Effect Of Biaxial Stress Research Articles

The effect of biaxial strain on the phonon-limited mobility in 4H-SiC MOSFETs

We investigate the effect of biaxial tensile stress at the interface of 4H-SiC metal-oxide-semiconductor field effect-transistors on the phonon-limited mobility using theoretical calculations. The band structure under strain is obtained by the first-principles calculations, and the electronic states and potential of the inversion layer at the interface are determined by the Schrödinger–Poisson method. The mobility is calculated using the Fermi's golden rules. We find that the biaxial strain reduces the energy difference between the first and second conduction band minima. This leads to an increase in polar-optical phonon scattering, which becomes the dominant factor in the mobility degradation under the tensile strain.

Giant and tunable Rashba spin splitting and quantum spin Hall effect in H-Pb-Cl

Rashba spin splitting and quantum spin Hall effect have attracted enormous interest due to their great significance in the application of spintronics. According to the first-principles calculation, we propose a two-dimensional hexagonal lattice material H-Pb-Cl, which realizes the coexistence of giant Rashba spin splitting and quantum spin Hall effect. Owing to the break of space inversion symmetry and the existence of intrinsic electric field, H-Pb-Cl has a huge Rashba spin splitting phenomenon (<i>α</i><sub>R</sub> = 3.78 eV·Å), and the Rashba spin splitting of H-Pb-Cl(–16%—16%) can be adjusted by changing the biaxial stress. By analyzing the electronic properties of H-Pb-Cl, we find that H-Pb-Cl has a huge band gap near the Fermi surface (1.31 eV), and the topological invariant <i>Z</i><sub>2</sub> = 1 of the system is caused by the inversion of s-p orbit, which indicates that H-Pb-Cl is a two-dimensional topological insulator with a huge topological band gap, and the gap is large enough to observe the topological edge states at room temperature. In addition, we further consider the effect of BN and graphane substrates on the topological band gap of H-Pb-Cl by using the H-Pb-Cl (111)-(1×1) /BN (111)-(2×2) and H-Pb-Cl(1×1)/ graphane (2×2) system, and find that the lattice mismatch between H-Pb-Cl (5.395 Å) and BN (2.615 Å) and between H-Pb-Cl (5.395 Å) and graphane (2.575 Å) are about 3% and 4.5%, respectively. According to our calculation results, H-Pb-Cl still retains the properties of topological insulator under the effect of spin orbit coupling, and is not affected by BN nor graphane. Our results show that the nontrivial topological band gap of H-Pb-Cl can be well preserved under both biaxial stress effect and substrate effect. In addition, H-Pb-Cl can well retain the nontrivial topological band gap under the stress of –16%–16%, and thus there are many kinds of substrate materials used to synthesize this material, which is very helpful in successfully realizing preparation experimentally. Our research provides a promising candidate material for exploring and realizing the coexistence of Rashba spin splitting and quantum spin Hall effect. And the coexistence of giant Rashba spin splitting and quantum spin Hall effect greatly broadens the scope of potential applications of H-Pb-Cl in the field of spintronic devices.

PP-wave reflection coefficient in stress-induced anisotropic media and amplitude variation with incident angle and azimuth inversion

The PP-wave reflection coefficient (i.e., the ratio of the amplitude of reflected P wave to the amplitude of incident P wave) has crucial practical applications in many field scenarios, such as seismic inversion and in-situ stress monitoring. However, the effect of biaxial stress, frequently encountered in the earth’s interior, on the PP-wave reflection coefficient is seldom studied. To fill this gap, we first formulate the P- and S-wave moduli and density in a biaxial-stress-induced anisotropic medium based on the acoustoelasticity theory. Then, the stress-dependent anisotropy parameters and normal/tangential rock weaknesses are proposed in the context of the stress-induced anisotropy model to obtain the corresponding effective elastic stiffness tensor and its spatial perturbation. Two stress-induced anisotropy factors (SIAF) are established to quantify the magnitude of anisotropy in a stress-induced anisotropic medium. The media with large SIAF tend to demonstrate strong anisotropy when stressed and tend to be more easily fractured from the perspective of engineering application. Furthermore, an approximate formula for the PP-wave reflection coefficient for biaxial-stress-induced anisotropic media is developed with the scattering theory. Numerical results illustrate how the reflection coefficients are affected by horizontal biaxial stress and demonstrate the feasibility and accuracy of our formula. Modeled and field inversion examples illustrate that SIAF can be reasonably inverted with our amplitude variation with incident angle and azimuth inversion method from azimuthal seismic data. Our results help to better understand the effect of biaxial stress on anisotropy and wave propagation in stress-induced anisotropic media.

