Dielectric Theory Research Articles

Physical properties and basic theory of dielectric

At the beginning of human understanding and application of electricity, dielectric materials have been in the world. At that time, however, the dielectric was used only as an insulating material to separate the current. Until the 1930s, the main object of research was insulating materials, mainly focusing on the dielectric constant, loss, conductance and breakdown of insulating materials. After the 1930s, with the emergence and development of new technology, dielectric has been far from being only used as insulation materials to the application, especially the appearance of polar dielectric and widely used, making people’s understanding of dielectric and its category and the past is very different. The research capacity has gradually evolved from the four main parameters of insulators to the study of the internal polarization process. This article from the dielectric polarization, dielectric loss, dielectric conductance and breakdown, dielectric thermal side note relaxation theory and its application of four chapters of the system to learn related content. The properties of dielectric are analyzed from the microscopic point of view, and the related theoretical hypotheses are established to reveal the corresponding macroscopic phenomena. The polarization, loss, conductance and breakdown properties of dielectric are analyzed. The dielectric constant ε, loss Angle tangent tanδ, conductivity γ and breakdown field intensity E are used to describe the properties of dielectric quantitatively.

Exciton radiative lifetime in a monoatomic carbon chain

Linear carbon-based materials such as polyyne and cumulene oligomers provide a versatile platform for nano-physics and engineering. Direct gap quasi-1D polyyne structures are promising for the observation of strong and unusual excitonic effects arising due to the two-dimensional quantum confinement. Recently, we reported on the observation of sharp exciton peaks in low temperature photoluminescence spectra of polyyne chains (Kutrovskaya S et al 2020 Nano Lett. 20 6502–9). Here, we analyze the time-resolved optical response of this system. We extend the non-local dielectric response theory to predict the exciton radiative lifetime dependence on the band-gap value and on the length of the chain. A good agreement between the experiment and the theory is achieved.

Reactivity of an air-stable dihydrobenzoimidazole n-dopant with organic semiconductor molecules

Summary 1,3-Dimethyl-2-(4-(dimethylamino)phenyl)-2,4-dihydro-1H-benzoimidazole, N-DMBI-H, is widely used as an air-stable n-dopant for organic semiconductors. Here, its reactivity is investigated with a variety of imide- and amide-containing semiconductor molecules that have reduction potentials in the range −0.54 to −1.10 V versus ferrocene. Reaction rates correlate poorly with these potentials. The more reactive of the imides form the corresponding radical anions cleanly, but kinetic isotope studies using N-DMBI-D indicate that the reaction proceeds via an initial hydride- or hydrogen-transfer step. For an amide- and ester-rigidified bis(styryl)benzene derivative the hydride-reduced product is stable under an inert atmosphere and can be observed directly; the radical anion can only be obtained in sub-stoichiometric yield and under certain reaction conditions. On the other hand, (N-DMBI)2 rapidly reduces all the imides and amides examined to the corresponding radical anions. The implications of these findings for dopant selection and use are discussed.

Optoelectronic Properties of Ternary Tetrahedral Semiconductors

The dielectric interpretation of crystal ionicity evolved by Phillips and Van Vechten (P.V.V) has been utilized to evaluate various ground state properties for broad range of semiconductors and insulators. Although, the relevance of P.V.V dielectric theory has been restricted to only simple ANB8-N structured compounds, which have a particular bond. Levine has broadened P.V.V. theory of ionicity to multiple bond and complex crystals and evaluated many bond parameters for ternary tetrahedral semiconductors. Some other researchers have extended Levine’s work with a concept of ionic charge product and nearest neighbour distance to binary and ternary tetrahedral crystals to evaluate the ground state properties. In this paper, a new hypothesis of average atomic number of the elements in a compound has been used to understand the some electronic and optical properties such as ionic gap (Ec), average energy gap (Eg), crystal ionicity (fi), electronic susceptibility (χ), and dielectric constant (ϵ) of ternary tetrahedral (AIIBIV and AIBIII) semiconductors. A reasonably acceptable agreement has been noticed between our evaluated values and other researchers reported values.

