AC Electrical Characterization Research Articles

Ultrafine iron particles/polystyrene composites: effects of gamma radiation and manufacture aging on the AC electrical characterization

The present investigation deals with the effects of the (gamma) γ-radiation and samples’ aging on the ac electrical properties of ultrafine iron polystyrene composites. The composites with an average thickness of 1.07 mm contain different iron particle concentrations (10, 20 and 30) by weight %. The results show that the ac electrical properties of the γ-irradiated composites are different from the non-irradiated ones. Rather relative changes in values after irradiation were registered for the impedance, dielectric constant, and the ac electrical conductivity. After irradiation, both the conductivity and the dielectric constant are enhanced relatively with the impedance becoming relatively lower in value. Also, the results show that the age of the samples affects the ac electrical properties of the tested composites. It has been found that after a few years, the electrical conductivity of the composites becomes lower in value compared to what it was a few years ago, which indicates that composites tend to lose their desired electrical properties with passage of time. So, as a potential solution for this physical behavior, the samples were exposed to γ-radiation in an attempt to enhance the metal–polymer bonding and release more free electrons within the composites. The properties such as impedance, dielectric constant, electrical conductivity of the composites were studied before and after γ-irradiation. Later, these studied electrical properties were compared with results reported few years ago. The frequency range applied in this study is consistent with Jonscher’s power law model.

Label-free, ultrasensitive and rapid detection of FDA-approved TBI specific UCHL1 biomarker in plasma using MWCNT-PPY nanocomposite as bio-electrical transducer: A step closer to point-of-care diagnosis of TBI

Traumatic Brain Injury (TBI), a major cause of mortality and neurological disability affecting people of all ages worldwide, remains a diagnostic and therapeutic challenge to date. Rapid, ultra-sensitive, selective, and wide-range detection of TBI biomarkers in easily accessible body fluids is an unmet clinical need. Considering this, in this work, we report the design and development of a facile, label-free, highly stable and sensitive, chemi-impedance-based sensing platform for rapid and wide range detection of Ubiquitin-carboxy terminal hydrolase L1 (UCHL1: FDA-approved TBI specific plasma biomarker), using carboxylic functionalized MWCNTs embedded polypyrrole (PPY) nanocomposites (PPY/f-MWCNT). The said nanocomposites were synthesized using chemical oxidative polymerization method. Herein, the functionalized MWCNTs are used as conducting fillers so as to increase the polymer's dielectric constant according to the micro-capacitor model, thereby augmenting both DC electrical conductivity and AC dielectric property of the nanocomposite. The proposed immunosensing platform comprises of PPY/f-MWCNT modified interdigitated microelectrode (IDμEs) array, on which anti-UCHL1-antibodies are immobilized using suitable covalent chemistry. The AC electrical characterization of the nanocomposite modified IDμEs, with and without the antibodies, was performed through generic capacitance vs. frequency (C–F, 1 KHz – 1 MHz) and capacitance vs. applied bias (C–V, 0.1 V–1 V) measurements, using an Agilent B1500A parametric analyzer. The binding event of UCHL1 peptides to anti-UCHL1-antibodies was transduced in terms of normalised changes in parallel capacitance, via the C–F analysis. Further, we have tested the detection efficiency of the said immunoassay against UCHL1 spiked human plasma samples in the concentration range 10 fg/mL – 1 μg/mL. The proposed sensing platform detected UCHL1 in spiked-plasma samples linearly in the range of 10 fg/mL – 1 ng/mL with a sensitivity and LoD of 4.22 ((ΔC/C0)/ng.mL−1)/cm2 and 0.363 fg/mL, respectively. Further, it showed excellent stability (30 weeks), repeatability, reproducibility, selectivity and interference-resistance. The proposed approach is label-free, and if desired, can be used in conjunction with DC measurements, for biosensing applications.

