Effect Of Uniaxial Stress Research Articles

Effect of Uniaxial Compressive Stress during Formation of Porous Aluminum by Mechanochemical Reaction on its Mechanical Properties

Porous Al is a lightweight material with excellent heat insulation and sound absorption properties and is expected to be used in a wide range of applications. A method based on mechanochemical reactions has been developed as an environmentally friendly approach to porous Al production. Pure Al powder reacts with pure water to form a coating layer of Al (OH)3 on the surface of the powder particles. Adjacent particles then bind together by adhesion of their coating layers. Since a large number of voids remain between the individual particles, the compact is classified as porous Al. In the present study, a mixture of pure Al powder and pure water was subjected to uniaxial compressive stresses ranging from 0 to 100 MPa to form porous Al. The mechanical properties of the resulting compact were evaluated in terms of the amount of H2 produced, the density, the Al (OH)3 texture, the amount of Al (OH)3 formed, and the results of subsequent compression tests. The density of the porous Al was found to increase with increasing compressive stress during formation. The largest amounts of H2 (800 ml) were produced under a compressive stress of 10 MPa. As the compressive stress was increased, the total amount of generated Al (OH)3 increased, was approximately constant from 30 to 50 MPa, and then decreased. The initial maximum stress, the plateau stress, and the absorbed energy increased with increasing compressive stress and were 100 MPa, 17.5 MPa, and 10.1 MJ/m3, respectively, for a compressive stress of 100 MPa.

Effect of Uniaxial Compressive Stress on the Partially Fatigued Soft Lead Zirconate Titanate Piezoelectric Ceramics

Uniaxial compressive stress was applied during fatigue process of soft lead zirconate titanate piezoelectric ceramics and their fatigue resistance was improved when the stress was larger than 20MPa. Before fatigue, compressive stress had a strong depolarization effect and restricted domains switching behavior under large electric field and domain walls motion under small electric field. However, in a partially fatigued state, while domains switching behavior was still restricted by compressive stress, domain walls motion was enhanced. Removal of the applied stress after partial fatigue induced the remnant polarization restored significantly.

Optimization of uniaxial stress for high electron mobility on biaxially-strained n-MOSFETs

The uniaxial stress effect for high electron mobility on biaxially-strained n-MOSFET is investigated by using a one-dimensional self-consistent Schrödinger–Poisson solver. The electron mobility model includes Coulomb, intravalley phonon, intervalley phonon, and surface roughness scattering. We have found that the uniaxial stress effect on biaxially-strained n-MOSFET is significantly different from the uniaxial stress effect on unstrained Si n-MOSFET. It is well known that longitudinal and transverse tensile uniaxial stresses are advantageous for strain-induced high electron mobility. However, we found that the uniaxial strain condition for electron mobility enhancement is changed when it is applied to the biaxially-strained n-MOSFET. To optimize the combined effect of uniaxial and biaxial strain, the longitudinal tensile and transverse compressive uniaxial stresses are advantageous and vertical stress is not helpful for biaxially-strained n-MOSFET.

On the threshold voltage of nanoscale bulk nMOSFETs with [110]/(001) uniaxial stress and quantum effects

Due to the large electron mobility gain cased by uniaxial stress along the [110] directions on (001) silicon substrate, in this paper, the impact of [110]/(001) uniaxial strain and quantum mechanical effects (QMEs) on the threshold voltage of strained-Silicon nMOSFETs is studied by developing a physically-based model. The impact of [110]/(001) stress on the band structure parameters such as density-of-state (DOS) in the conduction and valance band, band-gap and intrinsic carrier concentration is quantized first. Based on a modified threshold surface potential, the threshold voltage model is then proposed by solving the 2-D Poisson's equation and also by taking short channel effects, quantum effects and other secondary effects into consideration. Our analytical results agree with both TCAD and experimental data. The threshold voltage with the stress along arbitrary orientation can be analyzed analogously. This model can also be used for the design of nanoscale strained-Si nMOSFETs.

Experimental verification of the uniaxial stress-optic law in the terahertz frequency regime

The stress-optic law is fundamental to photoelasticity, and has been a prevalent method for measuring stress. However, its effectiveness in the terahertz (THz) regime has not been completely characterized. In this paper, the effects of uniaxial tensile stress on THz transmission through a polytetrafluoroethylene (PTFE) sample are investigated. Specifically, THz time domain spectroscopy (THz-TDS) has been used to measure the phase delay of transmitted THz radiation for different PTFE stress states. Differences in the refractive index of the PTFE are calculated from the measured phase delay. The calculated refractive index grows linearly with the applied stress, which can be considered a verification of the uniaxial stress-optic law in the terahertz frequency regime.

