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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]

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]

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]

Pure nickel was processed by accumulative roll bonding (ARB), and the change in electrical resistivity measured at 77K was about 2.2 nΩm after 8 ARB cycles. The change in electrical resistivity was estimated based on the microstructural parameters, such as, dislocation density of about 3 © 1014m-2 and density of grain boundaries of about 8Mm-1 after 8 ARB cycles. Those values were evaluated using X-ray diffraction and electron backscattering diffraction in a field emission-scanning electron microscope, respectively. The change in the electrical resistivity was associated with the above-mentioned microstructural parameters. [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]

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]

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]

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]

This study examines the impact of solid waste on groundwater quality around three municipal dumpsites in AkwaIbom State, Nigeria using resistivity and hydrochemical data. Thirty vertical electrical soundings and ten electrical resistivity tomography data were acquired across the area using Schlumberger array. The resistivity data which were analyzed with the aid of IPI2WIN software formed the input data for estimating and modeling leachate parameters. Twelve groundwater samples collected around the area were analyzed for physico-chemical parameters using Atomic Absorption Spectrometer (AAS). The leachate parameters computed from resistivity interpretation across the area show thickness (2 to 56 m); hydraulic conductivity (6.19 to 24.7 m/day); transmissivity (96.63 to 1351.18 m2/day) and erodibility (104.36 to 2948.94 m/day). The hydrochemical analyses reveal elevated values of Total Dissolved Solids, Cadmium and high electrical conductivity within the area. The leachate migration paths trend predominantly in NW-SE and NE-SW directions at Uyo and Oron, respectively. The hydrogeological risk models reveal that the static water level crisscrosses the leachate at 35 m in Oron, while Uyo area has 25 m gap between the leachate and the static water levels. The study concludes that Oron dumpsites really contaminated the groundwater quality and makes it unfit for the dwellers. [ABSTRACT FROM AUTHOR]

Metal oxides, in many cases, exhibit n-type semiconductors due to the existence of oxygen vacancies in the lattice. Therefore, the interactions of oxygen being in medium with oxygen vacancies during the annealing process can change concentrations of defects that will cause variations in optical and electric properties of such materials. However, research on such interactions for commercial FTO, ITO, and TiO2 products has been limited. This paper summarizes the results of some experiments conducted to determine the influence of thermal annealing media on the optical, electrical properties of thin films of these products. The thermal media considered are air medium, 101 torr low vacuum condition, and Argon gas environments, and the annealing condition is set at 450°C for 20 minutes. It is found that while FTO films change for the better after annealing, ITO films trend towards worse, and TiO2 films have the most photoconversion efficiency (Isc = 0.27 mA, η = 0.37%) under the moderate oxygen concentration environment. [ABSTRACT FROM AUTHOR]

This work presents the study results of zinc oxide (ZnO) thin films doped with elements of group IB, namely silver (Ag) and copper (Cu). The films were deposited on the Corning 1737F glass substrate using the solutions derived by sol-gel method. Effect of Ag and Cu doping on structural, surface morphology, and electrical properties were investigated. X-ray diffraction (XRD) analysis showed that both the undoped and doped ZnO thin films are polycrystalline in nature with (002) preferred orientation. The SEM images show the grown films composed with nanoparticles with sizes of about 30 to 50 nm. Doping result was verified by measurements of EDX to check compound elements, Hall effect for basic electric parameters, and UV-VIS. As a result, the EDX measurement revealed the doping ratio of Ag in ZnO as expected. Besides, the concentration of p-type carriers was between 1015 to 1017 cm-3, the resistivity was from 54 to 260 O·cm. Particularly, the band gap values were between 3.16 to 3.18 eV for the concentration of dopants between 1 to 3 mol. at% compared to that of 3.20 eV for ZnO films at room temperature. These results confirmed the success of introducing the dopants into ZnO matrix. The transport property of doped films also confirms the material nature throughout the characteristics including temperature dependence of electrical conductivity and Seebeck coefficient. In general, there was a clear change in material nature of ZnO films from n- to p-type with acceptable electrical property for thermoelectric applications. [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]

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]

This editorial celebrates the 10th anniversary of Journal of Advanced Dielectrics (JAD) which was launched in January 2011. [ABSTRACT FROM AUTHOR]

