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An electromechanically coupled model for the simulation of electric current flow in ZnO varistors is presented. The model is based on an equivalent circuit representation of the varistor microstructure, where the grain boundaries are modeled as nonlinear resistors in the circuit. This approach extends on previous circuit models by including the effect of mechanical stress on grain boundary conductivity. The 3D mechanical stress distribution in the material is calculated by the finite element method. Using this distribution, the electrical resistance of each grain boundary is determined by applying a self-consistent model for the trapped interface charge induced by piezoelectric polarization. Finally, the electric current flow patterns and the bulk conductivity of the material are computed using the nonlinear circuit model. The simulated IV-characteristics reveal a significant sensitivity of electrical conductivity to applied stress. For 2D and 3D ZnO varistor models, the simulations demonstrate the effect of current concentration along thin conducting paths depending on microstructure properties and on the mechanical stress condition of the material. [ABSTRACT FROM AUTHOR]

GaN is an excellent material choice for power devices due to its excellent properties such as super wide bandgap width and high electron mobility. However, the problem of temperature affects the thermo reliability and hinders the potential of GaN devices. In this paper, the electrical properties of GaN under temperature have been studied by the combination of numerical simulation and experimental research. The electric current change and electrical resistivity of polarized and depolarized GaN semiconductor samples were tested in an environment-test cabinet. Based on the influence of temperature, the expression of the resistivity curve vs temperature was established for polarized and depolarized GaN samples. It is shown that the resistivity model predictions are consistent with experimental results. The I–V characteristic curves under different temperatures were also measured. Thus, such a model is instructive to the reliable design of GaN high-temperature devices. The findings will be instructive to the optimal design of GaN electronic components. [ABSTRACT FROM AUTHOR]

In this study, we report a large magneto-thermal conductivity effect, potentially usable in heat flow switches and thermoelectric devices, in Ag2Te over a wide temperature range, including room temperature. When a magnetic field of μ0H = 9 T is applied to Ag2Te at 300 K along the direction perpendicular to the heat and electric currents, the thermal conductivity κ decreases by a remarkable 61%. This effect is mainly caused by the suppressed electronic thermal conductivity in association with a significant magnetoresistance effect, but the suppression of the thermal conductivity is larger than that of the electrical conductivity, presumably due to a field-induced decrease in the Lorenz ratio. Its very low lattice thermal conductivity, as low as 0.5 W m−1 K−1, also greatly contributes to the large relative magneto-thermal conductivity effect. The significant decrease in thermal conductivity and the 18% increase in the Seebeck coefficient S lead to a nearly 100% increase in the thermoelectric figure of merit zT = S2σTκ−1 despite the 43% decrease in electrical conductivity σ. [ABSTRACT FROM AUTHOR]

Semi-insulating GaN is a prerequisite for lateral high frequency and high power electronic devices to isolate the device region from parasitic conductive channels. The commonly used dopants for achieving semi-insulating GaN, Fe, and C cause distinct properties of GaN layers since the Fermi-level is located either above (Fe) or below (C) the midgap position. In this study, precursor-based doping of GaN in metalorganic vapor phase epitaxy is used at otherwise identical growth conditions to control the dopant concentrations in the layer. Using electric force microscopy, we have investigated the contact potentials of Fe- and C-doped samples with respect to a cobalt metal probe tip in dependence of on the dopant concentration. While in Fe-doped samples the sign of the contact potential is constant, a change from positive to negative contact potential values is observed at high carbon concentrations, indicating the shift of the Fermi-level below the midgap position. In vertical transport measurements, C-doped GaN layers with a dopant concentration of 4.6 × 1018 cm−3 exhibit up to 5 orders of magnitude lower dark current at room temperature and significantly lower temperature dependence than Fe-doped samples with a similar dopant concentration. Therefore, precursor-based carbon doping is the superior doping technique to achieve semi-insulating GaN. [ABSTRACT FROM AUTHOR]

