Interface Roughness Parameters Research Articles

Взаимодействие электромагнитной Н-волны с наноструктурой "диэлектрик-полупроводник-диэлектрик" с учетом анизотропии зонной структуры полупроводника

The problem of electromagnetic H-wave interaction with a layered "insulator-semiconductor- insulator" nanostructure is solved. We assume that the semiconductor layer thickness can be comparable to or less than the charge carrier de Broglie wavelength. Charge carrier surface scattering is taken into account by the Soffer boundary conditions. The electromagnetic wave frequency is less than the plasma resonance frequency. The constant energy surface is an ellipsoid of revolution. Analytical expressions are obtained for the reflection, transmission and absorption coefficients. Calculations are performed for the limiting cases of a degenerate and nondegenerate electron gas. We analyze the dependences of the optical coefficients on dimensionless parameters: the semiconductor layer thickness, the electromagnetic wave frequency and incidence angle, the chemical potential, the ellipticity parameter, the insulating layer permittivities, and the semiconductor-insulator interface roughness parameters.

Converting the Roughness of Model Interfacies into the Statistical Distribution of Elastic Parameters of the Layered Medium

In the paper, the effect of interface roughness on the elastic parameters of a layered medium is studied. Three-dimensional models of a layered medium with different material inside and outside the layer are considered. Initially, the first class of models is statistically generated with rough interfaces between the layers and fixed elastic parameters of the inner layers. Then the effective stiffness tensor is estimated for the equivalent homogeneous model. After that, new elasticity parameters of the inner layer are reconstructed for second class of models with flat interfacies. Thus, the roughness of the model interfacies is mapped into a statistical distribution of the stiffness tensor components for a fixed model geometry. In addition, an algorithm for extending the results of reconstructing the elastic tensors for arbitrary interface roughness parameters using bilinear regression of covariance matrices is proposed. The algorithm verification shows that the error in restoring the covariance matrix does not exceed 7%; i.e., one can use it in statistical modeling the second class of models with flat interfacies for the arbitrary interface roughness values and given physical parameters of layers in the first class of models.

Interfacial interaction and roughness parameters effects on the residual stresses in DCL-TBC system with different thickness distributions

Compared with the traditional Single-Ceramic-Layer Thermal Barrier Coating system (SCL-TBCs), the application of the Double-Ceramic-Layers Thermal Barrier Coating system (DCL-TBCs) can strengthen the thermal insulation performance and ameliorate the interfacial oxidation behavior. The residual stresses due to the mismatch of thermal expansion, are so important that they can lead to the spallation and delamination failure of the entire system. In present work, considering the evolution of failure positions in the DCL-TBCs, the effects of interfacial interaction and roughness parameters on the residual stresses were investigated under two different thickness distributions of the ceramic layer. Therein, the numerical models with the general periodic boundary have been developed. Results show that the morphology of the yttria partially stabilized zirconia (YSZ)/thermally grown oxide (TGO) interface can affect the stress distribution along the lanthanum zirconate (LZ)/YSZ interface in the TBCs with low thickness of YSZ, but this influence can be negligible if the YSZ is thick enough. The qualitative distribution of the residual stress along the LZ/YSZ interface is similar for various interfacial roughness parameters, and the maximum tensile stress is always presented at the peak of the LZ/YSZ interface. But for the YSZ/TGO interface, the increase in the roughness parameters can lead to the change of the maximum tensile stress position and even the transition of the stress state in the local region. Also, as the reference for judging the maximum tensile stress location, the critical wavelength was obtained based on the parametric calculation procedure, and the relationship between the critical wavelength and the YSZ/TGO interface amplitude has also been revealed. Moreover, the analysis results can also help to understand the failure mechanisms of the DCL-TBCs and provide a reference for further process optimization.

A detailed finite element analysis of composite bolted joint dynamics with multiscale modeling of contacts between rough surfaces

This paper presents the multi-scale modeling and finite element analysis of the dynamics of a composite structure with bolted joints. Microscale contact surface effects are considered and a single-degree-of-freedom (SDOF) stick-slip friction model is proposed. Interface mechanics parameters were solved using fractal contact theory and damping properties of the composite material were determined according to the elastic-viscoelastic correspondence principle. Then, by inputting calculated values for the penalty stiffness, damping coefficient, and material parameters, a finite element analysis of the overall and local dynamic response of the joint was carried out in ABAQUS. Simulated values of the resonance frequency and damping ratio of the structure were consistent with experimental results, thus validating the proposed model. Presence of the joint interface reduced the structural stiffness by 2% and increased energy dissipation by 30–40% compared to a rigid joint. Furthermore, the local interface energy dissipation was found to be influenced by both the excitation amplitude and preload. Finally, analysis of the interface roughness parameters showed that rougher surfaces facilitate preload relaxation.

