Changes In Dielectric Permittivity Research Articles

Structural and dielectric properties of (001) and (111)-oriented BaZr 0.2Ti 0.8O 3 epitaxial thin films

We have grown and characterized BaZr 0.2Ti 0.8O 3 (BZT) epitaxial thin films deposited on (001) and (111)-oriented SrRuO 3-buffered SrTiO 3 substrates by pulsed laser deposition. Structural and morphological characterizations were performed using X-ray diffractometry and atomic force microscopy, respectively. A cube-on-cube epitaxial relationship was ascertained from the θ–2 θ and φ diffractograms in both (001) and (111)-oriented films. The (001)-oriented films showed a smooth granular morphology, whereas the faceted pyramid-like crystallites of the (111)-oriented films led to a rough surface. The dielectric response of BZT at room temperature was measured along the growth direction. The films were found to be ferroelectric, although a well-saturated hysteresis loop was obtained only for the (001)-oriented films. High leakage currents were observed for the (111) orientation, likely associated to charge transport along the boundaries of its crystallites. The remanent polarization, coercive field, dielectric constant, and relative change of dielectric permittivity (tunability) of (111)-oriented BZT were higher than those of (001)-oriented BZT.

Ruthenium complex catalyzed oxidative conversion of aliphatic amines to carboxylic acids using bromamine-T: Kinetic and mechanistic study

Ruthenium(III) complex catalyzed oxidation of aliphatic amines with bromamine-T under alkaline condition proceeds efficiently to afford carboxylic acids in high conversion. Hexa-coordinated ruthenium(III) complex of the type [RuCl 2(PPh 3)(L)] (L, tridentate ligand derived by the condensation of o-phenylene diamine with salicylaldehyde) has been synthesized and it was used as a catalyst for the oxidative conversion of amines to carboxylic acids. The detailed mechanistic and kinetic investigations have been made for the oxidation reactions. Under similar experimental conditions all the amines proceed with a common oxidation mechanism and follows an identical kinetics with first-order dependence each on [Oxidant] o and [Amine] o, and fractional order with respect to [Catalyst] and [OH −]. To understand the detailed kinetics and mechanism of the reactions, the reactions have been subjected to changes in (i) dielectric permittivity, (ii) primary salt effect, (iii) halide ions and (v) temperature. The reactions were carried out at different temperature and the activation parameters have been calculated. From enthalpy–entropy relationships and Exner correlations, the isokinetic temperature ( β) of 382 K, calculated is much higher than the experimental temperature (313 K), indicating that, the enthalpy factor controls the rate. The observed results have been explained by a plausible mechanism and the related rate law has been deduced. The present method developed for the oxidation of amines to carboxylic acids by bromamine-T offers several advantages including high conversion, short reaction times, and stable, cost effective and relatively non-toxic reagents which make the reaction process simple and smooth.

Temperature induced dielectric polarization evolution in polycrystalline Pb(Cd 1/3Nb 2/3)O 3

The results of X-ray diffraction (XRD), scanning electron microscopy (SEM), dilatometric and dielectric measurements performed for the same polycrystalline Pb(Cd 1/3Nb 2/3)O 3 (PCN) sample are presented. These results reveal the complex character of polycrystalline PCN dielectric properties; in particular, no structural phase transition (PT) was observed. The thermal expansion coefficient indicates glass-like behaviour of PCN. The frequency and temperature dependencies of complex dielectric permittivity were measured and analyzed in terms of diffused/relaxor transition of the ferroelectric polarization. Temperature induced evolution of the relative dielectric permittivity was found to involve two processes. Dielectric permittivity changes, originating from thermally induced evolution of thermal equilibrium of interactions between main structural lattice and two sub-lattices present in the sample were interpreted in terms of thermal evolution of polar cluster sizes in the region of relaxor/glass-like transition.

Microstructural evolution and overall response of an initially isotropic ferroelectric polycrystal under an applied electric field

Based on the mechanism of domain switch in the constituent grains, a two-level micromechanical model is developed to study the microstructural evolution and nonlinear response of an initially isotropic, fully poled ferroelectric polycrystal under application of an electric field. First the reorientation process of ferroelectric domain in each crystallite is described by a kinetic equation and, with it and a dual-phase theory, its effective electromechanical moduli and polarization fields are determined. The overall response of the ferroelectric ceramic is then calculated self-consistently from the orientational average of its constituent grains. The developed theory is applied to a PLZT polycrystal with rhombohedral grains under an axial electric field. The calculated results provide significant insights into the heterogeneous evolution of new domain concentrations among the constituent grains, and illustrate how the initially isotropic polycrystal evolves into a transversely isotropic one. The changes of piezoelectric constant and dielectric permittivity of the polycrystal as the electric field increases are displayed, and the obtained overall electric displacement versus electric field ( D versus E) and strain versus electric field ( ε versus E) relations are found to be in general agreement with experimental observations.

