Search

In this paper, the results of studies on sub-micrometer planar structures used for aimed frequency-dependent electromagnetic radiation dissipation are presented. The proposed specific geometry of periodic parts of surface structures should enable the occurrence of phenomena related to selective reflectance and interference. The inner porous structure should lead to the formation of destructive interference of electromagnetic radiation and its dissipation. The investigated structures were irradiated by a Gaussian-type radiation source. The propagation was analyzed using the MEEP software package for electromagnetic simulation via the finite-difference time-domain method. The reflectance spectra were obtained by the Fourier transform of the response to the short pulse. The obtained results showed that the surface structures are mainly responsible for reflected electromagnetic spectrum composition, while the porous parts were responsible for thermal radiation dissipation. [ABSTRACT FROM AUTHOR]

In this paper, we present the results of systematic studies on optical wave propagation thru a dielectric, perforated waveguide with a variable radius of hole-type defect. Such structures represent photonic crystals-like behaviour due to a finite number of periodic perforations, and their properties are strongly dependent on the geometrical shape of the central irregularity. By changing the radius of this defect, we can show that the resonant mode is trapped and localized at the defect position, while if there is continuity preserved in the perforations, no resonant mode is observed. All calculations were made using finite difference time-domain method. [ABSTRACT FROM AUTHOR]

In this paper, nanostructured tin oxide doped with Nitrogen was investigated by first principle calculations. At first, band structure, density of states, and projected density of states were evaluated for pure tin oxide. Then, the effect of doping with Nitrogen was studied for cases when N replaces O atom, Sn atom, respectively, and in two interstitials situation. Results were compared with pure reference case. Except of one interstitial case, Nitrogen doping usually plays the role of a p-type doping, however the decrease of band gap occurs in all cases. [ABSTRACT FROM AUTHOR]

In this paper, the effect of nitrogen flow rates on the physical properties of thin TaN films deposited on glass and silicon substrates using reactive DC magnetron sputtering was experimentally studied. The structural and optical properties of the films were evaluated by X-ray diffraction, atomic force microscopy, and optical spectrophotometry. X-ray diffraction patterns revealed that the phase composition evolves from pure metallic δ-Ta body centred cubic to tantalum nitride δ-TaN rock-salt structure. However, when the N2 flow rate exceeds 2 sccm, the films will show a poorly defined crystallization composed of mixture of fcc TaN phase and amorphous phases. Scanning electron microscopy and atomic force microscopy images revealed that the films deposited at high nitrogen flow rate possess smooth surface, good quality and lower roughness. The optical characterisation confirms that they are two groups of samples. The first have an metallic character with high reflectance and the second group are more transparent with an dielectric character with an absorption gap around 1.8 eV. [ABSTRACT FROM AUTHOR]

This paper reports on molecular beam epitaxy of GaSe 2D-layers on GaAs(001) substrates at growth temperatures of TS ≈ 400-540 °C as well as studies of their structural and optical properties. Transmission electron microscopy and the Raman spectroscopy techniques have established a correlation between the molecular beam epitaxy growth conditions and the GaSe polytypes being formed. It has been shown that GaSe layers grown at TS ≈ 400 °C can be characterized as γ-GaSe polytype with a rhombohedral crystal lattice structure, whereas the layers grown at TS ≈ 500 °C have a hexagonal structure and possess a ε-GaSe polytype. The latter also exhibit strong near band-edge photoluminescence at T = 300 K. The strong anisotropy of the photoluminescence intensity in an array of GaSe nanoplatelets has been revealed. [ABSTRACT FROM AUTHOR]

This paper presents the results of electrical and optical measurements of 600 nm thick silicon dioxide on Si layers to which zinc ions have been implanted. Following ion implantation the samples were annealed in air at 1023 K for 2 h. For the samples immediately after preparation and being annealed, AC measurements of resistivity Rp, phase angle θ, capacity Cp, and dielectric loss factor tanδ were made as a function of frequency (measurement range 50 Hz-5 MHz) and the measurement temperature (20 K-375 K). On this basis, the frequency-temperature dependence of conductivity σ was prepared. The strong frequency dependence of conductivity indicates that in the Zn/SiO2 layer after annealing, the conductivity takes place by hopping exchange (tunneling) of electrons between nanoparticles of the Zn metallic phase or between ZnO. Moreover, there is a clear change in the nature of conductivity at high frequencies. The photoluminescence spectra of the as-implanted Zn-SiO2-nanocomposites exhibit a blue-green band. This band is caused by the formation of oxygen vacancies in silicon dioxide. The intensity of this peak is observed to grow with the increasing annealing temperature. Besides, a strong orange-red band was revealed in the photoluminescence spectra of the annealed sample. This emission may be attributed to the presence of oxygen interstitial/antisites. The effect of thermal annealing on light-emitting properties has been discussed. [ABSTRACT FROM AUTHOR]