In-plane uniaxial stress effects on the structural and electronic properties of BaFe2As2and CaFe2As2

Starting from the orthorhombic magnetically ordered phase, we investigate the effects of uniaxial tensile and compressive stresses along a, b, and the diagonal a+b directions in BaFe${}_{2}$As${}_{2}$ and CaFe${}_{2}$As${}_{2}$ in the framework of ab initio density functional theory (DFT) and a phenomonological Ginzburg-Landau model. While---contrary to the application of hydrostatic or $c$-axis uniaxial pressure---both systems remain in the orthorhombic phase with a pressure-dependent nonzero magnetic moment, we observe a sign-changing jump in the orthorhombicity at a critical uniaxial pressure, accompanied by a reversal of the orbital occupancy and a switch between the ferromagnetic and antiferromagnetic directions. Our Ginzburg-Landau analysis reveals that this behavior is a direct consequence of the competition between the intrinsic magneto-elastic coupling of the system and the applied compressive stress, which helps the system to overcome the energy barrier between the two possible magneto-elastic ground states. Our results shed light on the mechanisms involved in the detwinning process of an orthorhombic iron-pnictide crystal and on the changes in the magnetic properties of a system under uniaxial stress.

Physical Mechanism of Enhanced Uniaxial Stress Effect on Carrier Mobility in ETSOI MOSFETs

This paper presents the comprehensive study of strain effect on carrier mobility in ETSOI MOSFETs. We firstly demonstrate that the mobility enhancement ratio increases as SOI thickness (TSOI) decreases from 60 nm to 4 nm by applying the uniaxial <110> tensile stress parallel to the channel. On the other hand, by applying the uniaxial <110> tensile stress perpendicular to the channel, mobility enhancement ratio does not necessarily increase as TSOI decreases. We discuss this result in terms of deformation potential (Dac) and effective mass (m*).

Tuning the Light Emission from GaAs Nanowires over 290 meV with Uniaxial Strain

Strain engineering has been used to increase the charge carrier mobility of complementary metal-oxide-semiconductor transistors as well as to boost and tune the performance of optoelectronic devices, enabling wavelength tuning, polarization selectivity and suppression of temperature drifts. Semiconducting nanowires benefit from enhanced mechanical properties, such as increased yield strength, that turn out to be beneficial to amplify strain effects. Here we use photoluminescence (PL) to study the effect of uniaxial stress on the electronic properties of GaAs/Al0.3Ga0.7As/GaAs core/shell nanowires. Both compressive and tensile mechanical stress were applied continuously and reversibly to the nanowire, resulting in a remarkable decrease of the bandgap of up to 296 meV at 3.5% of strain. Raman spectra were measured and analyzed to determine the axial strain in the nanowire and the Poisson ratio in the <111> direction. In both PL and Raman spectra, we observe fingerprints of symmetry breaking due to anisotropic deformation of the nanowire. The shifts observed in the PL and Raman spectra are well described by bulk deformation potentials for band structure and phonon energies. The fact that exceptionally high elastic strain can be applied to semiconducting nanowires makes them ideally suited for novel device applications that require a tuning of the band structure over a broad range.

The effect of externally applied uniaxial compressive stress on the magnetic properties of power MnZn-ferrites

In this article, the effect of uniaxial compressive stress with magnitude up to ~53 MPa on the magnetic properties of power MnZn-ferrites of the general chemical formula Mn0.81Zn0.19Fe2+δΟ4 has been investigated. In addition, the effects of various process operational or material structural parameters such as sintering partial pressure of oxygen, final density and grain size on the stress sensitivity of the polycrystalline component have been studied. As found, the temperature of the secondary initial permeability maximum and the power loss minimum are reduced by ~0.5 °C MPa−1 while the magnetic flux density by ~1.4 mT MPa−1 upon the exertion of uniaxial compressive stress on the component. The sintering partial pressure of oxygen exhibits an optimum at which the material stress sensitivity becomes minimum. The results have been explained on the basis of variations induced in the anisotropy field as well as on the basis of the defect structure of the material and its dependency on the partial pressure of oxygen.

