Wedge-shaped Layers Research Articles

Large Antisymmetric Interlayer Exchange Coupling Enabling Perpendicular Magnetization Switching by an In-Plane Magnetic Field

The recently discovered antisymmetric interlayer exchange coupling (AIEC) plays pivotal roles in the magnetization switching of a synthetic antiferromagnet by inducing magnetization canting. Large AIEC is reported for perpendicularly magnetized $\mathrm{Pt}/\mathrm{Co}/\mathrm{Ir}/\mathrm{Co}/\mathrm{Pt}$ with wedge-shaped layers. The effective field of AIEC is related with symmetric interlayer exchange coupling, providing a guide for enhancing AIEC. We develop an extended Stoner--Wohlfarth model for a synthetic antiferromagnet, revealing key factors in its magnetization switching. Combining the theoretical knowledge and the experimental results, perpendicular magnetization switching is achieved solely by an in-plane magnetic field.

Optical Characterization of H-Free a-Si Layers Grown by rf-Magnetron Sputtering by Inverse Synthesis Using Matlab: Tauc–Lorentz–Urbach Parameterization

Several, nearly-1-µm-thick, pure, unhydrogenated amorphous-silicon (a-Si) thin layers were grown at high rates by non-equilibrium rf-magnetron Ar-plasma sputtering (RFMS) onto room-temperature low-cost glass substrates. A new approach is employed for the optical characterization of the thin-layer samples, which is based on some new formulae for the normal-incidence transmission of such a samples and on the adoption of the inverse-synthesis method, by using a devised Matlab GUI environment. The so-far existing limiting value of the thickness-non-uniformity parameter, Δd, when optically characterizing wedge-shaped layers, has been suppressed with the introduction of the appropriate corrections in the expression of transmittance. The optical responses of the H-free RFMS-a-Si thin films investigated, were successfully parameterized using a single, Kramers–Krönig (KK)-consistent, Tauc–Lorentz oscillator model, with the inclusion in the model of the Urbach tail (TLUC), in the present case of non-hydrogenated a-Si films. We have also employed the Wemple–DiDomenico (WDD) single-oscillator model to calculate the two WDD dispersion parameters, dispersion energy, Ed, and oscillator energy, Eso. The amorphous-to-crystalline mass-density ratio in the expression for Ed suggested by Wemple and DiDomenico is the key factor in understanding the refractive index behavior of the a-Si layers under study. The value of the porosity for the specific rf-magnetron sputtering deposition conditions employed in this work, with an Ar-pressure of ~4.4 Pa, is found to be approximately 21%. Additionally, it must be concluded that the adopted TLUC parameterization is highly accurate for the evaluation of the UV/visible/NIR transmittance measurements, on the H-free a-Si investigated. Finally, the performed experiments are needed to have more confidence of quick and accurate optical-characterizations techniques, in order to find new applications of a-Si layers in optics and optoelectronics.

Cap-layer-dependent oxidation of ultrathin cobalt films and its effect on the magnetic contrast in scanning electron microscopy with polarization analysis

We investigate the influence of a non-magnetic cap layer on the magnetic contrast of a Co film by scanning electron microscope with polarization analysis (SEMPA). Ex-situ sputter-deposited [Ir\Co\Pt]2 samples are terminated with wedge-shaped Pt layers with thicknesses ranging from 0 to 2 nm. The magnetic contrast almost vanishes at low capping, as well as towards the maximum Pt thickness. The highest contrast is found around 1 nm Pt cap layer, where about 25% of the contrast of a clean uncapped Co film is obtained. This contrast is sufficient to record high-quality SEMPA images. Energy-dispersive X-ray spectroscopy (EDX) reveals complete protection against oxidation from 1.1 nm onwards. Analysis of the contrast reduction towards higher coverages yields a spin-decay length of 0.7 nm in Pt for electrons with energies of roughly 6–10 eV above Fermi level. Quantitative EDX analysis indicates the formation of cobalt(II)hydroxide Co(OH)2 at a lower Pt coverage. The oxidation causes a roughening of the surface (4.5 Å RMS), while the surface of the closed Pt film is smooth (1.2 Å RMS), as proven by atomic force microscopy. Island growth of the Pt film on Co is observed, yielding a laterally inhomogeneous oxidation of uncovered patches up to an effective Pt coverage of about 0.9 nm.

