Search

The polarity dependence of the radiation hardness of single-crystalline ZnO bulk crystals is studied by irradiating the Zn-polar and O-polar c-planes with an 8 MeV proton beam up to the fluence of 4.2 × 1016 p/cm2. To analyze the hardness, radiation-induced defects were evaluated using positron annihilation (PA) analysis, and the recovery by post-annealing was examined using continuous-wave photoluminescence (PL) and time-resolved photoluminescence (TRPL) measurements. It was suggested by the PA and PL analyses that the major defects in both polarities were VZnVO divacancies. While the PA data did not show the clear dependence on the polarity, the PL and TRPL results showed that the Zn-polar c-plane had a little higher radiation tolerance than that of the O-polar c-plane, which was consistent with the result that the increase in the electrical resistance by proton beam irradiation was smaller for the former one. Considering these results in total, the polarity dependence is considered to be not so large, but the Zn-polar c-plane has a little higher tolerance than that of the O-polar one. [ABSTRACT FROM AUTHOR]

In this work, we study the basic processes during the initial stages of growth which control polarity in N-polar AlN films grown on c-plane sapphire substrates by metalorganic chemical vapor deposition. More specifically, we study the morphology and atomic structure of the films as dependent on nitridation conditions, i.e., duration and temperature, by atomic force microscopy, high resolution transmission electron microscopy ,and high resolution high-angle annular dark field scanning transmission electron microscopy. Our experimental results show that beyond a critical temperature of 1000°C in addition to an omnipresent two-dimensional aluminum-oxynitride layer, three-dimensional Al-polar AlN islands form. While the aluminum-oxynitride layer is unstable under high temperature growth conditions and results in N-polar films, Al-polar islands are stable and induce Al-polar columnar inversion domains in the N-polar AlN films. Appropriate nitridation conditions (approximately 10 minutes at T=850°C–950°C) and adjustment of growth parameters (reactor pressure, NH3 flux, etc.) prevent the formation of Al-polar islands, which is essential for achieving N-polar films free of inversion domains. [ABSTRACT FROM AUTHOR]

In this paper, the authors report rationally designed, innovative tri-layer flexible transparent conductive electrodes (TCEs) fabricated via thermal deposition. The proposed structure improves transparency compared with that of the traditional tri-layer electrode (dielectric/metal film/dielectric) by using metallic grid patterns (dielectric/metal grids/dielectric). The obtained MoO3/Ag grids/MoO3 TCEs show low sheet resistance and good mechanical properties. The sheet resistance of the proposed electrodes is 5.88 Ω/square and the transmittance reaches 76.5%, which are better than those of conventional MoO3/Ag film/MoO3 electrodes (6.12 Ω/square, <70%). The mechanical properties are significantly improved compared with those of MoO3/Ag film/MoO3 in the bending test under both tensile and compressive stress. The surface features of the MoO3/Ag grids/MoO3 TCEs were measured using the contact angle method to calculate the surface energy and polarity. The polarity is 0.5-0.26, which is better than those of indium tin oxide (0.35) and MoO3/Ag film/MoO3 (0.5-0.0058) electrodes for 0-800 bending cycles. The proposed flexible transparent electrodes show good optical, electrical, and mechanical characteristics and have potential for application in optoelectronics. [ABSTRACT FROM AUTHOR]

There are three possible ways of reducing the charge density (ns) in the N-polar high electron mobility transistors (HEMT) structures, by decreasing the channel thickness, applying reverse gate bias, or modifying the back-barrier. Understanding the behavior of 2DEG mobility as a function of ns is essential to design high performance HEMT devices. Experimental data show that in the N-polar HEMT structures, the 2DEG mobility reduces as the ns decreases by applying reverse gate bias or decreasing channel thickness, whereas in the Ga-polar HEMT structures, the 2DEG mobility increases as the ns in the channel decreases by applying reverse gate bias. In this paper, the 2DEG mobility as a function of ns is calculated in N-polar HEMTs for three different aforementioned cases, and is compared to that in the Ga-polar HEMT structures. It is shown that the conventional scattering mechanisms cannot explain these different behaviors. Two new scattering mechanisms, such as scattering from charged interface states and surface state dipoles (SSD), are introduced. It is revealed that in N-polar HEMT structures, reducing ns by applying reverse gate bias or decreasing channel thickness moves the charge centroid closer to the AlGaN-GaN interface. A combination of lower charge density (less screening of the scattering potential) and smaller distance between charge centroid and charged states at the interface leads to a severe mobility degradation in these cases. In contrast, reducing ns by modifying the back-barrier (decreasing back-barrier doping and/or decreasing AlGaN composition) in N-polar HEMT structures moves the charge centroid away from the interface. This behavior is similar to that in the Ga-polar HEMT structures. Therefore, in the last two mentioned cases, the 2DEG mobility first increases slightly as the ns decreases, and decreases slightly at very low charge densities. It is also shown that SSDs have large impact on the 2DEG mobility only in the N-polar (Ga-polar) HEMTs with thin channels (barriers). [ABSTRACT FROM AUTHOR]

Symmetry perception in dot patterns is tolerant to temporal delays of up to 60 ms within and between element pairs. However, it is not known how factors effecting symmetry discrimination in static patterns might affect temporal integration in dynamic patterns. One such feature is luminance polarity. Using dynamic stimuli with increasing temporal delay (SOA) between the onset of the first and second element in a symmetric pair, we investigated how four different luminance-polarity conditions affected the temporal integration of symmetric patterns. All four luminance polarity conditions showed similar upper temporal limits of approximately 60 ms. However psychophysical performance over all delay durations showed significantly higher symmetry thresholds for unmatched-polarity patterns at short delays, but also significantly less sensitivity to increasing temporal delay relative to matched-polarity patterns. These varying temporal windows are consistent with the involvement of a fast, sensitive first-order mechanism for matched-polarity patterns, and a slower, more robust second-order mechanism for unmatched-polarity patterns. Temporal integration windows for unmatched-polarity patterns were not consistent with performance expected from attentional mechanisms alone, and instead supports the involvement of second-order mechanisms that combines information from ON and OFF channels. [ABSTRACT FROM AUTHOR]

