Presence Of Interfacial Layer Research Articles

Interfacial Morphology and Mechanical Properties of Aluminium to Copper Sheet Joints by Electromagnetic Pulse Welding

This study investigated joining of Al to Cu sheets by electromagnetic pulse welding, which is a solid-state welding process that uses electromagnetic forces to join materials. The interfacial morphology and mechanical properties of the Al/Cu joints were analysed and related to the welding process parameters and weld properties. The centre section of the Al/Cu joints evolved from a non-welded to a welded zone. The welded zone started with a wavy interface, consisting of thick interfacial layers with defects and evolved to a relatively flat interface without an interfacial layer. The interfacial layer thickness is determined by both the discharge energy and the stand-off distance. A higher tensile force, up to 4.9 kN, was achieved at a higher energy and a lower stand-off distance of 2 mm. The tensile force is directly related to the weld width, since a higher tensile force is achieved for a higher weld width. In addition, the presence of interfacial layers can contribute to a small extent to a higher tensile force.

Physical and electrical properties of thermal oxidized Sm2O3 gate oxide thin film on Si substrate: Influence of oxidation durations

Growth of 150nm Sm2O3 films by sputtered pure samarium metal film on silicon substrates and followed by thermal oxidation process in oxygen ambient at 700°C through various oxidation durations (5min, 10min, 15min and 20min) has been carried out. The crystallinity of Sm2O3 film and existence of interfacial layer have been evaluated by X-ray diffraction, Fourier transform infrared and Raman analysis. Crystallite size and microstrain of Sm2O3 were estimated by Williamson–Hall plot analysis. Calculated crystallite size of Sm2O3 from Scherrer equation has similar trend with the value from Williamson–Hall plot. The presence of interfacial layer is supported by composition line scan by energy dispersive X-ray spectroscopy analysis. The surface roughness and surface topography of Sm2O3 film were examined by atomic force microscopy analysis. The electrical characterization revealed that 15min of oxidation durations with smoothest surface has highest breakdown voltage, lowest leakage current density and highest barrier height value.

Mixed matrix membranes based on polyetherurethane and polyesterurethane containing silica nanoparticles for separation of CO2/CH4 gases

The effect of silica nanoparticles on permeability of CO2 and CH4 for two types of nanocomposite membranes based on polyesterurethane and polyetherurethane has been studied. The distribution of silica nanoparticles loaded in the polymers was studied with scanning electron microscopy. Structural characteristics of the membranes were studied by infrared spectroscopy, X-ray diffraction and differential scanning calorimetry to confirm the interactions between PU segments and nanoparticles and the changes induced in PU microphase in the presence of silica. The permeability of CO2 and CH4 has been measured in order to determine the effect of silica on CO2/CH4 separation performance of ETPU and ESPU. The results demonstrated that inclusion of silica significantly increases the CO2 permeability and CO2/CH4 selectivity of nanocomposites. The nanocomposite membranes with matrix consisting of ESPU exhibited higher carbon dioxide permeability and also higher CO2/CH4 selectivity compared to ETPU-based nanocomposite membranes. In this article a new model for prediction of effective permeability of the nanocomposite membranes was proposed. To derive this model, the presence of interfacial layer at the surface of the nanoparticles, resulting in formation of void volumes at that layer, was taken into account. The proposed model showed fairly good prediction for the prepared nanocomposite membranes.

Deposition and post-deposition annealing of thin Y 2O 3 film on n-type Si in argon ambient

Thin (∼5.0 nm) Y 2O 3 films were deposited on n-type Si (1 0 0) substrate using RF magnetron sputtering. Detailed studies on the effects of post-deposition annealing (PDA) temperatures (400, 600, 800, and 1000 °C) in argon ambient on these films were performed by X-ray diffraction (XRD), Fourier transform infrared spectrometer (FTIR), field emission scanning electron microscopy, and atomic force microscopy. Interfacial layer (IL) of SiO 2 in between Y 2O 3 and the Si substrate for sample annealed from 400 to 800 °C had been suggested from the results of FTIR. As for sample annealed at 1000 °C, presence of IL might consist of both Y 2Si 2O 7 and/or SiO 2 through the detection of Y 2Si 2O 7 compound and Si–O chemical bonding from XRD and FTIR analysis, respectively. For as-deposited sample, no detectable chemical functional group at the IL was recorded. Electrical characteristics of the Y 2O 3 films were acquired by fabricating metal-oxide–semiconductor capacitor as test structure. An improvement in the breakdown voltage ( V B) and leakage current density ( J) was perceived as the PDA temperature increased. Of the PDA samples, the attainment of the lowest effective oxide charge, interface trap density, total interface trap density, and the highest barrier height at 1000 °C had contributed to the acquisition of the highest V B and lowest J.

