Bottom-up tailoring of plasmonic nanopeapods making use of the periodical topography of carbon nanocoil templates

Au nanoparticle chains embedded in helical Al₂O₃ nanotubes ("nanopeapods") are synthesized by annealing carbon nanocoils coated with Au by sputtering and Al₂O₃ by atomic layer deposition. Regular spacing between nanoparticles with a sharp size distribution is achieved by fragmentation of the Au coating in agreement with the pitch of the nanocoils arising from threea dimensional periodical topography of the carbon nanocoil templates. A strong plasmonic resonance behavior of the fabricated nanopeapods manifests itself in confocal laser scanning microscopy by a clear polarization contrast at red wavelengths, which is absent in the blue. Numerical simulations confirm an incisive resonance enhancement for longitudinal polarization and suggest the nanopeapods as promising candidates for highly efficient, ultrathin waveguides. The waveguiding properties of the nanopeapods are investigated by electron energy-loss spectroscopy and energy-filtered TEM imaging.