In the current study, we investigated sigmoidal current collector in lithium-ion battery (LIB). Traditionally, the active material in an LIB electrode is coated on a flat current collector. By rendering the current collector sigmoidal-shaped, cracking and debonding of active material layer could be promoted, which would considerably increase the internal impedance, as the LIB is mechanically abused, beneficial to thermal-runaway mitigation. The energy absorption capacity is also improved, enabling multifunctional LIB cell design. This technique has important relevance to large-sized LIB systems, for which cell robustness and fire safety are prioritized. [ABSTRACT FROM AUTHOR]

We describe the development of a conductive-probe atomic force microscopy method combined with a fine-wavelength-tunable light source and use it to observe the photovoltaic distribution on a cross-sectional surface of an amorphous-silicon solar cell in near-band-edge excitation. The light source's wavelength resolution is dλ = 1 nm, and its intensity is 1 µW/cm2 (10 mW/m2); this excitation condition is sufficiently fine and weak to investigate electrical properties in the near-band-edge wavelength range. The photovoltage is observed in the indium tin oxide (ITO) region, and the maximum photovoltage increases when we increase the excitation energy of the illumination light. However, the photovoltaic distribution parallel to the ITO layer becomes relatively localized as the excitation energy increases. This localized photovoltaic distribution suggests that the conductivity of the electric current path within the ITO layer should be inhomogeneous. [ABSTRACT FROM AUTHOR]

A gate voltage application in a Si-based spin metal-oxide-semiconductor field-effect transistor (spin MOSFET) modulates spin accumulation voltages, where both electrical conductivity and drift velocity are modified while keeping constant electric current. An unprecedented reduction in the spin accumulation voltages in a Si spin MOSFET under negative gate voltage applications is observed in a high electric bias current regime. To support our claim, the electric bias current dependence of the spin accumulation voltage under the gate voltage applications is investigated in detail and compared with a spin drift diffusion model including the conductance mismatch effect. The drastic decrease in the mobility and spin lifetime in the Si channel is ascribable to the optical phonon emission at the high electric bias current, which consequently reduced the spin accumulation voltage. [ABSTRACT FROM AUTHOR]

Magnesium oxide (MgO) is generally a wide band-gap oxide unable to conduct electric current in the bulk at room temperature. In this study, MgO nanocubes synthesized by self-burning micro-sized Mg metal powders in air showed electrical conductivity when they were sandwiched between two gold-mesh electrodes and steadily applied a voltage at room temperature (∼25 °C). In addition, a simultaneous light emission caused by the microdischarge of nitrogen molecules occurred adjacent to the cathode. The light emission was observed when traces of water vapor existed in the gas environment. In the case of a voltage pulse produced by switching off, transient emissions of Mg I and Mg II were detected on both sides of the electrodes. However, those steady and transient light emissions were not observed in the commercial MgO nanoparticles devoid of nanocubes. The light emissions shown in the cases of the steady-state might be caused by electron injection into the empty conductive states, which exist along the edges of MgO nanocubes, as a result of the spontaneous dissociation of water vapors at reactive sites of the nanocube surfaces as well as a result of the reduction of the energy barriers between the cathode and MgO nanocubes in contact. For transient emission, electrons trapped in the low coordinate sites were released with voltage pulse and neutralized the nearby Mg+ and Mg2+ ions, driving them into the excited neutral states, Mg I and Mg II. [ABSTRACT FROM AUTHOR]

Transformer oil-based nanofluids with TiO2 semiconductive nanoparticles exhibit substantially higher AC and positive impulse breakdown voltage levels than that of pure transformer oils. Thermally stimulated current method (TSC) and pulse electroacoustic technique (PEA) have been used to measure charge trap and transportation characteristics of pure oils and nanofluids. It is found that electron shallow trap density and charge decay rate are greatly increased in nanofluids, i.e., fast electrons may be converted to slow electrons by electron trapping and de-trapping in shallow traps of nanofluids, resulting in improved breakdown performance compared to that of pure oil. [ABSTRACT FROM AUTHOR]

We develop a simple continuum model for the current voltage characteristics of a material as measured by the conducting atomic force microscopy, including space charge effects. We address the effect of the point contact on the magnitude of the current and on the transition voltages between the different current regimes by comparing these with the corresponding expressions obtained with planar electrodes. [ABSTRACT FROM AUTHOR]

