Arrays of vertically aligned gold nanotubes are fabricated over several square centimetres which display a geometry tunable plasmonic extinction peak at visible wavelengths and at normal incidence. The fabrication method gives control over nanotube dimensions with inner core diameters of 15-30 nm, wall thicknesses of 5-15 nm and nanotube lengths of up to 300 nm. It is possible to tune the position of the extinction peak through the wavelength range 600-900 nm by varying the inner core diameter and wall thickness. The experimental data are in agreement with numerical modelling of the optical properties which further reveal highly localized and enhanced electric fields around the nanotubes. The tunable nature of the optical response exhibited by such structures could be important for various label-free sensing applications based on both refractive index sensing and surface-enhanced Raman scattering.

and enhanced non-linearities. [ 22 ] Self-assembled arrays of gold nanorods have recently attracted signifi cant interest as modular optical metamaterials, mainly as a result of their ease of fabrication and inherent optical anisotropy, presenting the opportunity to tailor the frequency onset of hyperbolic dispersion throughout the visible and infrared spectral range. [ 16,23 ] In this paper, we combine the functionality provided by metamaterials and photonic-crystal-type structures to demonstrate metamaterial-based photonic crystals, termed hyperbolic polaritonic crystals (HPCs). By employing a fully fl exible plasmonic nanorod metamaterial platform exhibiting hyperbolic dispersion and tunable epsilon-near-zero (ENZ) frequency [ 15,24 ] determining the plasmonic behavior of the metamaterial similar to the plasma frequency for bulk metals, [ 25 ] we show how both the resonant response of HPCs and their mode confi nement capability can be controlled. The unique approach described here provides the opportunity to tailor the HPC's optical response both extrinsically, through nanostructuring, and intrinsically through the metamaterial's effective permittivity design, including its hyperbolic dispersion, by dimensional nanorod array parameterization. As a result, HPCs comprised mainly of dielectric patches separated by metamaterial areas only a few nanorods across, provide a fl exible alternative to conventional plasmonic metals in applications requiring on-demand engineering of plasmonic behavior. They may also be used for light coupling to, and extraction from, waveguided modes of hyperbolic metamaterials, inaccessible via conventional or total-internal refl ection illumination due to their very high modal effective index, but which play a signifi cant role in conditioning both the non-linear response of hyperbolic metamaterials and their spontaneous emission properties.We consider metamaterials composed of plasmonic nanorod arrays ( Figure 1 a) fabricated in self-assembled anodic aluminum oxide (AAO) templates (see Methods in the Supporting Information). The typical extinction spectrum of the metamaterial under plane wave illumination shows two resonances linked to the plasmonic response of the metamaterial for the electromagnetic fi eld polarized along either short or long nanorod axis (Figure 1 a). [ 24 ] These optical properties result from the anisotropy of the metamaterial, which can be described using effective medium theory (EMT) by the effective permittivity tensor xx yy zz ( ) ( ) ( ) ε ω ε ω ε ω = ≠ (see the Supporting Information for details). The spectral dispersion of the permittivity tensor results from the coupling between the plasmonic resonances of the individual nanorods in the array. Hyperbolic dispersion, where ε xx , ε yy > 0 and ε zz < 0, is observed for frequencies lower than the effective plasma frequency (where Re( ε zz ) = 0) of the metamaterial (Figure 1 b). In this regime, the metamaterial has The optical properties of metallic nanoparticles, fi lms, and surfaces are determined by surfa...

Arrays of gold-coated nanodomes were fabricated on glass substrates using a soft nanoimprint lithography technique. Optical transmission measurements revealed complex plasmonic resonances that proved highly sensitive to the array dimensions, the thickness of the gold layer, and the refractive index of the surrounding medium. As one promising application for these structures, the refractive index sensing capabilities of the nanodome arrays were assessed.

Materials commonly used in the carrier transport layers of organic light‐emitting diodes, where transport occurs through the bulk, are in general very different from materials used in organic field‐effect transistors, where transport takes place in a very thin accumulation channel. In this paper, the use of a high‐performance electron‐conducting field‐effect transistor material, diperfluorohexyl‐substituted quaterthiophene (DFH‐4T), as the electron‐transporting material in an organic light‐emitting diode structure is investigated. The organic light‐emitting diode has an electron accumulation layer in DFH‐4T at the organic hetero‐interface with the host of the light‐emitting layer, tris(8‐hydroxyquinoline) aluminum (Alq3). This electron accumulation layer is used to transport electrons and inject them into the active emissive host‐guest layer. By optimizing the growth conditions of DFH‐4T for electron transport at the organic hetero‐interface, high electron current densities of 750 A cm−2 are achieved in this innovative light‐emitting structure.

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