Search

In the short note, we theoretically analyze a one-dimensional photonic crystal (1D PC) with a double defect structure for potential use in dual-channel optical filtering. Using the transfer matrix method, we calculate the transmission spectrum and identify two distinct peaks within the photonic band gap region, each corresponding to one of the defects. We also explore the impact of varying the number of unit cells between these defects. Our results suggest that this 1D PC with a double defect structure can serve as an effective tuned dual-channel optical filter. [ABSTRACT FROM AUTHOR]

Subject and Purpose. This paper presents numerical simulation results on the transmission spectra of a split-ring resonator (SRR) loaded with a thin film of yttrium iron garnet (YIG). The application of a magnetic core in the SRR is proposed for increasing the photon-magnon (P-M) coupling strength. The anticrossing effect in the frequency dispersion behavior of the SRR modes and YIG film ferromagnetic resonance modes, namely SRR-YIG coupled modes, is identified. The dimensional parameters of the SRR with a magnetic core are calculated, taking care to preserve the design compactness and striving to obtain a maximum possible spin-number-normalized coupling strength for such a system. The work has been aimed at evaluating the efficiency of applying the magnetic core as a part of the planar microwave resonator to enhance the P-M coupling strength. Methods and Methodology. The transmission coefficient |S21| spectra of electromagnetic waves propagating through the planar resonator with the YIG film under the ferromagnetic resonance condition are numerically studied using the CST Studio Suite package in the frequency domain. The spatial distribution function of the magnetic field strength is calculated for the two scenarios of YIG film location: near the magnetic core (between the SRR and the feeding stripline) and inside the magnetic core (in the SRR center). Also, for each of these two scenarios, the transmission coefficient |S21| spectra of the wave propagation through the feeding stripline in the region of SRR-YIG coupled modes are simulated with and without the magnetic core. The dispersion curves of the SRR-YIG coupled modes are obtained in analytical terms. Results. It has been shown that the magnetic core application increases the P-M coupling strength 2.0 times in the scenario of YIG film location near the magnetic core (between the SRR and the feeding stripline). When the YIG film is inside the magnetic core (in the SRR center), the P-M coupling strength rises 2.3 times compared to similar cases without the magnetic core. Conclusions. The suggested magnetic core application can be used to increase the P-M coupling strength in the SRR — magnetic film resonant system, striving to develop effective microwave-to-optical converters and create efficient information exchange between quantum computers.

Non-equilibrium Green's function (NEGF) and density functional theory (DFT) calculations are used to explore the impact of doping on the electron transport properties in a single tetracene molecule linked to gold electrodes using isocyanide anchoring groups. Boron (B) and Nitrogen (N) atoms are used for doping and co-doping (BN) of the carbon atoms placed at the edge of the tetracene molecule. It was found that the chemical doping of tetracene molecules mainly impacts the rectification trends compared to non-doped molecules. Our findings indicate that B doping significantly improves the rectification ratio compared to other dopants because of a greater difference between the current values under positive and negative biases as a result of asymmetric I-V characteristics. These inferences have also been assessed in terms of MPSH and transmission spectra. In addition, novel characteristic of negative differential resistance (NDR) is attained in single dopant molecular junctions. [ABSTRACT FROM AUTHOR]

We present mathematical theory for self-similarity induced spectral gaps in the spectra of systems generated by generalised Fibonacci tilings. Our results characterise super band gaps, which are spectral gaps that exist for all sufficiently large periodic systems in a Fibonacci-generated sequence. We characterise super band gaps in terms of a growth condition on the traces of the associated transfer matrices. Our theory includes a large family of generalised Fibonacci tilings, including both precious mean and metal mean patterns. We apply our analytic results to characterise spectra in three different settings: compressional waves in a discrete mass-spring system, axial waves in structured rods and flexural waves in multi-supported beams. The theory is shown to give accurate predictions of the super band gaps, with minimal computational cost and significantly greater precision than previous estimates. It also provides a mathematical foundation for using periodic approximants (supercells) to predict the transmission gaps of quasicrystalline samples, as we verify numerically. [ABSTRACT FROM AUTHOR]

A single-stage centrifugation method is used for the precipitation and crystallization of a solution of a hybrid halide perovskite compound of the CH3NH3PbI3 composition. The perovskite films are annealed in the temperature range of 80–140°C, during which the excess of the N-methylpyrrolidone solvent was removed by evaporation. The X-ray phase analysis of the synthesized perovskite layer is carried out. The morphology of the surface of the layers after crystallization and the transmission spectra in the optical range are studied. The experiments and research results showed that the optimal temperature regime for the formation and crystallization of lead triiodide methylammonium perovskite films is 100–110°C. The perovskite layers obtained in these processing regimes have a surface morphology with a uniform granular crystal structure and are highly uniform. Moreover, in solar cells based on perovskite-like CH3NH3PbI3 structures with an annealing temperature of 100–110°C, the short-circuit currents reached 16.0 mA/cm2. At the same time, at annealing temperatures of perovskite layers above 120°С, the maximum value of the short-circuit currents did not exceed 14.0 mA/cm2. [ABSTRACT FROM AUTHOR]