New permeation models for nanocomposite polymeric membranes filled with nonporous particles

In this article, permeation models for nanocomposite polymeric membranes (NCPMs) filled with nonporous particles are discussed and two new models for prediction of effective permeability of NCPMs are proposed. To derive these models, the presence of interfacial layer at the surface of the nanofiller particles as well as the impact of two important phenomena namely creating void volumes and increasing free volume at the interface layer are taken into account. The capability of the models for prediction of reliable results is checked against available experimental data on permeability of NCPMs and is also compared with other presented models for such membranes. The new proposed models show profound superiority over the well known models such as “Bruggeman model in limit” which offers fairly good prediction for NCPMs.

Effect of post metallization annealing on structural and electrical properties of Ge metal-oxide-semiconductor (MOS) capacitors with Pt/HfO 2 gate stack

We fabricated Ge metal-oxide-semiconductor (MOS) capacitors with Pt/HfO 2 gate stack and demonstrated the effects of post metallization annealing on their structural and electrical properties. Post metallization annealing was carried out at the temperatures of 500 and 600 °C for 30 min in oxygen (O 2) ambient. Post metallization annealing at both temperatures led to the reduction of the interface traps density ( D it) with a decrease in accumulation capacitance. By considering the presence of interfacial layer (IL) in-between HfO 2 and Ge, the effective work function ( Φ m,eff) values of Pt gate electrode after annealing at 500 and 600 °C, extracted from the relations of equivalent oxide thickness (EOT) versus flatband voltages ( V FB), were determined to be ∼4.05 and ∼5.43 eV, respectively. The presence of positive charge at the interface between HfO 2 and IL produced by the formation of oxygen-rich HfO 2/IL interface resulted in the minimization of Fermi level pinning in Ge, which could be responsible for relatively high Φ m,eff value of Pt gate electrode in Ge MOS capacitor with O 2 post metallization annealing at 600 °C.

Influence of interfacial layers upon the barrier properties of polymer nanocomposites

Recent experiments in the context of polymer nanocomposites (PNCs) have observed counter intuitive behavior in which the addition of impenetrable nanofillers into a rigid polymer matrix resulted in the enhancement of the composite membrane's permeability (and diffusivity) to gas penetrants. Existing theoretical models have rationalized these observations as arising from the presence of interfacial layers around the nanoparticles whose properties differ significantly from the bulk properties of the polymer. Similar influences of interfacial layers have also been noted in the context of other macroscopic properties of nanofiller-polymer mixtures. In this article, we present a numerical approach building upon such earlier theoretical ideas, which: (i) Uses a microscopically based polymer model to determine the penetrant diffusivity characteristics in interfacial layers; (ii) embeds the so-determined interfacial characteristics into a numerical homogenization procedure, which accounts for the overlap of interfacial layers (approximately) and multibody interactions (exactly). The numerical approach is used to elucidate the influence of polymer matrix stiffness, particle sizes and particle volume fractions upon the penetrant diffusivity properties of PNCs.

Studies of two distinct types of (Ba,Sr)TiO3∕Pt interfaces

High resolution transmission electron microscopy is used to investigate the interfacial layer at interfaces between (001) (Ba,Sr)TiO3 (BST) films and (111) Pt electrodes. Two distinct types of interfaces are observed. One case is the presence of interfacial layer with distorted structure, whereas another case is the good interfacial match without any interfacial layer. Based on the analyses of crystallographic relationships between BST and Pt, it is proposed that the in-plane lattice structure plays an important role in determining the feature of the interface. The impact of A-O and B-O terminations of BST films on the interfacial layer is also discussed.

Effect of surface layers on the constriction resistance of an isothermal spot. Part I: Reduction to an integral equation and numerical results

The problem of the constriction resistance of a circular spot on a half-space covered with a uniform layer of different material is considered. For the general case of any specified axisymmetric distributions of temperature over the spot and heat flux over the rest of the surface, the mixed boundary value problem governing the heat flow from the spot to the underlying layer-substrate composite is converted to a non-homogeneous Fredholm integral equation of the second kind. For the particular case of isothermal spot on otherwise insulated surface, the evaluation of the constriction resistance is reduced to the reciprocal of a simple integral with the solution of the relevant integral equation as integrand. The integral equation is solved numerically and very accurate results are obtained for the constriction resistance over four orders of magnitude variation of the ratio, τ, of layer thickness to spot radius and the ratio, kr, of layer to substrate conductivities for both conducting (kr > 1) and insulating (kr < 1) layers. An extensive discussion of the numerical results is presented with particular emphasis on their implications for the contact resistance of practical joints in the presence of interfacial layers. Further, in the light of the numerical results, two widely used analytical approximations for the constriction resistance – the first of which results from replacing the isothermal condition over the spot by a special flux (herein called the Equivalent Isothermal Heat Flux, EIHF) condition which is believed to render the spot nearly isothermal and the second is a consequence of the assumption (herein termed the Thin Insulating Layer Approximation, TILA) that, for thin insulating layers like oxide films, the heat flow in the layer region right beneath the spot is purely axial – are assessed as to their levels of accuracy and ranges of applicability with respect to both τ and kr.

