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The ability to control the optical properties of a material with an electric field has led to optical memory devices, communication systems, optical signal processing, or quantum cryptography. Understanding electro-optic effects, especially in thin films, would improve the efficiency of these applications. In particular, the influence of epitaxial strains is of prime importance. In addition, the active control of these effects would be of great interest to tailor the material to the desired performance. Here, we demonstrate through first-principle calculations that the linear electro-optic response (Pockels effect) of two silicon-compatible ferroelectrics is stable with respect to bi-axial strain and that the electro-optic response can be strongly enhanced through the electrical control of the polarization. We attribute the former to the lack of optical phonon softening and a weak elasto-optic response and the latter to the externally induced softening of a phonon of symmetry A 1. Our results are readily applicable to other polar materials and show that the electro-optic effect can be efficiently engineered to meet the performance criteria of future technologies. [ABSTRACT FROM AUTHOR]

Exchange-correlation (XC) effects in carrier electrons have a significant influence on the dielectric properties and electric characteristics of a material. In this study, momentum-transfer (q) resolved electron energy-loss spectroscopy was conducted to experimentally evaluate the XC effects of carrier electrons in LaB6 bulk crystals, whose nanoparticles have been used for near-infrared-light shielding filters. By measuring q dependence of plasmon energy due to carrier electrons and evaluating the deviation from the free electron gas model in random phase approximation, the dielectric correction factor due to the XC effects, i.e., the local field correction G(q), for the carrier electrons in LaB6 were experimentally derived. This experimental result confirmed that the XC effects are non-negligible for the carrier electrons in LaB6. Because the XC effects influence dipole surface plasmon energy of LaB6 nanoparticles, the evaluation of the XC effects is important for a precise understanding of the optical properties of LaB6 nanoparticles. [ABSTRACT FROM AUTHOR]

Microwave-induced thermoacoustic imaging (TAI) is a hybrid imaging technique that combines electromagnetic radiation and ultrasonic waves to achieve high imaging contrast and submillimeter spatial resolution. These characteristics make TAI a good candidate to detect material anomalies that change the material electric properties without a noticeable variation in material density. Conventional pulsed TAI systems work by sending a single short pulse to the imaged target and then detecting the generated pressure signal; therefore, a very high peak power microwave pulse or data averaging is needed to produce images with a high signal-to-noise ratio (SNR). In this paper, we propose to enhance the SNR of pulsed TAI systems by using non-coherent pulse compression. In this approach, a predefined pulse coded signal is used to illuminate the imaged sample and the received pressure signal is cross correlated with a template that is related to the power profile of the excitation signal. The proposed approach can be easily deployed to pulsed TAI systems without the need for major system modifications to the RF source because it only requires a timing circuit to control the triggering time of the RF pulses. In this paper, we demonstrate experimentally that the proposed approach highly improves the SNR of TAI signals and images and can be used to reduce the acquisition time by lowering the number of data averaging or reduce the required peak power from RF sources. [ABSTRACT FROM AUTHOR]

The imbalanced carrier mobility remains a bottleneck for performance breakthrough in even those organic solar cells (OSCs) with recorded power conversion efficiencies (PCEs). Herein, a counter electrode doping strategy is proposed to reshape the internal potential distribution, which targets to extract the low mobility carriers at far end. Device simulations reveal that the key of this strategy is to partially dope the active layer with a certain depth, therefore it strengthens the electric field for low mobility carriers near counter electrode region while avoids zeroing the electric field near collection electrode region. Taking advantage of these, PCE enhancements are obtained from 15.4% to 16.2% and from 16.9% to 18.0%, respectively, via cathode p-doping and anode n-doping. Extending its application from opaque to semitransparent devices, the PCE of dilute cell rises from 10.5% to 12.1%, with a high light utilization efficiency (LUE) of 3.5%. The findings provide practical solutions to the core device physical problem in OSCs. [ABSTRACT FROM AUTHOR]

Electrical resistance tomography (ERT) provides images of the electrical properties of subsurface materials leading to the distinction of different Earth's interior structures. The accuracy of electrical resistance imaging is strongly affected by the topographical variations so the lack of incorporation of topography information into the inversion process may produce erroneous anomalies in the resistivity section. Owing to the significance of the topography effects on the resistivity measurements, we use the Schwarz-Christoffel transformation approach to incorporate the irregular surface into the 2.5-dimensional forward solution in the framework of the finite difference method. This approach is implemented on synthetic cases to illustrate how the resistivity measurements are dependent on the topographic irregularities. Numerical experiments demonstrate that in the presence of topographic features between current and potential electrodes, the resistivity response does not reflect the realistic resistivity values of the subsurface even in the case of a homogeneous resistivity distribution. [ABSTRACT FROM AUTHOR]

3D-printed electronics belong to new approaches to how to build a complex object with multiple desired functions. For that purpose, materials with specific electric properties are needed: conductors, insulators, magnetics, or dielectrics with high permittivity. However, such materials are not commonly available in the form of filament for fused deposition modelling since the development is still ongoing. This paper describes the electrical properties of PETG-ceramic composite filaments. PETG (polyethylene terephthalate glycol-modified) was filled with titanium dioxide (10 and 20 wt.%) to increase the dielectric constant and, simultaneously, to preserve printing simplicity as the material key advantage. Dielectric spectroscopy and measurement of volume resistivity were performed on printed samples. Relative permittivity increased by 50% for a composite filled with 20 wt.% of ceramic particles (εr = 2.5÷4.4) against pure PETG. Permittivity and dielectric loss exhibited frequency and temperature independence. The prepared composite can be used for dielectric applications in electronics. [ABSTRACT FROM AUTHOR]

