Analytical expressions to describe nonparaxial diffraction of vortex laser beams during their propagation in free space are obtained. The beams excited by radially polarized TM0m (m = 1, 2, 3) modes of a dielectric waveguide resonator of a terahertz laser, which interact with a spiral phase plate with an arbitrary topological charge (n) are considered. The simulation is performed using the Rayleigh-Sommerfeld integral theory. It is shown that a phase plate with topological charges n = 1, 2 forms a field in the Fresnel zone, in which an azimuthal component appears. In this case, preservation of the radial and longitudinal components of the field is observed and the contribution of the longitudinal component to the total beam power remains insignificant. For a phase plate charge n = 1, the maximum of the field intensity is located on the axis, whereas the field distribution for n = 0 and n = 2 becomes ring-shaped. The maximum values of the field intensity are observed at a charge n = 1, while they decrease at n = 2. Phase distributions of the field transverse components of vortex laser beams are visualized. At a topological charge n = 1, they become a one-lobe helical structure, and a two-lobe structure with more pronounced helical twists of the azimuthal component for all the studied modes is observed at n = 2.
This review article describes in a concise form some of the latest achievements in semiconductor physics related to the topological and quantum properties of electron dynamics, in particular, in strong electric fields; new concepts in electronics based on the quantum degrees of freedom of electrons, which have led to the emergence of new branches distinct from traditional charge-based electronics. The recent emergence of picosecond-toattosecond time-resolved and scanning spectroscopy has prompted the development of quantum theory describing the detailed high-frequency behavior of electrons on very short temporal and spatial scales, of the order of a few interatomic distances. In fact, such a precise spatiotemporal dynamical picture represents, in a sense, the anatomy of electrons in the periodic potential of a crystal lattice. Specifically, our attention is focused on the following issues that have been actively discussed in leading scientific journals over the past decade: the Berry phase, orbitronics, Zitterbewegung (trembling motion), and effective mass dynamics. Although several specialized reviews already have devoted to the addressed topics, we believe that such review digest including most recent references can help the readers, including authors of SPQEO, to get more information about current trends in the modern semiconductor theory and applications.
Indotetracarbocyanines belong to a family of long cyanine dyes that easily change molecular shape from symmetric cyanine-like to asymmetric polyene state. Multiple factors affect the conformations of such molecules and therefore influence their photoluminescent emission. In this paper, we investigated the photophysical behavior of indotetracarbocyanine dyes in various solvent environments and in mixtures with singlewalled carbon nanotubes. The results revealed concentration-, aging-, and solvent-polarity dependent spectral features of such dyes, allowing us to establish key mechanisms for emission tuning. The spectral changes have been associated with symmetry-dependent molecular conformations of indotetracarbocyanines and their ability to interact with carbon nanotube surfaces. New emission bands emerge in the photoluminescence spectra due to dye-nanotube interactions, mediated by it-it stacking and electrostatic effects. This behavior is consistent with adsorption-induced aggregation of the dye on the nanotube surface and with the formation of new photoinduced emitting states.
The effect of the substrate material combined with a polytetrafluoroethylene (PTFE) overlayer on the sensitivity of optical sensors based on surface plasmon resonance (SPR) in the Kretschmann geometry has been investigated. The experiments were performed at a fixed excitation wavelength of surface plasmons using a gold plasmonsupporting layer. The testing of the sensor elements was carried out by cyclic displacement of ambient air by inert helium in the flow cell. A comparative analysis of the characteristics of SPR sensors on substrates made of F1 optical glass and styrene-acrylonitrile (SAN) polymer was carried out in both the presence and absence of a PTFE overlayer on the gold film surface. It was established that replacing the glass substrate with the polymer (SAN) causes an increase in sensitivity from 45.8 to 48.1 deg/RIU due to a decrease in the refractive index; however, it doubles the figure of merit (FOM) from 26.2 to 50.1 RIU-1. The application of the PTFE overlayer for both sensor types led to an increase in sensitivity: from 45.8 to 74.4 deg/RIU for the glass substrate, and from 48.1 to 52.1 deg/RIU for the polymer substrate. In addition to enhanced sensitivity, the use of the polymer material allows for reducing the cost of the final product, simplifying the stages of precision surface treatment. An additional advantage is the narrowing of the resonance curves, which significantly improves the accuracy of the resonance angle registration.
A simulation algorithm has been developed and geometric parameters of plane-focusing lenses for concentrator solar energy systems with Si photoconverters have been calculated. These lenses form a homogeneous image in the focal plane, so they are promising for use in such systems and allow minimizing thermal and electrical losses in solar modules caused by non-uniform illumination of the photoconverter surface. A technology of manufacturing stamp-matrixes by diamond microcutting has been developed. Based on the simulation results, a number of plane-focusing lens samples have been formed by thermopressing technique using metal matrices. The manufactured samples of square-shaped specialized transforming microprismatic structures have been experimentally investigated using a collimated laser beam.
