Stress homogenization and shear suppression in graphene-coated silicon substrate under nanoindentation: a molecular dynamics study

• Graphene coatings markedly enhance Si stiffness and hardness. • Graphene induces surface confinement at the graphene/Si interface. • Graphene coatings delay and constrain solid-state phase transformations in Si. • Deformation mechanisms are strongly governed by the number of coating layers. • Homogenization of normal stress and reduction of shear stress are observed. While graphene shows significant promise as a coating material for silicon (Si) substrates in next-generation electronics, photonics, and battery technologies, its fundamental surface strengthening mechanism at the atomic scale remains poorly understood. In this study, the protective performance of graphene on a monocrystalline Si substrate is systematically examined via large-scale molecular dynamics (MD) simulations. It is found that graphene coatings not only enhance the elastic modulus of Si, but also increase its hardness in a nonlinear fashion depending on the number of graphene layers and environmental temperatures. Stress/strain distribution, surface morphology and coordination number analyses reveal that these improvements are governed by two primary mechanisms: C–C bond stretching within the graphene coating layer(s) and surface confinement effect at the graphene/Si interface. In particular, the latter mechanism has been shown to promote the homogenization of normal stress and the attenuation of shear stress, which collectively delay the onset of plasticity and constrain the progression of pressure-induced solid-state phase transformations within the Si substrate during nanoindentation process. This atomistic understanding paves the way for optimizing graphene coatings in next-generation silicon-based technologies.