An exact geometry hybrid-mixed four-node laminated piezoelectric solid–shell element with temperature-dependent material properties using the sampling surfaces (SaS) method is proposed. The SaS method is based on the choice of an arbitrary number of SaS located at Chebyshev polynomial nodes inside the layers and interfaces to introduce temperatures, displacements and electric potentials of these surfaces as fundamental shell unknowns. This choice of unknowns with the use of Lagrange polynomials in the through-thickness approximations of temperature, temperature gradient, displacements, strains, electric potential, electric field and material properties leads to a compact and effective higher-order thermopiezoelectric shell formulation with temperature-dependent material properties. The developed hybrid-mixed piezoelectric solid–shell element is based on the Hu–Washizu variational principle and three-dimensional (3D) analytical integration, which provides excellent performance for coarse meshes. It can be useful for the 3D thermoelectroelastic analysis of thick and thin laminated piezoelectric shells under thermo-electro-mechanical loading, since the SaS shell formulation makes it possible to obtain the numerical solutions with a prescribed accuracy, which asymptotically approach exact solutions of the theory of thermopiezoelectricity as the number of SaS goes to infinity. [ABSTRACT FROM AUTHOR]

Lithium metal orthosilicates, Li2MSiO4 (M = Fe, Mn, Co, Ni, and their mixtures), have been attracting significant attention as alternative cathodes for next‐generation high energy Li‐ion batteries (LIBs). The high capacity of these cathodes is attributed to two reversible transitions, those of Li2MSiO4 to LiMSiO4 and LiMSiO4 to MSiO4 phases involving two Li+ ions per mole. However, due to their complex structures and phase transformation behaviors, these materials are not yet available for practical commercial applications. Rate capability is one of the most important properties of cathode materials that are affected by phase transformations. This review will comprehensively summarize the current knowledge of the rate‐dependent phase transformations of Li2MSiO4 materials based on various characterization tools to facilitate future developments of these high potential cathode materials for future LIBs. [ABSTRACT FROM AUTHOR]

As the electrical properties of biological tissues are highly sensitive to their physiological and pathological status, the noninvasive imaging method of electrical properties also has drawn much attention. Thermo-acoustic tomography with electric excitation (TATE) is a typical noninvasive method of electrical properties for biological tissues. To the best of our knowledge, however, there is no 3D simulation model of TATE. In this paper, a new mathematical model is built, and the 3D TATE equations have been deduced. The performance of TATE has been studied by a series of 3D simulation models, including the tumors with different background tissues, different sizes, and different conductivities. In the simulation results, the Joule heat distribution of tumors has been imaged clearly. In addition, a verification experiment has validated the mathematical model and simulation results. The simulation and experiment results also indicate that the mathematical model can describe TATE well and TATE has the potential to image the tumors with high contrast and high resolution. [ABSTRACT FROM AUTHOR]

High-frequency coaxial waveguide measurements are used to evaluate composition- and frequency-dependent complex permittivities and permeabilities of polycrystalline ferroelectric and ferrimagnetic ceramics. Material dielectric and magnetic property measurements were performed on ferroelectric barium titanate (BaTiO3) and ferrimagnetic yttrium iron garnet (YIG), with the upper measurement frequency bound below gyromagnetic resonance of YIG. These polycrystalline materials were chosen because of their widespread use in voltage- and magnetic field-tunable devices. Wideband frequency material measurements were used to predict dielectric and magnetic properties of various two-phase composite media incorporating BaTiO3 and YIG. Two effective medium theories were used: an asymmetric, modified Maxwell-Garnett type and a symmetric Bruggeman model. The Bruggeman effective medium model is extended to include three-phases. The three-phase Bruggeman predictive model is employed when controlled porosity is introduced into the composite and when two component phases are combined with polytetrafluoroethylene. [ABSTRACT FROM AUTHOR]

Phase change memory has been considered as the next generation in non-volatile electronic data storage. The property modulation of such materials by the doping of rare-earth elements has drawn a lot of attention, which motivates us to search for the optimal dopants and reveal the underlying mechanisms. Here, we investigate the role of Gd as a dopant in Ge2Sb2Te5, which exhibits higher crystalline resistance and better thermal stability and antioxidant capacity than the undoped counterpart. Moreover, Gd dopants suppress both the processes of phase transition and grain growth. The crystalline structure remains unchanged with Gd dopants and vacancies are randomly distributed. Furthermore, the bonding mechanism was theoretically investigated. In the amorphous state, Gd atoms modify the local structures around Ge, Sb, and Te atoms. The large coordination number of Gd and the "Gd–Te distorted pentagonal bipyramidal-like" structure can be attributed to the good thermal stability. These microscopic findings figure out some of the key issues about the bonding mechanism, electrical properties, and crystallization behaviors of Gd doped phase change memory materials, which could be useful for storage devices. [ABSTRACT FROM AUTHOR]

To prepare nonwoven mats constituted by submicrometric fibers of thermally responsive biopolyurethanes (TPU) modified with multiwalled carbon nanotubes (MWCNT), solution blow spinning (SBS) was used. The TPU was the product of synthesis using poly(butylene sebacate)diol, PBSD, ethyl ester L-lysine diisocyanate (LDI), and 1,3-propanediol (PD) (PBSe:LDI:PD) as reactants. TPU was modified by adding different amounts of MWCNT (0, 0.5, 1, 2, and 3 wt.%). The effect of the presence and amount of MWCNT on the morphology and structure of the materials was studied using field-emission scanning electron microscopy (FESEM) and Fourier-transform infrared spectroscopy (FTIR), respectively, while their influence on the thermal and electric behaviors was studied using differential scanning calorimetry (DSC) and capacitance measurements, respectively. The addition of MWCNT by SBS induced morphological changes in the fibrous materials, affecting the relative amount and size of submicrometric fibers and, therefore, the porosity. As the MWCNT content increased, the diameter of the fibers increased and their relative amount with respect to all morphological microfeatures increased, leading to a more compact microstructure with lower porosity. The highly porous fibrous morphology of TPU-based materials achieved by SBS allowed turning a hydrophilic material to a highly hydrophobic one. Percolation of MWCNT was attained between 2 and 3 wt.%, affecting not only the electric properties of the materials but also their thermal behavior. [ABSTRACT FROM AUTHOR]

