Frequency Dielectric Relaxation Research Articles

Effects of ion doping on the dielectric and electro-optical properties of chiral nematic liquid crystal

This study presents experimental findings pertaining to the use of the cationic surfactant cetyltrimethylammonium bromide (CTAB) as a dopant dispersed in cholesteric liquid crystal. The impact of the additive on the electrical and dielectric properties was investigated by dielectric spectroscopy. Compared with that in the pure counterpart, the dielectric relaxation frequency increased due to the added ions in the cholesteric liquid crystals impregnated with 0.01–0.5-wt% CTAB. Furthermore, by analyzing the dielectric spectra in a specific frequency range, the DC conductivity, ion density, and diffusion coefficient were calculated and compared. By fitting the experimental data into the Arrhenius equation, the activation energy was obtained as well. Our experimental results illustrated that all these physical properties were strongly dependent on the CTAB concentration and the temperature. This work also involved the electro-optical measurement in combination with the observation of optical texture. The ion addition provoked electrohydrodynamic flows in a surfactant-dispersed mixture, generating a homogeneous and transparent uniform lying helix state between two low-transmission optical states—the focal conic and dynamic scattering states. The operating frequency range of the dynamic scattering state was significantly broadened by the ionic dopant.

Exploring the role of impedance spectroscopy in assessing 405nm laser-induced inactivation of saccharomyces cerevisiae.

Impedance spectroscopy was employed to assess the electrical properties of yeast following 405nm laser irradiation, exploring the effects of visible, non-ionizing laser-induced inactivation as a more selective and safer alternative for photoinactivation applications compared to the use of DNA targeting, ionizing UV light. Capacitance and impedance spectra were obtained for yeast suspensions irradiated for 10, 20, 30, and 40min using 100 and 200 mW laser powers. Noticeable differences in capacitance spectra were observed at lower frequencies (40Hz to 1kHz), with a significant increase at 40min for both laser powers. β-dispersion was evident in the impedance spectra in the frequency range of 10kHz to 10MHz. The characteristic frequency of dielectric relaxation steadily shifted to higher frequencies with increasing irradiation time, with a drastic change observed at 40min for both laser powers. These changes signify a distinct alteration in the physical state of yeast. A yeast spot assay demonstrated a decrease in cell viability with increasing laser irradiation dose. The results indicate a correlation between changes in electrical properties, cell viability, and the efficacy of 405nm laser-induced inactivation. Impedance spectroscopy is shown to be an efficient, non-destructive, label-free method for monitoring changes in cell viability in photobiological effect studies. The development of impedance spectroscopy-based real-time studies in photoinactivation holds promise for advancing our understanding of light-cell interactions in medical applications.

Admittance Spectroscopy Study of Defects in β-Ga2O3

We present a comprehensive investigation of electrically active defects and transport properties in commercial (2¯01) edge-defined film-fed growth β-Ga2O3 using admittance spectroscopy measurements from 14 K up to 450 K. Isothermal capacitance-frequency measurements were conducted from 410 to 450 K to resolve a defect ∼0.8 eV below the conduction band edge and compared with deep-level transient spectroscopy and isothermal capacitance transient spectroscopy measurements. We report significant non-Arrhenius behavior of a defect ∼100 meV below the conduction band and apply the Arrhenius transformation matching method to extract its temperature-dependent activation energy and capture cross-section in the temperature range of 75 to 195 K. At low temperatures (<50 K), we use bias-dependent admittance spectroscopy to extract the electron mobility in β-Ga2O3 from the modified dielectric relaxation frequency. Finally, we discuss the potential of admittance spectroscopy for defect characterization in wide bandgap semiconductors in terms of the defect detection range, instrument requirements, and the frequency-temperature experiment space.

