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 Subjects -> MATHEMATICS (Total: 1021 journals)     - APPLIED MATHEMATICS (83 journals)    - GEOMETRY AND TOPOLOGY (21 journals)    - MATHEMATICS (757 journals)    - MATHEMATICS (GENERAL) (43 journals)    - NUMERICAL ANALYSIS (22 journals)    - PROBABILITIES AND MATH STATISTICS (95 journals) MATHEMATICS (757 journals)            First | 1 2 3 4
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Similar Journals
 Journal of Theoretical and Applied PhysicsJournal Prestige (SJR): 0.207 Citation Impact (citeScore): 1Number of Followers: 8     Open Access journal ISSN (Print) 1735-9325 - ISSN (Online) 2251-7235 Published by SpringerOpen  [236 journals]
• Effect of plasma oxidation parameters on physical properties of
nanocrystalline nickel oxide thin films grown by two-step method: DC
sputtering and plasma oxidation

• Abstract: Nanocrystalline nickel oxide (NiO) thin films were successfully grown on quartz substrates by two-step method. In the first step, nickel films were deposited on quartz substrates by DC magnetron sputtering technique. Then, the plasma oxidation of nickel films was used for preparation of nickel oxide. The effect of DC plasma power and treatment time on the structural, morphological and optical properties of the NiO films were investigated by different analyses. XRD results indicated that the plasma powers effectively influenced the structure of films, and the best crystallinity was obtained for plasma power of 15 w and treatment time of 20 min. The XPS, RBS and EDS analysis confirmed the presence of Ni and O elements. The FESEM and AFM images showed a granular structure with spherical shapes of grains. The optical band gap of the films synthesized under different plasma oxidation conditions was also discussed.
PubDate: 2019-09-19

• The experimental approach into the influence of external inductance on the
discharge characteristic of HiPIMS

• Abstract: The main objective of the current paper is to describe the effect of external inductance (EI) on the current discharge waveforms of HiPIMS at different pulse-on time (Pon) and its relation with static deposition rate and topographical properties of deposited titanium thin films, which is investigated by scanning electron microscope and atomic force microscope. It has shown that the higher the EI, independent of the Pon, the higher the peak power is. The delay time also extensively increases when an EI is implemented into the circuit. However, the rise time does not have a linear dependency with the EI and its behavior changes to some extent at different Pon. By increasing the EI from zero to 30 mH at Pon = 60 μs, the peak power subsequently rises from 11 to 32 kW at constant time-average power. Meanwhile, the deposition rate decreases from 8.5 to 1.5 nm/min, which is mainly attributed to the metal ions return to the target surface and nonlinear dependency of sputtering yield with applied voltage. It was also revealed that the higher peak power has no special effect on the surface roughness of titanium thin films deposited by HiPIMS.
PubDate: 2019-09-17

• Detection of overtone and combined peaks using Mn/Cu helical star-shaped
(pine-tree-like) sculptured thin films in surface-enhanced Raman
spectroscopy

• Abstract: Mn helical star-shaped (pine-tree-like) nano-sculptured thin films with three-, four-and fivefold symmetry on copper substrates were produced using oblique angle deposition method in conjunction with rotation of sample holder at certain angles. Raman spectroscopy of the samples which were subjected to impregnation by 4,4′-bipyridine (C10H8N2) solution was carried out by 632.8 nm wavelength laser. The analysis of the Raman spectra showed enhancement for the 4,4′-bipyridine main bands (1592 and 1297 cm−1) belonging to the C=C stretching mode, aromatic ring stretching ring and in-plane ring mode of 4,4′-bipyridine, same as results obtained for Ag nano-structures. In addition, overtone and combined peaks are detected that may be related to the particular sculptured structure of the thin films fabricated in this work and the laser wavelength used for Raman spectroscopy. UV–Vis (absorption mode) spectra showed consistent observations with the SERS results leading to important role of surface electromagnetic selection rule in intensification of SERS, in addition pointing out the importance of the effect of the size of hot spots on the frequency of the localized surface plasmonic oscillations.
PubDate: 2019-09-09

• A study of the corrosion of stainless steel 304L coated with a
190 nm-thick manganese layer and annealed with nitrogen flux in a
0.4-mole solution of H 2 SO 4  at different temperatures