Ultrafine Iron Particles/ Polystyrene Composites: Effects of Gamma Radiation and Manufacture Aging on the Ac Electrical Characterization

Ultrafine Iron Particles/ Polystyrene Composites: Effects of Gamma Radiation and Manufacture Aging on the Ac Electrical Characterization

Structure and AC electrical characterization for amorphous Se50Te50 thin-film fabricated by thermal evaporation technique

Se50Te50 alloy has been successfully fabricated utilizing the common melt quench technique. The Se50Te50 film was deposited onto a well-cleaned glass substrate at 298 K by thermal evaporation method. The film's thickness (~500 nm) was monitored by a quartz crystal monitor. Dielectric permittivities (ε′,ε″), dissipation factor, tan(δ), conductivity, σAC, modulus (M′,M″) and impedance parts (Z′,Z″)were determined based on the capacitance-voltage (Cm–V) and conductance-voltage (Gm/ω-V) measurements. AC electrical conductivity has two contributes, electronic and ionic conductivity. The main structural characteristics were checked utilizing EDAX, X-ray and SEM measurements.

Synthesis of graphene oxide and copper phthalocyanine, AC electrical characterization and tuning the bandgap of RGO-CuPc composite

Graphene oxide (GO) was synthesized in our laboratory by the improved Hummer’s method. Reduced graphene oxide/Copper Phthalocyanine (RGO-CuPc) composite was prepared through the chemical reduction of GO by Hydrazine hydrate. This composite was analyzed by FT-IR, UV–vis spectroscopy, FESEM microscopy, and the results showed that CuPc molecules were successfully attached on RGO sheets by π-π intermolecular interaction. Also, UV–vis spectroscopy results showed that the tuning of the bandgap is applicable for RGO-CuPc composite. Sandwich devices of RGO-CuPc thin film with aluminum electrodes (Al/RGO-CuPc/Al) were fabricated to investigate the AC electrical properties of RGO-CuPc composite over the frequency range of 102–105 Hz and temperature range of 298–393 K. The band theory is applicable to explain the thin film conduction mechanism. Also, this composite acts as a semiconductor with high electron mobility.

Alternating Current Electrical Characterization of Plasma Polymerized Pyrrole Thin Films

The alternating current (ac) electrical characterization of plasma polymerized pyrrole (PPPy) thin films have been discussed in this article. A parallel plate capacitively coupled glow discharge reactor was used to deposit PPPy thin films. To study the ac electrical conduction in the thin film, the variation of ac conductivity and dielectric constant of different thicknesses were investigated as the function of frequency and temperature. The observed frequency dependence of the ac conductivity is attributed to relaxations caused by the motion of electrons, which could be involved to hopping or tunneling between equilibrium sites. It is also concluded that, the ac conduction mechanism in PPPy thin films shows the correlated barrier hopping (CBH) model. The strong dependence of conductivity on frequency and the low activation energies of the carriers are also an indication of a hopping conduction mechanism at low temperatures. At high temperatures it may be due to the movements of thermally excited carriers from energy levels within the band gap. In conductivity vs temperature study a weak dependence of σac on temperature is observed which interprets the ac conduction mechanism as the hopping between localized states at the Fermi level. The observed frequency dependence of the dielectric constant in this study is attributed to the interfacial or space charge polarization and to the orientational polarization of molecular chains. On the other hand, the strong temperature dependence of dielectric constant at higher temperature and lower frequencies is attributed to the thermally activated electron hopping mechanism.

Synthesis and characterization of La3+ ions incorporated (PVA/PVP) polymer composite films for optoelectronics devices