Simplified biaxial tension stiffening model for the analysis of shear panels using softened membrane model

Many of the existing tension stress–strain relations for concrete used in smeared shear models consider the contribution of concrete in tension even after steel yielding. Although the contribution of concrete in tension is less significant than its contribution in compression, the use of these existing models often leads to overestimating the shear response of reinforced concrete (RC) panels. An improved concrete tension stiffening model incorporating the effect of biaxial stresses is proposed in this study. The effect of tension stiffening on the behaviour of shear panels under normal and shear stresses is investigated by incorporating tension stiffening in the softened membrane model (SMM). The existing SMM algorithm can be used to estimate the behaviour of RC panels subjected only to pure shear. In the proposed analysis using SMM, a new secant-based algorithm is used to estimate the behaviour of RC panels under combined normal and shear loads. Estimates from the proposed model are compared with estimates from original SMM and experimental results. The comparison shows that the proposed model provides better estimates of shear response for RC panels that undergo high shear strains than the original SMM. Furthermore, the proposed secant-based algorithm estimates panel behaviour under combined loading in reduced computational time.

Effects of biaxial residual stress components on mixed-mode fatigue crack propagation behavior in friction stir welded 7075-T6 aluminium alloy panel

Residual stress in friction stir weld (FSW) joint significantly affects fatigue performance. It can often combine critically with the applied load cause premature fatigue failure. Research on the residual stress effects on fatigue behavior is required to assess the damage tolerance issues in FSW joints. In this study, the effect of biaxial residual stress components (longitudinal residual stress and transverse residual stress) on mixed-mode crack propagation behavior in FSWed 7075-T6 fuselage panel was studied. Residual stress profiles across the welded plate were measured by X-ray diffraction technique. Fatigue crack propagation for mode mixity angles of 30°, 45° and 60° were carried out. The stress intensity factors (SIFs) at the crack tip were evaluated by finite element method and used to study the effect of biaxial residual stress and the individual component on mixed-mode crack behaviors. The results show that the variation of crack path is strongly linked with the residual stress component as well as the initial oblique crack angle. SIF components are affected by the individual residual stress component. Both two components are required to study the mixed-mode crack propagation in FSWs.

Biaxial stress and strain effects on optical and electronic aspects of B2C nanostructure: a first-principles calculation

Biaxial stress and strain effects on optical and electronic aspects of B2C nanostructure: a first-principles calculation

Impact of applied biaxial stress on the piezoelectric, elastic, and dielectric properties of scandium aluminum nitride alloys determined by density functional perturbation theory

The effects of biaxial in-plane stress on the elastic, dielectric, and piezoelectric (PE) properties of c-axis textured thin film wurtzite phase scandium aluminum nitride (w-ScxAl1−xN) alloys have been calculated with density functional perturbation theory. The in-plane stress σR was kept below 1 GPa covering compressive and tensile values and applied to alloy supercells represented with special quasi-random structures. An increasingly tensile biaxial stress (σR > 0) produces higher displacement-response internal-strain coefficients for the constituent atoms of the alloy and the related PE properties are more sensitive to σR when the fraction x increases. A significant rise of the relative dielectric permittivity ϵr,33η and softening of the stiffness coefficient c33E are also reported with σR > 0. The effective thin film PE strain coefficient d33,f and coupling coefficient k33,f2 show a relative increase of 22% and 26%, respectively, at σR = 1 GPa and x = 0.438. Both tensile σR and x tend to decrease the c/a cell parameter ratio of the wurtzite structure with a significant impact on the PE coefficients. Based on the decomposition of the stiffness, dielectric, and PE coefficients as well as the structural data, it is suggested that tensile biaxial stress enhances the hexagonal character of w-ScxAl1−xN in a qualitatively similar manner as the scandium nitride fraction x does. The manufacture and PE characterization of a beneficially stressed thin film of w-ScxAl1−xN on a substrate of w-InyAl1−yN with adjusted x, y values are suggested to confirm the calculated values of d33,f.