In order to study the dependence of water solubility and hydration behavior of nanoparticles on their surface polarity, we designed polar nanoparticles with varying surface polarity by assigning atomic partial charge to the surface of C60. The water solubility of the nanoparticle is enhanced by several orders of magnitude after the introduction of surface polarity. Nevertheless, when the atomic partial charge grows beyond a certain value (qM), the solubility continuously decreases to the level of nonpolar nanoparticle. It should be noted that such qM is comparable with atomic partial charge of a variety of functional groups. The hydration behaviors of nanoparticles were then studied to investigate the non-monotonic dependence of solubility on the surface polarity. The interaction between the polar nanoparticle and the hydration water is stronger than the nonpolar counterpart, which should facilitate the dissolution of the nanoparticles. On the other hand, the surface polarity also reduces the interaction of hydration water with the other water molecules and enhances the interaction between the nanoparticles which may hinder their dispersion. Besides, the introduction of surface polarity disturbs and even rearranges the hydration structure of nonpolar nanoparticle. Interestingly, the polar nanoparticle with less ordered hydration structure tends to have higher water solubility. [ABSTRACT FROM AUTHOR]

Magnetic vortex cores exhibit a gyrotropic motion and may reach a critical velocity, at which point they invert their z-component of the magnetization. We performed micromagnetic simulations to describe this vortex core polarity reversal in magnetic nanodisks with a perpendicular anisotropy. We found that the critical velocity decreases with the increase in perpendicular anisotropy, therefore departing from a universal criterion that relates this velocity only to the exchange stiffness of the material. This leads to a critical velocity inversely proportional to the vortex core radius. We have also shown that in a pair of interacting disks, it is possible to switch the core vortex polarity through a non-local excitation; exciting one disk by applying a rotating magnetic field, one is able to switch the polarity of a neighbor disk, with a larger perpendicular anisotropy. [ABSTRACT FROM AUTHOR]

We report on the study of the extraordinary Hall effect (EHE) in Co-Pd alloys, bi-layers, and multilayers. Polarity of the effect and its changes with aging and post-deposition annealing are attributed to a gradual intermixing and formation of interfacial Co-Pd alloys. In multilayers with sub-monoatomic layers of Co, the intermixing is mostly accomplished during the fabrication itself. In bi-layers and multilayers with thicker Co, the process of spontaneous interfacial alloying continues after the deposition with an effective room temperature alloying period of 100 days. As far as the EHE is concerned, the stabilized Co/Pd multilayers behave as alloys with effective concentration corresponding to the thickness ratio between the Co and Pd layers. [ABSTRACT FROM AUTHOR]

We report the influences of group-III source preflow, which were introduced prior to the growth of the low temperature GaN on the polarity, photoluminescence (PL), and crystallographic properties of GaN epilayers grown on nitridated c-plane sapphire substrates by metal-organic chemical vapor deposition. By studying the surface morphology evolutions under chemical etching in KOH, we found that with increasing the trimethyl-gallium (TMGa) preflow duration (t), the polarity of the GaN film can be changed from a complete N-polarity to a mixture of N-and Ga-polarity and further to a complete Ga-polarity. PL and high-resolution X-ray diffraction studies revealed that the impurity incorporation and the edge-and screw-type threading dislocations are strongly polarity dependent. A further study at the optimized t (i.e., 30 s for TMGa) shows that the polarity inversion of GaN can be realized not only by TMGa preflow but also by trimethyl-aluminium preflow and by trimethyl-indium preflow. A two-monolayer model was employed to explain the polarity inversion mechanism. [ABSTRACT FROM AUTHOR]

Magnetostatic interactions between vortices in closely spaced planar structures are important for applications including vortex-based magnonic crystals and spin torque oscillator networks. Analytical theories that include magnetostatic interaction effects have been proposed but have not yet been rigorously tested. Here, we compare micromagnetic simulations of the dynamics of magnetic vortices confined in three disks in an equilateral triangle configuration to analytical theories that include coupling. Micromagnetic simulations show that the magnetostatic coupling between the disks leads to splitting of the gyrotropic resonance into three modes and that the frequency splitting increases with decreasing separation. The temporal profiles of the magnetization depend on the vortex polarities and chiralities; however, the frequencies depend only on the polarity combinations and will fall into one of two categories: all polarities equal or one polarity opposite to the others, where the latter leads to a larger frequency splitting. Although the magnitude of the splitting observed in the simulations is larger than what is expected based on purely dipolar interactions, a simple analytical model that assumes dipole-dipole coupling captures the functional form of the frequency splitting and the motion patterns just as well as more complex models. [ABSTRACT FROM AUTHOR]

Interface polarization and interface zone have been widely utilized to account for the abnormally improved dielectric properties of composites although their formation is rather vague and their influence has never been directly measured. In this work, micro α-SiC was designed as the filler particles incorporated into poly(vinylidenefluoride-co-chlorotrifluoroethylene) with internal double bonds (P(VDF-CTFE-DB)) to construct polymer micro composites through solution casting method. The dielectric constant of the composites is found to be increasing linearly as SiC content increases at lower content and the highest value is obtained as 83 at 100 Hz, which is unusually higher than both pristine polymer (13@100 Hz) and SiC filler (17@100 Hz). By studying the dielectric properties of a bilayer model composite, the real dielectric permittivity of SiC sheet and P(VDF-CTFE-DB) layer has been directly measured to be significantly enhanced than their original value. The induced polarity between high polar PVDF units in polymer matrix and the electronhole dipoles in α-SiC is responsible for the elevated dielectric properties of both components, which could address the failure of binary series and parallel models in predicting the dielectric permittivity of 0-3 composites as well. The strong dependence of induced polarity on the volume content, thickness, and polar nature of both components strongly suggests establishing promising high induced polarity between polymer matrix and fillers may provide an alternative strategy for fabricating high-k composites. [ABSTRACT FROM AUTHOR]