Self-phase modulation (SPM) broadening of prompt laser spectra was studied in a transmission mode in natural and synthetic diamonds at variable laser wavelengths (515 and 1030 nm), pulse energies and widths (0.3–12 ps, positively chirped pulses), providing their filamentary propagation. Besides the monotonous SPM broadening of the laser spectra versus pulse energy, which was more pronounced for the (sub)picosecond pulsewidths and more nitrogen-doped natural diamond with its intra-gap impurity states, periodical low-frequency modulation was observed in the spectra at the shorter laser pulsewidths, indicating dynamic Bragg filtering of the supercontinuum due to ultrafast plasma and nanoplasmonic effects. Damping of broadening and ultra-modulation for the longer picosecond pulsewidths was related to the thermalized electron-hole plasma regime established for the laser pulsewidths longer, than 2 ps. Unexpectedly, at higher pulse energies and corresponding longer, well-developed microfilaments, the number of low-intensity, low-frequency sideband spectral modulation features counterintuitively increases, thus indicating dynamic variation of the periods in the longitudinal plasma Bragg gratings along the filaments due to prompt secondary laser–plasmon interactions. The underlying sub- and/or near-wavelength longitudinal nanoscale Bragg gratings produced by femtosecond laser pulses in this regime could be visualized in less hard lithium niobate by atomic force microscopy cross-sectional analysis in the correlation with the corresponding sideband spectral components, supporting the anticipated Bragg filtering mechanism and envisioning the corresponding grating periods. [ABSTRACT FROM AUTHOR]

The transformation of the transmission spectra of linearly polarized radiation passing through a symmetric photonic cell is studied based on numerical analysis. The cell consists of two layers of magnetic semiconductor with a graphene monolayer on each and a central dielectric layer located between the graphene monolayers. It is possible to achieve amplification in the near terahertz range in graphene layers due to charge carrier drift. Control of transmission spectra and polarization of transmitted radiation can be achieved by changing the Fermi energy of graphene layers, by changing the external magnetic field, and by changing the thickness of the dielectric layer and the orientation of the incident radiation polarization plane. [ABSTRACT FROM AUTHOR]

This study investigates the effects of annealing time on the optical and electrical properties of tin dioxide coatings, specifically surface resistivity and specific conductivity. The thickness of the film, as well as its density and void density, were calculated from the interference peaks. The results suggest that as the duration of annealing increases, the density of the film decreases and the void volume increases. The lack of interference peaks in the transmission spectra of films containing additives is caused by the development of dendritic structures within the films. As the annealing duration is extended to 6 h, the surface resistivity increases, resulting in a decrease in the specific conductivity of all films. As the duration of annealing increases, the surface resistivity of the films studied increases and therefore their overall quality decreases.

Context: The Adenine-based nanotube is theoretically designed, and its transmission spectra are investigated. The quantum-confined Adenine nanotube shows electronic transmission of the carrier at minimum stress. In this paper, the prediction of transmission spectra of the quantum-confined bio-molecular nanotube is investigated and deeply studied. Molecular level structure prediction and their electronic characterization can be possible with ab initio accuracy using a machine learning algorithmic approach. At the molecular level, it is difficult to predict quantum transmission spectra as these results are always hampered by the carrier backscattering effect. However, mostly these predictive models are available for intrinsic semi-conducting materials and other inorganic structures. Methods: Machine learning algorithms are designed to predict the electronic properties of the nano-scale structure. This task is even more difficult when quantum-confined molecular arrangements are considered, whose transmission spectra are sensitive to the confinements applied. This paper presents an effective machine learning algorithms framework for predicting transmission spectra of quantum-confined nanotubes from their geometries. In this paper, we consider regression machine learning algorithms to find maximum accuracy with varying configurations and geometries to excerpt their atoms' local environment information. The Hamiltonian components are then used to enable the utilization of the information to predict the electronic structure at any arbitrary sampling point or k-point. The theoretical basics introduced in this process help to capture and incorporate minor changes in quantum confinements into transmission spectra and provide the framework algorithm with more accuracy. This paper shows the ability to predict the accurate algorithmic models of the Adenine nanotube. In this framework, we have considered a tiny data set to achieve a rapid and reliable method for electronic structure determination and also propose the best algorithm for predictive model analysis. [ABSTRACT FROM AUTHOR]

Context: This study aims to investigate the electronic transport properties of tetracene molecule connected to gold (Au) electrodes with asymmetric anchoring groups. More specifically, we investigate the effect of asymmetric electrode coupling on the rectification ratio of tetracene-based molecular device. To introduce coupling asymmetry in these junctions, one end of the tetracene molecule is terminated with thiol (−SH) or isocyanide (−NC) while the other end with amine (−NH2) or nitro (−NO2) anchoring group. The results indicate that the electronic transport behavior is affected by the nature of molecule-electrode coupling, and the rectification ratio can be modulated by a proper choice of the anchoring groups. We reveal that the tetracene molecule when connected with isocyanide and amine combination exhibits remarkable rectifying performance (with a rectification ratio of 74) in contrast with other configurations. Furthermore, a prominent negative differential resistance (NDR) feature is observed when the molecule is connected with thiol as one of the anchors. Our present findings with excellent rectifying performance and negative differential resistance pave a new roadmap for designing multifunctional molecular devices. Methods: By applying non-equilibrium Green's function (NEGF) formalism combined with density functional theory (DFT) Atomistic Tool Kit software package, the electronic transport properties of tetracene molecule connected to gold electrodes with asymmetric anchoring groups have been investigated. The calculations were performed using the Perdew-Burke-Ernzerhof (PBE) parameterization of DFT within generalized gradient approximation (GGA) exchange-correlation functional. To improve calculation precision and save computational efforts, the molecule and anchor groups were double-ζ (DZ) polarized, while single-ζ (SZ) polarized basis set was used for gold electrodes. [ABSTRACT FROM AUTHOR]

