Delamination of MoS₂/SiO₂ interfaces under nanoindentation

Molybdenum disulphide (MoS₂) mounted on silicon dioxide (SiO₂) constitutes the fundamental functional components of many nanodevices, but its mechanical properties, which are crucial for the device design and fabrication, remain almost unexplored. Here, the mechanical properties of the multilayer MoS₂/SiO₂ system are investigated via nanoindentation experiments and molecular dynamics simulations. In terms of the mechanical properties, a comparative study of MoS₂/SiO₂ and graphene/SiO₂ systems is presented. The MoS₂/SiO₂ and graphene/SiO₂ systems are found to possess comparable Young's modulus and hardness values, but their mechanical responses and failure modes under indentation are totally different. Interface delamination failure accompanied by ring-like through-thickness cracking is observed in the MoS₂/SiO₂ system with a relatively thin MoS₂ layer, while no interface separation is found in indentation experiments for the graphene/SiO₂ system using the same layer thickness. The different failure modes observed between the MoS₂/SiO₂ and graphene/SiO₂ systems can be attributed to the comparable interface adhesion energy but very different bending stiffness values of the MoS₂ and graphene components. Specifically, compared with graphene, the larger bending stiffness of MoS₂ means that a larger bending force is experienced in the indentation process, overcoming the adhesion of the MoS₂/SiO₂ interface, which makes interface delamination much easier in the MoS₂/SiO₂ system.