Uniaxial Mechanical Stress Research Articles

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.

Nanorod orientation dependence of tunable Fano resonance in plasmonic nanorod heptamers

We present orientation dependence and tuning of Fano resonances in plasmonic gold nanorod heptamer nanostructures. The heptamer structures were formed by surrounding a central circular nanoparticle by six satellite nanorods in a hexagonal arrangement and the heptamer structures were then embedded in a thin flexible membrane. The Fano resonance was found to depend on the orientation of the nanorods within the heptamer and for a given orientation, the Fano resonance was dynamically tuned and its symmetry lowered by application of uniaxial mechanical stress. The expected spectral features were obtained by simulations and verified by experiments. The spectral features of the heptamer structures were further characterized by using detailed group theoretical analysis. We show that both sub-structural and mechanical tuning could be employed to engineer the Fano resonances in complex plasmonic molecules.

Effects of mechanical-bending and process-induced stresses on metal effective work function

Effective work function (EWF) change is investigated under both externally-applied mechanical stresses and process-induced stresses. Four-point wafer bending and ring bending techniques are used to generate uniaxial and biaxial mechanical stresses, respectively. For the process-induced stresses, bowing technique and charge pumping method are used for stress characterization and interface state measurement. It was found that higher stress presents in devices with thinner metal gate, regardless the thermal treatment cycle. EWF decreases under both tensile and compressive stress was observed due to the increase of defect activation energy lowering induced donor-like interface states.

Comparative Study of Biaxial and Uniaxial Mechanical Stress Influence on the Low Frequency Noise of Fully Depleted SOI nMOSFETs Operating in Triode and Saturation Regime

This paper presents an experimental comparative study of uniaxial and biaxial strain techniques influence on the low frequency noise of planar fully depleted SOI nMOSFETs operating in linear and saturation regimes. The comparison between devices from the same technology with these two strained techniques demonstrated a reduction of low frequency noise for devices with both strain technologies in linear regime for shorter devices (below 410 nm). In saturation regime the reduction of low frequency noise for uniaxial and biaxial strain also occurs, but does not depend on the channel length, and the reduction of low frequency noise in favor of both strain technologies is more pronounced for channel length of 160 nm.

In-situ neutron diffraction study of Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystals under uniaxial mechanical stress

In this paper, we report the phase transition behavior of ternary relaxor ferroelectric single crystals of 0.25Pb(In1/2Nb1/2)O3-0.44Pb(Mg1/3Nb2/3)O3-0.31PbTiO3 subject to a uniaxial mechanical stress up to 400 MPa. The resultant in situ neutron diffraction data are interpreted in terms of the polarization rotation theory and provide direct structural evidence for the stress-induced polarization rotation pathway deduced from studies of macroscopic physical properties under stress. It is suggested that an intermediate, metastable orthorhombic phase is induced above a critical pressure of ∼75 MPa. This critical stress level appears to be unaffected by sample poling although the ground states (at zero stress) for the poled and unpoled crystals are different. The critical stress level, however, does decrease with increasing temperature. The elastic behavior of the intermediate phases is also studied based on a calculation of the associated lattice strains.

Pressure stimulated electrical emissions from cement mortar used as failure predictors

The electrical signals emitted during the application of uniaxial compressive mechanical stress upon cement mortar specimens are observed and discussed in this paper. This work discusses the electrical signals that are detected when the specimens are excited by a stepwise uniaxial stress increase from a low level (σ L ) to a higher level (σ H ) at a fast or slow rate and consequently remain at a high pressure regime for a long time. When maintaining constant mechanical stress for a long time, creep phenomena are evident in the specimen and the corresponding electrical emissions are recorded and analyzed. The characteristics of the electrical signal give clear information regarding the breaking stress (σ F ) of the material. The electrical emission recordings are of great interest when the applied σ H is located in the vicinity of the failure stress; the emitted electrical current increases greatly due to the sequential formation and propagation of cracks that occurs in this stress region. Thus, by correlating the strain rate variations to the electrical emissions this methodology can be used to predict failure due to compressive stress in cement mortars.