Preparation and characteristics of conductive-bridge random access memory devices containing Ge2Sb2Te5 (GST) chalcogenide as the solid-state electrolyte, Ag as the active electrode, and W-Ti as the counter electrode are presented. As revealed by the electrical measurement, only the samples containing crystalline GST exhibited the resistive switching behaviors. With an insertion of ZnS-SiO2 dielectric layer at the Ag/GST interface and a postannealing at 100?°C for 1?min, the sample exhibited the best electrical performance with satisfactory cycleability and retention properties. Moreover, the forming-free and bi-directional polarity features were observed in such a sample type. Microstructure and composition analyses found the finely dispersed nano-scale Ag clusters in GST and, when electrical bias is applied, the migrating Ag ions may build up the connections in between neighboring Ag clusters. Moreover, grain boundaries in polycrystalline GST might be the main paths for Ag migration. The thread-like conduction channels in GST hence form, leading to the low resistance state of sample. On the contrary, the depletion of Ag in GST broke the connections in between Ag clusters when the electrical bias is reversed. This led to the rupture of conduction channels and, hence, the high resistance state of sample. The low operational voltage, forming-free, and bi-directional polarity features observed in (AZGW)T sample might also originated from the fine dispersion of Ag clusters in GST electrolyte. [ABSTRACT FROM AUTHOR]

Surface states and their influence on the Fermi level at the surface of GaN and AlN are studied using x-ray photoelectron spectroscopy (XPS). The effect of polarity on surface electronic properties was studied. Accurate modeling of the valence band edge and comparison with XPS data revealed the presence of donor surface states at 1.4 eV and acceptor states at energies >2.7 eV from the valence band in GaN. Al polar AlN showed acceptor states at energies >3.3 eV. Density of acceptor surface states was estimated to be between 1013 and 1014 eV-1 cm-2 in both GaN and AlN. The shift in charge neutrality levels and barrier heights due to polarity and the density of surface states on AlN and GaN were estimated from XPS measurements. Theoretical modeling and comparison with XPS data implied full compensation of spontaneous polarization charge by charged surface states. Barrier height measurements also reveal a dependence on polarity with φmetal-polar > φnon-polar > φnitrogen-polar suggesting that the N-polar surface is the most suitable for Ohmic contacts. [ABSTRACT FROM AUTHOR]

In this paper, positive, negative, and bipolar nanosecond pulses are employed to generate stable and diffuse discharge plasma using array needles-plate electrode configuration at atmospheric pressure. A comparison study of discharge images, electrical characteristics, optical emission spectra, and plasma vibrational temperature and rotational temperatures in three pulsed polarity discharges is carried on under different discharge conditions. It is found that bipolar pulse is beneficial to the excitation of diffuse dielectric barrier discharge, which can generate a room temperature plasma with more homogeneous and higher discharge intensity compared with unipolar discharges. Under the condition of 6mm electrode gap distance, 26 kV pulse peak voltage, and 150 Hz pulse repetition rate, the emission intensity of N2 (C3Πu → B3Πg) of the bipolar pulsed discharge is 4 times higher than the unipolar discharge (both positive and negative), while the plasma gas temperature is kept at 300 K, which is about 10-20K lower than the unipolar discharge plasma. [ABSTRACT FROM AUTHOR]

Polarity of semipolar GaN(1011) (1011) and GaN(20211) (2021) surfaces was determined with X-ray photoelectron diffraction (XPD) using a standard MgKα source. The photoelectron emission from N 1s core level measured in the a-plane of the crystals shows significant differences for the two crystal orientations within the polar angle range of 80-100° from the <0001> normal. It was demonstrated that XPD polar plots recorded in the a-plane are similar for each polarity of the GaN{1011} and GaN{2021} crystals if referred to <0001> crystal axes. For polarity determinations of all important GaN{h0hl} semipolar surfaces, the above given polar angle range is suitable. [ABSTRACT FROM AUTHOR]

Earlier, using phenomenological approach, we showed that in some cases polarizable models of condensed phase systems can be reduced to nonpolarizable equivalent models with scaled charges. Examples of such systems include ionic liquids, TIPnP-type models of water, protein force fields, and others, where interactions and dynamics of inherently polarizable species can be accurately described by nonpolarizable models. To describe electrostatic interactions, the effective charges of simple ionic liquids are obtained by scaling the actual charges of ions by a factor of 1/ √εel , which is due to electronic polarization screening effect; the scaling factor of neutral species is more complicated. Here, using several theoretical models, we examine how exactly the scaling factors appear in theory, and how, and under what conditions, polarizable Hamiltonians are reduced to nonpolarizable ones. These models allow one to trace the origin of the scaling factors, determine their values, and obtain important insights on the nature of polarizable interactions in condensed matter systems. [ABSTRACT FROM AUTHOR]

A field theory is proposed to extend the standard piezoelectric framework for linear elastic solids by accounting for the presence and motion of dislocation fields and assessing their impact on the piezoelectric properties. The proposed theory describes the incompatible lattice distortion and residual piezoelectric polarization fields induced by dislocation ensembles, as well as the dynamic evolution of these fields through dislocation motion driven by coupled electro-mechanical loading. It is suggested that (i) dislocation mobility may be enhanced or inhibited by the electric field, depending on the polarity of the latter, (ii) plasticity mediated by dislocation motion allows capturing long-term time-dependent properties of piezoelectric polarization. Due to the continuity of the proposed electro-mechanical framework, the stress/strain and polarization fields are smooth even in the dislocation core regions. The theory is applied to gallium nitride layers for validation. The piezoelectric polarization fields associated with bulk screw/edge dislocations are retrieved and surface potential modulations are predicted. The results are extended to dislocation loops. [ABSTRACT FROM AUTHOR]

