Out Of Plane Direction Research Articles

High electrical conductivity in out of plane direction of electrodeposited Bi2Te3 films

The out of plane electrical conductivity of highly anisotropic Bi2Te3 films grown via electro-deposition process was determined using four probe current-voltage measurements performed on 4.6 - 7.2 μm thickness Bi2Te3 mesa structures with 80 - 120 μm diameters sandwiched between metallic film electrodes. A three-dimensional finite element model was used to predict the electric field distribution in the measured structures and take into account the non-uniform distribution of the current in the electrodes in the vicinity of the probes. The finite-element modeling shows that significant errors could arise in the measured film electrical conductivity if simpler one-dimensional models are employed. A high electrical conductivity of (3.2 ± 0.4) ⋅ 105 S/m is reported along the out of plane direction for Bi2Te3 films highly oriented in the [1 1 0] direction.

Structural properties of Bi2−xMnxSe3 thin films grown via molecular beam epitaxy

The effects of Mn doping on the structural properties of the topological insulator Bi2Se3 in thin film form were studied in samples grown via molecular beam epitaxy. Extended x-ray absorption fine structure measurements, supported by density functional theory calculations, indicate that preferential incorporation occurs substitutionally in Bi sites across the entire film volume. This finding is consistent with x-ray diffraction measurements which show that the out of plane lattice constant expands while the in plane lattice constant contracts as the Mn concentration is increased. X-ray photoelectron spectroscopy indicates that the Mn valency is 2+ and that the Mn bonding is similar to that in MnSe. The expansion along the out of plane direction is most likely due to weakening of the Van der Waals interactions between adjacent Se planes. Transport measurements are consistent with this Mn2+ substitution of Bi sites if additional structural defects induced by this substitution are taken into account.

Out‐of‐plane strength reduction of unreinforced masonry walls because of in‐plane damages

SummaryThere are numerous studies on the behavior of Unreinforced Masonry (URM) walls in both in‐plane (IP) and out‐of‐plane (OP) directions; however, few aimed at understanding the simultaneous contribution of these intrinsic responses during earthquakes. Undoubtedly, even a strong URM wall shows weakened capacity in the OP direction because of minor cracks and other damages in the IP direction, and this capacity reduction has not yet been accounted for in seismic codes. In this study, performance of three URM walls is evaluated by several numerical analyses in terms of the OP capacity reduction because of IP displacements and failure modes. Several parameters influencing the OP capacity have been studied including aspect ratio, roof boundary condition, IP displacement and IP loading patterns. The results indicate that reduction in the OP capacity of URM walls varies from negligible to very high depending on boundary conditions, IP failure mode and IP damage severity. Moreover, IP loading pattern is more important in walls with higher aspect ratios because of their IP failure modes. Copyright © 2015 John Wiley & Sons, Ltd.

Effect of magnetic spins flipping process on the dielectric properties of α-Fe1.6Ga0.4O3 system

The α-Fe1.6Ga0.4O3 (Ga doped α-Fe2O3) sample has been stabilized in rhombohedral structure. The sample is a canted ferromagnet at 300 K and above. The spins structure starts flipping from in-plane direction to out of plane direction of the rhombohedral structure to exhibit an antiferromagnetic order below a typical temperature ∼ 215 K, known as Morin transition. The magnetic and dielectric properties of α-Fe1.6Ga0.4O3 system have been discussed in the temperature range 123 K to 350 K to examine the effect of magnetic spins flipping process on dielectric properties. The dielectric constant has shown an anomalous peak at ∼ 310 K, followed by a rapidly decrease of dielectric constant with temperature and becomes weakly temperature dependent below Morin transition. The temperature dependent dielectric constant is accompanied with the changes in electrical conductivity, dielectric loss and phase shift of the current with respect to applied ac voltage across the material. The magnetization and dielectric constant showed a linear relation over a wide range of temperature across the Morin transition. The dielectric constant at room temperature decreases under magnetic field, which indicates magneto-dielectric effect in the system. The signature of magneto-dielectric effect reveals a coupling between spins degrees of freedom (magnetic order) and charge degrees of freedom (electric polarization) in corundum structured non-traditional ferroelectric systems.

