Strain-induced Changes Research Articles

Mobility model based on piezoresistance coefficients for Ge 3D transistor

The conventional first order piezoresistance model has commonly been used to describe carrier mobility enhancement for low levels of process induced stress in Complementary Metal-Oxide-Semiconductor Field Effect Transistor (CMOS) technology. However, many reports show it failing to describe the nonlinear behavior observed at high levels of stress. In this paper, mobility model based on the modified piezoresistance model with nine stress-independent piezoresistance coefficients is proposed such that a mobility model can be applied correctly to calculate the strain-induced carrier mobility changes. Hence, the overall accuracy is improved compared to the conventional piezoresistance (PR) model. Its validation is confirmed with the results from TCAD simulations of carrier mobility for Ge Fin Field Effect Transistors (FinFET) and nanowire transistors.

Superplasticity of Ti-6Al-4V Titanium Alloy: Microstructure Evolution and Constitutive Modelling.

Determining a desirable strain rate-temperature range for superplasticity and elongation-to-failure are critical concerns during the prediction of superplastic forming processes in α + β titanium-based alloys. This paper studies the superplastic deformation behaviour and related microstructural evolution of conventionally processed sheets of Ti-6Al-4V alloy in a strain rate range of 10–5–10–2 s–1 and a temperature range of 750–900 °C. Thermo-Calc calculation and microstructural analysis of the as-annealed samples were done in order to determine the α/β ratio and the grain size of the phases prior to the superplastic deformation. The strain rate ranges, which corresponds to the superplastic behaviour with strain rate sensitivity index m ˃ 0.3, are identified by step-by-step decreasing strain rate tests for various temperatures. Results of the uniaxial isothermal tensile tests at a constant strain rate range of 3 × 10−4–3 × 10−3 s−1 and a temperature range of 800–900 °C are presented and discussed. The experimental stress-strain data are utilized to construct constitutive models, with the purpose of predicting the flow stress behaviour of this alloy. The cross-validation approach is used to examine the predictability of the constructed models. The models exhibit excellent approximation and predictability of the flow behaviour of the studied alloy. Strain-induced changes in the grain structure are investigated by scanning electron microscopy and electron backscattered diffraction. Particular attention is paid to the comparison between the deformation behaviour and the microstructural evolution at 825 °C and 875 °C. Maximum elongation-to-failure of 635% and low residual cavitation were observed after a strain of 1.8 at 1 × 10−3 s−1 and 825 °C. This temperature provides 23 ± 4% β phase and a highly stable grain structure of both phases. The optimum deformation temperature obtained for the studied alloy is 825 °C, which is considered a comparatively low deformation temperature for the studied Ti-6Al-4V alloy.

Precipitation behavior and high strain rate superplasticity in a novel fine-grained aluminum based alloy

The development of aluminum alloys with superior mechanical properties and high strain rate superplasticity is an important prerequisite for advancing applications of superplastic blow-forming technology. This study focuses on the effect of Ce and Fe additions on the microstructural parameters and tensile properties of a superplastic Al-4.8%Mg-0.6%Mn-0.15%Cr (AA5083-type) alloy. The studied alloy exhibits a bimodal particle size distribution with coarse crystallization origin inclusions and fine secondary precipitates. Both the coarse and fine particles lead to grain refinement. The coarse Ce-, Fe-, and Mn-rich intermetallic particles of crystallization origin provide evidence of a particle-stimulated nucleation effect. The semi-coherent Mn-enriched compact-shaped dispersoids with an Ashby-Brown contrast, a quasicrystalline structure, and a mean size of 38 nm are precipitated after low-temperature homogenization and exhibit a strong Zener pinning effect. The proposed thermomechanical treatment results in the development of a grain size of 4 μm and an ultimate tensile strength of 340 MPa in the recrystallized sheet. The superplastic deformation behavior in a strain rate range of 1 × 10−2 to 1 × 10−1 s−1 and the associated strain-induced changes in the grain structure and mechanical properties of the developed alloy are presented and discussed.