We investigate experimentally and theoretically the effects of two different types of conductivity, electrical and ionic, upon magic-angle spinning NMR spectra. The experimental demonstration of these effects involves 63Cu, 65Cu, and 127I variable temperature MAS-NMR experiments on samples of γ-CuI, a Cu+-ion conductor at elevated temperatures as well as a wide bandgap semiconductor. We extend previous observations that the chemical shifts depend very strongly upon the square of the spinning-speed as well as the particular sample studied and the magnetic field strength. By using the 207Pb resonance of lead nitrate mixed with the γ-CuI as an internal chemical shift thermometer we show that frictional heating effects of the rotor do not account for the observations. Instead, we find that spinning bulk CuI, a p-type semiconductor due to Cu+ vacancies in nonstoichiometric samples, in a magnetic field generates induced AC electric currents from the Lorentz force that can resistively heat the sample by over 200 °C. These induced currents oscillate along the rotor spinning axis at the spinning speed. Their associated heating effects are disrupted in samples containing inert filler material, indicating the existence of macroscopic current pathways between micron-sized crystallites. Accurate measurements of the temperature-dependence of the 63Cu and 127I chemical shifts in such diluted samples reveal that they are of similar magnitude (ca. 0.27 ppm/K) but opposite sign (being negative for 63Cu), and appear to depend slightly upon the particular sample. This relationship is identical to the corresponding slopes of the chemical shifts versus square of the spinning speed, again consistent with sample heating as the source of the observed large shift changes. Higher drive-gas pressures are required to spin samples that have higher effective electrical conductivities, indicating the presence of a braking effect arising from the induced currents produced by rotating a conductor in a homogeneous magnetic field. We present a theoretical analysis and finite-element simulations that account for the magnitude and rapid time-scale of the resistive heating effects and the quadratic spinning speed dependence of the chemical shift observed experimentally. Known thermophysical properties are used as inputs to the model, the sole adjustable parameter being a scaling of the bulk thermal conductivity of CuI in order to account for the effective thermal conductivity of the rotating powdered sample. In addition to the dramatic consequences of electrical conductivity in the sample, ionic conductivity also influences the spectra. All three nuclei exhibit quadrupolar satellite transitions extending over several hundred kilohertz that reflect defects perturbing the cubic symmetry of the zincblende lattice. Broadening of these satellite transitions with increasing temperature arises from the onset of Cu+ ion jumps to sites with different electric field gradients, a process that interferes with the formation of rotational echoes. This broadening has been quantitatively analyzed for the 63Cu and 65Cu nuclei using a simple model in the literature to yield an activation barrier of 0.64 eV (61.7 kJ/mole) for the Cu+ ion jumping motion responsible for the ionic conductivity that agrees with earlier results based on 63Cu NMR relaxation times of static samples [ABSTRACT FROM AUTHOR]

Influences of cracking of coating layer under applied tensile strain on V(voltage)-I(current) curve, critical current, and n-value of DyBa2Cu3O7-δ coated conductor were studied experimentally and analytically. The experimentally measured variations in V-I curve, critical current, and n-value with increasing applied strain and the correlation of n-value to critical current were described well by the partial crack-current shunting model of Fang et al. Also, the variations in the ratio of shunting current to overall critical current and the ratio of voltage developed in the cracked region to overall voltage with extension of crack, and the variation in critical current with the ratio of noncracked area to overall cross-sectional area of superconducting layer were revealed. [ABSTRACT FROM AUTHOR]

We calculated the electronic structures and the thermoelectric properties for type-I and type-VIII Ba8Ga16Sn30 (BGS) clathrates. The band structures show that type-I and type-VIII BGS are indirect semiconductors with band gaps of 0.51 eV and 0.32 eV, respectively. The calculated Seebeck coefficient of n-type type-I BGS is higher than that of n-type type-VIII BGS because of the larger density of states in type-I at the bottom of the conduction band. This is in good agreement with the experimental results. We also calculated the electrical conductivity and thermal conductivity due to charge carriers. Estimated thermoelectric figure of merit, ZT, exceeds 1.0 for both types. [ABSTRACT FROM AUTHOR]