Polymer rare-earth composite films PVA/PVP–xLa3+ (xwt%; x = 0, 3, 5, 10, and 15) were fabricated by the solution casting method. The structural parameters of these films were determined from X-ray diffraction (XRD) pattern analysis, and the complexation of La3+ ions with the polymer composite films was studied by Fourier transform infrared (FT-IR) spectroscopy. The optical energy gap (Eopt.) and the high-frequency refractive index (n) were determined from UV–Vis transmission spectra analysis. AC electrical conductivity and dielectric characterization of the polymer composite films have been investigated. The structural parameters of the inter-planar (d) spacing, crystallite length (D), and the average crystallite separation (R) and the FT-IR spectra indicate strong bonding of La3+ ions with the carbonyl groups of the polymer composite chains. The optical gaps of the films determined by Tauc’s relation and optical absorption fitting (ASF) exhibit a slight decrease by increasing La3+ ions content, whereas the refractive indices show a slight increase. High values of the dielectric parameter e′ and dielectric loss e″ were produced in pure PVA/PVP composite polymer films, and they tend to decrease by increasing La3+ ions content in the PVA/PVP composite films due to decreasing directional polarization and ionic polarization in the films with increasing La3+ ions content. The minimum energy loss occurred at 70 kHz and these materials may be selected to be used in energy applications. I–V characteristics show a linear-like ohmic behavior because La ions are bonded well in the structure of polymers and became part of it.

Synthesis and ac electrical characterization of nickel oxide nanofibers

In this study, we present the synthesis of nickel oxide nanofibers through electrospinning technique at optimum processing and heat treatment conditions. The diameter and uniformity of electro-spun nickel oxide nanofibers were investigated as a function of PVP concentration. Uniform and homogeneous composite nanofibers were observed for PVP:Ni(CH3COO)2·H2O ratio of 1:1. X-ray diffraction and scanning electron microscopy of samples calcined at 600 °C revealed the formation of uniform but porous single phase nickel oxide nanofibers of an average diameter Electrical properties of nickel oxide nanofibers, obtained at optimum conditions, were studied using inter-digitated electrodes type device. Temperature-dependent impedance spectroscopy revealed different electro-active regions (grain and grain boundaries) and their activation energies were 0.24 and 0.36 eV, respectively. These results suggested less resistive grain than grain boundary in the employed temperature range, and hence, two different transport mechanisms.

Influence of Cu incorporation on ionic conductivity and dielectric relaxation mechanism in NiO thin films synthesized by CBD

We present the influence of copper incorporation on ionic conductivity and dielectric relaxation mechanism of NiOthin films deposited by chemical bath deposition (CBD) method in this report. Structural and optical characterization of NiO and Cu:NiO thin films were carried out using XRD and UV–Vis spectroscopy. Increase in grain size and decrease in average microstrain in doped films were confirmed from XRD analysis. The spectrophotometric measurement shows band gap decreases with increase in dopant concentration. Impedance spectroscopy, modulus spectroscopy and dielectric study has been performed for ac electrical characterization. Impedance spectroscopy analysis confirmed enhancement of ac conductivity withCu incorporation suggesting an increase in charge carrier concentration due to doping. Enhancement in both real and imaginary part of dielectric constant was observed with Cu doping in NiO thin films. Activation energy to electrical transport process was determined from dc conductivity analysis and migration energy of charge carriers was determined from modulus spectroscopy analysis. Cole–Cole plot shows both grain and grain boundary contributes towards total resistance and capacitance. The overall resistance was found to decrease with Cu incorporation in NiO thin film. The observed results suggest hopping mechanism of charge carriers towards electrical conduction process.

Influence of Mn incorporation on ionic conductivity and dielectric relaxation process in CBD synthesized CdO thin films

We present the influence of manganese incorporation on ionic conductivity and dielectric relaxation mechanism of CdO thin films synthesized by chemical bath deposition (CBD) method. Structural, optical and ac electrical characterization of CdO and Mn:CdO thin films has been carried. The materials were characterized using X-ray diffraction and UV-VIS spectrophotometer. Increase in grain size and decrease in average microstrain in doped films were confirmed from XRD analysis. Decrease in band gap in doped films were observed from spectrophotometric measurements. Impedance spectroscopy analysis confirmed enhancement of ac conductivity with Mn incorporation suggesting an enhancement in charge carrier concentration due to doping. Enhancement in both real and imaginary part of dielectric constant was observed with Mn doping. Cole-Cole plot shows contribution of both grain and grain boundary towards total resistance and capacitance. The overall resistance was found to decrease with Mn incorporation in CdO film. Activation energy to electrical transport process was determined from dc conductivity analysis and migration energy of charge carriers was determined from modulus spectroscopy analysis. The observed results suggest hopping mechanism of charge carriers towards electrical conduction process.