This study investigates the effects of annealing time on the optical and electrical properties of tin dioxide coatings, specifically surface resistivity and specific conductivity. The thickness of the film, as well as its density and void density, were calculated from the interference peaks. The results suggest that as the duration of annealing increases, the density of the film decreases and the void volume increases. The lack of interference peaks in the transmission spectra of films containing additives is caused by the development of dendritic structures within the films. As the annealing duration is extended to 6 h, the surface resistivity increases, resulting in a decrease in the specific conductivity of all films. As the duration of annealing increases, the surface resistivity of the films studied increases and therefore their overall quality decreases. [ABSTRACT FROM AUTHOR]

In this study, we theoretically analyze a one-dimensional photonic crystal (1D PC) with a multidefect structure for potential use in multi-channel optical filtering. Using the transfer matrix method, we calculate the transmission spectrum and identify distinct peaks within the photonic band gap region, each corresponding to one of the defects. We also explore the impact of number of defect on transmission peaks reduces separation from 7.069 to 4.520 THz for number of defects (n) = 3–5. [ABSTRACT FROM AUTHOR]

Context: This study aims to tune the transport properties of tetracene single-molecule junctions with the proper choice and placement of side and anchoring groups. For the operationalization of the molecule that was anchored with thiol or isocyanide groups, two different side groups, amine and nitro, in two different positions, were taken into consideration. For unperturbed tetracene molecule, a prominent negative differential resistance (NDR) feature at 1.8 V was observed with the isocyanide anchoring group while the thiol anchoring group exhibits a plateau region over a bias voltage of 2.2 to 3.2 V. At a bias voltage that is dependent on the chemical or structural change of side or anchoring groups, NDR feature of varying degree was seen in all configurations. Results show that the current flowing through the thiol-anchored molecule perturbed with the amine group at S' position is relatively larger than other configurations because of the smaller HOMO-LUMO gap and broader transmission peaks resulting in a peak to valley current ratio (PVCR) of 1.22. In addition, multiple NDR regions were realized in nitro-perturbed isocyanide-anchored molecule at S position. These results suggest their promising applications in switches, logic cells, and storage devices. Methods: The modeling and simulation of side-group mediated anchored tetracene molecule through two electrodic systems were studied using density functional theory (DFT) combined with non-equilibrium Green's function (NEGF) in Virtual NanoLab-AtomistixToolkit (ATK). The electron transport properties were calculated using Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation (GGA) exchange-correlation function. To optimize computing time, gold electrodes were single zeta polarized whereas the molecule, anchor groups, and side groups were double zeta polarized. [ABSTRACT FROM AUTHOR]

A methodology, technique, and research results for the synthesis of films on a glass surface upon irradiation of aqueous solutions of copper sulfate with laser radiation are presented. The studies used the radiation of a yttrium-aluminum garnet laser, its second harmonic and the radiation of a semiconductor laser. Solutions with different concentrations of copper sulfate were used. The structure and and characteristics of the control films obtained as a result of drying solutions without exposure to laser radiation. Films synthesized under the action of laser optical characteristics of the films obtained in this case are compared with the structure radiation have both ordered and disordered structures. The characteristic dimensions of the structural elements of these films are 0.5-2 microns. For solutions with low concentrations, the density of the coating of glass substrates with films obtained under the action of laser radiation is much higher than the density of the coating with control films. The transmissions of the films were studied in the spectral range 300-1200 nm. It was found that the transmission of films obtained under the action of laser radiation and control films differ. [ABSTRACT FROM AUTHOR]

The transmission and reflection spectra of a one-dimensional microresonator structure with dielectric Bragg mirrors, the working cavity of which is filled with several "dielectric-graphene" or "semiconductor-graphene" periods with controlled material parameters, were obtained using transfer matrices and numerical methods. Carrier drift in graphene monolayers is created to achieve amplification, which makes it possible to use the hydrodynamic approximation to represent graphene conductivity in the terahertz range. The transformation of spectra is achieved both by changing the energy state of the graphene monolayers and by changing the external magnetic field. It is shown that amplification is observed in the region where the real part of the conductivity is negative as the chemical potential (Fermi energy) increases, and the coefficients T and R become substantially greater than unity. The results of the work may be of interest to developers of graphene-based controlled photonic devices. [ABSTRACT FROM AUTHOR]