Textured Microstructure and Dielectric Properties Relationship of BaNd2Ti5O14 Thick Films Prepared by Electrophoretic Deposition

AbstractAn alternative approach to tailor the temperature coefficient of permittivity (TCεr) of high Q dielectric BaO–Re2O3–TiO2 (Re: rare earth elements) thick films is presented. 10‐ to 80‐µm‐thick BaNd2Ti5O14 (BNT) films are fabricated by electrophoretic deposition on Pt foils under different processing conditions. Observed anisotropic grain growth is facilitated by constrained sintering. The increase of the sintering temperature increases markedly the aspect ratio of the grains, decreases the dielectric permittivity and TCεr changes from −114 to +12 ppm °C−1. By controlling the sintering temperature, near‐zero TCεr, high Q thick films can be fabricated with 45 < εr < 70. These findings are of technological relevance since they demonstrate that control of substrate constraint and sintering conditions can be used to control grain anisotropy and thus microwave properties of the BaO–Re2O3–TiO2. The thick films facilitate scaling to small device sizes for high frequency operation. Similar observations are expected in other microwave systems thus opening further technological opportunities.

Investigation of CdS thin films by a near-field microwave microprobe

Cadmium sulphide (CdS) thin films with different microstructures and morphologies were measured by using a near-field microwave microprobe (NFMM). The NFMM system was coupled to a dielectric resonator with a distance regulation system at an operating frequency f=4.1 GHz. The changes in dielectric permittivity of CdS thin films due to different annealing temperatures were investigated by measuring the reflection coefficient S 11. CdS thin films with different microstructures and morphology were characterized by X-ray diffraction, atomic force microscopy and NFMM.

Detection of methyl salicylate using polymer-filled chemicapacitors

Methyl salicylate (MeS) is used as a chemical warfare agent simulant to test chemical protective garments and other individual personal protective gear. The accurate and real-time detection of this analyte is advantageous for various testing regimes. This paper reports the results of MeS vapor exposures on polymer-filled capacitance-based sensors at temperatures ranging from 15 °C to 50 °C under dry and humid conditions. Multiple capacitors were arranged in an array on a silicon chip each having a different sorptive polymer. The sensors used parallel-plate electrode geometry to measure the dielectric permittivity changes of each polymer when exposed to water and MeS vapor. Of the four polymers tested against MeS, the optimal polymer displayed near or sub-parts-per-million detection limits at 35 °C (0–80%RH).

Decay of capacitance on ceasing formation of anodic oxide films on tantalum

The decrease with time in the capacitance of anodic oxide films on tantalum after ceasing film growth by reducing the field in the oxide was investigated. No dependence was observed of the amount and rate of change in relative dielectric permittivity on the initial current density. The kinetics of this effect are therefore different from those for the decay of the latent ionic conductivity.

Glassy dynamics in thin films of polystyrene

Glassy dynamics was investigated for thin films of atactic polystyrene by complex electric capacitance measurements using dielectric relaxation spectroscopy. During the isothermal aging process the real part of the electric capacitance increased with time, whereas the imaginary part decreased with time. It follows that the aging time dependences of real and imaginary parts of the electric capacitance were primarily associated with change in volume (film thickness) and dielectric permittivity, respectively. Further, dielectric permittivity showed memory and rejuvenation effects in a similar manner to those observed for poly(methyl methacrylate) thin films. On the other hand, volume did not show a strong rejuvenation effect.

Strain-mediated magnetoelectric coupling in BaTiO3-Co nanocomposite thin films

The authors present a metal-ceramic type composite film in which Co particles with the mean size of 70nm are uniformly dispersed in an insulating ferroelectric BaTiO3 (BTO) matrix. Transmission electron microscopy images revealed that the Co particle was tightly surrounded with the BTO matrix in atomic scales. The magnetostrictive strain-induced change in the relative dielectric permittivity was demonstrated by observing pronounced magnetodielectric effects under a static bias magnetic field. The present BTO-Co composite thin film also exhibited large dynamic magnetoelectric responses (160–170mV∕cmOe at 50kHz) at room temperature by virtue of a tight bonding between the two constituting piezoelectric and magnetostrictive phases.

