Out Of Plane Direction Research Articles

Anisotropic thermal expansion coefficient of multilayer graphene reinforced copper matrix composites

Multilayer graphene reinforced copper matrix (Cu-MLG) composites were fabricated via molecular-level mixing combined with vacuum hot-pressing (VHP). The MLG displayed a preferred orientation in the copper matrix, with the in-plane surface perpendicular to the hot-pressing direction, resulting in significant anisotropy in the thermal properties of Cu-MLG composites. Theoretical predictions were made using four models (Schapery, Kerner, Turner and mixture rule) to investigate the effect of the preferential orientation of MLG on the CTE anisotropy of Cu-MLG composites. The CTE anisotropy was further analyzed by carrying out molecular dynamics (MD) simulations to determine the variation in bond lengths for copper and MLG in different directions in the interface regions. The MLG bond length increased gradually with increasing temperatures in the in-plane direction, while in the out-plane directions, it increased significantly at first and then decreased at higher temperatures. The variations of bond lengths for MLG are consistent with the CTE anisotropy of the Cu-MLG composites in the same direction.

Influence of inhomogeneous refractive index fields on particle image velocimetry

The influence of inhomogeneous refractive index fields on particle image velocimetry (PIV) measurements is a well known problem, which leads to an unknown measurement uncertainty in, e.g., flame flows, shock waves and super sonic flows. Previous studies give only rough estimations of the measurement error due to inhomogeneous refractive index fields, and quantitative information is only available for special conditions such as a gradient of the refractive index independent of the viewing direction. Hence, the assessment of the spatial distribution of the quantitative measurement errors inside inhomogeneous refractive index distributions especially for stereoscopic and tomographic PIV is an open question. For this purpose, the flow measurement inside a hot jet flow is considered as an example, and a general analytic description of the error of the measured particle positions inside the hot jet flow is derived, numerically evaluated and finally validated by experiments. In particular, the determination of the particle position with triangulation is investigated, which is performed in stereoscopic and tomographic PIV. As a result, the measurement error is generally larger than for standard PIV without triangulation. The theoretically predicted errors of the measured particle position are validated with experiments and here amount to 11.7 µm for standard PIV and 17.3 µm for triangulation at the same distance from the center of the flow, respectively. Note that the error estimation requires the knowledge of the refractive index field that was determined by temperature measurements in the flow. Furthermore, the error analysis shows that for triangulation the measured particle position depends on the gradient and the curvature of the refractive index field, whereas for standard PIV the measured particle position only depends on the gradient of the refractive index. For the given temperature profile with a maximum temperature of 191 °C, the resulting flow velocity error is maximally 0.8 % with standard PIV, 1.7 % for the in plane and 2.9 % for the out of plane direction with stereoscopic PIV and 1.1 % with triangulation which is performed in tomographic PIV.

Synthesis and thermoelectric properties of Rashba semiconductor BiTeBr with intensive texture

Bismuth tellurohalides with Rashba-type spin splitting exhibit unique Fermi surface topology and are developed as promising thermoelectric materials. However, BiTeBr, which belongs to this class of materials, is rarely investigated in terms of the thermoelectric transport properties. In the study, polycrystalline bulk BiTeBr with intensive texture was synthesized via spark plasma sintering (SPS). Additionally, its thermoelectric properties above room temperature were investigated along both the in-plane and out-plane directions, and they exhibit strong anisotropy. Low sound velocity along two directions is found and contributes to its low lattice thermal conductivity. Polycrystalline BiTeBr exhibits relatively good thermoelectric performance along the in-plane direction, with a maximum dimensionless figure of merit (ZT) of 0.35 at 560 K. Further enhancements of ZT are expected by utilizing systematic optimization strategies.

Laminar fluid flow and heat transfer in non-circular sub-channel geometries of nuclear fuel bundle