Structural, optical and ac electrical characterization of CBD synthesized NiO thin films: Influence of thickness

We have studied the electrical conductivity, dielectric relaxation mechanism and impedance spectroscopy characteristics of nickel oxide (NiO) thin films synthesized by chemical bath deposition (CBD) method. Thickness dependent structural, optical and ac electrical characterization has been carried out and deposition time was varied to control the thickness. The material has been characterized using X-ray diffraction and UV-VIS spectrophotometer. Impedance spectroscopy analysis confirmed enhancement of ac conductivity and dielectric constant for films deposited with higher deposition time. Decrease of grain size in thicker films were confirmed from XRD analysis and activation energy of the material for electrical charge hopping process was increased with thickness of the film. Decrease in band gap in thicker films were observed which could be associated with creation of additional energy levels in the band gap of the material. Cole-Cole plot shows contribution of both grain and grain boundary towards total resistance and capacitance. The overall resistance was found to decrease from ~ 14.6 × 105Ω for 30min deposited film (~ 120nm thick) to ~ 2.42 × 105Ω for 120min deposited film (~307nm thick). Activation energy value to electrical conduction process evaluated from conductivity data was found to decrease with thickness. Identical result was obtained from relaxation time approach suggesting hopping mechanism of charge carriers.

Impact of tungsten oxidation conditions on the performance of Al2O3/WOx-based CBRAM devices

In this paper, we assess the impact of different W oxidation conditions on the electrical performance of Cu/Al2O3/WOx-based CBRAM devices. While HR-TEM characterization carried out on samples with three different oxidation conditions reveals that WOx is always in the crystalline phase in our oxidation temperature range, higher oxidation temperature leads to denser and thicker oxides. By performing DC and AC electrical characterization, we demonstrate that a careful engineering of the W oxidation conditions enables to boost the performance of these devices. In particular, we prove that a trade-off between density and thickness must be pursued in order to enlarge the memory window and extend the endurance lifetime with short (10ns) pulses.

Temperature and composition dependent density of states extracted using overlapping large polaron tunnelling model in MnxCo1−xFe2O4 (x=0.25, 0.5, 0.75) nanoparticles

We report detailed ac electrical and structural characterization of manganese cobalt ferrite nanoparticles, prepared by coprecipitation technique. X-ray diffraction (XRD) confirmed single-phase cubic spinel structure of the nanoparticles. Tetrahedral (A) and octahedral (B) group complexes were present in the spinel lattice as determined by Fourier Transform Infrared Spectroscopy (FTIR). Scanning Electron Microscope (SEM) images revealed presence of spherical shape nanoparticles having an average diameter ~50–80nm. Composition, temperature and frequency dependent ac electrical study of prepared nanoparticles interpreted the role of cationic distribution between A and B sites. Overlapping large polaron tunnelling (OLPT) conduction mechanism was observed from 290 to 200K. Frequency exponent s was fitted theoretically using OLPT model. High values of Density of States (DOS) of the order of 1022–1024eV−1cm−3 were extracted from ac conductivity for different compositions. We found that DOS was dependent on distribution of cations in the tunnel-type cavities along the a and b axis.

