Thin Sandwiches Research Articles

Solid State Joining of Thin Hybrid Sandwiches Made of Steel and Polymer: a Feasibility Study

The growing demand for more environmentally friendly vehicles has led to an increased use of light materials in the transportation industry with the aim to reduce structural weight, fuel consumption, and gas emissions, thereby boosting cost-effectiveness and recyclable properties. Complex multi-material steel-based components would allow to improve mechanical properties and minimize weight even further. In particular, new sandwich materials made by steel outer skins and a polymeric internal layer seems very promising for obtaining mechanical performance and lightness at the same time. Unfortunately, traditional welding techniques, like arc welding, laser welding, and resistance spot welding, usually used to join steels and aluminum alloys, cannot be applied for these materials due to their peculiar nature. In this paper, the feasibility of Friction Stir Welding to join thin sandwich components made of two steel outer layers and an internal polymeric layer was assessed. Both a pin and a pinless tool were used to weld the upper and the lower surface of the joint in order to obtain solid state bonding of the metal and fusion welding of the polymer at the same time.

Magneto-dynamic analysis of sandwiches composed of a thin viscoelastic-magnetorheological layer

This study’s relevance lies in the possibility of obtaining a smart sandwich structure with controllable dynamic properties, without compromising the main characteristics of conventional thin viscoelastic sandwiches. The proposed sandwich is composed of a micron-size viscoelastic-magnetorheological layer, which is obtained by adding spherical iron particles to a viscoelastic layer. Thin sandwiches with identical base layers and a viscoelastic core, with and without magnetic particles, are fabricated. Both the viscoelastic sandwich structure and viscoelastic-magnetorheological sandwich structure are experimentally characterised by a forced vibration test with resonance in a bandwidth between 0 and 1 kHz. This work analyses the influence of adding iron particles to obtain a smart thin sandwich. In addition, the vibrational response of the viscoelastic-magnetorheological sandwich structure under an external partial magnetic field, and the controllability of its dynamic properties by means of the magnetic field intensity and position, are studied.

Theoretical and numerical modeling of membrane and bending elastic wave propagation in honeycomb thin layers and sandwiches

Elastic wave propagation in honeycomb thin layers and sandwiches is investigated theoretically and numerically by using the Bloch wave transform, so the modeling of a unique primitive cell is sufficient to understand the wave propagation phenomena through the whole periodic structure. Both in-plane (with respect to the plane of the honeycomb layer) and out-of-plane waves are analyzed by developing finite element models formulated within the framework of the Mindlin–Reissner theory of plates. The dispersion relations and the phase and group velocities as function of frequency and of direction of propagation are calculated. The anisotropic behaviors and the dispersive characteristics of the studied periodic media with respect to the wave propagation are then analyzed. According to our numerical investigation, it is believed that the existence of bandgaps is probably not possible in the frequency domain considered in the present work. However, as an important and original result, the existence of the “backward-propagating” frequency bands, within which Bloch wave modes propagate backwards with a negative group velocity, is highlighted. As another important result, the comparison is made between the first Bloch wave modes and the membrane and bending/transverse shear wave modes of the classical equivalent homogenized orthotropic plate model of the honeycomb media. A good comparison is obtained for honeycomb thin layers while a more important difference is observed in the case of honeycomb sandwiches, for which the pertinence of finite element models is discussed. Finally, the important role played by the honeycomb core in the flexural dynamic behaviors of the honeycomb sandwiches is confirmed.

Electromagnetic Characteristics of Thin Polyethylene-Carbon-Polyethylene Films

A method of manufacturing a polyethylene – expanded carbon – polyethylene layered structures which allows thin (down to 90 μm) and flexible sandwiches to be easily made, is suggested. The electromagnetic properties of the manufactured composite materials at frequencies from 1 MHz to 3 GHz, 26–37.5 GHz, and 0.1–1.4 THz are analyzed. It is established that the material so obtained is opaque for the Ka microwave band due to high reflectivity (96–97%), does not transmit electromagnetic radiation of the terahertz range, has a high conductivity (up to 1 S/m) in the frequency range from 1 MHz to 1 GHz, and retains the main physical polyethylene properties (light weight, elasticity, and flexibility).