Numerical simulation of fully developed laminar fluid flow and heat transfer in non-circular sub-channel geometries representing a typical nuclear fuel bundle is carried out. The governing equations of fluid flow and heat transfer are reduced in the form of Poisson's equation and implemented in COMSOL multi physics code as classical PDEs. The fully developed laminar flow equations are solved on the non-circular sub-channel and fuel bundle geometries in a two dimensional domain cut in the longitudinal cross section. The domain is solved for the flow velocities in the out of plane direction by applying the pressure gradient as the boundary condition. The study is focused on the detailed analysis of the Poiseuille number (fRe) and average Nusselt number (Nu¯) in square and triangular pitched sub-channel geometries of rod bundle. These investigations are carried out for two distinct boundary conditions as axially uniform wall heat flux with uniform wall temperature in the periphery (H1 Boundary condition) and uniform wall heat flux in both axial and circumferential directions (H2 boundary condition) for different p/d ratios varying from 1 to 2. It is found that the fRe increases significantly from 6.5 to 24 for p/d ratio of 1–1.15 for the sub-channel shaped geometry. In case of the sub-channel shaped tube of the same p/d ratio, the fRe increases sharply upto p/d ratio ∼1.15 and then starts decreasing slightly till the p/d ratio of 1.5. Analyses are also carried out for square pitched bundles of different sizes varying from 2 × 2 to 10 × 10 to find the variation of fRe with p/d and W/d in the laminar flow regime. The effect of bundle size on the variation of bundle friction factor (fRe) reveals that for an equal p/d and W/d ratios, the change in bundle friction factor (fRe) is within 5% and the effect of bundle sizes vanishes. Correlations are developed to predict the flow and heat transfer characteristics as a function of p/d ratio for non-circular sub-channels by least square regression analysis.

Interface-engineered oxygen octahedral coupling in manganite heterostructures

Control of the oxygen octahedral coupling (OOC) provides a large degree of freedom to manipulate physical phenomena in complex oxide heterostructures. Recently, local tuning of the tilt angle has been found to control the magnetic anisotropy in ultrathin films of manganites and ruthenates, while symmetry control can manipulate the metal insulator transition in nickelate thin films. The required connectivity of the octahedra across the heterostructure interface enforces a geometric constraint to the 3-dimensional octahedral network in epitaxial films. Such geometric constraint will either change the tilt angle to retain the connectivity of the corner shared oxygen octahedral network or guide the formation of a specific symmetry throughout the epitaxial film. Here, we will discuss the control of OOC in manganite heterostructures by interface-engineering. OOC driven magnetic and transport anisotropies have been realized in LSMO/NGO heterostructures. Competition between the interfacial OOC and the strain further away from the interface leads to a thickness driven sharp transition of the anisotropic properties. Furthermore, octahedral relaxation leading to a change of p-d hybridization driven by interfacial OOC appears to be the strongest factor in thickness related variations of magnetic and transport properties in epitaxial LSMO films on NGO substrates. The results unequivocally link the atomic structure near the interfaces to the macroscopic properties. The strong correlation between a controllable oxygen network and the functionalities will have significant impact on both fundamental research and technological application of correlated perovskite heterostructures. By controlling the interfacial OOC, it is possible to pattern in 3 dimensions the magnetization to achieve non-collinear magnetization in both in-plane and out of plane directions, thus making the heterostructures promising for application in orthogonal spin transfer devices, spin oscillators, and low field sensors.

Effects of yarn defects and specimen size on impact compressive damages of 3-D angle interlock woven composites

The objective of this work is to investigate yarn defects and specimen size on the impact compressive properties of 3-D angle interlock woven composites (AIWCs). The size effects on impact compressive properties were tested along in plane and out of plane directions. A new finite element model, with inherent defects in the geometrical model of yarns, was established to simulate impact compressive properties of the 3-D AIWCs. The model was further used to analyze size effects on impact compressive properties of 3-D AIWCs. We found the size effect on the 3-D AIWCs was not apparent both in experimental and numerical results; however, the random defects in yarns had a great effect on the compressive properties of 3-D AIWCs along different directions. The yarns effects will weaken the compressive stiffness and strength significantly.

Effect of alkyl side chains on properties and organic transistor performance of 2,6-bis(2,2′-bithiophen-5-yl)naphthalene

Herein we report the synthesis and characterization of C2-symmetric 2,6-bis(5′-alkyl-2,2′-bithiophen-5-yl)naphthalene derivatives with alkyl side chains of various length and shape, including even the less commonly examined cyclohexyl and cyclohexylalkyl groups. By investigation of how these side chains influence solubility, self-assembly and charge mobility, we aimed to extend the knowledge of structure-function property relationship of the oligothiophene compounds. Charge mobilities observed in this study ranged from 10−3 to 10−1cm2 V−1s−1. The highest values referred to thin layers of derivatives end-capped with linear alkyl chains. XRD methods uncovered OFET-favorable layering of tilted molecular arrangement with the molecular long axes in the out of plane direction. Although the charge mobilities showed variation of as much as two orders of magnitude, XRD measurements of these derivatives revealed similar packing and self-assembly behavior. Hence, the charge mobility differences are more a result of the naturally diverse spatial demands of the tested alkyl groups, with the linear alkyl chains offering the tightest close packing of the π-conjugated backbone. On the other hand, the bulky 2-hexyldecyl group turned out to be the only group that made it possible to avoid insolubility of these derivatives and provided excellent solubility (23mg/mL of chloroform), while the charge mobility remained acceptable even of the spin-coated thin layers.

