Fabricating 3D freestanding metamaterials on elastic substrates via the shadow metal-sputtering and plastic deformation

3D metamaterials have gained considerable attention owing to their extraordinary optical properties and promising applications beyond natural materials. However, fabricating 3D metamaterials with high resolution and reliable controllability is still a significant challenge. Here, a novel approach to manufacturing various 3D freestanding plasmonic nanostructures on elastic substrates is demonstrated using the shadow metal-sputtering and plastic deformations. A critical step is constructing a freestanding "Γ-shape" gold structural array in poly(methyl methacrylate) (PMMA) hole array via the shadow metal-sputtering and following a multifilm transfer procedure. This "Γ-shape" structural array undergoes plastic deformation to form 3D freestanding metamaterials for removing the PMMA resist by the oxygen plasma. The approach allows accurate manipulations of the morphology, size, curvature, and bend orientation of 3D nanostructures. The spectral response of the 3D cylinder array was experimentally confirmed and understood by the simulations based on the finite element method (FEM). Moreover, the bulk refractive index (RI) sensitivity of up to 858 nm RIU^-1 was achieved theoretically for this cylinder array. The proposed approach provides a new possibility to realize the fabrication of 3D freestanding plasmonic metamaterials with high resolution and compatible planar lithography procedures.