Process Development for the Fabrication of a Three Axes Capacitive MEMS Accelerometer

This paper presents a new approach for the fabrication of a three-axis capacitive MEMS accelerometer that is capable of differentially sensing the acceleration in all three orthogonal axes. For the first time in literature, differential sensing for the out of plane direction is achieved by defining a movable sensing electrode on the structural layer of the SOI wafer that is sandwiched between two stationary electrodes defined on the glass substrate and the handle layer of the SOI wafer enabling the differential sensing. In this approach, individual lateral and vertical axis accelerometers are fabricated in the same die on an SOI wafer which is anodically bonded to a glass substrate.

Exchange bias in strained SrRuO3 thin films

Recently, it was found that the ferromagnetic SrRuO3 when combined with another ferromagnet in thin film form gives rise to exchange bias (EB) effect. However, we observed EB in single, strained, SrRuO3 thin films grown on diamagnetic LaAlO3 (100) substrates. It displays the training effect, which essentially confirms EB. The temperature dependence of the EB reveals the blocking temperature to be around ∼75 K. The strength of the exchange bias decreases with the increase in thickness of the film. We observe tensile strain in the out of plane direction. Further, the presence of in-plane compressive strain is observed through asymmetric reciprocal space mapping. Finally, we find a direct link between strain and EB. The evolution of strain with thickness matches well with the nature of scaled EB. It has been shown earlier by first principle calculations that this strain can induce EB in thin films.

Coupled electrical-thermal-pyrolytic analysis of carbon fiber/epoxy composites subjected to lightning strike

The high Joule heating of carbon fiber reinforced polymer composites (CFRP) subjected to lightning strike induces resin decomposition and carbon sublimation. The mechanism and characteristics of the change in composite material properties are the key basis of the numerical analysis and the optimal design of composite structures. In order to elucidate the damage phenomena caused by lightning strike, a tightly coupled electrical-thermal-pyrolytic analysis is conducted by introducing the numerical calculation of resin pyrolysis degree on the basis of thermal-electrical numerical analysis. Hence the electrical and thermal properties in both out-plane and in-plane directions are modeled as functions of the pyrolysis degree of the composite material, namely the material properties change with the component during the decomposition, which is revealed to be reasonable from both the numerical and the experimental results. The research is helpful for understanding the complicated relationships in the important damage process including electrical, thermal and chemical phenomena.

Strain-induced electronic phase transition and strong enhancement of thermopower ofTiS2

Using first principles density functional theory calculations, we show a semimetal to semiconducting electronic phase transition for bulk TiS 2 by applying uniform biaxial tensile strain. This electronic phase transition is triggered by charge transfer from Ti to S, which eventually reduces the overlap between Ti-(d) and S-(p) orbitals. The electronic transport calculations show a large anisotropy in electrical conductivity and thermopower, which is due to the difference in the effective masses along the in-plane and out of plane directions. Strain induced opening of band gap together with changes in dispersion of bands lead to three-fold enhancement in thermopower for both p- and n-type TiS2 . We further demonstrate that the uniform tensile strain, which enhances the thermoelectric performance, can be achieved by doping TiS2 with larger iso-electronic elements such as Zr or Hf at Ti sites.

