Dielectric Components Research Articles

Electronic structure and optical properties of iron based chalcogenide FeX2 (X = S, Se, Te) for photovoltaic applications: a first principle study

In present work, the electronic structure and optical properties of the FeX2 (X = S, Se, Te) compounds have been evaluated by the density functional theory based on the scalar-relativistic full potential linear augmented plane wave method via Wien2K. From the total energy calculations, it has been found that all the compounds have direct band nature, which determined by iron 3d states at valance band edge and anion p dominated at conduction band at Γ-point and the fundamental band gap between the valence band and conduction band are estimated 1.40, 1.02 and 0.88 eV respectively with scissor correction for FeS2, FeSe2 and FeTe2 which are close to the experimental values. The optical properties such as dielectric tensor components and the absorption coefficient of these materials are determined in order to investigate their usefulness in photovoltaic applications.

Role of the Crystal Lattice Constants and Band Structures in the Optoelectronic Spectra of CdGa2S4 by DFT Approaches

The electronical and optical properties of CdGa2S4 under high pressures were studied using the full potential linearized augmented plane wave (FP‐LAPW) method within the GGA and mBJ exchange correlation potentials from 0.0 to 16.92 GPa. The obtained results show that the lattice constants, bandgap values, and optoelectronic properties are sensitive to applied external pressures. The mBJ results indicate that the bandgap increases and the static dielectric constants decrease with increasing the pressure. The two none zero dielectric tensor components show considerable anisotropy between the perpendicular and parallel components. The maximum absorption for x direction in all pressures takes place in vacuum UV region. Also, the plasma frequency shifts to the higher energies with increasing the pressure for application in optical devices. The calculated results by mBJ are in close agreement with the experimental values.

Embedded nonlinear passive components on flexible substrates for microelectronics applications

This paper describes nonlinear dielectric composite passive components on flexible metallic substrates for transient protection of electronic devices, most notably against electrostatic discharge (ESD) and electrical overstress (EOS) conditions. In this case, the passive device comprises a polymer composite that contains nonlinear inorganic fillers, an electric field switchable dielectric ceramic Calcium Copper Titanate (CaCu3Ti4O12, CCT), in a metal insulator metal (MIM) configuration. Compatibility with PCB (printed circuit board) in line processing is demonstrated since the fabrication process described is a relatively low temperature process. Advantageously, the construction of such components are such that they can be embedded within a PCB (printed circuit board), thereby allowing miniaturization of the circuit design and can potentially be adopted in an industrial roll to roll manufacturing process. The dielectric characteristics of the CCT filler polymer composites are compared with well-known high dielectric constant Barium Titanate filler polymer composites for capacitor applications. Theoretical models based on effective medium theory are used to predict the dielectric properties of the CCT epoxy composites as a function of filler loading fractions. Maxwell Garnett model was found to provide the best fit to experimental data.

RESEARCH OF INFLUENCE OF HEIGHTENED TEMPERATURES ON THE OPERATIONAL CHARACTERISTICS OF TRANSFORMER OIL T-1500 IN FILM INSULATION SYSTEMS

The criteria parameters allowing to estimate authentically the thermostability of dielectric liquids’ operational properties are chosen. Change of transformer oil’s operational properties during its interaction with polypropylene and polyethylenetereftalate films under the influence of the heightened temperature is analysed. The influence of morphological features of polypropylene film’s surface on the thermostability of the impregnated dielectric film is revealed. Low degree of the interaction between the polyethylenetereftalate film and transformer oil T-1500 is defined.The reduction of the comparative light transmission coefficient illustrates the thermostimulated mutual dissolution in the system «polymer in the liquid». The consequent of this process is the degradation of the impregnated dielectric film components’ electrical characteristics. Analysis of kinetics of impregnating liquid’s light transmission can be informative and useful in comparative studies of various impregnated dielectric films, as well as for express diagnostics of impregnated film insulation during high-voltage pulse capacitors life tests

Development of radioisotopic-plasma technology for the protection of radio electronic means from powerful electromagnetic radiation