A Guideline for Tailoring Lattice Oxygen Activity in Lithium-Rich Layered Cathodes by Strain.

Lattice oxygen activity plays a dominant role in balancing discharge capacity and performance decay of lithium-rich layered oxide cathodes (LLOs). On the basis of density functional theory (DFT) and tight-binding theory, the activity of lattice oxygen can be improved by tensile strain and suppressed by compressive strain. To verify this conclusion, LLOs with large lattice parameters (L-LLOs) were synthesized taking advantage of the lattice expansion effect in nanomaterials. Compared with conventional LLOs with small lattice parameters (S-LLOs), particles in L-LLOs are imposed by tensile strain. L-LLOs show a larger initial discharge capacity and decay faster in the prolonged cycles than S-LLOs. Actually, most of the modified methods in LLOs can come down to strain-induced changes in lattice parameters. We believe this conclusion is a useful guideline to understand and tailor the lattice oxygen activity and may be generalized to other layered oxide cathodes involving anionic redox.

Strain-induced resistance change in V2O3 films on piezoelectric ceramic disks

We prepared a stacked structure consisting of a quasi-free-standing functional oxide thin film and a ceramic piezoelectric disk and observed the effect of the piezoelectric disk deformation on the resistance of the thin film. Epitaxial V2O3 films were grown by a pulsed laser deposition method on muscovite mica substrates, peeled off using Scotch tapes, and transferred onto piezoelectric elements. In this V2O3/insulator/top electrode/piezoelectronic disk/bottom electrode structure, the resistance of the V2O3 film displayed a variation of 60% by sweeping the piezoelectronic disk bias. With support from x-ray diffraction measurements under an electric field, a huge gauge factor of 3 × 103 in the V2O3 film was inferred. The sizeable resistance change in the V2O3 layer is ascribed to the piezo-actuated evolution of c/a ratios, which drives the material towards an insulating phase. A memory effect on the resistance, related to the hysteretic displacement of the piezoelectric material, is also presented.

A fiber Bragg grating based passive semicircular sensor architecture with fault monitoring

Abstract In the investigation, we investigate a fiber Bragg grating (FBG) based semicircular sensor architecture with fiber fault monitoring experimentally. Two erbium-doped fiber amplifiers (EDFAs) are used in the monitoring center to generate a broadband light source for sensing the strain and temperature simultaneously. Here, we utilize six FBG based sensors with different reflected wavelength for proof-of-concept demonstration. There is no optical filter used in the FBG sensor system for wavelength-selection. In addition, the proposed sensor system can monitor one to two fiber faults. In the measurement, the temperature- and strain-induced changes are also analyzed and discussed. Therefore, the proposed multiple FBG based semicircular sensor system not only can sense the temperature and strain simultaneously, but also can be used to monitor where is the fiber fault.

Strain-induced changes to the methanation reaction on thin-film nickel catalysts

We investigate how mechanical strain can directly manipulate the catalytic rate of a purely thermochemical reaction.

Strain-induced changes in AlGaN/GaN two-dimensional electron gas structures with low surface state densities

We report on the effects of applied external strain on AlGaN/GaN two dimensional electron gas structures exhibiting a negative strain dependence of the sheet carrier density (ns). Flexible AlGaN/GaN heterojunctions, grown on two-dimensional boron nitride (BN)-on-sapphire templates, were released from the substrate via strain-induced separation at the weak BN van der Waals interface and then transferred to flexible substrates. By releasing the AlGaN/GaN layer from the substrate, residual strain was removed which allowed for isolation and study of the effects of the externally applied strain. By bending samples, uniaxial strain up to 0.15% was applied as measured by the shifts in the GaN E2H Raman mode. Hall effect measurements revealed a 2.5% decrease in ns with 0.11% applied tensile strain, which is contrary to the increase expected from the piezoelectric effect. The observed decrease in ns is attributed to a relatively large increase in the AlGaN surface barrier height. This effect, which is rarely reported, is observable due to a low surface state density (2.2 × 1012 cm−2 eV–1) in the samples. Illumination was found to dramatically alter the ns-strain dependence, an effect potentially related to detrapping of electrons in the GaN buffer.