Electrochemical Growth of Surface Oxides on Nickel. Part 3: Formation of β-NiOOH in Relation to the Polarization Potential, Polarization Time, and Temperature

Electro-oxidation of Ni(poly) in 0.5 M aqueous KOH solution is examined at various polarization potentials (Ep), polarization times (tp), and temperatures (T) in the 0.7 ≤ Ep ≤ 1.2 V versus RHE, 60 ≤ tp ≤ 10,800 s, and 288 ≤ T ≤ 318 K ranges. The oxide chemical composition is determined using X-ray photoelectron spectroscopy (XPS) and its thickness using XPS depth profiling. XPS measurements demonstrate that such formed oxide layers are multilayer in nature and contain both β-Ni(OH)2 and NiO, with β-Ni(OH)2 being the predominant, outermost species and NiO forming a thin layer sandwiches between metallic Ni and β-Ni(OH)2. An increase of Ep, tp, and/or T results in an increase of the oxide thickness. XPS depth profiling measurements reveal that the thickness (d) of the β-Ni(OH)2 plus NiO layers is in the 2 ≤ d ≤ 11 nm range, depending on Ep, tp, and T. The electrochemical formation of β-Ni(OH)2 plus NiO follows an inverse-logarithmic growth kinetic law with the escape of metal cation from the metal into the oxide at the inner metal/oxide interface being the rate-determining step. The oxide growth is treated mathematically using the Mott–Cabrera oxide growth theory.

Neutron Scattering on Magnetic Thin Films

During the early 80s, advanced techniques for the deposition of ultra-thin metal films were developed. This led to the fabrication of new artificial materials consisting of different materials stacked in thin sandwiches (hetero-structures). The combination of these different types of materials gave rise to new physical phenomena. The first new phenomenon to be probed was the magnetic exchange coupling in super-lattices. It appeared that magnetic layers separated by non magnetic spacer layers can be magnetically coupled. The coupling can be ferromagnetic, anti-ferromagnetic or more complex (quadratic or even helical). The coupling can also change sign (from ferro to anti-ferro) as a function of the spacer layer thickness. Such phenomena were observed in rare-earth super-lattices (Gd/Y, Dy/Y, Gd/Dy, Ho/Y), transition metals super-lattices (Fe/Cr, Co/Cu, Fe/V, Co/Ru), and mixing of semiconductors and metals (Fe/Si, Fe/Ge). The field is still expanding as new systems are being synthesized, especially with magnetic semi-conducting materials (GaMnAs, EuS/PbS) or oxide materials (Fe2O3, Fe3O4, CoFe2O4, perovskites of the type ABMnO3).

Dielectric relaxation of Al/Lu2O3/Al thin film structures from 10 μHz to 10 MHz

Results of dielectric studies of lutetium sesquioxide layers examined in Al/Lu2O3/Al thin film sandwiches are reported. The dielectric measurements were carried out in the frequency range 10−5–107Hz and for temperatures from 292K to 500K. Results are presented as plots of frequency functions: the capacitance, the dielectric loss factor, tanδ(f) and also on the complex plane as Cole–Cole plots and Nyquist plots. The influence of the external voltage on C(U) and tanδ(U) was examined. Experimental data were analyzed taking into account thin insulating Lu2O3 film, near-electrode regions of Al/Lu2O3 and Lu2O3/Al interfaces and series resistance of electrodes and leads. The parameters of Lu2O3 film, near-electrode regions and resistance of contacts and leads were determined.

Superconductive properties of thin dirty superconductor–normal-metal bilayers

The theory of superconductivity in thin SN sandwiches (bilayers) in the diffusive limit is developed within the standard Usadel equation method, with particular emphasis on the case of very thin superconductive layers, d_S << d_N. The proximity effect in the system is governed by the interlayer interface resistance (per channel) \rho_{int}. The case of relatively low resistance (which can still have large absolute values) can be completely studied analytically. The theory describing the bilayer in this limit is of BCS type but with the minigap (in the single-particle density of states) E_g << \Delta substituting the order parameter \Delta in the standard BCS relations; the original relations are thus severely violated. In the opposite limit of an opaque interface, the behavior of the system is in many respects close to the BCS predictions. Over the entire range of \rho_{int}, the properties of the bilayer are found numerically. Finally, it is shown that the results obtained for the bilayer also apply to more complicated structures such as SNS and NSN trilayers, SNINS and NSISN systems, and SN superlattices.

Domain wall coupling in magnetic thin film sandwiches

Se ha estudiado el acoplamiento entre paredes magneticas en peliculas tipo sandwich de permalloy/Cu/permalloy, obtenidas por pulverizacion catodica, de espesores comprendidos entre 2000A/200A/2000A, para evaluar el campo de acoplamiento entre las paredes. Para realizar este estudio se han cortado la muestras de un tamano lo suficientemente pequeno para conseguir que la energia magnetostatica de la muestra sea del mismo orden de magnitud que la energia de la pared magnetica. Los resultados obtenidos muestran la posibilidad de conseguir dots magneticos de tamanos de micrometros con un comportamiento biestable.

