Cathodoluminescence and tip-plasmon resonance of Bi2Te3 triangular nanostructures

Bi2Te3, as a topological insulator, is able to support plasmonic emission in the visible spectral range. Thin Bi2Te3 flakes can be exfoliated directly from a Bi2Te3 crystal, and the shape of Bi2Te3 flakes can be further modified by focused ion beam milling. Therefore, we have designed a Bi2Te3 triangular antenna with distinct tip angles for the application of plasmonic resonance. The plasmonic emission of the Bi2Te3 triangular antenna is excited and investigated by cathodoluminescence in the scanning electron microscope. Enhanced tip plasmons have been observed from distinct tips with angles of 20º, 36º, 54º, 70º, and 90º, respectively. Due to the confinement of geometric boundaries for oscillating charges, the resonant peak position of tip plasmon with a smaller angle has a blue shift. Moreover, the dependence of plasmonic behavior on the excitation position has been discovered as well. This research provides a unique approach to fabricate Bi2Te3 nanostructures and manipulate the corresponding plasmonic properties.

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.