Direct Current Resistance Research Articles

Influence of reactive oxygen ambience on the structural, morphological and optical properties of pulsed laser ablated potassium lithium niobate thin films

The effect of oxygen ambience on the structure and properties of potassium lithium niobate (K 3Li 2Nb 5O 15: KLN) films prepared on glass substrates by pulsed laser ablation technique (PLD) are studied. The influence of annealing on the properties of vacuum deposited films is also investigated. The Gracing Incidence X-ray Diffraction (GIXRD) data suggests the tetragonal structure for the KLN film whose grain sizes increase on thermal annealing. The Atomic Force Microscopic (AFM) analysis reveals the four-fold symmetric nature of the grains in the films. Self assembly of grains in the form of rings and rods are observed in AFM images of the films deposited in an oxygen ambience of 2 Pa. The films deposited at higher oxygen ambience show a blue shift in optical band gap. The direct current (DC) resistance measurement on the films deposited at non-reactive ambience reveals resistivity in the range of kΩ m.

Synthesis of Li[Li0.2Ni0.2Mn0.6]O2 by radiated polymer gel method and impact of deficient Li on its structure and electrochemical properties

Layered Li[Li0.16Ni0.21Mn0.63]O2 and Li[Li0.2Ni0.2Mn0.6]O2 compounds were successfully synthesized by radiated polymer gel (RPG) method. The effect of deficient Li on the structure and electrochemical performance was investigated by means of X-ray diffraction, X-ray absorption near-edge spectroscopy and electrochemical cell cycling. The reduced Ni valence in Li[Li0.16Ni0.21Mn0.63]O2 leads to a higher capacity owing to faster Li+ chemical diffusivity relative to the baseline composition Li[Li0.2Ni0.2Mn0.6]O2. Cyclic voltammograms (CV) and a simultaneous direct current (DC) resistance measurement were also performed on Li/Li[Li0.16Ni0.21Mn0.63]O2 and Li/Li[Li0.2Ni0.2Mn0.6]O2 cells. Li[Li0.16Ni0.21Mn0.63]O2 shows better electrochemical performance with a reversible capacity of 158 mA hg−1 at 1C rate at 20 °C.

Protonic conduction processes of gamma-ray-irradiated perfluorosulfonic acid membranes

New protonic conduction processes of perfluorosulfonic acid membranes by gamma-ray irradiation at a dose of up to 240 kGy at room temperature in air have been found by direct current resistance measurement. The conductivities of the membranes at 373 and 300 K in vacuum are enhanced to approximately one and two orders of magnitude higher, respectively, than the conductivities of an unirradiated membrane. The new and original activation energies required for the conductivities in the temperature range below and above 343 K are determined to be 0.12 ± 0.05 and 0.84 ± 0.03 eV, respectively, which correspond to the potential energy of the hydrogen diffusion due to radiation-induced defects and the existing sulfonate group. By means of ultraviolet, visible, and infrared optical absorption and by hydrogen-ion-exchange capacity measurements, it is revealed that radiation-induced defects such as fluorocarbon and peroxy radicals, and C = O bonds included in carbonyl groups are related to the new proton conduction processes. The modification of hydrogen absorption characteristics due to the radiation-induced defects in near-surface regions induces the enhancement of the proton conductivity.

Direct current electrical and microwave properties of polymer-multiwalled carbon nanotubes composites

We report the results of effective direct current (dc) resistivities and alternating current (ac) complex permittivity measurements carried out on two series of polymer∕multiwalled (MW) carbon nanotube (CNT) composite samples as function of the CNTs volume fraction and temperature. The CNTs have typical aspect ratio over 100:1 and are quasiuniformly dispersed in two types of polymer host [epoxy and polystyrene (PS)-cobutyl acrylate latex] according transmission electron microscopy characterization. A percolation threshold occurs in the composites with the PS latex matrix when the CNT volume fraction is ≈0.012. In contrast, the set of resistivity data for samples containing epoxy resin as host matrix is not representative of an intrinsically percolation transition. Atomic force microscopy, coupled to the measurement of the local electric resistances, permits us to study the agglomerate distribution in both types of composites. The differences in morphology between the two series of polymer∕MWCNTs are attributed to interface effects between the elongated filler nanoparticles and the polymer chains. Comparison of the measured effective dc and ac resistivities, at temperatures ranging from 30to300K, with Sheng’s model supports the fact that charge transport in the composites follows a thermal fluctuation induced tunneling mechanism, in which the tunneling of the electrons through the thermally induced fluctuating potential barrier formed by a thin insulating polymer layer separating MWCNTs aggregates. The spectral behavior of permittivity is consistent with a power-law form. Several mixing laws were tested to represent the filler fraction dependence of the effective permittivity in the microwave range of frequencies; however, none of them is able to quantitatively describe the sets of data. The basic deficiency of these formulas is that they make no explicit reference to the internal length scales in the composite samples.