Thermal Analysis, Dielectric Response and Electrical Conductivity of Silicon Phthalocyanine Dichloride (SiPcCl2) Thin Films

This research is a detailed examination of the effect of post-annealing on the structure and electrical conductivity of silicon phthalocyanine dichloride (SiPcCl2) thin films. Differential thermal analysis (DTA) is used to determine the temperature limit of thermal stability for a sample of silicon phthalocyanine dichloride (SiPcCl2). The results of differential thermal analysis (DTA) proved that silicon phthalocyanine dichloride (SiPcCl2) is thermally stable up to 415 K. The dielectric behavior and the electrical conductivity of silicon phthalocyanine dichloride (SiPcCl2) thin films were investigated under a temperature effect from 303 K to 383 K and a frequency from 200 Hz to 20 MHz. The frequency and temperature dependence of dielectric loss and dielectric constant values were explained in terms of dielectric polarization theory. The alternative current (AC) conductivity response toward the frequency change obeys Jonscher’s power law. The correlated barrier hopping (CBH) model is utilized and adapted to fit the conduction mechanism in the high- and low-frequency regions. Both the complex electric modulus and the impedance formalisms are used to illustrate the dielectric characteristics of the silicon phthalocyanine dichloride (SiPcCl2). The potential height value of the hopping barrier, Wm, and activation energy value, Eac, for dielectric relaxation were determined.

Probing free carrier plasmons in doped semiconductors using spatially resolved electron energy loss spectroscopy

We report spatially resolved measurements of free carrier collective excitations in a doped semiconductor. Using $\ensuremath{\sim}10$ meV resolution electron energy loss spectroscopy (EELS) in an electron microscope with $\AA{}$ spatial resolution, we identify both surface and bulk carrier plasmons at infrared energies in a freestanding film of indium tin oxide (ITO). The interference patterns of long wavelength propagating surface carrier plasmons are revealed using spatially resolved EELS, from which we extract a dispersion relation. We further show that the energies of these plasmons vary near the surfaces and grain boundaries of the film due to band bending. Modeling based on dielectric theory agrees very well with experimental results. Finally, carrier plasmons in amorphous and crystalline ITO films are compared. These results should also be helpful for understanding the free carrier plasmons in other doped semiconductors in nanoscale volumes.

Relationship between zeolite structure and capture capability for radioactive cesium and strontium

Zeolites are widely used for capturing radioactive Cs+ and Sr2+, but the important structural factors determining their performance have not been clearly understood. To investigate the structure-property relationship, we prepared thirteen zeolites with various structures and Si/Al ratios. Ion-exchange experiments revealed that Cs+ exhibited an enhanced affinity to zeolites with high Si/Al ratios, which could be explained by the dielectric theory. Notably, zeolites containing 8-membered ring (8MR) showed extra-high Cs+ selectivity. Structural analysis using X-ray diffraction proved that Cs+ with an ionic diameter of 3.6 Å was selectively coordinated within 8MR having a cavity diameter of 3.6–4.1 Å. Such unique size-selective Cs+ coordination is analogous to ion complexation by macrocyclic organic ligands (e.g., crown ethers). Divalent Sr2+ showed decreasing affinity to zeolites as the Si/Al ratio increased, because of the increasing average Al–Al distance distribution. Sr2+ exchange exhibited an insignificant dependence on zeolite structures due to its strong hydration, which inhibited close interaction with zeolite frameworks. In terms of kinetics, Sr2+ exchange was significantly slower than Cs+ exchange because of the bulkiness of hydrated Sr2+ ions. Therefore, the micropore channels with large apertures (e.g., 12-membered ring) were beneficial for achieving fast ion-exchange kinetics, especially in the case of Sr2+.

Utilizing photonic crystal structure to design microstrip antenna with controllable dielectric constant substrate

A novel design method of microstrip patch antenna with photonic crystal substrate is proposed and analyzed. The method is different from the traditional one. Early work uses natural materials as the substrate to design microstrip patch antenna. In the work, dielectric cylinder arrays are designed based on periodic waveguide theory to realize the substrates with controllable dielectric constants. Meanwhile, applying dielectric cylinder array and microstrip antenna design theory, we designed and simulated a new type of antenna. The proposed antenna model is compared with homogeneous substrate structure antenna-based microstrip patch antenna and analyzed the radiation characteristics. The consistency of results shows that this method is feasible for antenna design. Afterwards, we fabricated a novel antenna with an equivalent dielectric constant of 2.94, which is further verify the feasibility of the method. Finally, the performance of designed antenna is analyzed with different cylinder height. The results show that the novel antenna design method maybe possess great significance to the design of high-gain miniaturized antenna.