In this paper, the effect of short-term nonthermal exposure to microwave radiation and pulsed magnetic field (PMF) on photoluminescence characteristics of SiC/por-SiC/Er2O3 structures has been considered. Analysis of the photoluminescence spectra of these structures has shown that the changes observed in the spectra under microwave and PMF exposure are explained by an increase in the migration mobility of dislocations, which in turn leads to a redistribution of recombination centers in the SiC/por-SiC/Er2O3 structure. The influence of PMF on the processes of redistribution of recombination centers in the SiC/por-SiC/Er2O3 structure has been shown more effective than microwave exposure. The mechanisms of action of both microwave radiation and PMF are considered to be those leading to increase in the migration ability of dislocations due to change in the internal state of interacting dislocations and lattice defects.
Influence of growth-sector structure on electrical characteristics of Schottky diodes and ohmic contacts fabricated on boron-doped high-pressure high-temperature (HPHT) growth diamond was investigated by correlating electrical measurements with mu-FTIR mapping of uncompensated boron concentration. The studied substrates exhibited pronounced multisectoral inhomogeneity of electrically active boron with systematic variation between the principal growth sectors. The Schottky structures revealed two characteristic transport regimes. In the lower-doped regions, the reverse current was mainly controlled by localized shunting defects, whereas in the higher-doped regions it increased strongly with uncompensated boron concentration and the contacts gradually changed their behavior from rectifying to nearly ohmic one, consistent with increasing contribution of tunneling-assisted transport. The specific contact resistance of the Ti/Pt/Au ohmic contacts decreased with the boron concentration and exhibited clear dependence on growth-sector affiliation. At comparable uncompensated boron concentrations, the contacts formed in the (001) and (113) sectors exhibited lower specific contact resistance than those formed in the (111) sector. The results demonstrate that the growth-sector structure of the boron-doped HPHT diamond influences not only spatial distribution of electrically active boron, but also transport characteristics of metal/diamond contacts therefore representing an important technological factor in fabrication and optimization of diamond-based electronic devices.
The paper considers an approach to evaluate the noise immunity of multispectral optoelectronic systems for transmitting information messages. The relevance of this work is determined by the need to increase the reliability of optical communication, identification, navigation, and control channels under background illumination, electromagnetic interference, optical disturbances, partial channel obstruction, and nonuniform spectral attenuation of signals. It is shown that a simple increase in the power of a single semiconductor emitter increases the amplitude of the received signal but does not eliminate the fundamental vulnerability of a single-spectral system to selective interference within the chosen wavelength range. It is shown that the real advantage of the multispectral approach is determined not only by the number of spectral channels but also by their statistical independence, differences in the spectral characteristics of interference, and the ability of individual channels to retain information content under difficult transmission conditions. The proposed model can be used for numerical simulation, experimental verification, and optimization of LED-based multispectral message transmission systems for autonomous moving objects, unmanned aerial vehicles, robotic platforms, and local sensor networks.
The structural, mechanical, electronic, thermodynamic, optical, and thermoelectric properties of zinc germanate (ZnGeO3) and cadmium germanate (CdGeO3) are theoretically predicted using first-principles calculations based on density functional theory (DFT). We examined the crystal and electronic band structures, as well as optical and thermoelectric properties. Both compounds have the perovskite structure with lattice parameters of 3.68 & Aring; for ZnGeO3 and 3.74 & Aring; for CdGeO3. The ZnGeO3 is more stable, with a minimal energy of -15832.079 Ry versus -15832.062 Ry for CdGeO3. The electronic band structure shows direct bandgaps of 2.8 eV for ZnGeO3 and 3.1 eV for CdGeO3, confirming their semiconducting nature. The calculated optical properties include the dielectric function and absorption coefficient. CdGeO3 has higher absorption peaks within the UV range. Thermoelectric performance is moderate, with the figure of merit values of 0.53 for ZnGeO3 and 0.59 for CdGeO3 at room temperature. These compounds show promise for optoelectronic applications, while their thermoelectric efficiency remains limited.