Bidirectional behavior of unreinforced masonry walls

SUMMARYMost of the studies related to the modeling of masonry structures have by far investigated either the in‐plane (IP) or the out‐of‐plane (OP) behavior of walls. However, seismic loads mostly impose simultaneous IP and OP demands on load‐bearing or shear masonry walls. Thus, there is a need to reconsider design equations of unreinforced masonry walls by taking into account bidirectional effects. The intent of this study is to investigate the bidirectional behavior of an unreinforced masonry wall with a typical aspect ratio under different displacement‐controlled loading directions making use of finite element analysis. For this purpose, the numerical procedure is first validated against the results of the tests on walls with different failure modes conducted by the authors. Afterward, the response of the wall systems is evaluated with increasing top displacement having different orientations. A set of 19 monotonic and three cyclic loading analyses are performed, and the results are discussed in terms of the variation of failure modes and load–displacement diagrams. Moreover, the results of wall capacity in each loading condition are compared with those of the ASCE41‐06 formulations. The results indicate that the direction of the resultant force, vectorial summation of IP and OP forces, of the wall is initially proportional to the ratio of stiffness in the IP and the OP directions. However, with the increase of damage, the resultant force direction inclines towards the wall's longitudinal direction regardless of the direction of the imposed displacement. Finally, recommendations are made for applicability of ASCE41‐06 formulations under different bidirectional loading conditions. Copyright © 2014 John Wiley & Sons, Ltd.

Effect of Mechanical Stress on Electrochemical Properties of Li Ion Batteries Cathodes

1. IntroductionRecently, all-solid state Li ion batteries are widely investigated to establish more reliable and flexible battery systems [1, 2]. Compared to conventional batteries with liquid electrolytes, all-solid-state batteries can be suffered from undesired strains induced at hetrointerfaces between solids due to differences of crystal structures and chemical/thermal expansion coefficients. Such a strain may cause performance improvement/deterioration or failure of all-solid-state batteries. For example, it was reported that charge and discharge properties of an Al electrode is affected by the strain [3]. Therefore, it is important to understand the effect of strain on the electrochemical properties for the design and development of all-solid-state batteries. The purpose of this study is to reveal the effect of strain on electrochemical behaviors of cathode materials for all-solid-state Li batteries. For this aim, dense thin film LiCoO2 (LCO) electrodes were fabricated on an Li ion conducting glass ceramics (LICGC) by the PLD method, and the variation of the chemical potential of Li in the electrode due to external strain was evaluated by measuring electromotive force (EMF) between compressively and tensely strained LCO electrodes.2. Experimental A schematic illustration of the specimen is shown in Fig.1. Dense thin film LCO electrodes were fabricated on both surfaces of an Li ion conducting glass ceramics LICGC (OHARA INC.) by the PLD method at 873 K with P(O2) of 20 Pa. Then, Al films as counter electrodes were also deposited next to the LCO electrodes by Ar ion sputtering at room temperature in Ar atmosphere of about 0.67 Pa. The Li contents of the LCO dense films were controlled by the electrochemical de-lithiation and estimated from the amount of the electricity passed through the cell. After the de-lithiation process, the Al electrode side was cut down. Two LCO electrodes were short circuited for about 24 hours to equilibrate the Li chemical potential. After the equilibration, the EMF between two LCO electrodes was measured with applying compressive and tensile strain to the upper and the lower LCO electrodes, respectively, by the four points bending method as shown in Fig.1.3. Results and Discussion The obtained LCO electrode was oriented in the direction of (003) along the out of plane direction, i.e., the Li conductive plane was almost parallel to the substrate. Fig.2 shows the result of OCV measurements under different strain states. The EMF was generated when the strain was applied to the specimen. The compressively strained LCO electrode was negatively charged while the tensely strained LCO electrode was positively charged. The EMF emerged immediately after the application of the strain, was kept at an almost constant value while keeping the constant strain state, and became nearly zero after the release of the strain. The observed EMF value increased as the applied strain increased. Since the generation of EMF represents the difference of Li chemical potential between the compressively and tensely strained LCO electrodes, it is considered that the structural deformation due to the external strain induces the Li chemical potential variation. In the presentation, we will discuss the origin of the EMF from the thermodynamical points of views.

