Perpendicular In-plane Directions Research Articles

Designs of Optomechanical Acceleration Sensors with the Natural Frequency from 5 Hz to 50 kHz

In many applications, such as space navigation, metrology, testing, and geodesy, it is necessary to measure accelerations with frequencies ranging from fractions of a hertz to several kilohertz. For this purpose, optomechanical sensors are used. The natural frequency of such sensors should be approximately ten times greater than the frequency of the measured acceleration. In the case of triaxial acceleration measurements, a planar design with two sensors that measure accelerations in two perpendicular in-plane directions and a third sensor that measures out-of-plane acceleration is effective. The mechanical characteristics of the existing designs of both in-plane and out-of-plane types of sensors were analyzed, and the improved designs were elaborated. Using numerical simulation, the dependencies of the natural frequency level in the range from several hertz to tens of kilohertz on the designs and geometric parameters of opto-mechanical accelerometers were modeled. This allows one to select the accelerometer design and its parameters to measure the acceleration at the assigned frequency. It is shown that the opto-mechanical accelerometers of the proposed designs have reduced dissipation losses and crosstalk.

Interface tomography of GaInAs/AlInAs quantum cascade laser active regions

We present a high-resolution electron tomography study of buried ultra-thin layers and their interfaces from the active region of a (Ga,In)As/(Al,In)As quantum cascade laser (QCL) test structure. Using a high-angle annular dark-field scanning transmission electron microscopy image series, a three-dimensional (3D) reconstruction of the complex layer structure is obtained. From this 3D information, we determine quantitative values for the chemical width and, simultaneously and independently, the root mean square roughness (rms) and lateral correlation length of the individual interfaces of a cascade using topographic height maps. The interfacial widths are comparably small for all interfaces within a cascade and the layer thicknesses show only a small standard deviation of less than one monolayer. The rms roughness is systematically lower at the direct (Ga,In)As-on-(Al,In)As interface compared to its inverse. In addition, using the one-dimensional height–height correlation function, different lateral correlation lengths along the two perpendicular in-plane directions are detected indicating a distinct anisotropy of the interface morphology. Our accurate and comprehensive results on the QCL test structure will serve as feedback to evaluate the growth process and help to assess the performance of corresponding future laser devices in detail.

The in-plane magnetic anisotropy in manganite film: A novel magnetic anisotropy induced by structural anisotropy

Magnetic anisotropy plays an important role in the development of manganite-based magnetic devices. Establishing a deeper understanding of the anisotropy in manganites is useful for controlling their magnetic properties. We have studied the structure, lattice strain, and magnetic properties of La0.5Ba0.5MnO3 (LBMO-5) films with the thickness of 12 nm–96 nm, grown on the (001) SrTiO3 (STO) substrate. The LBMO-5 films are grown with high crystalline quality. The orientation relationship between the LBMO-5 film and the STO substrate [(001)f//(001)s, (010)f//(010)s, and (100)f//(100)s] exists at the film/substrate interface. With increasing the thickness of the film to 48 nm, the LBMO-5 film is fully strain relaxed. The LBMO-5 film shows the out-of-plane magnetic anisotropy (OMA) along the three mutually perpendicular crystalline axis directions. Usually, the manganite films with tetragonal distortion show both the OMA and the in-plane magnetic isotropy. However, the in-plane magnetic anisotropy (IMA) along the two mutually perpendicular in-plane directions ([010]f and [100]f) is clearly observed in LBMO-5 films. We attribute this new observation of the IMA to the in-plane structural anisotropy along the two distinct crystalline axes. Our studies provide helpful guidance for the understanding and the tuning of the IMA.

Diboron-porphyrin monolayer: A new 2D semiconductor

We investigate a new 2D semiconductor material with BC10N2 stoichiometry based on the molecular structure of diboron porphyrin. Ab-initio molecular dynamics simulations indicate mechanical stability for temperatures up to T=4000 K. Electronic structure calculations based on density functional theory predict a 0.6 eV direct band gap. We employ the Boltzmann transport equation within the relaxation time approximation to analyze electronic transport properties as a function of charge carrier density at room temperature. The lattice thermal conductivity at room temperature was obtained from non-equilibrium molecular dynamics simulations, and we found anisotropic conductivities given by 160 and 115 W/m·K along perpendicular in-plane directions. The thermoelectric figure of merit ZT calculated at 300 K has a maximum value of 0.008. This result indicates that, in spite of its interesting anisotropic transport properties, BC10N2 is not a suitable candidate for thermoelectric applications.