Development of high-power density Li ion cell and module

After the development of the first version of our high-power lithium ion battery in 2000, we have been further improving its performance, such as the power and life. Our recent progress in the development on the new version (Gen 2) battery is presented. The prolonged cycle life test at 50 °C reached 900,000 cycles with a 50% increase in the direct current resistance (DCR), and the storage life test at 50 °C over 1 year showed a 20% increase in the DCR. These life test data suggested a much longer calendar life in real applications than our former lithium battery version. A new 48-cell module was developed, and it proved to have a high-power capability and good cold cranking performance as expected by the cell performance.

The direct current and microwave resistivities arising from domain wall scattering for Ni and Co films

The frequency dependences of surface resistances of ferromagnetic films were measured by a four-point van der Pauw method and a microwave micro-strip method, respectively, to evaluate the direct current (DC) and radio frequency (RF) resistivities arising from domain wall scattering. We observed that the magnetoresistances (MR) in nickel and cobalt films change manifestly as the current conducts from parallel (CIW) to perpendicular (CPW) to the domain walls, which were inspected by a magnetic force microscopy (MFM). The DC resistivity for currents conducting parallel to domain walls (CIW) is significantly smaller than that of the perpendicular (CPW) case. Whereas indistinguishable changes in CIW and CPW conductions were observed for signals increase to microwave frequency where films are configured in T-microstrips.

Preparation of Polymer-Metal Composites via In Situ Decomposition of Metal Salts by Frontal Polymerization

Composites containing powdered zinc, and zinc/lead acetate were prepared via frontal polymerization. In the case of the acetates, elemental metal was formed in an in situ decomposition process. The local area function was used to demonstrate the distribution of fillers, and the uniformity of the area fraction for the quantitative characterization of the distribution. With the use of metal acetates, composites of uniform metal distribution can be produced, unlike in systems with metal powder, where the metal particles are enriched at the margin of the sample. It can be established that the specific direct-current resistance significantly decreases in AA-TGDMA composites by the addition of zinc acetate, compared to that of the initial monomer mixture. On heating, the unreacted zinc acetate decomposes further, which results in the further decrease in electrical resistance.

Skin-Effect Self-Heating in Air-Suspended RF MEMS Transmission-Line Structures

Air-suspension of transmission-line structures using microelectromechanical systems (MEMS) technology provides the effective means to suppress substrate losses for radio-frequency (RF) signals. However, heating of these lines augmented by skin effects can be a major concern for RF MEMS reliability. To understand this phenomenon, a thermal energy transport model is developed in a simple analytical form. The model accounts for skin effects that cause Joule heating to be localized near the surface of the RF transmission line. Here, the model is validated through experimental data by measuring the temperature rise in an air-suspended MEMS coplanar waveguide (CPW). For this measurement, a new experimental methodology is also developed allowing direct current (dc) electrical resistance thermometry to be adopted in an RF setup. The modeling and experimental work presented in this paper allow us to provide design rules for preventing thermal and structural failures unique to the RF operation of suspended MEMS transmission-line components. For example, increasing the thickness from 1 to 3 mum for a typical transmission line design enhances power handling from 5 to 125 W at 20 GHz, 3.3 to 80 W at 50 GHz, and 2.3 to 56 W at 100 GHz (a 25-fold increase in RF power handling)