• Abstract: A method for enhancing the resistance against corrosion of stainless steel 304L coated with 190 nm-thick manganese film and annealed with nitrogen flux at constant temperature (723 K) is reported. The variable quantity in this work is the temperature of the corroding solution (293 K and 333 K). X-ray diffraction analysis was employed to investigate the crystallographical changes of the annealed samples; atomic force microscope and scanning electron microscope were used for the morphology and studying the roughness of their surfaces; polarization analysis, electrochemical impedance spectroscopy, and phase and Bode diagrams, as well as the Kramers–Kronig transformation, were employed to study the susceptibility of the samples to corrosion, at temperatures 293 K and 333 K in 0.4 M H2SO4 solutions. Our results, from all the above analyses, unanimously point to the fact that in the process of enhancing resistance to corrosion, the annealing stage is the most crucial for improving the coating and the crystal structure of the samples and that the adsorption of Mn is not sufficient for the enhancement of the surface layer. Moreover, it was observed that increasing the temperature of the solution decreases the resistance of the samples owing to an increase in the rate of corrosion.
PubDate: 2019-09-03

• Formation of highly nonlinear dust-acoustic solitary waves due to
high-temperature electrons and ions

• Abstract: The nonlinear propagation of dust-acoustic solitary waves (DASWs) in an unmagnetized dusty plasma consisting of two distinct temperature ions, two distinct temperature electrons and mobile dust fluid has been investigated by employing reductive perturbation method. It has been assumed that the two distinct temperature ions follow the Maxwell–Boltzmann distribution and nonthermal (Cairn’s) distribution separately while the two distinct temperature electrons follow the nonextensive (Tsallis) distribution and superthermal (Kappa) distribution separately. The system has been treated by deriving and solving a set of three highly nonlinear equations such as K-dV, modified K-dV and Gardner equations. It has been noted that the basic properties of the DASWs are significantly modified by the presence of the nonthermal ions, nonextensive electrons and superthermal electrons. The possible applications of this investigation in astrophysical, space and laboratory plasma systems have also been briefly addressed.
PubDate: 2019-09-01

• The effects of applying different bias voltages and phase differences on
performance of an asymmetric surface dielectric barrier discharge; an
experimental investigation

• Abstract: In the present research, the performance of the electrohydrodynamic force in an asymmetric surface dielectric barrier discharge actuator has been investigated at different bias voltages. The effects of DC, AC plus DC (DC-offset), and sinusoidal bias voltages on the force generation have been studied through measuring the electric wind velocity profiles, surface potential, and electric field. The results showed that applying DC and DC-offset biases to the lower electrode instead of connecting it to the ground in a typical case increased the charge deposition on the dielectric surface and consequently reduced the electrohydrodynamic force generation. This effect was also observed in case of exchanging these voltages with AC sinusoidal voltage of the upper electrode. In addition, as a new idea, two-phase shifted AC voltage was applied to the electrodes and the resulting changes have been studied. The obtained results at $$180^{^\circ }$$ phase difference were very noticeable and showed 46% improvement in the maximum velocity of the induced flow relative to the grounded electrode with the same input power. Using this technique, a certain wind velocity can be obtained at relatively lower voltages and input powers compared to the conventional case of grounding the lower electrode. Such a capability is significant in aerodynamic applications, where applying large values of the high voltages may disturb the operational systems.
PubDate: 2019-09-01

• Density functional theory study on the effect of Cu- and Na-substituted
layers on spin-dependent transport and TMR in the Fe/ZnO/Fe MTJ

• Abstract: Using density functional theory, effects of Na- and Cu-substituted layers on the spin-dependent electronic transport properties of Fe/ZnO/Fe magnetic tunnel junction based on zinc oxide barrier tunnel, with rock-salt crystalline structure, have been studied. In zero-bias voltage, conductance and tunneling magneto-resistance (TMR) ratio of structures are calculated. It is showed that substituted layers in the pristine junction greatly affect conductance and TMR ratio of this junction. The results indicated that Cu-substituted layer with reducing conductance of pristine structure in the antiparallel alignment configuration, and increasing its conductance in the parallel alignment, leads to a large TMR ratio, up to 1800%. Due to the large conductance of pristine and Cu-substituted devices in the parallel alignment, these structures would be very beneficial for experimental applications that require the spin-polarized current.
PubDate: 2019-08-31