Probing Dielectric Relaxation of Water at Electrochemical Interfaces with Low-Frequency SERS Spectroscopy

Dynamic and structural properties of hydrogen-bonded water molecules in liquid phase have a significant impact on many chemical and biological processes in aqueous systems. Therefore, the bulk behavior of water is quite actively studied from both experimental and theoretical point of view. In the frequency domain, collective motions of water molecules appear in the terahertz (THz) range. For example, the central frequency of Debye-type dielectric relaxation of water exists at around 1 cm-1, and that of the so-called fast Debye relaxation is found at around 10 cm-1. There are several spectroscopic means to obtain such low-frequency information in the bulk liquid of water. However, for interfacial water molecules interacting with a solid surface, their dynamic behavior of hydrogen-bond networks remains unexplored in the experimental research field, despite of the importance of such behavior to molecular-level understanding of heterogeneous electrochemical processes. The reason for lack of such information is due to lack of adequate surface-selective spectroscopic means. In this talk, in-situ observation of the relaxational and vibrational dynamics of water at electrochemical interfaces is demonstrated using low-frequency surface-enhanced Raman spectroscopy (SERS). In this spectroscopic method, not only intermolecular dynamics but also intramolecular vibrational behaviors of water can be simultaneously monitored due to the intrinsic nature of the inelastic scattering technique accessible in the wide frequency range covering both THz and mid-IR regions, which helps us to understand the relation between microscopic and macroscopic behaviors of water molecules.To obtain low-frequency SERS spectrum, volume Bragg grating filters were used for both monochromatization of He-Ne laser radiation of 632.8 nm and removal of Rayleigh scattered light [1]. SERS-active Au electrodes were prepared by electrochemical surface roughening of Au surface in 0.1M KCl solution. For SERS-active Pt electrodes, monoatomic Pt overlayers were formed on the roughened Au surfaces. SERS spectra for interfacial water were measured on these electrode surfaces under application of electrochemical potentials. The measured spectra were converted to density states of formats by reducing the Purcell factor, Bose-Einstein thermal factor, and frequency factor, which can unveil vibrational features in low-frequency range [2-5].The measured spectra clearly showed potential-dependent features in the THz region. According to the previously reported spectra for bulk water, these features were assigned to the fast Debye relaxation component and two intermolecular vibration modes of interfacial water layer. By analyzing the observed spectral features by the assistance of classical molecular dynamics (MD) simulations, we found that the potential-induced change of water orientation causes formation of local defects in hydrogen-bonded networks of interfacial water layer and the lateral mobility of such defects on negatively charged surface is larger than that on positively charged surface [6]. Figure shows the dynamical behavior of potential-induced defects in hydrogen-bonded networks of interfacial water molecules on negatively and positively charge surfaces. The details will be discussed in the presentation.[1] M. Inagaki, K. Motobayashi, K. Ikeda, J. Phys. Chem. Lett., 8, 4236-4240 (2017).[2] M. Inagaki, T. Isogai, K. Motobayashi, K. -Q. Lin, B. Ren, K. Ikeda, Chem. Sci., 11, 9807-9717 (2020).[3] M. Inagaki, K. Motobayashi, K. Ikeda, Nanoscale, 12, 22988-22994 (2020).[4] R. Kamimura, T. Kondo, K. Motobayashi, K. Ikeda, Phys. Status Solidi B, 259, 2100589 (2022).[5] T. Kondo, M. Inagaki, K. Motobayashi, K. Ikeda, Catal. Sci. Technol., 12, 2670-2676 (2022).[6] T. Isogai, M. Inagaki, M. Uranagase, K. Motobayashi, S. Ogata, K. Ikeda, submitted. Figure 1

High pressures as an effective tool to separate different contributions to the electrode polarization of polar liquids and solids

Electrode polarization effects are an important issue in electrochemistry. Here we report investigation of electrode polarization effects in ethanol (used as a model material), in solid and liquid phases at high pressures. Application of pressure has dramatic effect on electrode polarization. Firstly, it significantly reduces the fractional power exponent, which dominates the low-frequency electrode polarization impedance, from approximately 1 at ambient pressure to less than 0.1 at 1.3 GPa. At pressure we can observe transition of electrode polarization impedance from fractional frequency law to inversely proportional to frequency relationship. This transition observed for the first time solves the problem with analytical limitation of electrode polarization effects at higher frequencies. Experimental data fitting by the procedure proposed by us, enables extracting the temperature dependencies of dielectric constant and dielectric relaxation frequency in the solid phase of ethanol at high pressures.

