AC Characterization Research Articles

AC Characterization of modular superconducting fault current limiter unit

AC Characterization of modular superconducting fault current limiter unit

Combining dc and ac electrochemical characterization with micro Raman analysis on industrial DSCs under accelerated thermal stress

Dye Sensitized Solar Cells (DSCs) have achieved high power conversion efficiencies at a low cost. However, high stability remains an issue that impedes their commercialization and their degradation mechanisms are still under debate. In this study, we focus on accelerated thermal stressing of industrial DSCs at 85 °C for up to 290 h. The overall reduction of the DSCs efficiency (η) under this harsh stress is relatively small (about 20%) due to nearly 10% decrease in the Short Circuit Current (Jsc) and Open Circuit Voltage (Voc) and mainly occurs in the initial stage (within the first 54 h). The ageing mechanism is studied by combining the electrical, dc (J-V) and ac (impedance) characterization of the cells with their in-situ spectroscopic analysis under bias by micro-Raman. A sharp decrease in the recombination resistance at the sensitized photoelectrode/electrolyte interface is identified for the aged cell which is ascribed to trapping of triiodide species in the photoelectrode and accounts for the Voc drop of the cells. Jsc reduction could be justified by mitigation in the electron collection efficiency.

Electro-analytical method for the quantities evaluation of the silicon solar cell by DC and AC characterization technique

Mono and Poly- crystalline silicon (Si) based solar cell has proven to be the most efficient and matured technology till date. The present work reports an exact electro-analytical method for the evaluation of different performance parameters in the current voltage response of the Si solar cell by DC and AC characterization technique. The extracted solar cell parameters from DC and AC techniques were compared with each other under the proper limiting conditions of low and high forward bias. The DC and AC characterization are used to determine the bias dependence of ideality factor and series resistance, respectively. The current-voltage (J-V) characteristics is combined with the impedance spectroscopy (IS) measurements to reveal the various interfacial, resistive and recombination analysis of the silicon solar cell. Herein the experimentally obtained J-V characteristics under the illumination condition have been reconstructed by individually extracted parameters from DC and AC measurements. Moreover, the present mechanistic provides a simple tool for analysing the commercial Si solar cell with a wide applicability for other solar cells.

Sodium ion transport in polymorphic scandium NASICON analog Na3Sc2(PO4)3 with new dielectric spectroscopy approach for current-constriction effects

Conductivity, calorimetry, and in-situ XRD can be closely interrelated with each other in terms of the sodium ion ordering and rearrangements in NASICON structure. An intermediate phase transition at 103°C, not associated with heat effects, is evidenced for the first time, in addition to α–β and β–γ phase transitions at 64°C and 166°C. AC characterization of polycrystalline Na3Sc2(PO4)3 has been performed over the wide temperature range from 225 to −100°C. Strongly dispersive spectra of the low temperature monoclinic phase were systematically described by the total sample resistance connected by the several capacitive responses all in parallel: pure dielectric geometric capacitance and two Havriliak–Negami (HN) dielectric functions with opposite skewnesses. The capacitance strengths of HN functions are inversely proportional to the temperature and the relaxation times represent the thermally activated mobile charge carrier transport. While the higher frequency response with a negative skewness as γ=0.388 and β=1 is of a universal character common with many other solid electrolytes, known as K1 model, the lower frequency response with a positive skewness as γ⋅β≈1 where β≈0.59 and γ≈1.67 describes the current-constriction effects occurring in the polycrystalline Na3Sc2(PO4)3. The current-constriction effects are described by a homogeneous polarization throughout the sample with 4 times the hopping distance and 5 times the relaxation time of the K1 response. 14 model parameters competently simulate the AC behavior over a wide temperature and frequency range.

Why the pore geometry model could affect the uniqueness of the PSD in AC characterization

Fil: Toso, Juan Pablo. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - San Luis. Instituto de Fisica Aplicada ; Argentina. Universidad Nacional de San Luis. Facultad de Ciencias Fisico Matematicas y Naturales. Departamento de Fisica; Argentina

AC electrical characterisation and insight to charge transfer mechanisms in DNA molecular wires through temperature and UV effects.

