  Absorption efficiency profiles and localized surface plasmon resonance (LSPR)
wavelengths are reported for metallic core-shell nanoparticles (NPs) placed
over a BK7 glass substrate. A numerical study is performed with the vectorized
version of the discrete dipole approximation with surface interactions
(DDA-SI-v). Gold (Au) and silver (Ag) metallic components are used for the
simulations of two different core-shell structures. Absorption enhancement and
the hybrid modes of plasmon resonances of the core-shell structures are
compared by using a measure that defines a size configuration. It is observed
that a small volume fraction of the core sizes results in shell domination over
the plasmon response. An additional study is conducted to discern the
sensitivity of the refractive index of nanoparticles in different surrounding
environments. With a selected core-shell size configuration of Ag-Au pairs, a
significant absorption enhancement with a redshift of LSPR wavelength is
observed for both Ag core-Au shell and Au core-Ag shell NPs. The absorption
behavior of the bare metallic NPs and selected core-shell pairs in proximity to
an external probe is also analyzed. The gallium phosphide (GaP) and silicon
(Si) AFM tip usage are investigated with transverse electric (TE) and
transverse magnetic (TM) wave polarizations. It is observed that the dominance
of light polarization on the absorption enhancement of the NPs switches at
different wavelengths, where the dielectric transition for tip materials
occurs. These findings show the possible targeted uses of metallic core-shell
nanoparticles in several areas such as nanomanufacturing, localized heating,
bio-sensing, and material detection applications.