Superior mechanical flexibility and strained-engineered direct-indirect band gap transition of green phosphorene

Most recently, a phosphorus allotrope called green phosphorus has been predicted, which has a direct bandgap up to 2.4 eV, and its single-layer form termed green phosphorene shows high stability. Here, the mechanical properties and the uniaxial strain effect on the electronic band structure of green phosphorene along two perpendicular in-plane directions were investigated. Remarkably, we found that this material can sustain a tensile strain in the armchair direction up to a threshold of 35% which is larger than that of black phosphorene, suggesting that green phosphorene is more puckered. Our calculations also show that the Young's modulus and Poisson's ratio in the zigzag direction are four times larger than those in the armchair direction, which confirms the anisotropy of the material. Furthermore, the uniaxial strain can trigger the direct-indirect bandgap transition for green phosphorene, and the critical strains for the bandgap transition are revealed.

SIMULATION OF FRICTIONAL DISSIPATION UNDER BIAXIAL TANGENTIAL LOADING WITH THE METHOD OF DIMENSIONALITY REDUCTION

The paper is concerned with the contact between the elastic bodies subjected to a constant normal load and a varying tangential loading in two directions of the contact plane. For uni-axial in-plane loading, the Cattaneo-Mindlin superposition principle can be applied even if the normal load is not constant but varies as well. However, this is generally not the case if the contact is periodically loaded in two perpendicular in-plane directions. The applicability of the Cattaneo-Mindlin superposition principle guarantees the applicability of the method of dimensionality reduction (MDR) which in the case of a uni-axial in-plane loading has the same accuracy as the Cattaneo-Mindlin theory. In the present paper we investigate whether it is possible to generalize the procedure used in the MDR for bi-axial in-plane loading. By comparison of the MDR-results with a complete three-dimensional numeric solution, we arrive at the conclusion that the exact mapping is not possible. However, the inaccuracy of the MDR solution is on the same order of magnitude as the inaccuracy of the Cattaneo-Mindlin theory itself. This means that the MDR can be also used as a good approximation for bi-axial in-plane loading.

Local Elastic and Geometric Stiffness Matrices for the Shell Element Applied in cFEM

In this paper local elastic and geometric stiffness matrices of ashell finite element are presented and discussed. The shell finiteelement is a rectangular plane element, specifically designedfor the so-called constrained finite element method. One of themost notable features of the proposed shell finite element isthat two perpendicular (in-plane) directions are distinguished,which is resulted in an unusual combination of otherwise classicshape functions. An important speciality of the derived stiffnessmatrices is that various options are considered, whichallows the user to decide how to consider the through-thicknessstress-strain distributions, as well as which second-order strainterms to consider from the Green-Lagrange strain matrix. Thederivations of the stiffness matrices are briefly summarizedthen numerical examples are provided. The numerical examplesillustrate the effect of the various options, as well as theyare used to prove the correctness of the proposed shell elementand of the completed derivations.

In-plane magnetic anisotropy of La0.7Ca0.3MnO3 film grown on (0001) sapphire

La0.7Ca0.3MnO3 (LCMO) films were grown on (0001) single-crystal sapphire (α-Al2O3) substrate by pulsed laser deposition. In this work, the growth of (110) oriented LCMO film on sapphire was achieved by controlling the film's deposition conditions, specifically the substrate temperature. The fixed orientation relationship between the film and the substrate [(110)f∥(0001)s, (1—10)f∥(01—10)s, (001)f∥(2—110)s], was measured by high-resolution X-ray diffraction (HRXRD) and grazing incident X-ray diffraction (GIXRD) techniques. The LCMO film showed interesting in-plane magnetic anisotropy along the two mutually perpendicular in-plane directions, corresponding to [001]f as strong and [1—10]f as weak magnetization directions.

Nonpolar m-plane GaN/AlGaN heterostructures with intersubband transitions in the 5–10 THz band

This paper assesses intersubband (ISB) transitions in the 1–10 THz frequency range in nonpolar m-plane GaN/AlGaN multi-quantum-wells deposited on free-standing semi-insulating GaN substrates. The quantum wells (QWs) were designed to contain two confined electronic levels, decoupled from the neighboring wells. Structural analysis reveals flat and regular QWs in the two perpendicular in-plane directions, with high-angle annular dark-field scanning transmission electron microscopy images showing inhomogeneities of the Al composition in the barriers along the growth axis. We do not observe extended structural defects (stacking faults or dislocations) introduced by the epitaxial process. Low-temperature ISB absorption from 1.5 to 9 THz (6.3–37.4 meV) is demonstrated, covering most of the 7–10 THz band forbidden to GaAs-based technologies.

