Plasmonic quasicrystals (PlQCs), by integrating the properties of quasicrystals (rotational symmetry and long range ordering but lack translational symmetry) and surface plasmon polariton mediated effects, offer several advantages over plasmonic crystals (PlCs). For example, in PlQCs one could have broadband, polarization independent response. However, large area patterning by electron beam lithography requires precise lattice coordinates as well as a practical way to design the structures for specific spectral response. We demonstrate design and fabrication of large area quasicrystal air hole patterns of π/5 symmetry in metal film in which broadband, polarization and launch angle independent transmission enhancement is observed. We demonstrate bi-grating quasicrystals to show that designable transmission response is possible over visible to near infrared wavelength regions with about 15 times enhancement. These would be useful in many applications like energy harvesting, nonlinear optics and quantum plasmonics.

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Mie resonator arrays formed by embossing titanium dioxide (tio 2) nanoparticles (nps) from solution are investigated as optical coatings for anti-reflection applications. Compacted nanoparticle assemblies offer unique possibilities to tailor the effective refractive index (RI). Here, we demonstrate a simple table-top, low pressure, and low temperature method to fabricate structured optical coatings. TiO 2 nanostructures in the form of nanodisks support Mie resonances in the visible wavelength spectrum and exhibit strong forward scattering into the high index substrates, making them suitable as broadband anti-reflection coatings for solar cells. TiO 2 np-based nanodisk arrays are designed, fabricated, and characterized regarding their anti-reflection properties on Si, GaAs, and InP substrates and solar cells. Detailed finite-difference time-domain simulations are performed to optimize the tio 2 NP-based Mie resonator arrays for the broadband anti-reflection as well as to explain the measured reflectance spectra. The solar-weighted reflectance is used as a figure of merit (FoM). TiO 2 nanodisk arrays on Si show a FoM of ~ 7% in the 400-1,100 nm wavelength spectrum; similar values are obtained for GaAs and InP substrates. TiO 2 nanodisk arrays embossed directly on prefabricated planar single-junction Si, GaAs, and InP solar cells result in an appreciable increase (~ 1.3 times) in the short-circuit current densities. Recently, sub-wavelength dielectric Mie resonator arrays have been reported for applications such as omnidirectional broadband anti-reflection. 1,2 Si nanodisk arrays on Si substrates show low average surface reflectance over the visible-NIR wavelength region. 3 Surface reflection reduction 4-7 plays a major part in increasing the performance of solar cells. For inorganic semiconductor solar cell materials, e.g., Si and III-Vs, due to their high refractive indices (~ 3-4) the reflectance loss (~ 30-40%) is significant. To reduce this, the solar cell surface can either be structured directly or an additional (structured) optical coating can be used. Direct structuring of solar cells can degrade its performance due to process induced defects and surface recombination and invariably requires additional passivation procedures/coatings. Such issues become more significant for thin film solar cells (thickness of ~ 2 µm or less). These limitations may be overcome by depositing a structured optical layer instead. Anti-reflection coatings (ARCs) include commonly used traditional thin-film dielectrics (e.g., silicon dioxide (SiO 2) and silicon nitride (Si x N y)), metal nanoparticles, 8,9 and dielectric nanostructures 3,10,11. While thin film dielectrics are easier to fabricate, multilayers are often required to achieve broadband anti-reflection. Metallic nanoparticles suffer from parasitic absorption in the metal and the resonances are highly sensitive to the RI of the matrix below or around the nanoparticles. 12 High-index dielectric (e.g., Si) Mie resonator arrays placed on Si or substrates with similar refract...

Metasurfaces with sub-wavelength features are useful in modulating the phase, amplitude or polarization of electromagnetic fields. While several applications are reported for light manipulation and control, the sharp phase changes would be useful in enhancing the beam shifts at reflection from a metasurface. In designed periodic patterns on metal film, at surface plasmon resonance, we demonstrate Goos-Hanchen shift of the order of 70 times the incident wavelength and the angular shifts of several hundred microradians. We have designed the patterns using rigorous coupled wave analysis (RCWA) together with S-matrices and have used a complete vector theory to calculate the shifts as well as demonstrate a versatile experimental setup to directly measure the shifts. The giant shifts demonstrated could prove to be useful in enhancing the sensitivity of experiments ranging from atomic force microscopy to gravitational wave detection.

The production of superhydrophobic coatings inspired by the surface of plant leaves is a challenging goal. Such coatings hold a bright technological future in niche markets of the aeronautical, space, naval, building, automobile, and biomedical sectors. This work is focused on the adaxial (top) and abaxial (bottom) surfaces of the leaflet of the Ceratonia silique L. (carob), a high-commercial-value Mediterranean tree cultivated in many regions of the world. The adaxial and abaxial surfaces feature hydrophobic and superhydrophobic behaviors, respectively. Their chemical composition is very simple: monopalmitin ester and palmitic acid are protuberant in the epicuticular and intracuticular wax layers of the adaxial surface, respectively, whereas 1-octacosanol dominates in the abaxial wax layers. In both surfaces, epicuticular wax is organized along a randomly oriented and intricate network of nanometer-thick and micrometer-long plates, whose density and degree of interconnection are significantly higher in the abaxial surface. The measured tilting angles for the abaxial surface (12–70°) reveal unusual variable density and water adhesion of the nanostructured plate-based texture. Optical measurements demonstrate that light reflectance/absorbance of the glaucous abaxial surface is significantly higher/lower than that of the nonglaucous adaxial surface. In both surfaces, diffuse reflectance is dominant, and the absorbance is weakly dependent on the light incidence angle. We show that the highly dense nanostructured platelike texture of the epicuticular abaxial layer of the C. siliqua leaflet works as a sophisticated light and water management system: it reflects solar radiation diffusely to lower the surface temperature, and it has superhydrophobic character to keep the surface dry. Such attributes enable efficient gas exchange (photosynthesis and respiration), transpiration, and evaporation. To mimic for the first time the abaxial surface, a templation approach was adopted using poly­(dimethylsiloxane) (PDMS)/poly­(methylphenylsiloxane) (PMPS) positive/negative replicas and a soft polymer/siloxane negative replica produced by the sol–gel process. Because high topographical variations of the biotemplate and wax adhesion to the biohybrid film affected the replication quality, the reproduction of the wax texture via the synthesis of 1-octacosanol-grafted siloxane-based hybrid materials is proposed as a suitable route to duplicate the abaxial surface with high fidelity. The natural chemical/physical strategy adopted by the C. siliqua leaflet to face the harsh Mediterranean climate is a powerful source of bioinspiration for the development of diffuse reflecting and superhydrophobic material systems with foreseen applications as dual-functional antiglare and water-repelling coatings.