In order to protect REM from the impact of powerful pulse EMR, we proposed a radioisotopic-plasma technology for creating absorbing screens. For this purpose, it is proposed to use semiconducting materials with radioisotopic elements. This will provide for a significant absorption of EMR over a wide frequency range due to the creation of non-equilibrium state of electronic subsystems of different layers of material. We designed a generalized structure of absorbing material and carried out an analysis of the physical mechanisms that occur through the use of radioisotopic elements. It is demonstrated that the physical mechanisms that occur in the material define its dielectric permittivity and its comprehensive nature. We obtained an analytical expression for the reflection coefficient of the proposed absorbing material. A peculiarity of the analytical expression consists in the consideration of the impact of both its structure and changes in dielectric permittivity components that occur under the influence, first of all, of radioisotopic elements on the reflective characteristics of material. A procedure for determining the dielectric permittivity of the material was devised. The procedure consists in determining the kinetic equation to describe the state of electronic subsystem of layers in the material depending on the intensity of radioisotopic elements and the type of environment, finding a non-equilibrium distribution function, determining the components of dielectric permittivity, which makes it possible to assess the contribution of non-equilibrium state of electronic subsystem of separate layers in the material into the provision of required reflective and absorbing properties. We conducted assessment of absorbing and scattering properties of material. The estimates obtained demonstrate the feasibility of applying radioisotopic-plasma technology to create materials in order to protect REM from powerful EMR, especially under conditions of constraints on weight and size characteristics of absorbing screens.

Optical properties of lithium gallium oxide

The optical dielectric function tensor of orthorhombic single-crystal LiGaO2 was determined for polarizations along a, b, and c crystal-axis in the photon energy range from 0.04eV to 6.5eV by the generalized spectroscopic ellipsometry. In the far-infrared spectral range from 12.4meV to 40meV, the dielectric function was determined from conventional polarized transmittance and polarized reflectance measurements. Lineshape analysis of the dielectric function tensor major components allowed for a determination of the long-wavelength optical phonon characteristics, refractive indices dispersion, and parameters of interband and excitonic optical transitions.

Transient characteristics of discharge of polymer sample after electon-beam irradiation

Charging effect of dielectric material due to electron beam irradiation has a significant influence on the microdischarge phenomenon of dielectric microwave component by multipactor. The discharge process caused by internal electron leakage can relieve this undesirable charging effect. In this paper, we study the transient discharge characteristics of a dielectric sample after being irradiated by electron beam through numerical simulation. Both the charging and discharging processes of a dielectric sample are considered with a comprehensive model. The Monte-Carlo method is used to simulate the interaction between primary electrons and material atoms before the irradiation is interrupted, including elastic scattering and inelastic scattering. The elastic scattering is calculated with the Mott scattering model, and the inelastic scattering is simulated with the fast secondary electron model or Penn model according to electron energy. Meanwhile, the transport process of internal charges in the sample during the discharge period is simulated including the charge diffusion under the force of charge density gradient, the drift due to built-in E-field, and the trap caused by material defect. In this work, the discharge process is taken to begin at the very moment of charging reaching saturation, with the internal charges kept almost unchanged. A polymer material widely used in advanced component is considered in this work due to its remarkable charging effects. Distributions of internal charges of the sample during the discharge process are simulated, and influences of sample parameters, including sample thickness, electron mobility and trap density in the discharge process, are analyzed. The results show that internal charges move to the bottom of the sample during the discharging, leading to the surface potential reaching an ultimate state which is determined by trap density of the material. The position corresponding to the maximum internal charge density shifts towards the grounded bottom. Although a sample with a larger electron mobility means a faster discharge process, fewer free electrons in this sample result in less discharge quantity. The time constant of discharge process decreases with the increase of sample electron mobility in the form of similar linearity. Although a sample with a larger thickness can hold more internal charges, the increase of sample thickness may increase the distance of internal charges leak yet. Hence, the quantity of discharge first increases and then decreases with the increase of sample thickness. In addition, a larger trap density of a dielectric sample makes charge leak harder, resulting in a lower discharge quantity. Finally, the proportion of discharge quantity in saturated charge quantity decreases from 1 to 0 exponentially with the increase of sample trap density. As a conclusion, those sample parameters have their corresponding effects on discharge characteristics by means of different physical mechanisms. Sample electron mobility determines the discharge time constant obviously by affecting the electron transport speed. The sample thickness affects the discharge quantity by shifting the charging balance mode, and material defect impedes part of discharge quantity from trapping internal free electrons. This simulation method and results can help to recede the charging effect and estimate the evolution charging and discharging states of dielectric material during and after electron beam irradiation.