Reliability of reverse properties of power semiconductor devices:: Influence of surface dielectric layer and its experimental verification

Reliability of reverse properties of power semiconductor devices is an important condition for their practical application. Usual standard tests do not reveal total information concerning the technological genetic aspects of devices production. These aspects can be linked with individual technological operations, most frequently with preparation of semiconductor surface and its protection by dielectric layers. Properties of dielectric layers influence the time stability of reverse currents by means of a change of dielectric permittivity. This article analyses some physical causes of the time-instable behaviour of devices and also presents a special method and equipment for reliable tests.

Investigation of 2-D electromagnetic transients in a circular cylinder with time discontinuity in permittivity via the resolvent method

The resolvent method approach is proposed for analytically solving the time domain Volterra integral equation (TDVIE) which describes the electromagnetic fields in 2-D cylindrical structures with time changes in the permittivity. It is shown that the approach allows investigation of the electromagnetic field transformation due to an abrupt time change in dielectric permittivity inside a circular cylinder as well as the construction of the Green’s function for an initial-boundary value problem. Key mechanisms of electromagnetic field transformation are investigated and a qualitative distinction of the processes is shown that depends on an initial field configuration.

Aging phenomena in polystyrene thin films

The aging behavior is investigated for thin films of atactic polystyrene through measurements of complex electric capacitance. During isothermal aging process the real part of the electric capacitance increases with aging time, while the imaginary part decreases with aging time. This result suggests that the aging time dependence of the real and imaginary parts are mainly associated with change in thickness and dielectric permittivity, respectively. In thin films, the thickness depends on thermal history of aging even above the glass transition. Memory and `rejuvenation' effects are also observed in the thin films.

Atomic scale patterns formed during surface scanning by atomic force microscopy tips

In this work, tip sliding at the water/substrate interfacial region was used to investigate the pattern observed during image acquisition with atomic resolution in atomic force microscopy. The process responsible for the pattern formation is the oscillatory movement of the tip in the direction that is normal to scanning induced by a change in the water interfacial dielectric permittivity from ε≈4 at the interface to ε≈80 (bulk value) that results in a variation of the measured force acting on the tip of ≈30pN.

Dielectric and Pyroelectric Properties of Pb[(Fe1/3Sb2/3)xTiyZrz]O3 Ceramics

The temperature dependence of pyroelectric and dielectric properties was measured for polycrystalline Pb[(Fe 1/3 Sb 2/3 ) x Ti y Zr z ]O 3 where x = 0.1, y = 0.4–0.5 and x + y + z = 1 in the temperature range from 300 K to 650 K. The total pyroelectric effect was determined by measuring the pyroelectric current. The changes of dielectric permittivity ϵ′ confirmed the temperature points of the phase transitions occurring in Pb[(Fe 1/3 Sb 2/3 ) x Ti y Zr z ]O 3 . Two diffused phase transitions are observed in the system. The paraelectric-ferroelectric transition near T m is demonstrated by a maximum of dielectric permittivity. The anomaly on ϵ′(T) dependence near 530 K for y = 0.43 speaks for ferroelectric(tetragonal)-ferroelectric(rhombohedral) phase transition. For y > 0.44 this transition is definitely diffuse and the coexistence of tetragonal and rhombohedral phases is observed in a wide temperature range around 530 K. The temperature dependences of the pyroelectric coefficient confirmed the diffuse character of phase transitions in Pb[(Fe 1/3 Sb 2/3 ) x Ti y Zr z ]O 3 .

Investigations on the electrical and structural properties of polyaniline doped with camphor sulphonic acid

Polyaniline is chemically synthesised and doped with camphor sulphonic acid. FTIR studies carried out on these samples indicate that the aromatic rings are retained after polymerisation. The percentage of crystallinity for polyaniline doped with camphor sulphonic acid has been estimated from the X-ray diffraction studies and is around 56% with respect to polyaniline emeraldine base. The change in dielectric permittivity with respect to temperature and frequency is explained on the basis of interfacial polarisation. AC conductivity is evaluated from the observed dielectric permittivity. The values of AC and DC conductivity and activation energy are calculated. The activation energy values suggested that the hopping conduction is the prominent conduction mechanism in this system.

Single-step fabrication and characterization of photonic crystal biosensors with polymer microfluidic channels

A method for simultaneously integrating label-free photonic crystal biosensor technology into microfluidic channels by a single-step replica molding process is presented. By fabricating both the sub-micron features of the photonic crystal sensor structure and the >10 microm features of a flow channel network in one step at room temperature on a plastic substrate, the sensors are automatically self-aligned with the flow channels, and patterns of arbitrary shape may be produced. By measuring changes in the resonant peak reflected wavelength from the photonic crystal structure induced by changes in dielectric permittivity within an evanescent field region near its surface, detection of bulk refractive index changes in the fluid channel or adsorption of biological material to the sensor surface is demonstrated. An imaging detection instrument is used to characterize the spatial distribution of the photonic crystal resonant wavelength, gathering thousands of independent sensor readings within a single fluid channel.