In this study, AC characterisation of DNA molecular wires, effects of frequency, temperature and UV irradiation on their conductivity is presented. λ-DNA molecular wires suspended between high aspect-ratio electrodes exhibit highly frequency-dependent conductivity that approaches metal-like behaviour at high frequencies (∼MHz). Detailed temperature dependence experiments were performed that traced the impedance response of λ-DNA until its denaturation. UV irradiation experiments where conductivity was lost at higher and longer UV exposures helped to establish that it is indeed λ-DNA molecular wires that generate conductivity. The subsequent renaturation of λ-DNA resulted in the recovery of current conduction, providing yet another proof of the conducting DNA molecular wire bridge. The temperature results also revealed hysteretic and bi-modal impedance responses that could make DNA a candidate for nanoelectronics components like thermal transistors and switches. Further, these experiments shed light on the charge transfer mechanism in DNA. At higher temperatures, the expected increase in thermal-induced charge hopping may account for the decrease in impedance supporting the 'charge hopping mechanism' theory. UV light, on the other hand, causes damage to GC base-pairs and phosphate groups reducing the path available both for hopping and short-range tunneling mechanisms, and hence increasing impedance--this again supporting both the 'charge hopping' and 'tunneling' mechanism theories.

DC and AC Characterization of Pancake Coils Made From Roebel-Assembled Coated Conductor Cable

Roebel cables made of HTS coated conductors can carry high currents with a compact design and reduced AC losses. They are therefore good candidates for manufacturing coils for HTS applications such as motors and generators. In this paper we present the experimental DC and AC characterization of several coils assembled from a 5 meter long Roebel cable built at KIT, which differ in the number of turns and turn-to-turn spacing. Our experiments, supported by finite-element method (FEM) calculations, show that a more tightly wound Roebel coil, despite having a lower critical (and therefore operating) current, can produce a higher magnetic field than a loosely wound one. For a given magnetic field produced at the coil's center, all the coils have similar AC losses, with the exception of the most loosely wound one, which has much higher losses due to the relatively large current needed to produce the desired field. The experiments presented in this paper are carried out on the geometry of pancake coils made of Roebel cables, but they are exemplary of a more general strategy that, coupling experiments and numerical simulations, can be used to optimize the coil design with respect to different parameters, such as tape quantity, size, or AC loss, the relative importance of which is dictated by the specific application.

Deposition of Fe3O4 on oxidized activated carbon by hydrazine reducing method for high performance supercapacitor

Oxidized activated carbon/Fe3O4 (AC/Fe3O4) composites for supercapacitor electrodes were synthesized by a reduction method. Poly(vinylpyrrolidone) was added as a dispersing agent for homogeneous deposition of Fe3O4 on AC. The obtained products were identified as AC/Fe3O4 by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis. Morphological characterization of AC/Fe3O4 was carried out by field emission scanning electron microscopy (FE-SEM); the results clearly showed the formation of Fe3O4 nanoparticles about 30nm in diameter on AC. Moreover, by using N2 adsorption/desorption isotherm analysis, we confirmed that surface areas and pore volumes decreased with increasing Fe3O4 content. We also carried out electrochemical characterization of AC and AC/Fe3O4 composites. Remarkably, we found that the value of specific capacitance increased significantly from 99.4Fg−1 of raw AC to 202.6Fg−1 of AC/Fe3O4 composites at 10mVs−1 of scan rate. This result can be ascribed to a synergistic effect of the combination of electrical double-layer capacitance and pseudo-capacitance properties. This research represents a valuable contribution to the application of supercapacitor electrodes in regard to cost effectiveness and simple fabrication.

Identification and characterization of a new erythromycin biosynthetic gene cluster in Actinopolyspora erythraea YIM90600, a novel erythronolide-producing halophilic actinomycete isolated from salt field.