High-mobility transport anisotropy and linear dichroism in few-layer black phosphorus.

Two-dimensional crystals are emerging materials for nanoelectronics. Development of the field requires candidate systems with both a high carrier mobility and, in contrast to graphene, a sufficiently large electronic bandgap. Here we present a detailed theoretical investigation of the atomic and electronic structure of few-layer black phosphorus (BP) to predict its electrical and optical properties. This system has a direct bandgap, tunable from 1.51 eV for a monolayer to 0.59 eV for a five-layer sample. We predict that the mobilities are hole-dominated, rather high and highly anisotropic. The monolayer is exceptional in having an extremely high hole mobility (of order 10,000 cm2 V−1 s−1) and anomalous elastic properties which reverse the anisotropy. Light absorption spectra indicate linear dichroism between perpendicular in-plane directions, which allows optical determination of the crystalline orientation and optical activation of the anisotropic transport properties. These results make few-layer BP a promising candidate for future electronics.

Anisotropic iron motion in nitrosyl iron porphyrinates: natural and synthetic hemes.

The vibrational spectra of two five-coordinate nitrosyl iron porphyrinates, [Fe(OEP)(NO)] (OEP = dianion of 2,3,7,8,12,13,17,18-octaethylporphyrin) and [Fe(DPIX)(NO)] (DPIX = deuteroporphyrin IX), have been studied by oriented single-crystal nuclear resonance vibrational spectroscopy. Single crystals (both are in the triclinic crystal system) were oriented to give vibrational spectra perpendicular to the porphyrin plane. Additionally, two orthogonal in-plane measurements that were also either perpendicular or parallel to the projection of the FeNO plane onto the porphyrin plane yield the complete set of vibrations with iron motion. In addition to cleanly enabling the assignment of the FeNO bending and stretching modes, the measurements reveal that the two in-plane spectra from the parallel and perpendicular in-plane directions for both compounds have substantial differences. The assignment of these in-plane vibrations were aided by density functional theory predictions. The differences in the two in-plane directions result from the strongly bonded axial NO ligand. The direction of the in-plane iron motion is thus found to be largely parallel and perpendicular to the projection of the FeNO plane on the porphyrin plane. These axial ligand effects on the in-plane iron motion are related to the strength of the axial ligand-to-iron bond.

Effect of polytetrafluoroethylene-treatment and microporous layer-coating on the electrical conductivity of gas diffusion layers used in proton exchange membrane fuel cells

The purpose of this study is to investigate the effect of ploytetrafluoroethylene (PTFE)-treatment and microporous layer (MPL)-coating on the electrical conductivity of gas diffusion layers (GDLs), as used in proton exchange membrane fuel cells (PEMFCs). The results show that, for PTFE-treated GDLs, the electrical conductivity in orthogonal in-plane directions is almost invariant with the PTFE loading. On the other hand, the in-plane conductivity of the MPL-coated GDL SGL 10BE (50% PTFE) was found to be higher than that of the counterpart SGL 10BC (25% PTFE) and this was explained by the presence of more conductive carbon particles in the MPL of SGL 10BE. Further, the conductivity of each GDL sample was measured in two perpendicular in-plane directions in order to investigate the in-plane anisotropy. The results show that the electrical conductivity of the GDL sample in one direction is different to that in the other direction by a factor of about two. The contact resistance, the main factor affecting the through-plane conductivity, of PTFE-treated GDLs shows a different trend to the corresponding in-plane conductivity, namely it increases as the PTFE loading increases. On the other hand, the contact resistance of the MPL-coated GDL SGL 10BE (50% PTFE) was found to be lower than that of the counterpart SGL 10BC (25% PTFE) and again this was explained by the presence of more conductive carbon particles in the MPL of SGL 10BE. Also, it was noted that the MPL coating appears to have a positive effect in reducing the contact resistance between the GDL and the bipolar plate. This is most likely due to the compressibility of the MPL layers that allows them to fill in the ‘gaps’ that exist in the surface of the bipolar plates and therefore establishes a good contact between the latter plates and the GDLs. Finally, good curve fitting of the contact resistance as a function of the clamping pressure has been achieved.