We develop a criterion for spark-breakdown in non-uniform field geometries with positive polarity and small electrode separations so that breakdown evolves without the formation of a leader. We arrive at the spark-breakdown criterion by framing it in terms of gain and instability conditions, whose relative importance is established from an analysis of the experimental breakdown characteristics and correlations with streamer behavior in short gaps. Results are presented in the context of two generic geometries having coaxial and point-plane electrodes. For nearly uniform field situations, we re-confirm that the breakdown criterion obtained by the usual extension of either the Townsend or Meek criteria satisfactorily predicts the experimental results. On the other hand, for increasing non-uniformity, the results for the corona and spark branches of the breakdown characteristics are shown inconsistent with a breakdown criterion solely based on either the Townsend or streamer mechanisms. In particular, the avalanche gain factor, the primary component of the Townsend and streamer criteria, does not determine the spark breakdown criterion. Streamers can cross the gap for a significantly wide range of applied voltages without triggering a spark. We find that it is the instability condition, derived from a relation between the minimum Laplacian field in the gap and the local streamer body field (which we relate to the streamer sustaining field), that is sufficient for determining the spark threshold thereby yielding a breakdown criterion. [ABSTRACT FROM AUTHOR]

Nanosecond pulse driven dielectric barrier discharge plasma actuators are studied in quiescent air using a power supply capable of producing negative and positive polarity waveforms. High voltage pulses are applied to the exposed electrode of typical asymmetric actuator geometry. In addition to polarity, the effects of pulse amplitude, actuator length, and dielectric thickness are also investigated. Schlieren images are used to estimate the relative near surface gas heating, while electrical measurements are acquired simultaneously. Negative polarity pulses develop slightly more energy per unit length for thin dielectrics, while positive polarity is slightly higher for thick dielectrics. In most cases, the difference in per unit length energy produced by positive and negative pulses on equivalent actuators is not outside the measurement uncertainty. Negative polarity pulses are found to produce a stronger pressure wave for a given peak voltage and pulse energy across the test matrix. Results indicate that the negative polarity pulse more efficiently couples electrical energy to the near surface gas as heat. This suggests negative polarity pulses may be preferred for aerodynamic flow control applications employing this actuator arrangement. [ABSTRACT FROM AUTHOR]

We demonstrate the use of anomalous x-ray scattering of constituent cations at their absorption edge, in a conventional Bragg-Brentano diffractometer, to measure absolutely and quantitatively the polar orientation and polarity fraction of unipolar and mixed polar wurtzitic crystals. In one set of experiments, the gradual transition between c+ and c- polarity of epitaxial ZnO films on sapphire as a function of MgO buffer layer thickness is monitored quantitatively, while in a second experiment, we map the polarity of a lateral polar homojunction in GaN. The dispersion measurements are compared with piezoforce microscopy images, and we demonstrate how x-ray dispersion and scanning probe methods can provide complementary information that can discriminate between polarity fractions at a material surface and polarity fractions averaged over the film bulk. [ABSTRACT FROM AUTHOR]

Resistive switching was observed in Pt/SrTiO3/Pt capacitor devices. The switching depends on both the amplitude and polarity of the applied voltage and cannot be described as either bipolar or unipolar resistive switching. We term this behavior antipolar due to the opposite polarity of the set voltage relative to the previous reset voltage. A model based on electron injection by tunneling at interfaces and a Poole-Frenkel mechanism through the bulk is proposed. This model is quantified by use of a simple mathematical equation to simulate the experimental results. [ABSTRACT FROM AUTHOR]

A strong injection level dependence of the effective minority carrier lifetime (τeff) is typically measured at low injection levels for undiffused crystalline silicon (c-Si) wafers symmetrically passivated by a highly charged dielectric film. However, this phenomenon is not yet well understood. In this work, we concentrate on two of those possible physical mechanisms to reproduce measured τeff data of c-Si wafers symmetrically passivated by atomic layer deposited Al2O3. The first assumes the existence of a defective region close to the c-Si surface. The second assumes asymmetric electron and hole lifetimes in the bulk. Both explanations result in an adequate reproduction of the injection dependent τeff found for both n- and p-type c-Si wafers. However, modeling also predicts a distinctly different injection dependence of τeff for the two suggested mechanisms if the polarity of the effective surface charge is inverted. We test this prediction by experimentally inverting the polarity of the effective surface charge using corona charges. From the experiments and simulations, it is concluded that surface damage is the most likely cause of the significant reduction of τeff at low injection levels. [ABSTRACT FROM AUTHOR]

The article discusses an optimization strategy designed to improve the International Seismological Centre (ISC) earthquake focal mechanism computations. The authors detail how this can minimize an objective misfit function before describing how the optimized automatic picker to increase the number of first motion auto-picked polarities.

The aim of this research was to determine in which areas of the bovine body surface the electrodes should be placed to record T waves with stable polarity and morphology by using bipolar and unipolar leads to detect alterations in the conduction of the ventricular repolarization impulse. One hundred animals of both sexes from different age groups were used. Each T-wave form was numerically coded and its polarity was classified. Sixteen different forms of T waves were observed, presenting four types of polarity: positive, negative, biphasic +/- and biphasic -/+. In the bipolar shoulder lead IH, the T wave was largely negative or biphasic +/-; and it was positive or biphasic -/+ in the remaining bipolar leads. The T-wave was negative or in some cases biphasic +/- in the unipolar basal leads of the heart. Positive or biphasic polarity was always obtained in the apical leads -/+ and four to six different forms were recorded. It is concluded that, in the areas located towards the base or the apex of the heart, leads can be used originating electrocardiographic records with great stability in the polarity of the T wave and in which the quantity of different forms detected is very reduced, with great predominance of the pointed one, so that they become a very useful reference to diagnose the alterations in the conduction of the repolarization impulse through the cardiac ventricles. [ABSTRACT FROM AUTHOR]