Recent years have seen a considerable research interest in multiferroic materials for their potential application as sensors and actuators. However, the scarcity of these materials in a single phase and the weak coupling of their ferroic components have directed research toward multiferroic heterostructures. These systems operate by coupling the magnetic and electric properties of two materials, generally ferromagnetic and ferroelectric, via strain. In this paper, thin films have been grown by chemical solution deposition (CSD) using spin coating technique using rotations peed of 4500 rpm and time of 50 s and dried at 120○C for 20 min. The optical, dielectric, magnetic, ferroelectric, ferromagnetic, and piezoelectric properties of thin films have been investigated by Uv- Visible spectrophotometer (300-2500) nm, X-Ray Diffraction (XRD), Vibrating Sample Magnetometer (VSM), Transmission Electron Microscope (TEM), and Scanning Electron Microscope (SEM) respectively. PZT/CFO thin films deposited at different temperatures from 400 °C, 500 °C and 600 °C. The as-deposited PZT/CFO show week piezoelectricity and the effective piezoelectric coefficient d33 because the materials deposited on the films not only the PZT layer but also the CFO layer, which decreases the piezoelectricity of these films. PZT/CFO Films were then recorded to enhance all physical properties (dielectric, optical, structural, surface morphology, and magnetic properties) as the sintering temperature increased. The images of a thin film before and after treatment with Nd-YAG, which have Power from 10 mw to 5300 mw, Pulse width: 7 ns pulsed laser, Repetition Rate: 10 HZ, and wavelength spectrum in (IR, Vis) laser beam indicate that sample prepared before treated has a lot of porous and agglomeration which decreases after treatment. [ABSTRACT FROM AUTHOR]

Infrared (IR) optical fibers based on crystals and ceramics of the AgBr–AgI system are transparent in the IR range from 3 to 26 μm, which is of interest for thermal imaging, laser technique, and spectroscopy. High photo- and radiation resistances make these materials especially attractive for solving the problems of optical radiation transfer in aggressive environment. To design optical equipment, it is necessary to have information on the electric properties of materials, which are most completely characterized by current–voltage characteristics (CVCs). In this work, we consider the dependences of the CVCs of optical materials of the AgBr–AgI system in the form of plates with thicknesses from 0.1 to 1.7 mm and AgI concentrations from 4 to 76 mol % on the composition and temperature in the range of 298–453 K. It is found that an increase in the AgI concentration in the AgBr–AgI crystals leads to a decrease in electric conductivity. The conductivity of AgBr–AgI ceramics is two–three orders of magnitude higher than that of the corresponding crystals at the same temperatures and applied voltages. The conductivity of ceramics is comparable with the conductivity of solid electrolytes. The β-AgI–α-AgI phase transition at a temperature of 463 K causes a jump in the conductivity of the AgBr–AgI ceramics. The IR transmission of the studied material was measured before and after electrical breakdown. It was found that electrical breakdown decreases the transmission by more than 20% in the entire spectral range. Information on the breakdown voltage for materials of the AgBr–AgI system with different compositions is important for ensuring reliability and safety of electrotechnical equipment using optical devices based on these materials. In this study, we observed deterioration of the optical properties of crystalline materials of the AgBr–AgI system with applying some voltage difference and determined the breakdown voltage. The breakdown voltage is determined by applying direct-current voltage, but it is the same in the case of alternating-current voltage. [ABSTRACT FROM AUTHOR]

Examples of electric properties of various crystalline materials, insulators and semiconductors, liquid crystals, films, and nanostructures are presented. Among crystals, particular attention is paid to piezoelectrics, pyroelectrics, and ferroelectrics, whose dielectric properties depend strongly on the external electric field and temperature. The electro-optic properties of these materials, as well as the photovoltaic effect and photorefraction, are considered. Liquid crystals, whose optical properties depend strongly on applied electric field, are considered separately. The electric properties of materials are widely used in most diverse fields of science and technology. [ABSTRACT FROM AUTHOR]

Expanding new avenues for renewable energy and reducing the consumption of fossil fuels in a time of ever-increasing demand for energy is challenging. Thermoelectricity, associated with generating electric power due to an applied temperature gradient or thermal flow due to an applied voltage, offers the potential to utilize some of this "free" energy in all-solid-state conversion devices for power generation. [Extracted from the article]

Tin sulfides, SnxSy, are an important class of materials that are actively investigated as novel photovoltaic and water splitting materials. A first-principles evolutionary crystal structure search is performed with the goal of constructing the complete phase diagram of SnxSy and discovering new phases as well as new compounds of varying stoichiometry at ambient conditions and pressures up to 100 GPa. The ambient phase of SnS2 with P 3 ¯ m 1 symmetry remains stable up to 28 GPa. Another ambient phase, SnS, experiences a series of phase transformations including α-SnS to β-SnS at 9 GPa, followed by β-SnS to γ-SnS at 40 GPa. γ-SnS is a new high-pressure metallic phase with P m 3 ¯ m space group symmetry stable up to 100 GPa, which becomes a superconductor with a maximum Tc = 9.74 K at 40 GPa. Another new metallic compound, Sn3S4 with I 4 ¯ 3 d space group symmetry, is predicted to be stable at pressures above 15 GPa, which also becomes a superconductor with relatively high Tc = 21.9 K at 30 GPa. [ABSTRACT FROM AUTHOR]

The decarbonization of energy to meet the low-carbon energy strategy set for 2050 has led to a continuous increase in the contribution of electricity generated from renewables to our growing energy demands, where their inherent intermittency of supply must be addressed by a step-change in energy storage. 10.3390/en14041139 2 Mirzaeian M., Abbas Q., Hunt M.R.C., Hall P. Pseudocapacitive Effect of Carbons Doped with Different Functional Groups as Electrode Materials for Electrochemical Capacitors. Additionally, the nonstop emerging demands of modern technologies still require the design of versatile energy-storage/power supply systems, ensuring a secure and continuous supply of energy on a large scale with wide ranges of power and energy densities commensurate with each application. [Extracted from the article]

Perovskite solid solution materials, namely, 0.67BiFeO 3 -0.33BaTiO 3 , were synthesized by spark plasma sintering method. The effects of the spark plasma sintering temperature on phase purity, microstructure, and electric properties of the as-prepared materials were investigated. The materials could be referred as pseudocubic phases based on the X-ray diffraction patterns. The bulk density first increased and then decreased. The 880 °C-sintered-ceramics had the maximal density and a compact microstructure with grain size of 0.77 ± 0.34 μm. The dielectric constant as a function of temperature exhibited a broad peak. At the optimal spark-plasma-sintering temperature, enhanced ferroelectric properties were observed with a value of P r ∼ 21 μC/cm2. This investigation on the spark plasma sintering process confirms it as an efficient approach to prepare outstanding performance BiFeO 3 –BaTiO 3 ceramics. [ABSTRACT FROM AUTHOR]

