Change In Dielectric Constant Research Articles

Effects of Dy2O3 on the Dielectric Property, Phase Composition, and Microstructure of the Low Temperature Sintered Aln Ceramics

The effects of Dy2O3 on the phase composition, microstructure, and the dielectric property, especially, dielectric constant, of AlN ceramics sintered at low-temperature (1650oC), were investigated systematically. X-ray diffraction (XRD) was employed to indentify the phase compositions of the ceramics during the sintering. Scanning electronic microscopy (SEM) was used to observe the microstructures of the AlN ceramics. The results show that the dielectric constant changes with the amount of Dy2O3. When the amount of Dy2O3 is less than 0.93 wt.%, the dielectric constant increases with the increased amount of Dy2O3. The dielectric constant of the AlN ceramics is higher than 200 when the amount of Dy2O3 is 0.93 wt.%. However, when the amount of Dy2O3 is more than 0.93 wt.%, the dielectric constant decreases with the increased amount of Dy2O3. The dielectric constant of the AlN ceramics with 1.87 wt.% Dy2O3 is only about 15, which closed to the theoretical value of pure AlN ceramics. The analysis illuminated that the grain phases changed from Al2O3-rich aluminate to AlDyO3 which existed at triple pockets with the increased amount of Dy2O3, the former can improve the dielectric constant greatly due to ion relaxation polarization.

Coulomb Green’s function and image potential near a planar diffuse interface, revisited

In this work, we revisit the problem of calculating the Coulomb Green’s function and the image potential near a planar diffuse interface in which the dielectric constant changes continuously in a transition layer between two dielectrics. In particular, we extend previous work in two ways. Firstly, a new diffuse interface model, termed the quasi-harmonic interface model, is constructed, for which analytical calculation of Green’s function and the image potential is easy to achieve and need not use any special function. Secondly and also more importantly, a robust semi-analytical numerical procedure to build Green’s functions for general diffuse interface models is developed in analogy to the analysis of transmission lines, thus opening the way to treat in principle any well-behaving and physically plausible dielectric permittivity profile for the transition layer. Numerical experiments are given to illustrate the quasi-harmonic diffuse interface model, and to validate the semi-analytical numerical method particularly by demonstrating its convergence as the number of the sublayers used to partition the transition layer goes to infinity.

Influence of the temperature and deformation‐dependent dielectric constant on the stability of dielectric elastomers

AbstractThe performance of dielectric elastomers is affected by temperature and deformation, but very few models account for the effect of both factors. Recent experiments showed that the dielectric constant of the most widely used dielectric elastomer varies significantly with respect to temperature and deformation. We propose a model to study the influence of changes in dielectric constant on the electromechanical stability of dielectric elastomer. The model predicts the stability criteria with physical interpretation of its dependence on dielectric constant and electrostrictive coefficient. The numerical simulation indicates that the stress due to electrostriction relies on the temperature and deformation dependent dielectric constant and contributes to enhance the stability of the dielectric elastomer. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

The effect of PECVD plasma decomposition on the wettability and dielectric constant changes in silicon modified DLC films for potential MEMS and low stiction applications

We have carried out investigations aimed at understanding the mechanism responsible for a water contact angle increase of up to ten degrees and a decrease in dielectric constant in silicon modified hydrogenated amorphous carbon films compared to unmodified hydrogenated amorphous carbon films. Our investigations based on surface chemical constituent analysis using Raman spectroscopy, x-ray photoelectron spectroscopy (XPS), SIMS, FTIR, contact angle / surface energy measurements and spectroscopic ellipsometry suggests the presence of hydrophobic chemical entities on the surface of the films. This observation is consistent with earlier theoretical plasma chemistry predictions and observed Raman peak shifts in the films. These surface hydrophobic entities also have a lower polarizability than the bonds in the un-modified films thereby reducing the dielectric constant of the silicon modified films measured by spectroscopic ellipsometry. Ellipsometric dielectric constant measurement is directly related to the surface energy through Hamaker's constant. Our current finding is expected to be of benefit to understanding stiction, friction and lubrication in areas that range from nano-tribology to microfluidics.