Effect of Microwave Heating on the Dielectric Properties and Components of Iron-Fortified Milk

With the iron-fortified milk as research object, this paper makes a research on the influence of iron on the dielectric properties and wave absorption properties and effect of nutritional components, such as casein and whey protein in milk, and thermostability in the process of microwave heating, and rapid heat transfer method in ferrous gluconate–milk and ferrous chloride–milk, respectively. The results show that the iron of ionic form has greater influence to convert microwave to heat energy and the effect of microwave absorption properties was greater for ferrous chloride than for ferrous gluconate at high concentration. The effect of different forms of iron on the composition of milk was different, and the composition of milk systems was more stable by microwave heating, but the rapid heat transfer method is superior in the aim of increasing the nutritional value of milk. The ferrous gluconate–milk system has a better thermal stability than ferrous chloride–milk system. From the aspect of dielectric induction, the paper discovers the response rules of iron and evaluates the microwave thermal safety of the traditional and the iron-fortified products by microwave heating.

Formation of silver nanoparticles with dielectric shell on the silver-containing glass during laser evaporation and ablation

We demonstrate a new method of silver nanoparticles formation on a silver-containing glass surface due to its irradiation by a pulsed CO2 and YAG:Nd lasers. The particles are formed as a result of reduction of silver ions from the glass at the edges of a laser torch emerging during evaporation and ablation. The settled particles are then fixed on sample surface by a shell of glass dielectric components. The method allows creating plasmonic nanostructures on the glass surface for sensing applications.

Approach for fine‐tuning of hybrid dimer antennas via laser melting at the nanoscale

Asymmetric metal‐dielectric nanostructures are demonstrated superior optical properties arising from the combination of strong enhancement of near‐fields and controllable scattering characteristics which originate from plasmonic and high‐index dielectric components. Here, being inspired by the recent advances of the asymmetric hybrid nanoparticles fabrication [Dmitry Zuev, et al., Adv. Mater. 28, 3087 (2016)], we suggest and study numerically a novel type of hybrid dimer nanoantennas. The nanoantennas consist of asymmetric metal‐dielectric (Au/Si) nanoparticles and allow tuning of the near‐ and far‐field properties via laser induced reshaping of the metal part at the nanoscale. We demonstrate an ability to modification of the scattering properties, near‐field distribution profilis, normalized local density of states, and radiation patterns of the nanoantenna upon the laser reshaping. The parameters used to investigate these effects correspond to experimentally demonstrated values. image

In situ magneto-optical ellipsometry data analysis for films growth control

In this work we present the way of ferromagnetic films study by means of magneto-ellipsometry. The method of interpretation of in situ magneto-optical ellipsometry spectra for real time growth control is described. The method has been successfully tested on Si/SiO2/Fe films within the model of a homogeneous semi-infinite medium. As a result, the dielectric tensor components for Fe layer were calculated using a developed approach.

Optical generation in an amplifying photonic crystal with an embedded nanocomposite polarizer

We show the possibility of selective polarization generation in an amplifying photonic crystal structure via the use of an embedded film of a sub-wavelength thickness with uniformly oriented metallic elongated nanoparticles chaotically distributed in the volume of a semiconductor. Such nanocomposite polarizer presents a uniaxial crystal with different values of dielectric permittivity components along and perpendicular to the polar axis of the nanoparticles. Dispersion of the dielectric permittivity of the nanocomposite is defined by the concentration and shape factor of the nanoparticles. Wavelength dependence of imaginary part of the nanocomposite permittivity possesses a resonance behavior resulting from plasmon resonance in nanoparticles. We show that this allows, depending on the relative orientation of the nanocomposite anisotropy axis and the polarization direction of the light, to achieve the mode discrimination of the photonic structure in the vicinity of a resonance of one of the permittivity components, where the absorption of the nanocomposite layer is maximal. Also we vary the parameters of the nanocomposite polarizer to obtain the optimal conditions of optical generation at the given wavelength.

Effect of film thickness on the width of percolation threshold in metal-dielectric composites

The effect of thickness on the width of the percolation threshold in metal-dielectric composite films was examined. The distribution of current intensities through cubic networks of metal and dielectric components was determined using Kirchhoff's equations. From the tail of current distribution, the width of the percolation threshold was defined using Lévy statistics, and determined as a function of the film thickness for a system size 100. In the 2D-3D crossover region, the percolation width decreases as a power-law with a power exponent of 0.36±0.01.

