Dielectric spectroscopy of aluminum oxide (γ-Al2O3)

Aluminum oxide (Al2O3) are continuously demonstrating the functional characteristics in devices. The physiochemical properties of hydrothermally as-grown Aluminum oxide (Al2O3) have been investigated in this research article. The as-prepared material was confirmed as γ- phase formation of Al2O3. The average crystallite size was found ∼ 78 nm, whereas the particles were found in nano scale too. Moreover, the absence of impurity in EDS analysis, and the presence of the bending vibrations of Al-O-Al and Al-O band in FTIR characterization further confirmed the absence of impurity in the material. Evaluated dielectric properties such as a relatively high dielectric constant, and low dielectric loss indicated the good optical quality of γ- Al2O3. Impedance and modulus spectroscopic studies showed the non-Debye type relaxation in γ- Al2O3 with an average relaxation time of 5.8 μs. Overall, the dielectric spectroscopy analysis of γ- Al2O3 indicates the promising applications of γ- Al2O3 in devices as dielectrics.

Universal law for the vibrational density of states of liquids

An analytical derivation of the vibrational density of states (DOS) of liquids, and, in particular, of its characteristic linear in frequency low-energy regime, has always been elusive because of the presence of an infinite set of purely imaginary modes—the instantaneous normal modes (INMs). By combining an analytic continuation of the Plemelj identity to the complex plane with the overdamped dynamics of the INMs, we derive a closed-form analytic expression for the low-frequency DOS of liquids. The obtained result explains, from first principles, the widely observed linear in frequency term of the DOS in liquids, whose slope appears to increase with the average lifetime of the INMs. The analytic results are robustly confirmed by fitting simulations data for Lennard-Jones liquids, and they also recover the Arrhenius law for the average relaxation time of the INMs, as expected.

Analysis of Transport Properties of the Randomly Moving Electrons in Metals

In this critical analysis on the base of randomly moving (RM) electrons, presented the resistivity dependence on temperature for elemental metals both above and below the Debye’s temperatures. There also are presented the general relationships for estimation of the average diffusion coefficient, the average velocity, mean free path and average relaxation time of RM electrons on the Fermi surface at mentioned temperature range. It is shown that the scattering of RM electrons mainly is due to electronic defects associated with distortion of the periodic potential distribution in the periodic lattice, and accounting the exchange of the thermal energies between phonon and RM electron. The calculation results of resistivity dependence on temperature in the temperature range from 1 K to 900 K are demonstrated for Au and W and compared with the experimental data. There also is presented the simple method for determination of the basic kinetic characteristic dependences on temperature only from the resistivity dependence on temperature. It is at first time determined for Au and W the temperature dependences of the mean free path, average diffusion coefficient, average relaxation time of RM electrons from 1 K to 900 K.

Physical Meanings of Fractal Behaviors of Water in Aqueous and Biological Systems with Open-Ended Coaxial Electrodes

The dynamics of a hydrogen bonding network (HBN) relating to macroscopic properties of hydrogen bonding liquids were observed as a significant relaxation process by dielectric spectroscopy measurements. In the cases of water and water rich mixtures including biological systems, a GHz frequency relaxation process appearing at around 20 GHz with the relaxation time of 8.2 ps is generally observed at 25 °C. The GHz frequency process can be explained as a rate process of exchanges in hydrogen bond (HB) and the rate becomes higher with increasing HB density. In the present work, this study analyzed the GHz frequency process observed by suitable open-ended coaxial electrodes, and physical meanings of the fractal nature of water structures were clarified in various aqueous systems. Dynamic behaviors of HBN were characterized by a combination of the average relaxation time and the distribution of the relaxation time. This fractal analysis offered an available approach to both solution and dispersion systems with characterization of the aggregation or dispersion state of water molecules. In the case of polymer-water mixtures, the HBN and polymer networks penetrate each other, however, the HBN were segmented and isolated more by dispersed and aggregated particles in the case of dispersion systems. These HBN fragments were characterized by smaller values of the fractal dimension obtained from the fractal analysis. Some examples of actual usages suggest that the fractal analysis is now one of the most effective tools to understand the molecular mechanism of HBN in aqueous complex materials including biological systems.

