Abstract
We study the interplay between localized surface plasmon resonances from metallic cores and electromagnetic resonances from semiconducting shells in core@shell nanoparticles in the optical and near-infrared regions. To this end, we consider silver (Ag) spheres as plasmonically active nanoparticles with radii 20 nm, covered with shells of silicon (Si) up to 160 nm in thickness. We use the classical Lorenz-Mie theory to calculate the response of the core@shell nanoparticles to an external electromagnetic field that reveals a high degree of tunability of the Ag surface plasmons with a varying Si shell thickness, and a consequent merging of their Mie resonances. In contrast with pure metallic systems, the use of a low-bandgap semiconducting shell allows for a unique interrelation between its strong characteristic magnetic dipole mode and the localized surface plasmon resonance of the metallic core. This allows control over the forward and backward scattering efficiencies in the near-infrared in accordance with the predictions based on the Kerker conditions. Employing several other core@shell materials (Al@Si, Au@Si and Ag@Ge), we show that this approach to tailoring the absorption and scattering efficiencies, based on Kerker’s conditions, can be further generalized to other similar core@shell systems.
Highlights
Metallic nanoparticles exhibit collective oscillations of their surface conduction electrons in an incident electromagnetic field
To study the interaction between plasmonic modes from a metallic core and modes from a semiconductor shell, we focus on spherical core@shell particles having a Ag core with a fixed 20 nm radius and covered by a Si shell with thickness up to 160 nm
Core@Shell particles containing other materials we examine the effects of (a) changing the shell material to another low bandgap semiconductor, Ge, which has a bandgap of 0.66 eV, and, (b) the core material alternatively to Al or Au
Summary
Metallic nanoparticles exhibit collective oscillations of their surface conduction electrons in an incident electromagnetic field. The dominant dipolar LSPR of metallic particles is in the near-ultraviolet or visible region due to the high plasma frequency, and metallic particles suffer from significant losses in the near-infrared (NIR) region [10]. To this end, doped conventional semiconductors such as silicon and germanium have been explored as potential candidates for plasmonics and nanophotonic applications in the NIR [11, 12]. The minimum carrier concentration to obtain metal-like optical properties in the NIR for semiconductors, such as silicon, is about 1021 cm−3 [14]
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