We detail a mathematical framework for photoconductive gain applied to the detection of single photons. Because photoconductive gain is derived from the ability to measure current change for an extended period, its magnitude is reduced as detection speed is increased. We theoretically show that high-speed detection is still possible as long as the noise spectrum of the device is 1/f in nature. Using signal analysis techniques, we develop tools to apply to device noise spectra to determine the performance of single-photon detectors that utilize photoconductive gain. We show that there is no speed penalty when one considers the signal-to-noise ratio for the fundamental 1/f noise typical of high electron mobility transistors. We outline a technique for quickly characterizing a detector’s sensitivity and speed through purely electrical measurements of the device’s noise spectra. Consequently, the performance of the detector can be determined and optimized without conducting optical measurements. Finally, we employ this analysis to a quantum dot, optically gated field-effect transistor and verify our results with optical measurements. [ABSTRACT FROM AUTHOR]

Phonon-plasmon coupled mode Raman spectra of n-type GaInAsSb were measured at room temperature as a function of electron concentration. A relatively simple spectral model for the electronic contribution to the dielectric function was evaluated to determine the electron concentration from the bulk coupled mode spectra. The electron concentration was determined from a Raman spectrum by minimizing the sum of the squared residuals between a measured and a simulated spectrum. The only two fitting parameters were the Fermi energy and a plasmon damping parameter. The electron concentrations determined from the fits to the Raman spectra were compared to the electron concentrations determined from single magnetic field Hall effect measurements that were corrected to account for carriers in two conduction band minima. Compared to the results obtained from the Hall effect measurements, the electron concentrations obtained using Raman spectroscopy were as much as ≈19% lower at low doping levels but not more than ≈1% higher at higher doping levels. At lower carrier concentrations, the deviations are attributed to limitations of the spectral model. At higher carrier concentrations, the two methods were in good agreement. However, given the known limitations of this relatively simple spectral model, this agreement may be fortuitous; i.e., elements of the spectral model that tend to increase the apparent carrier concentration may be offset by elements that decrease the apparent carrier concentration. [ABSTRACT FROM AUTHOR]

We have carried out calculations of current-voltage characteristics for the electron tunnel current through a junction with a thin insulating ferroelectric barrier assuming that interface transmissions for the left and right interfaces noticeably differ due to dissimilarity of the interfaces. Obtained conductance versus voltage and current versus voltage curves exhibit well distinguishable asymmetric hysteresis. We show that the asymmetry in the hysteretic effects could originate from the asymmetric bias voltage profile inside the junction. In particular, we analyze the hysteresis asymmetries occurring when the bias voltage distribution is low sensitive to the spontaneous polarization reversal. [ABSTRACT FROM AUTHOR]

This paper presents a study on the effect of carbon black (CB) and short carbon fibers (SCFs) on shape memory polymer (SMP) actuation by applying electric current. The coexistence of CB and SCF electrically conductive networks, supporting each other, resulting in significant improvement of electrical properties, was supported by optical microscopy, while the roles of particulate and fibrous fillers were distinguished by scanning electron microscopy. In sequence, the volume resistivity curves of one filler systems and two fillers systems were figured out and compared. Moreover, experimental results substantiated that the actuation voltage of two-filler SMP composites’ shape recovery was prominently lower in comparison with that of one-filler systems at the same filler content. Additional, the response of glass transition temperature (Tg) and thermomechanical properties to filler content and two fillers’ synergic effect were characterized and illuminated experimentally. [ABSTRACT FROM AUTHOR]

The frequency dependent low-field circular ac susceptibility χ=χ′-jχ″ of a nearly nonmagnetostrictive Co68.2Fe4.3Si12.5B15 amorphous wire annealed at 470 °C is determined by impedance Z measurements under stepwise decreased longitudinal dc field Hdc from 216 to -216 A/m after premagnetization at 16 kA/m. It is found that compared with the results of the classical eddy-current model, the measured low-frequency loss factor is larger by an anomaly factor η between 1.5 and 3, depending on the value of Hdc. However, the χ(f) curve at each value of Hdc may be well fitted by an eddy-current model of bamboo-domain wall displacements if the material conductivity is replaced by a greater effective one and a proper value of effective domain size is chosen. The physical mechanism of such a fitting is discussed based on previous studies on anomalous dc circular susceptibility. This anomalous χ(f,Hdc) leads to an anomalous magnetoimpedance Z(Hdc) with a two-peak feature when frequency is high. [ABSTRACT FROM AUTHOR]

