Magnetic nanofilms of nickel prepared at the liquid-liquid interface

Thin films of metallic nickel with a thickness of the order of 20 nm have been prepared at the organic-aqueous interface at room temperature by the reaction of nickel cupferronate [Ni(C₆H₅N₂O₂)₂] in toluene medium and sodium borohydride (NaBH₄) in aqueous medium. The films were characterized with transmission electron microscopy, scanning electron microscopy and atomic force microscopy. Thicker Ni films could be prepared by carrying out the reaction at the interface at 60 °C. The Ni nanofilms exhibit superparamagnetic behavior.     

Magnetically textured ferrofluid in a non-magnetic matrix: Magnetic properties

Texturing of two different magnetic fluids were carried out in paraffin wax under the influence of an external magnetic field. The textured samples were characterized using magnetization measurement and a.c. susceptibility techniques. The results are discussed in the light of ratio of anisotropic energy to magnetic and thermal energies.     

Dislocations at the interface between sapphire and GaN

GaN layers grown by metal organic vapour phase epitaxy on sapphire were imaged by synchrotron radiation X-ray topography. The threading dislocations could not be resolved in the topographs due to their high density, but a smaller density of about 10⁵ cm⁻² defects were seen in the interface between GaN and sapphire by utilizing large-area back-reflection topography for the sapphire substrates. The misfit dislocation images in the topographs form a well-resolved cellular network, in which the average cell size is roughly 30 μm. Different cell shapes in the misfit dislocation networks are observed on different samples. Also, images of small-angle grains of similar size were found in transmission section topographs of the GaN layers.     

The interface properties of Ar-annealed nitrided oxides

The gate–oxide interface properties as well as the oxide–substrate interface properties of MOS capacitors with various nitridation conditions were studied. For comparison, samples were annealed in O₂ and Ar ambients. Experimental results show that both annealing ambients yield similar interface density and electron traps on the oxide–substrate interface. However, Ar-annealed nitrided oxides have higher capacitance and fewer electron traps on the gate–oxide interface.     

Defect compensation at the interface between directly bonded silicon wafers

Abstract

In smart power applications, the Si/Si bonded interface must be electrically transparent for the high voltage bipolar transistor. The bonded interface resistance variation (measured by spreading resistance analysis) is consistent with a potential barrier due to positively charged interface states, whatever the semiconductor type. With a proper preimplanted boron dose, the potential barrier can be reduced and even removed, probably by defect compensation. For a p/p bonded interface, a 7 × 10¹¹ at cm^?2 boron preimplantation leads to no resistance variation near the interface. The ion dose must be adjusted depending upon the substrate type, its resistivity, its flatness and the quality of the prebonding etching. Comparing the spreading resistance results and SUPREM simulations, the interface states density is calculated to be roughly 5 × 10¹⁰ cm^?2 and it does not drastically affect the boron diffusion length.     

Moving crack at the interface between two dissimilar magnetoelectroelastic materials

Summary Analytical solutions for an anti-plane Griffith crack moving at the interface between two dissimilar magnetoelectroelastic media under the conditions of permeable crack faces are formulated using the integral transform method. The far-field anti-plane mechanical shear and in-plane electrical and magnetic loadings are applied to the magnetoelectroelastic materials. Expressions for stresses, electric displacements, and magnetic inductions in the vicinity of the crack tip are derived. Field intensity factors for magnetoelectroelastic material are obtained. The stresses, electric displacements and magnetic inductions at the crack tip show inverse square root singularities, and it is found that the dynamic stress intensity factor (DSIF), the dynamic electric displacement intensity factor (DEDIF) and the dynamic magnetic induction intensity factor (DMIIF) are independent of the remote electromagnetic loads. The moving speed of the crack has influence on the DEDIF and the DMIIF. When the crack is moving at lower speeds 0 ≤ M≤ M_c1 or higher speeds M_c2 < M < 1, the crack will propagate along its original plane, while in the range of M_c1 < M < M_c2 , the propagation of the crack possibly brings about the branch phenomena in magnetoelectroelastic media.     

Saturation effects in the phonon reflection at a quartz-liquid helium interface

The reflection coefficient of longitudinal 25-GHz phonons at a quartz-liquid ⁴He interface was measured for various phonon intensities. For thoroughly cleaned quartz surfaces a reflection coefficient of 1 independent of the incident intensity was found. When the sample was covered with a thin hydrocarbon film, however, the reflection coefficient dropped by typically 5–10% when the phonon intensity was low. At high intensities this extra phonon loss disappeared, suggesting the saturation of the inelastic processes at the quartzhelium interface.Based on a doctoral thesis submitted by H. Schubert in partial fulfilment of the requirements for the degree Dr. rer. nat. at the Technische Universität München.     