Spin accumulation in disordered topological insulator ultrathin films

Topological insulator (TI) ultrathin films differ from the more commonly studied semi-infinite bulk TIs in that the former possess both top and bottom surfaces where the surface states localized at different surfaces can couple to one another across the finite thickness of the film. In the presence of an in-plane magnetization, the TI thin films display two distinct phases depending on which of the inter-surface coupling or the magnetization is stronger. In this work, we consider a Bi2Se3 TI thin film system with an in-plane magnetization and numerically calculate the resulting spin accumulation on both surfaces of the film due to an in-plane electric field to linear order. We describe a numerical scheme for performing the Kubo formula calculation in which we include impurity scattering and vertex corrections. We find that the sums of the spin accumulation over the two surfaces in the in-plane direction perpendicular to the magnetization and in the out of plane direction are antisymmetric in Fermi energy around the charge neutrality point and are non-vanishing only when the symmetry between the top and bottom TI surfaces is broken. The impurity scattering, in general, diminishes the magnitude of the spin accumulation.

Blue and red shifted temperature dependence of implicit phonon shifts in graphene

We have calculated the implicit shift for various modes of frequency in a pure graphene sheet. Thermal expansion and Grüneisen parameter which are required for implicit shift calculation have already been studied and reported. For this calculation, phonon frequencies are obtained using force constants derived from dynamical matrix calculated using VASP code where the density functional perturbation theory (DFPT) is used in interface with phonopy software. The implicit phonon shift shows an unusual behavior as compared to the bulk materials. The frequency shift is large negative (red shift) for ZA and ZO modes and the value of negative shift increases with increase in temperature. On the other hand, blue shift arises for all other longitudinal and transverse modes with a similar trend of increase with increase in temperature. The q dependence of phonon shifts has also been studied. Such simultaneous red and blue shifts in transverse or out plane modes and surface modes, respectively leads to speculation of surface softening in out of plane direction in preference to surface melting.

Magnetic and exchange bias properties of YCo thin films and IrMn/YCo bilayers

We report on the structural and magnetic properties of YCo thin films and IrMn/YCo bilayers. X-ray diffraction infer that all the films are amorphous in nature. Magnetization versus magnetic field measurements reveal room temperature soft ferromagnetism in all the YCo films. Thin films which were grown at 100W sputter power with growth rates of 0.677, 0.694 and 0.711Å/sec show better morphology and composition than 50W (0.333, 0.444 and 0.277Å/sec) grown films. Perpendicular exchange bias in as deposited bilayers is evident for IrMn/YCo bilayers. Exchange bias (EB) decreases in case of in plane measurements and enhances for out of plane measurements after perpendicular field annealing. EB is more in case of out of plane direction due to large perpendicular anisotropy in comparison with in plane direction. Above the critical thickness, EB variation is explained on the basis of random field model in the Heisenberg regime, which has been proposed by Malozemoff. Indeed there exists an inverse relationship between EB and IrMn layer thickness. Evidenced vertical shift apart from the horizontal shift for magnetization loops is attributed to frozen magnetic moments in one of the layers at the interface. Present results would prove to be helpful in spintronic device applications.

Thermoelectric characteristics in out-of plane direction of thick carbon nanotube-polystyrene composites fabricated by the solution process

When sheet-like flexible devices are placed on heat sources, a thermal flow is induced along the out-of-plane direction in regards to the device surface. To obtain carbon nanotube-based (CNT-based) thermoelectric devices that work under thermal flows along the out-of-plane direction, it is indispensable to fabricate sufficiently thick CNT-based materials that will allow for an out-of-plane temperature difference to occur. Therefore, we investigated the out-of-plane thermoelectric characteristics of thick CNT-polymer composites (thickness=0.74–0.84mm), which were fabricated by over-coating a dense CNT-dispersed solution, and found that the electrical and thermal conductivities of the composites in the out-of-plane direction were significantly lower than those in the in-plane direction, respectively. We observed that the composites’ figure of merit values in the out-of plane direction was approximately one order of magnitude lower than those in the in-plane direction. This anisotropy in the characteristics of thick CNT-polystyrene composites may be caused by the orientation of the CNTs along the in-plane direction. Therefore, the results indicate that controlling the orientation of CNTs in thick composites is a key factor to improve the performance of devices that work on the basis of temperature differences along the out-of plane direction.