Damage by radicals and photons during plasma cleaning of porous low-k SiOCH. II. Water uptake and change in dielectric constant

Porous dielectric materials provide lower capacitances that reduce RC time delays in integrated circuits. Typical low-k materials include porous SiOCH—silicon dioxide with carbon groups, principally CH3, lining the pores. With a high porosity, internally connected pores provide pathways for reactive species to enter into the material. Fluorocarbon plasmas are often used to etch SiOCH, a process that leaves a fluorocarbon polymer on the surface that must later be removed. During cleaning using Ar/O2 or He/H2plasmas,reactions of radicals that diffuse into the SiOCH and photons that penetrate into the SiOCH can remove –CH3 groups. Due to its higher reactivity, cleaning with Ar/O2plasmas removes more –CH3 groups than He/H2 plasmas, and so produce more free radical sites, such as –SiO2• (a –SiO2–CH3 site with the –CH3 group removed).Upon exposure to humid air, these free radical sites can chemisorb H2O to form hydrophilic Si–OH which can further physisorb H2O through hydrogen bonding to form Si–OH(H2O). With the high dielectric constant of water, even a small percentage of water uptake can significantly increase the effective dielectric constant of SiOCH. In this paper, we report on results from a computational investigation of the cleaning of SiOCH using Ar/O2 or He/H2plasmas and subsequent exposure to humid air. The authors found that plasma cleaning with He/H2 mixtures produce less demethylation than cleaning with Ar/O2plasmas, as so results in less water uptake, and a smaller increase in dielectric constant. The water that produces the increase in dielectric constant is roughly half chemisorbed and half physisorbed, the latter of which can be removed with mild heating. Sealing the pores with NH3plasma treatment reduces water uptake and helps prevent the increase in dielectric constant.

Ion Transport with Charge-Protected and Non-Charge-Protected Cations in Alcohol-Based Electrolytes Using the Compensated Arrhenius Formalism. Part I: Ionic Conductivity and the Static Dielectric Constant

The temperature dependence of ionic conductivity and the static dielectric constant is examined for 0.30 m TbaTf- or LiTf-1-alcohol solutions. Above ambient temperature, the conductivity increases with temperature to a greater extent in electrolytes whose salt has a charge-protected cation. Below ambient temperature, the dielectric constant changes only slightly with temperature in electrolytes whose salt has a cation that is not charge-protected. The compensated Arrhenius formalism is used to describe the temperature-dependent conductivity in terms of the contributions from both the exponential prefactor σo and Boltzmann factor exp(-Ea/RT). This analysis explains why the conductivity decreases with increasing temperature above 65 °C for the LiTf-dodecanol electrolyte. At higher temperatures, the decrease in the exponential prefactor is greater than the increase in the Boltzmann factor.

Magnetodielectric effect in CdS nanosheets grown within Na-4 mica

CdS nanosheets of thickness 0.6 nm were grown within the interlayer spaces of Na-4 mica. Magnetization measurements carried out in the temperature range 2–300 K showed the composites to have weak ferromagnetic-like properties even at room temperature. The saturation magnetization (MS) at room temperature was found to be higher than that reported for CdS nanoparticles. The higher value of MS may be ascribed to the presence of a large number defects in the present CdS system, due to a large surface to volume ratio in the nanosheets as compared to that of CdS nanoparticles. The nanocomposites exhibited a magnetodielectric effect with a dielectric constant change of 5.3% for a magnetic field of 0.5 T. This occurred due to a combination of magnetoresistance and Maxwell-Wagner effect as delineated in the model developed by Catalan.

Mechanical, electrical, and thermal properties of irradiated low-density polyethylene by electron beam