The phenomenon of electrical conductivity maxima of molten salts versus temperature during orthobaric (closed-vessel) conditions is further examined via ab initio simulations. Previously, in a study of molten BiCl3, a new theory was offered in which the conductivity falloff at high temperatures is due not to traditional ion association, but to a rise in the activation energy for atomic ions hopping from counterion to counterion. Here this theory is further tested on two more inorganic melts which exhibit conductivity maxima: another high-conducting melt (SnCl2, αmax = 2.81 Ω-1 cm-1) and a low-conducting one (HgBr2, smax = 4.06 10-4 Ω-1 cm-1). First, ab initio molecular dynamics simulations were performed and again appear successful in reproducing the maxima for both these liquids. Second, analysis of the simulated liquid structure (radial distributions, species concentrations) was performed. In the HgBr2 case, a very molecular liquid like water, a clear Grotthuss chain of bromide transfers was observed in simulation when seeding the system with a HgBr+ cation and HgBr3 - anion. The first conclusion is that the hopping mechanism offered for molten BiCl3 is simply the Grotthuss mechanism for conduction, applicable not just to H+ ions, but also to halide ions in post-transition-metal halide melts. Second, it is conjectured that the conductivity maximum is due to rising activation energy in network-covalent (halide-bridging) melts (BiCl3, SnCl2, PbCl2), but possibly a falling Arrhenius prefactor (collision frequency) for molecular melts (HgBr2). [ABSTRACT FROM AUTHOR]

Nickel sulfide (NiS) thin film has been deposited on glass substrates by spray-pyrolysis at 325 ± 5 °C. The precursor aqueous solution was synthetized using hexahydrated nickel nitrates and thiourea. The structural, morphological, optical and electrical properties were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-visible spectroscopy and four probes electrical measurements. The XRD analysis confirmed the hexagonal structure of NiS thin film, which was found to crystalize along [010] direction with an average crystallites size of 10.5 nm. The lattice parameters are a = b = 3.420 Å and c = 5.300 Å in the space group P63/mmc. The optical properties of the films were investigated through the transmittance and the reflectance measurements. The results revealed that the material exhibits a direct optical band gap of 1.03 eV. The elementary composition analysis confirmed the presence of Ni and S with a stoichiometry ratio (Ni/S) of 1.05. The morphology analysis revealed a homogenous crack-free, compact appearance and a granular surface in all scanned areas. The average roughness of the surface was 6.48 nm. On the other hand, the film exhibits a high electrical conductivity ca. 1.10 x 105 S/cm at room temperature. The above results show that the prepared NiS in this study has a good crystallization, dense morphology, good stoichiometric ratio and high conductivity; therefore, it stands as a potential candidate for application in supercapacitors as an electrode material. [ABSTRACT FROM AUTHOR]

This paper focuses on the potential of epoxy resin/aluminum nitride (EP/AIN) nanocomposites through experiments and simulation for the packaging material of a 15 kV SiC-IGBT module. For this purpose, space charge, AC breakdown, thermal conductivity and glass transition temperature $(T_{\mathrm{g}})$ are measured. The electric stress reduction effect in EP/AIN nanocomposites is compared to the traditional packaging material at high-frequency AC and square voltages at 150 °C using the electric field simulation. The experimental results show that the 2 wt% EP/AIN nanocomposite exhibits the least space charge accumulation, highest AC breakdown strength and $T_{\mathrm{g}}$ amongst the tested nanocomposites. The offset of metallization layers plays a crucial role in the impact of the electrical properties of packaging materials on the electric field of the packaging structure. When the offset of metallization layers is zero, the maximum electric stress in the EP/AIN nanocomposites is lower than the traditional packaging material, both under the AC and square voltages. In the EP/AIN nanocomposites, as the frequency or the nano-AIN content increases, the maximum electric stress decreases under the AC voltages. Traditional packaging materials have a steeper transient electric field variation than EP/AIN nanocomposites, although the transient process is smoother at higher frequencies under square voltages for all the considered materials. A simplified physical model is proposed to explain the electric field distribution variation in the packaging structure under the AC voltages. [ABSTRACT FROM AUTHOR]

Electrical anisotropy is increasingly recognized as an important aspect of the resistivity models required to explain magnetotelluric (MT) observations. However, a limited number of practical MT inversion algorithms that can consider anisotropy have been published to date. To address this problem, we have developed a three‐dimensional (3‐D) MT inversion algorithm that recovers a 3‐D resistivity model that considers arbitrary electrical anisotropy. The inversion uses the same inversion algorithm as the widely used ModEM inversion algorithm, and a novel forward modeling algorithm to consider the anisotropic Earth. The algorithm was tested on both synthetic and field MT data. Inversions considered both a completely general anisotropy tensor with six components and approximations with less parameters. Synthetic inversions show that the two horizontal components of resistivity and the anisotropy strike can be well recovered, while the vertical component of resistivity is poorly resolved, primarily because current flow in MTs is dominantly horizontal. The synthetic examples confirm the limitation of the axial anisotropic inversion technique when applied to MT data produced by a resistivity model with arbitrary anisotropy. The synthetic inversions also showed that inversion of data from an isotropic model will not result in an artificially anisotropic model. Compared to the isotropic inversion model of the real MT data, the anisotropic model clearly shows some features that are consistent with the mapped geology. As expected, the results showed that a given data set can be fit by a range of models, with an inherent trade‐off from 3‐D heterogeneity to 3‐D anisotropy. This uncertainty can be reduced with the use of prior information in the inversion. Plain Language Summary: The resistivity model of real Earth generally contains anisotropic features. Field magnetotelluric (MT) data may be significantly influenced by these features. To interpret such data, inversion algorithms which can consider electrical anisotropy are highly demanded. However, a limited number of practical MT inversion algorithms that can consider anisotropy have been published to date. To address this problem, we have developed a three‐dimensional (3‐D) MT inversion algorithm that recovers a 3‐D resistivity model that considers arbitrary electrical anisotropy. The algorithm was tested to be effective on both synthetic and field MT data. Compared to the isotropic inversion models of the tested MT data, the resolved anisotropic models are more reliable. Key Points: A three‐dimensional non‐linear conjugate gradient inversion algorithm is implemented for the inversion of magnetotelluric (MT) data to produce an electrical resistivity model with arbitrary anisotropyInversion examples of synthetic and real MT data validate the usefulness of the algorithmReal MT data inversion obtains an anisotropic model which is more consistent with the mapped geology than the corresponding isotropic model [ABSTRACT FROM AUTHOR]

