Thickness Of Transition Layer Research Articles

Estimation of received pulse from sea bottom with a transition layer using elastic finite difference time domain method

Recently, ocean acoustic thermometry is being planned in shallow water. Characteristics of sound propagation in shallow water are influenced by bottom media because sound propagation is affected by acoustic boundary conditions of the water-sediment interface. To investigate characteristics of sound propagation in shallow water, it is necessary to develop an accurate numerical method to model sound propagation. Elastic finite difference time domain method (elastic FDTD) is very accurate and is useful for range-dependent models in shallow water. Therefore, we calculate the sound waveform reflected from the sea bottom with a transition layer in shallow water using elastic FDTD. It is assumed that a 1.5-kHz transducer is placed at 50-m depth. The influence of the sea bottom with the transition layer is calculated for a 400-m range. To determine the influence of thickness of the transition layer to sound propagation, we calculate sound pulses as transition layers of varying thickness. Results show that fluctuation of the pulse amplitude depends on the transition layer thickness if the thickness is greater than one wavelength. A sea bottom with a transition layer clearly affects sound propagation in shallow water.

The effect of oxygen on segregation-induced redistribution of rare-earth elements in silicon layers amorphized by ion implantation

A model of segregation-induced redistribution of impurities of rare-earth elements during solid-phase epitaxial crystallization of silicon layers amorphized by ion implantation is developed. This model is based on the assumption that a transition layer with a high mobility of atoms is formed at the interphase boundary on the side of a-Si; the thickness of this layer is governed by the diffusion length of vacancies in a-Si. The Er concentration profiles in Si implanted with both erbium and oxygen ions are analyzed in the context of the model. It shown that, in the case of high doses of implantation of rare-earth ions, it is necessary to take into account the formation of Rm clusters (m = 4), where R denotes the atom of a rare-earth element, whereas, if oxygen ions are also implanted, formation of the complexes ROn (n = 3–6) should be taken into account; these complexes affect the transition-layer thickness and segregation coefficient.

Elastodynamic wave propagation in graded materials: Simulations, experiments, phenomena, and applications

A two-dimensional numerical simulation model for the elastodynamic wave propagation in two linear elastic, isotropic, joint half-spaces is presented. The border between the two half-spaced is graded in a way, that the values of the elastic properties and the densities vary smoothly (sinusoidally) from the values of one continuum to the values of the other continuum within a transition zone of a defined thickness. It is demonstrated, that a graded layer leads to a frequency and wavelength dependent refraction and reflection behavior of elastodynamic waves. Numerical results show that wavelengths which are long compared with the transition layer thickness are dominantly reflected whereas short waves are dominantly transmitted, a phenomena which does not occur in the case of an infinitely thin transition layer. Furthermore the frequency dependent reflection and transmission behavior of elastodynamic waves is verified experimentally. There the interface between two vapor deposited films is graded due to intermetallic diffusion effects. These graded microstructures are analyzed with a short-pulse-laser-acoustic set-up. The corresponding frequencies of the elastodynamic waves which are filtered with these functionally graded microstructures are in the range of 0.5 THz.

New Linear-Parabolic Rate Equation for Thermal Oxidation of Silicon

We propose a new oxidation rate equation for silicon supposing only a diffusion of oxidizing species but not including any rate-limiting step by interfacial reaction. It is supposed that diffusivity is suppressed in a strained oxide region near SiO(2)/Si the interface. The expression of a parabolic constant in the new equation is the same as that of the Deal-Grove model, while a linear constant makes a clear distinction with that of the model. The estimated thickness using the new expression is close to 1 nm, which compares well with the thickness of the structural transition layers.

$\Gamma$-convergence of the Allen-Cahn energy with an oscillating forcing term

We consider a standard functional in the mesoscopic theory of phase transitions, consisting of a gradient term with a double-well potential, and we add to it a bulk term modelling the interaction with a periodic mean zero external field. This field is amplified and dilated with a power of the transition layer thickness $\eps$ leading to a nontrivial interaction of forcing and concentration when $\eps \to 0$. We show that the functionals $\Gamma$-converge after additive renormalization to an anisotropic surface energy, if the period of the oscillation is larger than the interface thickness. Difficulties arise from the fact that the functionals have non constant absolute minimizers and are not uniformly bounded from below.

Vibrational Spectroscopic Study of the Interface of SiO2/Si(100) Fabricated by Highly Concentrated Ozone: Direct Evidence for Less Strained Si–O–Si Bond Angle

The interface structure of SiO2/Si(100) synthesized with a highly concentrated ozone gas was analyzed by Fourier-transformed infrared absoption spectroscopy (FT-IR). The position of a transverse optical (TO) phonon peak of Si–O–Si asymmetric stretching vibration, which is a function of a Si–O–Si bond angle, remains constant at 1065 cm-1 within a ∼2 nm thickness of an ozone-oxide film. This result indicates that the thickness of structural transition layers at this interface where the Si–O–Si angle is distorted due to the stress at the interface is considerably limited, which is in contrast to a thermal oxide film on Si(100) showing the existence of structural transition layers.