Shake table tests for the seismic assessment of hollow brick internal partitions

The collapse of hollow brick internal partitions is one of the most widely reported nonstructural damage after an earthquake, especially in the European area. Full-scale experimental tests on standard hollow brick partitions are described in the paper. In particular, bidirectional shaking table tests are performed in order to investigate the seismic performance of hollow brick partitions, subjecting the partition simultaneously to interstorey relative displacements in their own plane and accelerations in the out of plane direction. A steel test frame is properly defined in order to simulate the seismic effects at a generic building storey. A set of five couples of accelerograms are selected matching the target response spectrum provided by the U.S. code for nonstructural components in order to investigate a wide range of seismic input. Three damage states are considered in this study and correlated to an engineering demand parameter, i.e. the interstorey drift ratio, through the use of a damage scheme. The tested specimen exhibits significant damage for 0.3% interstorey drift and extensive damage for drift close to 1%. The correlation between the dynamic characteristics of the test setup, in terms of damping ratio and natural frequency, and the recorded damage is shown.

Comparing study of magnetic properties of Co–CeO2 thin films with (111) and (100) preferred orientations

In recent years, diluted magnetic oxides (DMOs) have been intensively studied aiming for using for spin injection and transportation. In this paper, DMOs of cobalt doped CeO2 (CCO) films with varied cobalt content (0–10%) were fabricated on Al2O3 (0001) substrates by both pulsed laser deposition (PLD) and magnetron sputtering respectively. Pulsed laser deposited and sputtered CCO films showed CeO2 (111) and (100) preferred orientations respectively. These two types of films with different crystallinity had almost the same magnetic and magneto-optical properties, such as room temperature ferromagnetism, non-linearly dependent of the moments on cobalt content, anisotropic magnetisation with an easy axis in out of plane direction and giant Faraday effect. The largest Faraday rotation value of ∼4500° cm−1 at 650 nm wavelength was obtained, for both PLD and magnetron sputtered films. The successful fabrication of ferromagnetic CCO films with controllable preferred orientations on Al2O3 (0001) substrates would be useful to facilitate epitaxial multilayered thin film devices fabrication.

Thickness Dependent Structure and Magnetic Properties in <sup>57</sup>Fe/Ti/Co Multilayers

Structural and magnetic properties of57Fe/Ti/Co multilayers (MLs), prepared by Ion beam sputtering on Si substrate have been studied as a function of trilayers (TLs) thickness and modulation periods. X-ray reflectivity (XRR) shows the successful growth of high-quality layered structures along with up to 3rdorder Bragg peaks with distinct Kiessig oscillation. X-ray diffraction (XRD) and Mössbauer studies evidence the formation of different phases mainly at the interfaces. Soft magnetic properties with high saturation values (~800emu/cm3) and high anisotropy field (~20kOe) are observed in the room temperature magnetization curve. The in plane value of coercivities are 18Oe and 60Oe for the 12 and 24 TLs respectively while in the out-of plane direction it increases to nearly 8 and 12 times respectively. The 12 TLs sample shows the presence of two fold anisotropy whereas the 24 TLs sample shows an isotropic behaviour. Low temperature DC magnetization studies evidence the presence of weak antiferromagnetic coupling while the Kelly Henkel plots for these samples show that the dominant exchange interactions between the grains are ferromagnetic.

Upper critical fields and anisotropy of Ca1−xLaxFe2As2 single crystals

The superconductivity of Ca1−xLaxFe2As2 single crystals with various doping levels was investigated via electromagnetic measurements for out-plane (H ∥ c) and in-plane (H ∥ ab) magnetic field directions. Obvious double superconducting transitions, which can survive in magnetic fields up to several tesla, were observed in the medium-doped (x = 0.13) sample. Two kinds of distinct upper critical field (Hc2) phase diagrams were established for the low superconducting phase with Tc lower than 15 K and the high superconducting phase with superconducting transition temperature (Tc) of over 40 K, respectively. Both kinds of phase diagram exist in the medium-doped sample. Unusual upward curvature near Tc was observed in Hc2 phase diagrams and analyzed in detail. Temperature dependences of anisotropy for different doping concentrations were obtained and compared. Both superconducting phases manifest extremely large anisotropies, which may originate from the interface or intercalation superconductivity.