Temperature-Dependent and Dielectric Relaxation of Porous Silicon Prepared by Electrochemical Etching

In the electronic devices based on porous silicon (PS) is important understand the physical mechanisms governing the electrical behaviour in the PS/c-Si structure. In order to investigate the conduction mechanisms in the PS/p-Si heterojunction, we prepared the PS by electrochemical etching. The temperature dependence of the porous silicon was studied in the range from 240 K to 320 K. On the other hand, the AC electrical measurements were performed from 101 to 107 Hz in a range of 0,7 to 1,2 V, at room temperature. The calculated activation energies were close to 0,90 eV. The physical mechanisms involved in the Ag/porous silicon contacts and porous silicon/p-Si interface can be obtained from the voltage dependence of the fitting parameters according to electrical model circuits in DC and AC. We found the dielectric behavior of the samples; the relaxation region is presented at high frequency and at low temperatures resulting in a long dielectric relaxation time. The best known metalloid element for semiconductor manufacturing is the chemical element silicon; technologies based on this element are present in our daily lives, but silicon has its limitations. In crystalline form, it is not considered useful as magnetic, biomedical, or optical material. Thereby, this is where development and research for this material are important. Porous silicon has attracted much attention because of its low dimensional semiconductor structure. Since the first work by Koshida et al. [1] there have been published several papers dedicated to the DC and AC electrical characterization of porous silicon layers [2-4]. The electrical properties of these devices are strongly dependent not only on the properties of porous silicon, also on the quality of the metal/PS or PS/Si interfaces [5-7]. AC impedance analysis is a powerful tool and has been widely used to analyze the electrical performance of both metal-semiconductor junctions and p-n junctions [1,5]. The analysis of the frequency-capacitance-voltage characteristics present in an ideal abrupt junction has to be studied to understand the three capacitances effects in the heterojunction PS/c-Si as Low-Frequency Dispersion phenomenon (LFD), depletion capacitance (Cdep) and geometric capacitance (C0) [7]. An important aspect in these structures is the electrical contacts analysis on the PS layer and what is the dependence behavior when the voltage and temperature is variable [4]. Various authors have been reported different mechanism, Schottky junctions due to the metal contact [8], the Ohmic conduction is dominated by the bulk resistance [9] and the power law Space Charge Limit Current (SCLC) [7].

Bionanoelectronics Platform with DNA Molecular Wires Attached to High Aspect-Ratio 3D Metal Microelectrodes

In this study, the investigation of attachment of DNA molecular wires and ropes to high aspect-ratio three-dimensional (3D) metal microelectrodes and their subsequent electrical characterization as part of a bionanoelectronics platform is reported. The 3-D microelectrode architecture consists of mainly high aspect-ratio microelectrode structures (75 μm height and above) patterned from relatively thick layers of negative tone photoresist and covered by sputtered gold on their top surface. DNA attachments on 3-D microelectrode structures was demonstrated using oligonucleotide-DNA self-assembly and thiol-gold covalent bonding. Further, DC and AC electrical characterization of double-stranded λ-DNA molecular wires in a dry environment and suspended between high aspect-ratio 3D microelectrodes 75 μm away from the substrate (to heights unprecedented so far in the literature which thereby eliminate interference of substrate) is presented. Electrical characterizations based on I-V and AC impedance analysis of several repeatable data points of attachment with varying λ-DNA concentration (500 ng/μL to 1.5 ng/μL) showed measurable and significant conductivity of λ-DNA molecular wires with some band-gap; thereby establishing it as semi-conductor at low-frequencies (<100 Hz) and a very good conductor at high-frequencies (∼1 MHz). We believe that the research presented here represents a significant departure from previous studies and makes unique contributions through (i) more accurate direct conductivity measurement of DNA molecular wires facilitated by suspension of the DNA away from the substrate, and (ii) AC impedance measurement of DNA molecular wires in dry-state attachment (relevant for long-term viability studies) that suggest metal-type low impedance at high-frequencies. The significant conductivity of λ-DNA molecular wires (similar to metals) observed at high-frequencies (|Z| < 5 KΩ) opens up substantial opportunities.