An upper bound on the coarsening rate for mushy zones in a phase-field model

We prove an upper bound on the coarsening rate for solutions of a phase field model with arbitrarily complicated patterns of phases. The analysis is performed in a regime corresponding to the late stages of phase separation, in which the ratio between the transition layer thickness and the length scale of the pattern is small, and is also small compared to the square of the ratio between the pattern scale and the system size. The analysis extends the method of Kohn and Otto (Comm.\ Math.\ Phys.\ 229 (2002), 375-395) to deal with both temperature and phase fields.

Interface Properties of Metal–Oxide–Semiconductor Structures on 4H-SiC{0001} and (1120) Formed by N2O Oxidation

4H-SiC(0001), (0001), and (1120) have been directly oxidized by N2O at 1300°C, and metal–oxide–semiconductor (MOS) interfaces have been characterized. The interface state density has been significantly reduced by N2O oxidation on any face, compared to conventional wet O2 oxidation at 1150°C. Planar n-channel metal–oxide–semiconductor field-effect transistors (MOSFETs) fabricated on 4H-SiC(0001), (0001) and (1120) faces have shown effective channel mobilities of 26, 43, and 78 cm2/Vs, respectively. Secondary ion mass spectrometry analyses have revealed a clear pileup of nitrogen atoms near the MOS interface. The thickness of the interfacial transition layer can be decreased by N2O oxidation. The crystal face dependence of the interface structure is discussed. A simple consideration of chemistry indicates that NO, generated from the decomposition of N2O, may be a more efficient oxidant of carbon than O2.

Modified Porod's law estimate of the transition-layer thickness between two phases: test of triangular smoothing function

An analytical method to estimate the thickness of the interface between two phases from small-angle scattering (SAS) data has been developed using Porod's law modified by a triangular smoothing function. The convolution with a `top-hat' function describing a sharp density profile results in a semi-sigmoidal density profile. This analytical method allows an interfacial layer thickness to be estimated from the negative slope of a Porod plot. The interfacial layer thickness (T) obtained from this model is related to similar models, namely a linear (E) and a sigmoidal density profile (σ) model, as follows:T= 21/2E= 2(61/2)σ, where σ is the standard deviation of the Gaussian function and does not represent the boundary thickness itself. The interfacial layer thickness obtained from any convolution method is a model-dependent parameter.

Diffusion processes in NiTi/Si, NiTi/SiO 2 and NiTi/Si 3N 4 systems under annealing

We present a nanometric scale analysis of the NiTi/Si, NiTi/SiO 2 and NiTi/Si 3N 4 systems before and after annealing at 500 °C during 30 min, by secondary ion mass spectrometry and electron-induced X-ray emission spectroscopy. Before annealing, a few nanometers thick transition layer forms at the interface of each system. Under annealing, a NiSi 2 layer forms in the NiTi/Si system over several tens of nanometers, whereas a TiO x diffusion barrier builds up at the NiTi/SiO 2 interface. A few nanometers thick mix layer composed of TiSi 2, TiN and NiSi 2 forms at the NiTi/Si 3N 4 interface. This interface presents an intermediate reactivity under annealing between that of NiTi/Si and NiTi/SiO 2.

Morphological Transition of the Regular Structure of Poly(styrene-block-butadiene-block-styrene) at the Interface with Poly(xylenyl ether)

It has been found that poly(styrene-block-butadiene-block-styrene) (SBS) forms a regular structure and the structure transforms into another regular structure at the interface with poly(xylenyl ether) (PXE). This study examines the order−order transition phenomena with a transition electron microscopy (TEM) and an atomic force microscopy (AFM). According to TEM observations, the thickness of the morphological transition area depends on a temperature and time. In some cases, the thickness of the new regular structure's area could reach 1000 nm. Such phenomena have not been reported yet. A layer of which viscoelasticity changes continuously is observed at the interface of PXE and SBS with an atomic force microscopy (AFM), and the thickness of the layer is almost same as the thickness of the morphology transition layer observed with TEM.