Many factors have been identified to influence the electrical transport characteristics of graphene field-effect transistors. In this report, we examine the influence of the exposure current level used during electron beam lithography (EBL) for active region patterning. In the presence of a self-assembled hydrophobic residual layer generated by oxygen plasma etching covering the top surface of the graphene channel, we show that the use of low EBL current level results in higher mobility, lower residual carrier density, and charge neutrality point closer to 0V, with reduced device-to-device variations. We show that this correlation originates from the resist heating dependent release of radicals from the resist material, near its interface with graphene, and its subsequent trapping by the hydrophobic polymer layer. Using a general model for resist heating, we calculate the difference in resist heating for different EBL current levels. We further corroborate our argument through control experiments, where radicals are either intentionally added or removed by other processes. We also utilize this finding to obtain mobilities in excess of 18 000 cm2/V s on silicon dioxide substrates. We believe these results are applicable to other 2D materials such as transition metal dichalcogenides and nanoscale devices in general. [ABSTRACT FROM AUTHOR]

Diodes incorporating a bilayer of an organic semiconductor and a wide bandgap metal oxide can show unipolar, non-volatile memory behavior after electroforming. The prolonged bias voltage stress induces defects in the metal oxide with an areal density exceeding 1017m-2. We explain the electrical bistability by the coexistence of two thermodynamically stable phases at the interface between an organic semiconductor and metal oxide. One phase contains mainly ionized defects and has a low work function, while the other phase has mainly neutral defects and a high work function. In the diodes, domains of the phase with a low work function constitute current filaments. The phase composition and critical temperature are derived from a 2D Ising model as a function of chemical potential. The model predicts filamentary conduction exhibiting a negative differential resistance and nonvolatile memory behavior. The model is expected to be generally applicable to any bilayer system that shows unipolar resistive switching. [ABSTRACT FROM AUTHOR]

Tunable absorption based on graphene metamaterial with nanodisk structure at near-infrared frequency was investigated using the finite difference time domain method. The absorption of the nanodisk structure which consisting of Au-MgF2-graphene-Au-polyimide (from bottom to top) can be tuned by the chemical potential of graphene at certain diameter of nanodisk. The permittivity of graphene is discussed with different chemical potential to obtain tunable absorption. It is shown that the increased value of the chemical potential of graphene can lead to blue-shifted of the absorption peaks and the values decreased. Moreover, dual-band and triple-band absorption can be achieved for resonance frequencies at normal incidence. Compared with diameter of nanodisks, the multilayer structure shows multi-band absorber, and an omnidirectional absorption at 195.25 THz is insensitive to TE/TM polarization. This omnidirectional polarization insensitive absorption may be applied by optical communications such as optical absorber, near infrared stealth, and filter. [ABSTRACT FROM AUTHOR]

Electrical resistivity methods are one of the powerful methods for the detection and evaluation of shallower geophysical properties. This method was carried out at Hit area, western Iraq, in two stages; the first stage involved the use of 1Dimensional Vertical Electrical Sounding (VES) technique in three stations using Schlumberger array with maximum current electrodes of 50m. The second stage included the employment of two dimension (2D) resistivity imaging technique using dipole-dipole array with a-spacing of 4m and n-factor of 6 in two stations. The 1D survey showed good results in delineating contaminated and clear zones that have high resistivity contrast. Near the main contaminated spring, the 2D resistivity imaging technique was applied in four sections length (100 m) using a dipole-dipole array position coincided with the three points VES. We compared the results of the interpretation of imaging the techniques 2D and VES. We found that the 2D imaging resistivity technique was better than VES survey in determining the distribution of pollution under the surface in the area surveyed. It was also found that the polluted water is located about 5 m below the surface. The largest amount of leakage was found towards the northeast and coincided with the direction of the groundwater movement. Spring water has leaked from outside the region through the Kubaisah area. Most of this water is contained in quaternary deposits and karst gypsum fractures. [ABSTRACT FROM AUTHOR]

The objective of this work is to evaluate the effect of scale dependent mechanical and electrical properties on electrical contact resistance (ECR) between rough surfaces. This work attempts to build on existing ECR models that neglect potentially important quantum- and size-dependent contact and electrical conduction mechanisms present due to the asperity sizes on typical surfaces. The electrical conductance at small scales can quantize or show a stepping trend as the contact area is varied in the range of the free electron Fermi wavelength squared. This work then evaluates if these effects remain important for the interface between rough surfaces, which may include many small scale contacts of varying sizes. The results suggest that these effects may be significant in some cases, while insignificant for others. It depends on the load and the multiscale structure of the surface roughness. [ABSTRACT FROM AUTHOR]

Single-phase Sodium (Na), Samarium (Sm) substituted Strontium Bismuth Titanate (SNSBTi I-V) ceramics were synthesized by solid-state double sintering approach via high energy planetary ball mill for 20 hours grinding. X-ray diffraction (XRD) study confirms the primary structure and orthorhombic distortion of crystal. Scanning electron microscopy (SEM) shows the grain orientation and densified plate-like grain structure of SNSBTi I-V. The complex impedance spectroscopy method was used to study the temperature and frequency dependent electric properties of the material using a high-frequency LCR meter. Z'' versus frequency plots have shown the peak shifting to higher frequencies with increasing concentration of Na, Sm. It is also found that the magnitude of the peaks decreases with increasing temperature. The grain and grain boundary relaxation mechanisms of SNSBTi I-V have been identified using Nyquist plots; the resistance, capacitance and relaxation times were obtained from Z-view software. It is seen that the grain and grain boundary resistances decreased with the increasing concentration of Na and Sm of SBTi ceramics. [ABSTRACT FROM AUTHOR]

