Dependence Of Residual Strain Research Articles

Optical properties of InI3: Density functional theory calculations and experimental results

The electronic and optical properties of InI3 have been investigated by both experimental and theoretical approaches. The First Principle electronic structure and optical properties were calculated by Density Functional Theory (DFT) formalism using Full Potential Linearized Augmented Plane Wave plus local orbitals (FP-LAPW + lo) implementing different appropriate exchange-correlation functionals in WIEN2k code. The calculations were also carried out implementing other functionals and only TB-mBJ results tally the closest with experimental results. The optical measurements of a well characterized InI3 films indicate the band gap as of direct type and residual strain dependant. The stress free intrinsic band gap Eg = 2.8 eV (average of Eg⊥c and EgIIc) has been determined from the residual strain dependence of the band gap in closest agreement with theoretically calculated value of 2.9 eV. Both theory and experiment show that the band gap is anisotropic along and perpendicular to c-axis. The electron effective mass me*=0.79m0 and the hole effective mass mh*=0.85m0 have been determined from the band structure. The experimental and theoretical optical properties match reasonably well.

Analysis of Active and Passive Deformation of Expanded Polystyrene Foam under Short-Term Compression

In this paper, we undertake a detailed analysis of the active and passive deformation of expanded polystyrene (EPS), which is used as a thermal insulating layer in building partitions, under short-term compressive loading. The values of residual strain in 10-40 kg/m3 density EPS after monotonically increasing loading under active deformations of 20%, 30%, 40%, 50%, and 60% with the following complete removal are determined. These values are a physical sign of the elastic-plastic state of EPS. It has been shown that the final destruction of cells takes place in EPS when the active strain reaches 50%. Empirical equations are proposed to estimate the residual strain of EPS based on density with determination coefficients varying from 0.744 to 0.986 at a confidence level of 90%. Moreover, graphical interpretations with regression equations for residual strain dependence on density and compressive strength, as well as density and active strain, were proposed with determination coefficients equal to 0.779 and 0.717, respectively.

Residual strain dependence on the matrix structure in RHQ-Nb3Al wires by neutron diffraction measurement

We prepared three types of non-Cu RHQ-Nb3Al wire sample with different matrix structures: an all-Ta matrix, a composite matrix of Nb and Ta with a Ta inter-filament, and an all-Nb matrix. Neutron diffraction patterns of the wire samples were measured at room temperature in the J-PARC ‘TAKUMI’. To obtain the residual strains of the materials, we estimated the lattice constant a by multi-peak analysis in the wires. A powder sample of each wire was measured, where the powder was considered to be strain free. The grain size of all the powder samples was below 0.02 mm. For the wire sample with the all-Nb matrix, we also obtained the lattice spacing d by a single-peak analysis. The residual strains of the Nb3Al filament were estimated from the two analysis results and were compared. The resulting residual strains obtained from the multi-peak analysis showed a good accuracy with small standard deviation. The multi-peak analysis results for the residual strains of the Nb3Al filaments in the three samples (without Cu plating) were all tensile residual strain in the axial direction, of 0.12%, 0.12%, and 0.05% for the all-Ta matrix, the composite matrix, and the all-Nb matrix, respectively. The difference in the residual strain of the Nb3Al filament between the composite and all-Nb matrix samples indicates that the type of inter-filament material shows a great effect on the residual strain. In this paper, we report the method of measurement, method of analysis, and results for the residual strain in the three types of non-Cu RHQ-Nb3Al wires.

Strain-dependent Recovery Behavior of Single Chondrocytes

One of the challenges facing researchers studying chondrocyte mechanobiology is determining the range of mechanical forces pertinent to the problems they study. One possible way to deal with this problem is to quantify how the biomechanical behavior of cells varies in response to changing mechanical forces. In this study, the compressibility and recovery behaviors of single chondrocytes were determined as a function of compressive strains from 6 to 63%. Bovine articular chondrocytes from the middle and deep zones were subjected to this range of strains, and digital videocapture was used to track changes in cell dimensions during and after compression. The normalized volume change, apparent Poisson's ratio, residual strain after recovery, cell volume fraction after recovery, and characteristic recovery time constant were analyzed with respect to axial strain. Normalized volume change varied as a function of strain, demonstrating that chondrocytes exhibited compressibility. The mean Poisson's ratio of chondrocytes was found to be 0.29 +/- 0.14, and did not vary with axial strain. In contrast, residual strain, recovered volume fraction, and recovery time constant all depended on axial strain. The dependence of residual strain and recovered volume fraction on axial strain showed a change in behavior around 25-30% strain, opening up the possibility that this range of strains represents a critical value for chondrocytes. Quantifying the mechanical behavior of cells as a function of stress and strain is a potentially useful approach for identifying levels of mechanical stimulation that may be germane to normal cartilage physiology, functional tissue engineering of cartilage, and the etiopathogenesis of osteoarthritis.