In this paper, for the first time, we introduce a simple way for finding the nonlinear optical properties of nanoparticles. The Michelson interferometer was used for calculating nonlinear refractive index. In comparison with conventional methods, the interferometry has high sensitivity and uses a single coherent beam that reduces the complexity and cost of experimental setup. The He-Ne laser with 75 mW laser irradiation at 632.8 nm was applied to different concentrations of TiO2 nanoparticles as a notable sample. By analysing the changes at interferometric patterns of different samples, the magnitude of (n2) was obtained in 10-8 cm²/W order. To confirm the interferometry results, the common Z-scan method was used to measure the nonlinear refractive index which reveals that the results are in good agreement with the interferometry method. [ABSTRACT FROM AUTHOR]

In this paper we present the results of optical and spectral characteristics of the quasibinary glassy system Bi-As2S3. From the obtained spectra we determined the optical band gap and the level of structural disorder for different doping atoms content. The decrease of the optical gap with increase on Bi atoms content was discussed in terms of chemical composition and arrangement of structural units, using the Raman spectroscopy results. The Wemple-DiDomenico model was used to describe the refractive index behavior and correlations between linear and nonlinear optical quantities of investigated chalcogenides, yielding significant parameters for the structural analysis. Having obtained high values of nonlinear refractive index, potential applications of these materials in telecommunication systems are discussed. [ABSTRACT FROM AUTHOR]

The I2-II-IV-VI4 series of quaternary chalcogenides semiconductors have drawn wide interest for their potential application as solar-cell absorbers. In this paper, we present a study of electronic and optical properties of the equilibrium kesterite structure (KS) of Cu2ZnGeS4 (CZGS) calculated by means of the full potential linearized augmented plane wave method. For this purpose, we used the Wien2k code based on the density functional theory with the generalized gradient approximation (GGA), modified Becke-Johnson exchange potential (mBJ) and the Hubbard potential U. The TB-mBJ is used alone or combined with U (TB-mBJ, and TB-mBJ+U). The results are compared with other theoretical results and the available experimental ones. The obtained results show that the top of the valence band is mainly composed by the Cu d orbital while the bottom of the conduction band is a mixture of Ge s and S p states. It was found that KS-CZGS has a direct band gap of 0.3, 1.8 and 2.0 eV using GGA, GGA+TB-mBJ and GGA+TB-mBJ+U, respectively. It is observed that states exist above the Fermi level (0 eV) with a width of 0.3 and 0.2 eV when we use GGA and GGA+TB-mBJ, while these states come down under the Fermi level when using GGA+TB-mBJ+U. The optical properties are calculated and an almost isotropic behavior is found in contrast to the reported properties of the stannite phase. This behavior can be linked to the charge density and the structure. [ABSTRACT FROM AUTHOR]

A recent experimental study found the phase transition from cubic to tetragonal phase at 17.2 GPa in BaZrO3. In this paper, we investigate the structural, electronic, elastic, and optical properties of BaZrO3 in the cubic and tetragonal structures under pressure by using first-principle density-functional theory. The main results are summarized as follows: (1) An indirect band structure is displayed for both cubic and tetragonal phases. The band gap increases by ≈1 eV as a result of the phase transition. (2) The elastic constants Cij's indicate that the cubic and tetragonal phases are mechanically stable. The easiest deformation mechanism in both phases is the shear along the (100) plane. (3) The real and imaginary parts of dielectric function for the cubic and tetragonal phases shift towards higher energies with pressure. Our results are in agreement with the available experimental and prior theoretical data. [ABSTRACT FROM AUTHOR]

The paper reports a growth of the high-quality Gd3Ga5O12 (GGG) homoepitaxial films by the liquid phase epitaxy technique using the PbO-B2O3 and PbO-B2O3-V2O5 fluxes. The influence of the flux composition containing V2O5 as well as the growth temperature is discussed basing on the optical absorption and the electron probe micro analysis results. [ABSTRACT FROM AUTHOR]

This paper reports the synthesis, crystal structure, surface morphology, optical and electrical properties of Mgdoped Sn2S3 thin films deposited by spray pyrolysis technique. All the films exhibit orthorhombic crystal structure with a (211) preferential orientation. Crystallite size calculations based on the Debye-Scherrer formula indicated that the Sn2S3 crystallite size increases with Mg content from 27.97 nm to 33.58 nm. Scanning electron microscopy images showed that all the films were very smooth composed of nanoneedle and nanoplate shaped grains. The band gap energy of the films exhibits a blue shift from 1.94 eV to 2.09 eV with increase in Mg concentration. Resistivity values of the undoped and Mg-doped Sn2S3 films were found to be in the order of 0.1 Ω cm. From the obtained results it is observed that the Sn2S3 film coated with 2 wt% Mg concentration exhibits better physical properties. [ABSTRACT FROM AUTHOR]