Electric-field-driven ion migration can significantly modulate the electric and magnetic properties of solids, creating novel functionalities useful for advanced electromagnetic devices. Earlier works have used vertically stacked structures for this purpose, in which the redox process results from ion migration driven by a vertical electric field through the interfaces. However, the existence of the interfaces between the dissimilar layers causes the oxidation and reduction processes to have high and asymmetric energy barriers, which means that a large electric field is required to control the devices. Here, we show that in a partially oxidized single GdOx wire using a lateral electric field configuration, low and symmetric energy barriers for the oxidation and reduction processes can be achieved. We provide evidence that the redox process is the result of the lateral motion of oxygen ions by directly visualizing the electric-field-driven real-time ionic motion using an optical microscope. An electric field as low as 105 V/m was able to drive oxygen ions at room temperature, allowing controllable modulation of the electrical resistance using a lateral electric field. A large negative magnetoresistance was also observed in the GdOx wire, and its magnitude was significantly enhanced up to 20% at 9 T through oxygen ion control. Our results suggest that the electrical and magnetic properties of single GdOx can be efficiently controlled through oxygen ion motion driven by a lateral electric field, which paves the way for fully functional electromagnetic devices such as artificial synapses. Biomimetic devices: Oxygen ion migration mimics synapse function A new approach for creating tiny wires that move oxygen ions instead of electrons can offer researchers efficient control over devices with brain-like conductivity. According to neuroscientists, synapses, the junctions where two neurons meet, store information by activating different types of conductive states. Soogil Lee and Kab-Jin Kim from the KAIST institute in Daejeon, South Korea, and colleagues report similar behavior in nanoscale-thin wires made from gadolinium oxide, a rare-earth material in which oxygen ions can move freely. By pushing ions in the wire laterally between a cathode and an anode using an electric field, the team could establish two different conductivity levels due to slight changes in redox chemistry. The simplicity of this design enables lower-energy ion manipulation than previous studies employing vertically stacked films of gadolinium oxide and other metals. Electric-field-driven ion migration is an effective way to control many physical properties such as electric and magnetic properties of materials. In this research, we demonstrated that remarkably small electric field as low as 105 V/m can effectively modulate resistance of a GdOx microwire due to the lateral motion of oxygen ions. This result enables mimicking a synaptic device with low power consumption like as a brain. Furthermore, huge MR modulation of the GdOx microwire with the electric field provides novel functionality as an electromagnetic device. [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]

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]

The electronic properties of p-type, n-type, and ambipolar spiro materials have been investigated using a combination of photoemission spectroscopy, electron energy-loss spectroscopy, and density functional based calculations. Our results provide insight into the occupied density of states as well as the electronic excitation spectra. Comparison of experimental and theoretical data allows the identification of the orbitals responsible for charge transport and optical properties. [ABSTRACT FROM AUTHOR]

Electronic absorption and magnetic circular dichroism were recorded for five cyclophanes with ethano bridges: [2.2]paracyclophane, (1,2,4)[2.2.2]cyclophane, (1,2,4;1,2,5)[2.2.2]cyclophane, (1,2,3,4,5,6)(1,2,3,4,5,6)cyclophane, and trans-[2.2]metacyclophane. Spectral and structural analyses were based on geometry optimization and calculations of transition energies, carried out using density functional theory methods. The assignments have been proposed for several electronic transitions observed in the region below 52 000 cm-1. The observation of transitions which should be forbidden in the high D2h symmetry [2.2]paracyclophane suggests a twisted ground state structure of D2 symmetry, although the former structure with large amplitude vibrations at room temperature cannot be excluded. The PBE0 functional turned out to appropriately reproduce the inter-ring distances and electronic transition energies. [ABSTRACT FROM AUTHOR]