We explored spectral diversity in infrared (IR, 4–25 μm) imaginary (k) and real (n) indices of refraction (optical constants) for 26 surface soils that originated from global dust entrainment regions. The k spectra were derived from optical transmission spectra of KBr pellets containing dispersed dust and the n spectra were estimated with the subtractive Kramers–Kronig (SKK) method. We compared k and n obtained by this study with previously published values. Our optical constants from the KBr technique are comparable in magnitude and spectral shape to those from previous studies that used dust aerosols re-suspended in a chamber. This suggests that the SKK method can offer a reliable mechanism for measuring IR spectra of both optical constants for soils. The soils used here exhibit additional spectral variability compared with past studies. We note that the appearance and the shift in positions of the strongest absorption peaks are due to combinations of silicates with overlapping absorption, rather than being related to a single mineral. We note that all dust optical constants have substantially lower magnitudes compared to those of pure minerals. Our results can improve estimates of mineral dust radiative effects and support quantification of surface mineral estimates using satellite and ground-based remote sensing. [ABSTRACT FROM AUTHOR]

Transmission spectra of a symmetric microresonator structure, with dielectric Bragg mirrors, are obtained. The working cavity of the structure is partially filled by a layer of a quarter-wave thickness of finely layered "graphene–semiconductor" medium, with material parameters controlled by external electric and magnetic fields. It is shown, that the transformation of the spectra is achieved both by changing the energy state of the graphene layers and by changing the external magnetic field. The spectral characteristics for the inverted and doped states of graphene layers are established. [ABSTRACT FROM AUTHOR]

We theoretically investigate optical bistability/multistability and transmission spectrum in a quadratically coupled optomechanical system consisting of an optical cavity with quantum dot molecules inside it. The optomechanical cavity is driven by a strong pump laser and a weak probe field. We observed that the optical tristability in the presence of quadratic optomechanical coupling transforms into optical bistability in the absence of quadratic optomechanical coupling. We further investigate this hybrid system's absorption and dispersion spectrum by changing the various control parameters like quadratic optomechanical coupling and intensity of strong pump laser field. In addition, we observed the superluminal effect of the transmitted probe field by calculating the group velocity index of light, which is influenced by system parameters. Such results may be useful for designing all-optical switching and novel quantum photonic devices. [ABSTRACT FROM AUTHOR]

The proposed Fiber Bragg Grating (FBG) sensor investigated spectral features applying finite element numerical (FEM) analysis method. The wave optics module applied the Maxwell's equations and confined the electromagnetic perfectly. The best optimized chosen parameters are 1.45, 1.5 for clad and core refractive indices, respectively, for a better FWHM of 20 nm approximately with the highest reflectivity of 93.5%. As a sensor, the FBG is developed in a D form with optimum specifications. An etched FBG's sensitivity to the surrounding medium's refractive index (RI) has been documented. For the analyte index (AI) range of 1.3–1.39 by 9 um etching diameter, the optimal wavelength sensitivity (WS) and resolution are 118.7 nm/RIU and 1 × 10−3 RIU, respectively. [ABSTRACT FROM AUTHOR]

Metaconcrete is a newly manmade concrete where traditional aggregates are partially replaced by resonant aggregates. The metaconcrete slab can attenuate vibration in the specific frequency bandgap which are created by the locally resonant aggregates. To enhance the attenuation performance of metaconcrete slab, a dual-resonant aggregate was designed and embedded into the metaconcrete slab. Firstly, a mass-in-(massin-mass) analytical model is used to predict the bandgap characteristics of dual-resonant aggregates metaconcrete. Then, eigenfrequency investigation is conducted to acquire the dispersion curve of the periodic unit cell by using finite element software COMSOL Multiphysics. The effects of the mass and stiffness ratios parameters on the characteristics of bandgap are studied. The frequency responses of the dual-resonant aggregates metaconcrete reveal that the dual-resonant aggregates metaconcrete slab can acquire vibration wave mitigation in two designed frequency bands. The results offer a base for the optimal design of the metaconcrete slab for structural protections resist vibration loading. [ABSTRACT FROM AUTHOR]

In this communication, the TMM for the analysis of transmission characteristics of MCP based PCs is employed. The periodic structure of air/right‐hand‐MCP, in asymmetric form (AB)N, is considered as RHPPC. The transmission characteristics of the same structure are analyzed with symmetrically introduced defect layer of MCP for different values of the magnetizing field. It is observed that this binary RHPPC in both cases acts as good reflectors in low and high frequency ranges for low magnetic field between 0.4T to 1.2T; and the bandgaps vanish at higher magnetic field above 1.2T, in both types of PCs. Further, it is noticed that the transmittance in defect introduced PC is low in comparison to corresponding PC without defect, for a particular value of magnetic field up to 1.2T. The defective RHPPC exhibits defect modes in the bandgap regions. Hence, an increase in magnetic field decreases the bandgaps and consequently increases the transmission in both cases; while impact of defect is to reduce the transmission. The lowest reverse transmission peak for the defective PC obtained with the value of magnetic field from 2.0T to 2.4T shows more transmission as compared to that of the PC without defect. The insights of this comparative analysis can be used in designing tunable microwave transmitters. [ABSTRACT FROM AUTHOR]