The conduction relaxations of polycrystalline La0.5Ca0.5Mn0.95Fe0.05O3 upon imposing rectangle electric current pulses (with minute time scale) are studied in details. We observe clear “overshooting” features of the conduction relaxation at both the front and rear edges of the current pulse so long as the pulse is sufficiently high. The Joule heating effect and the intrinsic stabilization of the ferromagnetic metal phase by the current pulse are linked in understanding our observations, and these effects may be applicable for resistance switching function. [ABSTRACT FROM AUTHOR]

The author calculates precisely the induced currents in striated YBa2Cu3O7 coated conductors covered partially by segmented pieces of normal metal, connecting the individual superconducting stripes. It is shown that the induced current density is below the critical current density of the superconducting stripes and the coupling losses are acceptable low, ensuring in addition sufficient current sharing between the stripes. Thus, the proposed structure can be applicable at ac conditions without twisting procedure. The ratio of the current closed between the normal plates to the current flowing in the superconducting stripes and the losses in the substrate are also discussed. The total current flowing through the whole length of the superconductor, which has to be closed at the ends, is also acceptable low. In addition, the frequency range, in which the magnetic flux can fully penetrate both between the stripes and into the normal segments, is given. [ABSTRACT FROM AUTHOR]

The dependences of series resistance, ideality factor, and junction voltage of light-emitting diodes (LEDs) on applied voltage or current were characterized accurately using alternating current (ac) behavior combined with I-V plot (ac IV method). The deep saturation of junction voltage and simultaneous decrease of ideality factor of LEDs at large forward current, which imply the pinning of quasi-Fermi levels, were observed. Comparing with our recent study of the similar phenomenon of laser diodes, in which the junction voltage jumps abruptly to a saturated value at lasing threshold, the changes of junction voltage of LEDs are gradual. In addition, the decrease of series resistance with the increasing current and the negative capacitance effect of LEDs were also investigated. [ABSTRACT FROM AUTHOR]

Scanning tunneling microscopy and electrical conductivity of redox molecules in conducting media (aqueous or other media) acquire increasing importance both as novel single-molecule science and with a view on molecular scale functional elements. Such configurations require full and independent electrochemical potential control of both electrodes involved. We provide here a general formalism for the electric current through a redox group in an electrochemical tunnel contact. The formalism applies broadly in the limits of both weak and strong coupling of the redox group with the enclosing metal electrodes. Simple approximate expressions better suited for experimental data analysis are also derived. Particular attention is given to the effects of the Debye screening of the electric potential in the narrow tunneling gap based on the limit of the linearized Poisson-Boltzmann equation. The current/overpotential relation shows a maximum at a position which depends on the ionic strength. It is shown, in particular, that the dependence of the maximum position on the bias voltage may be nonmonotonous. Approximate expressions for the limiting value of the slope of the current/overpotential dependence and the width of the maximum on the bias voltage are also given and found to depend strongly on both the Debye screening and the position of the redox group in the tunnel gap, with diagnostic value in experimental data analysis. [ABSTRACT FROM AUTHOR]

In the ideal case, noise measurements with four contacts minimize the contribution of the contact interface. There is a need to characterize conductance noise and noise correction factors for the different geometries provided with four contacts, as already is the case for resistivity measurements with van der Pauw structures. Here, we calculate the noise correction factors for two geometries with a pair of sensors and a pair of current driver electrodes placed in a square array. The first geometry investigated is a very large film compared to the distance L between four circular electrodes, which are placed in a square array far away from the borders of the film. The second is a square-shaped conductive film with side length L and provided with four quarter-circle corner contacts with radius l. The effect of the conductance noise in the film can be observed between current free sensors in a four-point measurement or between current carrying drivers in a two-point measurement. Our analytical expressions are based on approximations to solve the integrals [path_integral](J·J)2dA and [path_integral]|J|4dA for the voltage noise measured across a pair of sensors, SVQ, and across the drivers, SVD, respectively. The first and second integrands represent the squared dot product of the current density and adjoint current density and the modulus of the current density to the fourth power, respectively. The current density J in the samples is due to the current I passing through the driver contacts. The calculated expressions are applicable to samples with thickness t