We explore different resistance states of La0.325Pr0.300Ca0.375MnO3-Ti interfaces as prototypes of non-volatile memory devices at room temperature. In addition to high and low resistance states accessible through bipolar pulsing with one pulse, higher resistance states can be obtained by repeatedly pulsing with a single polarity. The accumulative action of successive pulsing drives the resistance towards saturation, the time constant being a strong function of the pulsing amplitude. The experiments reveal that the pulsing amplitude and the number of applied pulses necessary to reach a target high resistance value appear to be in an exponential relationship, with a rate that results independent of the resistance value. Model simulations confirm these results and provide the oxygen vacancy profiles associated to the high resistance states obtained in the experiments. [ABSTRACT FROM AUTHOR]

Oxide semiconductor systems are often electrostatically doped with ionic liquids as gate insulators towards modulating carrier density and inducing phase transitions, while simultaneously serving as a means to probe their electronic phase diagram. The electronic and electrochemical properties of ionic liquid/correlated oxide interfaces are, therefore, important in interpreting such field-effect phenomena. Here, we use DEME-TFSI and VO2 as a model system to investigate the interface properties, slow relaxations, as well as field-effect in electric double layer transistor geometry. The stability of these interfaces is probed by combination of current-voltage measurements, x-ray photoelectron spectroscopy, impedance spectroscopy, and constant current charging. Three-terminal field effect transistor-type devices fabricated by photolithography are used to investigate kinetics of channel resistance modulations under varying gate bias polarity. Bias regions for reversible modulation of channel conductance have been determined. A time-dependent transconductance effect and as large as 20× increase in conductance are observed. [ABSTRACT FROM AUTHOR]

Using low density arrays of bistable magnetic nanowires as a model dipolar system, it is shown that the dipolar interaction field coefficient can be measured from the remanence curves as well as from other functions of the isothermal remanent magnetization and the DC demagnetization remanence obtained as an affine transformation of the Wohlfarth relation. Based on mean field arguments, these measurements are used to subtract and remove the contribution of the configuration dependent dipolar interaction field from the major loop and remanence curves. The corrected remanence curves are first used to obtain the intrinsic switching field distribution of the nanowire array and then to validate this approach showing that they yield results consistent with the Wohlfarth relation for an assembly of noninteracting particles, thus providing a self-consistent procedure to verify the measured values of the interaction field and its removal from the measurements. [ABSTRACT FROM AUTHOR]

Solvent polarity effect on the absorption spectra and fluorescence spectra of a series of multibranched structure triphenylamine derivations (Ph-G0, Ph-G1, and Ph-G2) were analyzed to reveal the factors that determine the two-photon absorption (TPA) ability in these molecules. It was found that the dominate factor is the extent of intramolecular charge transfer upon photoexcitation, rather than coherent coupling between branches. This result suggests that it is more effective to change the electron withdrawing ability or electron giving ability of branches and core than simply increase the number of branches for enhancing the TPA ability in multibranched structure molecules. [ABSTRACT FROM AUTHOR]

X ray photoelectron diffraction (XPD) patterns of polar zinc oxide (ZnO) surfaces were investigated experimentally using hard x rays and monochromatized Cr Kα radiation and theoretically using a cluster model approach and a dynamical Bloch wave approach. We focused on photoelectrons emitted from the Zn 2p3/2 and O 1s orbitals in the analysis. The obtained XPD patterns for the (0001) and (000[formula]) surfaces of a ZnO single crystal were distinct for a given emitter and polarity. Polarity determination of c-axis-textured polycrystalline ZnO thin films was also achieved with the concept of XPD, even though the in-plane orientation of the columnar ZnO grains was random. [ABSTRACT FROM AUTHOR]

We report a correlation between polarity distribution and piezoelectric response of Li-doped zinc oxide (Zn1-xLixO) films prepared by a facile chemical solution deposition (CSD) method. The correlation supports the importance of controlling the polarity distribution for obtaining high piezoelectric response of ZnO films. Although the Zn1-xLixO films were easily prepared on Inconel substrates by heating randomly-stacked nanoparticle films, Zn0.97Li0.03O and Zn0.94Li0.06O films showed high piezoelectric response of 5.6-5.8 pC/N and high O-polarity distribution ratio of 76-74%. This study presents the CSD method is promising as a low-cost and large-area fabrication method of piezoelectric ZnO films. [ABSTRACT FROM AUTHOR]

We report on fundamental structural and optical properties of lateral polarity junctions in GaN. GaN with Ga- to N-polar junctions was grown on sapphire using an AlN buffer layer. Results from scanning electron microscopy and Raman spectroscopy measurements indicate a superior quality of the Ga-polar GaN. An extremely strong luminescence signal is observed at the inversion domain boundary (IDB). Temperature dependent micro photoluminescence measurements are used to reveal the recombination processes underlying this strong emission. At 5 K the emission mainly arises from a stripe along the inversion domain boundary with a thickness of 4-5 μm. An increase of the temperature initially leads to a narrowing to below 2 μm emission area width followed by a broadening at temperatures above 70 K. The relatively broad emission area at low temperatures is explained by a diagonal IDB. It is shown that all further changes in the emission area width are related to thermalization effects of carriers and defects attracted to the IDB. The results are successfully used to confirm a theoretical model for GaN based lateral polarity junctions. Due to the strong and pronounced emission of IDBs even at elevated temperatures, it is demonstrated that lateral polarity junctions exhibit a strong potential for future high efficiency devices. [ABSTRACT FROM AUTHOR]

The dynamics of laser generated plasma plumes expanding within confining surfaces display a two-phase nature. Early phase enhancement due to hydrodynamic containment results in higher temperatures, densities, and average charges states in comparison to freely expanding plasma plumes. Later phase dynamics result in rapid decay of the plasma plume due to lossy plasma-surface interactions. This paper examines laser plasma generation and expansion within rectangular aluminium cavities biased to high voltages (Vbias = ±9 kV). 'Hydro-electro-dynamic' confinement of the laser plasma plumes and the expansion dynamics were studied via space and time resolved visible emission spectroscopy. The charged confining cavities displayed enhanced emission, higher electron densities (Ne) and longer emission durations compared to those of an unbiased cavity. This behavior is attributed to the influence of the electric fields in the cavity on the charged particle dynamics within the cavity volume. The degree of enhancement depended strongly on the applied polarity. [ABSTRACT FROM AUTHOR]