A study of net-section resistance of high strength steel bolted connections

This article presents an experimental and numerical investigation on the net section resistance of high strength steel (HSS) bolted connections subject to double shear. A total of 22 HSS and 11 mild steel (MS) bolted connection specimens were tested to net section fracture. HSS grades of Q690 and Q960, and MS grade of Q345 were studied. Although the HSS material has relatively lower ductility and a lower ratio of tensile strength to yield strength (fu/fy) than those of the MS material, in general, the HSS connection specimens were able to reach the connection efficiency (i.e. the ratio of the ultimate load of the connection specimens to the calculated net section resistance) of above 1.0. Subsequently, the structural behaviour of the connections was studied by finite element (FE) analysis. The effects of material ductility and fu/fy ratio on the stress development across the net section of the specimens were examined. It was found that HSS materials possess sufficient ductility to allow an efficient stress redistribution across the net section. Besides, the beneficial influence of the ‘reinforcement’ or the biaxial stress effect due to the presence of holes in the connection increases the ultimate capacity of the perforated main plate, and hence the HSS specimens were able to reach the net section resistance. However, the overall deformation capability of the HSS specimens was significantly lower than that of the MS specimens. A reliability analysis was carried out to re-examine the partial factor used in the current design equation for predicting the net section resistance in Eurocode 3.

Bayesian Spectroscopy with a Replica Exchange Monte Carlo Method on an Excitonic Absorption Spectrum of a Cu2O Thin Crystal

To study a bi-axial stress effect in a Cu2O thin crystal sandwiched by paired MgO substrates, we have applied Bayesian spectroscopy to decompose an absorption spectrum with employing a replica exchange Monte Carlo (RXMC) method. The absorption spectrum includes broad bands of an inter-band transition and an exciton continuous state simultaneously with excitonic resonance transitions. However, it had been difficult to decompose correctly because of a bottleneck in optimal solution search efficiency. To relieve the bottleneck, we introduced the RXMC method and succeeded in decomposing all spectral components. Posterior probabilities of the band-gap energy and the exciton binding energy distribute at lower energy side than those in stress-free bulk crystals, which provides statistical evidence to show that the bi-axial stress remains in the Cu2O thin crystal sandwiched by MgO substrates.

The influence of surface stress and surface-induced internal residual stresses on the size-dependent behaviors of Kirchhoff microplate

The present paper develops a size-dependent Kirchhoff microplate model with surface effects by using simplified strain gradient elasticity theory and surface elasticity theory. This new model is able to capture size-dependent behaviors and surface effects. The most noticeable difference of the proposed model from the existing plate models about microplates is that not only strain gradient and surface stress are taken into account, but also the surface-induced internal residual stresses are considered. Based on whether the plates having surface-induced internal residual stress or not, their governing equations have distinct differences. An extended Kantorovich method is employed to provide approximate closed-form solution for the rectangular microplate with simply supported boundary conditions. For the microplate with biaxial initial residual surface stress, the numerical results reflect that when the simply supported microplates do not have surface-induced internal residual stresses, internal length scale and biaxial surface residual stress have significant influence on the static bending of the microplates. However, when the simply supported microplates have nonzero surface-induced internal residual stresses, the effects of internal length scale and biaxial surface residual stress become very weak. It indicates that the effect of surface-induced internal residual stresses can counteract most of the effects of internal length scale and surface residual stress. This work provides a more general model for the analysis of microplate problems.

Bayesian Spectroscopy on Polarization Dependent Photoluminescence Spectra of Doubly‐Split Excitons in a Cu2O Thin‐Crystal Sandwiched by MgO Substrates

By using Bayesian spectroscopy, we studied polarization dependence of photoluminescence (PL) spectra in doubly‐split 1S yellow ortho‐excitons in a Cu2O thin‐crystal recrystallized in a small gap between paired MgO substrates. In these thin‐crystals, biaxial stresses are expected to be involved due to a small lattice mismatch between Cu2O and MgO. Under a planar‐isotropic biaxial stress, the cubic symmetry degrades to the tetragonal one in Cu2O, and subsequently, the ortho‐exciton state splits into two states having different symmetries. Consequently, the resonant PL intensities of the doubly‐split ortho‐excitons are expected to show different polarization dependencies. To elucidate such biaxial stress effect, we measured polarization dependence of the PL spectra at 4.2 K. Although resonant weak PL bands of the doubly‐split exciton states and their intense phonon sidebands co‐exist, we succeeded in decomposing to the respective spectral components by the Bayesian spectroscopy with a replica exchange Monte Carlo algorithm. As a result, it is found that the resonant PL band appearing on higher energy side shows hardly polarization dependence, whereas the resonant PL band appearing on lower energy side is further weak and shows noticeable polarization dependence. These results can be explained by the selection rule and polarization dependences on the transition matrix elements of quadrupole transitions of the doubly‐split ortho‐exciton states, and it clearly shows that the crystal symmetry degrades to D4h by the isotropic biaxial stress involved in the Cu2O thin‐crystals.

