It is shown that the space fluctuations of concentration of conducting inclusions might be responsible for the well-known disagreement between theory and experiment at determining microwave losses in metal-dielectric mixture: the theories (percolation theory, effective medium theory, etc.) predict much lower losses than those measured in experiment. It is demonstrated that if the effective skin depth in the regions occupied by the fluctuation is comparable to the mean diameter of these regions we can expect additional losses.

The complete spectrum of eigenwaves including surface plasmon polaritons (SPP), dynamic (bulk) and complex waves in the layered structures containing semiconductor and metallic films has been explored. The effects of loss, geometry and the parameters of dielectric layers on the eigenmode spectrum and, particularly, on the SPP modes have been analysed using both the asymptotic and rigorous numerical solutions of the full-wave dispersion equation. The field and Poynting vector distributions have been examined to identify the modes and elucidate their properties. It has been shown that losses and dispersion of permittivity qualitatively alter the spectral content and the eigenwave properties. The SPP counter-directional power fluxes in the film and surrounding dielectrics have been attributed to vortices of power flow, which are responsible for the distinctive features of SPP modes. It has been demonstrated for the first time that the maximal attainable slow-wave factor of the SPP modes guided by thin Au films at optical frequencies is capped not by losses but the frequency dispersion of the actual Au permittivity.

A permanent growth of the thin-film electronics market stimulates the development of versatile technologies for patterning thin-film materials on flexible substrates. High repetition rate lasers with a short pulse duration offer new possibilities for high efficiency structuring of conducting, semi-conducting and isolating films. Lasers with the picosecond pulse duration were applied in structuring the complex multilayered Cu(InGa)Se2 (CIGS) solar cells deposited on the polyimide substrate. The wavelength of laser radiation was adjusted depending on optical properties both of the film and the substrate. A narrow processing window of laser fluence and pulse overlap was estimated with both 1064 nm and 355 nm irradiation to remove the molybdenum backcontact off the substrate. The selective removal of ITO, ZnO and CIGS layers was achieved with 355 nm irradiation in the multilayer structure of CIGS without significant damage to the underneath layers. Use of the flat-top laser beam profile should prevent inhomogeneity in ablation. The EDS analysis did not show residues of molybdenum projected onto the walls of ablated channel due to melt extrusion. Processing with picosecond lasers should not cause degradation of photo-electrical properties of the solar cells but verification is required.

The work we present in this article is an investigation of the optimal dielectric behaviour of a ternary composite based on a mixture of epoxy resin, titanates and oxides. Titanates are known by their capacity to provide high dielectric constant values that make their use very important in system of telecommunication, transmission microwaves, and in integrated circuit technology. A comparative study is established on two types of oxides added to titanates of either calcium, barium, or magnesium following different proportions. The protocol used to characterise different mixtures is the Time Domain Reflectometry (TDR). The acquired results show a good concordance between the experimental values of the ternary mixture dielectric constant and the theoretical models deduced from the Lichtenecker modified law. The copper oxide (CuO) is revealed to be more influential than the magnesium oxide (MgO) on the added titanate because of an insignificant dielectric behaviour that the latter presents. On the other hand, the linear behaviour of $\varepsilon_{s}$ appeared with a CuO concentration round about 15% in a RE.BT.CuO mixture. For a fixed barium titanate fraction (27%) this linear evolution is located between the upper and the lower limits derivative from direct and inverse Wiener laws.

This paper reports the examination of the evolution of polyaniline-organic solvent interactions in the temperature range of 294–353 K. For this purpose, rheological and dielectric investigations have been undertaken for dispersions of plast-doped polyaniline in two different solvents (dichloroacetic acid and formic acid/dichloroacetic acid mixture). Dielectric permittivity has been investigated using the open ended coaxial line method in the frequency range of [100 MHz, 10 GHz]. Dielectric loss spectra of both dispersions showed a relaxation peak which was well fitted by Havriliak-Negami function. The relaxation was attributed to a Maxwell Wagner Sillars relaxation within polyaniline clusters. The difference found between relaxation parameters of the pure solvent and polyaniline dispersions was attributed to the solvent/polyaniline interactions. The relaxation time relative to the PANI/DCAA dispersion followed an Arrhenius law. While a Vogel-Fulcher-Tammann law was found for the relaxation time of PANI/DCAA-FA dispersion. Above a certain temperature, 318 K for PANI/DCAA and 313 K for PANI/DCAA-FA, the rheological parameters of the dispersions changed, thus indicating a morphological change of polyaniline in the dispersion. In the same range of temperature, α and β relaxation parameters undergo significant changes. Those changes in dielectric and rheological parameters seem to be related to a structural change occurring in the polyaniline organic dispersion systems while increasing temperature. An interesting correlation between permittivity and viscosity was obtained.