Effect of uniaxial stress on photon localization of one-dimensional photonic crystal with a mirror symmetry

In this paper, the transfer matrix method is used to study the characteristics of the photon localization in the mirror heterogeneous structure which has three periods and one-dimensional photonic crystal in uniaxial stress change. In a mirror structure triply-periodic photonic crystal system, its mirror structure destroys the orderliness of the photonic crystal and produces a defect state, so the transmission peaks of a photon localization appear in the photonic band gap wider center. The study shows that when a uniaxial stress is exerted on the mirror structure with three-periodic photonic crystal, the photon localization transmittance peak dramatically changes with the stress. When a weak external mechanical stress is applied to the photonic crystal, photonic crystal forms a tensile strain which induces the change in the photonic crystal structure and significantly affects the rate of the transmittance peak transmittance of photon localization. The results show that the transmission peak transmittance is significantly influenced by the uniaxial stress. These features provide a theoretical reference for the design of ultra-high-sensitivity pressure sensor with the photonic crystal structure.

Effect of Mechanical Stress on Magnetic States and Hysteresis Characteristics of a Two‐Phase Nanoparticles System

In terms of the two‐phase nanoparticles model, the effect of mechanical stress on the magnetic state of both uniaxial and multiaxial heterophase magnetic is investigated. The spectrum of critical fields of reversal of phases′ magnetic moments was calculated and phase diagrams were drawn to assess the effect of mechanical stress on the degree of metastability of two‐phase nanoparticles′ magnetic states. By the example of epitaxial cobalt‐coated γ‐Fe2O3 particles, a theoretical analysis of the effect of uniaxial mechanical stress on the magnetization of a system of noninteracting heterophase nanoparticles is investigated. It was shown that tension reduced and compression increased coercive force Hc, while the residual saturation magnetization Irs was not changed under the influence of mechanical stress.

Effect of uniaxial stress on electroluminescence, valence band modification, optical gain, and polarization modes in tensile strained p-AlGaAs/GaAsP/n-AlGaAs laser diode structures: Numerical calculations and experimental results

The effects of uniaxial compression in [110] direction on energy-band structures, heavy and light hole mixing, optical matrix elements, and gain in laser diodes with “light hole up” configuration of valence band levels in GaAsP quantum wells with different widths and phosphorus contents are numerically calculated. The development of light and heavy hole mixing caused by symmetry lowering and converging behavior of light and heavy hole levels in such quantum wells under uniaxial compression is displayed. The light or heavy hole nature of each level is established for all considered values of uniaxial stress. The results of optical gain calculations for TM and TE polarization modes show that uniaxial compression leads to a significant increase of the TE mode and a minor decrease of the TM mode. Electroluminescence experiments were performed under uniaxial compression up to 5 kbar at 77 K on a model laser diode structure (p-AlxGa1−xAs/GaAs1−yPy/n-AlxGa1−xAs) with y = 0.16 and a quantum well width of 14 nm. They reveal a maximum blue shift of 27 meV of the electroluminescence spectra that is well described by the calculated change of the optical gap and the increase of the intensity being referred to a TE mode enhancement. Numerical calculations and electroluminescence data indicate that uniaxial compression may be used for a moderate wavelength and TM/TE intensity ratio tuning.

Wavelength‐modulated excitonic spectra in green series of Cu2O thin films sandwiched by MgO plates

AbstractIn order to clarify uniaxial stress effects on a green excitonic series in Cu2O, we measured temperature dependence of wavelength modulated (WM) absorption spectra of a Cu2O thin film sandwiched by MgO plates. In these spectra, excitonic resonances of 2P∼4P states are clearly observed even at 180 K. From these resonance spectral structures at each temperature, it is found that the band gap of the green series shifts to lower energy side than that of bulk crystals and the red shift becomes obvious with cooling down to 7 K. These results indicate that the trapping potential for the green excitons is formed by the uniaxial stress due to a lattice mismatch between the Cu2O and MgO (© 2012 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Electro-Elastic Tuning of Single Particles in Individual Self-Assembled Quantum Dots

We investigate the effect of uniaxial stress on InGaAs quantum dots in a charge tunable device. Using Coulomb blockade and photoluminescence, we observe that significant tuning of single particle energies (≈-0.22 meV/MPa) leads to variable tuning of exciton energies (+18 to -0.9 μeV/MPa) under tensile stress. Modest tuning of the permanent dipole, Coulomb interaction and fine-structure splitting energies is also measured. We exploit the variable exciton response to tune multiple quantum dots on the same chip into resonance.