Synchrotron XRD study of residual stress in a shot peened Al/SiCp composite

In the present study, residual strain profiles in shot peened specimens of 2124-T4 aluminium alloy matrix composite reinforced with 17vol% particulate silicon carbide (SiCp) were measured by means of synchrotron-based diffraction using monochromatic, high energy X-ray beams. The stress state was considered in relation with the microstructural and morphological modifications induced in the material by shot peening. Strain-induced changes in the lattice parameters were deduced from diffraction measurements made by two detectors mounted in the horizontal and vertical diffraction planes, providing information on lattice strains in two nearly mutually perpendicular in-plane directions. On the basis of these data, residual strain and stress profiles through the specimen thickness were reconstructed for both phases (silicon carbide and aluminium alloy). Microstructural characterization was performed by means of optical and scanning electron microscopy (SEM), and particle distribution and hardness modification were identified. The effect of shot peening on the reinforcement and matrix stress states was evaluated. The findings are discussed in the context of process optimization for fatigue resistance improvement in aluminium alloy-based MMCs.

Interface structure and anisotropic strain relaxation of nonpolar wurtzite (112¯) and (101¯) orientations: ZnO epilayers grown on sapphire

The interface properties between nonpolar ZnO and sapphire have been studied using high resolution transmission electron microscopy. Two nonpolar orientations are investigated: a- and m-orientations corresponding to [112¯0] and [101¯0] crystallographic directions. After the definition of the epitaxial relationships and the resulting initial lattice mismatch, we show that nonpolar ZnO can be grown on sapphire with perfectly flat interfaces. Geometrical misfit dislocations are observed at the interface ZnO/sapphire and their density gives the residual strain in the layer. A strong anisotropy in the strain relaxation is found along the two perpendicular in-plane directions. This anisotropy may be explained in terms of initial anisotropic mismatch yielding different relaxation processes. A domain matching epitaxy is observed in m- and a-oriented layers for mismatches larger than 9% while a lattice matching epitaxy, in which the relaxation is driven by nucleation and glide of dislocations, is observed in a-oriented ZnO along the [0001] in-plane direction. In order to explain the observed relaxation the activated slip systems are calculated for both nonpolar orientations as a function of the in-plane stress due to the anisotropic mismatch. There is a major difference from the polar orientations. Low energy prismatic slip systems can be effective for plastic relaxation in the nonpolar orientations because they are no longer parallel to the growth direction, which is the case of c-oriented layers, nor to the applied stress. Our results can be directly extended to other nonpolar wurtzite structures such as III-nitrides.

On new symplectic elasticity approach for exact free vibration solutions of rectangular Kirchhoff plates

In the classical approach, it has been common to treat free vibration of rectangular Kirchhoff or thin plates in the Euclidian space using the Lagrange system such as the Timoshenko’s method or Lévy’s method and such methods are the semi-inverse methods. Because of various shortcomings of the classical approach leading to unavailability of analytical solutions in certain basic plate vibration problems, it is now proposed here a new symplectic elasticity approach based on the conservative energy principle and constructed within a new symplectic space. Employing the Hamiltonian variational principle with Legendre’s transformation, exact analytical solutions within the framework of the classical Kirchhoff plate theory are established here by eigenvalue analysis and expansion of eigenfunctions in both perpendicular in-plane directions. Unlike the classical semi-inverse methods where a trial shape function required to satisfy the geometric boundary conditions is pre-determined at the outset, this symplectic approach proceeds without any shape functions and it is rigorously rational to facilitate analytical solutions which are not completely covered by the semi-inverse counterparts. Exact frequency equations for Lévy-type thin plates are presented as a special case. Numerical results are calculated and excellent agreement with the classical solutions is presented. As derivation of the formulation is independent on the assumption of displacement field, the present method is applicable not only for other types of boundary conditions, but also for thick plates based on various higher-order plate theories, as well as buckling, wave propagation, and forced vibration, etc.

Epitaxial growth and magnetic properties of La0.7Sr0.3MnO3 films on (0001) sapphire

In this letter the authors report the growth of (110) oriented La0.7Sr0.3MnO3 films on (0001) single-crystal sapphire substrate. Growth of La0.7Sr0.3MnO3 (LSMO) films with a fixed orientation was achieved by carefully controlling the deposition conditions, specifically the substrate temperature. The fixed orientation relationship between the film and the sapphire substrate ((110)f‖(0002)s, (1¯10)f‖(01¯10)s, (002)f‖(2¯110)s), has been explained via domain matching epitaxy, where there is perfect matching in one direction and 19% planar misfit in the perpendicular direction. LSMO films showed interesting magnetic anisotropy along the two mutually perpendicular in-plane directions, corresponding to [002]f as strong and [1¯10]f as weak magnetization directions.