The effect of electron-beam (EB) irradiation on the mechanical, electrical, and thermal properties of low-density polyethylene (LDPE) was studied The LDPE was irradiated by using 3 MeV EB machine at doses ranging from 25 to 250 kGy in air at room temperature and analyzed for mechanical, thermal, and electrical properties. It was revealed by differential scanning calorimetry analysis that the crystallinity of the EB-radiated LDPE decreased slightly as verified by a marginal reduction in the densities, enthalpy, and melting points. Thermogravimetric analysis test showed that the thermal degradation of LDPE improved by increasing irradiation. The results obtained from both gel content and hot set tests, indicating whether the applicable LDPE has been properly cross-linked or not, showed that under the EB irradiation conditions employed, the cross-linking of the LDPE samples occur mainly in the amorphous region, and the cross-linking density at each irradiation dose depends almost on the amorphous portions of the LDPE. A significant improvement in the tensile strength of the neat LDPE samples was obtained upon EB up to 250 kGy with a concomitant decline in elongation at break. The results on the electrical properties revealed that the surface resistance, volume resistivity, and dielectric strength of the LDPE increase with irradiation dose and reaches a maximum at a 250 kGy irradiation dose. No considerable change of breakdown voltage, dielectric constant, and dielectric loss factor were observed with increasing irradiation dose. The enhancement in the heat deformation, hardness, and thermal aging properties of LDPE upon EB irradiation, suggests that irradiated LDPE is more thermally and mechanically stable than virgin LDPE.

Effect of ultra-fine fly ash on the dielectric behavior of CFSC under stress

Small size particle of ultra-fine fly ash was contributed to the dispersion of carbon fiber in composite in the preparation process. The dispersibility of carbon fiber in composite was associated with self-sensing property of composite. The effect of ultra-fine fly ash on the change in relative dielectric constant of carbon fiber sulphoaluminate cement composite under stress was investigated. The sensitivity, accuracy and reversibility of the change in relative dielectric constant under stress have been improved when 10% content (by mass of cement) of ultra-fine fly ash was added into carbon fiber sulphoaluminate cement composite (CFSC). Besides promoting micro capacitor creation, ultra-fine fly ash could endow CFSC with excellent mechanical property and weaken the ions polarization effect. The combination of above three effects upgraded the dielectric behavior of CFSC under stress.

Capacitive humidity sensors based on the dielectrophoretically manipulated ZnO nanorods

In this paper, the capacitive relative humidity sensors based on dielectrophoretically manipulated ZnO nanostructure were constructed and studied. The humidity-sensitive ZnO nanorods were first synthesized by the thermal decomposition technique and deposited among the micromachined electrodes pairs via dielectrophoretic manipulation. The manipulated samples were detected as the capacitive sensors in which the nanostructured ZnO acted as the sensing elements. The capacitive humidity sensors were constructed by detecting the variations of the ZnO dielectric constant changing with the humidity environment. The results showed that the sensor had high humidity sensitivity, good stability, fast response/recovery time and well reproducibility. The dielectrophoresis manipulation can also improve the sensitivity of the sensor efficiently.

Improved light scattering and surface plasmon tuning in amorphous silicon solar cells by double-walled carbon nanotubes

Surface plasmon resonance was observed to red shift in hexagonal nanohemisphere Ag array covered by double-walled carbon nanotubes. By altering the density of carbon nanotubes, the surface plasmon resonance can be tuned from 563nm to 586nm and the light scattering is enhanced in the spectral range from orange to red. This leads to improved performance of amorphous silicon solar cells deposited on top, which yields a short-circuit current density of 14.07mA/cm2 and a power conversion efficiency of 6.55% under the illumination of AM 1.5G. This carbon nanotubes' density-dependent surface plasmon shift is attributed to the dielectric constant change around the periodic Ag nanostructure, which can be applied to other solar cell materials by fine-tuning the surface plasmon resonance to enhance the absorption at wavelength where the active layer is less absorptive.

Single-Walled Carbon Nanotubes Based Chemicapacitive Sensors

Carboxylated single-walled carbon nanotubes (SWNTs) based chemicapacitive gas sensors were fabricated by AC dielectrophoretically aligning SWNTs across microfabricated gold electrodes with controlled density/device resistance. Two different sensing configurations (i.e., horizontal/in-plane and vertical/out-of-plane) were utilized to compare their sensing performance. Upon exposure to water vapor at room temperature, the response (R = [(C--C0)/C0] x 100%) increased with an increase in water vapor concentration similar to that of resistance response. In horizontal configuration, the response was increased with an increase in device resistance which might be attributed to preferentially alignment of semiconducting SWNTs during initial phase of alignment. However, the response was independent of device resistance in vertical/out-of-plane configuration which indicated that the sensing mechanism is based on the change of dielectric constant of gate and atmosphere.

