Optical Properties of Silver-Coated Silicon Nanowires: Morphological and Plasmonic Excitations

ABRAHAM M; M. LESTER

PLASMONICS

SPRINGER

Lugar: Berlin; Año: 2013 p. 1 - 14

1557-1955

The optical extinction spectra of micro- andnanoparticles made up of high-contrast dielectrics exhibita set of very intense peaks due to the excitations ofmorphology-dependent resonances (MDRs). These kind ofresonances are well known at the microscopic scale as whis-pering gallery modes. In this work, we study numericallythe optical spectra corresponding to a core?shell structurecomposed by an infinite silicon nanowire coated with asilver shell. This structure shows a combination of bothexcitations: MDRs and the well-known surface plasmonresonances in dielectric metallic core?shell nanoparticles(Ekeroth Abraham and Lester, Plasmon 2012) . We com-pute in an exact form the complete electromagnetic responsefor both bare and coated silicon nanowires in the range of24?200 nm of cross-sectional sizes. We take into accountan experimental bulk dielectric function of crystalline sil-icon and silver by using a correction by size of the metaldielectric function. In this paper, we consider small silvershells in the range of 1?10 nm of thickness as coatings.We analyze the optical response in both the far and nearfields, involving wavelengths in the extended range of 300?2,400 nm. We show that the MDRs excited at the coreare selectively perturbated by the metallic shell throughthe bonding and antibonding surface plasmons (SPs). Thisperturbation depends on both the size of the core and thethickness of the shell, and, as a consequence, weget an efficient tuneable and detectable simple sys-tem. Our calculations apply perfectly to long nanotubescompared to the wavelength for the two fundamentalpolarizations (s, p).