Distributed Strain Sensing Using Electrical Time Domain Reflectometry With Nanocomposites

The objective of this study is to validate distributed strain sensing using electrical time domain reflectometry (ETDR) with multi-walled carbon nanotube (MWCNT)-based thin film sensing elements. The proposed ETDR sensor composed of two types of transmission lines: parallel-wire-type transmission line and parallel-plate-type transmission line, ( i.e. , with MWCNT-based sensing elements). The hypothesis was that the greater strain-induced impedance changes of the nanocomposite would enhance ETDR sensing performance. In this paper, four different types of ETDR sensing elements were subjected to one-cycle uniaxial tensile strains to validate strain sensing. Three sensing elements were then integrated in an ETDR setup, and strain patterns were applied for validating their distributed strain sensing behavior.

Strain-induced magnetization changes and magneto-volume effects in ferromagnets with cubic symmetry

Abstract Field-induced magnetization changes and magnetovolumetric strain in bulk ferromagnetic materials with cubic crystalline structure are investigated. Semi-phenomenological approach is developed using a minimal parametrization of the magnetic moment changes obtained from the first-principle calculations based on density functional theory (DFT) for dependence of the magnetization with the volume strain in bulk Fe and Ni crystals. Field-induced stress contributions that can be useful for the case of epitaxial ultra-thin films under a tetragonal distortion are also investigated by taking into account a distinct field-dependent contributions coming from strain in-plane and along the out-of-plane direction. Our present approach is useful for measurements of the magnetization and the magnetostriction of ferromagnetic materials.

Picosecond acoustic-excitation-driven ultrafast magnetization dynamics in dielectric Bi-substituted yttrium iron garnet

Using femtosecond optical pulses, we have investigated the ultrafast magnetization dynamics induced in a dielectric film of bismuth-substituted yttrium iron garnet (Bi-YIG) buried below a thick Cu/Pt metallic bilayer. We show that exciting the sample from Pt surface launches an acoustic strain pulse propagating into the garnet film. We discovered that this strain pulse induces a coherent magnetization precession in the Bi-YIG at the frequency of the ferromagnetic resonance. The observed phenomena can be explain by strain-induced changes of magnetocristalline anisotropy via the inverse magnetostriction effect. These findings open new perspectives toward the control of the magnetization in magnetic garnets embedded in complex heterostructure devices.

Ferromagnetic resonance manipulation by electric fields in Ni81Fe19/Bi3.15Nd0.85Ti2.99Mn0.01O12 multiferroic heterostructures

We investigated electric-field modulation of ferromagnetic resonance (FMR) in Ni81Fe19 (NiFe)/Bi3.15Nd0.85Ti2.99Mn0.01O12 (BNTM) heterostructures at room temperature. BNTM thin films were deposited on a Pt (111)/Ti/SiO2/Si (100) substrate by the sol-gel method. The strain effect is produced by the electric field applied to the BNTM layer, which results in the FMR spectrum shift by tuning of the magnetic anisotropy of the NiFe microstrip devices. A strain-induced magnetic anisotropy change of 332 fJ/Vm is obtained by analyzing the experimental FMR spectra. We discussed an influence on spin orbit torques by applying an electric field to a ferroelectric (FE) layer via coupling to polarization with FMR experiments evidencing. The torque ratios τa/τb increased at first and then declined from the positive to negative electric field. As the value of the applied electric field changes from 129 kV/cm to 0 kV/cm, the variation of the torque ratios τa/τb (the field-like torque τa and damping-like torque τb) is about 0.07. Our results reported in this work demonstrate a route to realize a large magneto-electric coupling effect at room temperature and provide some insights into possible applications of the ferromagnetic/FE device.

