM) potentials, referred to as Baskes, Lee, and Lee-modified. The effects of several key parameters such as size, temperature, and strain rate are investigated. A preliminary examination of the three MEAM potentials reveals that Lee and Lee- modified models outperform Baskes model in predicting the thermal expansion coefficient and surface energies. The uniaxial tensile simulations show that some mechanical properties such as Young's modulus and tensile strength exhibit size-dependence while there is little size- effect on the failure strain. A novel parameter named the ductile failure probability is introduced to quantify the failure behavior of the nanowire during the tensile test, which scales from 0 for the pure brittle to 1 for the pure ductile mode failure. Overall, the ductile failure probability increases with decreasing size and increasing temperature in all of the three models. The Baskes nanowires exhibit the most ductile failures among the three models whereas most Lee-modified nanowires fail through fractures on the (111) plane. The Lee model shows some intermediate levels of ductile failure behavior. The difference due to the strain rate is very small, but overall nanowires become slightly more brittle as the strain rate decreases.
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