Domain-wall magnetostatic coupling in permalloy/Cu sandwiches

We have studied, by means of numerical simulation, the structure of domain walls in permalloy thin film monolayers and sandwiches consisting of two permalloy layers separated by a Cu interlayer. The calculated transition thicknesses between Bloch and Néel domain walls increase notably for the sandwiches with respect to monolayers. The structures obtained for uncoupled walls show quite similar patterns for the Néel walls and their corresponding quasi-walls. When coupled, the quasi-walls disappear and so the energy of the pair is reduced approximately to half the energy of the uncoupled pair. Results have been tested in thin film permalloy sandwiches obtained from a sputtering system.

Mechanical behavior and sound generation efficiency of prestressed, elastically clamped and thermomechanically driven thin film sandwiches

A model of thermomechanically driven plates as used, e.g., for acoustic microresonators is reported. The model describes the quasibuckling, excitation, fundamental frequency and vibration mode of multilayered plates under plane strain. The plates consist of stacked thin films with individual elastic modulus, Poisson's ratio, prestress, heat capacity and coefficient of thermal expansion. Membrane edges are elastically clamped to lateral supports. In thin plates two driving mechanisms are identified: the first couples the thermomechanical bending moment to the curvature of the vibration mode; the second couples the thermomechanical line stress to the periodic length change of the vibrating quasibuckled structure. Results of the model include vibration amplitude, sound field pressure, emitted power and quality factor as functions of the membrane properties. Maximum output is obtained close to the quasibuckling transition of the structures, where their resonance frequency is minimum. Largest sound pressures are generated by structures with rigid supports or with vanishing initial bending moment. The model shows excellent agreement with experimental data from micromachined resonant silicon membranes.

Ion beam induced magnetic nanostructure patterning

Using results from previous work on the initial stages of ion beam mixing in metallic multilayers, we developed a method allowing us to pattern the magnetic properties of Pt/Co thin film sandwiches and multilayers without affecting their optical or topographical properties. Excellent control of local coercivity or magnetic anisotropy is obtained in the irradiated areas. We produced arrays of 1 μm wide stripes with perpendicular magnetic anisotropy, separated by 1 μm wide paramagnetic stripes, and studied domain wall motion in these structures. Calculations show that nanometer scale resolution can be achieved. Besides its interest for micromagnetics studies, the technique holds promise for applications in high density magnetic recording and magnetic sensor technologies.

SEM investigation of pillared microstructures formed by electrochemical anodization

The results of SEM investigations of structured (pillared) layers formed by electrochemical processing of Al-Ta thin film sandwiches are presented. The basic parameters of the internal microstructure and natural morphology of Al anodic oxide films and pillared structured layers formed on them are given. Two methods of multistep electrochemical processing of aluminum films during porous anodic oxide films formation were developed to improve the morphology of pillared microstructures. Analysis of experimental data shows that the developed methods allow us to obtain the ordered pillared microstructures with high aspect ratio (≥ 4), radius 15 to 35 nm, and pillar density (3.0 to 8.5) x 10 9 cm -2 . High reproducibility of physical and morphological parameters of the structured layers for large-area samples is achieved. Such pillared matrices can be used for manufacturing of the microelements based on the mesoscopic and quantum effects: solar cells, controlled and uncontrolled emitter matrices for flat panel displays and emission cathodes, cathode luminescent displays, functional screens and polarizors for optoelectronics, etc.

Test structures to measure the heat capacity of CMOS layer sandwiches

We report novel thermal characterization microstructures to measure the heat capacity of CMOS thin film sandwiches. This parameter is relevant, e.g., for the dynamic response of thermal CMOS microtransducers and for the thermal management of integrated circuits. The test structures were fabricated using a commercial 2-/spl mu/m CMOS process, followed by maskless micromachining. The propagation of heat waves in the structures is monitored, which provides the thermal conductivity and heat capacity of CMOS thin film sandwiches. At 300 K, volumetric heat capacities of (1.71/spl plusmn/0.12)/spl times/10/sup 6/ Jm/sup -3/K/sup -1/ and (2.41/spl plusmn/1.88)/spl times/10/sup 6/ Jm/sup -3/K/sup -1/ were obtained for the sandwich of CMOS dielectrics and for the lower CMOS metal, respectively. These values do not deviate significantly from available bulk data of such materials.