Adhesive wear mechanisms in the presence of weak interfaces: Insights from an amorphous model system

Engineering wear models are generally empirical and lack connections to the physical processes of debris generation at the nanoscale to microscale. Here, we thus analyze wear particle formation for sliding interfaces in dry contact with full and reduced adhesion. Depending on the material and interface properties and the local slopes of the surfaces, we find that colliding surface asperities can either deform plastically, form wear particles, or slip along the contact junction surface without significant damage. We propose a mechanism map as a function of material properties and local geometry, and confirm it using quasi-two-dimensional and three-dimensional molecular dynamics and finite-element simulations on an amorphous, siliconlike model material. The framework developed in the present paper conceptually ties the regimes of weak and strong interfacial adhesion together and can explain that even unlubricated sliding contacts do not necessarily lead to catastrophic wear rates. A salient result of the present paper is an analytical expression of a critical length scale, which incorporates interface properties and roughness parameters. Therefore, our findings provide a theoretical framework and a quantitative map to predict deformation mechanisms at individual contacts. In particular, contact junctions of sizes above the critical length scale contribute to the debris formation.

Relation between Adhesion and Interfacial Roughness Parameters of Plasma-sprayed Yttria-stabilized Zirconia Coatings

Relation between Adhesion and Interfacial Roughness Parameters of Plasma-sprayed Yttria-stabilized Zirconia Coatings

Roughness Effects on the Fracture Energy between FRP and Concrete

The single test is carried out on totally 54 concrete samples with 6 different interface-roughness conditions, as to delve into the influence of concrete surface roughness on the concrete-FRP interface. Accordingly the closed-form solution based on the compressive strength and interface roughness parameters of concrete is acquired. As the research result indicates, the extremum and extreme point exist in terms of influence of concrete surface roughness on fracture energy, the model acquired in line with the test data is appropriately applicable under the condition 0.34≤ fi ≤0.56, and such model is overall applicable under the concrete strength of 30MPa≤ fc0 ≤50MPa. The model proposed hereof in this paper is superior to the existing models, as not only the significant contribution made by concrete strength to fracture energy is considered, but the influence of concrete surface roughness on interface is highlighted.

On connection between statistical integral equations and statistical inference in ocean acoustics and sonar

Under what circumstances do statistics of source and waveguide parameter values derived from an application of statistical inference, such as Bayesian or Maximum Entropy, reflect the temporal and spatial inhomogeneities of the waveguide? The statistics of the objective function is influenced by model error that reflects the non-deterministic features of the waveguide and the source. This connectivity is explored with a new derivation of statistical equations previously discussed by Dozier and Tappert. The resulting statistical integral equations provide the relationship between the fluctuations in the waveguide to those of the acoustic field. Then, the idea is to infer, from an ensemble of measured acoustic data, marginal probability distributions for the Green’s functions and mode coupling matrix coefficients. This is accomplished by inferring the statistics of the source and the physical properties of an ocean waveguide such as range-dependent sound speed layers in the water column and the seabed, and layer interface roughness parameters. The inferred statistics of the mode coupling operator and Green’s functions, and the noise spatial correlation then become input into the statistical integral equations. In principle these modeled acoustic field statistics can then be compared to the measured field statistics. [Work supported by ONR Code 32 OA.]

The Influence of Morphology on the Charge Transport in Two-Phase Disordered Organic Systems

ABSTRACTIn this work we use a three-dimensional Pauli master equation to investigate the charge carrier mobility of a two-phase system, which can mimic donor-acceptor and amorphous-crystalline bulk heterojunctions. Our approach can be separated into two parts: the morphology generation and the charge transport modeling in the generated blend. The morphology part is based on a Monte Carlo simulation of binary mixtures (donor/acceptor). The second part is carried out by numerically solving the steady-state Pauli master equation. By taking the energetic disorder of each phase, their energy offset and domain morphology into consideration, we show that the carrier mobility can have a significant different behavior when compared to a one-phase system. When the energy offset is non-zero, we show that the mobility electric field dependence switches from negative to positive at a threshold field proportional to the energy offset. Additionally, the influence of morphology, through the domain size and the interfacial roughness parameters, on the transport was also investigated.