Dynamic Tuning and Symmetry Lowering of Fano Resonance in Plasmonic Nanostructure

We present dynamic tuning and symmetry lowering of Fano resonances in gold heptamers accomplished by applying uniaxial mechanical stress. The flexible heptamer structure was obtained by embedding the seven-gold-nanocylinder complex in a polydimethylsiloxane membrane. Under uniaxial stress, the Fano resonance exhibited opposite spectral shifts for the two orthogonal polarizations parallel and perpendicular to the mechanical stress. Furthermore, a new resonance was observed for polarization parallel to the mechanical stress but not for the perpendicular polarization. The experimental results showed good agreement with the numerical simulations. A detailed group theoretical analysis showed that the symmetry lowering caused by the mechanical stress not only splits the originally degenerate mode but also modifies the originally optically inactive mode into an optically active mode, which then interacts strongly with a closely spaced mode and exhibits anticrossing behavior. The symmetry tuning enabled by applying mechanical stress is a simple and efficient way to engineer the nature of coupled plasmon resonances in complex nanostructures. The mechanically tunable plasmonic nanostructures also provide an excellent platform for dynamically tunable nanophotonic devices such as tunable filters and sensors.

Effect of mechanical stresses on the initial susceptibility and hysteresis characteristics of an ensemble of nanoparticles

Effect of uniaxial mechanical stresses on the initial susceptibility, saturation remanence, and coercive force of materials in which single-domain nanoparticles are carriers of magnetic properties has been studied theoretically. It has been shown that at small elastic stresses the above characteristics vary linearly; with increasing stresses, the growth of tensile stresses leads to a nonmonotonic variation of these characteristics, and the growth of compressive stresses, to a continuous decrease in the susceptibility and remanence and to an increase in the coercive force. With increasing plastic deformations, the position of the maximum in the stress dependence of the saturation remanence (or initial susceptibility) and the position of the minimum in the coercive force dependence are shifted to the region of greater values.

Comparison between SOI nMOSFET's under Uniaxial and Biaxial Mechanical Stress in Analog Applications

This work presents a study comparing the analog performance of uniaxially and biaxially strained planar Silicon-on-Insulator nMOSFETs for a wide range of channel lengths. The study is performed via two-dimensional numerical and process simulation and supported by experimental measurements. The comparison between devices from the same technology with these two strained techniques demonstrated that higher intrinsic voltage gain is obtained for biaxial mechanical stress. However, the transconductance is higher for uniaxial mechanical stress for shorter devices (below 550 nm) leading to larger unity gain frequency. On the other hand, despite both strain techniques degrades the output conductance, this degradation with channel length shortening is less pronounced for devices under biaxial mechanical stress.

Biomechanical wall properties of human intracranial aneurysms resected following surgical clipping (IRRAs Project)

Background and purpose Individual rupture risk assessment of intracranial aneurysms is a major issue in the clinical management of asymptomatic aneurysms. Aneurysm rupture occurs when wall tension exceeds the strength limit of the wall tissue. At present, aneurysmal wall mechanics are poorly understood and thus, risk assessment involving mechanical properties is inexistent. Aneurysm computational hemodynamics studies make the assumption of rigid walls, an arguable simplification. We therefore aim to assess mechanical properties of ruptured and unruptured intracranial aneurysms in order to provide the foundation for future patient-specific aneurysmal risk assessment. This work also challenges some of the currently held hypotheses in computational flow hemodynamics research. Methods A specific conservation protocol was applied to aneurysmal tissues following clipping and resection in order to preserve their mechanical properties . Sixteen intracranial aneurysms (11 female, 5 male) underwent mechanical uniaxial stress tests under physiological conditions, temperature, and saline isotonic solution. These represented 11 unruptured and 5 ruptured aneurysms. Stress/strain curves were then obtained for each sample, and a fitting algorithm was applied following a 3-parameter ( C 10, C 01, C 11) Mooney–Rivlin hyperelastic model. Each aneurysm was classified according to its biomechanical properties and (un)rupture status. Results Tissue testing demonstrated three main tissue classes: Soft, Rigid, and Intermediate. All unruptured aneurysms presented a more Rigid tissue than ruptured or pre-ruptured aneurysms within each gender subgroup. Wall thickness was not correlated to aneurysmal status (ruptured/unruptured). An Intermediate subgroup of unruptured aneurysms with softer tissue characteristic was identified and correlated with multiple documented risk factors of rupture. Conclusion There is a significant modification in biomechanical properties between ruptured aneurysm, presenting a soft tissue and unruptured aneurysms, presenting a rigid material. This finding strongly supports the idea that a biomechanical risk factor based assessment should be utilized in the to improve the therapeutic decision making.