[100]-tilt grain boundary Josephson junctions with misorientation of the c-axis directions have been fabricated using epitaxial (Hg0.9Re0.1)Ba2CaCu2Oy [(Hg,Re)-1212] thin films grown on SrTiO3 bicrystal substrates. Two types of the [100]-tilt junctions, that is, the mountain-type junction and the valley-type junction, of which a-b planes formed a mountain shape and a valley shape along the grain boundaries, respectively, were examined for various misorientation angles (θ). Both the types of junctions showed resistively shunted junction-type current-voltage (I-V) characteristics with relatively high characteristic voltages in a wide temperature range from 4.2 to 110 K. The valley-type junctions exhibited properties superior to those for the mountain-type junctions, such as very low excess current and much homogeneous current distribution, which is attributed to different film growth mode near the grain boundaries. They also exhibited the products of the critical current (Ic) and the normal-state resistance (Rn) as high as 3.0–4.2, 1.0–1.4, and 0.2–0.4 mV at 4.2, 77, and 100 K, respectively. The misorientation angle dependences of junction parameters for the [100]-tilt junctions were compared with those for conventional [001]-tilt junctions with misorientation of the a-b plane directions. The Rn and the IcRn products for the [100]-tilt junctions were substantially larger than those for the [001]-tilt junctions. Large hysteresis in the magnetic-field dependence of Ic was observed for the applied field larger than a certain threshold value, suggesting flux penetration between the CuO2 planes. [ABSTRACT FROM AUTHOR]

The electrical properties of heavily Al doped single and nanocrystalline 4H–SiC layers on semi-insulating 4H–SiC substrate, prepared by multienergy, high-fluence Al implantation and subsequent furnace annealing, are investigated by sheet resistance and Hall effect measurements. Ion beam induced crystallization is used to prepare the nanocrystalline SiC layers. The doping levels are chosen around the solid solubility limit of 2×1020 cm-3 in the range from 5×1019 to 1.5×1021 cm-3. The comparison of the results shows that heavily Al doped single crystalline SiC layers have superior conduction properties. The lowest resistivities measured at room temperature are 0.08 and 0.8 Ω cm for the single crystalline and nanocrystalline samples, respectively. Recent results on enhanced Al acceptor activation in nanocrystalline SiC cannot be confirmed. There is an upper limit for the hole concentration in the nanocrystalline samples independent of the Al supersaturation level in the as-implanted state due to outdiffusion of Al in excess to the solid solubility limit during annealing. In contrast to the nanocrystalline SiC layers the as-implanted Al profile in single crystalline material remains stable after annealing even for concentrations above the solid solubility limit. Therefore, in single crystalline material efficient impurity band conduction due to strongly interacting acceptors can be achieved in the range of supersaturation. For lower doping levels impurity band conduction is more effective in nanocrystalline SiC. [ABSTRACT FROM AUTHOR]

We report ultrafast (∼2.7 ps, instrument limited) switching responses of a multienergy-implanted GaAs:As+ photoconductive switches (PCSs) with suppressed trailing edge and reduced dark current. This material is highly resistive with dark current as low as 0.94 μA at a bias of 40 V. The carrier mobility of the former is ∼590 cm2/V s, resulting in a small-signal optical responsivity of ∼2 mA/W. Pumped at 100 mW and biased at 80 V, the multienergy-implanted GaAs:As+ PCS exhibits peak response (0.35 V) comparable to the best result of single-energy-implanted ones. The improvement on photoconductive response is crucial for the generation of shorter terahertz emission pulses from spiral antennas fabricated on multienergy-implanted GaAs:As+ (0.8 ps) than single-energy-implanted GaAs (1.2 ps), with the central frequency blueshifted to 0.2 THz (from 0.15 THz) and the spectral bandwidth broadened to 0.18 THz (from 0.11 THz). [ABSTRACT FROM AUTHOR]