Inherent advantages of optical-based sensing devices motivate a need for materials with useful optical responses that can be utilized as thin film functional sensor layers. Transparent conducting metal oxides with large electrical conductivities as typified by Al-doped ZnO (AZO) display attractive properties for high temperature optical gas sensing through strong optical transduction of responses conventionally monitored through changes in measured electrical resistivity. An enhanced optical sensing response in the near-infrared and ultraviolet/visible wavelength ranges is demonstrated experimentally and linked with characteristic modifications to the dielectric constant due to a relatively high concentration of free charge carriers. The impact of light scattering on the magnitude and wavelength dependence of the sensing response is also discussed highlighting the potential for tuning the optical sensing response by controlling the surface roughness of a continuous film or the average particle size of a nanoparticle-based film. The physics underpinning the optical sensing response for AZO films on planar substrates yields significant insight into the measured sensing response for optical fiber-based evanescent wave absorption spectroscopy sensors employing an AZO sensing layer. The physics of optical gas sensing discussed here provides a pathway towards development of sensing materials for extreme temperature optical gas sensing applications. As one example, preliminary results are presented for a Nb-doped TiO2 film with sufficient stability and relatively large sensing responses at sensing temperatures greater than 500 °C. [ABSTRACT FROM AUTHOR]

Metamaterials constructed from conductive elements are lossy, and the structures act as sources of noise, whose spectrum is modified by the resonant nature of the medium itself. Furthermore, inside the medium, the noise is present as waves, which are standing waves for finite length samples. We present direct measurements of the noise spectra for a simple metamaterial comprising arrays of LC resonator elements, and compare them with the predictions of a circuit model incorporating Johnson noise. We find excellent agreement between the measured data and the model, reproducing both the resonant structure and the bandwidth of the noise spectrum, thus confirming the concept of noise waves in these metamaterials. These noise features match the frequency ranges where the metamaterial properties are useful, showing that noise is an inevitable companion to metamaterial performance in practical situations. [ABSTRACT FROM AUTHOR]

Military applications employ metallic objects with different shapes, which must produce low radar cross-section (RCS) to avoid detection and destruction from explosive devices. A plasma-based artificial magnetic conductor (AMC) unit cell with crossed arrow shape is employed for reconfigurable RCS reduction bandwidth from metallic objects. Loading metallic objects with AMC unit-cell elements changes its surface to high impedance surface which reduces the electromagnetic waves reflected from these objects. The plasma material reconfigurable electric properties effect on controlling the RCS reduction bandwidth is introduced. The plasma conductivity controls the RCS reduction band of the ± 90° bandwidth of the AMC unit-cell element and also controls the zero-crossing frequency. The proposed plasma AMC unit-cell is designed to operate in the frequency band from 9 GHz to 13 GHz. Different hybrid AMC element arrangements are designed to mimimize the RCS over wide frequency band. Different metallic surfaces are studied include planar, cylindrical, and spherical sheets. The effect of radii of curvature of conformal surfaces with convex and concave curvatures is explained. A full-wave simulation using the finite integration technique (FIT) is applied to examine the proposed constructions. [ABSTRACT FROM AUTHOR]

We review some of the insights that electronic‐structure calculations has brought about the properties of the materials with the largest electric polarization known – supertetragonal perovskite oxides. These are materials whose structure corresponds to a perovskite that has been substantially strechted along one of its pseudocubic axes. They grow in different forms: bulk crystals (such as BiCoO3), epitaxial films (such as BiFeO3), nanowires whose inside is under negative pressure (such as PbTiO3), and others. Electronic structure calculations based on density‐functional theory have revealed that supertetragonality potentially exist for many perovskite oxides under the right conditions, and they have helped explain why some of those conditions are easy to reach for some of the materials of the family, but not for others. [ABSTRACT FROM AUTHOR]

This study investigates the electrical observation of the formation of a 360° magnetic domain wall (360DW) in an elliptical Co ring structure. Because the 360DW consists of two 180° domain walls, a decrease in resistance is observed in the switching process due to anisotropic magnetoresistance (AMR). Certain AMR measurements exhibit an increase in the resistance in the switching process, indicating that a flux-closure vortex state is formed without first forming a 360DW state. The difference between the 360DW and vortex state in the switching process reflects differences in the DW depinning mechanism from the onion state. The minor loop of the AMR measurements is also dependent on the initial magnetic configuration between the 360DW and the vortex state. [ABSTRACT FROM AUTHOR]

An analytical model is developed for the carrier density distribution and the associated Dember type electric field/voltage in the waveguide layer of a high-power semiconductor laser for arbitrary levels of doping and injection. Nonlinear resistance of the waveguide layer is analysed; it is shown that at a very high injection level, doping the waveguide layer leads to almost negligible decrease in its effective resistance. [ABSTRACT FROM AUTHOR]

The Hall and Seebeck coefficients, electrical resistivity, and thermal conductivity of polycrystalline NiSi3P4 were characterized from 2 to 775 K. Undoped NiSi3P4 behaves like a narrow gap semiconductor, with activated electrical resistivity ρ below room temperature and a large Seebeck coefficient of ∼400 μV/K at 300 K. Attempts to substitute boron for silicon resulted in the production of extrinsic holes, yielding moderately doped semiconductor behavior with ρ increasing with increasing temperature above ∼150 K. Hall carrier densities are limited to approximately 5 × 1019 cm-3 at 200 K, which would suggest the solubility limit of boron is reached if boron is indeed incorporated into the lattice. These extrinsic samples have a Hall mobility of ∼12 cm2/V/s at 300 K, and a parabolic band equivalent effective mass of ∼3.5 times the free electron mass. At 700 K, the thermoelectric figure of merit zT reaches ∼0.1. Further improvements in thermoelectric performance would require reaching higher carrier densities, as well as a mechanism to further reduce the lattice thermal conductivity, which is ∼5 W/m/K at 700 K. Alloying in Ge results in a slight reduction of the thermal conductivity at low temperatures, with little influence observed at higher temperatures. [ABSTRACT FROM AUTHOR]

