Tunable Optical Response Based on Au@GST Core-Shell Hetero-nanostructures

Active control over the optical response has been investigated extensively, which is highly required in next-generation photonic devices. Here, we report a core-shell nanostructure combined with the plasmonic nanostructure with an active phase change material, termed as Au@GST, where the individual Au nanoparticle is wrapped by isolated active Ge₂Sb₂Te₅(GST) tuning medium as the shell. We demonstrate the active control of optical response by the simultaneous control of size and crystallization degree of the phase change shell within each isolated core-shell nanostructure. The hetero-nanostructures are synthesized by direct sputtering of stoichiometric GST on Au nanoparticles with different sizes based on a seeding effect of the metal nanostructures. The tunable optical response is enabled by inducing the GST shell phase states between amorphous and crystalline phases through thermal annealing, accompanied by high optical contrast. We demonstrate the tunable optical response (from 570 to 630 nm) of the hetero-nanostructures by tailoring the GST shell’s optical property. The experimental results show that the optical response of the Au@GST core-shell hetero-nanostructures exhibits high sensitivity to the size of the nanoparticles (GST thickness and Au diameter). The simulation results are in good agreement with the experiments. This confirms the dominant role of the phase states on the optical modulation. Furthermore, this study provides a single-step and lithography-free 3D printing process to arrange the hybrid Au@GST core-shell nanostructures in a large area deliberately, giving additional flexibility to control over the architecture and geometry. Such Au@GST core-shell hetero-nanostructures have the potential for active control of nanophotonic devices, such as super-resolution imaging and programmable metasurfaces.