We investigate theoretically, the optical response for a cavity optomechanical system containing a Kerr non-linear substrate. The optomechanical cavity's moving membrane interacts linearly and quadratically with the radiation pressure of the photons. We found that the quadratic non-linear coupling and Kerr non-linearity strongly influence the system's optical multistability. Further, the transmission spectrum is observed under the influence of both non-linearities. Our theoretical results show that the width of the spectrum alters significantly by tuning the non-linearities present in the system. In addition, our results show that a peculiar positive value of quadratic optomechanical coupling is instrumental in generating Normal Mode splitting while the absence and negative value of quadratic optomechanical coupling inhibit the Normal-Mode splitting. [ABSTRACT FROM AUTHOR]

The methodology, technique, and results of studying the formation of films on the glass surface during laser irradiation of water solutions of copper sulfate with radiation are presented. The nanosecond radiation of an yttrium-aluminum garnet laser with a generation wavelength λ = 1.06 μm was used. Solutions with different concentrations of copper sulfate were applied. The structure of the films obtained in this case was compared with the structure of the films obtained as a result of drying solutions without exposure to laser radiation. The resulting films have both ordered and disordered structures. The characteristic dimensions of the structural elements of the films are 0.5–10 μm. The transmission of films in the visible spectral region (400–800 nm) was studied. In general, the resulting films are transparent in this area. Their transmission hardly depends on the wavelength, but it is different for different concentrations of the used solutions of copper sulfate. [ABSTRACT FROM AUTHOR]

[Display omitted] • Elucidation of transport properties of tetracene molecule with symmetrical electrodes. • Significant NDR feature observed with highest PVCR with Ag electrode combination. • Metallic, semi-metallic or non-metallic behavior with different set of electrodes. • Selection of suitable electrode materials for molecular devices is emphasized. Density functional theory in combination with non-equilibrium Green's function is employed to study the electron transport properties of tetracene-based molecular junctions formed with silver, gold, copper and platinum electrodes. The physical origin of the IV curves is discussed by analyzing their density of states, molecular projected self-consistent Hamiltonian, transmission spectra, conductance trends and HOMO-LUMO gap at different operating voltages. The results indicate that till a low bias voltage of 1.4 V, the tetracene molecule shows metallic behavior with silver and copper electrodes while semi-metallic and non-metallic nature with gold and platinum electrodes respectively is observed. The zero bias conductance is found to be greatest for Ag followed by Cu and Au with the least in Pt. Furthermore, it is worth mentioning that negative differential resistance feature is observed in molecular junctions with all the electrodes except Pt, with the highest peak-to-valley current ratio of 1.283 found in Ag-Tetracene-Ag molecular junction. [ABSTRACT FROM AUTHOR]

Self-phase modulation (SPM) broadening of prompt laser spectra was studied in a transmission mode in natural and synthetic diamonds at variable laser wavelengths (515 and 1030 nm), pulse energies and widths (0.3–12 ps, positively chirped pulses), providing their filamentary propagation. Besides the monotonous SPM broadening of the laser spectra versus pulse energy, which was more pronounced for the (sub)picosecond pulsewidths and more nitrogen-doped natural diamond with its intra-gap impurity states, periodical low-frequency modulation was observed in the spectra at the shorter laser pulsewidths, indicating dynamic Bragg filtering of the supercontinuum due to ultrafast plasma and nanoplasmonic effects. Damping of broadening and ultra-modulation for the longer picosecond pulsewidths was related to the thermalized electron-hole plasma regime established for the laser pulsewidths longer, than 2 ps. Unexpectedly, at higher pulse energies and corresponding longer, well-developed microfilaments, the number of low-intensity, low-frequency sideband spectral modulation features counterintuitively increases, thus indicating dynamic variation of the periods in the longitudinal plasma Bragg gratings along the filaments due to prompt secondary laser–plasmon interactions. The underlying sub- and/or near-wavelength longitudinal nanoscale Bragg gratings produced by femtosecond laser pulses in this regime could be visualized in less hard lithium niobate by atomic force microscopy cross-sectional analysis in the correlation with the corresponding sideband spectral components, supporting the anticipated Bragg filtering mechanism and envisioning the corresponding grating periods.

The transformation of the transmission spectra of linearly polarized radiation passing through a symmetric photonic cell is studied based on numerical analysis. The cell consists of two layers of magnetic semiconductor with a graphene monolayer on each and a central dielectric layer located between the graphene monolayers. It is possible to achieve amplification in the near terahertz range in graphene layers due to charge carrier drift. Control of transmission spectra and polarization of transmitted radiation can be achieved by changing the Fermi energy of graphene layers, by changing the external magnetic field, and by changing the thickness of the dielectric layer and the orientation of the incident radiation polarization plane.