Periodic crack system in a layered elastic wedge

ABSTRACTThree-dimensional periodic mode I crack problems for an elastic layered wedge are reduced to an integro-differential equation principal part of which is the same as in the classical Griffith problem for one crack in an elastic full space. The infinite system of elliptic cracks, with equal spaces between neighbouring cracks, is situated in the middle of the wedge parallel to its edge. The faces of the wedge with cracks are layered, with sliding support, by identical elastic incompressible wedge-shaped layers so that the system of three wedges have the same edge (for example, rubber–metal–rubber system). Three types of boundary conditions on the outer layered wedge faces are considered (sliding or rigid support, stress-free state). The regular asymptotic method is used to solve the problems effective for fairly big spaces between the cracks as well as for big distances between the cracks and the edge of the wedge. The stress intensity factor (SIF) is calculated for different geometric parameters. It is shown that the solution, including the SIF, for close cracks does not practically depend on the type of the outer boundary conditions.

Combinatorial optimization of evaporated bilayer small molecule organic solar cells through orthogonal thickness gradients

Abstract We report on a combinatorial optimization procedure applied to heterojunction small molecule organic solar cells made of evaporated copper phthalocyanine (CuPc) and 3,4,9,10-perylenetetracarboxylic bisbenzimidazole (PTCBI). Our strategy consists of depositing both light harvesting compounds as orthogonally arranged wedge-shaped layers to then determine the optimum thicknesses which yield the highest photoconversion efficiency. The device performance is locally assessed by means of light-beam induced current images. A quantitative model of co-locally measured Raman images allows determining the corresponding local thicknesses of the active layers. The spatial correlation of both datasets (i.e. local photocurrent density and active layer film thicknesses) enables the rapid optimization of the photovoltaic system studied employing a single functional device, reducing in approximately 20 times the use of resources and time.

A strip cut in a composite elastic wedge

Integral equations of new three-dimensional problems concerning a cut in the plane of symmetry of a composite elastic wedge are obtained. The wedge consists of three wedge-shaped layers with a common apex, connected by a sliding clamp: in the middle there is a compressible layer with a cut, to the sides of which two identical incompressible layers are pressed. For the case of a strip cut emerging on the edge of the composite wedge, using the method of paired integral equations, the problem is reduced to Fredholm integral equations of the second kind. An expression is obtained for the stress intensity factor.

Three-dimensional contact problems for a composite elastic wedge

The integral equations of new three-dimensional contact problems for a composite elastic wedge are obtained by reducing a boundary problem of the theory of elasticity to a Hilbert problem extended according to Vekua using complex Fourier and Kontorovich–Lebedev transforms. The wedge consists of two wedge-shaped layers with a common vertex and different aperture angles joined by a sliding restraint and the layer that is remote from the punch is incompressible. Three types of boundary conditions are considered on one face of the incompressible layer: when there are no stresses and when there is a sliding or rigid restraint. When the contact area is unknown, the method of non-linear boundary integral equations of the Hammerstein type is used that allows the contact area and the contact pressure to be determined simultaneously.

Spatial mapping of photocurrents in organic solar cells comprising wedge-shaped absorber layers for an efficient material screening

In this work we present a facile route to an efficient experimental screening of new materials and to a layer thickness optimization in solution processable polymer photovoltaic devices. Therefore, we developed a method of fabricating solar cells with wedge-shaped active layers. Spatially resolved measurements of the solar cell short circuit current densities for different light absorbing polymers under white light allow for a quick conclusion about the optimum active layer thickness within the device. To demonstrate the generality of this experimental approach we studied the well-established photoactive blends from poly-(3-hexylthiophene-2,5-diyl) and [6,6]-phenyl C61-butyric acid methyl ester (P3HT:PC61BM) or poly[N-9′-hepta-decanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] and [6,6]-phenyl C71-butyric acid methyl ester (PCDTBT:PC71BM). The short circuit current densities are in very good agreement with optoelectronic device simulations and results from sample-by-sample measurements.

The three-dimensional problem of a thin inclusion in a composite elastic wedge

The three-dimensional problem of a thin rigid elliptic inclusion in the middle of a composite elastic wedge is investigated. The wedge consists of three connected wedge-shaped layers connected by a sliding clamp, in which the layer containing the inclusion is incompressible. The outer faces of the composite wedge are also under sliding-clamp conditions. The inclusion is completely bonded to the elastic medium in the contact region. Using Fourier and Kontorovich–Lebedev transformations, a system of integral equations of the problems are derived for the shear contact stresses. A regular asymptotic method is used to solve this system. Calculations are carried out. The results can be used for calculations on the strength of rubber-metal articles and structures having a corner line.