Novel metamaterial, based on wire medium embedded into magnetized ferrite, is studied. Waves in unbounded ferrites filled with wire media, surface wave at the interface of this metamaterial and the air as well as waves in a ferrite slab adjacent to a wire medium are considered. Different geometries of wires arrangement and different magnetization directions are discussed. Effective permeability was introduced for the case where both plasma and magnetic properties take place. Dispersion diagrams and applicability of the Drude model for the description of the wire medium in a host matrix, possessing high permittivity and permeability, are discussed.

In polymer light emitting diodes (PLEDs) each semiconducting polymer chain consists of a large number of conjugated segments linked by kinks or twists and each one of them behaves like a separated straight strand. The length and orientation of the conjugated strands relative to the electrodes surface depend on the deposition conditions used. Atomistic results have shown that the molecular properties of the conjugated strands depend on their length, which can affect the electronic processes involved in PLEDs. The aim of this work is to study the influence of the average conjugation length within the polymer layer on charge injection, trapping and recombination in PLEDs for all polymer strand orientations relative to the electrodes surface obtained experimentally by different techniques. For that purpose we use a mesoscopic model that considers the morphology and the molecular properties of the polymer. Our results show that by increasing the average conjugation length of the active polymer layer the amount of charge injected into the device increases and the recombination probability occurs preferentially in segments longer than the average conjugation length, both effects having implications on the performance of polymer LEDs.

In this article we study helical inclusions of a certain shape (called the “optimal shape”), such that the electric, magnetic, and magneto-electric polarizabilities are equal, and discuss unusual refractive and absorptive properties of artificial chiral materials based on such inclusions. We propose a new method of analytical calculation of resonant susceptibility of non-canonical, but true three-dimensional spirals. This method takes into account spiral trajectories and effective concentration of conduction electrons.

Pulsed laser deposition method was used to prepare Bi2Te3 thermoelectric thin films on a soda lime glass substrate at room temperature. Surface morphology of Bi2Te3 thin films was studied by AFM (atomic force microscopy) images. The influence of thermal annealing in vacuum condition on microstructure and surface morphology of films was investigated in wide range of temperature. The results demonstrate that annealing induces a transition from amorphous to polycrystalline structures and increases electrical conductivity. X-ray diffraction analysis proves that the film annealed at 300 °C for 120 min appears in large grain size polycrystalline structure but film annealed at 400 °C in the same condition has a preformed crystal growth texture in (006) direction.

Evanescent coupling is used to couple light from an organic Lambertian emitter into a single mode planar waveguide. Either an organic light emitting diode (OLED) directly excites the waveguide mode or an OLED pumps a photoluminescent (PL) material layer located directly on the waveguide. At the out-coupling grating the guided light is diffracted onto an array of organic photodiodes acting as a spectrometer. A spectral resolution of down to 16 nm could be achieved with integrated optoelectronic system.

The elucidation of physical properties of organic materials is important for further optimization of related electronic and optoelectronic devices. Here we review briefly various first-principles computational tools for the modeling of these materials by investigating key structural, electronic, and chemical properties of prototype organic semiconductors. In particular, we discuss the site-selectivity for band formation in pentacene and rubrene, hydrogenation and transformations of metal-free phthalocyanines, and the bonding topology in a hybrid organic-inorganic system.

First principles density functional calculations are used to study the uniaxial strain effects on the energy band structures of single- and multi-walled boron nitride nanotubes. Simulation results show that tensile strain induces a slight decrease in band gaps, while small and large compressive strains induce slight increases and decreases of band gaps, respectively. The maximum change of the band gap is ~0.5 eV. The band structures of all the nanotubes are not sensitive to uniaxial strain, which means that the boron nitride nanotubes could be used in blue and UV light-emitting devices under large uniaxial strain.

A technique incorporating the reflection matrix of a semi-infinite discrete layered periodic structure is employed to analyze the electromagnetic properties of a half-space filled with a layered metamaterial.