Magnetic properties of transition-metal multilayers studied with X-ray magnetic circular dichroism spectroscopy

The detailed understanding of the magnetic properties of transition-metal multilayers requires the use of state-of-the-art experimental techniques. Over the last few years, the X-ray magnetic circular dichroism (XMCD) technique has evolved into an important magnetometry tool. This paper is an overview of the principles and unique strengths of the technique. Aspects covered include the quantitative determination of element-specific spin and orbital magnetic moments and their anisotropies through sumrule analyses of experimental spectra. A discussion is presented on how the spin and orbital magnetic moments in transition-metal thin films and sandwiches are modified relative to the bulk. We show that a thin film of a nonmagnetic metal such as Cu may become magnetically active when adjacent to a magnetic layer, and a thin film of a ferromagnetic metal such as Fe may become magnetically inactive. The orbital moment is found to become anisotropic in thin films; it can be regarded as the microscopic origin of the magnetocrystalline anisotropy.

TBIS measurements performed by MOKE for the study of soft ferromagnetic thin films and sandwiches: In-plane and biaxial anisotropies, local anisotropy and dispersion

Magneto-optic effects have been proved to be a premier tool for the study of magnetic thin films. In the case of films thinner than 1000 Å and if there is no appreciable variation of the magnetic structure through the thickness, the magneto-optic effects provide complete information. It is noteworthy that transverse biased initial susceptibility (TBIS) measurement is very sensitive, for it allows a precise determination of the anisotropy field and, moreover, to quantify the anisotropy dispersion distinguishing between short- and long-range magnetization fluctuations in the plane of the film the origin of which is different. If the samples are deposited on glass substrates, by performing TBIS measurements with a magneto-optic transverse Kerr effect (MOKE) we can obtain information of the processes occurring at both film/air and glass/film interfaces, providing information of the variation of the magnetic properties through the thickness. We have successfully applied this technique for the study of thin films and sandwiches, focusing our attention on the following items: 1. (1) Uniaxial in-plane anisotropy, local anisotropy and anisotropy dispersion in transition metal-rare-earth thin films. We have investigated the dependence of the uniaxial anisotropy and its dispersion on the rare-earth substituted and on the composition. Using the ripple theory we have evaluated the local anisotropy as a function of the rare-earth content, and we have found a very nice correlation between macroscopic and local anisotropies, allowing us to establish the origin of the macroscopic anisotropy in these alloys. 2. (2) TBIS measurements can also be used as an alternative technique to measure perpendicular anisotropy. We have developed a theoretical model to explain the particular behaviour of TBIS curves in the most general case when both in-plane and perpendicular anisotropies are present (biaxial anisotropy). From the fit of the experimental curves to the theoretical model we can obtain the in-plane and the perpendicular anisotropy fields. 3. (3) When the samples are not magnetically homogeneous, they may present different magnetic phases which may be made evident by our technique. 4. (4) We recently extended this technique to the study of ferromagnetic double-layered and sandwiched films. In these systems the magnetic and magneto-optical properties are strongly influenced by the coupling at the interfaces. The high sensitivity of our procedure allowed us to distinguish between two contributions to the anisotropy dispersion in sandwiched films: a well-known term due to the in-plane anisotropy skew (long-range fluctuations of the in-plane easy axis) and a contribution due to the existence of a weak perpendicular anisotropy.

Quantum effects in the giant magnetoresistance (GMR) of magnetic multilayers

We present a quantum-statistical theory using the Kubo formalism to describe both CIP (current in plane) and CPP (current perpendicular to the plane) giant magnetoresistance (GMR) of thin magnetic sandwiches. It is shown that GMR for both geometries oscillates with the thicknesses of the sandwich's layers due to the confinement of electrons in quantum wells. The deviation of the GMR dependence on the angle γ between the magnetizations of successive layers from linear cos γ dependence is predicted. It is shown that for CIP geometry this deviation is large only for a large value of the parameter( k F ↑ − k F ↓)/( k F ↑ + k F ↓), where k F ↑(↓) is Fermi momentum of spin-up (down) electron, but for CPP GMR for noncollinear configuration of the magnetizations a new mechanism (interference between spin-up and spin-down electron waves) is predicted, and the deviation from linear cos γ dependence in this case is large even for small values of the parameter ( k F ↑ − k F ↓)/( k F ↑ + k F ↓), but not for very large values of the parameter ( k F ↑ − k F ↓)/(1/ l ↑ + 1/ l ↓), where l ↑(↓) is the mean free path for spin-up(down) electron.