AC electrical and optical characterization of epoxy–Al2O3 composites

The AC electrical and optical characterizations of epoxy–alumina (Al2O3) composites have been investigated. Sheets filled with alumina were prepared with different alumina concentrations (0, 2, 5, 8, 10, and 15 wt%). The AC electrical properties were measured by using impedance spectroscopy as a function of applied frequency in range from 50 kHz to 1 MHz and filler concentration. The results obtained showed that the applied frequency and filler concentration was found to influence the AC electrical conductivity and dielectric behavior of the prepared composites. The UV-optical results obtained were analyzed in terms of the absorption formula for non-crystalline materials. The absorption coefficient and the optical energy gap (Eopt) have been obtained from the direct allowed transitions in k-space at room temperature. The tail widths (ΔE) of the localized states in the band gap were evaluated using the Urbach-edges formula. It was found that both (Eopt) and (ΔE) vary with the alumina concentration dispersed in the epoxy matrix. The refractive index (n) for the composites was determined from the collected transmittance and reflectance spectra. The dispersion behavior of the refractive index is discussed in terms of the single oscillator model.

Excellent humidity sensing properties of cadmium titanate nanofibers

We report humidity sensing characteristics of CdTiO3 nanofibers prepared by electrospinning. The nanofibers were porous having an average diameter and length of ∼50–200nm and ∼100μm, respectively. The nanofiber humidity sensor was fabricated by defining aluminum electrodes using photolithography on top of the nanofibers deposited on glass substrate. The performance of the CdTiO3 nanofiber humidity sensor was evaluated by AC electrical characterization from 40% to 90% relative humidity at 25°C. The frequency of the AC signal was varied from 10−1 to 106Hz. Fast response time and recovery time of 4s and 6s were observed, respectively. The sensor was highly sensitive and exhibited a reversible response with small hysteresis of less than 7%. Long term stability of the sensor was confirmed during 30 day test. The excellent sensing characteristics prove that the CdTiO3 nanofibers are potential candidate for use in high performance humidity sensors.

Synthesis and AC Electrical Characterization of Co Doped Bismuth Manganite Nanoparticles

Multiferroic bismuth manganites (BiMnO3) possess both ferromagnetic and ferroelectric properties. Their electrical properties can be controlled by doping for useful applications. In this work single-phase cobalt doped bismuth manganite nanoparticles having general formula BiMn1-xCoxO3 (x=0, 0.2, 0.4, 0.6) were synthesized by co-precipitation method. Structural properties like lattice parameters and crystallite size of samples were determined by the data obtained by X-rays diffraction. The dielectric constant (ε) and dielectric loss tangent (tanδ) of samples were investigated as a function of frequency from 20Hz-3MHz using ac measurement data. For all the compositions dielectric constant was decreased with increasing frequency, however it increased with the increase in cobalt content. However cobalt addition causes a decrease in loss tangent as compared to pure BiMnO3 composition. The origin of this behavior is discussed in terms of Maxwell-Wagner and Koops model. Substitution of Mn with Co, in BiMnO3-based compounds is supposed to cause better properties in terms of tangent loss.

Wide frequency range ac electrical characterization of thick-film microvaristors

ZnO-based thick-film microvaristors were investigated using impedance spectroscopy. Properties of planar and sandwich structures on alumina and LTCC substrates with different electrode material are compared. Experimental characteristics are approximated with electrical equivalent circuit. Fabrication technology influence on proposed model parameters is presented. Temperature dependent behavior is shown. Schottky barrier height was calculated as 0.46 eV and three electrop trap levels with activation energy of 0.17 eV, 0.25 eV and 0.38 eV were found.

Impedance spectra under forward and reverse bias conditions in gold/porous silicon/p‐Si structures

AbstractAbstract – The AC electrical characterization of Au/porous silicon/p‐Si structure is presented. The low porosity porous silicon layers were prepared by electrochemical etching in p‐type silicon 〈100〉 with two resistivities. The AC electrical measurements capacitance–conductance–frequency were performed from 5 Hz to 10 MHz, at room temperature in the DC range of ±2 V. We studied two structures; first a conductor type Au/PS/Au and second diode type Au/PS/p‐Si/Al. We found the relationship between the bias voltage in the PS/p‐Si heterostructures with the depletion region formation and the conduction mechanism presents in these structures. (© 2011 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)