Collective Relaxation Processes in Nonchiral Nematics

Nematic–nematic transitions in a highly polar nematic compound are studied, in thick cells in which the molecules are aligned parallel to the substrates but perpendicular to the applied electric field, using dielectric spectroscopy in the frequency range 1 Hz to 10 MHz over a wide temperature range. The studied compound displays three nematic phases under cooling from the isotropic phase: ubiquitous nematic N; high polarizability NX; and ferroelectric nematic NF. Two collective processes were observed. The dielectric strength and relaxation frequency of one of the processes P2 showed a dependence on the thickness of the cell. The process P1 is the amplitude mode, while the process P2 is the phason mode.

Novel Dielectric Nanogranular Materials with an Electrically Tunable Frequency Response (Adv. Electron. Mater. 6/2023)

Granular-Type Frequency Filters Tunable frequency filters that can span a range of frequencies show promise in multi-band operation applications. In article number 2201218, Nobukiyo Kobayashi, Hiroshi Masumoto, and co-workers find that nanogranular materials, composed of nanoscale metallic granules within a host matrix, possess a controllable dielectric relaxation frequency by a DC electric field.

Formation of silver particles in [PVA:CS:PEG]-AgNO3 based biopolymer electrolyte membranes: Structural and electric transport properties study

[Chitosan (CS)-poly(vinyl) alcohol (PVA)-polyethylene glycol (PEG-200)]+xwt% silver nitrate (AgNO3) (x = 0, 10, 20, 30, 40) based biopolymer blend electrolytes (BPBEs) were prepared using solution casting method. FTIR results show the interaction of Ag+/NO3− with the constituents of polymers CS/PVA. XRD results reveal that the amorphousness increases with increasing AgNO3 concentration. Optical morphological (OM) images show that the silver, Ag(o) particles are agglomerated on the surface of the membrane. Temperature dependent dc conductivity (σdc) and dielectric relaxation frequency (fr) for BPBEs follow the Arrhenius type behavior and the sample containing 30 wt% salt has optimum dc conductivity, σdc∼1.7×10−4 S/cm at 30oC with lowest activation energy∼ 0.16 eV. The ac conductivity spectra follow the Jonscher's power law (JPL) with power law exponent, s > 1. The scaling of AC conductivity and loss tangent (tanδ) spectra were performed with respect to temperatures/concentrations of salt. The dielectric permittivity study reveals that the electrode polarization effect predominates at low frequencies. The Ionic Transference Number (ITN) measurement was used to determine the nature species of charge carrier, either ionic or electronic. The linear sweep voltammetry (LSV), result shows that 30% AgNO3containing sample has the electrochemical stability window (ESW) ∼+1.5 to -1.5 V.

Novel Dielectric Nanogranular Materials with an Electrically Tunable Frequency Response

AbstractThe electrical modulation of the functionality of matter is of significant interest in physics and multifunctional tunable electronic device applications. Here, new dielectric materials with nanogranular structures comprised of nano‐sized Co granular metals dispersed in a Mg‐fluoride‐based dielectric matrix are explored. The dielectric relaxation frequency (fr), which represents a sharp decrease in dielectric permittivity in dielectrics, can be tuned by a DC electric field (E). As E increases, the position of fr first shifts to the low‐frequency side and then to the high‐frequency side, achieving a tunable fr in a certain frequency range. The ability to electrically modulate the relaxation frequency may help construct novel tunable frequency filters. The dielectric properties are theoretically examined based on the asymmetric electron tunnelling model that considers the size difference of granular pairs, offering an insightful understanding of the structure‐property relationship in disordered granular solids.

Frequency and time domain characteristics of the insect visual system in optic flow

Frequency and time domain properties of the monochromatic, dichromatic, and trichromatic visual system in an insect have been studied. The research method is based on the representation of the optical flow field of the insect visual system in the form of a dynamic link with an input and output. The Gaussian function was used to approximate the spectral curves. The study of the inertial properties of such a link in the time domain was performed by applying signals to its input in the form of a δ-function or a unit function. The steady-state forced oscillations at the output of the investigated dynamic link are determined when a harmonic effect is applied to the input. A technique for constructing spectral sensitivity curves for monochrome, dichromatic, and trichromatic vision of insects in the frequency domain is proposed; it has been established that the spectra exhibit the properties of ultra wideband signals. It has been found that the dynamic link of the insect visual system is capable of amplifying the optical signal over ultraviolet and blue parts of the spectrum in the time and frequency domain. It has been revealed that at a frequency equal to or higher than the frequency of dielectric relaxation, the optical flow field of the insect's visual system does not sense electromagnetic radiation. This phenomenon is most pronounced in ultraviolet and blue parts of the spectrum. It has been established that the optical signal wideband index μ varies from 0.41 to 1.21; thus, the visual system of an insect has ultra wideband properties. It has been shown that the number of periods of light oscillations in the visual system of insects, which has a spectrum in the form of a Gaussian curve, is related to the exponent μ by a simple relationship. New knowledge gained can be used for creation of matrix solid-state photodetectors in ultraviolet and blue parts of the spectrum.