Nanostructured fumed metal oxides for thermal interface pastes

Fumed metal oxides (13 nm aluminum oxide particles and 20–25 nm zinc oxide particles), which are in the form of porous agglomerates of nanoparticles, are effective as thermally conductive solid components in thermal pastes. They are as effective as carbon black, but are advantageous in their electrical non-conductivity. Without fuming, the oxides are less effective. By coating with silane, which decreases the viscosity of the paste, they are even more effective. The organic vehicle (polyol esters) and solid component content (2.4–4.0 vol.%) are chosen to attain conformability and spreadability. The use of either 4.0 vol.% silane coated fumed zinc oxide or 2.4 vol.% silane coated alumina gives thermal pastes that are more effective than commercial thermal pastes (Ceramique and Shin-Etsu). Fumed zinc oxide is superior to non-fumed zinc oxide in improving the thermal stability. Silane coating of the fumed zinc oxide further improves the thermal stability. Fumed alumina does not affect the thermal stability, but silane coated fumed alumina improves the thermal stability. Though silane coated fumed zinc oxide is superior to silane coated alumina in enhancing the thermal stability, it is slightly inferior in the phase separation tendency.     

Magnetic and superconducting properties of niobium oxides

Low temperature magnetic susceptibilities of niobium oxides have been measured. A homogeneous sample of NbO prepared by arc melting and checked by using X-ray and metallographic techniques exhibits no ferromagnetism but becomes superconducting at 1.20°K.     

Magnetic susceptibility study on Li-Mn spinel oxides

Li-Mn spinel oxide particles were prepared by the solid state reaction using Mn₃O₄ particles and Li-hydroxide monohydrate, and the effects of the reaction temperature on the produced phase were studied with the powder X-ray diffraction and the magnetic susceptibility measurement. From the lattice constant variation versus the reaction temperature, it was found that the spinel oxides prepared by low temperature reaction were cation deficient type, and that the cation deficient degree decreased with an increase in the reaction temperature. The asymptotic Curie temperature (Weiss constant), derived from the temperature dependent magnetic susceptibility, was always negative, and it implied that the antiferromagnetic coupling among Mn ions is dominant. The absolute value of the Weiss constant increased with the reaction temperature, took a maximum at the reaction temperature around 750°C, and then decreased with a further increase in the reaction temperature. These were attributed to the variation of the average valence of Mn ions. At the reaction temperature, where the absolute value of the Weiss constant takes a maximum, the non-stoichiometry of Li-Mn spinel oxide becomes minimum. In the specimen prepared above the temperature, it was likely that there existed oxygen vacancy, and the phase transformation between cubic and orthorhombic structures was found in the DSC curves.     

Molecular weight and polydispersity effects on interdiffusion at the interface between polystyrene and poly(vinyl methyl ether)

Time dependence and the effect of polystyrene (PS) and poly(vinyl methyl ether) (PVME) molecular weight and polydispersity on interdiffusion at the interface of PS and PVME were investigated with attenuated total reflection infrared spectroscopy (ATR-FTIR). The time dependence of interdiffusion was studied by varying the thickness of the slow-diffusing component, PS, and the results were analysed using a combination of Fickian and Case II models. PS samples with molecular weights ranging from 1.0 × 10⁵ to 3.0 × 10⁶, above the entanglement molecular weight, were used to study the effect of molecular weight on interdiffusion. PS samples with controlled polydispersity ranging from 1.1–3.0 were prepared using a trimodal distribution constructed from monodisperse PS samples. The polydispersity of the PS samples was controlled by varying the number average molecular weight of the distributions while keeping the weight average molecular weight constant. To study the effect of PVME molecular weight and molecular weight distribution on interdiffusion, PVME was fractionated three times from an aqueous solution to increase its molecular weight from 9.9 × 10⁴ to 1.7 × 10⁵ and reduce its polydispersity index from 2.1 to 1.4, respectivley.     

Individual interface traps at the Si-SiO2 interface

In submicrometre-sized metal-oxide-semiconductor field-effect transistors, MOSFETs, the alternate capture and emission of carriers at individual Si-SiO₂ interface defects generates discrete switching in the source-drain resistance. The resistance changes are observed in the drain current as random telegraph signals (RTSs) or as stepped transients after a strong perturbation of the trap occupation. The study of individual defects in MOSFETs has provided a powerful means of investigating the capture and emission kinetics of interface traps, it has demonstrated the defect origins of low-frequency (1/f) noise in MOSFETs, and it has provided new insight into the nature of defects at the Si-SiO₂ interface. The analysis of individual interface defects has shown that a Coulomb energy of several hundred millivolts is involved in the transfer and localization of the single charge carrier into the interface trap.     

