Mechanical properties and deformation behaviors of surface-modified silicon: a molecular dynamics study

The mechanical properties and deformation behaviors of monocrystalline silicon coated by an amorphous SiO2 film with different thicknesses are explored by nanoindentation process with molecular dynamics (MD) simulation. The results indicate that the calculated indentation modulus increases with the growing indentation depth for monocrystalline silicon with and without amorphous SiO2 film, while the modulus decreases with increasing film thickness at the same indentation depth. The derived hardness during indentation process, which is more sensitive to amorphous SiO2 film thickness, is complex due to the plastic deformation of SiO2 film, illustrating a deformation-induced softening behavior. The plastic deformation of amorphous SiO2 film exhibits four periods during whole indentation process, namely densification, densification–rupture transition, rupture during loading and elastic recovery during unloading, which are reasonably verified by CN number of silicon atoms and Si–O bond number within SiO2 film as a function of indentation depth. It is concluded that the SiO2 film acts as a medium to dissipate the energy and to transmit the stress from indenter to underlying silicon substrate. The MD results show that the differences of phase distribution between silicon with and without SiO2 film at the same penetration depth are driven by the stress.