Effects of surface modification with reactive mesogen on the anchoring strength of liquid crystals

We studied the effects of polymer chain ordering in the alignment layer and resulting molecular interactions on the surface anchoring energy by introducing a reactive mesogen (RM) coating to the alignment layer. Directionally polymerized RMs on the rubbed alignment layer decrease the steric repulsion and increase the electronic interaction with liquid crystal molecules, and, as a result, the surface anchoring energy is enhanced in both the out-of plane and in-plane directions. We also demonstrated that this enhanced surface anchoring energy can be used to improve the response time characteristics of liquid crystal displays.

Ionization within the Local Cavity by Hot White Dwarfs

ABSTRACTWe present estimates of the contribution from 33 nearby (d < 100 pc) hot DA white dwarfs to the total ionization of the Local Cavity. The EUV spectra of these white dwarfs have been derived using non-LTE stellar atmosphere models (with the inclusion of metals where necessary) to calculate the incident flux at the Earth using up-to-date distances and interstellar column densities. Our model spectra give a very good approximation to the spectra obtained with observations from the NASA Extreme Ultraviolet Explorer satellite. The number of Lyman continuum photons per second emitted by each of the white dwarfs for wavelengths over the 30–912 Å range was then derived. Using these numbers, the respective sizes of the ionized Strömgren spheres of HII were then calculated for each star under the assumption of ambient interstellar electron density values of ne = 0.04 cm-3 and 0.10 cm-3. The location and sizes of these ionized regions have been plotted on a 3D map of the neutral absorption contours of the local ISM, as derived for both in-plane and out of plane directions. A similar procedure was also carried out for the determination of the sizes of the ionized HeII regions surrounding the same 33 white dwarfs. We conclude that only a few of the very hottest DA white dwarfs located within the Local Cavity can possess appreciably sized ionized Strömgren spheres of HII and HeII. The size of these ionized regions can potentially range between 20 pc and 40 pc in diameter, dependent on the ambient value of the electron density of the interstellar medium. However, the volumetric filling factor of these ionized spheres within the Local Cavity is small (∼6%), even at the lowest value of electron density considered in this study (i.e., ne = 0.04 cm-3). Thus, the contribution from DA white dwarfs to the ionization of both the local interstellar cloud complex and other clouds located within the Local Cavity is of secondary importance compared to the ionization contribution provided by the two early B-type stars of ϵ and β CMa.

An Analytical Model for Repulsive Electrostatic Microactuator Using a Conformal Mapping Technique

Electrostatic microactuators are able to produce a repulsive force in the out-ofplane direction. The electrostatic microactuators use an asymmetric electric field surrounding the top and bottom surfaces of the moving fingers to produce a repulsive force. The displacement of moving finger is not limited by the “pull-in” effect. In addition, the usage of a repulsive force leads to the elimination of the sticking problem. In this paper, an analytical model for the repulsive-force, and the fringe capacitance of a microactuator is developed putting the moving plate thickness in consideration using conformal mapping techniques. With this technique, electric field lines are geometrically approximated to separately model the different capacitive components. These components are finally combined to obtain the equivalent fringe capacitance. The model reveals the maximum out-of-plane displacement. Rules are derived based on the analytical model for tuning and optimization of the microactuator performance. Simulations are conducted to verify the analytical model. In addition, the mechanism for generating the repulsive force is explained.