Numerical simulation of time-dependent fracture of graded bimaterial metallic interfaces

Stationary cracks along and near interfaces between two time-dependent materials are simulated using the finite element method (FEM) to examine crack tip fields and candidate driving force parameters for crack growth. Plane strain conditions are assumed. In some cases, a thin transition layer is included between the two materials. This transition layer features a functionally graded blend of properties of the two materials. An example of such a system is that of weld metal (WM) and base metal (BM) in a weldment, with the transition layer corresponding to the heat-affected zone (HAZ). Numerical solutions for the stress and strain fields of homogeneous and heterogeneous Compact Tension (C(T)-type) specimens are presented. The equivalent domain integral technique is employed to compute the J-integral for elastic-plastic cases as well as the C(t)-integral and transition times for creep behavior. Results from parametric studies are curve-fit in terms of transition layer thickness and crack position, inelastic property mismatches, and other independent model parameters. Results indicate that the incorporation of functionally graded transition layer regions leads to less concentrated stress and strain components along interfaces ahead of the crack tip. It is also shown that the computed fracture parameters are influenced by the transition layer properties.

Hydrogen plasma induced microcrystallization in layer-by-layer growth scheme

Significant improvement in the microcrystallization in Si:H network has been demonstrated by introducing layer-by-layer (LBL) growth and H-plasma treatment on the stacking layers. During the development of microcrystalline network, the amorphous incubation layer as well as the microcrystalline transition layer thickness has been reduced efficiently by the enhanced reactivity of atomic H from the surface into the bulk through the growth zone, so that the virtual saturation in crystallization is obtained at a significantly low thickness. The growth process becomes more flexible because of the inclusion of additional independent parameter, namely, the time span of H-plasma exposure (tP) on the growing surface, compared to the conventional process.

Determination of the transition-layer thickness of a crystalline polymer by using small-angle x-ray scattering

The thickness of transition layer of a crystalline polymer is generally calculated by one-dimensional electron density correlation function. If the transition layer of the crystalline polymer is diffusive, the corrected Porod's law is an effective method to deal with the diffuse transition layer of pseudo two-phase material. The method of Porod's law is used to compute the thickness of transition layer of crystalline polymer and compared with that of correlation function. The conclusion is that the two methods obtain identical thickness of the transition layer.

Lattice-Boltzmann model based on field mediators for immiscible fluids.

In this paper, a lattice BGK (Bhatnagar-Gross-Krook) model is proposed for immiscible fluids. Collision operator is decoupled considering mutual and cross collisions between lattice particles, with three independent parameters related to the species diffusivity and to the viscosity of each fluid. Field mediator's concept, described by Santos and Philippi [Phys. Rev. E 65, 046305 (2002)], is extended to the framework of the lattice-Boltzmann equation and interference between mediators and particles is modeled by considering that there is a deviation in particles velocity, proportional to the mediators' distribution at the site. A Chapman-Enskog analysis is performed leading to theoretical predictions of the macroscopic equations inside the transition layer and to the transition-layer thickness. Chapman-Enskog analysis is restricted to near-equilibrium states and was unable to predict the correct second-order interfacial tension dependence on the modeled long-range fields intensity. Interfacial tension was, only, correctly retrieved using a nonequilibrium solution. Theoretical predictions are compared with simulation results and the model is tested considering its ability in describing the dynamical behavior of the interface and Galilean invariance.

Detection and Modeling of the Core-Annulus Transition in Industrial and Pilot Plant Risers

The core-annulus structure is essential to the modeling and optimization of riser reactors such as used in Fluid Catalytic Cracking. This paper presents results of measurements taken with various probes in a pilot plant and in an industrial riser. The instantaneous probe signals were analyzed with sophisticated signal analysis methods based on the detection of cycles and the determination of the correlation dimension.In a pilot plant riser, a core-annulus structure was identified with optical and momentum probe measurements. Cycle analysis of the optical probe measurements showed that the annulus was unstable: its thickness fluctuated with an average cycle time of 0.3 s. There were waves at the core-annulus boundary. In an industrial riser, a similar core-annulus structure could be identified with temperature and momentum probe measurements. Local temperature measurements are much easier to perform in an industrial riser than momentum probe measurements but can provide, with cycle analysis, the location of the core-annulus transition. Analysis of the momentum probe and temperature signals showed that the thickness of the wavy transition layer between core and annulus was about the same in the pilot plant and the industrial riser, meaning that the relative range of fluctuations in annulus thickness was much smaller in the larger industrial riser.A model was developed to predict the time-averaged transition between core and annulus. This model, which had been successfully used to predict the annulus thickness in dilute-phase vertical pneumatic transport lines, assumes that the annulus thickness is such that the riser pressure drop is minimized. Measurements and model predictions were in good agreement.