Modulation of surface plasmon wave by photo-induced refractive index changes of CdSe quantum dots

We demonstrate an all-optical modulation of surface plasmon resonance by photo-irradiation induced dielectric constant change of CdSe quantum dots on the gold surface. The dipole-dipole interaction between the surface plasmon and the photo-induced excitons in the dots gives rise to a shift in the surface plasmon resonance peak. This shift is found to sensitively reflect a tiny change in the dielectric constant, which is useful for investigating the nonlinear effect in active plasmonic components.

Speciation of ternary complexes of lead(II), cadmium(II) and mercury(II) with L-dopa and phenanthroline in propanediol-water mixtures

The formation constants of ternary complexes of title systems have been determined pH-metrically in biologically relevant conditions at an ionic strength of 0.16 mol dm-3 and 303 K. The overall stability constants have been evaluated using MINIQUAD75 computer program. The complexation equilibria have been derived on the basis of species distribution diagram. In the present study L-Dopa and 1, 10-phenanthroline are found to be compatible ligands, proving greater stability of ternary complexes as compared to binary ones. The trend in variation of stability constants with change in dielectric constant of medium is explained on the basis of electrostatic and non-electrostatic forces. Distributions of the species with pH at different compositions of propanediol-water mixtures are also presented. The factors responsible for the compatibility of both the ligands have also been discussed.

Synthesis, Structure, Thermal and Electrical Behavior of La-Doped Bismuth Titanate Ceramics

In this paper, we report the properties of bismuth titanate (Bi4Ti3O12, BIT) based nano powders with variation of La content synthesized by well known conventional solid state reaction method. These BIT based ceramic samples sintered above 1000°C had density in the range of 95 to 98% of the theoretical density. The effect of La-doping on structural, thermal and electrical properties of BIT has been studied. The results of XRD, TGA-DSC showed the presence of La-content which shifts the peaks to higher level. The change of dielectric constant, dc conductivity of BIT ceramics were observed as increase in the La concentration from x = 0 to 0.45.

Stability Constants of Some Biologically Important Pyrazoles and Their Ni2+Complexes in Different Dielectric Constant of Medium

The proton-ligand stability constants of some biologically important new pyrazoles and formation constants of their complexes with Ni(II) were determined at 0.1 mol dm-3ionic strength and at 303.15 K in different dielectric constant of dioxane-water mixture by potentiometric method. The Calvin-Bjerrum's pH-titration technique as used by Irving and Rossotti was used for determination of stability constants. The results enabled to study the electrostatic forces of attraction between metal ion and ligand with changes in dielectric constant of the medium.

Magneto electret State of Porous Polypropylene and Investigation on Surface Charge Characteristics