Erythromycins (Ers) are clinically potent macrolide antibiotics in treating pathogenic bacterial infections. Microorganisms capable of producing Ers, represented by Saccharopolyspora erythraea, are mainly soil-dwelling actinomycetes. So far, Actinopolyspora erythraea YIM90600, a halophilic actinomycete isolated from Baicheng salt field, is the only known Er-producing extremophile. In this study, we have reported the draft genome sequence of Ac. erythraea YIM90600, genome mining of which has revealed a new Er biosynthetic gene cluster encoding several novel Er metabolites. This Er gene cluster shares high identity and similarity with the one of Sa. erythraea NRRL2338, except for two absent genes, eryBI and eryG. By correlating genotype and chemotype, the biosynthetic pathways of 3′-demethyl-erythromycin C, erythronolide H (EH) and erythronolide I have been proposed. The formation of EH is supposed to be sequentially biosynthesized via C-6/C-18 epoxidation and C-14 hydroxylation from 6-deoxyerythronolide B. Although an in vitro enzymatic activity assay has provided limited evidence for the involvement of the cytochrome P450 oxidase EryFAc (derived from Ac. erythraea YIM90600) in the catalysis of a two-step oxidation, resulting in an epoxy moiety, the attempt to construct an EH-producing Sa. erythraea mutant via gene complementation was not successful. Characterization of EryKAc (derived from Ac. erythraea YIM90600) in vitro has confirmed its unique role as a C-12 hydroxylase, rather than a C-14 hydroxylase of the erythronolide. Genomic characterization of the halophile Ac. erythraea YIM90600 will assist us to explore the great potential of extremophiles, and promote the understanding of EH formation, which will shed new insights into the biosynthesis of Er metabolites.

Superconducting-Ferromagnetic Transistor

We report experimental results on the dc and ac characterization of multiterminal SFIFSIS devices (where S, I, and F denote a superconductor (Nb), an insulator (AlO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> ), and a ferromagnetic material (Ni), respectively), which display transistor-like properties. We investigated two types of such superconducting-ferromagnetic transistors (SFTs): ordinary devices with a single acceptor (SIS) junction, and devices with a double acceptor. The devices with the single SIS acceptor were investigated and demonstrated a modulation of the maximum Josephson current as a function of the SFIFS current injection level. For devices of the second type, by applying an ac signal (in the kilohertz range) with a constant dc bias current to the injector (SFIFS) junction, we observed a voltage gain of about 25 on the double acceptor with the operating point chosen in the subgap region of the acceptor current-voltage characteristic. We also observed an excellent input-output isolation in our SFIFSIS devices. The experiments indicate that, after optimization of the device parameters, they can be used as input/output isolators and amplifiers for memory, digital, and RF applications.

AC characterization of bulk organic solar cell in the dark and under illumination

Abstract Impedance spectroscopy has been used widely to evaluate the transport processes in photovoltaic, mainly based on inorganic semiconductors, structures – solar cells. The aim of this research was to characterize improved organic bulk photovoltaic (PV) solar cells exploiting this method. Progress in technology of investigated organic solar cell involves the use of an active layer based on low band gap type of polymer. The organic PV cell with front transparent electrode and rear metal electrode and active layer produced by Konarka Technologies was analyzed by electrical DC and AC measurements. Current–voltage ( I – V ) characteristics in the dark and under illumination were measured and basic PV parameters were calculated. AC measurements, both under illumination and in the dark conditions, were processed in order to identify electronic behavior using equivalent AC circuit which was suggested by fitting of measured impedance data. Circuit with the best correlation to measured data is analyzed in details. Voltage and frequency dependences of fitted equivalent circuit components and calculated parameters are explained and presented in the paper.