Trans-dimensional joint inversion of seabed scattering and reflection data

This paper examines joint inversion of acoustic scattering and reflection data to resolve seabed interface roughness parameters (spectral strength, exponent, and cutoff) and geoacoustic profiles. Trans-dimensional (trans-D) Bayesian sampling is applied with both the number of sediment layers and the order (zeroth or first) of auto-regressive parameters in the error model treated as unknowns. A prior distribution that allows fluid sediment layers over an elastic basement in a trans-D inversion is derived and implemented. Three cases are considered: Scattering-only inversion, joint scattering and reflection inversion, and joint inversion with the trans-D auto-regressive error model. Including reflection data improves the resolution of scattering and geoacoustic parameters. The trans-D auto-regressive model further improves scattering resolution and correctly differentiates between strongly and weakly correlated residual errors.

The study of transport properties in rough ferromagnetic semiconductor rough junctions

The effect of self-affine interface roughness on spin filter tunnelling as a function of interface roughness parameters and the temperature dependent barrier parameters at low biases is studied. The interface roughness is described by the k-correlation model and in terms of self-affine scaling by root-mean-square (rms) deviation Δ, correlation length ξ, and the roughness exponent H(0≤H≤1). In general, the spin-dependent transmission probability is strongly sensitive to roughness and reduced for the case of spin up and down directions in all configurations. Our numerical results show that the roughness affects spin polarization (SP) and tunnelling magnetoresistance (TMR) at different temperatures and decreases the maximum achievable TMR and SP.

Effects of hydrogen/deuterium absorption on the magnetic properties of Co/Pd multilayers

The effects of hydrogen (H2) and deuterium (D2) absorption were studied in two Co/Pd multilayers with perpendicular magnetic anisotropy (PMA) using polarized neutron reflectivity (PNR). PNR was measured in an external magnetic field H applied in the plane of the sample with the magnetization M confined in the plane for {\mu}_o H= 6.0 T and partially out of plane at 0.65 T. Nominal thicknesses of the Co and Pd layers were 2.5 {\AA} and 21 {\AA}, respectively. Because of these small values, the actual layer chemical composition, thickness, and interface roughness parameters were determined from the nuclear scattering length density profile ({\rho}_n) and its derivative obtained from both x-ray reflectivity and PNR, and uncertainties were determined using Monte Carlo analysis. The PNR {\rho}_n showed that although D2 absorption occurred throughout the samples, absorption in the multilayer stack was modest (0.02 D per Pd atom) and thus did not expand. Direct magnetometry showed that H2 absorption decreased the total M at saturation and increased the component of M in the plane of the sample when not at saturation. The PNR magnetic scattering length density ({\rho}_m) revealed that the Pd layers in the multilayer stack were magnetized and that their magnetization was preferentially modified upon D2 absorption. In one sample, a modulation of M with twice the multilayer period was observed at {\mu}_o H= 0.65 T, which increased upon D2 absorption. These results indicate that H2 or D2 absorption decreases both the PMA and total magnetization of the samples. The lack of measurable expansion during absorption indicates that these changes are primarily governed by modification of the electronic structure of the material.

Dependence of Threshold Current Density on the Waveguide Ridge Width in Quantum-Cascade Lasers

We make a systematic study to find the dependence of the threshold current density of a mid-infrared quantum-cascade laser on the waveguide ridge width. The optical and thermal parameters of the waveguide are calculated with a finite-element method, and gain is found from a self-consistent rate equation model with energy-balance. The results show the existence of an optimal ridge width that minimizes the threshold current density of the laser. The influence of the interface roughness parameters on laser performance is also discussed.

Deposition and characterization of titania–silica optical multilayers by asymmetric bipolar pulsed dc sputtering of oxide targets

Titania–silica (TiO2/SiO2) optical multilayer structures have been conventionally deposited by reactive sputtering of metallic targets. In order to overcome the problems of arcing, target poisoning and low deposition rates encountered there, the application of oxide targets was investigated in this work with asymmetric bipolar pulsed dc magnetron sputtering. In order to evaluate the usefulness of this deposition methodology, an electric field optimized Fabry Perot mirror for He–Cd laser (λ = 441.6 nm) spectroscopy was deposited and characterized. For comparison, this mirror was also deposited by the reactive electron beam (EB) evaporation technique. The mirrors developed by the two complementary techniques were investigated for their microstructural and optical reflection properties invoking atomic force microscopy, ellipsometry, grazing incidence reflectometry and spectrophotometry. From these measurements the layer geometry, optical constants, mass density, topography, surface and interface roughness and disorder parameters were evaluated. The microstructural properties and spectral functional characteristics of the pulsed dc sputtered multilayer mirror were found to be distinctively superior to the EB deposited mirror. The knowledge gathered during this study has been utilized to develop a 21-layer high-pass edge filter for radio photoluminescence dosimetry.