The thermohaline structure and evolution of the deep waters in the Canada Basin, Arctic Ocean

Below the sill depth (at about 2400 m) of the Alpha-Mendeleyev ridge complex, the waters of the Canada Basin (CB) of the Arctic Ocean are isolated, with a 14C isolation age of about 500 yr. The potential temperature θ decreases with depth to a minimum θ m≈−0.524°C near 2400 m, increases with depth through an approximately 300 m thick transition layer to θ h≈−0.514°C, and then remains uniform from about 2700 m to the bottom at 3200–4000 m. The salinity increases monotonically with depth through the deep θ m and transition layer from about 34.952 to about 34.956 and then remains uniform in the bottom layer. A striking staircase structure, suggestive of double-diffusive convection, is observed within the transition layer. The staircase structure is observed for about 1000 km across the basin and has been persistent for more than a decade. It is characterized by 2–3 mixed layers (10–60 m thick) separated by 2–16 m thick interfaces. Standard formulae, based on temperature and salinity jumps, suggest a double-diffusive heat flux through the staircase of about 40 mW m −2, consistent with the measured geothermal heat flux of 40–60 mW m −2. This is to be expected for a scenario with no deep-water renewal at present as we also show that changes in the bottom layer are too small to account for more than a small fraction of the geothermal heat flux. On the other hand, the observed interfaces between mixed layers in the staircase are too thick to support the required double-diffusive heat flux, either by molecular conduction or by turbulent mixing, as there is no evidence of sufficiently vigorous overturns within the interfaces. It therefore seems, that while the staircase structure may be maintained by a very weak heat flux, most of the geothermal heat flux is escaping through regions of the basin near lateral boundaries, where the staircase structure is not observed. The vertical eddy diffusivity required in these near-boundary regions is O(10 −3) m 2 s −1. This implies Thorpe scales of order 10 m. We observe what may be Thorpe scales of this magnitude in boundary-region potential temperature profiles, but cannot tell if they are compensated by salinity. The weak stratification of the transition layer means that the large vertical mixing rate implies a local dissipation rate of only O(10 −10) W kg −1, which is not ruled out by plausible energy budgets. In addition, we discuss an alternative scenario of slow, continuous renewal of the CB deep water. In this scenario, we find that some of the geothermal heat flux is required to heat the new water and vertical fluxes through the transition layer are reduced.

Confocal two-photon spectroscopy of red mercuric iodide

One- and two-photon fluorescence of red mercuric iodide single crystal was studied using confocal laser scanning microscopy and spectroscopy at room temperature. There is a clear difference in the fluorescence spectra for one- and two-photon excitation. With two-photon excitation, a fluorescent band is found at the band gap and its central wavelength shifts toward lower energy with increasing depth below the surface, whereas the fluorescent band for one-photon excitation remains invariant with depth. There is an approximately 70 μm thick defect transition layer near the surface and the defect concentration decreases approximately linearly from the surface to the bulk. The band-gap energy at room temperature is determined as 2.12 eV, which is consistent with previous studies.

Compositional transition layer in SiO 2/Si interface observed by high-resolution RBS

The compositional transition layer in SiO 2/Si(1 0 0) interface is studied with high-resolution Rutherford backscattering spectroscopy (HRBS). The HRBS spectra of thin SiO 2 films on Si, which are prepared by pyrogenic oxidation, are measured at various incident angles. The spectrum shows a sharp Si surface edge and a relatively broad edge corresponding to the SiO 2/Si interface. The thickness of the compositional transition layer in the SiO 2/Si interface and the energy loss straggling are determined simultaneously from the observed spectra. The obtained thickness of the transition layer is 0.53±0.08 nm. The obtained energy loss straggling agrees with the empirical formula given by Yang et al.

High Transition Temperature Shape Memory Alloys for Micro-actuator Systems

ABSTRACTA new generation of thin film shape memory alloy (SMA) for MEMS micro-actuator has been developed, in which film structure and chemistry are optimized, for enhanced higher transition temperature, higher strain recovery rate as well as reduced actuation time by improving the heat transfer rates. Thin film TiPdNi was produced using Ion Beam Assisted Deposition (IBAD) technique both by in-situ heat treating during deposition and followed by post processing heat treatment. Films deposited on unheated substrates were found to be highly amorphous with minimal B2 austenite crystallization, while films deposited on heated substrates produced a highly crystallized twinned B19 martensitic structure through the bulk of the film. For films deposited on heated substrates, a 70 nm thick transition layer was found to exist between the bulk film and silicon substrate. Severe delamination and oxidation as a result of post heat treatment on IBAD deposited samples made in-situ heat treatment most suitable for processing thin film SMAs for MEMS applications. The desire to introduce this innovative technology to the field of SMA micro-actuators is based on two primary advantages of IBAD process over existing technology used to apply thin film SMAs. First, the chemical composition and grain size of the applied coating can be precisely controlled over a wide range of values. Second, the SMA can be deposited as thin films ≤ 2 μm thick with smaller grain size, much denser than films applied using sputter deposition technology. The effects of various processing parameters, and post processing heat treatment, on properties of the thin film SMA were studied.