Thin ZnO films were chemically obtained from two organic compounds. Chelate (or intracomplex) compounds zinc diethyldithiocaramate and zinc acetylacetonate were used as precursors. The effects of precursor type, growth rate, and post-growth annealing of the films were investigated. The microstructure and optical properties of the films were studied and compared using X-ray diffraction (XRD), atomic force microscopy, Raman scattering, and photoluminescence. The XRD results indicated that all the ZnO films had a polycrystalline hexagonal structure and a preferred orientation with the c-axis perpendicular to the substrate. The morphological and optical properties differ markedly for various ZnO films. The reasons of transformation and the nature of optical transitions were discussed. The most intensive UV emission was obtained for the ZnO films grown from zinc acetylacetonate. The ultraviolet/visible emission intensity ratio was 15, comparable to that of epitaxial ZnO films. A simple way for fabricating high-quality ZnO films was presented.
Detection of concealed remote optical surveillance systems has become a critical issue due to ease of deployment of such systems and their ability to transmit video signals with minimal effort. This work investigates feasibility of using an active laser detection system to detect optoelectronic surveillance devices under challenging conditions, including bright daylight. The detection system is based on laser light retroreflection (the cat-eye effect), which enhances the detection efficiency due to strong back-reflection of the laser beam from optical components of the observed devices. Typical apertures of the surveillance systems such as smartphone cameras with diameters up to 2 mm and photographic lenses with diameters up to 20 mm are analyzed. Maximum detection ranges for different power levels of the active laser system are evaluated. The numerical modeling results have shown strong agreement with experimental measurements on real atmospheric paths up to 200 m. The findings confirm practical potential of active laser detection as an effective and robust method for counter-surveillance applications.
Influence of annealing atmosphere on the structural properties of annealed multilayered [Fe/Pt]& times;4 thin films was investigated. The films were deposited onto thermally-oxidized SiO2(100nm)/Si(100) substrates by direct current magnetron sputtering at room temperature and subsequently annealed in a temperature range of 500 to 900 degrees C in flowing Ar, N2, and Ar + H2 atmospheres to induce structural phase transitions and chemical ordering. Synchrotron analysis revealed that ordered face-centered tetragonal L10FePt phase formed after annealing at 500 degrees C regardless of the atmosphere used. Among the studied conditions, annealing in N2 at 800 degrees C provided higher degree of chemical ordering, strong [001] crystallographic texture, and higher tetragonality of the L10-FePt phase, making the latter the most favorable for magnetic data storage applications. The surface roughness increased at rising the temperature. However, its magnitude also depended on the annealing atmosphere, being comparatively lower after annealing in Ar compared to treatment in reactive environments such as N2 or Ar + H2. Furthermore, annealing in Ar atmosphere promoted formation of a non-stoichiometric Fe1+xPt3-x solid solution and surface oxides (Fe3O4 -> Fe2O3 -> FeO) alongside with the L10-FePt phase.
This paper addresses the perturbed Fokas-Lenells equation with a cubic-quartic form of dispersive effects and the Kerr law of self-phase modulation structures. The chromatic dispersive effect is replaced with a collective count of third-and fourth-order dispersions when the count on CD runs low. The Laplace-Adomian decomposition scheme made this numerical study possible. Both bright and dark optical solitons are studied using this principle. The error count is impressively low, thus making this numerical approach a viable one.
The properties and applications of perfluoropolymer nanocomposite thin films deposited from the gas phase are summarized, and the development trends in this field are discussed in this review. The perfluoropolymer matrix protects metal nanoparticles from corrosion, imparts superhydrophobic properties to surfaces, extends the lifetime of medical implants, and improves the performance of functional layers in organic light-emitting diodes, among other applications. Dyes and metal nanoparticles incorporated into the PTFE matrix demonstrate unique properties, making these materials promising for optical and biomedical applications.
The work investigates temperature-dependent charge accumulation and relaxation processes, as well as the current-voltage characteristics of Ag|Ag7-x(PxGe1-x)S5I|Se heterostructures with different Ge/P ratios. The current-time dependences I(t) were studied in a potentiostatic mode (0.4 V, 600 s) followed by discharge (0 V, 600 s) at 20 degrees C and 60 degrees C. It is shown that the relaxation is described by a bi-exponential model with time constants tau(1) and tau(2), corresponding to fast interfacial and slow diffusion processes, respectively. It was established that with increasing temperature, the relaxation times decrease due to the activation of Ag+ ion transport and the softening of selenium. Arrhenius analysis revealed different activation energies for the fast (similar to 0.1...0.3 eV) and slow (similar to 0.05...0.15 eV) processes. The current-voltage characteristics exhibit nonlinear and asymmetric behavior with current maxima associated with interfacial polarization and the formation of Ag2Se. The minimum relaxation times are observed for the composition Ag6.5P0.5Ge0.5S5I.
