Modulated Nanoindentation (MoNI) -- a novel characterization tool of two-dimensional materials and nanotubes

We report~on~a novel Atomic Force Microscopy (AFM) based technique with sub-angstrom vertical resolution -- Modulated~Nanoindentation~(MoNI).~MoNI~has been applied to measure the radial elasticity of multi-walled nanotubes.~Recently~the~interlayer~coupling of~two-dimensional materials (such~as~graphene and~MoS$_{2})$ characterized by~strong in-plane bonds and weak interlayer interactions has been studied by~MoNI~combined with semi-analytical methods (SAM) and DFT calculations.~The out-of-plane stiffness of varied 2D materials and its dependence on number of layers~and intercalated water~has been investigated in different environmental conditions.~This~non-destructive~technique~provides~a new path to study the interlayer elastic coupling and the Van der Waals forces in~few-layer-thick~2D materials,~offering the possibility to understand how interlayer coupling is related to the electronic, phononic, and thermal properties of 2D materials.