Nonlinear Mechano-Optical Behavior and Strain-Induced Structural Changes of l-Valine-Based Poly(ester urea)s

The uniaxial mechano-optical behavior of a series of amorphous l-valine-based poly(ester urea) (VAL-PEU) with varying diol lengths was studied to elucidate the molecular mechanism associated with their thermal shape memory properties. A custom, real-time measurement system was used to capture the true stress, true strain, and birefringence during the temporary shape programming at stretching temperatures above the glass transition temperature (Tg). The mechano-optical response of VAL-PEUs exhibits an initial photoelastic behavior related to enhanced segmental correlation at low temperatures above the Tg. A characteristic temperature, defined as the liquid–liquid (Tll) transition (rubbery–viscous transition), was found at about 1.05 Tg (K) (at Tg + 15 °C) at strain rate of 0.017 s–1, above which the segmental contacts largely “melt” and the initial slope of the stress-optical curves becomes temperature independent. This temperature corresponds to the temperature where mean relaxation time for the polymer i...

Impact of Strain-Induced Changes in Defect Chemistry on Catalytic Activity of Nd2NiO4+δ Electrodes.

It is well known that defect chemistry plays a vital role in determining the electronic structure, ionic conductivity, and catalytic activity of metal oxides, as demonstrated in perovskite-based oxides to achieve desired functionalities. In this work, we explored the possibility of tuning the defect chemistry and hydrogen oxidation reaction (HOR) activity of Nd2NiO4+δ model thin films by controlling the lattice strain. Highly textured Nd2NiO4+δ thin films with different strain states were prepared on (110)- and (100)-oriented single-crystal yttrium-stabilized zirconium (YSZ) substrates using pulsed laser deposition. Electrochemical impedance spectroscopy results indicated that the NNO(100) film on the YSZ(110) substrate with larger tensile strain in the a- b plane and compressive strain along the c axis exhibited higher HOR activity than the NNO(110) film on the YSZ(100) substrate at 500-600 °C. The enhancement in HOR activity is attributed to the strain-induced difference in the oxygen defect concentration, as confirmed by high-resolution X-ray diffraction analysis. We believe that the correlation among the strain state, defect chemistry, and catalytic properties is helpful for rational design of more efficient electrode materials.

The influence of mechanical activation on the dielectric and dynamic properties and structural parameters of the solid solution of Pb(Zr0.56Ti0.44)O3

The impact of mechanical activation on the dielectric properties, structural parameters, and lattice dynamics of the Pb(Zr0.56Ti0.44)O3 solid solution was investigated. The solution features coexisting metastable tetragonal (T) and rhombohedric (R) phases, whose ratio can be altered by applying the uniaxial compression load up to 320 MPa under torsion in Bridgman anvils. The strain-induced changes of the unit cell parameters, dielectric permittivity, Debye characteristic temperatures, temperature-dependent Debye-Waller factors, and mean square displacements were critically analyzed.

Noncontact Strain Monitoring of Osseointegrated Prostheses.

The objective of this study was to develop a noncontact, noninvasive, imaging system for monitoring the strain and deformation states of osseointegrated prostheses. The proposed sensing methodology comprised of two parts. First, a passive thin film was designed such that its electrical permittivity increases in tandem with applied tensile loading and decreases while unloading. It was found that patterning the thin films could enhance their dielectric property’s sensitivity to strain. The film can be deposited onto prosthesis surfaces as an external coating prior to implant. Second, an electrical capacitance tomography (ECT) measurement technique and reconstruction algorithm were implemented to capture strain-induced changes in the dielectric property of nanocomposite-coated prosthesis phantoms when subjected to different loading scenarios. The preliminary results showed that ECT, when coupled with strain-sensitive nanocomposites, could quantify the strain-induced changes in the dielectric property of thin film-coated prosthesis phantoms. The results suggested that ECT coupled with embedded thin films could serve as a new noncontact strain sensing method for scenarios when tethered strain sensors cannot be used or instrumented, especially in the case of osseointegrated prostheses.