• Numerical modeling of a DBD in glow mode at atmospheric pressure

• Abstract: In this work, a fluid model of helium glow discharge at atmospheric pressure in a dielectric barrier discharge configuration has been developed and the discharge was numerically simulated. The transport equations for charged and excited species are self-consistent coupled to the Poisson equation for the electrical field calculation. A finite difference method technique is adopted; a detailed numerical procedure modeling is given. The addition of some nitrogen impurities to the helium successfully reproduced the discharge evolution during the breakdown. The numerical results showed that the discharge has a structure similar to DC low-pressure glow discharges and confirms the establishment of the glow regime at atmospheric pressure under very adequate conditions. The profiles of physical and electrical discharge parameters knowing that, particle densities, electric field, drift velocity, voltages and discharge current are presented and analyzed. A detailed study was made of the effect of nitrogen impurities on the stability of the glow mode of the discharge, and on the evolution of its parameters.
PubDate: 2019-08-30

• Effect of doped Zn–PbI 2 nanostructures on structural and electrical
properties of photodetector applications

• Abstract: The present study focuses on the structural and electrical properties of doped zinc–lead iodide (Zn–PbI2) as-deposited film. Lead iodide (PbI2) nanostructure was successfully prepared by thermal evaporation method on a glass substrate at room temperature. The analysis, characterization, and structural properties of PbI2 were achieved using X-ray diffraction (XRD) and scanning electron microscopy. The PbI2 was polycrystalline and had a hexagonal structure as proved using XRD. The measured values are in agreement with other experimental and theoretical data. Furthermore, the present research studied the effect of doping on the physical properties of lead iodide with zinc dopants at different weights (0.02, 0.04, 0.06, and 0.08) mg. The electrical properties of the fabricated metal–semiconductor–metal photodetector based on PbI2 and Pb1−xZnxI2 layers prepared on glass substrates by thermal evaporation method were investigated. The obtained results of Schottky barrier heights for Pb0.98Zn0.02I2 were significant. The current–voltage characteristics of the Pb0.98Zn0.02I2 thin film have acted as a Schottky contact in dark and under white light, 460-nm light. The light responsivity has shown a peak at 460-nm chopped light. At a bias voltage of 1, 3, and 5 V, the photocurrent rise and decay times were investigated. The device has shown faster response times for 460-nm light. This fast response was attributed to the high quality of polycrystalline and showed a high quantum efficiency of 9.19 × 102% when it was illuminated by 460-nm light under the bias of 3 V.
PubDate: 2019-08-30

• Low relativistic effects on the modulational instability of rogue waves in
electronegative plasmas

• Abstract: Relativistic ion-acoustic waves are investigated in an electronegative plasma. The use of the reductive perturbation method summarizes the hydrodynamic model to a nonlinear Schrödinger equation which supports the occurrence of modulational instability (MI). From the MI criterion, we derive a critical value for the relativistic parameter $$\alpha _{1}$$ , below which MI may develop in the system. The MI analysis is then conducted considering the presence and absence of negative ions, coupled to effects of relativistic parameter and the electron-to-negative ion temperature ratio. Under high values of the latter, additional regions of instability are detected, and their spatial expansion is very sensitive to the change in $$\alpha _{1}$$ and may support the appearance of rogue waves whose behaviors are discussed. The parametric analysis of super-rogue wave amplitude is performed, where its enhancement is debated relatively to changes in $$\alpha _{1}$$ , in the presence and absence of negative ions.
PubDate: 2019-08-16

• Double critical coupled ring resonator-based add–drop filters

• Abstract: In this paper, we introduced double-critical coupling condition (DCCC) for lossy mode couplers of the add–drop resonator to achieve the desirable and tunable signals required for optical communication and photonics sensors applications. The performance of add–drop resonator under double-critical condition is simulated and analyzed. Some equations were derived for optical parameters including full width at half maximum (FWHM), the out-of-band rejection ratio (OBRR), quality factor and the crosstalk of the add–drop resonator, and the output signals were examined as a function of DCCC. Based on double-critical condition, the OBRR values larger than 40 dB, the crosstalk larger than 50 dB, highest quality factor of 9000 and the FWHM as small as 0.17 nm were realized in silicon add–drop resonator, which are quite compatible with the reported experimental data. Double-critical condition shows that the lossless coupling is not enough condition to acquire high-quality filtered signal with a large crosstalk and in presence of coupling losses, the DCCC can determine the optimum relation between the strength of coupling coefficients and the coupling losses.
PubDate: 2019-08-15