Electrical resistance of the elastomeric material polychloroprene filled with multiwalled carbon nanotubes (CNTs) dispersed by using an imidazolium based ionic liquid has been measured experimentally and calculated theoretically, as a function of the applied compression/decompression force F. Both experimental and theoretical results show that the electrical resistance R of the composite exhibits non-monotonic dependence on F. This observed non-monotonic dependence R(F) is explained by different mechanisms of conductivity that are specific to the respective domains of the magnitude of the compression/decompression force F. At small F, the observed decrease of conductivity with increasing F is found to be caused by the change of an average contact distance between CNTs. At higher F, the observed increase of R with increasing F is caused by the dependence of the per-particle surface area on F. The experimentally observed dependence R(F) is adequately described by the developed theory that relies on establishing the exact relation between the CNT network structure and the electrical response of the composite. Theoretical dependence between the conductivity of the composite and the applied stress is obtained using the percolation model of the electrical conductivity of CNT network that shows excellent quantitative agreement with the experimental results. [ABSTRACT FROM AUTHOR]

A density functional theory study of the structural and electronic properties and relative stability of narrow hydrogen passivated sp3 silicon nanotubes of different growth orientations is presented. All nanotubes studied and their corresponding wire structures are found to be meta-stable with the wires being more energetically stable. Silicon nanotubes show a dramatic bandgap increase of up to 68% with respect to the corresponding wires. Furthermore, a direct relation between the bandgap of the system and the molar fraction of the passivating hydrogen contents is found. These results suggest that by careful control over their crystallographic growth orientation, dimensions, and chemical composition it should be possible to design and fabricate silicon nanotubes with desired electronic properties. [ABSTRACT FROM AUTHOR]

A set of diabatic potential energy surfaces, that describe the D + DBr → Br(P1/2,3/2) + D2 reaction, is constructed based on MRCI/aug-cc-pV5Z calculations at 29 526 grid points. Time-dependent wave packet calculations are performed for ground-state DBr initially with collision energies up to 2.0 eV to investigate possible electronic nonadiabaticity in this reaction. Reaction probabilities and integral cross sections are calculated. The results show negligible nonadiabatic effects for the title reaction in the energy range considered here, confirming experimental work of Zare and co-workers. In addition, the calculated thermal rate constants are in good agreement with experimental ones. [ABSTRACT FROM AUTHOR]

Valence alternation pair (VAP) states are formed by a closed-shell combination of two space- and charge-separated topological defect centres. These pairs of defects, although historically invoked to explain the electronic properties of bulk inorganic glassy materials (e.g., amorphous silicon dioxide) via the concept of negative-U defects, have more recently been found in a number of theoretical studies of silica surfaces and nanoscale silica clusters. Using density functional theory we systematically probe the structure and internal stability of VAPs in a number of silica nanoclusters with respect to the separation of the two constituent defect centres. We find that VAP states in nanosilica are strongly stabilised by the attractive electrostatic interaction between their separated oppositely charged component defects such that VAPs can persist up to an internal separation of a least 1.5 nanometres. Beyond this distance VAPs become unstable with respect to an open-shell combination of topological defects, virtually indistinguishable from two isolated open-shell defect centres. Finally, we theoretically analyse the possibility of experimental observation of VAP states through their infra-red vibrational spectra. [ABSTRACT FROM AUTHOR]

Here, we report the synthesis of variable sized magnetite (Fe3O4) nano-hollow spheres in one step template free solvothermal method and their size dependent magnetic and electrical properties. Size of the hollow spheres is varied from 100 nm to 725 nm by changing the concentration of capping agent. Trace of Verway transition is found for all sets of spheres and the Verway transition temperature (TV) increases with increasing size of the spheres. The domain structure of these spheres changes from pseudo single domain to multi domain state as the size increases from 100 nm to 725 nm as evident from Day plots. This change in domain structure also changes the magnetic and electric properties of these spheres. Temperature dependent of high field magnetization of the hollow spheres can be well explained by Bloch's power law with higher than the bulk value of Bloch constant. The Bloch exponent varies from 1.94 to 1.69 with increasing size of the spheres. Frequency dependence of electrical conductivity (σ) shows Jonscher's power law type behaviour and bigger spheres are found to be more conductive than smaller ones due to their multidomain configuration. [ABSTRACT FROM AUTHOR]

Magnetic properties of compacted Sm0.1Ca0.9MnO3 nanoparticles with average particle size of 25 and 60 nm have been investigated. It was found that the relative volume of the ferromagnetic phase decreases with decreasing particle size. Magnetization curves measured in field cooled and zero field cooled mode separate near the transition temperature TC and remain different even in magnetic field of 15 kOe. AC-susceptibility is strongly frequency dependent below TC, although the temperature of the maximum depends on frequency only slightly. Magnetization hysteresis loops exhibit horizontal and vertical shifts, relatively small in 60 nm and much larger in 25 nm particles, due to size-dependent exchange bias effect. The exchange bias field and the coercive field depend in a non-monotonic way on cooling magnetic field, while the asymmetry of remanence magnetization and magnetic coercivity increase monotonously with the increase of cooling field. Applied pressure enhances Curie temperature TC of nanoparticles with a pressure coefficient dTC/dP ≈ 0.6 K kbar-1, close to that of the bulk, suggesting that magnetic state of the core is similar to the bulk state. The thermoremanance and isothermoremanance curves provide fingerprints of irreversible magnetization originating from the presence of glassy component. We have ascribed the magnetic behavior of the nanoparticles to a core-shell scenario with phase separated core containing ferromagnetic clusters embedded in an antiferromagnetic matrix and partially disordered antiferromagnetic or paramagnetic shell. The suppression of the ferromagnetic phase in the core with decreasing particle size may account for the enhancement of the exchange bias effect seen in smaller particles. [ABSTRACT FROM AUTHOR]