Raman studies of In 0.53Ga 0.47As/InP multi quantum wells

We report Raman scattering studies on two well characterized multi-quantum well samples of InGaAs/InP—one having 4 equal wells of 7.8 nm width (sample A) while the other has 4 unequal wells of widths 2.5, 3.9, 7.8 and 15 nm (sample B). Raman spectra of both these samples show two strong peaks at approximately 290 and 330 cm −1 due to bulk InGaAs and InP, respectively. Weak peaks at 245.7, 263.1, 276.8 cm −1 were observed apart from the InGaAs peak and a shoulder at 316.1 cm −1 near InP peak in sample A. Periodic Raman peaks were observed in both samples due to folded zone LA phonons. The presence of interfacial layers at the hetero-interfaces was evident from Raman lines.

Effect of series resistance on the forward current-voltage characteristics of Schottky diodes in the presence of interfacial layer

In order to make an accurate determination of Schottky diode parameters such as the ideality factor, the barrier height and the series resistance [using forward current-voltage ( I- V) characteristics in the presence of an interfacial layer], a novel calculation method has been developed by taking into account the applied voltage drop across the interfacial layer ( V i). The parameters obtained by accounting for the voltage drop V i have been compared with those obtained without considering the above voltage drop. To examine the consistency of this approach, the comparison has been made by means of Schottky diodes fabricated on a n-type semiconductor substrate with different bulk thickness. It is shown that the voltage drop across the interfacial layer will increase the ideality factor and the voltage dependence of the I- V characteristics. In addition, it is shown that the series resistance value increases as the semiconductor bulk thickness has been increased.

X-RAY Diagnostics of Large-Period Lattice-Matched InGaAs/InP Superlattices

ABSTRACTThe interfacial structure of InGaAs/InP superlattices grown on (100) InP by metalorganic molecular beam epitaxy has been studied by fully dynamical simulations of high-resolution x-ray diffraction curves of the (200) and (400) reflectjon. The superlattice under investigation is lattice-matched and has a long period of ∼630Å. This kind of structure creates a very symmetrical x-ray pattern enveloping a large number of closely spaced satellite intensities with pronounced maxima and minima. It appears in the dynamical analysis that the position and shape of these maxima and minima is extremely sensitive to the number N of monolayers and atomic spacing d of the InGaAs and InP layer, as well as the presence of interfacial layers and impurities.

Optical properties of very thin, nonideal multilayer superlattice stacks

In this study, the theory of very thin, nonideal multilayer stacks is developed, and the computed wavelength variation of the transmissivity and reflectivity is compared with that measured on experimentally prepared silver-silicon monoxide layer stacks. The model imputes a step-function character to the complex index of refraction along the layer structure, and nonideality is accounted for by allowing for the likely presence of interfacial layers between each primary layer pair and also for the possibility that the thickness of the individual layers may vary randomly within some limit of error. Abeles's transfer matrix technique is used to arrive at the characteristic matrix of the stack, and additive corrective matrices are derived to account for the effects due to interfacial layers and the random layer thickness variation.

The barrier height change and current transport phenomena with the presence of interfacial layer in MIS Schottky barrier solar cells

In this comprehensive study, several interesting results which are different from those previous are reported. We find the barrier height decreases for n-type and increases for p-type when positive ions are introduced into the insulating layer. The increase of open circuit voltage can be traced to the suppression of the dark saturation current by the depletion field induced by the positive charge, and to the diminution of the majority tunneling current by the oxide potential barrier. The tunneling probabilities for majority and minority carriers are different; there are only a finite amount of majority carriers with thermionic energy greater than q( V bi − V s ) which can surmount the depletion potential and tunnel into the metal, whereas the photogenerated minority carriers derive kinetic energy in the depletion layer making tunneling easier. Transport coefficients for electrons to transmit from metal to semiconductor and from semiconductor to metal are different for the departure of built in potentials during illumination.

Reverse I-V characteristics in Au-GaAs Schottky diode in the presence of interfacial layer

The existence of an interfacial layer in an Au-GaAs Schottky diode may be revealed by measuring its I-V characteristics at very low reverse bias voltage. It is shown in this letter that a voltage dividing factor m can be used [see (2) of the text] to describe the effect of the interfacial layer on the I-V characteristics of the diode at low bias voltage.