• Edge of magnetized electronegative plasma ion source in the presence of

• Abstract: This paper develops a theoretical model for formation of multilayers in the magnetized electronegative plasma at the edge of plasma ion source. The impacts of positive ion temperature and collisions are studied and quantified by obtaining the structure of the plasma sheath. By adding the negative ions into the discharge, the solutions of Poisson’s equation become oscillatory. A finite temperature for the positive ions and also the collisions results in a change in the behavior of such oscillatory solutions. Here, it is assumed that the collision frequency depends on the positive ions velocity and thermal positive ions flow is adiabatic. The spatial distribution of the species density, electric potential, and positive ion velocity is calculated for different values of positive ion temperature and negative ion concentration for two limiting cases where the collision frequency either is constant or depends linearly on velocity. In addition, the influence of the plasma parameters such as negative ion density and temperature and positive ion temperature is investigated on the space charge and positive ion flux as well as parameter space region. It is also shown that the presence of the negative ion into the plasma ion source influences the extracted positive ion flux and increases the positive ions intensity.
PubDate: 2019-08-12

• Growth and characterization of TiAlN nanoparticles using low-energy plasma
focus device

• Abstract: In this experimental study, a 1.5-kJ plasma focus device of Mather type was employed to grow titanium aluminum nitride (TiAlN) coatings at room temperature on 316 stainless steel sub-layer. The anode of the device was made of Titanium and Aluminium. A mixture of N2 and Ar gases was used as the work gas for TiAlN deposition. TiAlN nanoparticles were formed on stainless steel with 0° of the degree with respect to the anode axis by different shots at 5 cm above the anode. X-ray diffraction results indicated the formation of the TiAlN structure on stainless steel. Scanning electron microscopy images demonstrated the approximately uniform growth of TiAlN nanoparticles on the surface. EDX analysis results showed that an increase in the number of the shots increased the deposition of TiAlN on the sub-layer. According to the atomic force microscopy images, the mean thickness of the surface increased as the shots increased in number. Microhardness test results of the thin layers showed that an increase in the number of the shots increased the hardness of the samples.
PubDate: 2019-07-27

• Instrumentation for modeling of discharge processes in ignition capacitive
systems

• Abstract: In this article, developing a computer model allowing to obtain analytically the dependences of the discharge current i(t) and voltage in a spark discharge U(t) on the given discharge circuit parameters is carried out. A toolkit for evaluating the characteristics of capacitive ignition systems of various types at the stages of creating new circuit technical solutions and engineering has been developed. The obtained results allow to significantly reduce the time for evaluating the potential of ignition systems without carrying out sufficiently complex and labor-intensive experimental studies. The resulting dependences i(t) and U(t) allow to determine and calculate all the main parameters of spark discharges in plugs—energy, power and duration of discharges, as well as the maximum value of the discharge current.
PubDate: 2019-07-24

• Estimation of lattice strain in alumina–zirconia nanocomposites by X-ray
diffraction peak profile analysis

• Abstract: Zirconia nanoparticles were synthesized by a solution combustion technique. Zirconia nanoparticles were grown inside alumina templates to control the crystal size. The alumina templates were characterized by pores of sizes of approximately 6–8 nm. X-ray diffraction line profile analysis using Williamson–Hall method and Warren and Averbach revealed that the alumina templates were characterized by negligible defect-related effect of lattice distortion. Rietveld structure refinement did not reveal any gross difference with the literature reported values for cell parameters ‘a’ and ‘c’ and fractional atomic coordinates x and z for Al and O atoms indicating no large-scale bond deformation. The template X-ray reflections in the nanocomposites are skewed in nature which indicates some distortion of the templates might have taken place. The distortion is, however, plastic in nature which is evident from the higher level of lattice distortion viz. 0.2% of lattice microstrain.
PubDate: 2019-07-20

• Heat capacity and entropy of Gaussian spherical quantum dot in the
presence of donor impurity

• Abstract: The energy states of shallow donor impurity in GaAs/AlGaAs quantum dot heterostructure with Gaussian potential have been calculated by the shifted 1/N expansion method. The effects of the impurity on the ground state energy and average statistical energy have been investigated. The present calculations show that the donor impurity modifies significantly the electron energy levels of spherical quantum dot and thermal properties. In addition, we have also displayed the variations of the heat capacity and entropy of donor impurity in quantum dot with the radius, confining potential depth, dimension and temperature. The comparison shows that our results are in very good agreement with the theoretical reported work.
PubDate: 2019-06-04