Single-Pole Eight-Throw RF MEMS Rotary Switch

The design, fabrication, and measured performance of a novel single-pole eight-throw radio-frequency (RF) microelectromechanical systems (MEMS) rotary switch are described. The concept of this rotary switch is based on the adaptation of the axial gap wobble motor. A prototype switch has been made using separately fabricated stator, rotor, and cap components that are then assembled. A rigorous procedure was setup to investigate the direct current (dc) contact resistance over a total of four million rotor contact closures, with half a million closures made on each of the eight stator contacts. It was found that there was no obvious systematic trend in contact resistance over time. An average contact resistance of 2.5 Omega was recorded; however, values as low as 1.0 Omega were also found. The assembled rotary switch demonstrated an excellent RF performance. With the inclusion of feed lines, the insertion loss was 2.65 dB at 20 GHz, after renormalizing the measurement reference impedance. When the loss of the feed lines is subtracted, the worst-case on-state intrinsic insertion loss of the rotary switch is only 2.16 dB at 20 GHz. A worst-case off-state isolation of 31 dB was also measured over the 20-GHz bandwidth. The effective performance figure-of-merit for this switch in an arbitrary position was calculated to be 10.7 THz. To the authors' knowledge, this is the first example of a true single-pole multiple-throw RF MEMS rotary switch

Pulsed laser deposition of La 0.67Ca 0.33MnO 3 thin films on LiNbO 3 and surface acoustic wave studies

Surface Acoustic Waves on piezoelectric substrates can be used to investigate the dynamic conductivity of thin films in a non-contact and very sensitive way, especially at low conductivities. Here, we report on such surface acoustic wave studies to characterize thin manganite film like La 0.67Ca 0.33MnO 3, exhibiting a Jan Teller effect with a strong electron phonon interaction and a metal insulator transition at high temperatures. We report on the deposition of La 0.67Ca 0.33MnO 3 on piezoelectric substrates (LiNbO 3 in different crystal cuts, employing a pulsed laser deposition technique. The structural quality of the thin films are examined by X-Ray Diffraction, Scanning Electron Microscope and Energy Dispersive X-ray spectroscopy. For the electrical characterization, we employ the surface acoustic wave technique, accompanied by conventional direct current resistance measurements for comparison.

Combination of conventional geophysical methods for sounding the composition of rock glaciers in the Swiss Alps

AbstractThe composition of rock glaciers was sounded by a combination of conventional geophysical methods near the lower limit of mountain permafrost in the Swiss Alps. P‐wave velocity, direct current (DC) resistivity and year‐round ground surface temperatures were measured on 32 talus‐derived rock glaciers. Subsurface P‐wave velocities differ significantly between non‐vegetated (probably active/inactive) rock glaciers and vegetated (probably relict) rock glaciers. DC resistivities reflect structural differences in the rock glaciers (e.g. bouldery or pebbly, ice‐cemented or highly ice‐rich) rather than thermal differences (i.e. frozen or unfrozen). The combination of these methods provides reliable thermal and structural information on subsurface deposits. In addition, mean annual ground surface temperatures are equally good indicators of the distribution of permafrost as bottom temperatures of snow. Copyright © 2006 John Wiley & Sons, Ltd.

Role of Spontaneous Current Oscillations during High-Efficiency Electrotransformation of Thermophilic Anaerobes

Current oscillations at about 24 MHz were observed during electrotransformation (ET) of the thermophilic anaerobes Clostridium thermocellum ATCC 27405, C. thermocellum DSM 1313, and Thermoanaerobacterium saccharolyticum YS 485, using a pulse gated by a square signal generated by a custom generator. In experiments in which only the field strength was varied, all three of these strains resulted in a one-to-one correspondence between the appearance of current oscillations and successful ET. Oscillations accompanied ET of both C. thermocellum strains only at field strengths of > or =12 kV/cm, and ET was only observed above the same threshold. Similarly, for T. saccharolyticum, oscillations were only observed at field strengths of > or =10 kV/cm, and ET was only observed above the same threshold. When a passive electrical filter consisting of an inductor and resistor in parallel was added to the system to prevent the development of oscillations, ET efficiencies were reduced dramatically for all three strains at all field strengths tested. The maximum tested field strength, 25 kV/cm, resulted in the maximum measured transformation efficiency for all three strains. At this field strength, the efficiency of ET in the absence of oscillations was decreased compared to that observed in the presence of oscillations by 500-fold for C. thermocellum ATCC 27405, 2,500-fold for C. thermocellum DSM 1313, and 280-fold for T. saccharolyticum. Controls using the same apparatus with Escherichia coli cells or a resistor with a value representative of the direct current resistance of typical cell samples did not develop oscillations, and ET efficiencies obtained with E. coli were the same with or without the electrical filter included in the pulse generator circuit. The results are interpreted to indicate that spontaneously arising oscillations have a large beneficial effect on transformation efficiency in the system employed here and that the development of oscillations in this system is affected by the cell species present.