Formation of high-quality and relaxed SiGe buffer layer with H-implantation and subsequent thermal annealing

High-quality, thin relaxed Si0.8Ge0.2 layers grown on Si(100) by ultrahigh-vacuum chemical vapor deposition (UHVCVD) have been formed with hydrogen (H)-implantation and subsequent thermal annealing. H-implantation was used to introduce a layer with a high density of defects (cavities) below a 200-nm-thick strained Si0.8Ge0.2. The peak of the implanted profile was located just ∼50nm below the Si0.8Ge0.2/Si interface. The dependence of residual strain in pseudomorphic Si0.8Ge0.2 layer on the annealing temperature has been investigated. By adjusting the dose of H-implantation and the subsequent annealing conditions, almost relaxed (∼95%) Si0.8Ge0.2 layers with a smooth surface were achieved. The method provides a simple approach for the formation of thin relaxed Si0.8Ge0.2 with reduction in surface roughness for advanced complementary metal-oxide-semiconductor electronic devices.

Growth pressure dependence of residual strain and threading dislocations in the GaN layer

We investigated the generation of threading dislocations (TDs) and the relaxation of the compressive strain in the GaN/sapphire (0001) grown by metalorganic chemical vapor deposition. With decreasing the growth pressure, the a-axis lattice constant of GaN film and the width of the (002) and the (101) rocking curve increases. This indicates that the density of TDs in GaN epilayers increases with the lattice constant a of GaN film. The fact that the width of the (101) rocking curves increases much more than that of the (002) rocking curve indicates that the residual strain in GaN on sapphire reduces mainly by generating the edge-type TDs. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Residual strain dependence of optical characteristics in GaN layers grown on (0001) sapphire substrates

GaN layers were grown on (0001) sapphire substrates by metalorganic chemical vapor deposition with various growth conditions. Some samples were grown with pressures higher than atmospheric. The residual strain in the epitaxial layer was estimated by measuring the lattice constants using x-ray diffraction. The optical quality was evaluated in terms of the threshold power density of stimulated emission. The residual strain perpendicular to C face, εzz, ranged from 0.058% to 0.125%. The strain ratio under biaxial stress (Δc/c)/(Δa/a), is estimated to be −0.46 from the relation between the lattice constants a and c. From the photoluminescence spectra with weak excitation, δEA/δεzz for undoped GaN is estimated to be 16.4 eV. The threshold power density decreased from 2.77 to 0.59 MW/cm2 as the strain increased, suggesting that the strain relaxation process is accompanied by a generation of defects which act as nonradiative recombination centers.

SOL thickness dependence of residual strain in SOI material

The structural properties of commercial SOI (silicon on insulator) wafers have been investigated against SOL (silicon over-layer) thickness. It is found that the upper part of a standard SOI material constantly exhibits a rather large amount of residual stress. It is shown that the repartitions of residual stresses depend on the final SOL thickness.

Residual thermal strain of metals in heating-cooling cycles

Metallic samples subjected to heating-cooling cycles undergo a permanent change in their length. The difference between the initial length and the length at the end of the cycle (residual strain) depends on the maximum temperature attained during the cycle. This dependence of residual strain on the maximum temperature of the cycle is similar for all of the examined metals (polycrystalline copper, aluminium, iron, gold, lead and single-crystal copper). Upon further increasing this temperature, the metal residual strain changes from positive to negative values. The temperature at which the maximum positive residual strain occurs is characteristic for each metal. The value of the residual strain and the temperature at which it changes its sign depend on the previous thermal history of the metal.

New approach to the mechanism of strain release in lattice-mismatched epitaxial films

A new approach is presented for calculation of the dependence of residual strain in regions near the surface on the thickness of CdTe(100) films on GaAs(100) substrates. The present results are obtained assuming that the misfit dislocation density is proportional to the strain. Application of our model to the ZnSe/GaAs(100) system is also discussed. It is found that our model fits experimental results quite well.

Neutron Diffraction as a Tool for Non-Destructive Evaluation of Ceramics

AbstractNeutron diffraction is a powerful probe of the properties of condensed matter. In recent years neutron diffraction has been applied to the non-destructive evaluation of mechanical characteristics of engineering components. This paper presents examples of applications to ceramic composites including the measurement of position dependence of residual strain, grain size and minority phase concentration. In addition, an example of volume-averaged crystallographic texture is presented.

Dependence of residual strain on size in small epitaxial islands

Abstract Vincent's measurements of the average strain in small Sn islands grown epitaxially on SnTe between 140°C and 200°C showed a saw-tooth dependence on island width. He explained this behaviour by assuming that a given interfacial mismatch cannot be entirely compensated by an integral number of dislocations, and that the residual part must be accommodated by elastic strain. The present considerations show how a saw-tooth dependence can be calculated on the basis of lowest energy using a model in which the interaction at the interface of the overgrowth and substrate is represented by a periodic potential. The resutls of the calculations support the approximations suggested by Vincent and others.