This paper presents experimental results on electrical explosions of thin tungsten wires at wire currents of 0.04–0.4 kA and current rise times of several tens of nanoseconds. The experiment was performed for both negative and positive polarity of the high-voltage electrode. In addition to conventional current and voltage measurements, the current to a grounded cylindrical collector placed between the exploded wire and the return conductor was measured. The collector current was observed only for a 6 μm wire exploded with the high-voltage electrode being at a negative potential. In all other test modes (a 6 μm wire exploded with electrode positive polarity, 6 μm wire exploded with electrodes enclosed in ceramic tubes, 30 μm wires exploded with electrode negative and positive polarities) no collector current was detected. A model of the discharge initiation during a wire explosion (WE) in vacuum has been proposed which is based on the supposition that a surface discharge develops over the electrodes. The presence of plasma-emitted electrons at the cathode surface makes it possible to interpret the experimental results on WEs at different electrode polarities reported both in this paper and in previous publications. [ABSTRACT FROM AUTHOR]

The crystal orientation and piezoelectric properties of solution grown ZnO nanorods on Ag films were measured by quantitative piezoelectric force microscopy (PFM). The polarity of the rods, important for many device applications, was determined to be oriented [0001] from the substrates. This indicates that the prevalence of the [0001] oriented crystals is dominated by the fastest growing direction in solution. The average value of the d33 piezoelectric coefficient was measured to be 4.41 pm/V, with a standard deviation of 1.73 pm/V among the 198 individual rods. For calibration and comparison, PFM measurements were also performed on single crystals of x-cut quartz, z-cut periodically poled and single domain LiNbO3, and z-cut ZnO. Repeated measurements on individual rods establish that the run-to-run variation of a single rod is similar to that of single crystal measurements on quartz and LiNbO3. Hence, the observed rod-to-rod variation is not due to measurement uncertainty. Potential origins of this rod-to-rod difference will be discussed. [ABSTRACT FROM AUTHOR]

We studied the phase behavior of charged and sterically stabilized colloids using confocal microscopy in a low polarity solvent (dielectric constant 5.4). Upon increasing the colloid volume fraction we found a transition from a fluid to a body centered cubic crystal at 0.04150.0005, followed by reentrant melting at 0.11650.0015. A second crystal of different symmetry, random hexagonal close packed, was formed at a volume fraction around 0.5, similar to that of hard spheres. We attribute the intriguing phase behavior to the particle interactions that depend strongly on volume fraction, mainly due to the changes in the colloid charge. In this low polarity system the colloids acquire charge through ion adsorption. The low ionic strength leads to fewer ions per colloid at elevated volume fractions and consequently a density-dependent colloid charge. [ABSTRACT FROM AUTHOR]

The positive and negative polarity discharge current pulse forms were examined between steel cylinder-Al2O3 plane electrodes in helium glow and pseudoglow discharges under atmospheric pressure at 10 kHz. The theoretically determined current pulses agreed very closely in form and magnitude with those recorded experimentally. The electronic and ionic charge carrier components comprising the negative polarity current pulse were found to be very nearly equal in magnitude, in contradistinction to the positive polarity pulse, where the electronic charge carrier component was dominant. This larger electronic charge carrier component was reflected in the magnitude of the corresponding photocurrent pulse, which substantially exceeded that of the negative polarity counterpart. The glow discharge regime current pulse forms were also compared to the pulse forms characterizing pseudoglow discharges, also obtained at 10 kHz but at a more elevated voltage, as well as with those recorded at a reduced frequency of 4 kHz but at the same value of applied voltage. Good agreement was also found to exist between the experimentally determined ultrahigh-speed image patterns of the propagating positive and negative discharges and the corresponding calculated electron density contours within the gap. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Theoretical Raman spectra of the complex-forming ionic liquids LaCl[sub 3] and ScCl[sub 3], derived from molecular dynamics computer simulations, are presented. These simulations, which use polarizable ion interaction models, have previously been shown to predict structural properties in excellent agreement with diffraction experiments. The dependence of the polarizability of the melt on the ionic positions, which determines the Raman spectrum through the time dependence of the polarizability correlation function, is modeled on the basis of ab initio electronic structure calculations carried out on alkali chlorides. New simulation techniques are introduced in order to allow the spectrum to be calculated with acceptable statistics. The calculated spectra are in semiquantitative agreement with experimental data. The distinctive bands which appear in the spectra of such complex melts are linked to the vibrations of the transient coordination complexes which form in these melts and new interpretations for the origin of several well-known features are proposed. The simulations thus enable a link between the structure of a melt as perceived through Raman spectroscopy and through diffraction experiments to be made. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The influence of plasma inertia and temperature and wall polarity on the formation of a stationary charged sheath between the plasma and a conducting wall was considered. A criterion for stationary sheath existence for both negative and positive wall polarities was formulated and applied to several special cases. It was shown, in particular, that a sheath is not formed in a two-beam plasma with cold electrons and cold or warm supersonic ions. The formation of a discontinuity-like a shock wave at a thermal singularity was analyzed. Consideration of special cases showed that conditions for the steady sheath are compatible with the condition for shock wave formation (supersonic ions) only in the case of positive wall potential, hot electrons and warm ions, moving to the wall with velocity greater then the ion-sound velocity. The determined maximum wall positive potential at which no discontinuity forms is φ[sub c]=[ZT[sub e]-T[sub i] ln(1+(ZT[sub e]/T[sub i]))]/2Ze, where T[sub e] is the electron temperature, and T[sub i] and Ze are the ion temperature and charge. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