Improved piezoelectricity of porous cellulose material via flexible polarization-initiate bridge for self-powered sensor

Self-powered piezoelectric sensors based on cellulose nanocrystal (CNC) porous materials are light-weight and portable, whereas using unmodified CNCs can hardly obtain enough piezoelectric properties without external strong polarization due to its irreversible deformation caused by low toughness. Here, we bonded rod-like CNCs with a soft polymer, poly ethylene glycol (PEG), and hypothesized that PEG could toughen the material and its dielectric signal could induce the CNC polarization. We further adsorbed graphene (GR) as surface electrodes to prepare a CNC-PEG-GR piezoelectric porous material with density of 0.096 g·cm−3. The voltage output reached maximum when the frequency matched the dielectric relaxation frequency of PEG. We also increased the length-diameter ratio of porous material pores from 1.1 to 3.3 by adjusting its freeze-drying process, and the voltage output could reach to 0.7 V at a moderate ratio. They could be conveniently integrated into portable self-powered sensors applied to the intelligent wearable electronic devices.

Structure, Dielectric, and Electrochemical Studies on Poly(Vinylidene Fluoride‐Co‐Hexafluoropropylene)/IonicLiquid 1‐Ethyl‐3‐Methylimidazolium Tricyanomethanide‐Based Polymer Electrolytes

Solid polymer electrolyte films blended with ionic liquid 1‐ethyl‐3‐methylimidazolium tricyanomethanide (EMImTCM) and poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVdF‐HFP) are prepared via solution cast technique. The physical characterization of polymeric film is performed by X‐ray diffraction (XRD), polarized optical microscopy (POM), Fourier transform infrared spectroscopy (FTIR), and thermo‐gravimetric analysis (TGA) studies. The gel electrolyte film with 300 wt% of IL shows the high ionic conductivity value of 3.7 × 10−2 S cm−1, and operating voltage from −0.5 to 1.5 V, i.e., electrochemical stability window (ESW) ≈ 2.0 V. The dielectric properties of the polymeric films such as dielectric constant, dielectric loss tangent (Tan δ), relaxation frequency, and time are evaluated.

Frequency dependence of dielectric permittivity and conductivity of functionalized carbon nanotube-nematic liquid crystal nanocomposite

The addition of carbon nanotubes (CNTs) to nematic liquid crystal (NLC) medium is known to enhance the orientational order along with the enhancement in electro-optical and dielectric properties of the liquid crystal (LC). The studies on the dielectric behavior of LC-nanocomposites at wide range frequencies are essential for optimizing the LC based device performances. The nanocomposites of octadecylamine functionalized single-walled carbon nanotubes (ODA-SWCNTs) with NLC are studied with the aid of dielectric spectroscopy. The important parameters of LCs relevant to display related applications such as dielectric permittivity, relaxation frequency, threshold voltage, and conductivity are investigated over a wide range of frequency and temperatures in planar as well as homeotropic configurations. The doping of ODA-SWCNTs into the NLC increases the local orientational order in the nematic matrix due to the strong interaction between LC and CNT molecules. The optimum doping decreases threshold voltage due to enhancement of dielectric anisotropy and decrease in splay elastic constant. The experimental data obtained from impedance spectroscopy measurements are fitted with a suitable equivalent electric circuit model, and the estimated electrical components are studied as a function of temperature. Investigation on interfacial and bulk properties of pure and ODA-SWCNT nanocomposites of 7CB NLC are also discussed.

