Robin M. Cole

Stretchable metal-elastomer nanovoids for tunable plasmons

A range of flexible metal-elastomer nanostructures are fabricated using a self-assembly and casting technique. Such nanostructures support plasmons, which have energies and field distributions that are strongly dependent on the structure geometry or position within an array. In particular, truncated spherical metal cavities embedded within a flexible three-dimensional elastomer film can be elastically deformed without tearing, modifying their shape and mechanically tuning their resonant plasmon modes. Such structures make possible the fabrication of low cost elasto-optic films and tunable substrates for surface enhanced Raman spectroscopy.

Electrodeposition of highly ordered macroporous iridium oxide through self- assembled colloidal templates

Iridium oxide electrodeposited through a self-assembled colloidal template has an inverse opal structure. Monolayers present long range hexagonal arrangements of hemispherical nanocavities while multilayers present 3D honeycomb structures with spherical voids. The films are amorphous, have several electroactive redox states and are electrochromic. The nanostructure modifies their reflectivity thus indicating that these films could be used as tunable photonic devices.

The fabrication of plasmonic Au nanovoid trench arrays by guided self-assembly

Plasmonic devices, which will enable on chip optical communication, rely on the interaction of light with free charges, and are key to optical sensing and waveguiding [1]. In previous work [2, 3], we have shown that spherical nanoscale voids in metal possess different, and potentially more useful, plasmonic modes than nanoscale metal particles. However, only by making linear arrays of such nanovoid structures it is possible to guide plasmons in specific geometric directions and fabricate plasmon waveguides which will enable on chip optical communication. In this work, single and multilayer arrays of gold voids have been fabricated through self assembly of sub-micron polystyrene spheres in V-shaped trenches in silicon, followed by selective area electrodeposition. Angle-dependent dispersion characteristics reveal the existence of localized plasmons. This is the first experimental evidence of linear plasmon arrays in templated self assembled structures.

Mapping gigahertz vibrations in a plasmonic?phononic crystal

We image the gigahertz vibrational modes of a plasmonic-phononic crystal at sub-micron resolution by means of an ultrafast optical technique, using a triangular array of spherical gold nanovoids as a sample. Light is strongly coupled to the plasmonic modes, which interact with the gigahertz phonons by a process akin to surface-enhanced stimulated Brillouin scattering. A marked enhancement in the observed optical reflectivity change at the centre of a void on phononic resonance is likely to be caused by this mechanism. By comparison with numerical simulations of the vibrational field, we identify resonant breathing deformations of the voids and elucidate the corresponding mode shapes. We thus establish scanned optomechanical probing of periodic plasmonic-phononic structures as a new means of investigating their coupled excitations on the nanoscale.

Fabrication of plasmonic Au nano-void trench arrays by guided self-assembly

Plasmonic devices, which will enable on chip optical communication, rely on the interaction of light with free charges, and are key to optical sensing and waveguiding [1]. In previous work [2, 3], we have shown that spherical nanoscale voids in metal possess different, and potentially more useful, plasmonic modes than nanoscale metal particles. However, only by making linear arrays of such nanovoid structures it is possible to guide plasmons in specific geometric directions and fabricate plasmon waveguides which will enable on chip optical communication. In this work, single and multilayer arrays of gold voids have been fabricated through self assembly of sub-micron polystyrene spheres in V-shaped trenches in silicon, followed by selective area electrodeposition. Angle-dependent dispersion characteristics reveal the existence of localized plasmons. This is the first experimental evidence of linear plasmon arrays in templated self assembled structures.

Active plasmon tuning of metal-elastomer nanostructures

Surface plasmon metal-elastomer nanostructures are actively tuned by stretching mechanically-tuneable elastomeric films. Tuneable plasmonic resonances and unusual inter-particle coupling are experimentally demonstrated. Such structures are highly suitable for developing optimal Raman and fluorescence sensors.

Templated self-assembly and nano-plasmonics of nano-void surfaces

Three-dimensionally nano-structured metal surfaces containing nano-scale voids produce strong localised plasmons. We show here the correlation between physical structure and photonic and electronic properties for several significant applications.

Fabrication of Nano-Structured Gold Arrays by Guided Self-assembly for Plasmonics

Gold inverse spherical nanoscale voids have been fabricated in linear arrays for directional plasmon measurements in the visible spectral range. We show that by KOH anisotropic etching in Si, we are able to make V-grooves in which latex spheres of the order of 500 nm self-assemble with largely defect-free cubic symmetry. Both single layer and multilayer assembly in a face-centered close-packed (FCC) lattice can be achieved by varying the width of the trenches. This template is subsequently used for electrodeposition of gold to create the inverse spherical nanovoids.