This paper describes the theoretical investigation of enhancement in temperature sensitivity using one-dimensional (1D) symmetric defective photonic crystal (PC) containing Si (Silicon) and Bi4Ge3O[Formula: see text] (Bismuth Germanate, BGO) material. The proposed sensor consists of a defect layer (air defect) sandwiched between two 1D-PCs with a symmetrical and asymmetrical structure composed of Si and BGO, respectively. Sensor performance has been evaluated by calculating the transmittance spectra of the proposed structure. In order to obtain the transmittance spectra, a transfer matrix method (TMM) is employed. The principle of temperature sensing is based on the shift in the resonant wavelength (or peak) of the transmission mode with a change in temperature. This is due to the temperature-dependent refractive index of the Si and BGO layers. Analysis of the transmittance spectra shows that temperature sensitivity of 1D-PC structure can be enhanced by using a symmetric defective PC with and without an external defect layer over asymmetric defective PC. It is found that symmetric defective PC with and without defect shows sensitivity equal to 0.173[Formula: see text]nm/∘C and 0.140[Formula: see text]nm/∘C, whereas asymmetric defective PC shows 0.125[Formula: see text]nm/∘C, for the same parameters. Further, the results show that symmetric defective 1D-PC (without the presence of any external defect layer) gives a higher Q-factor than a symmetric and asymmetric defective 1D-PC with an external defect layer. The proposed structure is cost-effective, easy to fabricate and compact in size.

By the method of rapid radiation heating (at a speed of 20-25 K/s) of Au and Ag films with a thickness of 4-35 nm to temperatures of 573-693 K in air and in the process of vacuum deposition of silver on heated (up to 700 K at a heating rate of 10 K/s ) glass substrates formed Au and Ag NPs arrays with nanoparticle sizes from several tens to hundreds of nanometers, the position λSPR of which is in the range of 520-597 nm for Au NPs and 424-509 nm for Ag NPs. It is established that the average size of nanoparticles depends on the thickness of gold and silver films and the annealing temperature. The results testify that glass substrates with arrays of randomly distributed gold NPs can be used as effective SERS-substrates for the investigation of Raman spectra of nanosized (50-100 nm) chalcogenide films.

At present various oxide of metal semiconductors play a significant role in the field of electronics. Most of the semiconductor devices exploit the special characteristics of the junction between a p-type and n-type semiconductor. These devices can be made extremely small in size and they are incredibly fast in their response. Generally metal have good reflectivity in the electromagnetic region of infrared and visible radiation. Indium oxide material doped with tin (ITO) is recently used in the substrate material for various applications, because it has special properties of low resistivity and high optical transmittance in the visible region. In this paper, we prepare ITO films with different tin concentration (5%, 10%, 15%, 20%, 30%, 40%, 50%, 60% and 70%) using acrylamide sol gel dip coated method and its results were reported. TCO materials have good electrical conductivity and optical transparency, and also it has n-type semiconductor with a band gap between 3.5 and 4.3 eV. An X-ray study indicates all the prepared samples had bixbyte structure. Optical behaviour of materials can be understood in the near infrared and visible spectrum. Some optical parameters of refractive index, extinction coefficient and dielectric constant of ITO films are calculated from the data received from the UV transmission studies. Using W-D model the dispersion of refractive index was calculated. The optical band gap, oscillator energy, dispersion energy and optical conductivity and N/m* ratio were estimated and this material is well suitable for dye sensitized solar cell and sensor application. [ABSTRACT FROM AUTHOR]

The transmission and reflection spectra of a one-dimensional microresonator structure with dielectric Bragg mirrors, the working cavity of which is filled with several “dielectric-graphene” or “semiconductor-graphene” periods with controlled material parameters, were obtained using transfer matrices and numerical methods. Carrier drift in graphene monolayers is created to achieve amplification, which makes it possible to use the hydrodynamic approximation to represent graphene conductivity in the terahertz range. The transformation of spectra is achieved both by changing the energy state of the graphene monolayers and by changing the external magnetic field. It is shown that amplification is observed in the region where the real part of the conductivity is negative as the chemical potential (Fermi energy) increases, and the coefficients T and R become substantially greater than unity. The results of the work may be of interest to developers of graphene-based controlled photonic devices.

In a layered structure containing nano-scale layers, we have presented the possibility of increasing the wave transmission in the visible region by adding the top and bottom cap layers. It is found that, the structure containing both the top and bottom cap layers (S3) yields larger transmittance than the structures S1 without any cap or S2 just with one cap layer. The maximum transmittance in the visible range can be increased from 33% to 67%. In addition, for the TE mode (the TM mode) the maximum value of transmission in the S1 and S2 structures occurs at angles close to normal incidence while in the S3 multilayer it happens around 1 rad, that is, the behavior of the TE mode is the opposite of the TM mode. Also, when the incident angle varies, the band edges experience a blue shift. The amount of TE shift is more pronounced than TM one. [ABSTRACT FROM AUTHOR]

Thin films of tin oxide and composite systems based on them have found the greatest applications in solar energy. The properties of oxides depend on the obtaining technology and following processes. The choice of the optimal solution maturation time influences the functional properties of the films. In this research, solutions with the adding different volume of concentrated aqueous solution of ammonia (NH4OH) per 100 ml of the system were prepared: 0.8 ml (pH=1.40), (pH=1.46) and 1.6 ml (pH=1.49). This enabled the study of the properties of films obtained from solutions of different acidity. The resistance of the films was measured in the 10 different parts of the films. In addition, the effect of the isothermal annealing time at 2500C on the structural and optical properties of the samples was investigated. As a result of this study, there was found the correlation between an increase in the duration of annealing and a decrease in the transparency of films obtained from the SnCl4/EtOH. The annealing at temperature 2500C within 6 hours led to a change in transparency of films from 93% (?=550nm) to 88%. The further increase of the annealing duration up to 9 hours does not affect the transparency of films. [ABSTRACT FROM AUTHOR]