Three-dimensional contact problems with friction for a composite elastic wedge

Contact problems for a composite elastic wedge in the form of two joined wedge-shaped layers with different aperture angles joined by a sliding clamp, where the layer under the punch is incompressible, are studied in a three-dimensional formulation. Conditions for a sliding or rigid clamp or the absence of stresses are set up on one face of the composite wedge. The integral equations of the problems are derived taking account of the friction forces perpendicular to the edge of the wedge. The method of non-linear boundary integral equations of the Hammerstein type is used when the contact area is unknown. A regular asymptotic solution is constructed for an elliptic contact area. By virtue of the incompressibility of the material of the layer in contact with the punch, this solution retains the well known root singularity in the boundary of the contact area when account is taken of friction.

Influence of the shape of the layers in photo -cured dental restorations on the shrinkage stress peaks—FEM study

Objective The aim of the paper is to analyse an influence of the shape of the layers in photo-cured dental restorations of Class I on distribution of shrinkage stresses along the tooth-restoration interface. The study is a continuation of the previous considerations (Kowalczyk and Gambin (2008) [1]), where techniques, which reduce stress concentration at the top of the tooth-restoration interface, were considered. The analysis leads to proposition of new layer forming techniques, which diminish the stress peaks at the interface and prevent the crack propagation process. Methods To find the stress distributions in the dental restoration layers and the tooth tissues the finite element method implemented in the ABAQUS (Simulia, Providence, USA) software is used. For Class I restoration of the premolar tooth, the axisymmetrical model is assumed. The restoration is made of four layers of a photo-cured composite. Between the tooth tissues and the restoration, a layer of bonding agent 0.01 mm thick is placed and modeled by FEM with help of the cohesive elements. The assumed model takes into account an influence of changes of elastic properties and viscous effects. For each case of the restoration layers system, the Huber–Mises stresses are analysed. Results The investigations show that the stresses near the restoration-tooth tissue interface are reduced due to viscous flow of the cured material and due to existence of a thin layer of the bonding agent. However, the stress distribution both, in the restoration and in the tooth tissues, is strongly dependent on a shape of the filling layers. Numerical simulations disclose that stress peaks are located at the top corners of each layer. The top corners of the last layer are the places where microleakage may occur. Stress concentrations at the corners of the preceding layers may lead to a growth of uprising crack. It will be shown that the flat layers in the restoration create relatively high values of the stress peaks. The rounded layers, with shapes close to those used in dental practice, reduce maximal stresses about 40%. According to a common opinion of dentists, the wedge-shaped layers give the best result. In the present paper, another way of the shrinkage stress reduction is proposed. Before the layering, one can cover the surface of the tooth cavity with a thin “pre-layer”. Next, the remainder cavity may be filled with flat, rounded or wedged layers. It will be shown, that in the fillings with the pre-layers, stress peaks are reduced up to 75%, with respect to the fillings composed of the rounded layers only. The proposed method considerably reduces the shrinkage stress, both in the tooth restoration, as well as, in the tooth tissues. Significance The fillings with the pre-layer are easy in application and its analysis gives promising results. The pre-layer may be applied with other layers of different shapes, and its thickness may vary. The method is recommended for cavities with a great loss of the tooth tissue.

Interlayer exchange coupling in Fe∕MgO∕Fe magnetic tunnel junctions

Interlayer exchange coupling (IEC) in fully epitaxial Fe∕MgO∕Fe(001) tunnel junctions with wedge-shaped MgO layers is measured at room temperature from the unidirectional shift of the Kerr hysteresis loop. It is found that the IEC is antiferromagnetic for small MgO thickness but changes sign at 0.8nm. Ab initio calculations of IEC show that this behavior can be explained by the presence of O vacancies in the MgO barrier which makes IEC antiferromagnetic for thin barriers. With increasing MgO thickness the resonance contribution to IEC from localized defect states is reduced resulting in the ferromagnetic coupling typical for perfect MgO barriers.