This paper obtains soliton solutions to nonlinear directional couplers in optical metamaterials by the aid of trial function method. Three types of couplers are studied. Four forms of nonlinearity are considered. Bright, dark, and singular soliton solutions are retrieved. These soliton solutions appear with certain constraint conditions that guarantee their existence. [ABSTRACT FROM AUTHOR]

Tracking detectors to be used in the future high-luminosity particle physics experiments have to be simultaneously radiation hard and cost efficient. Magnetic Czochralski silicon wafers can be grown with sufficiently high resistivity (several k Ω cm) and well-controlled high oxygen concentration. Significant research and development activity aiming to develop particle detectors made of high resistivity magnetic Czochralski silicon has been ongoing during the past decade. Beam test results presented in this paper show that n-type magnetic Czochralski silicon strip detectors can be operated with acceptable signal-to-noise ratio at least up to a 1 MeV neutron equivalent (neq) fluence of 1 x 1015 cm-2. The improved radiation hardness, compared to more commonly used float zone silicon, can be explained by the more beneficial electric field distribution inside the detector bulk. We have demonstrated a S/N of > 10 for full-size strip detectors attached to readout electronics at a fluence of 1 x 1015 neq/cm-2. These findings are supporting our transient current technique measurements. [ABSTRACT FROM AUTHOR]

In this paper use of selected optical methods of a hematocrit measurement has been presented. Elaborated methods have numerous advantages: relatively simple configurations, potentially low cost and high resolution. Investigation confirmed their ability to determine the hematocrit value with appropriate measurement accuracy. Furthermore, simultaneous use of complementary optical methods can substantially increase measurement reliability, because low-coherence interferometric measurement is based on physical (mainly optical) properties of the investigated object, while Raman spectroscopy is based on study of its molecular composition. [ABSTRACT FROM AUTHOR]

Zinc oxide (ZnO) thin films have become technologically important materials due to their wide range of electrical and optical properties. The characteristics can be further adjusted by adequate doping processes. In this paper, aluminum-doped zinc oxide thin films have been prepared on glass substrates using a sol-gel route and the radio-frequency magnetron sputtering process. The stoichiometry could be easily adjusted by controlling the nano-sized precursor concentration and the thickness by dip-coating cycles. On the other hand, the mixed N2O/Ar plasma gas provided adequate N doping for the RF sputtering process. The results showed the low electrical resistivity of 21.5 Ωcm with the carrier concentration of - 3.21 × 1018 cm-3 for the n-type aluminium-doped zinc oxide film. They were 34.2 Ωcm and + 9.68 × 1016 cm-3 for the p-type aluminium-doped zinc oxide film. The optical transmittance has been as high as 85-90% in the 400-900 nm wavelength range. The aluminium-doped zinc oxide (2 at.% Al) films exhibited the hexagonal wurzite structure with (002) preferred crystal orientation. The electrical characteristics were depicted by the gradual increase in N and NO that occupy the oxygen vacancies. [ABSTRACT FROM AUTHOR]

This paper presents the results of the structural, morphological and optical analysis of In:CdS thin films prepared by chemical bath deposition and successive ionic layer adsorption and reaction techniques. X-ray diffraction patterns showed the hexagonal phase of cadmium sulfide and it has been found that the amount of atomic percentage of indium increases the intensity of the preferential orientation (002) plane in chemical bath deposition In:CdS thin films. Compositional analysis confirmed the replacement of Cd ions by In ions and morphological analysis confirmed the lesser grain size and dense morphology in chemical bath deposition In:CdS thin films. Increase in In concentration in successive ionic layer adsorption and reaction In:CdS thin films leads to an increase in the optical transmission up to 80% and the higher band gap and therefore the results of this investigation enabled to understand the significance of preparation technique. [ABSTRACT FROM AUTHOR]

This paper represents an overview about exciton systems in the molecular nanostructures (ultra thin films and superlattices) and their implications on optical properties, primarily on absorption coefficient, which is given in the form of dielectric permittivity. With utilization of Green's function method, we have calculated dispersion law, spectral weight of exciton states and dielectric permittivity for every type of nanostructures. All obtained results are compared with optical properties in bulk crystals. Dielectric permittivity in all types of nanostructures shows very narrow and discrete dependence of external electromagnetic field frequency, which is a consequence of the expressed quantum effects, very thin thickness in these structures (or at least one dimension confinement) and boundary conditions. [ABSTRACT FROM AUTHOR]