English

The stress strain behavior of nanostructure carbon reinforced rubber composites was studied. The effect of both uniaxial and biaxial tensile stress on electrical conductivity of our samples was investigated. We have noticed that electrical conductivity decreased on applying uniaxial loading and increased with increasing biaxial tensile ones. Both elastic modulus and yield points in uniaxial and biaxial mode of stress were obtained and compared with increasing the concentration of nano-filler. Calculated values of the knee point strains have been obtained, and we made a fitting for our experimental results.

Stress-Mediated Enhancement of Ionic Conductivity in Fast-Ion Conductors.

Finding solid-state electrolytes with high ionic conductivity near room temperature is an important prerequisite for developing all-solid-state electrochemical batteries. Here, we investigate the effects of point defects (vacancies) and biaxial stress on the superionic properties of fast-ion conductors (represented by the archetypal compounds CaF2, Li-rich antiperovskite Li3OCl, and AgI) by using classical molecular dynamics and first-principles simulation methods. We find that the critical superionic temperature of all analyzed families of fast-ion conductors can be reduced by several hundreds of degrees through the application of relatively small biaxial stresses (|σ| ≤ 1 GPa) on slightly defective samples (cv ∼ 1%). In AgI, we show that superionicity can be triggered at room temperature by applying a moderate compressive biaxial stress of ∼1 GPa. In this case, we reveal the existence of a σ-induced order-disorder phase transition involving sizable displacements of all the ions with respect to the equilibrium lattice that occurs prior to the stabilization of the superionic state. In CaF2 and Li3OCl, by contrast, we find that tensile biaxial stress (σ < 0) favors ionic conductivity as due to an effective increase of the volume available to interstitial ions, which lowers the formation energy of Frenkel pair defects. Our findings provide valuable microscopic insight into the behavior of fast-ion conductors under mechanical constraints, showing that biaxial stress (or, conversely, epitaxial strain) can be used as an effective means to enhance ionic conductivity.

Bond strength prediction for plain bars under lateral tensile compressive stresses

The bond strength of plain bars plays an important role in assessing the anchorage capacity of historical buildings. For plain bars, the bond strength greatly depends on the frictional effect, and can easily be affected by the lateral stress around the bars. For bars located in the beam–column joint, the lateral compressive–tensile stresses from gravity and earthquakes might be applied simultaneously. To date, the effect of such biaxial stresses on the bond strength of plain bars has not been evaluated in an analytical manner. Consequently, an analytical approach combining both theoretical and numerical solutions to the bond strength of plain round bars under biaxial tensile compressive stresses is developed. Comparison between test data and the results calculated by the proposed analytical model shows that the model is well capable of predicting the bond strength for different concrete and bars. Moreover, the comparative studies between the proposed analytical model and closed-form solutions show that the partial separation of the bond interface due to the biaxial stresses cannot be ignored in predicting the bond strength of plain bars. Finally, a simplified model with acceptable precision is suggested to substitute for the numerical procedure in the proposed analytical model.

Influences of small defects on torsional fatigue limit of 17-4PH stainless steel

The sensitivity of 17-4PH stainless steel to small defects under torsional fatigue loading condition at a stress ratio of R=−1 is examined in the high-cycle fatigue regime. Fatigue crack initiation and growth behaviors are observed, and fractographic investigations are performed. As a key geometric parameter, area is used to investigate the influence of small defects on torsional fatigue limit. Further, the results are compared to the data obtained in the uniaxial fatigue tests, which allows the effect of biaxial stresses on the surface of the material to be discussed.

Electronic and optical properties of beryllium sulfide monolayer: Under stress and strain conditions

Electronic and optical properties of two-dimensional graphene-like structure of beryllium sulfide (BeS) have been studied in the framework of the density functional theory. Different values of stress and strain are exerted for tuning electronic and optical parameters. The electronic results show that both biaxial stress and strain effects cause band gap reduction with different rates. Also, we have red and blue shifts in the optical absorption spectrum peaks by applying strain and stress, respectively. Our results express that BeS monolayer can be the promising candidate for the future nano-devices.