In this article, we have obtained the transmission spectra of a microresonator structure with Bragg mirrors, the working cavity of which is filled with a magnetically active finely layered ferrite-semiconductor structure with material parameters controlled by an external magnetic field. It is shown that a change in the external field and the size of the cavity (filling layer thickness) provokes a controlled rearrangement of the transmission spectrum of TM and TE waves. The polarization characteristics of the microcavity, their dependence on the external field, and the ratio of the thicknesses of the layers that make up the period of the ferrite-semiconductor structure are investigated. [ABSTRACT FROM AUTHOR]

The synthesis of surface-active structures is important for creating many applications. The structural formation of SnO 2 thin films in the range from 1.4 to 1.53 pH is studied in this work. This process occurs on the surface of the sample in the range of 1.4 to 1.49 and in the volume in the range of 1.51 to 1.53. SnO 2 is formed after annealing at 400 ∘ C, according to XRD. Doping NH 4 OH to solution stimulates particle coagulation and gel formation. All of these have an impact on the transparency of samples investigated by spectrophotometric methods. By increasing the pH, the resistance raises at room temperature. The E g calculation along the fundamental absorption edge shows that it is greater than 3.6 eV' for SnO 2 films. According to the Burstein–Moss effect, a change of the bandgap is related to the increased concentration of the free charge carriers. Elemental analysis has shown that chlorine ions are considered to be additional sources of charge carriers. The value pH = 1.49 is critical since there is a drastic change in the structure of the samples, the decrease in transparency is replaced by its increase, and the energy of activation of impurity levels is changed. [ABSTRACT FROM AUTHOR]

The paper presents the results of a study of the optical reflection and transmission spectra of a silicon single crystal p-Si (100) with silicon nanowires grown on both sides and porous silicon p-Si (100) on a single crystal substrate in the spectral range 0.2 ÷ 1.7 μm. The layers of nanowires had a thickness of 5.5 µm, 20 µm, 50 µm and a porosity of 60 %. The porous silicon layers had a thickness of 5 μm, 50 μm and a porosity of 45 %, 55 % and 65 %. The change in the energy band structure in single-crystal silicon nanowires and in a single-crystal matrix of porous silicon is shown.

The effect of Al2O3 – CuI oxide films on the photoelectric parameters of silicon solar cells (SCs) has been studied. The largest increase in the external quantum efficiency of photoelectric conversion of SCs in the near UV range is observed for monolayer films of the 50Al2O3 – 50CuI composition, heat-treated at 280 °C for 30 min, which corresponds to a relative increase in the photocurrent upon exposure to radiation of spectral composition AM1.5 (1000 W/m2 ) by more than 35 %. This confirms the efficiency of using re-emitting Al2O3 – CuI films to increase the efficiency of silicon SCs.

The paper considers one of the numerical methods to solve problems of scattering electromagnetic waves on the systems formed by parallel-oriented cylindrical elements – two-dimensional photonic crystals. The method is based on the classical partition approach used for solving the wave equation. Тhe method principle is to represent the field as the sum of the primary field and the unknown secondary field scattered on the medium elements. The mathematical expression for the latter is written as the infinite series according to elementary wave functions with unknown coefficients. In particular, the N elements-scattered field is found as the sum of N diffraction series in which one of the series is composed of the wave functions of one body and the wave functions in the remaining series are expressed in terms of the eigenfunctions of the first body using addition theorems. Further, to meet the boundary conditions, on the surface of each element, we obtain systems of linear algebraic equations with the infinite number of unknowns – the required expansion coefficients, which are solved by standard methods. A feature of the method is the use of analytical expressions to describe diffraction on a single element of the system. In contrast to most numerical methods, this approach allows one to obtain information on the amplitude-phase or spectral characteristics of the field only at the local points of the structure. The high efficiency of this method stems from the fact that there is no need to determine the field parameters in the entire area of space occupied by the multi-element system under consideration. The paper compares the calculated results of the transmission spectra of two-dimensional photonic crystals using the considered method with the experimental data and numerical results, obtained by other approaches, and demonstrates their good agreement.

Optical spectra were investigated in a spectral range of (300 - 700) nm for CuAlS2 single crystals. Transmission and wavelength modulated transmission spectra demonstrated presence of some impurity absorption bands in the region of optical transparency of crystals. Optical functions (real and imaginary components of the dielectric function, refractive index and extinction coefficient) have been calculated from the optical reflection spectra by means of the Kramers-Kronig relations. A strong anisotropy and birefringence have been revealed for CuAlS2 crystals. Two isotropic points have been found in (100) oriented platelets around 380 nm and 530 nm. The position of the isotropic point around 530 nm was found to be strongly influenced by the technological conditions of crystal growth and platelet thickness, it being situated at 535 nm for a platelet with thickness of 223 μm. An optical band-pass filter was constructed with such a platelet placed between two Gran-Thompson prism crossed polarizers.