This article describes a mathematical relationship between the slip parameter α and the slip length b for a slip boundary condition applied to the transverse-shear model for a quartz-crystal acoustic wave device. The theory presented here reduces empirical determination of slip to a one-parameter fit. It shows that the magnitude and phase of the slip parameter, which describes the relative motion of the surface and liquid in the transverse-shear model, can be linked to the slip length. Furthermore, the magnitude and phase of the slip parameter are shown to depend on one another. An experiment is described to compare the effects of liquid-surface affinity on the resonant properties of a transverse-shear mode wave device by applying different polar and nonpolar liquids to surfaces of different polarity. The theory is validated with slip values determined from the transverse-shear model and compared to slip length values from literature. Agreement with literature values of slip length is within one order of magnitude. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The coercivity and resistivity of a Pt/Co/AlOx/Pt junction are measured under sustained voltage application. High bias voltages of either polarity are determined to cause a strongly enhanced, reversible coercivity modification compared to low voltages. Time-resolved measurements show a logarithmic development of the coercive field in this regime, which continues over a period as long as 30 min. Furthermore, the resistance of the dielectric barrier is found to change strongly and reversibly on the same time scale, suggesting an electrochemical process is taking place within the dielectric. It is argued that the migration of oxygen vacancies at the magnet/oxide interface could explain both the resistance variation and the enhanced electric field effect at high voltages. A thermal fluctuation aftereffect model is applied to account for the observed logarithmic dependence. [ABSTRACT FROM AUTHOR]

For more reliable HVDC power transmission systems, it is necessary to enhance HVDC electrical insulation performance in power equipment such as an oil-immersed AC/DC converter transformer. In this paper, the electric field distributions under AC, DC steady-state (DC-SS) and DC polarity reversal (DC-PR) conditions are discussed in oil-pressboard (PB) composite insulation structures. Firstly, based on discussion about the charge accumulation and charge dynamics at oil/PB interfaces, the contribution ratio of deposited charges under DC-SS to the following emerging electric stresses at DC-PR conditions are quantitatively clarified. Secondly, we found that the DC electric field distributions could significantly be controlled by PB arrangement in oil. In particular, both PB configurations and the conductivity ratios of oil and PB would play critical roles to determine electric field distribution, under DC-SS conditions. Furthermore, using an actual AC/DC converter transformer structure, electrical insulation performances under various testing conditions such as AC, DC-SS and DC-PR conditions were comparatively investigated. It was concluded that the most critical testing condition against breakdown strength could be the DC-PR conditions under the higher conductivity ratio of oil and PB. [ABSTRACT FROM AUTHOR]

The utilization of charged domain walls (CDWs) as nanoelectronic devices requires three technological aspects to be developed: (1) controllable CDW creation, (2) tuning of CDW geometry, and (3) CDW removal. We have studied CDW formation in lithium niobate single crystals during polarization reversal using liquid and solid-state electrodes, as well as their combination. It was shown that CDW can be formed by two alternative procedures: (1) by forward switching for the liquid electrode at the Z+ polar surface and solid at the Z− one, (2) by backward switching for solid at the Z+ polar surface and liquid at the Z− one. The created CDW can be transformed to an almost neutral domain wall by the application of the field pulse of the reverse polarity for both procedures. As a result, the tilt of the formed CDW can be tuned reversibly in the range from 0.2° to 1.2° resulting in a change between isolated and highly conductive states. We have demonstrated that the created CDW can be used as a nanoelectronic channel for local electrolysis opening the additional possibilities for ferroelectric lithography. [ABSTRACT FROM AUTHOR]

In the context of traction drives with required torque transient capabilities and a classically wide flux weakening speed range, this paper gives design considerations of a particular double-polarity (DP) five-phase machine. Beyond its intrinsic fault tolerance due to its five phases, its specificity is the ability to develop torques of comparable values under three kinds of supply: with only first, third or both first, and third sinusoidal currents. This property, due to first $(E_{1})$ and third $(E_{3})$ harmonic electromotive forces of comparable values, gives more degrees of freedom for the control of the machine. Unlike three-phase sinusoidal machine, flux weakening is no more the unique solution when maximum voltage is reached. Thanks to the extra degrees of freedom in this kind of machines, more possibilities for the control of the torque and current supply can be applied. At first, elements for the choice of slots/poles combination of such DP machines are given. Then, in the case of an interior permanent magnet synchronous machine, possible adaptations of the rotor are proposed in order to bring the double p/3p polarity property. The last design criterion considered is the level of eddy-current losses, important at high frequencies. For the proof of the concept effectiveness, a prototype with a five-phase fractional-slot concentrated winding of 40 slots and 16/48 poles is presented with results from the experimental setup and finite element modeling. A comparison with the equivalent no-fault-tolerant three-phase 24 slots/16 poles machines is also carried out. [ABSTRACT FROM AUTHOR]

Highlights • Linear relationships exist between AN and CL, the slopes are polarity-dependent. • Negative polarity conductors accumulate more glaze ice than positive one. • For ice-covered conductors, CL of negative is bigger, AN of positive is bigger. Abstract Corona performance of transmission lines in foul weather conditions, icing particularly, have attracted widely attentions. In this research, the influence of voltage polarity on corona performance of two icing categories, glaze and soft rime icing, is studied in corona cage via artificial icing method. The most important finding of this research is that a linear relationship is found between audible noise (AN) and the corona loss (CL) in dB above 1 W/m for the first time, the slopes of the line are voltage polarity-dependent. A 10.4 dBA and 13.7 dBA variation in the AN value for a 10 dB increase in the CL for negative and positive voltage respectively, with little influence icing categories. Moreover, the negative polarity conductors are attending to accumulate much more glaze ice than positive polarity conductors. Taylor cones and hemispheres are observed on the tip of glaze icicles when subjected to DC and AC electric field, respectively. For both icing categories, the CL of negative polarity conductors are bigger than that of positive polarity conductors, the contrary is the case of AN. When the voltage gradient is greater than 18.0 kV/cm, contrary to popular perception, the generated CL and AN of glaze ice-covered conductor are bigger than that of rain condition and fair weather, respectively. [ABSTRACT FROM AUTHOR]