Evaluation of brick infill walls under in-plane and out-of-plane loading

In this paper, the in-plane (IP) and out-of-plane (OP) interaction of masonry infill walls with various length-to-height ratios and vertical forces from dead and live loads are studied. For this purpose, calibrated numerical simulation for IP and OP behaviors of infilled frames has been exploited. In this method, first, the vertical loads are applied, then increasing IP displacement is imposed at the top of the models and finally OP demands are applied to the walls up to their failure. Two different methods of applying OP loading are studied: increasing static uniform pressure on the wall, and increasing dynamic acceleration. Three levels of IP displacement demands are considered: at the first reduction of tangential stiffness for IP force-displacement response, at the maximum IP strength, and at the displacement related to 20 % reduction of IP strength. The results obviously show that up to the point of the maximum IP strength capacity, the OP behavior of the considered models slightly enhanced due to the effects of improved arching actions originated from the development of IP compressive diagonal struts. Moreover, slight differences exist between the static and dynamic loadings in OP direction, hence proving the accuracy of the equivalent static loading in determining OP capacity for the studied infilled frames. Comparing the results of masonry infilled frames with those of the corresponding masonry walls indicate that the IP displacements negatively affect the OP strength in the latter, even at small IP displacement demands; however, the rate of OP strength reduction in larger IP drift ratios is lower compared to that of the corresponding infilled frame.

Sound absorption and reflection from a resonant metasurface: Homogenisation model with experimental validation

Efficient manipulation of sound waves by some resonant acoustic metasurface designs has recently been reported in the literature. This paper presents a general theoretical framework for the description of sound wave interaction with the resonant metasurface that is independent of the nature of resonators and the excitation. The equations governing the behaviour of the metasurface are upscaled from the rigorous description of its unit cell using the two scale asymptotic homogenisation. The procedure relies on the existence of the boundary layer confined in the vicinity of the resonators operating in the deep subwavelength regime. The model is capable of describing sound interaction with the array of resonators positioned above or upon the substrate, so that the out of plane direction becomes an additional degree of freedom in the design. It is shown that at the leading order, the behaviour of the resonant surface is described in terms of the effective admittance, whose unconventional properties makes it possible to achieve the total sound absorption at multiple frequencies, broadband absorption, the phase reversal of the reflected wave at resonance and the control of the enclosure modes. The theory is validated by experiments performed in the impedance tube and in the anechoic environment using a surface array of spherical Helmholtz resonators with the extended inner neck. Experimental results confirm the effectiveness and robustness of the resonant surface for control of sound waves.

Effect of heat treatment on interface driven magnetic properties of CoFe films

We report systematic studies on non-magnetic Ta underlayer and cap layer driven microstructural and magnetic properties at a wide temperature range for CoFe films. All the films were grown at room temperature and post annealed at different annealing temperatures (TA=200°C, 250°C, 300°C, 350°C, 400°C and 450°C). The in-plane magnetic hysteresis (M–H) loops of 10nm thick CoFe single layer films, grown directly on thermally oxidized Si substrate, exhibit anisotropic nature for TA above 250°C. However, the CoFe (10nm) films grown on the 5nm thick Ta underlayer show reduced anisotropy. Moreover, with underlayer and cap layers (2nm) the anisotropy is disappeared. The in-plane coercivity (HC) shows a strong variation with TA, underlayer and cap layers. HC increases significantly with Ta underlayer and cap layers. The out of plane M–H loops exhibit increase in the remanence magnetization and squareness with both Ta underlayer and cap layers due to transition of in-plane magnetization component to the out of plane direction. The atomic force microscopic observations revealed that grain/particle size and shape depend strongly on TA and Ta layers. Moreover, a large reduction in the surface roughness is observed with the Ta cap layer. The magnetic domain patterns depend on the TA, and Ta layers. However, for Ta/CoFe/Ta films no clear domains were observed for all the TA. Hence, the Ta cap layers not only protect the CoFe magnetic layer against the heat treatment, but also show a smooth surface at a wide temperature range. These results could be discussed on the basis of random anisotropy model, TA, underlayer and cap layers driven microstructure and magnetization orientation of the CoFe films.

Thermoelectric properties of magnetic configurations of graphene-like nanoribbons in the presence of Rashba and spin–orbit interactions

In this paper we investigate the influence of spin–orbit interaction and two types of Rashba interaction (intrinsic and extrinsic) on magnetic and thermoelectric properties of graphene-like zigzag nanoribbons based on the honeycomb lattice. We utilize the Kane-Mele model with additional Rashba interaction terms. Magnetic structure is described by the electron-electron Coulomb repulsion reduced to the on-site interaction (Hubbard term) in the mean field approximation. We consider four types of magnetic configurations: ferromagnetic and antiferromagnetic with in-plane and out-of plane direction of magnetization. Firstly, we analyze the influence of extrinsic Rashba coupling on systems with negligible spin–orbit interaction, e.g. graphene of an appropriate substrate. Secondly, we discuss the interplay between spin–orbit and intrinsic Rashba interactions. This part is relevant to materials with significant spin–orbit coupling such as silicene and stanene.