• Structural, electronic and optical properties of graphene-like nano-layers
MoX2(X:S,Se,Te): DFT study

• Abstract: Using the first principle calculations, the structural, electronic and optical properties of the monolayer graphene-like MoX2 sheet are calculated. Our results show that the chalcogenide atoms in the stability and the lattice parameters of the MoX2 sheet have a key role, although it is known that the electronic properties are more dependent on the metal atoms in these sheets. Our data also confirm semiconductor behavior of the MoX2 monolayers with direct band gap for S, Se and Te chalcogenides. Compared with the bulk compounds, they have similar structural properties but represent unique electronic and optical properties that can be used in nano-devices, nano-electronics and so on. In this work, the investigation of the chalcogenide atoms role in modifying the optical properties of these single-layer sheets, such as absorption and refraction coefficients, is carried out; the dielectric constant plays an important role. We also try to study the possibility of using these compounds on the solar energy industries and optical devices.
PubDate: 2019-06-03

• Efficient single-layer light-emitting diodes based on organic–inorganic
lead halide perovskite and tuning luminescence properties

• Abstract: Because of the interesting features of the organic/inorganic halide perovskite (e.g., CH3NH3PbX3, X = Cl, Br) materials, such as long electron–hole diffusion length, high absorption coefficient and adjustable band gap, they have attracted a great deal of attention. In this research, CH3NH3PbX3 (X = Br, Cl) are synthesized and perovskite-based single-layer and perovskite-based bilayer diodes are fabricated. Using electron beam deposition technique, thin films of CH3NH3PbX3 (X = Br, Cl) hybrids with excellent homogeneity are manufactured. Absorption spectrum, X-ray spectrum and photoluminescence spectrum of organic/inorganic halide perovskites along with electroluminescence spectra, SEM micrographs and current–voltage characteristic of perovskite-based light-emitting diodes are investigated. Perovskite-based bilayer diodes are evaluated for the first time. The difference between the emission wavelengths of single-layer and bilayer diodes is the main characteristic of bilayer diodes.
PubDate: 2019-05-11

• Comparing the structural and magnetic properties of FePt/MgO/Si and
FePt/Ag/Si granular nanolayers

• Abstract: The properties of L10-FePt nanoparticles can be improved in the presence of MgO and Ag interlayers in direct sputtering and annealing method, respectively. Such properties are crystal and compound ordering, nanostructure and crystal orientation. In this work, FePt nanoparticles in ferromagnetic L10-fct phase were synthesized using sputtering method on Ag and MgO layers. According to XRD analyses, the impact of the presence of these two kinds of interlayer on crystal structure and its orientation has been investigated. Furthermore, the effect of the presence of 10% Ag on these properties has been studied and their granular layer nanostructures were characterized through the FE-SEM analysis. The results show that the presence of Ag as nanocompound and interlayer is desirable on declining the transition temperature and controlling the size during annealing. The presence of MgO as a sublayer in direct synthesis leads to the formation of 10 nm monosize smaller nanoparticles. According to VSM analysis, MgO and Ag sublayers have increased the magnetic coercivity of the FePt nanoparticles by 3.4 times and 3.7 times, respectively.
PubDate: 2019-05-06

• Employing constant photocurrent method for the study of defects in silicon
thin films

• Abstract: Different optical characterization techniques have been performed on a series of microcrystalline silicon thin films deposited using very high-frequency-assisted plasma-enhanced chemical vapor deposition process. The constant photocurrent method has been employed to study the defects states in density of states spectra of hydrogenated microcrystalline silicon thin films. The photocurrent measurements demonstrate anisotropy in the optoelectronic properties of the material. We have analyzed the optical absorption coefficient from UV spectroscopy and with the help of constant photocurrent method. The spectra have been analyzed in broad region and are presented for both the cases, i.e., surface and bulk light scatterings. The spectra were interpreted in terms of disorder, resulting defect density, crystalline/amorphous volume fractions and material morphology. The subgap-related parameters such as absorption coefficient, characteristic energy E0 of tail states and density of subgap defect states together with an estimate of the bandgap of silicon films prepared at various crystalline fractions have also been estimated. The density of localized tail states is found to fall exponentially toward the gap with band tail width of about 110 meV.
PubDate: 2019-03-06

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