In-plane and through-plane gas permeability of carbon fiber electrode backing layers

The absolute gas permeability of several common gas diffusion layer (GDL) materials for polymer electrolyte membrane fuel cells was measured. Measurements were made in three perpendicular directions to investigate anisotropic properties. Most materials were found to display higher in-plane permeability than through-plane permeability. The permeability in the two perpendicular in-plane directions was found to display significant anisotropy. Materials with the most highly aligned fibers showed the highest anisotropy and the permeability could differ by as much as a factor of 2. In-plane permeability was also measured as the GDL was compressed to different thicknesses. Typically, compression of a sample to half its initial thickness resulted in a decrease in permeability by an order of magnitude. Since the change in GDL thickness during compression can be converted to porosity, the relationship between measured permeability and porosity was compared to various models available in the literature, one of which allows the estimation of anisotropic tortuosity. The effect of inertia on fluid flow was also determined and found to vary inversely with permeability, in agreement with available correlations. The results of this work will be useful for 3D modeling studies where knowledge of permeability and effective diffusivity tensors is required.

Polarization mode control of two-dimensional photonic crystal laser having a square lattice structure

We investigate in detail control methods of polarization mode in a two-dimensional square-lattice photonic crystal laser. In order to control the polarization mode using the square lattice, we investigate the eigenmode of the electromagnetic field against the possible symmetry groups of a square lattice. Both the electromagnetic field distributions of lasing oscillation mode and the band diagram are significantly influenced by the symmetry groups. In the case of the square lattice structure, symmetries "p1", "pm", "p2", and "pmm" are suitable for obtaining the unidirectional polarization mode. Among these symmetry groups, the symmetry group "pmm" is especially interesting considering the simplicity of the eigenmode of the electromagnetic field. In order to obtain the symmetry group "pmm", we deform the unit cell structure of a square lattice from circular to elliptical and investigate the properties of symmetry group "pmm" in detail. The elliptical ratio of the unit cell structure can modify the coupling balance of a lightwave propagating in two perpendicular in-plane directions and can control the eigen energy of each band edge.

Thermal expansion of cross-ply and woven carbon fibre–copper matrix composites

Abstract This paper presents thermal expansion data for cross-ply and woven copper matrix–carbon fibre composites (Cu–C f MMCs) that were prepared by diffusion bonding. Thermal expansion was measured in two perpendicular in-plane directions of plate samples. For cross-ply samples (57 vol.%fibres) the mean coefficient of thermal expansion (CTE) between −20 and 300°C changed from approximately 6.5×10 −6 /°C to 3.5×10 −6 /°C during heating/cooling. The in-plane CTE increases with decreasing fibre content. Composites with woven arrangement of carbon fibres show a slightly higher CTE at elevated temperature.

Structure and dynamics of an 2D hydrogen bonded adlayer — imidazole on grafoil

The structure and dynamics of imidazole adlayers adsorbed on the basal planes of graphite have been investigated by neutron scattering. Experiments were performed on the banana multidetector diffractometer DIB and the IN6 time-of-flight spectrometer at the ILL, additional and preliminary data were obtained with the SV4 triple axis spectrometer at the DIDO reactor in Jülich. The main results have been obtained for coverages of about one monolayer. After completion of one monolayer any excess imidazole forms 3D microcrystallites. At low temperatures, 20 < T < 170 K, the adsorbed molecules form linear hydrogen bonded chains, that are arranged in a registered (8√3 × 2)R30° rectangular 2D lattice. Above 240 K a fluid phase is observed. The first-order phase transition from 2D solid to 2D fluid proceeds through a coexistence region 170 < T < 240 K. The inelastic incoherent scattering from the 2D solid adlayer reveals a phonon density of states of an anharmonic registered molecular arrangement. The low frequency modes are enhanced if compared to the phonon spectrum of bulk imidazole. In the high temperature fluid phase quasi-elastic scattering from anisotropically diffusing molecules has been observed. The diffusion constants for the two locally perpendicular in-plane directions at 286 K are D 1 = 8×l0 −5 cm 2 /s and D 2 = 4×10 −6 cm 2 /s. Alternative models for the diffusive motions in the fluid are discussed.