Characteristics of the near-tail dawn magnetopause and boundary layer

Abstract. The paper discusses properties of the near-tail dawnside and boundary layer, as obtained from Cluster plasma and magnetic field measurements during a single skimming orbit on 4 and 5 July 2001 that included 24 well-defined crossings by all four spacecraft. As a result of variations of the interplanetary magnetic field, the magnetic shear across the local varied between ~0° and ~180°. Using an improved method, which takes into account acceleration and thickness variation, we have determined the orientation, speed, thickness and current for the 96 individual crossings. The orientations show clear evidence of surface waves. Magnetopause thicknesses range from ~100 to ~2500km, with an average of 753km. The speeds range from less than 10up to more than 300, with an average of 48. Both results are consistent with earlier ISEE and AMPTE results obtained for the dayside magnetopause. Importantly, scaling the thicknesses to the ion gyro radius or the ion inertial length did not reduce the large dynamic range. There is also no significant dependence of thickness on magnetic shear. Current densities range from ~0.01 up to ~0.3uA, with an average value of 0.05 . By including some extra crossings that did not involve all four spacecraft, we were able to apply the Walén test to a total of 60 by Cluster 1 and 3, and have classified 19 cases as rotational discontinuities (RDs), of which 12 and 7 were sunward and tailward of an X-line, respectively. Of these 60 crossings, 26 show no trace of a boundary layer. The only with substantial boundary layers are into the plasma mantle. Of the 26 without a boundary layer, 8 were identified as RDs. Since reconnection produces wedge-shaped boundary layers emanating from the X-line, RDs without may be considered close to the X-line, in which case the observed magnetic shear and Alfvén Mach number should be representative of the conditions at the X-line itself. It is therefore important that four of the eight cases had shear angles ≤100, i.e. the reconnecting fields were far from being anti-parallel, and that all eight cases had Alfvén Mach numbers MA>1 in the adjoining magnetosheath. Another important conclusion can be drawn from the without a that were tangential discontinuities (TDs). To observe TDs with no at such large distances from the subsolar point appears to rule out diffusion over large portions of the as an effective means for plasma transport across the magnetopause.

Ｃｏ／Ｒｈ（１１１）多層膜の層間磁気結合と磁気異方性

It is known that a Co/Rh multiplayers system show strong interlayer exchange coupling and perpendicular magnetic anisotropy. In this study, we fabricated two series of Co/Rh(111) multilayers: one with a wedge-shaped Rh layer and a Co layer of constant thickness, and the other with Rh layers constant thickness and wedge-shaped Co layers. The former were used for investigation of the interlayer coupling and the latter for investigation of magnetic perpendicular anisotropy. For the Rh wedged multilayers, spin flip was observed in the M-H curve, indicating the coexistence of anti-ferro magnetic coupling and perpendicular anisotropy. The Co wedged multilayers exhibited the perpendicular magnetic anisotropy for Co layer thicknesses less than 12 A. From the Co layer thickness dependence of the magnetic perpendicular anisotropy, we found that the perpendicular anisotropy of Co/Rh (111) can be dominated by the strain produced by lattice mismatch.

Growth of thin Co films on W( [formula omitted]) and Au( [formula omitted]) layers prepared on Al 2O 3( [formula omitted

Thin epitaxial W(1 1 0)/Co and Au(1 1 1)/Co films were prepared by molecular beam epitaxy on single crystal sapphire Al 2O 3(1 1 2 ̄ 0) substrates and investigated by means of low energy electron diffraction and Auger electron spectroscopy. The growth of W on Al 2O 3(1 1 2 ̄ 0) was found to depend strongly on substrate temperature and film thickness. W films deposited at a substrate temperature T p=1200 K with a film thickness d W⩾100 Å revealed a bcc(1 1 0) structure with a mean terrace size of 40 Å. Epitaxial growth of Au was achieved at T p=300 K with a layer thickness d Au=30 Å for a deposition onto the W(1 1 0) substrate layers. The structural properties of thin Co films grown at T p=300 K on the W(1 1 0) and Au(1 1 1) substrate layers were studied as a function of Co film thickness for wedge-shaped layers. The Co films were found to grow epitaxially in both cases with distinct growth modes and lattice strains.

Effect of Sulfuric Acid Solution on Fracture Strength of Silicon Nitride Ceramics/Nickel Joints.

The nickel metal joined to silicon nitride ceramics using silver-copper-titanium brazing and titanium filler was placed in a sulfuric acid solution at 323K for up to 214h. Joining strengths were measured by the 4-point bending test. Microstructures of the reaction layer and porous layer were investigated with a scanning electron microscopy and an electron probe microanalyzer. Fracture strength of the normal joint was 245MPa before soaking and decreased to 170MPa after 16h and to 100MPa after 144h in 1N H2SO4. Three regions were observed on the fracture surface: the region I at the reaction layer/brazing layer interface, the region II at the bonding interface neighborhood in porous layers (in silicon nitride) and the region III at the silicon nitride/reaction layer interface. In the porous layer of the silicon nitride was formed yttrium-oxide and aluminium-oxide elute by the soaking the sintering aid in the grain boundary of silicon nitride. The growth of the porous layers occurred on the joint surface of silicon nitride ceramics with different roughness due to the ground surface roughness of the test piece. The wedge-shaped porous layers were formed a residual stress on the interfacial side of the silicon nitride ceramics joints.