Thermoelasticity of a Fabric Membrane Composite for the Stratospheric Airship Envelope Based on Multiscale Models

As a main structure of the stratosphere airship, the typical envelope material is flexible fabric membrane composite. The high-low alternated temperature of the stratosphere has a great influence on the mechanical property of the envelope material. Thermoelasticity of the envelope material is first investigated based on a micromechanical model. The modulus and coefficient of thermal expansion of the material are simulated respectively and compared with the measured results. It can be concluded that the material owns the similar nonlinearity character both in warp and weft directions and the modulus in both directions increase to a steady-state value gradually from a relatively small value. The coefficients of thermal expansion of the material in two directions in the plane are quite small compared with the out-plane direction because of the constraint effect between yarns and matrix. The thermal distribution and the deformation of the envelope material in different temperatures are carried out at last. It is expected that the results are significative for the engineering design.

Density functional theory study of the electronic structure and the thermoelectric properties of strained Mn4Si7

The strain effect on electronic structure and thermoelectric properties of Higher Manganese Silicides (HMSs) Mn4Si7 was studied using Density Functional Theory (DFT) and through solving Boltzman Transport Equation (BTE). We found that the tensile strain attempts to reduce the band gap while the compressive strain not much affect to band gap. The Seebeck coeficient was found to be increased with increasing temperature, which is very consistent to experiments. The electrical conductivity and power factor show highly degree of anisotropy, where in-plane direction is more dominant. The different behavior of electrical conductivity along in-plane and outof plane direction was explained due to the change of band dispersion in the valence band maximum (VBM).

Density functional calculations of a staggered FeSe monolayer on aSrTiO3(110) surface

We investigate the electronic and magnetic properties of FeSe monolayer on the anisotropic SrTiO$_3$ (110) surface. With compressive strain along $[1\bar{1}0]$ direction from the substrate, the monolayer FeSe possesses a staggered bipartite iron lattice with an height difference around 0.06\AA~ along the out-plane direction. The staggering causes stronger magnetic frustration between the collinear and checkerboard antiferromagnetic orders, and the strain elongates one electron and two hole pockets along the strain direction and the remaining hole pocket along the orthogonal direction. The strain-induced band splitting at $\Gamma$ can also result in a band inversion to drive the system into a topologically nontrivial phase. The absence of strong superconducting suppression on the staggered lattice suggests that the superconducting pairings may be insensitive to the modification of interactions and hopping parameters between two Fe sublattices.

Research on Failure Modes and Key Parameters of Corrugated Steel Shear Walls

The corrugated steel plate shear wall is an effective and economical lateral load resisting system. And the thin steel plate is easy to buckle. And it is necessary to use much more thickness or ribs to prevent the buckle at out of plane direction, which is not economical or complicated to construct. A number of corrugated shear walls are analyzed by nonlinear static pushover analysis method. And failure modes, buckling, the ultimate capacity, and shear force-drift curves are studied. The results showed that the corrugated steel plate can be designed according to the failure modes, in order to have a desirable failure mode that the corrugated steel plate yield before buckling.

Relationship Between Lamellar Structure and Elastic Modulus of Thermally Sprayed Thermal Barrier Coatings with Intra-splat Cracks

The elastic modulus of plasma-sprayed top coating plays an important role in thermal cyclic lifetime of thermally sprayed thermal barrier coatings (TBCs), since the thermal stress is determined by the substrate/coating thermal mismatch and the elastic modulus of top coating. Consequently, much attention had been paid to understanding the relationship between elastic modulus and lamellar structure of top coating. However, neglecting the intra-splat cracks connected with inter-splat pores often leads to poor prediction in in-plane modulus. In this study, a modified model taking account of intra-splat cracks and other main structural characteristics of plasma-sprayed yttria-stabilized zirconia coating was proposed. Based on establishing the relationship between elastic modulus and structural parameters of basic unit, effects of structural parameters on the elastic modulus of coatings were discussed. The predicted results are well consistent with experimental data on coating elastic modulus in both out-plane direction and in-plane direction. This study would benefit the further comprehensive understanding of failure mechanism of TBCs in thermal cyclic condition.