Evaluation of crack growth at the weld interface between bronze and steel

We have carried out experimental and numerical investigations of crack growth at the electron-beam-welded interface of a CTS sample made of two different materials – bronze and steel. The location of the initial crack was varied in each of the material zones. During dynamic experiments, the trajectory of the crack growth was observed and recorded by means of a CCD camera. The experimentally evaluated crack paths were compared with those predicted by numerical calculations. The numerical model of the CTS sample was created in the FE system FRANC/FAM. The key parameter, having the biggest influence on the numerical path, was determined, and the numerical and experimental results were compared. Due to inhomogeneous material properties, a “correction factor” based on the variation in the Young’s modulus was developed. With this function, conformity of the numerical and experimental results was achieved.     

Effects of intermetallic formation at the interface between copper and lead-tin solder

An investigation was undertaken of the role of intermetallics in determining the strength of soldered joints, using copper and a lead-tin solder as the materials of interest. Joints formed at various times and temperatures were tested in shear, and measurements of the thickness of the two intervening intermetallic layers formed were taken. The temperature of formation was found to have the greatest effect on the strength, with the strength decreasing as the temperature increased. Failure at the interface occurred in two stages. In all cases, the first stage consisted of fracture within the intermetallic layer, accounting for partial separation of the interface only. The area of the interface showing this kind of behaviour increased with both time and temperature. Final stages of failure involved shear within the solder immediately above the intermetallic layers. The two intermetallic phases found at the interface were determined by X-ray diffraction to be Cu₆Sn₅ and Cu₃Sn. Both intermetallics were found for all joint-forming conditions investigated. The growth of Cu₆Sn₅ reached a limiting value for times longer than 30min, but increased in thickness with temperature. Cu₃Sn also increased in thickness with temperature, but showed linear increases with time; the rate of increase was greater for the higher temperatures.     

Human biological reactions at the interface between bone tissue and polymethylmethacrylate cement

This study investigated cytotoxicity of cement fragments harvested from two prosthesis revisions by the MTT test using L929 fibroblasts and human osteoblasts. The results did not show any toxicity of the extracts prepared after 48 and 78 months implantation. We consider that no MMA monomer has been released from the cement fragments. Histological studies on undecalcified samples harvested around revising prosthesis from 11 patients were used to evaluate tissue reactions at the bone–cement interface after 2–168 months implantation. Cement and prosthesis particles (5–35 m) either dispersed or forming a layer were observed. A fibrous tissue layer, osteolysis, and osteonecrosis areas were observed at the interface. Besides, fibroblasts, macrophages, and multinucleated giant cells were also observed. New bone formation with osteoid, osteoblasts, and endochondral ossification with fibrocartilaginous tissue has been observed. The tissue reactions seemed to decrease with time. However, osseous trabeculae fractures were observed in the samples after 19 months. Although we consider that monomer toxicity, exothermic reaction, and particles formation may cause short-term prosthesis loosening; the trabeculae fractures may be due to prosthesis and bone cement micromovements. This fractures and particles formation may cause long-term prosthesis loosening.     

Mechanochemical reaction at the interface between a metal plate and oxide powders

A new geometry is proposed and explored for the investigation of mechanochemical reactions. Typical displacement reactions between an oxide (PbO, CuO, and WO₃) and Al as the reducing metal are studied, but instead of starting with a mixture of two powder reactants, Al is introduced in the form of a plate attached to the inside wall of the milling vial and only the oxide is milled in powder form. Consequently, the reaction takes place at the surface of the aluminium plate, where the microstructure can be investigated easily using SEM. The phase composition is followed by XRD. Of the three oxide components, the reaction is the fastest with PbO due to the intense ductile mixing at the interface. The current configuration can be utilized for the investigation of any mechanochemical or mechanical alloying process where at least one of the components can be prepared in the form of a ductile plate that is capable of withstanding the multiple impacts from the milling balls.     

The evolution of radial fingers at the interface between two viscous liquids

The problem of determining the evolution of a radial finger in a Hele-Shaw cell filled with two different viscous liquids is formulated in terms of a Fredholm integral equation of the second kind. This integral equation possesses a unique continuous solution for any viscosity ratio β greater than zero and less than or equal to infinity, as long as the curvature is well defined and continuous at each point of the interface curve. The case of β equal to infinity corresponds to the flow configuration of only one liquid (liquid-gas). The requirement of continuous curvature implies that the kernel of the integral equation is nowhere singular.     

Harmonic generation at an unbonded interface—I. Planar interface between semi-infinite elastic media

An analysis is made of the nonlinear dynamics of a system composed of an unbonded planar interface separating two semi-infinite linear elastic media. The unbonded interface, by definition, cannot support tension and hence opens up in the tension phase of a propagating disturbance, if it is not already open. The opening and closing of the interface is the origin of the nonlinearity. This is perhaps the simplest nonlinear problem involving continuous media, since the problem reduces to the consideration of a pair of independent first order ordinary differential equations involving the center of gravity and width of the gap. In the case of an incident sinusoidal wave the second harmonic generation efficiency is determined as a function of the ratio of the ambient hydrostatic pressure to the stress amplitude of the incident wave.