In this paper, the nonlinear responses and optical properties modification in SK3 glass sample are investigated. The nonlinear responses measurements were performed by using of nonlinear transmission monitoring of 200 fs at 800 nm laser pulses. The optical power limiting threshold of the sample is measured to be about 40 mJ/cm2. The decrease of transmitted intensity is about 63% compared to the theoretical linear transmission at 270 mJ/cm2 incident pulse energy. For prediction of the experimental nonlinear behavior results, a theoretical model based on three-photon absorption and absorption of free carriers is presented. By fitting of experimental data with theoretical model, three-photon absorption coefficient and free-carrier absorption cross-section are reported. The photo-induced optical properties modification of the SK3 sample is investigated also. The modifications that appear as darkening are observed below breakdown threshold intensity. To analyses of modified region sizes, the laser pulse energy accumulation model is applied. [ABSTRACT FROM AUTHOR]

The paper presents a theoretical research of changes of optical properties of various nanofilm molecular crystals which are caused by the presence of two parallel and close borders. We used combined analytical-numerical calculation to find the allowed energy states of excitons and their spatial distribution (per layers) along the axis perpendicular to surface planes. We determined permittivity for the observed models of these ultrathin dielectric films and explored the influence of boundary parameters on the occurrence of discrete (per frequencies) and selective (per layers) absorption. The conditions for occurrence of smallest number of resonant absorption lines have been found and their localization has been defined. [ABSTRACT FROM AUTHOR]

The results of experimental investigations of diffuse (volume) nanosecond elevated-pressure discharges in a non-uniform electric field at a time resolution of a recording system being equal to ≈ 100 ps are presented in this paper. The application of the runaway electrons preionized diffuse discharge is promising for obtaining high-power radiation pulses in the VUV and UV spectral region. [ABSTRACT FROM AUTHOR]

This paper presents optical properties of SiO2 opals infiltrated with SbSI and inverted SbSI opals for the first time. Registered reflectance spectra exhibit Bragg's peaks connected with photonic band gap. Calculated photonic band structure has been compared with experimental results. [ABSTRACT FROM AUTHOR]

In this paper, the effect of a subwavelength thin layer on all-optical diode action in a one-dimensional photonic crystal is investigated. The photonic multilayer structure is considered as (BA)6(AB)6C(AABB)6, where layers A and B are nonlinear and linear materials respectively, and C is a thin layer with positive or negative-index material. The results are shown that by introducing a thin layer with different optical properties the all-optical diode efficiency is controllable. In our numerical results, the transmission contrast of the structure, without the thin layer is obtained as 0.63, with a positive index material layer nearly zero and with a negative index material thin layer about 0.75. [ABSTRACT FROM AUTHOR]

Chiral nematic liquid crystals are very interesting materials to infiltrate photonic crystal fibers since they are characterized by unique optical properties such as selective Bragg reflection, circular dichroism, and optical activity. In this paper the latest experimental results of the photonic crystal fibers filled with new chiral nematic liquid crystals are presented. Spectral properties of the light propagating in the photonic liquid crystal fibers have been measured and analyzed. [ABSTRACT FROM AUTHOR]

The paper deals with the optical fibre current sensor based on new optical fibre made of glass with a high value of refractive index. This kind of glass was developed to meet the requirements of these optical fibres. The aim of investigations was to develop a new optical fibre with adequate magneto-optical properties and a relatively weak linear birefringence resulting from the process of its production. These features are of essential importance for optical fibre current sensors. The results of investigations concerning such optical fibres have been presented, displaying satisfactory magneto-optical properties, as well as only low linear birefringence induced by stresses arising in the course of their manufacturing. [ABSTRACT FROM AUTHOR]

The aim of this paper is the theoretical investigation of Fe3+ doped in the ordered phase of LiAl5O8. We used the shell model and pair potential approximation to optimize the geometric structure of LiAl5O8. This approach enables the modeling of the crystal field parameters of LiAl5O8 and then calculates the energy levels scheme of Fe3+ ions doped in tetrahedral sites in the title crystal. Consistent crystal field analysis and the energy level splittings for LiAl5O8 doped with Fe3+ ions was performed in the frame of the exchange charge model of crystal field. The comparison of the theoretically obtained results for energy levels with the experimental data, yields satisfactory agreement and confirms the validity of the exchange charge model. [ABSTRACT FROM AUTHOR]

The aim of this paper is to present a comparison of the energy level schemes of Cr3+ (3d3 electrons) and Co2+ (3d7 electrons), each of ions doped, separately, in MgF2 crystal. We report on the detailed and consistent crystal field analysis of Cr3+ spectra in MgF2 crystal and compare with results, previously obtained, for Co2+, doped in same host matrix. The results are based on application of the exchange charge model of crystal field to the calculation of crystal field parameters and energy levels of both ions doped in MgF2.The calculations have been performed on previously optimized geometry of MgF2 crystal. The obtained results are compared with experimental data and discussed. [ABSTRACT FROM AUTHOR]