Highly luminescent nanocomposites of nematic liquid crystal and hybrid quantum dots CdSe/CdS with ZnS shell

This work is focused on synthesis of highly luminescent hybrid CdSe/CdS ”core/shell” quantum dots (QDs) with different core sizes and an additional ZnS shell. These quantum dots were doped into a nematic liquid crystal (NLC) phase to obtain new composites. According to the dielectric and femtosecond laser spectroscopy data, sizes of the QD cores and built-up additional ZnS shells are correlated with luminescence and dielectric characteristics of the ZhK-1282 and QD composites. With larger QD cores in the ZhK-1282, a decrease in dielectric relaxation frequency of the LC molecules rotating around their short axis is observed, same for the activation energy of this process. A shift to a shorter wavelength of the LC main luminescence peak and the strong luminescence quenching effect can be observed for the composites with the 2 nm QD cores. This effect is the result of nonradiative excitation energy transfer from LCs to QDs in the composite. The adhesion work values have been calculated for all the samples, alignment substances and substrates. Optimized homeotropic aligning layers with the best composite anchoring parameters have been selected both for normal glass and glass with a sputtered indium tin oxide (ITO) layer.

DIELECTROMETRIC STUDY OF RADIATION PROTECTION ABILITY OF ULTRA-DISPERSED NANODIAMONDS

Radiation protection ability of the ultra-disperse nanodiamonds (UDD) is studied based on the measurements of dielectric permittivity of red blood cells (RBC) affected by cancer. Wistar rats with Guerin's carcinoma were treated by X-ray 5.8 Gy. Some rats received UDD with food during 5 days prior to the X-ray. The groups with UDD, X-ray, and both UDD and X-ray treatments were compared to the control group. The complex dielectric permittivity of the RBC was measured by microwave dielectrometry. It was shown, tumor development leads to the increase in the dielectric permittivity and relaxation frequency. The irradiation promotes further growth of the parameters, while UDD uptake leads to insignificant changes in comparison to the control group. Therefore, UDD occur the radioprotective effect promoting repair, compensation and restoration of body tissues that is demonstrated by normalization of the dielectric parameters of RBC.

RELAXATION FREQUENCY SHIFT IN TRIGLYCINE SULFATE UNDER THE INFLUENCE OF SILICA NANOPARTICLES AT LOW FREQUENCIES

The present work is devoted to clarifying the influence of silica nanoparticles on dielectric relaxation frequencies of a classical ferroelectric – triglycine sulfate at low frequencies (102 – 107 Hz) from 20 ˚C to phase transition point for composite samples prepared at different composition weight ratios. Theresults indicated the reduction of relaxation frequency with increasing the silica content due to the intensified interaction between nanoparticles and tryglycine sulfate inclusion. The nature of this interaction was thoroughly discussed in this study.

Effect of carbonaceous oil palm leaf quantum dot dispersion in nematic liquid crystal on zeta potential, optical texture and dielectric properties

In the present work, the dispersion of oil palm leaf based carbonaceous quantum dots (OPL QDs) in nematic liquid crystal (NLC) E 48 eutectic mixture has been reported. The dispersed systems with concentrations 0.1, 0.2, and 0.3 wt% are designated respectively, as MIX 1, MIX 2, and MIX 3. The objective of this study is to analyze the results on the zeta potential, optical texture, dielectric constant, dielectric loss, conductivity, dielectric strength, relaxation frequency, specific power loss and total power loss of pure and OPL QDs dispersed nematic E 48 system. Zeta potential measurement has been performed in the solution state to ensure dispersion stability. The optical textures and dielectric results are recorded after filling the respective samples in sample cells. The core findings in the present study show that the zeta potential varies from − 23.43 mV to + 28.07 mV that signifies the stability of OPL QDs suspension in LCs. Specific power loss (SPL) and total power loss (TPL) are found to be least for MIX 1 which shows that the problem of high power consumption in LCDs can be resolved by dispersing a small weight percent concentration of OPL QDs in LC medium (MIX 1). Improved molecular alignment in the dispersed system has been observed from the textural study which finds its application in good contrast display devices. The color change in the aligned textures with temperature has been attributed to the birefringence change. The porous nature of carbonaceous OPL QDs has its application in supercapacitors. The benchmark results of this study highlight the effect of temperature and frequency on dielectric parameters for both planar and homeotropic state of E 48 LCs. OPL QDs dispersed system display increased conductivity for MIX 3. The decrease in the activation energy for OPL QDs dispersed system in comparison to pure LC material E 48 is a consequential result of the potential barrier change. The increment in the dielectric strength and relaxation frequency of OPL QDs dispersed system is noticed in comparison to pure E 48. These outcomes open the door for the applicability of present LCs in the field of both display and non-display devices like sensors, supercapacitors, low power consumption displays, energy conversion, and electrical storage devices as well as advanced smart systems.