Fabrication and AC characterization of magneto-impedance microsensors for alternating magnetic field measurement

Multilayered magneto-impedance microsensors (Finemet/Copper/Finemet) were elaborated by microfabrication pro- cess using bi-layers lift-off method. A post-annealing step was carried out at 300 ◦ C for 1h under magnetic field, which led to induce a longitudinal or transversal anisotropy in the magnetic films. A method based on a double amplitude demodulation was proposed for the sensitivity characterization corresponding to the AC magnetic field measurement capability. According to these alternating magnetic field characterizations, the sensitivity, the linearity and the bandwidth of the microsensor were obtained. The highest sensitivity is around 4200 Ω/T and the measurable sensor bandwidth reaches up to 300 kHz. The sensor presented no hysteresis since a DC bias field larger than anisotropy field is applied.

OFETs with sub-100 nm channel length fabricated by wafer-scale NIL and comprehensive DC and AC characterizations

Solution processed poly(3-hexylthiophene) organic field effect transistors with channel lengths down to 88nm were fabricated by thermal nanoimprint lithography with 4-inch wafer-scale molds. Polymer based working templates avoided the damage of the high-valuable silicon master wafer during the imprint process caused by the high pressure at high temperature. This technique realized an improved throughput compared to chip-scale nanoimprint techniques reported in our previous works. It can be applied to produce large-area OFETs matrices used e.g. in display backplanes. The DC and AC response of OFETs with different channel dimensions were characterized including the transfer and output characteristics, short channel effects, effective charge carrier mobility, the frequency dependent transconductance, and the switching speed limits. Finally, the achievements as well as the therefrom induced limitations by downscaling OFETs channel lengths were summarized.

Recombination kinetics in a silicon solar cell at low concentration: electro-analytical characterization of space-charge and quasi-neutral regions.

The present work reports a detailed electro-analytical framework for studying commercially available mono-crystalline silicon solar cells under varying illumination conditions to explore their application in the up-and-coming field of low concentration photovoltaics (LCPVs). The effect of low concentration illumination (>1-12 suns) on performance indicating parameters, i.e., short circuit current, open circuit voltage, fill factor, efficiency and ideality factor, was investigated using DC characterization. The same framework can be used for AC characterization in order to explore diffusion capacitance, transition capacitance, diffusion resistance and recombination kinetics under varying illumination. Recent developments in the impedance spectroscopy technique have broadened its horizon and have allowed its use in addressing unexplored material and performance aspects of mono-crystalline Si solar cells under non-equilibrium conditions. The obtained DC and AC experimental results are coupled with theoretical treatment to demonstrate the characteristic features of charge recombination in the space-charge region and the quasi-neutral region.

Fractional Modeling of the AC Large-Signal Frequency Response in Magnetoresistive Current Sensors

Fractional calculus is considered when derivatives and integrals of non-integer order are applied over a specific function. In the electrical and electronic domain, the transfer function dependence of a fractional filter not only by the filter order n, but additionally, of the fractional order α is an example of a great number of systems where its input-output behavior could be more exactly modeled by a fractional behavior. Following this aim, the present work shows the experimental ac large-signal frequency response of a family of electrical current sensors based in different spintronic conduction mechanisms. Using an ac characterization set-up the sensor transimpedance function Zt(if) is obtained considering it as the relationship between sensor output voltage and input sensing current, . The study has been extended to various magnetoresistance sensors based in different technologies like anisotropic magnetoresistance (AMR), giant magnetoresistance (GMR), spin-valve (GMR-SV) and tunnel magnetoresistance (TMR). The resulting modeling shows two predominant behaviors, the low-pass and the inverse low-pass with fractional index different from the classical integer response. The TMR technology with internal magnetization offers the best dynamic and sensitivity properties opening the way to develop actual industrial applications.

