Dorota A. Pawlak

Roadmap on optical metamaterials

Optical metamaterials have redefined how we understand light in notable ways: from strong response to optical magnetic fields, negative refraction, fast and slow light propagation in zero index and trapping structures, to flat, thin and perfect lenses. Many rules of thumb regarding optics, such as mu = 1, now have an exception, and basic formulas, such as the Fresnel equations, have been expanded. The field of metamaterials has developed strongly over the past two decades. Leveraging structured materials systems to generate tailored response to a stimulus, it has grown to encompass research in optics, electromagnetics, acoustics and, increasingly, novel hybrid materials responses. This roadmap is an effort to present emerging fronts in areas of optical metamaterials that could contribute and apply to other research communities. By anchoring each contribution in current work and prospectively discussing future potential and directions, the authors are translating the work of the field in selected areas to a wider community and offering an incentive for outside researchers to engage our community where solid links do not already exist.

Compendium of natural hyperbolic materials

Artificially structured hyperbolic metamaterials (HMMs) - uniaxial materials with opposite signs of permittivity for ordinary and extraordinary waves - are one of the most attractive classes of metamaterials. Their existing in nature counterpart natural (homogeneous) hyperbolic materials (NHMs) has several advantages but has not yet been analyzed extensively. Here, based on literature-available data on permittivity as a function of wavelength, we review materials with naturally occurring anisotropy of permittivity in specific wavelength ranges. We suggest the best choice of materials that may act as NHMs depending on the wavelength, strength of the dielectric anisotropy (SDA), and losses.

Interacting plasmon and phonon polaritons in aligned nano- and microwires

The availability of macroscopic, nearly periodic structures known as eutectics opens a new path for controlling light at wavelength scales determined by the geometrical parameters of these materials and the intrinsic properties of their component phases. Here, we analyze the optical waveguiding properties of eutectic mixtures of alkali halides, formed by close-packed arrangements of aligned cylindrical inclusions. The wavelengths of phonon polaritons in these constituents are conveniently situated in the infrared and are slightly larger than the diameter and separation of the inclusions, typically consisting on single-crystal wires down to submicrometer diameter. We first discuss the gap mode and the guiding properties of metallic cylindrical waveguides in the visible and near-infrared, and in particular we investigate the transition between cylinder touching and non-touching regimes. Then, we demonstrate that these properties can be extended to the mid infrared by means of phonon polaritons. Finally, we analyze the guiding properties of an actual eutectic. For typical eutectic dimensions, we conclude that crosstalk between neighboring cylindrical wires is small, thus providing a promising platform for signal propagation and image analysis in the mid infrared.

Ferroelectric based tuneable SRR based metamaterial for microwave applications

We discuss the possibility of achieving tunable split ring resonators at microwave frequencies. One method is to use varying capacitance values to tune the magnetic resonance frequency. As another method ferroelectric thin films can be employed to obtain active response from the split ring resonators. We report the experimental measurements that are performed for single split ring resonators at microwave frequencies.

Solid-state NMR and x-ray diffraction studies of ionic complex of 1,8-bis(dimethylamino)naphthalene (DMAN) with picrolonic acid

An ionic complex of 1,8-bis(dimethylamino)naphthalene with picrolonic acid was studied by 13C and 1H magic angle spinning and x-ray diffraction. Structural and spectroscopic features of this compound were investigated. The detailed x-ray structure of this complex is described. A multicentre model of hydrogen bonding in proton sponges {[Me2N—H· · ·NMe2]+· · ·Xδ−} is proposed and the influence of weak intermolecular intractions with the nearest electronegative atom in crystal lattice of a proton sponge on the strong intramolecular [N—H· · ·N]+ hydrogen bonding is demonstrated. It appears that weak interactions of electronegative atoms with the nearest methyl hydrogen atoms can influence the localization of the proton in the intramolecular [N—H· · ·N]+ hydrogen bridge.

Temperature and atmosphere tunability of the nanoplasmonic resonance of a volumetric eutectic-based Bi₂O₃-Ag metamaterial.