Chemical Bonding, Permittivity and Elastic Properties in Locally Modified Organosilicate Glass

AbstractChanging local electronic polarizability and chemical bonding in OSG in such a way that the effective permittivity - and consequently the electrical performance of the Cu/low-k structure - deteriorates only slightly and that adhesion and stiffness are improved significantly is an extremely challenging task [1], [2]. As the interconnect line spacings continue to shrink, optimization of the electrical and mechanical properties of the ILD material becomes increasingly important for Cu/low-k integration since the effect of thin regions that have been modified by special treatments on the effective material properties, e. g. keff, increases. Composition and chemical bonding, changed by plasma or beam treatments, effect the materials properties significantly. Plasma processes for resist stripping, trench etching and post-etch cleaning remove C and H containing molecular groups from the near-surface layer of OSG. Electron-beam interaction with OSG changes the chemical bonding in the low-k material. In this paper, the effect of chemical bonding on permittivity and elastic modulus is studied. Compositional analysis and chemical bonding characterization of structured ILD films with nanometer resolution is done with electron energy loss spectroscopy (EELS). The fine structure near the C-K electron energy loss edge, allows to differentiate between C-H, C-C, and C-O bonds, and consequently, between individual low-k materials and their modifications. Dielectric permittivity changes are studied based on VEELS (valence EELS) measurements and subsequent Kramers-Kronig analysis. The elastic modulus is determined with atomic force microscopy (AFM) in force modulation (FM) mode. Nanoindentation was applied as a complementary technique to obtain reference data.

Ageing of Adhesive Bonds with Various Surface Treatments, Part 1: Aluminium–Dicyandiamide Cured Epoxy Joints

ABSTRACT Ageing studies on adhesive-bonded aluminium–dicyandiamide cured epoxy joints prepared using a variety of different surface treatments were carried out using 100% humidity and cycling the joints between 42–48–42 °C every hour. The pretreatments include a chromic acid, silica/siloxane pretreatment, nonrinse chrome pretreatment, titanium/zirconium (Ti/Zr) pretreatment, and anodised substrate with no pretreatment. Dielectric spectroscopy measurements were used to characterise the rate of the water uptake and monitor the conversion of the surface oxide to hydroxide. These data were correlated with the changes that occurred in the mechanical strength of the bonds. The changes in the surface structure were observed using electron microscopy and elemental analysis conducted using X-ray photoelectron spectroscopy. The dielectric permittivity changes observed were similar for all the different pretreatments, indicating that the predominant process was water absorption. However, small differences were observed that reflect the different surface treatments used. Ageing at an elevated temperature of 70 °C provided definite evidence of hydration of the surface oxide layer. Electron microscopy of the fracture surface indicated oxide-to-hydroxide conversion and was reinforced by X-ray photoelectron spectroscopy. Predominantly, the changes in the mechanical strength observed at low temperature are consistent with the plasticization of the adhesive. However, at the elevated temperature of 70 °C, evidence for weakening of the interfacial layer by hydration becomes evident as a reduction in the mechanical strength. The dielectric measurements allowed the changes in the bond to be followed nondestructively. The mechanical strength of the etched-only pretreatment aged surprisingly well and at the lower temperature of ageing was comparable with the no-rinse chrome and titanium/zirconium pretreatments. The least durable was the PT2Cr-free treatment; however, all treatments showed a significant level of durability at low temperature.

Optical characterization of a dual-frequency hybrid aligned nematic liquid crystal cell

The dielectric anisotropy of a highly dispersive dual-frequency nematic liquid crystal (MDA-00-3969 (Merck KGa)) has been determined using the optical fully-leaky guided-mode technique. A 4Vrms sinusoidal voltage was applied across a 5microm hybrid aligned nematic (HAN) cell at various frequencies in both the positive and negative dielectric anisotropy regime. Optical data was collected at each frequency enabling the director profile in each case to be determined using a multi-layer optics model in combination with a liquid crystal free-energy minimization routine. The thresholdless response of the HAN cell combined with the extreme sensitivity of the optical characterization technique has allowed subtle changes in dielectric permittivity with frequency to be observed. The resulting measured dispersion shows excellent agreement with a single Debye-type relaxation model.