Instability of flat disks with respect to the formation of twisted ribbons in smectic-A*monolayers

Smectic-A* monolayers self-assembled from aqueous solutions of chiral fd viruses and a polymer depletant can assume a variety of shapes such as flat disks and twisted ribbons. A first order phase transition from a flat disk to a ribbon occurs upon lowering the concentration of polymer depletant or the temperature. A theoretical model based on the de Gennes model for the smectic-A phase, the Helfrich model of membrane elasticity, and a simple edge energy has been previously used to calculate the disk-ribbon phase diagram. In this paper we apply this model to the nucleation process of ribbons. First, we study the "rippled disks" that have been observed as precursors of ribbons. Using a model shape proposed by Meyer which includes rippling in both the in-plane and out-of-plane directions, we study the energetics of the disks as functions of the edge energy modulus (a measure of the polymer concentration) and the mean curvature modulus k. We find that as the edge energy modulus is reduced the radial size of the ripples grows rapidly in agreement with experimental observations. For small enough k we find that the out-of-plane size of the ripples grows but its value saturates at a fraction of the twist penetration depth, too small to be experimentally observable. For large k the membrane remains flat though rippled in the radial direction. Such membranes do not have negative Gaussian curvature and thus will not likely spawn twisted ribbons. We also study the creation of twisted ribbons produced by stretching the edge of a flat membrane in a localized region. In experiments using a pair of optical traps it has been observed that once the membrane has been sufficiently stretched a ribbon forms on the stretched edge. We study this process theoretically using a free energy consisting of the Helfrich and edge energies alone. We add a small ribbonlike perturbation to the protrusion produced by stretching and determine whether it is energetically favorable as a function of the size of the protrusion. In qualitative agreement with experiment we find a nonzero value for the critical size of the protrusion needed to make a ribbon energetically favorable, though the value we find is an order of magnitude lower than the experimental value possibly due to our neglect of the director field. As in the case of the rippled disks we find that the mean curvature energy acts as a barrier between the disk and twisted ribbon structures.

CoFeB spin polarizer layer composition effect on magnetization and magneto-transport properties of Co/Pd-based multilayers in pseudo-spin valve structures

In this work, we used CoxFe80-xB20 (x = 60, 40, 20) as spin-polarizing layers (SPLs) in order to investigate the composition of the CoFeB-SPL on the magnetoresistance in Co/Pd multilayers-based pseudo-spin-valves (PSVs) with perpendicular magnetic anisotropy (PMA). In both soft layer and hard layer, the PMA was achieved by tuning the interface anisotropy and bulk anisotropy between SPL and Co/Pd multilayers. For all the films, giant magnetoresistance (GMR) was found to decrease with increasing SPL thickness in the as-deposited case, irrespective of the CoFeB atomic composition and saturation magnetization (Ms). However, interesting behavior is observed when the films were post annealed. Although GMR degradation is expected after annealing, a peak of GMR was observed after post annealing the samples at 250 °C. This peak is stronger for the samples with thicker SPLs than those with thinner SPLs. Nonetheless, further increase in annealing temperature causes a reduction in GMR which is found to be larger in Co rich atomic composition samples with a lower Ms. In the case of thicker CoFeB SPL (15 Å), the magnetization of overall composite (Co/Pd)/CoFeB soft layer appears to be canted from out of plane direction. Among the three compositions investigated, Co60Fe20B20 polarizer shows a stronger PMA due to its lower Ms, leading to the weaker demagnetizing field. In addition, this study also indicates that the crystallographic texture of Co/Pd multilayers plays a role in GMR of PSV stack structures.

Experimental and Finite Element Based Investigations of In-Plane and Out-of-Plane Properties of Aluminum Honeycomb

Experimental and Finite Element analysis was used for the investigation of the effect of cell size and thickness on the compressive properties of Aluminium honeycomb core. Honeycomb cores were compressed experimentally in in-plane and out of plane directions. The effect of sample size, cell size and thickness on the elastic modulus, yield strength and plateau stress was investigated through FEA. It was found that the mechanical response was independent upon the sample size in in-plane direction. The smallest cell size honeycomb core was deformed at higher yield stress. Similarly, with increase in cell wall thickness, the modulus of the core increased.