Leakage current of Pt/(Ba0.7Sr0.3)TiO3 (BST)/YBa2Cu3O7-δ capacitors on a (001) SrTiO3 substrate was studied. By modeling a low-dielectric constant layer, a so-called dead layer, between the Pt/BST interface as a parasitic capacitor in series with the bulk layer capacitor, the leakage current of Pt/BST interface was well analyzed based on the modified Schottky emission equation. Furthermore, a two-step schematic energy band diagram is proposed to explain the carrier transport through the Pt/BST interface. [ABSTRACT FROM AUTHOR]

We report a study of long-lived photoexcited states in single crystals of functionalized forms of pentacene: the 6,13-bis(triisopropylsilylethynyl)pentacene and the 6,13-bis(triethylsilylethynyl)pentacene. These materials are organic semiconductors with band gaps in the range ≈1 eV. The relaxation rate of these states is thermally activated, as determined from time-and temperature-dependent measurements of the photoconductivity after illumination, and these states can be produced in a stable population at temperatures below 150 K. Consequently, after the low-temperature illumination, thermally stimulated current (TSC) is observed in the dark current with an increasing temperature. Analysis of the TSC signal allows estimation of energies associated with the excited states. Possible mechanisms for the current associated with the photoexcited states are discussed, and preliminary iodine-doped studies of the material are also presented. [ABSTRACT FROM AUTHOR]

Electrical contact to amorphous silicon nanoparticles was established with a method that self aligns the contacts to the particles. Charge transport characteristics were studied as a function of temperature and voltage. The conduction in these devices was not limited by the metal/semiconductor barrier; rather it was limited by charge trapping in the particles themselves. The data are well fit to theory. It was shown that the space charge limited current (SCLC) model fits the medium voltage range (2–6 V), while space charged limited current with Frenkel–Poole effect fits the relatively high voltage range (5–8 V). Using a model for space charge limited current in the presence of an exponential distribution of traps, we estimate that the trap density is 2×1019 cm-3. Based on SCLC enhanced with Frenkel–Poole effect, the activation energy measured at high voltage was determined to 0.44 eV. This agrees well with the medium voltage activation energy, 0.41 eV. [ABSTRACT FROM AUTHOR]

We present a theoretical model to describe electrical spin injection from a ferromagnetic contact into a conjugated organic semiconductor. In thermal equilibrium the magnetic contact is spin polarized, whereas the organic semiconductor is unpolarized. The organic semiconductor must be driven far out of local thermal equilibrium by an electric current to achieve significant spin current injection. However, if the injecting contact has metallic conductivity, its electron distribution cannot be driven far from thermal equilibrium by practical current densities. Thus, quasi-equilibration between the conjugated organic semiconductor and the metallic contact must be suppressed to achieve effective spin injection. This requires a spin-dependent barrier to electrical injection that may be due either to tunneling through the depletion region of a large Schottky barrier or to tunneling through a thin, insulating, interface layer. Schottky barrier formation on conjugated organic semiconductors differs from that on inorganic semiconductors inasmuch as contacts made to organic semiconductors often follow near-ideal Schottky behavior, thus permitting the energy barrier to electrical injection to be varied over a wide range by using metals with different work functions. In addition, insulating tunnel barriers to organic semiconductors based on organic molecules can be conveniently fabricated using self-assembly techniques. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In metallic ferromagnets, an electric current is accompanied by a flux of angular momentum, also called spin current. In multilayers, spatial variations of the spin current correspond to drive torques exerted on a magnetic layer. These torques result in spin precession above a certain current threshold. The usual kind of spin current is associated with translation of the spin-up and spin-down Fermi surfaces in momentum space. We discuss a different kind of spin current, associated with expansion and contraction of the Fermi surfaces. It is more nonlocal in nature, and may exist even in locations where the electrical current density is zero. It is larger than the usual spin current, in a ratio of 10 or 100, at least in the case of one-dimensional current flow. The new spin current is proportional to the difference Δμ¯=10[sup -3] eV between spin-up and spin-down Fermi levels, averaged over the entire Fermi surface. Conduction processes, spin relaxation, and spin-wave emission in the multilayer can be described by an equivalent electrical circuit resembling an unbalanced dc Wheatstone bridge. And Δμ¯ corresponds to the output voltage of the bridge. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The effect of an electric current on the indentation of nickel and copper samples was studied. Rectangular bars of nickel (99.7% pure) or copper (99.9% pure) with dimensions of 3x5x70 mm were polished and mounted on a sample holder which provided electrical contacts at the sample ends. A dc current I in the range of 0-15 A was injected parallel to the bar axis during Vickers indentation tests with loads of 0.25, 0.5 and 1 N. The tested surfaces were examined by scanning electron microscopy, and by x-ray diffraction. The nickel microhardness increased as a function of the current up to 10% for 1≤3-6 A, depending on the indenter loading, and then decreased monotonically by as much as 20-25%. The microhardness of the copper samples varied by less than 5% with I, except at a load of 0.25 N, where it increased up to 17% for I≤3 A, then decreased for 3