A complete framework for characterization and modelling of organic semiconductor materials is here reported. Multifunctional testbeds have been developed to analyze different organic semiconductors through hybrid demonstrators.

A new class of negative refractive index (NRI) transmission line is proposed. Differential operational amplifiers are used to form the required lumped elements, i.e., negative-impedance-converted (NIC) inductors and capacitors. When the gain of the differential operational amplifiers in the NIC circuits is very large over the entire frequency band, the equivalent material parameters are non-dispersive, and the phase response of the new NRI transmission line can be complimentary to that of a conventional transmission line over the entire frequency band. As an application example, a broadband 1:4 power divider based on the proposed NRI transmission line is studied.

Metallic Ag-nanoparticles have been synthesized by catalyst free chemical and photochemical reduction processes. During photochemical synthesis, the samples were illuminated independently by unpolarized and radially-polarized continuous laser beams (λ = 632.8 nm). The nanoparticles were characterized by bright-field transmission electron microscopy (TEM), linear absorption spectroscopy and fluorescence excitation/emission spectroscopy. Compared to other growth-conditions, sample prepared under radially polarized beam essentially displays well-separated, spherical nanoparticles with a narrow size distribution around average size of 6 nm. In addition, an outstanding enhancement in the fluorescence as large as 39% has been achieved along with observation of distinct localized surface plasmon states. Though the sample produced under unpolarized light could exhibit discrete plasmon states, better resolved states were observed in case of use of radially-polarized beam. It is expected that the radially polarized light could induce resonance energy transfer and hence could control growth conditions giving rise to absolutely unclustered Ag-nanoparticles. Detecting such localized surface plasmon states and understanding conditions of high quantum yield would be promising for single molecule fluorescence, superresolution microscopy and other nanoscopic applications.

The electric field responses of strongly nonlinear dielectric composites that consist of elliptical strongly nonlinear dielectric inclusions which are randomly oriented and embedded in different strongly nonlinear dielectric media in the dilute limit are investigated. By using the decoupling approximation, the effective nonlinear coefficients ($\chi_{e}$) are determined for varying the contrast between the nonlinear coefficients of inclusions and medium $(\chi_{i}/\chi_{m})$ with the aspect ratio, the ratio between semi major and semi minor axes, as parameters. The results show that increasing the aspect ratios within the range of 1 to 10 does not affect $\chi_{e}$ for low contrast $(\chi_{i}/\chi_{m}$ from 0.4 to 2.5). For high contrasts, the larger the aspect ratios, the greater the effects on $\chi_{e}$ are observed with enhancement and suppression of $\chi_{e}$ being observed at $\chi_{i}/\chi_{m}>1$ and $\chi_{i}/\chi_{m}<1$, respectively.

The recent development of innovative organic materials with intriguing features such as their flexibility, lightness, low cost and easy manufacturability, has driven researchers to develop innovative smart applications based on such kind of materials. In this work, all-organic electromechanical transducers, with both sensing and acting capabilities are proposed. The actuator and sensor models have been identified by using a grey box approach, as a function of membrane geometric parameters. The obtained models have been validated through comparison among estimated and experimental data.

The general approach to a design of miniature microwave devices based on a combination of transmission line sections with positive and negative dispersion is considered. Such lines, which are also known as right- and left-handed transmission lines, exhibit different dispersion characteristics. Using combination of these lines gives additional degrees of freedom for improvement of microwave device performance. At the same time, there is a possibility to decrease dimensions of the devices drastically. The following passive devices are under consideration: broadband digital phase shifters, directional couplers, dual-band resonators and filters exhibiting no spurious response. The potential benefit of this approach to the design of microwave devices is discussed. 


This paper presents the principle of two types of conformable and controllable spherical radome based on Electromagnetic Band Gap (EBG) materials operating at around 10 GHz. The EBG structure is composed of a grid of metallic wires conformed on a hollow spherical object. Two switching control configurations are considered: (1) between an EBG structure made of electrically continuous wires and another one made of discontinuous wires, and (2) between two EBG structures made of discontinuous wires where each has a different period of discontinuities. Both switching configurations are simulated and experimentally characterized on passive prototypes. An excellent agreement is observed between simulations and measurements. The radiation patterns of two types of antennas, a horn antenna and a meteorological antenna, are also measured in the presence of the radome.