Relative contributions to the plasmon line shape of metal nanoshells

Nanoshells are mesoscopic particles consisting of a dielectric core coated with a metal shell, in particular gold or silver, of uniform nanometer scale thickness. This topology supports plasmon excitations with frequencies that are sensitively dependent on the relative radii of the nanoparticle's core and shell. The plasmon linewidth for this geometry is typically quite broad, nominally 100 nm or more in wavelength at plasmon resonance wavelengths in the near infrared. Several distinct physical mechanisms control the plasmon lineshape: phase retardation effects, including multipolar plasmon contributions; inhomogeneous broadening due to core and shell size distributions; and electron scattering at the shell interfaces. These mechanisms are examined in terms of their relative contributions to the plasmon line shape for nanoshells fabricated with diameters of 100-250 nm.