Growth of Engineered Human Myocardium With Mechanical Loading and Vascular Coculture

The developing heart requires both mechanical load and vascularization to reach its proper size, yet the regulation of human heart growth by these processes is poorly understood. We seek to elucidate the responses of immature human myocardium to mechanical load and vascularization using tissue engineering approaches. Using human embryonic stem cell and human induced pluripotent stem cell-derived cardiomyocytes in a 3-dimensional collagen matrix, we show that uniaxial mechanical stress conditioning promotes 2-fold increases in cardiomyocyte and matrix fiber alignment and enhances myofibrillogenesis and sarcomeric banding. Furthermore, cyclic stress conditioning markedly increases cardiomyocyte hypertrophy (2.2-fold) and proliferation rates (21%) versus unconditioned constructs. Addition of endothelial cells enhances cardiomyocyte proliferation under all stress conditions (14% to 19%), and addition of stromal supporting cells enhances formation of vessel-like structures by ≈10-fold. Furthermore, these optimized human cardiac tissue constructs generate Starling curves, increasing their active force in response to increased resting length. When transplanted onto hearts of athymic rats, the human myocardium survives and forms grafts closely apposed to host myocardium. The grafts contain human microvessels that are perfused by the host coronary circulation. Our results indicate that both mechanical load and vascular cell coculture control cardiomyocyte proliferation, and that mechanical load further controls the hypertrophy and architecture of engineered human myocardium. Such constructs may be useful for studying human cardiac development as well as for regenerative therapy.

Effect of pressure and mechanical stress on the electronic properties of AlN and GaN

The fundamental properties of the AlN and GaN compounds with a wurtzite structure under external hydrostatic pressure, uniaxial mechanical stress σ⊥ along the hexagonal axis, and biaxial mechanical stress σ⊥ in the basal plane of the unit cell have been considered in terms of first-principles calculations in the frame-work of the density functional theory. The pressures of the phase transitions from the structures of wurtzite and zinc blende to the structure of rock salt have been obtained. The behavior of the structural parameters, interband transitions, and positions of the charge neutrality level has been investigated. The calculated pressure coefficients of the band gap are as follows: ∂E g /∂p = 40.9 meV/GPa, −∂E g /∂σ | = −4.2 meV/GPa, and −∂E g /∂σ ⊥ = 45.2 meV/GPa for AlN and ∂E g /∂p = 33.0 meV/GPa, −∂E g /∂σ | = 23.6 meV/GPa, and −∂E g /∂σ ⊥ = 9.6 meV/GPa for GaN. The pressure coefficients of the charge neutrality level in almost all cases are substantially smaller than the corresponding values obtained for the band gap E g .

Study of Weak Electric Current Emissions on Cement Mortar under Uniaxial Compressional Mechanical Stress up to the Vicinity of Fracture

An experimental technique that deals with the detection of weak electric signals emitted during the application of temporal uniaxial stress on solid materials has been applied on cement mortar samples. These electric signals are met in the literature as Pressure Stimulated Currents (PSC). Two different stress techniques were applied: uniaxial compressional stress at a) a low and b) at a high rate. Both qualitative and quantitative characteristics of the PSC are correlated with the mechanical state of the samples with respect to crack creation and propagation in the bulk of the material and consequently with the stages of composite damage.

Compact modeling of CMOS transistors under variable uniaxial stress

This paper presents a novel implementation of variable uniaxial mechanical stress model to be used with DC circuit simulation, e.g. using BSIM3v3 transistor model. Based on transistor measurements under various uniaxial stress conditions two stress-dependent parameters are identified, namely the carriers mobility and to a lesser extend the carrier saturation velocity. The effect of the parasitic source/drain resistance on the piezoresistive coefficient determination is addressed in detail. Using the fundamental piezoresistive coefficients, the model has implemented a general relation to calculate the coefficients for arbitrary directions of current and stress in the (0 0 1) silicon (Si) plane. The extended transistor model allows for simulating the effect of uniaxial stress on any MOSFET geometry, under different operation conditions and for any combination of the drain current and stress orientations in the (0 0 1) silicon (Si) plane. The method proposed in this paper is validated by static and dynamic stress-dependent simulations and comparison with experimental data. The method is simulator-independent and can be adapted to other bulk CMOS technologies including SOI processes.

Refractive indices of K2ZnCl4 crystals in an incommensurate phase under uniaxial stresses

The influence of uniaxial mechanical stresses directed along the principal crystallophysical axes on refractiveindex temperature dependences in K2ZnCl4 crystals was studied. It is established that the refractive indices ni are quite sensitive to uniaxial stresses. Significant baric shifts of the paraphase–incommensurate–commensurate phase transition points to different temperature regions were observed, which is due to the effect of the uniaxial stress on the K2ZnCl4 crystal structure. It is found that applying uniaxial pressure increases the value of the temperature hysteresis of the commensurate–incommensurate phase transition.