Microstructures of intergrown phyllosilicate grains from Verrucano metasediments (northern Apennines, Italy)

Interleaved phyllosilicate grains (IPG) of various compositions are widespread in low-grade Verrucano metasediments of the northern Apennines (Italy). They are ellipsoidal or barrel shaped, up to 300–400 μm long and they are often kinked and folded; phyllosilicate packets occur as continuous lamellae or as wedge-shaped layers terminating inside the grain. Using electron microscopy techniques (SEM, TEM) six types of IPG have been distinguished on the basis of their mineralogical composition: (1) Chl+Ms ± Kln; (2) Chl+ Ms+Pg ± Kln; (3) Ms+Prl ± Pg; (4) Ms+Prl+Su; (5) Ms+Prl+Chl+Su; (6) Su+Ms. Types (1) and (2) are mainly composed of chlorite, with Ms and Pg as minor phases; Kln grows on Ms in highly weathered samples. Types (3), (4), (5), and (6) are composed of muscovite, with intergrown Prl, Chl, Su and new-formed muscovite. The IPG show all kinds of contacts: from coherent grain boundaries with parallel basal planes and along-layer transitions to low- and high-angle grain boundaries. The IPG formed on pristine minerals such as chlorite and muscovite. The transformations took place during the prograde and retrograde metamorphic path of the rocks: they were facilitated by deformation and they occurred in equilibrium with a fluid phase, which allowed cation diffusion. Prograde reactions [Chl = Ms (or Pg); Ms = Prl; Ms = Chl] involve dehydration and sometimes a decrease in volume, whereas retrograde reactions (Ms = Kln; Ms = Su) involve hydration and an increase in volume. These transformations do not simply occur through an interchange of cations, but often involve deep structural changes: transitions from one phyllosilicate to another generally proceed through dissolution-recrystallization reactions. In conclusion, Verrucano IPG represent microstructural sites which have not completely equilibrated with the whole rock and whose mineral assemblage depends on the original composition of the microstructural sites.

Structural and magnetic analysis of MBE-grown Fe/Si/Fe and Fe/Ge/Fe sandwiches

The structure and the interlayer exchange coupling in MBE-grown nominal Fe/Ge 1− x Fe x /Fe( x=0.0, 0.25, 0.33, 0.5) and Fe/Si/Fe sandwiches with wedge-shaped spacer layers were investigated. In the case of Fe/Si a sample with a wedge-shaped magnetic layer was also studied. From a structural analysis with LEED and from a magnetic analysis with the magneto-optical Kerr effect, it is concluded that the Si spacer transforms into an SiFe alloy with the deposition of Fe. A strong antiferromagnetic coupling is found in the case of Fe/Si, but no antiferromagnetic coupling is found for Fe/Ge 1− x Fe x . It appears that the coupling behavior in Fe/Si(SiFe)/Fe sandwiches as a function of spacer thickness is monotonous rather than oscillatory.

Novel sample preparation technique for the study of multicomponent phase diagrams

A technique for alloy sample preparation, based on thin film deposition, has been developed for a study of binary and ternary compositions. Thin elemental wedge-shaped layers of the components were gradually sputtered in an alternating manner to form multilayered structure. The samples obtained had compositions which depended upon their location on the substrate. Such samples, containing differently composed AuAgCu alloys were heat treated to promote formation of stable phases. The alloys thus formed were studied by X-ray diffraction and various microscopic techniques. This article demonstrates the advantages of this method over conventional bulk-based methods.

Orientational dependence of the exchange biasing in molecular-beam-epitaxy-grown Ni80Fe20/Fe50Mn50 bilayers (invited)

The exchange biasing field (Heb) and coercive field (Hc) of molecular-beam-epitaxy-grown Cu/Ni80Fe20/Fe50Mn50 samples in [111], [001], and [110] orientations have been investigated by longitudinal Kerr effect measurements. Ni80Fe20 and Fe50Mn50 were deposited as orthogonal wedge-shaped layers on single-crystal Cu substrates in a magnetic field, enabling the study of the thickness dependence of Heb and Hc on a single sample for each orientation. A strong dependence of Heb and Hc on the growth orientation is observed. The results are interpreted in terms of the observed noncollinear spin structure of the antiferromagnet and a comparison is given with the predictions from recent theoretical models.