Methodical aspects of determining the elasticity of electrical insulating coatings

We have studied the elasticity of 12 different types of polymeric protective coatings. In the course of pure-bending deformation of rectangular plates—specimens, we controlled their dielectric continuity using an electric-spark flaw detector, measured the direct-current resistance, and looked for the appearance of indications of the fracture of the coating surface under a microscope with a ×30 magnification. We have established that highly elastic coatings lose their dielectric continuity under relative strains an order of magnitude lower than those corresponding to the appearance of cracks on the surface. We have concluded that evaluation of the elasticity of coatings by the criterion of loss of their dielectric continuity is the most correct and reliable approach. We also describe the procedure of tests of specimens.

Development of Three Dimensional LIGA Process to Fabricate Spiral Microcoil

The LIGA process has been developed as a 2.5-dimensional processing method on Si wafers to date. However, we have succeeded in extending the LIGA process to 3D for the first time. 3D-LIGA was achieved by the technical development of 3D X-ray lithography and worm injection molding replication technology with unscrewing. These technologies began from the development of equipment and have developed into quite original technologies. By combining this 3D-LIGA process with a metallization technique that consists of flat and smooth electroplating and isotropic chemical etching, a spiral copper microstructure with a linewidth of 10 µm, a pitch of 20 µm and a thickness of 2 µm was formed on a cylindrical surface made from LCP with a length of 1 mm and a diameter of 0.48 mm. Furthermore, we applied the process to fabricate a spiral microcoil and estimated the electrical properties of the microcoil. The numbers of turns were 15, the inductance was 91 nH and the quality factor was 5.8 for a frequency of 1 GHz. Direct-current resistance was measured as 99 Ω.

Applications of high power density lithium ion batteries

In 2003, we developed a new type of lithium ion battery for the light vehicle application, in which 14 cells of 7 Ah were integrated into a battery pack. It has the high rate discharge capability up to 5 C rate (35 A), a energy density of 74 Wh kg −1, and the low temperature discharge capacity at −5 °C more than 90% of that at 25 °C. The life cycle test of 100% depth of discharge (DOD) at 35 °C showed the capacity fading around 10% after 500 cycles, which confirmed much longer practical life than 2 years. Recently, we have developed a new high power cell. It has the capacity of 5.5 Ah, and has the output power density of 3000 W kg −1 at 50% state of charge (SOC) and at 25 °C for 5 s discharge basis, and the input power density of 2200 W kg −1 at the same conditions. The new cells showed much less increase in direct current resistance (DCR) in both the cycle life test and the storage life test than the cells developed before, which consequently implied much longer calendar life than our previous ones developed in 2000.

Influence of GGBS on durability and corrosion behavior of reinforced concrete

The durability of ground granulated blast furnace slag (GGBS) concretes and the corrosion behavior of reinforced concrete beams under various loading ratios were investigated. Prismatic beam specimens with a size of 150mm×150mm×900mm were subjected to various sustained loadings (37 and 75% of the ultimate load) and exposed to 3.5% NaCl solution. A direct current (1mAcm−2) was applied to accelerate the corrosion process. Open circuit potential (OCP) and direct current polarization resistance were obtained to evaluate the rebar corrosion. Deflection and residual loading rigidity of the beam were measured at the end of the experiment. In addition, rapid chloride penetration test (RCPT) and permeability test were conducted on GGBS concretes. Test results indicate that partial replacement of cement by GGBS has inhibiting effects on both total charge-pass and permeability. Slag addition and sustained loading have significant effect on corrosion rate and flexural rigidity of reinforced concrete beams.

