Plasmonic Emission of Bullseye Nanoemitters on Bi₂Te₃ Nanoflakes

Topological insulators, such as Bi₂Te₃, have been confirmed to exhibit plasmon radiation over the entire visible spectral range. Herein, we fabricate bullseye nanoemitters, consisting of a central disk and concentric gratings, on the Bi₂Te₃ nanoflake. Due to the existence of edge plasmon modes, Bi₂Te₃ bullseye nanostructures are possible to converge light towards the central disk. Taking advantage of the excellent spatial resolution of cathodoluminescence (CL) characterization, it has been observed that plasmonic behaviors depend on the excitation location. A stronger plasmonic intensity and a wider CL spectral linewidth can be obtained at the edge of the central disk. In order to further improve the focusing ability, a cylindrical Pt nanostructure has been deposited on the central disk. Additionally, the finite element simulation indicates that the electric-field enhancement originates from the coupling process between the plasmonic emission from the Bi₂Te₃ bullseye and the Pt nanostructure. Finally, we find that enhancement efficiency depends on the thickness of the Pt nanostructure.