Photometric model of diffuse surfaces described as a distribution of interfaced Lambertian facets

The Lambertian model for diffuse reflection is widely used for the sake of its simplicity. Nevertheless, this model is known to be inaccurate in describing a lot of real-world objects, including those that present a matte surface. To overcome this difficulty, we propose a photometric model where the surfaces are described as a distribution of facets where each facet consists of a flat interface on a Lambertian background. Compared to the Lambertian model, it includes two additional physical parameters: an interface roughness parameter and the ratio between the refractive indices of the background binder and of the upper medium. The Torrance-Sparrow model--distribution of strictly specular facets--and the Oren-Nayar model--distribution of strictly Lambertian facets--appear as special cases.

Backscattering from an elastic target near a water-sediment interface at oblique incidence: First results of tank experiments

Sound scattering from a target situated near a water-sediment interface was studied in laboratory conditions in order to control separately all the parameters involved in the scattering process. Targets of different sizes were ensonified with wide band transducers covering the frequency range 200 kHz to 1 MHz. First, the target scattering strength was measured in the free space conditions, and the scattering strength of the water-sediment interface was measured at oblique incidence. These characteristics were used to provide a rough estimate for the signal-to-noise ratio for the second set of experiments where the target was situated near the interface to study effects of target-boundary interactions. The intensity of the total scattered field was measured as a function of the beamwidth, transducer/object and object/interface distances, frequency, grazing angle, target size and the interface roughness parameters. The interface considered here is a flattened sand surface which was studied earlier [Ivakin and Sessarego, High frequency scattering from flattened sand sediments: effects of granular structure, J. Acoust. Soc. Am., 122, (5) 2007]. The targets were spherical glass beads of different size. Side scan sonar images are presented and possibilities of their qualitative interpretation are discussed.

Interface-roughness parameters in InAs quantum wells determined from mobility

For zero temperature we present theoretical results for the transport properties of the electron gas in InAs quantum wells in the presence of interface-roughness scattering. We show how to analyze experimental data in connection with interface-roughness scattering. By comparison with recent experimental results obtained for the mobility of InAs quantum wells, we determine the interface roughness parameters as Δ=3.2Å and Λ=14Å. We predict the single-particle relaxation time (Dingle temperature) and a possible metal-insulator transition in these InAs quantum well structures.

Self-consistent scattering analysis ofAl0.2Ga0.8N/AlN/GaN/AlN heterostructures grown on 6H-SiC substrates using photo-Hall effect measurements

Hall effect measurements on undopedAl0.2Ga0.8N/AlN/GaN/AlN heterostructures grown on 6H-SiC substrates were carried out as a function of thetemperature (30–300 K) and magnetic field (0–1.4 T). Measurements were carried outunder dark and after-illumination conditions. After the dark measurements, thesamples were illuminated with a blue light emitting diode for 30 min, and then thesame measurements were carried out for the after-illumination condition. Themagnetic field dependent Hall results were analyzed and the 2DEG contribution wasfound using the quantitative mobility spectrum analysis (QMSA) technique. Aself-consistent scattering analysis between the dark and illuminated conditions wasimplemented. The importance of this implementation was to find an indirect way tolocate more certain fit parameters, such as interface roughness parameters and thebackground impurity value, which cannot be found using dark measurement dataalone.

Bottom and top AF/FM interfaces of NiFe/FeMn/NiFe trilayers

X-ray reflectivity analyses were performed in the Si/WTi (7 nm)/NiFe (30 nm)/FeMn (13 nm)/NiFe (10 nm)/WTi (7 nm) exchange-biased system prepared by magnetron sputtering under three different argon working pressures. Layer-by-layer analyses were realized in order to obtain the interfacial roughness parameters quantitatively. For a fixed argon pressure, the root-mean-square roughness (including the atomic grading) of the upper (FeMn/NiFe) interface are greater than that for the lower one in all studied samples. Argon working pressure also has severe influence over the NiFe/FeMn interfaces, being more pronounced at the upper interfaces.

Electronic transport studies of a systematic series of GaAs∕AlGaAs quantum wells

The results of experimental transport studies involving a series of five narrow Al0.1Ga0.9As∕GaAs quantum wells with well widths ranging from 7.9to33.0nm are reported. The total transport scattering rate measured in thin AlGaAs∕GaAs quantum wells is typically limited by electron scattering from the interfacial roughness of the quantum well. For a relatively low constant electron density (ne∼5.8×1010cm−2), the authors find that interfacial roughness is the dominant scattering mechanism for L⩽16.0nm and describe the data using a finite quantum well model with adjustable interfacial roughness parameters. Temperature dependence data are also presented.