Nanoplasmonic materials are intensively studied due to the advantages they bring in various applied fields such as photonics, optoelectronics, photovoltaics and medicine. However, their large-scale fabrication and tunability are still a challenge. One of the promising ways of combining these two is to use the self-organization mechanism and after-growth engineering as annealing for tuning the properties. This paper reports the development of a bulk nanoplasmonic, Bi2O3-Ag eutectic-based metamaterial with a tunable plasmonic resonance between orange and green wavelengths. The material, obtained by a simple growth technique, exhibits a silver nanoparticle-related localized surface plasmon resonance (LSPR) in the visible wavelength range. We demonstrate the tunability of the LSPR (spectral position, width and intensity) as a function of the annealing temperature, time and the atmosphere. The critical role of the annealing atmosphere is underlined, annealing in vacuum being the most effective option for a broad control of the LSPR. The various potential mechanisms responsible for tuning the localized surface plasmon resonance upon annealing are discussed in relation to the nanostructures of the obtained materials.

Ab Initio Study of Divalent

Divalent 3d transition metal impurities (V, Cr, Mn, Fe, Co, Ni, and Cu) in KMgF3 and BaLiF3 have been investigated by local-spin-density approximation (LSDA)-based ab initio calculations using an ultrasoft pseudopotential method and a planewave basis set. The results of numerical calculations show that the 3d transition metal impurities exhibit mid-gap levels and that the electronic transition from impurity levels to the conduction band results from the absorption of vacuum ultraviolet (VUV) light with energy lower than band-gap width. Therefore, 3d transition metal contaminations in KMgF3 and BaLiF3 should be avoided for VUV lithographic lens applications.

3d

Statistical analysis of structural parameters of garnet and garnet-like structures retrieved from the Inorganic Crystal Structure Database has revealed strong correlations between them. The degree of correlation depends on doping site and garnet type. Structural parameters are not equally sensitive to changes imposed by doping. The strongest correlation exists between the unit-cell parameter and the doping-ion radius. In the case of doping at the dodecahedral sites, the most sensitive parameter is the shortest dodecahedral distance. Principal component analysis (PCA) clearly shows that the first component explains most of the variation of structural data. It has a geometric basis and correlates with the effective radii of the doping ion. Partial correlation helps to identify the strongest relations between pairs of variables when the influence of other structural variables on them is controlled. It appears that in some cases partial correlation has a different sign when compared with the results of the standard correlation technique.

Transition Metal Impurities in KMgF3 and BaLiF3

Abstract Structural and spectroscopic properties of solid dianil of 2-hydroxy-5-methyl-isophthaldehyde have been investigated. This is a Schiff base containing intramolecular O–H…N hydrogen bonding. Single crystal X-ray diffraction shows that the possibly equivalent hard structural parameters (bond lengths and the valence angles) of the title molecule are hardly differentiated by an asymmetric hydrogen bonding and different conformations of the anil wings. 13 C MAS NMR results are more sensitive and they clearly show the influence of [O–H…N] hydrogen bonding on the chemical shifts of the central ring carbon atoms.

Correlation between structural parameters of garnet and garnet-like structures

Surface-directed passivation of p-doped silicon (Si) substrate was achieved by its biofunctionalisation with hexahistidine (His6)-tagged cytochrome c553 (cyt c553), a soluble electroactive photosynthetic protein responsible for electron donation to photooxidised photosystem I (PSI). Five distinct variants of cyt c553 were genetically engineered by introducing the specific linker peptides of 0–19 amino acids (AA) in length between the cyt c553 holoprotein and a C-terminal His6-tag, the latter being the affinity ‘anchor’ used for the specific immobilisation of this protein on the semiconductor surface. Calculation of 2D Gibbs free energy maps for the five cyt c553 variants showed a significantly higher number of thermodynamically feasible conformations of immobilised cyt c variants containing longer linker peptides. Here we show that the distinct cyt c553-based Si bioelectrodes display some characteristics of the p–n-type diodes, albeit varying in the level of dark saturation current J0 considered as the charge recombination parameter. These combined bioinformatic and electrochemical analyses indicate that the cyt c553 variants with longer linker peptides, up to 19AA in length, allow for more structural flexibility of immobilised cyt c553 in terms of both, orientation and distance of the haem group with respect to the Si surface, and promote the efficient biopassivation of the semiconductor substrate. Incorporation of the specifically immobilised 19AA cyt c553 variant into the all-solid-state biophotoelectrodes containing light harvesting PSI module enhanced biophotovoltaic performance of the PSI biophotoelectrode compared to the analogous device devoid of cyt c553.