The current stimulated atomic diffusion in YBa2Cu3O7–δ superconducting bridges is investigated. A superconductor to insulator transition can be induced by the current controlled electromigration process, whereas the partial recovery of the superconducting state can be achieved by inverting the polarity of the bias. Interestingly, the temperature dependence of the current density JEM(T), above which atomic migration takes place, intersects the critical current density Jc(T) at certain temperature T*. Therefore, for T < T*, the current-induced dissipative state cannot be accessed without leading to irreversible modifications of the material properties. This phenomenon could also lead to the local deterioration of high critical temperature superconducting films abruptly penetrated by thermomagnetic instabilities. [ABSTRACT FROM AUTHOR]

Abstract We compare results from a preliminary analysis of two years of ARTEMIS magnetopause boundary crossings at lunar distances with available empirical models. We remove the effects of variable solar wind flow directions and aberration angles to study the magnetotail cross-section as a function of solar wind conditions. The average magnetopause distance from the central axis is 26 R E , but this distance ranges from 10 R E for high solar wind dynamic pressures and strong northward IMF orientations to 39 R E for low solar wind dynamic pressures and weak southward IMF orientations compared to the nominal solar wind conditions. The time-independent Howe and Binsack (1972) model describes the average location of the crossings very well. For high solar wind dynamic pressures, the Lu et al., (2011) model performs best, while for low pressures the Petrinec and Russell (1996) model gives the closest prediction. As predicted by theory and seen in past studies, the magnetotail cross-section is suggestive of prolate during intervals of strong IMF By, but oblate during intervals of strong IMF Bz. Any asymmetric variation of the tail boundary with respect to the sign of IMF By was not observed. The decreasing size of boundary with the increasing dynamic pressure was found when dynamic pressures are smaller than 2 nPa. Although the scatter is larger, the tail size for pressures larger than 2 nPa suggests a constant radius. The tail boundary size decreases as the strength of IMF Bz increases regardless of its polarity. However, it was also observed that an even stronger southward IMF Bz can cause larger magnetopause size in the presence of large dynamic pressures. Highlights • Magnetopause boundary at x = −60Re is a circle with a radius of 26.3 Re for all IMF. • Tail magnetopause radius at lunar distances shows large scatter from 10 Re to 40 Re. • Magnetopause models fail to represent extreme magnetopause positions at x = −60Re. • Magnetopause size at x = −60Re is smallest for + IMF Bz and strong dynamic pressure. • Larger magnetopause at lunar distances occurs with weak southward IMFs close to zero. [ABSTRACT FROM AUTHOR]

A celebrated theorem of Stiebitz 13 asserts that any graph with minimum degree at least s+t+1 can be partitioned into two parts that induce two subgraphs with minimum degree at least s and t, respectively. This resolved a conjecture of Thomassen. In this article, we prove that for s,t≥2, if a graph G contains no cycle of length four and has minimum degree at least s+t−1, then G can be partitioned into two parts that induce two subgraphs with minimum degree at least s and t, respectively. This improves the result of Diwan in 5, where he proved the same statement for graphs of girth at least five. Our proof also works for the case of variable functions, in which the bounds are sharp as showing by some polarity graphs. [ABSTRACT FROM AUTHOR]

Highlights • Use of P and S waveform polarities to interpret the thermochemical structure of the upper mantle. • Large number of crossing paths and reflection points of PP/SS beneath the Atlantic. • Epicentral distance dependence of observed polarities. • Modelling of reflection coefficients for precursors to PP and SS waves. • A combined effect of water and iron can explain our polarity observations. Abstract We investigate the velocity and density structure of the mantle beneath the Northern Atlantic at a depth of 410 km where the olivine to wadsleyite phase transformation occurs. Measuring polarities of precursor arrivals to PP seismic waves that reflect at this transition we analyze over 1700 teleseismic seismograms from 13 different source-receiver combinations using the advantages of high-resolution array seismology methods and crossing ray paths. The final dataset consists of 45 events with M w ≥ 5.8 with a good coverage of reflection points beneath the investigation area. We find several events where the polarity of the precursor signal is opposite to that of the PP wave, however, events with same polarity of precursor and PP wave are also observed. We test several causes for changing polarity of reflections at the 410 km discontinuity and find out that there is a dependence of the polarity on epicentral distance. We computed the reflection coefficients of the precursor wave using the Zoeppritz equations with the initial values of density, V P and V S of a pyrolite model for the olivine-wadsleyite phase transition and varied the values by ±10% above and below 410 km depth. More than 729 million combinations of density, compressional and shear wave velocities for olivine and wadsleyite layers were tested to find the combinations that can explain our polarity-distance observations. While the best-fitting models have a smaller positive contrast than pyrolite in density, a small negative contrast for P and S wave velocities is needed. Possibilities to explain these values include combination of a hydrous wadsleyite layer beneath, and anhydrous or Fe-enriched olivine above the boundary. [ABSTRACT FROM AUTHOR]

Rarely does research in the history and philosophy of science lead to new empirical results, but that is exactly what has happened in one of the essays of this special issue: Rang and Grebe-Ellis have developed new experimental techniques to perform measurements Goethe proposed 217 years ago. These measurements fit neatly with Goethe’s idea of polarity—his complementary spectrum is not only an optical, but also a thermodynamical counterpart of Newton’s spectrum. I use the new measurements, firstly, to argue against the asymmetries between light and darkness posited by Lyre and Schreiber; and, secondly, to explicate the alternative theory (the heterogeneity of darkness) that Goethe had introduced to urge scientific pluralism. In my replies to exegetical criticism by Böhler, Hampe and Zemplén, I show that the main goal of Goethe’s Farbenlehre was indeed to expose symmetries between light and darkness. Furthermore, I argue that it is worthwhile to focus on the experiments, arguments and hypotheses of the Farbenlehre, and not merely on rhetorical, narrative or stylistical aspects, as Böhler and Hampe would have it. Goethe’s criticism of Newton is often dismissed, but it is in fact surprisingly relevant today. [ABSTRACT FROM AUTHOR]