Parylene C (C8H7Cl)n thin films were deposited along the Si(100) index on a p-type Si substrate at room temperature by a vapor deposition polymerization method. The effects of film thickness on the crystalline structure, roughness, dielectric and electrical properties of parylene C films were investigated. X-ray diffraction has confirmed an amorphous structure in thinner films (d < 40 nm ≈ Rg: gyration radius) and a semicrystalline structure in thicker films (d < 40 nm). The roughness (Rms) varied according to a power law depending on the thickness Rms ∼ dβ with β = 0.22 ± 0.05. The effect of the diffusion monomers and chains relaxations in volume are the main factors limiting the evolution of the surface roughness according to film thickness for d < 40 nm and the crystalline size effect for d > 40 nm due to surface energy minimization when the film gets thicker. The dielectric constant increases as a power law according to film thickness [variant_greek_epsilon]′ = dβ with β = 0.042 ± 0.04 for d < 1000 nm and 0.0138 ± 0.02 for d > 1000. This is interpreted as caused by the decreasing of voids and discontinuities of the material with increasing film thickness. The leakage current density J suddenly increases with decreasing film thickness especially for d < 1000 nm, referring to a more pronounced amorphous content, but it is practically thickness independent from d > 10 000 nm and it shows a value of a bout 4 × 10-8 A/m for an applied field of 20 MV/m. [ABSTRACT FROM AUTHOR]

The use of increasingly strong magnetic fields in magnetic resonance imaging (MRI) improves sensitivity, susceptibility contrast, and spatial or spectral resolution for functional and localized spectroscopic imaging applications. However, along with these benefits come the challenges of increasing static field (B0) and rf field (B1) inhomogeneities induced by radial field susceptibility differences and poorer dielectric properties of objects in the scanner. Increasing fields also impose the need for rf irradiation at higher frequencies which may lead to elevated patient energy absorption, eventually posing a safety risk. These reasons have motivated the use of multidimensional rf pulses and parallel rf transmission, and their combination with tailoring of rf pulses for fast and low-power rf performance. For the latter application, analytical and approximate solutions are well-established in linear regimes, however, with increasing nonlinearities and constraints on the rf pulses, numerical iterative methods become attractive. Among such procedures, optimal control methods have recently demonstrated great potential. Here, we present a Krotov-based optimal control approach which as compared to earlier approaches provides very fast, monotonic convergence even without educated initial guesses. This is essential for in vivo MRI applications. The method is compared to a second-order gradient ascent method relying on the Broyden-Fletcher-Goldfarb-Shanno (BFGS) quasi-Newton method, and a hybrid scheme Krotov-BFGS is also introduced in this study. These optimal control approaches are demonstrated by the design of a 2D spatial selective rf pulse exciting the letters 'JCP' in a water phantom. [ABSTRACT FROM AUTHOR]

The effects of hot-pressing sintering on the phase composition, microstructure, thermal and electrical properties of AlN ceramics with CeO 2 –CeF 3 additives were studied. During hot-pressing sintering, high pressure reduced the grain boundary phase CeAlO 3 and decreased the concentration of oxygen in AlN ceramics. The hot-pressing sintered AlN samples had a much higher thermal conductivity of 191.9 W/m·K than pressureless sintered ones because of the great reduction of grain boundary phases and oxygen impurities in AlN ceramic. As the carbon content in hot-pressing sintered sample was very high, carbon contamination led to the decrease in electrical resistivity and changes in polarization mechanisms for AlN ceramics. The relaxation peak in the dielectric temperature spectrum with an activation energy of 0.64 eV for hot-pressing sintered samples was caused by electrons from free carbon at low temperature. Overall, hot-pressing sintering can effectively increase the thermal conductivity and change the electrical properties of AlN ceramics. [ABSTRACT FROM AUTHOR]

A novel, efficient, versatile strategy was carried out to fabricate highly porous ceramic parts based on the combination of strong colloidal gel ink fabricated with high boiling point organic solvents and DIW technique. The preparation and optimization of inks and the effect of heating temperature on the phase composition, microstructure, mechanical properties and dielectric properties of ceramic parts were systematically investigated. The strong colloidal ink exhibits excellent ambient stability and printability. The sintering temperatures bring about the evolution of phases, structural mechanical properties and dielectric properties of ceramic parts. Ultimately, Si 2 N 2 O single wall ceramic parts with a frame density of 1.07˜1.14 g/cm3 and an apparent porosity of 53.13 ± 1.29% were successful fabricated. The dielectric constant and dielectric loss of Si 2 N 2 O sample (1650℃) are only 4.24 and 0.0049, respectively. This strategy provides a reference for in-situ synthesis of high-performance porous ceramic components based on the DIW. [ABSTRACT FROM AUTHOR]

Dielectric waveguides are being intensively studied as accelerating structures excited by an electron bunch. Rectangular dielectric structures are used both to test the principles of new accelerating schemes and to study the electric properties of filling materials. Several dielectric materials used as fillers of waveguides have anisotropic properties (sapphire, ceramic films). Anisotropy can have a significant effect on the wakefields generated by an electron bunch in a structure. The paper presents an analytical calculation of Vavilov–Cherenkov radiation generated by a relativistic electron bunch in a rectangular waveguide filled with a transversely inhomogeneous transversely isotropic dielectric. A method for constructing an orthogonal basis of the transverse operator with its subsequent use to find the wakefield is presented. A dispersion relation for the structure and expressions for the wakefield created by a point electron bunch in a transversely isotropic rectangular dielectric structure are obtained. Based on the formalism presented, parameters of an accelerating structure based on sapphire, allowing the generation of fields above 100 MV/m, are calculated. [ABSTRACT FROM AUTHOR]

Using the Hartree-Fock (HF) and second-order Mo\ller-Plesset perturbation theory (MP2) methods with the 6-31G(d) basis set, we have investigated the chain length dependence of the longitudinal dipole moment and longitudinal components of the static linear polarizability, first and second hyperpolarizabilities of fluorinated polyacetylene chains. It is found that geometry changes caused by the electron correlation (EC) effects imply in marked increases of the electric properties but to obtain a reliable description it is necessary to properly account for both geometric and electronic changes. Based on the fast convergence pattern presented by the MP2/HF ratios and from the converged HF oligomeric results, we have estimated the MP2 electric properties of long chains. The asymptotic value for the MP2 second hyperpolarizability per unit cell is estimated in 1.9 × 108 a.u. This result is one order of magnitude larger than the corresponding result reported for the unsubstituted polyacetylene chains. [ABSTRACT FROM AUTHOR]