The ac complex conductivity δ*( f ) of polyaniline (PAN) films at different doping levels and different temperatures, in the 1-100 KHz frequency range, are reported. The results are typical of a disordered medium where the real component of ac conductivity is frequency independent at low frequencies, rising for higher values of frequencies. In order to interpret both the real and the imaginary components of δ*( f ), we developed a model which considers the doped PAN as a disordered insulating matrix, sprinkled with conductive islands generated by doping, as indicated by energy dispersed x-ray microanalysis. The conduction through the insulating matrix obeys the random free energy barrier model, while in the conductive islands a metallic frequency-independent conductivity is considered. From the fittings we obtained the activation energy value of the maximum energy barrier of the doping mechanism and estimated the concentration of hopping sites. [ABSTRACT FROM AUTHOR]

Investigates gate-current instability in boron-doped polycrystalline-silicon gate metal-oxide-silicon structures. Reversibility of current-increase characteristics for positive and negative bias cycles; Absence of positive charge buildup at the Si-SiO2 interface; Formation of a conductive region; Model for current instability.

Investigates the electric current and attractive force between spherical dielectric particles surrounded by a conducting film and situated in a nonpolar liquid. Analytical approach of the study; Numerical results; Effects of oil and particle conductivity parameters.

Addresses the dynamics of melting in current-carrying conductors. Dependence of temperature at the front of phase transition upon the distance from the axis of the conductor; Ratio of electric conductivities in liquid and solid phases; Cause of the change of the electric current distribution in the conductors.

Studies the application of the finite element method to heat conduction problems where the heat generation is due to electric current flowing through the body. Information on the governing equations; Details on the finite element formulation; Description of the thermal switching device.

Presents calculations and measurements of current as a function of voltage I(V), and conductivity at low voltage as a function of temperature, G(T). Manner in which the current was modeled; Technique used in obtaining the shape of the conduction-band edge; Description of the physical model.

Presents a study which examined radiation-induced conductivity (RIC) of polymers in different gases. Properties of RIC of polymers; Details of the experimental techniques used; Behavior of the dark current observed in the absence of radiation.

Presents a study that solved the three-dimensional flow of heat in a wire carrying a current and immersed in a liquid. Measurement of the surface conductance of copper in petroleum ether; Quantity of the measured surface conductance; Agreement of the results with a simplified one-dimensional heat-flow problem.

Presents a study that examined electrical conduction phenomena in polyimide films with particular attention devoted to the separation of interface and bulk phenomena. Temperature range by which the measurements were conducted; Effective work function for aluminum-polyimide; Dependence of the currents on electrode material.

The transport eddy-current loss of a nearly nonmagnetostrictive CoFeSiB amorphous wire under a large longitudinal bias field can be several times greater than the value commonly expected by the classical model. Related to the overlarge circular susceptibility under the same condition, this is attributed to the formation of disklike soft-magnetic microstructures around hard magnetic inclusions randomly embedded in a soft magnetic matrix. [ABSTRACT FROM AUTHOR]