Electromagnetic response of nanoparticles with a metallic core and a semiconductor shell

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.

Near-infrared visualisation of single microparticle electrochemistry for batteries

“…30 For the strongly lightabsorbing LiCoO 2 particles, presumably the scattering cross section would be positively related to the penetration depth when the particle is not fully transparent to the light of given wavelengths. However, since the scattering is highly sensitive to nanoscale surface morphology and phase differences 25 and the mathematics involves solving complex wave functions, 31,32 a concise, formulated dependence for the irregular, rough microparticle is unavailable. Nevertheless, the positive relationship between the wavelength and the scattering cross sections (indicated by the bright regions in Fig.…”