Volume 4, Issue 3 - Special issue: Nanophotonics / Issue editor: Ning Dai

The nano- and microstructures of titanium dioxide (TiO 2 ) photoanodes in photovoltaic cells have a large impact on their photon to electron performances, including light harvesting, photogenerated electron separation, transport and recombination. This review will focus on anodic TiO 2 nanotubes (NTs) for the enhancement of photon conversion or light harvesting when incorporated in sensitized solar cells, which is valuable for increased photocurrent densities and solar cell efficiencies. By modulating the electrochemical processes which have a great impact on TiO 2 NT geometry, excellent optical properties can be achieved, resulting in the enhanced absorption of incident light and reduced light loss via reflection, penetration or transformation. The results indicate that the control of structures and morphologies of TiO 2 NTs is critical to the optimization of their applications in sensitized solar cells.

In this review, we present a brief introduction on the spoof surface plasmons supported on corrugated metallic plates with nearly zero thickness. We mainly focus on the propagation characteristics of spoof surface plasmon polaritons (SPPs), excitation of planar SPPs, and several plasmonic devices including the bending waveguide, Y-shaped beam splitter, frequency splitter, and filter. These devices are designed and fabricated with either planar or conformal plasmonic metamaterials, which are validated by both full-wave simulations and experiments, showing high performance. We also demonstrate that an ultrathin textured metallic disk can support multipolar spoof localized surface plasmons, either with straight or curved grooves, from which the Fano resonances are also observed.

Ultra-thin films with low surface roughness that support surface plasmon-polaritons in the infra-red and visible ranges are needed in order to improve the performance of devices based on the manipulation of plasmon propagation. Increasing amount of efforts is made in order not only to improve the quality of the deposited layers but also to diminish their thickness and to find new materials that could be used in this field. In this review, we consider various thin films used in the field of plasmonics and metamaterials in the visible and IR range. We focus our presentation on technological issues of their deposition and reported characterization of film plasmonic performance.

We review our recent works on a particular type of metamaterials (MTMs), which are metallic plates drilled with periodic arrays of subwavelength apertures typically in fractal-like complex shapes. We first show that such MTMs can well mimic plasmonic metals in terms of surface plasmon properties, but with plasmon resonances solely dictated by their aperture geometries rather than the constitutional materials. We then develop an effective-medium description for such plasmonic MTMs based on the mode expansion theory. Based on these theoretical understandings, we show that such MTMs exhibit several interesting applications, such as superlensing, hyperlensing, and enhancing light-matter interactions, which are demonstrated by microwave experiments or full-wave simulations.

Noble metal nanostructures have drawn attentions of researchers in many fields due to their particular optical properties. Controlling the metal nanostructures’ size, shape, material, assembly, and surrounding environment can tune their unique plasmonic features that are important for practical applications. In this review, we firstly discuss some novel metal nanostructures synthesized through wet chemical methods and their fundamental plasmonic properties. Then, some applications of these chemically synthesized nanostructures in plasmonics are highlighted, including surface-enhanced Raman spectroscopy, plasmonic sensing, optical nanoantennas, and plasmonic circuitry. Plasmonic nanostructures provide the ways to manipulate light at the nanometer scale and open the prospects of developing nanophotonic devices for sensing and information technologies.