Carriers Motion Research Articles

Analysis of FDS Characteristics of Oil-impregnated Paper Insulation under High Electric Field Strength Based on the Motion of Charge Carriers

Frequency Domain Spectroscopy (FDS) is a powerful tool to study the dielectric properties of oil-paper insulation, which is widely used under high electric field strength. The motion of charge carriers under high electric field strength will cause new dielectric characteristics in FDS curves, from which more information could be extracted for insulation state assessment. In this paper, FD spectra are measured under high electric field strength. The electric field dependence of the loss peak in middle frequency and the characteristics of dielectric loss in low frequency are studied. With the influence of trapping on the motion of charge carriers under electric field being considered, charge carriers hopping polarization model and charge carriers motion dependent conductance model are proposed. The trap energy level of oil-paper insulation decreases when the moisture content increases, thus, the motion characteristics of charge carriers change, leading to decreasing loss peak in middle frequency and inverse dielectric loss characteristics in low frequency. These two models introduce the influence of traps on carrier motion into the dielectric response and enable one to gain a better understanding of the dielectric properties of oil-paper insulation under high electric field strength.

Particles-on-surface sensor with potential barriers embedded in a semiconductor target

Recently, we calculated an effect of surface charges on potential barriers embedded inside a Si target. As a result, electrons and holes transport in a semiconductor target could be controlled by ionized atoms or molecules situated inside the surface adsorbate layer. Since GaAs possesses higher electron mobility than Si, in this paper we calculate the potential distribution and charge carriers motion dependences on the GaAs target surface charge value and dopant concentration. Computer simulation was implemented using the software COMSOL Multiphysics. The obtained results can help to improve a design of GaAs radiation detector, particle detector, surface charge detector, biochemical sensor, etc.

Observation of open-orbit Fermi surface topology in the extremely large magnetoresistance semimetal MoAs2

While recent advances in band theory and sample growth have expanded the series of extremely large magnetoresistance (XMR) semimetals in transition metal dipnictides $TmPn_2$ ($Tm$ = Ta, Nb; $Pn$ = P, As, Sb), the experimental study on their electronic structure and the origin of XMR is still absent. Here, using angle-resolved photoemission spectroscopy combined with first-principles calculations and magnetotransport measurements, we performed a comprehensive investigation on MoAs$_2$, which is isostructural to the $TmPn_2$ family and also exhibits quadratic XMR. We resolve a clear band structure well agreeing with the predictions. Intriguingly, the unambiguously observed Fermi surfaces (FSs) are dominated by an open-orbit topology extending along both the [100] and [001] directions in the three-dimensional Brillouin zone. We further reveal the trivial topological nature of MoAs$_2$ by bulk parity analysis. Based on these results, we examine the proposed XMR mechanisms in other semimetals, and conclusively ascribe the origin of quadratic XMR in MoAs$_2$ to the carriers motion on the FSs with dominant open-orbit topology, innovating in the understanding of quadratic XMR in semimetals.

Charge Carriers Motion in P3HT:Capped ZnO Nanoparticles Blend Films; Impact of Capping Agents

<p class="TTPAbstract">Blend of conjugated polymer poly(3-hexylthiophene) or P3HT and Zinc Oxide nanoparticles (ZnO-NP) has been intensively used as active material for high performance hybrid solar cells. However, agglomeration of ZnO-NP hinders efficient charge carrier<span lang="IN">s</span> transfer both from P3HT to ZnO-NP and <span lang="IN">their </span>transport within ZnO-NP which cause to low performance of solar cells. Capping of ZnO-NP is currently applied to avoid this agglomeration effect. In this study, we used three different capping agents to cap ZnO-NP, namely small semiconducting molecules squaraine, 2-naphthalene and insulating polymer polyvinylpyrrolidone. We <span lang="IN">conducted</span> temperature dependence of photoinduced infrared absorption spectroscopy to study charge carriers motion in the P3HT:capped ZnO nanoparticles blend films. The measurement was carried out with light irradiation of 532 nm and temperature ranging from 78 to 300 K. The spectra were analyzed by a bimolecular carrier recombination method with Arrhenius activation energy. Two parallel charge carrier recombination processes are observed, namely polarons recombination along polymer chain (intra-chain) and inter-chain polarons recombination in the P3HT-chains. At low temperatures, polarons recombine along polymer chains (intra-chain) with activation energy between 19-23 eV for all samples. However, the inter-chain polaron motion is influenced by capping agents as shown by a variation in its activation energy ranging from 28 to 58 eV.</p>