Conductivity Analysis of Bi<sub>4</sub>Ti<sub>3</sub>O<sub>12</sub> Ferroelectric Ceramic: A Comprehensive Study from the Dynamic Aspects of Hopping Conduction

Objectives: We focus solely on a comprehensive conductivity analysis of Bi 4 Ti 3 O 12 ceramic, in a bid to bring seminal ideas for dielectric components, in particular frequency and temperature ranges. Methods/Statistical Analysis: The synthesis of Bi 4 Ti 3 O 12 ceramic is based on a mechanical activation method. The following sintering at 1273 K ascertains the Bi 4 Ti 3 O 12 appears to be of single phase crystallizes in orthorhombic form, whose conductivity is determined from the dielectric function in the context of Kramers-Kronig relation on which of this is measured in the frequency domain at varying temperatures. The evaluation of conductivity data is mainly in terms of activation energy. Findings: We find that the separately discussed dc and ac conductivities in similar manner are best isolated into two distinct temperature regions. Charge transport by hopping to the target localized states is the relevant conduction mechanism in bringing insights into the dynamic responses. Variable range and small polaron hopping models associated with the adiabatic small polaron are the decent choices, each of which explaining the dc conductions in these temperature regions. The former involves distant hops, whereas the latter denotes as nearest-neighbour hopping. The percolation treatments applied in the dc conductivity yield promising results if different percolation expressions are used. The correlation between dc and ac conductions for each temperature is irrefutably made through the Barton-Nakajima-Namikawa fitting. In frequency dependence ac regions, the thermally activated hopping carriers are transported in a correlated to a random manner between preferred sites. Performing a Summerfield ac scaling in these temperature regions leads to different scenarios in view of time-temperature superposition principle. Applications/Improvements: Further experiments are encouraged to support the hopping conduction mechanisms from another aspect in order to prompt the use as energy storage function in the electromagnetic application.

Optoelectronic behavioral study of defect-chalcopyrite semiconductors XGa2Te4 (X = Zn, Cd)

In this work, electronic structure and optical properties investigations for defect-chalcopyrite semiconductors ZnGa2Te4 and CdGa2Te4 are presented using full potential linearized augmented plane wave method. Energy bands and density of states (DOS) computations are performed using different flavors of exchange and correlations. The calculations are performed using Wu-Cohen generalized gradient approximation (WC-GGA), Perdew et al. (PBE-sol) and the most accurate modified Becke and Johnson (mBJ) potentials. Our investigations show that energy bands and DOS computed using mBJ potential are in better agreement with the available experimental data. Optical properties such as, dielectric tensor components, absorption spectra, reflectivity, refractivity, dielectric loss, are investigated using mBJ potential. Imaginary peaks of di-electric tensor ε2(ω), are interpreted by means of inter-band transitions from valence to conduction band. High intensity absorption curves from 3 to 5eV, energy band gap depicted for ZnGa2Te4 (1.61eV) and CdGa2Te4 (1.78eV) materials indicates their applicability for solar photovoltaic and other optoelectronic applications.

On the propagation of Voigt waves in energetically active materials

If Voigt-wave propagation is possible in a dissipative anisotropic dielectric material characterised by the permittivity dyadic , then it is also possible in the analogous energetically active material characterised by the permittivity dyadic , where is the hermitian conjugate of . This symmetry follows directly from a theoretical analysis of the necessary and sufficient conditions for Voigt-wave propagation in anisotropic materials. As a consequence of this symmetry, a porous dissipative material that exhibits Voigt-wave propagation can be used to construct a material that allows the propagation of Voigt waves with attendant linear gain in amplitude with propagation distance, by means of infiltration with an electrically or optically activated dye, for example. This phenomenon is captured by the Bruggeman formalism for homogenised composite materials based on isotropic dielectric component materials that are randomly distributed as oriented spheroidal particles.