Electronic properties of benzene in water were investigated by a sequential quantum mechanical/molecular dynamics approach. Emphasis was placed on the analysis of the structure, polarization effects, and ionization spectrum. By adopting a polarizable model for both benzene and water the structure of the benzene-water solution is in good agreement with data from first principles molecular dynamics. Further, strong evidence that water molecules acquire enhanced orientational order near the benzene molecule is found. Upon hydration, the quadrupole moment of benzene is not significantly changed in comparison with the gas-phase value. We are also reporting results for the dynamic polarizability of benzene in water. Our results indicate that the low energy behaviour of the dynamic polarizability of gas-phase and hydrated benzene is quite similar. Outer valence Green's function calculations for benzene in liquid water show a splitting of the gas-phase energy levels associated with the 1e1g(π), 2e2g, and 2e1u orbitals upon hydration. Lifting of the orbitals degeneracy and redshift of the outer valence bands is related to symmetry breaking of the benzene structure in solution and polarization effects from the surrounding water molecules. [ABSTRACT FROM AUTHOR]

Chirality is a crucial factor in a single-walled carbon nanotube (SWCNT) because it determines its optical and electronic properties. A chiral angle spanning from 0° to 30° results from twisting of the graphene sheet conforming the nanotube wall and is equivalently expressed by chiral indexes (n,m). However, lack of chirality control during SWCNT synthesis is an obstacle for a widespread use of these materials. Here we use first-principles density functional theory (DFT) and classical molecular dynamics (MD) simulations to propose and illustrate basic concepts supporting that the nanocatalyst structure may act as a template to control the chirality during nanotube synthesis. DFT optimizations of metal cluster (Co and Cu)/cap systems for caps of various chiralities are used to show that an inverse template effect from the nascent carbon nanostructure over the catalyst may exist in floating catalysts; such effect determines a negligible chirality control. Classical MD simulations are used to investigate the influence of a strongly interacting substrate on the structure of a metal nanocatalyst and illustrate how such interaction may help preserve catalyst crystallinity. Finally, DFT optimizations of carbon structures on stepped (211) and (321) cobalt surfaces are used to demonstrate the template effect imparted by the nanocatalyst surface on the growing carbon structure at early stages of nucleation. It is found that depending on the step structure and type of building block (short chains, single atoms, or hexagonal rings), thermodynamics favor armchair or zigzag termination, which provides guidelines for a chirality controlled process based on tuning the catalyst structure and the type of precursor gas. [ABSTRACT FROM AUTHOR]

Electrical properties, including leakage currents, threshold voltages, and deep traps, of AlGaN/GaN heterostructure wafers with different concentrations of carbon in the GaN buffer layer, have been investigated by temperature dependent current-voltage and capacitance-voltage measurements and deep level transient spectroscopy (DLTS), using Schottky barrier diodes (SBDs). It is found that (i) SBDs fabricated on the wafers with GaN buffer layers containing a low concentration of carbon (low-[C] SBD) or a high concentration of carbon (high-[C] SBD) have similar low leakage currents even at 500 K; and (ii) the low-[C] SBD exhibits a larger (negative) threshold voltage than the high-[C] SBD. Detailed DLTS measurements on the two SBDs show that (i) different trap species are seen in the two SBDs: electron traps Ax (0.9 eV), A1 (0.99 eV), and A2 (1.2 eV), and a holelike trap H1 (1.24 eV) in the low-[C] SBD; and electron traps A1, A2, and A3 (∼1.3 eV), and a holelike trap H2 (>1.3 eV) in the high-[C] SBD; (ii) for both SDBs, in the region close to GaN buffer layer, only electron traps can be detected, while in the AlGaN/GaN interface region, significant holelike traps appear; and iii) all of the deep traps show a strong dependence of the DLTS signal on filling pulse width, which indicates they are associated with extended defects, such as threading dislocations. However, the overall density of electron traps is lower in the low-[C] SBD than in the high-[C] SBD. The different traps observed in the two SBDs are thought to be mainly related to differences in microstructure (grain size and threading dislocation density) of GaN buffer layers grown at different pressures. [ABSTRACT FROM AUTHOR]

The geometric and electronic properties of the titanium carbide TiC5 cluster in its neutral and anionic charge states have been investigated using density functional theory (DFT) at the B3LYP level. The nonplanar six-membered ring-type or “butterflylike” structures are found to be the equilibrium geometric structures of TiC5 and TiC5-. Time-dependent DFT is used in the calculation of the excited states. The theoretical assignment at the B3LYP level for the features in the photoelectron spectrum is given. All results obtained are in good agreement with the available experimental data. [ABSTRACT FROM AUTHOR]