Local gradient Bernoulli–Euler beam model for dielectrics: effect of local mass displacement on coupled fields

The size-dependent behaviour of a Bernoulli–Euler nanobeam based on the local gradient theory of dielectrics is investigated. By using the variational principle, the linear stationary governing equations of the local gradient beam model and corresponding boundary conditions are derived. In this set of equations the coupling between the strain, the electric field and the local mass displacement is taken into account. Within the presented theory, the process of local mass displacement is associated with the non-diffusive and non-convective mass flux related to the changes in the material microstructure. The solution to the static problem of an elastic cantilever piezoelectric beam subjected to end-point loading is used to investigate the effect of the local mass displacement on the coupled electromechanical fields. The obtained solution is compared to the corresponding ones provided by the classical theory and strain gradient theory. It is shown that the beam deflection predicted by the local gradient theory is smaller than that by the classical Bernoulli–Euler beam theory when the beam thickness is comparable to the material length-scale parameter. The obtained results also indicate that the piezoelectricity has a significant influence on the electromechanical response in a dielectric nanobeam. The presented mathematical model of the dielectric beam may be useful for the study of electromechanical coupling in small-scale piezoelectric structures.

Graphene Platelets-Based Magnetoactive Materials with Tunable Magnetoelectric and Magnetodielectric Properties.

We fabricate hybrid magnetoactive materials (hMAMs) based on cotton fibers, silicone oil, carbonyl iron and graphene nanoplatelets (nGr) at various mass concentrations . The obtained materials are used as dielectric materials for manufacturing plane electrical capacitors. The equivalent electrical capacitance and resistance are measured in an electric field of medium frequency f, without and respectively with a magnetic field of magnetic flux density B in the range from 0.1 T up to 0.5 T. The results are used to extract the components and of the complex relative permittivity , and to reveal the magnitude of the induced magnetoelectric couplings and magnetodielectric effects . It is shown that , , and MDE are significantly influenced by and . We describe the underlying physical mechanisms in the framework of dipolar approximation and using elements of dielectric theory. The tunable magnetoelectric and magnetodielectric properties of hMAMs are useful for manufacturing electrical devices for electromagnetic shielding of living organisms.

Calculations of energy deposition and ionization in the 2019 novel coronavirus by electron beam irradiation

Using Monte Carlo methods, this study investigates energy deposition of energetic electrons and ionization in the 2019 novel coronavirus by electron irradiation, which are important characteristic quantities related with biological damage formation. The inelastic scattering of low-energy electrons (<10 keV) was calculated by dielectric theory. The optical energy-loss functions of viral proteins and RNA were derived from an empirical method in the energy-loss range <40 eV and the calculation of optical parameters of the biomolecules. The densities and distributions of energy deposition and ionization were calculated from the stopping power and inelastic cross-sections in the electron-cascade simulation. Electrons with primary energies of approximately 1–3 keV produced significant energy deposition and ionization in the target coronavirus. More energetic electrons were less effective due to the larger electron range and fewer scattering events in the coronavirus.

Bond characteristics and microwave dielectric properties of (Li0.5Ga0.5)2+ doped Mg2Al4Si5O18 ceramics

Cordierite ceramic is one kind of important electronic materials for radio frequency circuit. In this work, Mg2-x (Li0.5Ga0.5)xAl4Si5O18 (0 ≤ x ≤ 0.1) ceramics with pure cordierite phase, were successfully synthesized via the traditional solid state reaction method. The dependence of microwave dielectric properties on the crystal structure was analyzed in detail by the complex chemical bond theory (P–V-L theory) and classical dielectric polarizability theory. The dielectric constant (εr) was mainly related to the density, bond ionicity and ionic polarizability of Mg2-x (Li0.5Ga0.5)xAl4Si5O18 ceramics. The quality factor (Q × f) was in relationship to the lattice energy, atomic packing fraction and centrosymmetry of [Si4Al2O18] hexagonal ring in cordierite crystal structure. The temperature coefficient of resonant frequency (τf) value was dominated by the bond energy and distortions of [MgO6] octahedron. The maximum values of Q × f = 50,560 GHz and εr = 4.72 were obtained for undoped Mg2Al4Si5O18 and Mg1.98Li0.01Ga0.01Al4Si5O18, respectively.

Deformation of Emulsion Droplet with Clean and Particle-Covered Interface under an Electric Field.