Physical Mechanism of Enhanced Uniaxial Stress Effect on Carrier Mobility in ETSOI MOSFETs

not Available.

Effect of uniaxial stress on the birefringence of triglycine sulphate crystals doped with L threonine

The temperature and spectral dependences of the birefringence Δn i of triglycine sulphate (TGS) crystals with L-threonine impurity have been investigated. Doping with L-threonine is found to reduce the temperature dependence of Δn i of TGS crystals. The baric coefficients of shift of the phase-transition (PT) point, ∂T c /∂σm, are found to be somewhat smaller than those for pure TGS crystals, which is confirmed by the increase in the hardness of TGS crystals after doping. The temperature and spectral dependences of the combined piezoelectric constants π im 0 have been calculated. The stepwise changes in all piezoelectric constants at the PT of doped crystals are found to be much smaller than those for pure crystals.

Effect of tensile stress on the in-plane resistivity anisotropy in BaFe2As2

The effect of uniaxial tensile stress and the resultant strain on the structural/magnetic transition in the parent compound of the iron arsenide superconductor, BaFe$_2$As$_2$, is characterized by temperature-dependent electrical resistivity, x-ray diffraction and quantitative polarized light imaging. We show that strain induces a measurable uniaxial structural distortion above the first-order magnetic transition and significantly smears the structural transition. This response is different from that found in another parent compound, SrFe$_2$As$_2$, where the coupled structural and magnetic transitions are strongly first order. This difference in the structural responses explains the in-plain resistivity anisotropy above the transition in BaFe$_2$As$_2$. This conclusion is supported by the Ginzburg-Landau - type phenomenological model for the effect of the uniaxial strain on the resistivity anisotropy.

An experimental investigation of corrosion of X100 pipeline steel under uniaxial elastic stress in a near-neutral pH solution

In this work, the effect of uniaxial elastic stress on corrosion of X100 pipeline steel in a near-neutral pH solution was investigated by localized electrochemical impedance spectroscopy (LEIS), corrosion potential and electrochemical impedance measurements, surface analysis techniques as well as finite element analysis. No effect of the static elastic stress on electrochemical corrosion potential of the steel is detected. The critical failure strain of corrosion scale formed on the steel surface is calculated to be 0.00357–0.00417, which is higher than the maximum strain of 0.0029 generated on the specimen. Thus, corrosion scale does not fracture during loading. No difference in the steady-state corrosion potential could be detected upon application of an elastic tensile or compressive stress. If the scale is pre-formed on the steel surface, the applied dynamic elastic load would “weaken” the scale by expanding its pores, and thus, increase the steel corrosion. While a dynamic tensile stress enhances the steel corrosion, the dynamic compressive stress would inhibit corrosion of the steel. This work provides important recommendations for pipeline safety design, where the corrosion enhancement due to the dynamic elastic stress should be considered.

Magnetostrictive properties of directional solidification Fe82Ga9Al9 alloy

Fe82Ga9Al9 alloy rod was prepared by the directional solidification (DS) method. The effects of uniaxial compressive stress on magnetostriction of the alloy and the temperature dependence of magnetostriction were investigated. The results show that the magnetostriction increases from 135 × 10−6 at 2.3 MPa to 221 × 10−6 at 53 MPa and then remains at this value between 53 MPa and 90 MPa. This enhancement results from domain rotation under the compressive stress. The temperature dependence results show that the saturated magnetostriction decreases by 11% (25 °C–120 °C) and 13% (25 °C–100 °C) for samples with 0 MPa and 15 MPa compressive stress applied, respectively. This decrease is due to reduced magnetic crystalline anisotropy as the temperature increases. Under the compressive stress conditions, the magnetostriction decreases more notably.

Effect of Mechanical Stresses on the Coercive Force of the Heterophase Non-Interacting Nanoparticles

The theoretical analysis of the effect of uniaxial stress on the magnetization of the system of noninteracting nanoparticles is done by an example of heterophase particles of maghemite, epitaxially coated with cobalt ferrite. It is shown that stretching leads to a decrease in the coercive force Hc, and compression leads to its growth. The residual saturation magnetization Irs of nanoparticles does not change. With increasing of interfacial exchange interaction, coercive force varies nonmonotonically.