Biaxial strain effects on photoluminescence of Ge/strained GeSn/Ge quantum well

A Ge/GeSn/Ge single quantum well with 5% Sn content was grown by chemical vapor deposition on a Si substrate using Ge2H6 and SnCl4 precursors. External biaxial tensile strain was mechanically applied to the Ge/Ge0.95Sn0.05/Ge quantum well for the photoluminescence measurement. Note that the Ge0.95Sn0.05 layer is still under compressive strain due to the large internal compressive strain of the GeSn, although the external bending produces the tensile strain. The direct emission of tensily strained Ge buffer shifts toward lower energy, while the direct emission of pseudomorphic Ge0.95Sn0.05 quantum well does not have significant shift. The strain-induced energy changes of heavy holes and light holes in the Γ valley are extracted by fitting the photoluminescence spectra. Based on the nonlocal empirical pseudopotential method and the model-solid theory, a type-I band alignment is used for the fitting of photoluminescence spectra. The experimentally extracted band edge shifts from the photoluminescence measurement have good agreement with theoretical calculation.

Probing the optical characteristics of MoS2 under external electrical fields using polarized Raman spectroscopy

Raman spectroscopy effectively revealed a strain-induced electronic structure change during polarization-dependent studies on molybdenum disulfide (MoS2). Initially, we used a polarized Raman system to obtain the polarization-dependent Raman spectra of single-, bi-, and tri-layer MoS2 and analyzed their vibration modes. We determined that the in-plane () mode of vibration was double-degenerate whereas the out-of-plane (A1g) mode of vibration was not. We also observed the mode to be independent of polarization, and the A1g mode to be quadratically dependent on the cosine of the polarization angle. The experimental data agreed strongly with the theoretical models. We present the Raman spectra collected with applied top gate voltages and operational frequencies for an MoS2 transistor. The Raman signal intensities, peak positions, and linewidths of two active modes were calculated under different applied top gate voltages and operational frequencies. The broadening of linewidth for the out-of-plane mode was a result of the strengthening of electron–phonon coupling with increasing gate voltage. Owing to the electric potential across the metal-MoS2 interface, a dramatic frequency shift can be observed. For the AC operational mode, the Raman signals can be regarded as constant in the proper operational frequency region.

In Situ Strain Tuning of the Dirac Surface States in Bi2Se3 Films.

Elastic strain has the potential for a controlled manipulation of the band gap and spin-polarized Dirac states of topological materials, which can lead to pseudomagnetic field effects, helical flat bands, and topological phase transitions. However, practical realization of these exotic phenomena is challenging and yet to be achieved. Here we show that the Dirac surface states of the topological insulator Bi2Se3 can be reversibly tuned by an externally applied elastic strain. Performing in situ X-ray diffraction and in situ angle-resolved photoemission spectroscopy measurements during tensile testing of epitaxial Bi2Se3 films bonded onto a flexible substrate, we demonstrate elastic strains of up to 2.1% and quantify the resulting changes in the topological surface state. Our study establishes the functional relationship between the lattice and electronic structures of Bi2Se3 and, more generally, demonstrates a new route toward momentum-resolved mapping of strain-induced band structure changes.

Strain-induced dimensional phase change of graphene-like boron nitride monolayers

We investigate the coupling between the electronic bandgap and mechanical loading of graphene-like boron nitride (h-BN ) monolayers up to failure strains and beyond by means of first-principles calculations. We reveal that the kinks in the bandgap-strain curve are coincident with the ultimate tensile strains, indicating a phase change. When the armchair strain is beyond the ultimate tensile strain, h-BN fails with a phase transformation from 2D honeycomb to 1D chain structure, characterized by the ‘V’-shape bandgap-strain curve. Large biaxial strains can break the 2D honeycomb structures into 0D individual atoms and the bandgap closes.