Molecular dynamics simulation of the martensitic phase transformation in NiAlalloys

Using molecular dynamics simulations with an embedded-atom interatomic potential, westudy the effect of chemical composition and uniaxial mechanical stresses on themartensitic phase transformation in Ni-rich NiAl alloys. The martensitic phase has atetragonal crystal structure and can contain multiple twins arranged in domainsand plates. The transformation is reversible and is characterized by a significanttemperature hysteresis. The magnitude of the hysteresis depends on the chemicalcomposition and stress. We show that applied compressive and tensile stresses reduceand can even eliminate the hysteresis. Crystalline defects such as free surfaces,dislocations and anti-phase boundaries reduce the martensitic transformationtemperature and affect the microstructure of the martensite. Their effect canbe explained by heterogeneous nucleation of the new phase in defected regions.

Influence of uniaxial mechanical stress on the high frequency performance of metal-oxide-semiconductor field effect transistors on (100) Si wafer

The effects of uniaxial mechanical stress on the radio frequency performance of n- and p-metal-oxide-semiconductor field effect transistors (MOSFETs) are investigated up to 10 GHz. Under tensile stress, the gate transconductance (gm) increases in the n-MOSFETs while it decreases in the p-MOSFETs, whereas the results were vice versa for compressive stress. The total gate capacitance (CG) extracted from scattering parameters increases (decreases) under tensile (compressive) stress for both n- and p-MOSFETs, which is explained by the variation in the effective mass perpendicular to the Si/SiO2 interface. The cut-off frequency (fT) varies in inverse proportion to the CG variation.

Quantitative determination of domain distribution inSrTiO3—competing effects of applied electric field and mechanical stress

Below its ordering temperature at 105 K, perovskite-typeSrTiO3 exhibits a tetragonal phase with three different structural domains that are stronglyinfluenced by the application of uniaxial mechanical stresses and electric fields. A carefulneutron diffraction study of superlattice reflections provides full quantitative informationabout the varying domain distributions under external loads as a function of temperature.It is shown that electric field and uniaxial stress exhibit competitive effects and thesimultaneous application leads to a complex redistribution behaviour of the tetragonaldomains. The results are discussed in the context of the formation of a field inducedferroelectric phase at low temperatures. The experimental findings demonstrate that itspolarization is always perpendicular to the tetragonal axis and the polar phase hasorthorhombic symmetry.

Uniaxial Stress Engineering for High-Performance Ge NMOSFETs

Ge channel is one of the promising performance boosters for replacing Si channel in future complementary metal-oxide-semiconductor technology. The uniaxial stress technology can further enhance the performance of Ge MOSFETs. In this paper, the uniaxial stress effect on Ge NMOSFETs was experimentally and theoretically investigated. The gate dielectric in the Ge NMOSFETs was fabricated by using the novel radical oxidation technique. The high quality of the gate dielectric allowed high vertical field mobility measurements. By applying mechanical uniaxial stress on the fabricated Ge NMOSFETs, the mobility enhancement was experimentally obtained. The physical mechanism of mobility enhancement under such strain indicates that the device performance of Ge NMOSFETs in the ballistic transport regime can achieve as much as 48% drive current gain beyond the 15 nm technology node.

Laser-Induced Current Transients in Strained-Si Diodes

Laser-induced current transients are measured on uniaxially stressed silicon (Si) N+/P diodes using a high speed measurement system. Controlled external mechanical stress along the (110) direction is applied via a four-point bending jig while the samples are irradiated using a cavity-dumped dye laser with a wavelength of 590 nm. A decrease in the peak current is observed for increasing tensile stress applied to the diode. Unlike tensile stress, compressive stress increases the peak current. Charge collection is observed to decrease with tensile and increase with compressive stress. These results suggest that uniaxial mechanical stress alters the current transients due to strain-induced changes in electron mobility along the (001) direction. The average effective electron mass along the (001) direction increases with tensile and decreases with compressive stress resulting from the splitting of degenerate conduction band valleys and the repopulation of electrons from higher to lower valleys. The Florida object oriented device simulator (FLOODS) is used to explain the mechanism of current transients in unstressed and stressed diodes. FLOODS is also used to predict results for values of applied stress ( ~ 1 GPa) beyond those that can be obtained using the bending jig (~ 240 MPa).