Grain size effects on indentation-induced plastic deformation and amorphization process of polycrystalline silicon

Abstract

The deformation behavior and amorphization process of polycrystalline and single-crystalline silicon are investigated using molecular dynamics (MD) simulations and compared with the previous nanoindentation experiments. In order to unravel the grain size effect on the deformation mechanism, the indentation simulations of polycrystalline silicon with the different grain sizes are performed, and all grains follow the inverse Hall-Petch relation. The results reveal that Young’s modulus of polycrystalline silicon is much greater than Young’s modulus obtained in the 〈1 0 0〉 direction single-crystalline silicon due to the random crystallographic orientation and strong anisotropy of polycrystalline silicon at nanoscale. The nucleation of amorphization in both single-crystalline and polycrystalline silicon appears always beneath the indenter due to the maximum shear stress, controlling the plastic deformation during the indentation process. The horizontal expansion of amorphization region is faster and larger than the vertical expansion of amorphization region due to two reasons: the limit of indentation stress along the depth direction is compared with along the width direction; the grain boundary is the most possible path of weak connection, and produces the complex stress distribution for the propagation of amorphization region. The smaller grain size leads to the stronger gradient strain, especially in the region of upper surface.