Charge Carriers Motion in P3HT:Capped ZnO Nanoparticles Blend Films; Impact of Capping Agents

<p class="TTPAbstract">Blend of conjugated polymer poly(3-hexylthiophene) or P3HT and Zinc Oxide nanoparticles (ZnO-NP) has been intensively used as active material for high performance hybrid solar cells. However, agglomeration of ZnO-NP hinders efficient charge carrier<span lang="IN">s</span> transfer both from P3HT to ZnO-NP and <span lang="IN">their </span>transport within ZnO-NP which cause to low performance of solar cells. Capping of ZnO-NP is currently applied to avoid this agglomeration effect. In this study, we used three different capping agents to cap ZnO-NP, namely small semiconducting molecules squaraine, 2-naphthalene and insulating polymer polyvinylpyrrolidone. We <span lang="IN">conducted</span> temperature dependence of photoinduced infrared absorption spectroscopy to study charge carriers motion in the P3HT:capped ZnO nanoparticles blend films. The measurement was carried out with light irradiation of 532 nm and temperature ranging from 78 to 300 K. The spectra were analyzed by a bimolecular carrier recombination method with Arrhenius activation energy. Two parallel charge carrier recombination processes are observed, namely polarons recombination along polymer chain (intra-chain) and inter-chain polarons recombination in the P3HT-chains. At low temperatures, polarons recombine along polymer chains (intra-chain) with activation energy between 19-23 eV for all samples. However, the inter-chain polaron motion is influenced by capping agents as shown by a variation in its activation energy ranging from 28 to 58 eV.</p>

Modeling and manufacturing of a micromachined magnetic sensor using the CMOS process without any post-process.

The modeling and fabrication of a magnetic microsensor based on a magneto-transistor were presented. The magnetic sensor is fabricated by the commercial 0.18 μm complementary metal oxide semiconductor (CMOS) process without any post-process. The finite element method (FEM) software Sentaurus TCAD is utilized to analyze the electrical properties and carriers motion path of the magneto-transistor. A readout circuit is used to amplify the voltage difference of the bases into the output voltage. Experiments show that the sensitivity of the magnetic sensor is 354 mV/T at the supply current of 4 mA.

Gravity Effect on Electrical Field Generation and Charge Carriers Transfer During Combustion Synthesis of Sulfides

The effect of gravity on the electric potential generated by the combustion synthesis of zinc sulfide is analyzed using the numerical simulation. Recent experimental studies on generation of electric voltage during combustion synthesis of zinc sulfide (ZnS) have revealed high voltage signals (4 V) with duration about 1 s, which are much higher than those produced by the gas-solid and solid-solid combustion reactions studied previously. These data have raised the question about mechanism of such a phenomenon. In our previous work we developed a novel (distributed) model describing the electric potential generation during combustion synthesis of sulfides (CSS) that didn't count the effect of gravity. In this paper the simulations of heat - mass transfer, charge carriers motion, and voltage profiles taking into account the Earth gravity effect. The simulations confirms that the gravitation force strongly affects the emission of negatively charged sulfur ions as well as electrons and has a significant impact on the amplitude and temporal evolution of the combustion induced voltage. The voltage reduction up to four times has been observed numerically in the case when gravity acts in the direction coincident to that of the propagating combustion wave. Vice versa, the significant acceleration of the combustion and the voltage amplification due to the advection is simulated when gravity acts in the direction opposite to that of the propagating combustion wave.

A Newly Developed Self-Contained Inclinometer for Offshore Platform Anchor Monitoring

This paper presents the research and development of a special self-contained Inclinometer based on the requirement of offshore platform monitoring. The device records the anchors inclination completely and accurately, providing information for stress analysis of the anchor chain. Laboratory calibration, platform movement simulation experiment, and real platform testing confirmed the instrument can meet the measurement requirements. The instrument is high-precision, energy-economical, mass-storage and user-friendly. Its able to work underwater continuously for up to one year. In addition, the small size minimizes the interference caused by the carriers motion. Compared with its foreign counterparts, the new instrument is inexpensive, so its suitable for extensive multi-point measurement. Now it has been installed in LH11-1 platform in the South China Sea for measurement of anchor chain inclination. Its the first time to employ measuring device with autonomous right in offshore platform monitoring in China.