Design And Field Trial Application of Foam In Production Wells to Improve Conformance

Abstract Many of the hydrocarbon vertical miscible floods in the Keg River carbonate reefs of the Rainbow Field are at a mature stage, of reservoir depletion, and are characterized by thin oil sandwiches, high gas recycle and declining oil production. Under these adverse conditions, conventional workover techniques to control gas recycle and improve oil productivity have diminishing success. In considering alternative strategies to reduce gas coning, Husky felt that injection of a gas-blocking foam barrier into a gas cone hadthe potential to be a cost-effective treatment. This paper describes the experimental foam treatments conducted on two production wells, each in a different miscible flood pool. Aspects of the laboratory work, numerical coning simulation, well selection process and foam placement strategy that went into the field treatment design are presented. On one well, the foam-forming surfactant was injected as an aqueous solution to allow in situ foam generation, and also as a surface generated preformed foam. Neither method was successful in improving the performance of this well. On the other well, where only preformed foam was injected, the treatment was successful in reducing gas-oil ratio (GOR) and improving-oil production over a 14 month period. Much of the experience gained from the field treatments will facilitate the efficient planning, design, implementation and evaluation of future foam projects. Introduction Husky Oil Operations Ltd. operates a number of mature hydrocarbon vertical miscible floods in the Keg River carbonate reefs of Rainbow Field, Alberta, Canada. Many of the wells in these floods are already completed at or close to the base of the remaining oil sandwich, and are experiencing increasing solvent/chase gas coning and declining oil productivity as the oil zone thins under continued injection and production. With little or no room to move in the oil pay, conventional workover strategies of cement squeezing and reperforating lower have diminishing application. In evaluating innovative methods to mitigate gas production, foam chemicals were considered. The potential of foam as a blocking or mobility reduction agent to gas flow has been well documented(1–5). Due to potentially high adsorption losses, foam only has a chance of working from the injection side if it is able to reduce mobility in a relatively small channel volume between injection and production wells, or if the channel is isolated from the rest of the reservoir away from the injection well (minimum volume of rock contacted). However, most of the Keg River reefs have relatively good communication throughout, and in most FIGURE 1: Keg River "A" Pool. Keg River structure contour map. Available In Full Paper. cases, tracing has shown the channels to be relatively large. Consequently the focus was diverted away from an expensive, large volume foam treatment at an injector to a much smaller, near wellbore treatment at a producer. Adsorption of foam-forming surfactant onto reservoir rock would not be a big problem if the amount of rock contacted could be kept to a minimum.

Singularities in the field dependence of the magneto-optical Kerr effect in thin magnetic sandwiches

We consider an antiferromagnetically coupled sandwich consisting of two ferromagnetic transition-metal layers separated by a thin non-magnetic spacer layer, e.g. Fe/Au/Fe. We calculate, using the Kubo formalism, the influence of the angle γ between the magnetizations in the two ferromagnetic layers on the magneto-optic Kerr effect. Similarly to previously observed oscillations of the magneto-optic Kerr effect as a function of layer thickness, we predict quantum singularities in the Kerr signal as a function of γ, i.e. as a function of the external field. The observation of these singularities would provide further confirmation of the existence of quantum well states in these systems.

Magnetization reversal in CoFe/Ag/Fe/ZnSe thin layer sandwiches

In recent work [J. Appl. Phys. 70, 10 (1991)] the spin valve effect (SVE) was measured in CoxFe1−x/Ag/Fe(x&amp;lt;0.7) thin layer sandwiches grown by molecular beam epitaxy. The field dependence of the SVE was correlated with VSM magnetization data taken on the samples. It was found that only at low fields was there a correlation between the SVE resistance and the magnetization data. These results indicated a more complex reversal mechanism that included substantial magnetizations in directions not measured in traditional VSM measurements. In order to more accurately determine the field-dependent magnetization of the samples during reversal, the longitudinal and transverse Kerr effects were measured on the layers. The particular geometry used to measure the Kerr effects was for the light scattering plane to be perpendicular to the applied magnetic field. The transverse Kerr effect data, which in this geometry are sensitive to the magnetization parallel to the applied magnetic field, replicated the VSM data. The longitudinal Kerr effect, which is sensitive to the net magnetization perpendicular to the applied field (in the plane of the film), indicated a substantial perpendicular magnetization component. Based upon previous work on epitaxial iron films, it appears that the magnetization reversal process proceeds by transitions between easy axes. From these measurements, the anomalous resistances observed as a function of the applied magnetic field in J. Appl. Phys. 70, 10 (1991), are explained by having one of the films soft, and two easy axes in the plane of the other film.