DC and AC Characterization of MgO Magnetic Tunnel Junction Sensors

We have fabricated multiple MgO magnetic tunnel junctions (MTJ) with 1.7 nm oxide, which are connected in series, and layed out in a serpentine geometry. We performed DC tunnel magnetoresistance measurements and AC impedance spectroscopy with crossed DC magnetic fields in the easy and hard axis directions. A simple <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$RLC$</tex></formula> circuit model is used to fit our data and characterize the dependence on capacitance <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$(C)$</tex></formula> and inductance <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$(L)$</tex></formula> of magnetization orientation of the MTJ sensors. We have found in our samples that <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$C$</tex></formula> and <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$L$</tex></formula> are higher in antiparallel than in parallel configuration. We discuss possible reasons for the existence of this field dependence and show the evolution of magnetic field vs. capacitance curve from memory mode into sensing mode at high frequencies.

Temperature and frequency dependencies of AC and dielectric characterizations of copper tetraphenyl porphyrin thin films

The AC conductivity and dielectric properties of the copper tetraphenyl porphyrin, CuTPP films have been investigated in the frequency range 42 Hz–5 MHz and in the temperature range 303–473 K. The AC conductivity of CuTPP is controlled by the correlated barrier hopping model. The activation energy for alternating current mechanism decreases with increasing frequency which confirms the hopping conduction to the dominant mechanism as compared with the DC activation energy. The dielectric constant ɛ′ and dielectric loss ɛ″ show noticeable dependence on frequency and temperature. The dielectric relaxation mechanism was explained on the basis of complex dielectric modulus.

AC characterization of organic thin-film transistors with asymmetric gate-to-source and gate-to-drain overlaps

This paper presents S-parameter characterization and a corresponding physics-based small-signal equivalent circuit for organic thin-film transistors (OTFTs). Furthermore, the impact of misalignment between the source/drain contacts and the patterned gate on the dynamic TFT performance is explored and a simple method to estimate the misalignment from the measured S-parameters is proposed. An excellent fit between theoretical and experimental S-parameters is demonstrated. For this study, OTFTs based on the air-stable organic semiconductor dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (DNTT) having a channel length of 1μm and a gate-to-contact overlap of 5 or 20μm and being operated at a supply voltage of 3V are utilized. The intentional asymmetry between gate-to-source and gate-to-drain overlaps is precisely controlled by the use of high-resolution silicon stencil masks.

Activated carbon from carrot dross combined with magnetite nanoparticles for the efficient removal of p-nitrophenol from aqueous solution

Activated carbon from carrot dross (AC) was prepared, magnetized and used for the removal of p-nitrophenol from aqueous solution. The magnetization of AC was carried out by mixing the AC with diluted Fe3O4 sol in two different mass ratios of Fe3O4/AC. The characterization of both magnetized and original AC were studied by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, surface area measurement, elemental analyses, zero point charge measurement, and vibrating sample magnetometer. The surface area measurement of AC and magnetic activated carbons of carrot dross (MAC) with two mass ratios of Fe3O4/AC (1/8 and 1/5) were 447, 435, and 340m2g−1, respectively. Batch sorption studies for the AC and MAC were carried out at different pH values, solid to liquid ratios, contact times, and initial concentrations of the pollutant in the presence and absence of ultrasonic irradiation. The sorption isotherms were obtained in the range of 50–500mgL−1. The results for the AC and MAC in the absence of ultrasound and for MAC in the presence of ultrasound fit well with Freundlich isotherm. In contrast, the results for AC in the presence of ultrasonic irradiation fit well with Langmuir model. In the case of AC, the values of intraparticle diffusion rate constant in the presence of ultrasound were greater than conventional method. In the case of MAC, the presence of magnetite nanoparticles on the surface of activated carbon led to a lower surface area but, the magnetic property of MAC facilitated the separation of solid phase from aqueous solution much easier than AC.

Modeling Stressed MOS Oxides Using a Multiphonon-Assisted Quantum Approach—Part II: Transient Effects

Multifrequency charge pumping analysis has been performed using a multiphonon-assisted charge trapping model in the view of analyzing the oxide region in energy and position that can be characterized using charge pumping (CP) characterization. Transient phenomena observed during CP and ac characterization (hysteresis loops) have been modeled, and the role of out-of-equilibrium quasi-Fermi levels in proximity of the Si/SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> interface has been studied in detail.