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, 2 (3), e1501536
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Intrinsically Core-Shell Plasmonic Dielectric Nanostructures With Ultrahigh Refractive Index

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Intrinsically Core-Shell Plasmonic Dielectric Nanostructures With Ultrahigh Refractive Index

Zengji Yue et al. Sci Adv.

Abstract

Topological insulators are a new class of quantum materials with metallic (edge) surface states and insulating bulk states. They demonstrate a variety of novel electronic and optical properties, which make them highly promising electronic, spintronic, and optoelectronic materials. We report on a novel conic plasmonic nanostructure that is made of bulk-insulating topological insulators and has an intrinsic core-shell formation. The insulating (dielectric) core of the nanocone displays an ultrahigh refractive index of up to 5.5 in the near-infrared frequency range. On the metallic shell, plasmonic response and strong backward light scattering were observed in the visible frequency range. Through integrating the nanocone arrays into a-Si thin film solar cells, up to 15% enhancement of light absorption was predicted in the ultraviolet and visible ranges. With these unique features, the intrinsically core-shell plasmonic nanostructure paves a new way for designing low-loss and high-performance visible to infrared optical devices.

Keywords: Topological insulator; core shell; dielectric; plasmonics; refractive Index.

Figures

Fig. 1
Fig. 1. Optical parameters of topological insulator BSTS single crystals.
(A) Refractive index, n, and extinction coefficient, k, of the insulating bulk of topological insulator BSTS crystals. The inset shows the intrinsic structures of topological insulator BSTS single crystals with surface states and bulk states. (B) Dielectric function, ε, of the insulating bulk of topological insulator BSTS nanocones. (C) Refractive index, n, and extinction coefficient, k, of the metallic surface of topological insulator BSTS crystals. (D) Dielectric function, ε, of the metallic surface of topological insulator BSTS crystals.
Fig. 2
Fig. 2. Intrinsically core-shell topological insulator BSTS nanocone arrays fabricated on the surface of flat BSTS crystal sheets.
(A) A schematic drawing of intrinsically core-shell nanostructures of 3D topological insulator BSTS nanocones. The red part is a metallic shell, and the yellow part is a dielectric core. (B) An enlarged 3D AFM image of four BSTS nanocones with d = 300 nm and h = 450 nm. (C) A 2D AFM image of BSTS nanocone arrays with d = 300 nm, h = 450 nm, and p = 600 nm. The scale bar is 1000 nm. (D) A 3D AFM image of these BSTS nanocone arrays.
Fig. 3
Fig. 3. Plasmonic absorption spectra of core-shell BSTS nanocone arrays.
(A) Normalized absorption spectra (1 − R) of BSTS nanocone arrays with different p, ranging from 400 to 1200 nm. The nanocone base diameter (d) ranges from 200 to 600 nm. (B) Absorption spectra of BSTS nanocone arrays with fixed d = 500 nm and different p. The p parameter ranges from 1000 to 1300 nm.
Fig. 4
Fig. 4. FDTD simulation of the electromagnetic field distribution in BSTS nanocone arrays.
(A) Nanocone arrays with d = 300 nm and p = 600 nm at a wavelength of 395 nm. (B) Nanocone arrays with d = 400 nm and p = 800 nm at a wavelength of 406 nm. (C) Nanocone arrays with d = 500 nm and p = 1000 nm at a wavelength of 411 nm. (D) Nanocone arrays with d = 600 nm and p = 1200 nm at a wavelength of 430 nm. The plasmon resonances are localized and enhanced on the surfaces of BSTS nanocones.
Fig. 5
Fig. 5. Backward light scattering by core-shell BSTS nanocone arrays.
(A) A schematic diagram of a home-built dark-field microscope for light scattering measurements. The bottom of the system is the light source, and the black disc is a patch stop that blocks the central beam. The blue arrows represent incident light, and the red arrows represent the scattered light. Only scattered light can be detected by the objective lens. (B) Images of backward light scattering by the nanocone arrays with d = 300 nm and p = 600 nm. The bright spots are the strong scattered light.
Fig. 6
Fig. 6. Plasmon resonances enhanced light absorption in ultrathin a-Si solar cells simulated using FDTD.
(A) Configuration of a-Si solar cells with core-shell BSTS nanocone arrays integrated into the back of a-Si thin films. The BSTS particles replace Al as the back electrodes of solar cells. (B) Optical absorptions in a-Si thin-film solar cells without (black curve) and with (red curve) BSTS nanocone arrays. The BSTS nanocone arrays achieve broadband enhancements of light absorptions in the visible frequency range.

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