Tuning of optical properties by atomic layer deposition

A combination of deposition strategies was applied in order to synthesize Au nanoparticle chains embedded in helical Al₂O₃ nanotubes ("nanopeapods"). Carbon nanocoils were grown by chemical vapour deposition and coated with Au by sputtering with a subsequent Al ₂O₃ coating by atomic layer deposition. Rayleigh instabilities were made use of in order to fragment the Au coating into nanoparticles with a sharp size distribution. The pitch of the nanocoils arising from three-dimensional periodical topography of the carbon nanocoil templates induced a regular spacing between the nanoparticles. The nanoparticle chains show a strong plasmonic resonance behaviour visible as clear polarization contrast at red wavelengths, which is absent in the blue upon excitation with a confocal laser scanning microscope. The fabricated nanopeapods are suggested promising candidates for highly efficient, ultrathin waveguides.