Non Linear Modeling of Mixed Ionic Electronic Conductors

A nonlinear model for the study of Mixed Ionic Electronic Conductors (MIEC) is presented in this paper. The model is time dependent and takes into account electrical carriers motion, the electrical behavior of the MIEC-metal interface and the kinetics of the chemistry occurring at the MIEC surface. By applying a small potential input complex impedances are computed.

Modeling and Analysis of High-Temperature Superconductor Terahertz Photomixers

Photomixing phenomenon in superconductors is studied. For a photo-excited superconductor film the fundamental equations for the carriers motion inside the superconductor material have been used in connection with the two-temperature model to find an analytic expression for the generated terahertz (THz) photocurrent inside the film. The dependency of the resulting photocurrent on the material and laser parameters, temperature, and photomixer configuration for a photomixer made of YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// high-temperature superconductor is studied.

Spin Ladders : From 1 to 2 dimensions

We first review the general properties of the spin ladder compounds, a new class of low dimensional strongly correlated systems of fermions which exhibit specific original properties. Of particular interest is the versatility of these systems, in some cases reminiscent of quasi-one dimensional conductors, and in, other cases reminiscent of quasi-two dimensional high-T c superconductors, depending on the ladder structure (number of legs), Umklapp scattering, doping of charge carriers, external parameters such as temperature, pressure and magnetic field. The understanding of the dimensional crossover, from one dimension to two dimensions, when these parameters are varied is, therefore, particularly important. A related question is the interplay between the spin gap in the magnetic excitation spectrum and the superconducting temperature under pressure, observed in these compounds, in obvious relationship with high-T c superconductors physics. To get more insights into the pressure induced superconducting transition, we have focused our interest on doped coupled ladder systems. We have studied the effect of Umklapp process on two-leg Hubbard ladders with half-filled bands which strongly reduces the interladder hopping and promotes SDW correlations at the expense of superconducting ones. To provide information on the confinement-deconfinement phenomenon induced by the hopping process under pressure, we have investigated the orbital effect of a magnetic field on a system of weakly coupled Hubbard ladders, which induces a reduction in the effective dimensionality of the system, by confining the carriers motion within the ladders. We conclude by suggesting promising studies in the context of ladder materials.

Hydration and conductivity studies of polymer–water interactions in polyacrylamide hydrogels

The conductivity and hydration mechanisms of polyacrylamide (PAA) hydrogels have been investigated by means of (a) equilibrium and dynamic water sorption isotherms, (b) thermally stimulated depolarization currents (TSDC) techniques in the temperature range 77 to 300 K and (c) broad band dielectric relaxation spectroscopy (DRS) in the frequency range 10−2 to 106 Hz and the temperature range 230 to 330 K. A systematic analysis of our combined results indicates that water molecules up to a critical hydration value, hc, of about 0.15 g of water/g of dry weight are irrotationally bound to primary hydration sites and do not contribute themselves to the dielectric spectra. This hc value is in accordance with equilibrium isothermal measurements on the same samples. Moreover, a reorganization of water in the hydrogels seems to take place for h≥0.8. The Arrhenius behaviour of DC-conductivity, σdc, as well as of the loss tangent, tan δ, and electric modulus, M″, dispersions, with an activation energy of the order of 0.8 eV, suggests that the observed phenomena have a common origin and that the conductivity mechanism is not governed by the co-operative motion of the polymeric chains, the charge carriers (protons) motion occurring probably through the water-filled micropores of the hydrogel.

Electrical behaviour of La1.33−xM3xTi2O6 perovskites (M=Li, Na and K)

Structural characterization and ionic conductivity properties of the La1.33−xM3xTi2O6 (M=Li, Na and K) perovskite-type series are reported. From X-Ray diffraction data two different symmetries, tetragonal and orthorhombic, were observed as a function of the ionic size of alkaline cations as well as their proportion in the compounds. Crystallographic features seem to influence on the two possible conduction mechanisms. Orthorhombic samples allow the charge carriers motion through a 3D pathway whereas in the tetragonal ones mobile cations only can move into the A-planes in which are located.