Micron-thick layers of (Cr 1-x Ga x) 2 O 3 solid solutions were grown by modified mist chemical vapor deposition (mist-CVD) with three different Ga concentrations. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) methods were used to analyze the quality of the films. They showed good crystallinity, homogeneity and coalescence of the samples. Solid solution contents estimation was performed via applying Vegard's law to XRD data and by its results the highest reached Cr:Ga ratio is approximately 1:1. Transmission spectra of solid solutions demonstrated blue-shift of the absorption edge with increase of the Ga contents. Optical bandgap increased from 3.06 eV for undoped Cr 2 O 3 sample to 3.73 eV for the layer with the highest Ga concentration. • High-quality micron thick crystal layers of the (Cr 1-x Ga x) 2 O 3 were grown by modified mist-CVD technique on the sapphire. • Cr to Ga ratio in the layers was up to 1:1 without decomposition of the solid solution in them. • Blue shift of the absorption edge and optical bandgap with higher Ga contents is observed in acquired solid solution layers. [ABSTRACT FROM AUTHOR]

We explored spectral diversity in infrared (IR, 4–25 μm) imaginary (k) and real (n) indices of refraction (optical constants) for 26 surface soils that originated from global dust entrainment regions. The k spectra were derived from optical transmission spectra of KBr pellets containing dispersed dust and the n spectra were estimated with the subtractive Kramers–Kronig (SKK) method. We compared k and n obtained by this study with previously published values. Our optical constants from the KBr technique are comparable in magnitude and spectral shape to those from previous studies that used dust aerosols re-suspended in a chamber. This suggests that the SKK method can offer a reliable mechanism for measuring IR spectra of both optical constants for soils. The soils used here exhibit additional spectral variability compared with past studies. We note that the appearance and the shift in positions of the strongest absorption peaks are due to combinations of silicates with overlapping absorption, rather than being related to a single mineral. We note that all dust optical constants have substantially lower magnitudes compared to those of pure minerals. Our results can improve estimates of mineral dust radiative effects and support quantification of surface mineral estimates using satellite and ground-based remote sensing.

Transmission spectra of a symmetric microresonator structure, with dielectric Bragg mirrors, are obtained. The working cavity of the structure is partially filled by a layer of a quarter-wave thickness of finely layered “graphene–semiconductor” medium, with material parameters controlled by external electric and magnetic fields. It is shown, that the transformation of the spectra is achieved both by changing the energy state of the graphene layers and by changing the external magnetic field. The spectral characteristics for the inverted and doped states of graphene layers are established.

Copyright of Electronic Processing of Materials / Elektronnaya Obrabotka Materialov is the property of Institute of Applied Physics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

We show new approaches to developing acoustic liquid sensors based on phononic crystals. The proposed phononic crystal integrates fluidic elements. A solid block with periodic cylindrical holes contains a defect—a liquid-filled cylindrical cavity. We pay attention to acoustic excitation and the readout of the axisymmetric cylindrical resonator eigenmode of the liquid-filled defect in the middle of the phononic crystal structure. This mode solves the challenge of mechanical energy losses due to liquid viscosity. We also analyze the coupling effects between oscillations of liquid and solid systems and consider coupling issues between piezoelectric transducers and the liquid-filled cavity resonator. The numerical simulation of the propagation of acoustic waves through the phononic crystal sensor was carried out in COMSOL Multiphysics Software. The phononic crystal was made of stainless steel with mechanically drilled holes and was fabricated for experimental verification. We show that a tuning of the solid–liquid vibrational modes coupling is the key to an enhanced level of sensitivity to liquid properties. Besides (homogeneous) water–propanol mixtures, experimental studies were carried out on (disperse) water–fuel emulsions. [ABSTRACT FROM AUTHOR]

The concentration areas of the existence of various coordination compounds in the PbCl2–(NH2)2CS system were determined by plotting the distribution diagrams and diagrams of the prevalence of complex species in the initial solution. As shown by X-ray diffraction analysis, at deposition temperatures of 300–500°С PbS films crystallize in the cubic system, with the unit cell parameter being independent of the deposition temperature. The band gap of the synthesized PbS was determined by optical spectrometry; it is 0.41–0.45 eV for direct allowed transitions. [ABSTRACT FROM AUTHOR]

The experimental results regarding optical absorption and steady-state photoconductivity of amorphous single-layer structures (Al–As0.40S0.30Se0.30–Al, Al–Ge0.09As0.09Se0.82–Al, and Al–Ge0.30As0.04S0.66–Al) and of an amorphous heterostructure (Al–As0.40S0.30Se0.30/Ge0.09As0.09Se0.82/Ge0.30As0.04S0.66–Al) at different values of the voltage, with positive or negative polarity, applied to the illuminated top Al electrode are presented and discussed. The complex structure of the photocurrent spectra is attributed to the different values of the optical bandgap of the involved amorphous layers (Eg ≈ 2.0 eV for As0.40S0.30Se0.30 and Ge0.09As0.09Se0.82 and Eg ≈ 3.0 eV for Ge0.30As0.04S0.66). The obtained experimental results are discussed taking into account the light absorption depending on the nature and the thickness of each amorphous layer, on the wavelength, and on contact phenomena at the interfaces between different layers and between the amorphous layers and the metal electrodes with different work functions.