The electrohydrodynamic deformation of an emulsion droplet with a clean and particle-covered interface was explored. Here, the electrohydrodynamic deformation was numerically and experimentally demonstrated under the stimuli of moderate and strong electric fields. The numerical method involves the coupling of the Navier–Stokes equation with the level set equation of interface tracking and the governing equations of so-called leaky dielectric theory. The simulation model developed for a clean interface droplet was then extended to a capsule model for densely particle-covered droplets. The experiments were conducted using various combinations of immiscible oils and particle suspensions while the electric field strength ~105 V/m was generated using a high voltage supply. The experimental images obtained by the camera were post-processed using an in-house image processing code developed on the plat-form of MATLAB software. The results show that particle-free droplets can undergo prolate (deformation in the applied electric field direction) or oblate deformation (deformation that is perpendicular to the direction of the applied electric field) of the droplet interface, whereas the low-conductivity particles can be manipulated at the emulsion interface to form a ‘belt’, ‘helmet’ or ‘cup’ morphologies. A densely particle-covered droplet may not restore to its initial spherical shape due to ‘particle jamming’ at the interface, resulting in the formation of unique droplet shapes. Densely particle-covered droplets behave like droplets covered with a thin particle sheet, a capsule. The deformation of such droplets is explored using a simulation model under a range of electric capillary numbers (i.e., the ratio of the electric stresses to the capillary stresses acting at the droplet interface). The results obtained are then compared with the theory and experimental findings. It was shown that the proposed simulation model can serve as a tool to predict the deformation/distortion of both the particle-free and the densely particle-covered droplets within the small deformation limit. We believe that this study could provide new findings for the fabrication of complex-shaped species and colloidosomes.

Ab initio path integral monte carlo simulation of the uniform electron gas in the high energy density regime

The response of the uniform electron gas (UEG) to an external perturbation is of paramount importance for many applications. Recently, highly accurate results for the static density response function and the corresponding local field correction have been provided both for warm dense matter [2019 J. Chem. Phys. 151 194104] and strongly coupled electron liquid [2020 Phys. Rev. B 101 045129] conditions based on exact ab initio path integral Monte Carlo (PIMC) simulations. In the present work, we further complete our current description of the UEG by exploring the high energy density regime, which is relevant for, e.g. astrophysical applications and inertial confinement fusion experiments. To this end, we present extensive new PIMC results for the static density response in the range of 0.05 ≤ rs≤ 0.5 and 0.85 ≤ θ ≤ 8. These data are subsequently used to benchmark the accuracy of the widely used random phase approximation and the dielectric theory by Singwi, Tosi, Land, and Sjölander (STLS). Moreover, we compare our results to configuration PIMC data where they are available and find perfect agreement with a relative accuracy of 0.001 − 0.01%. All PIMC data are available online.

Rotational diffusion dynamics of Alexa flour dyes in aqueous organic environment

The rotational reorientation times of three dye probes namely Alexa fluor-350 (neutral but polar), Alexa fluor-430 (monoanion) and Alexa fluor-488 (dianion) were determined in series of binary mixtures of DMSO-water, DMA-water, and 2-propanol-water. All the three series of mixtures show bivalued profile for viscosity as a function of mole fraction of organic solvent in water. The dielectric properties such as dielectric constant (ε) and Debye dielectric relaxation time (τD) of solutions change considerably across the composition range. The variation of rotational reorientation time (τr) with viscosity (η) for all the probes is studied. Alexa fluor 350 and alexa fluor 488 show hook type profile in all the three series of aqueous mixtures with rotational reorientation time (τr) being longer in organic solvent rich zone compared to water rich zone mainly due to dielectric friction and hydrogen bonding. Alexa fluor 430 shows hook type profile in 2-propanol-water mixtures similar to other two probes but in DMSO-water and DMA-water it has almost linear profile as rotational reorientation dynamics is almost similar in both organic solvent rich zone and water rich zone. The hook type profiles obtained suggest the importance of local molecular structure of binary mixture and its interaction with probe. Results obtained are discussed in light of SED (hydrodynamic) theory, dielectric friction theories and friction due to hydrogen bonding.

Optical properties of molybdenum in the ultraviolet and extreme ultraviolet by reflection electron energy loss spectroscopy.

Optical properties of polycrystalline molybdenum are determined from ultraviolet up to extreme ultraviolet by reflection electron energy loss spectroscopy (REELS). Calculations are performed within the dielectric response theory by means of the quantitative analysis of electron energy losses at surfaces QUEELS-ϵ(k,ω)-REELS software [Surf. Interface Anal.36, 824 (2004)SIANDQ0142-242110.1002/sia.1774] that allows the simulation of inelastic scattering cross sections, using a parametric energy loss function describing the optical response of the material. From this energy loss function, the real and imaginary parts of the dielectric function, the refractive index, and the extinction coefficient are deduced and compared with previously published results.