An optical model of a heterogeneous light-converting film based on a YAG:Ce3+ photoluminescent phosphor in epoxy resin is considered. The dependence of the distance between the phosphor microparticles in the suspension on the mass fraction of the powder and the densities of the components of the initial suspension is determined. Within the framework of the proposed model of the composite film, the coefficients of specular reflection and transmission within the region of isotropic scattering are simulated. It is demonstrated that optimizing the material composition by the amount of the photoluminescent component allows one to significantly reduce the coefficient of specular reflection of the UV pump radiation.
Use of metallic orthopedic implants (screws, plates, intramedullary rods) has several problems, such as inadequate biological integration and high infection risk. This review summarizes current insights on functional coatings for metallic orthopedic implants concerning their osteoinductive, osteoconductive, immunomodulatory, and antimicrobial properties and evaluating their clinical application potential. Key bioactive coatings include hydroxyapatite and bioactive glass, alongside with nanostructured and ion-doped layers. The deposition techniques, namely plasma spraying, sol-gel technology, anodization, electrophoretic deposition, and gas-detonation spraying, are analyzed. It is ascertained that the hydroxyapatite and bioactive glass coatings substantially enhance biocompatibility and properties, while nanostructuring enhances cell adhesion and minimizes inflammatory responses. Antimicrobial coatings with silver, antibiotics, and bactericidal agents significantly reduce infectious complications. Among coating deposition methods, plasma spraying, sol-gel processes, and gas-detonation spraying show notable industrial applicability. Multifunctional and "smart" coatings demonstrate strong clinical efficiency and promise widespread adoption. Advancements in coating technology and optimization of material compositions will decrease complications and enhance treatment outcomes for patients with bone injuries and defects.
The current paper recovers optical soliton solutions with Kudrashov's proposed self-phase modulation structure and with fractional temporal evolution. This model could control and mitigate the Internet bottleneck effe & scy;t, a severe hindrance to Internet traffic flow across intercontinental distances. Two independent integration approaches have made this retrieval possible. A wide spectrum of soliton solutions emerged with the collective applications of the integration schemes. The parameter constraints for the existence of these solitons are also presented.
Perovskite solar cells (PSCs) have become a rising star in the horizon of photovoltaics due to their cost-effectiveness and simple fabrication process. Despite their prospects, the viability of their commercialization has been hampered due to low power conversion efficiency (PCE) and hysteresis. In this paper, caffeine was incorporated into methylammonium lead iodide (MAPbI3) with different wt% (0.5, 1.0, and 1.5 wt%) to fabricate perovskite solar cell devices. The effects of caffeine inclusion were probed to uncover its influence on enhancing light absorption, improving crystallinity, boosting the device performance, and mitigating the disparity in current-voltage measurement (hysteresis). The presence of caffeine results in improved absorption, diminished band gap, and improved film crystallinity. Perovskite solar cells with caffeine molecules demonstrated improved metric parameters (PCE, fill factor FF, short-circuit current density Jsc, and open-circuit voltage Voc) compared to a pure device without caffeine. Particularly, the device with 1.0 wt% caffeine in MAPbI3 shows the best performance with PCE of 14.072%, FF of 0.640, Jsc of 23.083 mA/cm2, and Voc of 0.953 V. The disparity in currentvoltage measurement for all caffeine-based devices was reduced. Specifically for the device with 1.0 wt% of caffeine, the hysteresis index is 0.0300. The device without caffeine shows PCE = 6.157%, FF = 63.9%, Jsc = 10.132 mA/cm2, and Voc = 0.951 V, and performs worse than all caffeine-based devices. The enhanced device performance observed in the caffeinemodified perovskite is primarily attributed to reduced series resistance and concentration of non-radiative recombination centers, leading to more efficient charge transport and increased carrier lifetime within the absorber layer.
This work reports the calculated dependence of the localized surface plasmon resonance (LSPR) parameters and damping mechanism on nanoparticle size of unconventional transition metals, including zinc, silver, rhodium, rhenium, molybdenum, tantalum, titanium, and scandium, within the size range of 10 to 400 nm. The study applies Mie theory to determine the peak energies, amplitude, and full width at half maximum (FWHM) of LSPR as a function of size, shape, and material type. We have found that the parameters of LSPR depend on electron structure and damping mechanisms. LSPR amplitude decreased systematically for individual nanoparticles (NPs) for sizes 10...200 nm, after which, a similar trend was exhibited due to radiative damping. Au, Sc and Ag are the only metal NPs that exhibited a significant FWHM of LSPR at sizes approximately below 40 nm. For all investigated transition metal NPs, smaller NPs exhibited higher absorption and lower scattering, while larger NPs showed narrower FWHM and red-shifted LSPR peaks due to retardation effects and multipolar plasmon excitations. The analysis highlights that some transition metal NPs exhibit optical characteristics similar to those of gold, silver, and copper, making them a good alternative for the mentioned ones at specific NP sizes.