High cycle torsional fatigue properties of 17-4PH stainless steel

Sensitivity to small defects under torsional fatigue loading condition is examined in the high cycle fatigue regime. Fatigue crack initiation and small crack growth behaviors were observed during fatigue testing and fractographic investigations were performed. The results are compared to the data obtained in the uniaxial fatigue tests, which allows the effect of biaxial stresses on the surface of material to be discussed. Finally, an approach for predicting the fatigue limit of 17-4PH stainless steel under torsional and tension-compression fatigue loadings is presented.

Tuning of the electronic and optical properties of single-layer boron nitride by strain and stress

Electronic and optical properties of boron nitride monolayer have been studied by full potential augmented plane waves plus local orbital (FP-APW+lo) in the framework of the density functional theory. For achieving new applications, biaxial stress and strain effects on electronic and optical properties have been investigated. The results show that by exerting stress and strain on BN nanosheet, we can control energy band gap of this nanostructure. Optical calculations present that applying stress and strain does not have remarkable influence on the reflectivity spectrum while it changes energy gap direction. All obtained results express that BN monolayer is a good candidate for optoelectronic applications.

Direct Observation of the Biaxial Stress Effect on Efficiency Droop in GaN-based Light-emitting Diode under Electrical Injection.

Light-emitting diode (LED) efficiency has attracted considerable interest because of the extended use of solid-state lighting. Owing to lack of direct measurement, identification of the reasons for efficiency droop has been restricted. A direct measurement technique is developed in this work for characterization of biaxial stress in GaN-based blue LEDs under electrical injection. The Raman shift of the GaN E2 mode evidently decreases by 4.4 cm−1 as the driving current on GaN-based LEDs increases to 700 mA. Biaxial compressive stress is released initially and biaxial tensile stress builds up as the current increases with respect to the value of stress-free GaN. First-principles calculations reveal that electron accumulation is responsible for the stress variation in InxGa1−xN/GaN quantum wells, and then reduces the transition probability among quantum levels. This behavior is consistent with the measured current-dependent external quantum efficiency. The rule of biaxial stress-dependent efficiency is further validated by controlling the biaxial stress of GaN-based LEDs with different sapphire substrate thicknesses. This work provides a method for direct observation of the biaxial stress effect on efficiency droop in LEDs under electrical injection.

Ge1 − xSix on Ge-based n-type metal–oxide semiconductor field-effect transistors by device simulation combined with high-order stress–piezoresistive relationships

The considerably high carrier mobility of Ge makes Ge-based channels a promising candidate for enhancing the performance of next-generation devices. The n-type metal–oxide semiconductor field-effect transistor (nMOSFET) is fabricated by introducing the epitaxial growth of high-quality Ge-rich Ge1−xSix alloys in source/drain (S/D) regions. However, the short channel effect is rarely considered in the performance analysis of Ge-based devices. In this study, the gate-width dependence of a 20nm Ge-based nMOSFET on electron mobility is investigated. This investigation uses simulated fabrication procedures combined with the relationship of the interaction between stress components and piezoresistive coefficients at high-order terms. Ge1−xSix alloys, namely, Ge0.96Si0.04, Ge0.93Si0.07, and Ge0.86Si0.14, are individually tested and embedded into the S/D region of the proposed device layout and are used in the model of stress estimation. Moreover, a 1.0GPa tensile contact etching stop layer (CESL) is induced to explore the effect of bi-axial stress on device geometry and subsequent mobility variation. Gate widths ranging from 30nm to 4μm are examined. Results show a significant change in stress when the width is <300nm. This phenomenon becomes notable when the Si in the Ge1−xSix alloy is increased. The stress contours of the Ge channel confirm the high stress components induced by the Ge0.86Si0.14 stressor within the device channel. Furthermore, the stresses (Syy) of the channel in the transverse direction become tensile when CESL is introduced. Furthermore, when pure S/D Ge1−xSix alloys are used, a maximum mobility gain of 28.6% occurs with an ~70nm gate width. A 58.4% increase in mobility gain is obtained when a 1.0GPa CESL is loaded. However, results indicate that gate width is extended to 200nm at this point.