A PCB Sensor for Detecting Icing Events

Ice formation can be problematic on surfaces, such as roads, bridges, wings, and sensitive plants. A simple low-cost sensor for detecting the formation of ice has been developed using standard low-cost commercial printed circuit board fabrication techniques. The sensor consists of a capacitive interdigitated electrode structure, realized in the top Cu layer of the circuit board and covered with a polymeric solder mask. The sensor's capacitance is measured at 1 and 64 kHz, and then, the ratio of the two capacitances is computed. The ratio is then compared with a threshold value of 2.0. Icing results in the capacitance ratio exceeding 2.0, whereas dry conditions or water result in a ratio of less than 2.0. This technique exploits the dielectric relaxation properties of ice, in which ice has a high dielectric constant below the relatively low dielectric relaxation frequency of ≤3 kHz and a low dielectric constant well above that frequency. The sensor was evaluated in air, water, and ice over a temperature range of −30 to 34 °C and successfully identified ice every time.

Capacitance Measurement of Cerium Oxide Thin Film Capacitors

IntroductionCerium oxide (CeOx) is an attractive material for large volume on-chip decoupling capacitors, owing to its high dielectric constant (k) of 28. Commonly, a definite frequency dispersion in the small-signal capacitance measurement is observed in the frequency sweep, and larger capacitance values can be obtained at low frequency in the kHz range. The dielectric relaxation is reported to originate from the interface polarization between the polycrystalline grains in the films. In this work, the thickness-dependent polarization and the capacitance measurement under a DC voltage application are characterized.Fabrication processCeOx films with thicknesses from 8 to 20 nm were deposited by e-beam evaporation on an n+Si substrate with a W layer atop. Another W layer was deposited on CeOx layers and patterned to form electrodes. After the Al back contact formation, the samples are annealed at 420oC.ResultsFig. 1 shows the frequency dispersion of the capacitors with different CeOx thicknesses measured at 0 V. The dielectric relaxation frequency shifts to higher frequency while thinning the thickness, which is useful for capacitor application. The transient current upon 1 V application is shown in fig. 2. After a high charge current, one can observe a decay in the transient current, indicating the delay in the polarization. The capacitance of the samples can be obtained by taking the integral of the charge current and is shown in fig. 3. Comparable capacitance values were obtained with the small-signal measurements. 2 to 3 times higher capacitance values can be achieved with respect to the ionic polarization.ConclusionHigh capacitance values measured in the small-signal setup were confirmed by direct current measurement by DC voltage application. An even higher capacitance can be obtained with the thinner film.

Phase Change Behavior of NaCl-H2O Binary Solution Under the Control of AC Electric Field

Cryopreservation, which refers to preservation of cells or tissues at subzero temperatures, inevitably involves the problem of cryoinjury caused by ice crystals. The application of an external electric field during the freezing process has been shown to be a promising approach to produce miniature ice grains and decrease the fraction of ice crystallization at a slow cooling rate. Thus, the dielectric and thermodynamic properties of NaCl-H2O binary solutions at subzero temperatures were tremendously important for understanding the mechanism of ice formation under the manipulation of an AC electric field in biopreservation. However, there was still a lack of relevant information in the literature. The first objective of this study was to systematically measure the dielectric spectrum of 0.9% NaCl-H2O binary solutions at temperatures ranging from -100°C to 0°C with a cooling/heating rate of 2°C/min. We further measured the thermodynamic properties of a 0.9% NaCl-H2O binary solution while applying a series of electric fields near its dielectric relaxation frequency. The effect of the electric field on the crystal morphology was studied last. Pure water was selected as the control group. The results showed that an AC electric field can alter the thermodynamic process and thus the phase transition and ice crystal structure could be manipulated. It was concluded that the AC electric-assistant preservation method will be a promising technology in cryopreservation.