Multilayer Ferrite Inductor Substrate for Ceramic-Based High Current Point-of-Load (POL) Converter

Abstract High power-density and high efficiency are the two driving forces for point-of-load (POL) converters used in portable electronics and other applications where system miniaturization is required. Discrete passive components, especially bulky inductors, have become the bottleneck for downsizing POL converters. Low-temperature sintered Ni-Cu-Zn ferrite tapes for multilayer chip inductors have been widely studied and used in high-frequency power electronics applications. In our previous study, a low-profile, planar inductor substrate with lateral flux pattern was fabricated using mixed commercial low-fire Ni-Cu-Zn ferrite tapes and compatible low temperature co-fired ceramic (LTCC) processing. However, thermal interface material was used between active circuit board and passive layer (ferrite substrate), which increases the total volume of the converter and becomes a potential threat for reliability due to the mismatch of coefficient of thermal expansion among different layers. Additionally, this hybrid integration method requires labor-intensive manual steps which are not compatible with cost-sensitive power electronics market. A fully ceramic-based POL module with integrated multilayer ferrite inductor has been proposed. The circuit and other components are designed to be directly built on top of the multilayer ferrite inductor substrate. This presented work focuses on the development of the multilayer ceramic substrate with embedded planar, lateral-flux inductor by co-firing of ferrite and dielectric tapes with conductor paste. Commercial dielectric LTCC and ferrite tapes were chosen for the fabrication of multilayer ferrite inductor substrate. Different silver pastes were co-fired with ceramic tapes to form the inductor winding. The sintering behavior and compatibility of dielectric, magnetic, and conductive components in one co-firing process was studied in order to realize a cohesive multilayer ceramic substrate. The embedded inductors present lower inductance than pure ferrite inductors sintered alone using the same profile when the output current is smaller than 10 A. The inductance of both types of inductors are very similar when output current is above 15 A. The inductor embedded in dielectric tapes exhibits higher core loss density than its counterpart. Future work will focus on the integration of high current POL module using this developed multilayer ferrite inductor substrate.

Anisotropy, phonon modes, and free charge carrier parameters in monoclinicβ-gallium oxide single crystals

We derive a dielectric function tensor model approach to render the optical response of monoclinic and triclinic symmetry materials with multiple uncoupled infrared and farinfrared active modes. We apply our model approach to monoclinic $\beta$-Ga$_2$O$_3$ single crystal samples. Surfaces cut under different angles from a bulk crystal, (010) and ($\bar{2}$01), are investigated by generalized spectroscopic ellipsometry within infrared and farinfrared spectral regions. We determine the frequency dependence of 4 independent $\beta$-Ga$_2$O$_3$ Cartesian dielectric function tensor elements by matching large sets of experimental data using a point by point data inversion approach. From matching our monoclinic model to the obtained 4 dielectric function tensor components, we determine all infared and farinfrared active transverse optic phonon modes with $A_u$ and $B_u$ symmetry, and their eigenvectors within the monoclinic lattice. We find excellent agreement between our model results and results of density functional theory calculations. We derive and discuss the frequencies of longitudinal optical phonons in $\beta$-Ga$_2$O$_3$. We derive and report density and anisotropic mobility parameters of the free charge carriers within the tin doped crystals. We discuss the occurrence of longitudinal phonon plasmon coupled modes in $\beta$-Ga$_2$O$_3$ and provide their frequencies and eigenvectors. We also discuss and present monoclinic dielectric constants for static electric fields and frequencies above the reststrahlen range, and we provide a generalization of the Lyddane-Sachs-Teller relation for monoclinic lattices with infrared and farinfrared active modes. We find that the generalized Lyddane-Sachs-Teller relation is fulfilled excellently for $\beta$-Ga$_2$O$_3$.

Inkjet printing of polyimide insulators for the 3D printing of dielectric materials for microelectronic applications

ABSTRACTIn this article, we report the first continuous fabrication of inkjet‐printed polyimide films, which were used as insulating layers for the production of capacitors. The polyimide ink was prepared from its precursor poly(amic) acid, and directly printed on to a hot substrate (at around 160 °C) to initialize a rapid thermal imidization. By carefully adjusting the substrate temperature, droplet spacing, droplet velocity, and other printing parameters, polyimide films with good surface morphologies were printed between two conducting layers to fabricate capacitors. In this work, the highest capacitance value, 2.82 ± 0.64 nF, was achieved by capacitors (10 mm × 10 mm) with polyimide insulating layers thinner than 1 μm, suggesting that the polyimide inkjet printing approach is an efficient way for producing dielectric components of microelectronic devices. © 2016 The Authors Journal of Applied Polymer Science Published by Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43361.

Superparamagnetic Fe3O4/MWCNTs heterostructures for high frequency microwave absorption

Superparamagnetic Fe3O4 nanocrystals anchored on multiwalled carbon nanotubes (MWCNTs) were fabricated using co-precipitating technique which nicely integrates the magnetic and dielectric components into a synergistic microwave absorber.