The transport properties of conductive fiber composites are strongly dependent on the interactions between the conductive contents and their overall distribution, which is associated with the percolation and conduction of the relevant fibrous network. In this study, the fibers are modeled as randomly distributed three-dimensional cylinders with each cylinder consisting of a nonconductive core covered by a permeable conductive layer. By discretizing the interconnected surfaces of individual fibers, a finite element method is applied to evaluate the equivalent electrical conductivity of the entire system. Monte Carlo simulations are performed to quantify the relationships between the conductivity and the following factors: (1) the volume fraction, (2) the solidity of fibers, (3) the thickness of the coating layer, (4) the fiber aspect ratio, and (5) the distribution of the fiber orientation angles. In comparison with the model consisting of solid fibers, it has been shown that the coated structure can attain much higher conductivity. The associated percolation properties are also estimated from the computed conductivity, and the results show good agreement with those reported in the literature. These findings can be used as guidance in designing the next generation of multiscale conductive composites. [ABSTRACT FROM AUTHOR]

The electroluminescence intensity from Si cells under the forward bias was found to have one to one quantitative agreement with the minority carrier diffusion length. Based on the diffusion equation and simple p-n diode model, the electroluminescence intensity was analyzed relative to the cell performance. Electroluminescence intensity is proportional to the product of the injected minority carrier density and the effective diffusion length. The diode ideality factor n can be deduced by measuring the electroluminescence intensity as a function of the forward injection current. Among various crystalline silicon cells including single and polycrystalline types, the measured electroluminescence intensity at a fixed forward current has a tight relationship with the open circuit voltage of each cell, which gives a very convenient way to evaluate cell performance. [ABSTRACT FROM AUTHOR]

The temperature dependence of the specific resistance ρc in annealed Ti/Al/Ni/Au contacts on n-type GaN was monitored, obtaining information on the current transport mechanisms. After annealing at 600 °C, the contacts exhibited a rectifying behavior and became Ohmic only after high temperature processes (>700 °C), with ρc in the low 10-5 Ω cm2 range. The results demonstrated that the current transport is ruled by two different mechanisms: thermoionic field emission occurs in the contacts annealed at 600 °C, whereas field emission dominates after higher temperature annealing. The significant physical parameters related to the current transport, i.e., the Schottky barrier height and the carrier concentration under the contact, could be determined. In particular, a reduction of the Schottky barrier from 1.21 eV after annealing at 600 °C to 0.81 eV at 800 °C was determined, accompanied by a strong increase of the carrier concentration, i.e., from 2×1018 cm-3 in the as-prepared sample to 4.6×1019 cm-3 in the annealed contacts. The electrical properties were correlated to the microstructure of the interfacial region, providing a scenario to explain the transition from Schottky to Ohmic behavior in annealed Ti/Al/Ni/Au contacts. [ABSTRACT FROM AUTHOR]

The article discusses influence of the electrode types on the settings of the welding power source in welding industry. Topics include decrease in the role of manual arc welding in welding industry as productive processes such as MIG/MAG welding are becoming increasingly important; properties Electrode types which are usually classified based on the chemical composition of the electrode cladding and core; and electrical conductivity and the flow properties of the base material.

Metallic matrix composites reinforced with carbon nanomaterials continue to attract interest because of their excellent mechanical, thermal, and electrical properties. However, two critical issues have limited their commercialization. Uniform distribution of carbon nanomaterials in metallic matrices is difficult, and the interfaces between the nanomaterials and matrices are weak. Microscope-based analysis was recently used to quantitatively examine these microstructural features and investigate their contributions to the composites' mechanical, thermal, and electrical properties. The impacts of the microstructure on these properties are discussed in the first section of this review. In the second section, the various microscopic techniques used to study the distribution of carbon nanomaterials in metallic matrices and their interfaces are described. [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]