Dielectric properties of single wall carbon nanotubes-based gelatin phantoms

In this work, we report the dielectric properties of Single wall Carbon Nanotubes (SWCNTs)-based phantom that is mainly composed of gelatin and water. The fabricated gelatin-based phantom with desired dielectric properties was fabricated and doped with different concentrations of SWCNTs (e.g., 0%, 0.05%, 0.10%, 0.15%, 0.2%, 0.4% and 0.6%). The dielectric constants (real [Formula: see text] and imaginary [Formula: see text] were measured at different positions for each sample as a function of frequency (0.5–20[Formula: see text]GHz) and concentrations of SWCNTs and their averages were found. The Cole–Cole plot ([Formula: see text] versus [Formula: see text] was obtained for each concentration of SWCNTs and was used to obtain the static dielectric constant [Formula: see text], the dielectric constant at the high limit of frequency [Formula: see text] and the average relaxation time [Formula: see text]. The measurements showed that the fabricated samples are in good homogeneity and the SWCNTs are dispersed well in the samples as an acceptable standard deviation is achieved. The study showed a linear increase in the static dielectric constant [Formula: see text] and invariance of the average relaxation time [Formula: see text] and the value of [Formula: see text] at room temperature for the investigated concentrations of SWCNTs.

Investigating the dielectric properties and low-frequency relaxation process of TlGaSe2 crystals

The dielectric and impedance spectra of TlGaSe2 crystals have been studied at temperatures in the 100–500 K range in the alternating current (AC [Formula: see text]1 V). It has been shown that the conductivity of TlGaSe2 crystals is mainly an ionic characteristic at temperatures above 400 K. The well-defined peak at the frequency dependence of the imaginary part of impedance [Formula: see text] is observed in the 215–500 K temperature range. In a constant field, there occurs a significant decrease in electrical conductivity [Formula: see text] in due course. The ionic contribution to conductivity (76% at [Formula: see text]) has been estimated from a kinetic change in electrical conductivity [Formula: see text] under the influence of a constant electric field. The diagram analysis in a complex plane [Formula: see text] has been conducted by applying the method of an equivalent circuit of the substation. It has been determined that the average relaxation time of the electric module of the sample is [Formula: see text].

Effect of changing water salinity on complex conductivity spectra of sandstones

We analyzed the influence of pore fluid composition on the complex electrical conductivity of three sandstones with differing porosity and permeability. The fluid electrical conductivity ([Formula: see text]) of sodium and calcium chloride solutions was gradually increased from 25 mS/m to 2300 mS/m. The expected linear relation between [Formula: see text] and the real component of electrical conductivity ([Formula: see text]) of the saturated samples was observed. The imaginary component ([Formula: see text]) exhibits a steeper increase at lower salinities that flattens at higher salinities. For a glauconitic sandstone and a high porosity Bunter sandstone, [Formula: see text] approaches an asymptotic value at high salinities. Sodium cations result in larger values of [Formula: see text] than calcium cations in solutions of equal concentration. Debye decomposition was used to determine normalized chargeability ([Formula: see text]) and average relaxation time ([Formula: see text]) from spectral data. The behavior of [Formula: see text] is comparable to [Formula: see text] as both parameters measure the polarizability. At lower salinity, the relation between [Formula: see text] and [Formula: see text] approximates a power law with an exponent of [Formula: see text]. The average relaxation time shows only a weak dependence on [Formula: see text]. The normalized chargeability of sandstone samples can be described by the product of the pore space related internal surface and a quantity characterizing the polarizability of the mineral-fluid interface that depends on fluid chemistry. We introduce a new parameter, the specific polarizability, describing this dependence. We propose relations between polarizability and fluid chemistry that could be used to estimate pore space internal surface across samples of varying [Formula: see text]. We observe a consistent maximum polarizability for quartz dominated siliceous material.

ULTRAFAST HEAT DISSIPATION DYNAMICS OF SILVER NANOPARTICLES

Time-resolved fluorescence spectroscopy has been employed to study the ultrafast heat dissipation dynamics of silver nanoparticles dispersed in methanol, tetrahydrofuran, and hexane. The average relaxation time obtained is in the order of several hundreds of picoseconds indicating lack of band-edge emission where lack of scaling of these times with the thermal conductivity of the surrounding medium indicate disparate heat dissipation pathways.