This paper reports preparation of porous polypropylene magneto electret and its investigation on its surface charge characteristics. The electrets were prepared under the combined action of heat and magnetic field. Influences of polarizing temperature and magnetic field on MEs state of polypropylene were studied. Five different forming temperatures and five different magnetic field strength were used for the surface charge study of magnetoelectrets. Surface charge was found to be of the order of 10 -10 C. Negative iso charge was found in all the magnetoelectrets. The decay of surface charge was studied continuously for 30 days and corresponding time constant were calculated. Keywords - Dielectric, Magnetoelectrets (MEs), porous polypropylene, magnetic field, surface charge. I. INTRODUCTION Dielectric samples showing persistent polarization is termed as 'Electrets' (1) in analogy with magnet because in many ways an electret is the electrostatic counterpart of magnet. The first electret resembling Heaviside's was prepared by Eguchi (2) by solidifying the molten mixture of carnauba wax and resin in an intense electric field. In an electret, the dielectric is in state of persistent polarization, i.e. the polarized state continues to stay in the dielectric for considerably long time even after the removal of polarizing field. Electrets are classified depending on the physical agency that produces polarization in dielectric under the influence of an external field. The various types of electrets known so far are thermo, photo, radio, cathode, electro and magneto etc. In 1964, Bhatnagar (3) while observing the effect of magnetic field on carnauba wax for detecting Hall Effect, found that magnetic field in conjunction with heat energy (physical agency), could bring about the polarization in carnauba wax. The study of initial charge, i.e surface charge measured immediately after the electret formation, its subsequent reversal in polarity and decay with time and the amount of residual charge (final charge) almost permanently retained by it, has helped a great deal in understanding the electret state in the dielectric. The method of study of charge trapped within the electreted dielectric, by the modern technique of thermally stimulated current (TSC), (4) has added much more to our knowledge about the electret state. Thus the study of surface charge is one of the basic and important studies; hence it is undertaken for the porous polymers polypropylene for the present work. From the study of surface charge on magnetoelectret, Khare and Bhatnagar propounded a 'Two charge Theory (5) analogous to the two charge theory of Gross and Gemant (6) on thermoelectret. According to the two charge theory on magnetoelectret, the net surface charge is the resultant of two types of charges known as the 'isocharge' and the 'idiocharge'. The isocharge is the charge of the same sign on the surface of electret which may be +ve or -ve depending upon the substance while idiocharge is a charge due to polarization of the dielectric which has opposite charges on the opposite surfaces of electret. The two charge theory which explains the magnetoelectret surface charge is later found to be capable of explaining several phenomena associated with the magnetoelectret state in the dielectric, such as change in dielectric constant, refractive index susceptibility etc. In present study, The surface charge study on porous polypropylene magneto electrets consists in the study of initial charge on either surface of the sample and its dependence on various forming parameters, such as strength of the magnetic field, the constant elevated temperature subsequent measurement of surface charge is done continuously for about a month, to study the possible reversible of charge, its decay with time and the charge finally retained by the sample. These studies give an assessment of strength, stability and retentivity of charge, besides providing us with information regarding the polarization process responsible for the induction of magnetoelectret state in the substance. The results of surface charge study are discussed in the following sections.

Signal enhancement of protein binding by electrodeposited gold nanostructures for applications in Kretschmann-type SPR sensors

We propose a novel Kretschmann-type surface plasmon resonance (SPR) sensor chip having a surface covered with electrodeposited gold nanostructures to enhance the sensitivity of SPR biosensing. The nanostructure is three-dimensional and has a larger surface area than a conventional flat surface chip, which increases the amount of protein binding and also induces a large change in the effective dielectric constant of the sensing area. The gold nanostructures were formed by electrodeposition under galvanostatic conditions, so their size could be controlled by manipulating the deposition time and current. The sensing characteristics, including the concentration dependence and noise level, indicated that the performance of the resulting chip (called a Au-black chip) was equivalent to that of a conventional sensor chip. We also determined the optimal electrodeposition conditions to obtain a sharp SPR curve for protein detection assay; the optimal thickness of the gold layer was 50-60 nm. Enhanced protein sensing was demonstrated by using a binding assay of anti-BSA antibody and BSA molecules. The protein binding signal was several times higher than that of the conventional assay. The insights into electrodeposition for SPR sensing presented here will enable improved sensitivity for detecting low-concentration and small proteins.

Carbon-Nanotube-Based FR-4 Patch Antenna as a Bio-Material Sensor

This paper presents the development and design of proximity coupled feed patch antenna as a bio-sensor. This sensor system consists of a two-layer Flame Retardant (FR-4) patch antenna coated with Multi Walled Carbon Nanotubes (MWCNTs) for absorbing bio-molecules. The best design of patch antenna is chosen based on simulation results using Computer Simulation Technology (CST) microwave studio software. After adding bio-material on the top of antenna and interaction with MWCNTs based on the changes in the effective dielectric constant, the resonant frequency of patch antenna is changed. Experimental results have shown 1 MHz change in resonant frequency of patch antenna upon exposure to ethanol. Based on operating frequency (5 GHz) this technique can be used in network sensor systems to measure bio-materials in future research.

Slow light in one dimensional metallic-dielectric photonic crystals due to sign change of the effective dielectric constant

We numerically show slow light can be achieved in one dimensional metallic-dielectric photonic crystals as a result of sign change of the effective dielectric constant. Due to the occurrence of slow light, rainbow trapping effect is realizable in chirped one dimensional metallic-dielectric photonic crystals where thicknesses of metal slabs linearly increase. The results imply the potential applications in constructing nanoscale optical buffer, memories, filter, sorter, etc. for high density integration of optical circuits.