Solvothermal reaction of strontium ions with selected N‐containing and/or V‐shaped carboxylates led to the crystallization of six new coordination polymers: [Sr(2‐PZC)2] (1), [Sr(2,5‐PDC)(DMF)] (2), [Sr(2,5‐PDC)(DMA)] (3), [Sr(IDA)2] (4), [Sr(SBA)(H2O)2].DMF (5) and [Sr2(FBA)2(H2O)2(DMA)2].DMA (6) where, 2‐PZC=2‐pyrazinecarboxylate, 2,5‐PDC=2,5‐pyridinedicarboxylate, IDA=iminodiacetate, SBA=4,4′‐sulfonyldibenzoate and FBA=4,4′ (hexafluoroisopropylidene)bis(benzoate). Crystal structures were determined by single‐crystal X‐ray diffraction analysis and further characterized by powder X‐ray diffraction, elemental analysis, IR spectra, and TG analyses. Single crystal of 1 shows the occurrence of distorted rings made of twelve strontium carboxylate polyhedra connected in 3D. The structures of 2, 3, 5 and 6 are characterized by the presence of strontium carboxylate columns made of edge‐sharing SrOn polyhedra but connected differently to each other through organic linkers. The solids 2 and 3 are isostructural and contain rhombic channels which are occupied by the coordinated solvents. In solid 4, strontium occurred in a rare octahedral geometry bridged by IDA2− extending into 2D sheets. The structural features of 5 and 6 synthesized using V‐shaped ligands show 2D square‐shaped channel network. All the solids showed dielectric constants in the range 8–20. The solvent‐less 1 showed a relatively low dielectric constant (∼8) in comparison to 2, 3 and 4. The solids 5 and 6 with flexible ligands showed higher dielectric constants (∼17 and ∼20 respectively). [ABSTRACT FROM AUTHOR]

Chemical impurities in dielectric materials are one of the reasons that reduce the height of charge injection barrier. These impurities create energy states in dielectric band gap, which impact on the injection process. Chemical impurities that are studied in this paper include carbonyl, vinyl, and conjugated double bond impurities. These types of chemical impurities are the most common in technical dielectric polymers such as polyethylene. These impurities are studied using the computational quantum mechanics in the scope of density functional theory (DFT). The computed barrier in the present work is carried out using a new technique based on correcting the underestimation in polyethylene band gap due to the DFT computations. It is found that terminal carbonyl and conjugated double bond produce the lowest injection barrier for electrons and holes, respectively. The depth of these impurity states are compared with that developed in bulk PE and at the interface with other metals. The similarity in calculated barrier for electrons and holes is in agreement with the experimental observations. This paper concludes that chemical impurities cannot alone explain the activation energy of conduction of 1 eV. [ABSTRACT FROM AUTHOR]

Mineral oil has been used in power transformers for more than 100 years. Extensive research has been conducted on mineral oil substitutes in many countries due to the requirements of green energy and environmental protection. Natural esters are good substitutes for mineral oil. They present fire safety, environmental, and insulation ageing advantages over mineral oil. However, natural esters possess high viscosity, high dielectric loss, high acidity, and poor oxidation stability, and these properties require changing the structural design of transformers. In this study, a novel three-element (mineral, soybean, and palm) mixed insulation oil was successfully developed. This mixed insulation oil combines the advantages of mineral oil and natural esters, and its key parameters satisfy the requirement of IEC 60296:2012. The thermal and electrical properties of the novel three-element mixed insulation oil, including viscosity, heat transfer performance, permittivity, resistivity and breakdown voltage, were studied comprehensively. Comparison of the thermal and electrical properties of the novel mixed insulation oil with those of common mineral oil showed that the former exhibits better performance than the latter and is suitable for use in power transformers. [ABSTRACT FROM AUTHOR]

For many technical applications nanofillers are added to polymeric materials in order to modify the electrical, thermal or mechanical properties. However, nanoparticles tend to agglomerate, which can have a great impact on their ability to influence the macroscopic material characteristics. To overcome the limited insight provided by two-dimensional images, the focus of this study is on theoretical and experimental techniques to quantify the three-dimensional dispersion of particles in nanocomposites. For this purpose three different nanocomposites based on epoxy are produced in the lab by means of a nanomizer. Thin slices with a thickness of 200 nm each are cut and the three-dimensional nanoparticle distribution is reconstructed from serial transmission electron microscopy images. By means of the three-dimensional free-space length and the three-dimensional pair-correlation function two methods are provided to analyze the dispersion of the nanoparticles with respect to its agglomeration, uniformity or randomness. This way the nanofiller distributions of the investigated nanocomposites can be characterized quantitatively. [ABSTRACT FROM AUTHOR]