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We report computational results on the optical response of quarter-wave periodic, modified periodic and optimized photonic crystals based on Ge and MgF2 materials. Transfer matrix method and pattern-search optimization algorithm have been combined to achieve high performance structures destined to spectral control in thermophotovoltaic systems. Our computations demonstrate that the pattern-search algorithm is readily applicable to optimal design of photonic crystals within reduced computing time. High optical performance and spectral efficiency have been achieved.

Mixed thin films of (SnS 2 ) x (CdS) 1−x (0 ≤ x ≤ 1) were deposited by spray pyrolysis technique decomposition of aqueous solutions of Cadmium chloride (CdCl 2 ) and Tin chloride (SnCl 2 ) on glass substrates at a substrate temperature of 350 °C. Structural properties of the obtained films were studied by X-ray diffraction analysis. The surface morphology and elemental analysis of the films has been examined using scanning electron microscopy (SEM) and Energy-dispersive X-ray spectroscopy (EDX). Optical properties of the deposited films were obtained using transmittance measurements in the wavelength range [200–2500 nm].Some optical parameters such as, high frequency dielectric constant e ∞, lattice high frequency dielectric constant e L and the dispersion parameters (oscillation energy E 0 and the dispersion energy E d ) were estimated by analyzing the refractive index data. The direct optical band gap value of these films varies from 2 to 2.41 eV. We have observed that (SnS 2 ) x (CdS) 1-x thin films conductivity obeys the Meyer–Neldel rule (E MN = 32 meV), which is interpreted as disorder parameter. The room temperature electrical resistivity of CdS (x = 0) films was found to be 2.22 10 +4 Ω cm and it decreases when content of Sn in mixed films increases and reaches the optimum value of resistivity 2.32 10 −2 Ω cm for the concentration x = 0.5. The carrier concentration was found to vary from −1.26 10 +12 to −4.50 10 +20 cm −3 and corresponding hall mobility varied from 6.51 10 +1 to 2.64 10 +1 cm 2 /VS.

The optical absorbance of four ternary thin films, i.e. MgSiP2, MgGeP2, MgSiAs2, MgGeAs2 have been theoretically examined over a wide range of wavelength from 300 nm to 800 nm. The combination of first-principle electronic structure calculations and the optical matrix approach for modeling the multilayer assembly have been employed for theoretical studies. The analysis of the calculated absorbance spectra at room temperature with unpolarized light and normal incidence, revealed that MgGeAs2 with a direct energy band gap of 1.6 eV exhibit a considerable high optical absorption, where a thickness of 3.2 μm of this thin film is sufficient to absorb 90% of the incident light and generates a maximum photocurrent of ∼23 mA/cm2.

The zinc oxide thin films, highly transparent, doped aluminium were prepared on glass substrates by the reactive chemical spray method. The incorporation nature of Al atoms in the ZnO lattice was determined by X-ray diffraction and optical analyses. Indeed, for low doping ⩽2%, the results of X-ray spectra analysis show a simultaneous reduction of lattice parameters (a and c), this variation, which follows VEGARD’s law, tends to indicate a substitution of Zn by Al. By against for doping >2% the increase in the lattice parameters thus the grain sizes, in accordance with the VEGARD’s law can be explained by occupation of the interstitial sites by Al atoms. Beyond 4%, the material tends to get disorderly and the crystallites orientation is random. The studied optical properties show that the variation of the optical gap follows a law of the x3/2 form for x

We theoretically investigate the possibility of enhancing light absorption in graphene-based one dimensional photonic crystal. We demonstrate that it is possible to achieve total light absorption at technologically important wavelengths using one-dimensional graphene-based photonic crystals. By means of the transfer matrix method, we investigate the effect of refractive indices and layer numbers on the optical response of the structure. We found that it is possible to achieve one peak, multi-peak or broadband, and complete optical absorption. As a result, the proposed photonic structures enable myriad potential applications such as photodetection, shielding and optical sensing.

A first principles study of structural, electronic and optical properties of zinc aluminum oxide (ZnAl 2 O 4 ) by means of the full potential linear augmented plane wave method is presented. The local density approximation is used for the exchange-correlation potential. A direct band gap of 4.19 eV, in agreement with experiment ( E g =3.9 eV), was determined. ZnAl 2 O 4 is transparent in the visible spectral region; the excitonic transition associated with the fundamental band gap is 4.17 eV. The refractive index value is 1.74 in the ultraviolet spectral region.

Some works take into account the shearing deformation of frictional material, but its effect on the transient response has not yet been considered. In this paper, optimal deformation angle and resonance frequency of frictional material are investigated. Force expressions in the stator/rotor interface are developed. Mechanical characteristics taking into account the effect of shearing deformation are deduced and presented. It is shown that the shearing deformation affects the initial state as well as on the steady state. Also, the fast time response of the motor is deduced. Results of the simulation are validated using the measurements made by other researchers on traveling wave piezoelectric motor AWM90-X, Daimler-Benz type, and a prototype USM(AWM-90).

Polycrystalline films of Bi2S3 compound have been prepared, at substrate temperature of 570 K, from Bismuth chloride (BiCl3) and Thiourea (CS (NH2)2) solutions. The structural characterisation has been carried out by the X-ray diffraction analysis (XRD). Study of optical properties shows that Bi2S3 compound has an allowed indirect transition at 1.43 eV energy. The photoelectrical parameters (diffusion length and lifetime) have been determined from the study of the photoconductivity.

Thin layers of bismuth trisulfide (Bi2S3) have been prepared for the first time by the spray pyrolysis method on glass substrates from bismuth chloride (BiCl3) and thiourea (CS(NH2)2) solutions with a concentration of 0.2 M. Films deposited on substrate at 570 K have a polycrystalline structure with crystallites size in the order of 120 A. X-Ray characterization by grazing angles diffraction (GAD) at 0.4 and 2° shows crystalline structures in surface and volume. Diffraction spectra of these films are indexed in the orthorhombic system. Studies of optical absorption in the energy range 1.5–4 eV indicate an optical gap of 1.66 eV. The Hall effect measurements indicate a carrier concentration of n=3.45×1017 cm−3.

Polycrystalline films of Sn 2 S 3 compound were prepared on glass substrates by the spray pyrolysis technique at a substrate temperature of 270 ∘ C using tin chloride (SnCl 2 ) and thiourea (Cs(NH 2 ) 2 ) solutions with a concentration of 0.1 M. The X-ray diffraction pattern reveals an orthorhombic structure and an average grain size equal to 130 A. The optical properties of the films were studied using optical transmittance and reflectance measurements over the wavelength range 200–2500 nm. The variation of refractive index n and extinction coefficient k with photon energy are reported. The dispersion of the refractive index in Sn 2 S 3 is analysed using the concept of a single oscillator. The values of oscillator energy E 0 and dispersion energy E d are determined to be 3.98 eV and 13.5 eV, respectively. The optical constants confirm that the Sn 2 S 3 thin films have a direct band gap of 2 eV. A value of 4.35×10 −3 (Ω cm) −1 for the room temperature conductivity is found using the four-probe method.

We propose the use of a pattern search optimization technique in combination with a seed preprocessing procedure to determine the optical constants and thickness of thin films using only the transmittance spectra. The approach is quite flexible, straightforward to implement, and efficient in reaching the best fitting. We demonstrate the effectiveness of the method in extracting optical constants, even when the films are not displaying interference fringes. Comparison to a real-coded genetic algorithm shows that the modified pattern search is fast, almost accurate, and does not need any parameter adjustments. The approach is successfully applied to extract the thickness and optical constants of spray pyrolyzed nanocrystalline CdO thin films.