Optical Properties of Gold Pyramidal Shells

We present an investigation of the optical properties of gold pyramidal shell nanoparticles. Theory shows a multiresonance spectrum at near-infrared wavelengths that is consistent with the measured extinction spectra of particles that are fabricated using a soft-lithography technique. In addition to electric dipole and electric quadrupole resonances, the calculations identify an unusual plasmon mode, which involves oscillation of the polarization perpendicular to the direction of both the incident polarization and wave vector. We show that this TE-like resonance can be suppressed by truncating the tip of the pyramid or by increasing the shell thickness without adversely affecting the in-plane dipole and quadrupole resonances.