Development of a high power lithium secondary battery for hybrid electric vehicles

A lithium secondary battery (Type II cell) for hybrid electric vehicles (HEV) was developed on the basis of previous battery techniques (Type I cell with amorphous carbon/Li 1 + x Mn 2O 4). It used an improved cathode material and more advanced electrolyte. Cell performances of the Type II cell were evaluated and compared with a Type I cell of the same cell size, i.e. 40 ϕ (diameter) ×108 mm (length). The Type II cell discharged 5.9 Ah, which was 1.5 times higher than the amount discharged by the Type I cell (3.8 Ah). The former had an input–output power of 800 W at 45% SOC (state of charge) and 25 °C, which was 1.3 times higher than that of the latter (600 W at around 40%). Moreover, the former had an input–output power of more than 100 W at −30 °C, though the Type I cell output power was only 50 W. A pulse charge–discharge cycle test with 167 W input and 260 W output for a 30–70% SOC range and a storage test at 50% SOC were carried out at various temperatures for the Type II cell. Less than a 15% DCR (direct current resistance) increase was observed in the pulse mode cycle test after 450 K cycles at 50 °C. No more than a 25% DCR increase was detected after 240 days in the 50% SOC storage test even at 65 °C. The activation energies for capacity change and DCR change in the storage test were also estimated for the Type II cell.

Electro-thermal resistance of GaAs interconnects

This paper describes the effect of steady-state heating on the electrical and thermal resistance of interconnects on GaAs. Examined is a typical dual-layer metal interconnect system, common to GaAs processing. The interconnect system is considered in three parts, the interconnect metals, the Si3N4 dielectric surrounding the metal, and the AlxGa1−xAs epitaxial substrate. Using a mean-dering line as a test structure, measurements show how the direct current (DC) resistance increases with both temperature and dissipated power. Thermal resistors are proposed to account for self-heating and thermal coupling.

Electrical properties of screen-printed NiMn 2O 4+ δ

The direct current (dc) resistance versus temperature ( R– T) characteristics and the alternating current (ac) impedance of thick screen-printed films made of ceramic NiMn 2O 4+ δ thermistor material have been analysed. Electron transport in spinel NTCR thermistors is commonly described by an Arrhenius hopping model ( R ∼ T exp( T 0/ T)) for nearest neighbour hopping (NNH) or by different variable range hopping (VRH) models ( R ∼ T 2 p exp( T 0/ T) p ). In screen-printed films dc conduction was well described by VRH with p ∼ 0.5, indicating that the shape of the density of states (DOS) was parabolic. Values of T 0 ranged from 1.90 × 10 5 K to 1.97 × 10 5 K. Impedance spectroscopy was carried out at a frequency range of 5 Hz–6 MHz between 60 °C and 220 °C. For frequencies below ∼2.7 MHz the complex impedance was well described by a standard equivalent circuit, based on one parallel resistance–capacitance ( RC) element. Plots on the complex plane of the imaginary versus real parts of the impedance ( Z″– Z′ loci) showed one regular semicircle at each temperature, from which the capacitance and resistance of the RC element were determined. The capacitance was found to be in the order of 1 × 10 −12 F at all temperatures, indicating a grain effect. The ac resistance versus temperature characteristics were in very good agreement with the dc results and followed the same VRH model with p ∼ 0.5. At frequencies above 2.7 MHz the impedance could not be described by a standard RC element.

An Efficient Surface-Impedance Boundary Condition for Thin Wires of Finite Conductivity

To include dispersive loss into a sub-cell thin-wire model, a new implementation of a surface-impedance boundary condition (SIBC) is proposed. The surface-impedance function is approximated in the frequency domain by a series of first-order rational functions allowing straightforward transform into time domain. The contribution of the wire radius is included in the surface-impedance function extending the model to very thin or poorly conducting metal wires. Further, the SIBC includes the direct-current (dc) resistance. The approximation for the SIBC is chosen such that the dependence on the wire radius and conductivity can be removed prior to the computation of the approximation coefficients. Consequently, the wire radius and conductivity can be varied without re-computing the coefficients. The proposed model is compared with an existing SIBC wire model based on the high-frequency approximation and Prony's method, NEC-2 generated reference data, and analytical results. The results indicate enhanced accuracy at a reduced computational cost as compared with an existing model.