Transient electrohydrodynamics of a liquid drop at finite Reynolds numbers

Transient electrohydrodynamics of a liquid drop at finite Reynolds numbers is studied by computer simulations. The governing equations of the problem are solved using a parallelized front tracking/finite difference method in the framework of the Taylor–Melcher leaky dielectric theory. The effect of the dielectric properties of the fluids on the dynamic response of the drop is studied by considering three representative fluid systems, which encompass all the regions of the deformation–circulation map. A parametric study is performed over a range of capillary number , the Ohnesorge number squared and the viscosity ratio to explore the effect of these parameters on the dynamic response. At low to intermediate capillary numbers, the dynamic response resembles that of a first- or second-order mechanical system, where the deformation settles to a steady state monotonically or through oscillations. However, beyond a threshold capillary number, the dynamic response becomes nonlinear. It is shown that the Ohnesorge number squared and the viscosity ratio are the key parameters that determine the transition from a monotonic response to an oscillatory one (and vice versa) in density-matched fluid systems. To predict the dynamic response of nearly spherical drops at arbitrary , an analytical equation is developed, which results in a critical Ohnesorge number squared that demarks a monotonic response from an oscillatory one. Investigations on the effect of the viscosity ratio on the dynamic response shows that the relaxation time (for monotonic response) increases with an increase in and that the steady state deformation correlates positively with for oblate drops; however, depending on the corresponding regions of prolate drops on the deformation–circulation map, correlates positively or negatively with . A long-standing misconception regarding the oblate region is also rectified by development of a normal stress map, which determines the relative importance of the electric pressure and the normal hydrodynamic stress in setting the sense of the deformation of the drop.

Equilibrium Solvation, Electron-Transfer Reactions, and Stokes-Shift Dynamics in Ionic Liquids.

A microscopic theory of solvent response by room-temperature ionic liquids is formulated based on the dynamic longitudinal susceptibility of liquid's charge density. The susceptibility function combines the structural information in terms of reciprocal-space structure factors with the memory function responsible for solvation dynamics. The charge-density structure factors and corresponding intermediate scattering functions are analyzed here by molecular dynamics simulations. They show the existence of two drastically different time scales of charge-density fluctuations. Faster, stretched-exponential dynamics are consistent with dielectric measurements. It contributes to the Stokes-shift dynamics of coumarin-153 optical dye calculated with the new theory and compared to experimental reports. The second, much slower and exponential, relaxation shows the phenomenology of de Gennes narrowing: the relaxation time passes through a strong maximum at the wave vector representing the first peak of the structure factor. This peak, which is particularly sharp for the charge density, contributes significantly to the equilibrium free energy of solvation, thus invalidating dielectric theories of solvation for ionic liquids. Dynamics of charge density fluctuations at the length scale consistent with the sharp peak require long observation times. Electron-transfer reactions occurring on faster time-scales are not affected by these slow dynamics. Nonergodic reorganization energy of electron transfer, accounting for the observation window established by the reaction time, drops sharply when the reaction rate crosses the main peak in the Stokes-shift loss spectrum. The dependence of the reorganization energy on the reaction rate strongly affects the energy-gap law of electron transfer, with a tendency for a shallow or entirely disappearing inverted region.

Transforming terahertz plasmonics within subwavelength hole arrays into enhanced terahertz mission via Smith-Purcell effect.

We illustrate the transformation of terahertz plasmonics within an array of rectangular sub-wavelength holes (RSHs) into coherent and enhanced terahertz emission via Smith-Purcell effect. The radiative plasmonic modes within each RSH of the array are successively excited by an free-electron beam, which then generate coherent radiation by constructive interference. Compared with the case without taking plasmonics into consideration, the radiation field intensity is enhanced by more than an order of magnitude, affording a promising way of developing high-power terahertz radiation. We perform detailed analysis of the plasmonic modes within the RSH by using the dielectric waveguide theory, and the results are verified by numerical simulations. The influences of the RSH parameters on the radiation properties are revealed and discussed.

Evaluating the Solvent Stark Effect from Temperature-Dependent Solvatochromic Shifts of Anthracene.

The solvent Stark effect on the spectral shifts of anthracene is studied with temperature‐dependent solvatochromic measurements. The Stark contribution Δv Stark to the absorption shift Δv p in polar solvents is measured to be Δv Stark=(53±35) cm−1, in reasonable agreement with dielectric continuum theory estimate of 28 cm−1, whereas the major shift Δv p∼300 cm−1 presumably originates from the solute quadrupole. We pay attention to the accurate correction of Δv p for the nonpolar contribution that is crucial when the shifts are modest in magnitude.