Effect Of Uniaxial Tensile Strain Research Articles

Influence of uniaxial tensile strain on magnetization behavior of Fe-9wt%Ni steel

This study investigated the effects of uniaxial tensile strain on the magnetization process of an Fe-9wt%Ni (9Ni) alloy to increase understanding of its magnetic behavior. As the applied strain was increased from 0 to 14 %, the magnetization curve changed remarkably, particularly under a high-intensity magnetic field, and magnetic flux density, relative permeability, remanence, and coercive force degraded significantly, especially at strains greater than the upper yield point. Increase in tensile strain caused increase in hysteresis losses, primarily because strain induced crystal defects, which affected the rearrangement of magnetic domains. Increased dislocation density was the primary contributor to the observed deterioration in magnetic properties; changes in texture and phase had little influence. This finding indicates that strain-induced deformation strongly affects the magnetic behavior of 9Ni alloys; this insight will be useful in research aimed at mitigating welding defects such as arc blow, that are attributed to the magnetization of Ni steel.

Effects of uniaxial tensile strain on the release of small molecules from silicone rubber

AbstractSilicone rubber materials may be subject to mechanical strains which can affect the transport properties of small molecules loaded in the materials such as plasticizers and active molecules, hence deteriorating their intended mechanical properties or affecting their performance as carriers of active molecules. Therefore, it is important to understand the effects of mechanical strains on transport of small molecules in the silicone rubber matrix. In this work, silicone rubber sheets loaded with 2 wt% triacetin were stretched and held at four different lengths up to 125% engineering strain. The mass transfer coefficients and diffusion coefficients of triacetin in the strained silicone rubber were determined by monitoring the release of triacetin using headspace gas chromatography–mass spectrometry. It was found that there was no significant change of diffusion coefficient as the applied strain increased, which might result from two microstructure changes that had conflicting effects on diffusion: chain orientation and free volume deformation.

Effect of uniaxial tensile strain on binding energy of hydrogen atoms to vacancy-carbon-hydrogen complexes in α-iron

• The hydrogen binding energy to vacancies under uniaxial tensile strain was calculated. • The binding energy of hydrogen atoms to vacancies decreased with increasing strain. • The binding energy of hydrogen to vacancy-C complexes increased with increasing strain. • The hydrogen retention was estimated under uniaxial tensile strain. The hydrogen binding energy to vacancies or vacancy-carbon complexes in α -Fe under uniaxial tensile strain was calculated using the density functional theory. The solution energies of hydrogen and carbon decreased with an increase in the uniaxial tensile strain. With increasing strain, the binding energy of hydrogen atoms to vacancies also decreases; however, the binding energy of the vacancy-carbon complexes increases. The hydrogen retention was estimated under exposure to hydrogen gas. In the strained area, both the hydrogen concentration of the interstitial hydrogen atoms and the number of hydrogen atoms trapped in the vacancies increased. Therefore, hydrogen retention increased with increasing strain; however, the change in the hydrogen binding energy did not have a strong impact on the hydrogen retention. The presence of vacancies affects hydrogen retention more strongly. Although the binding energy of hydrogen atoms to vacancy-carbon complexes increased, the hydrogen retention in the Fe-C alloy was lower than that in pure Fe.

Predicting a novel two-dimensional BN material with a wide band gap

Based on density functional theory, a new two-dimensional boron nitride, Pmma BN, is proposed and studied in detail for the first time. The stability of Pmma BN is demonstrated by phonon spectra, ab initio molecular dynamics simulations at 300 and 500 K, and in-plane elastic constants. The orientation dependences of the Young’s modulus and Poisson’s ratio show that Pmma BN has large mechanical anisotropy. Pmma BN is an indirect band gap semiconductor material with a band gap of 5.15 eV, and the hole and electron effective mass have high anisotropy. The electron carrier mobility of Pmma BN along the x and y directions is similar, while the hole carrier mobility along the y direction is more than twice that along the x direction. By studying the effect of uniaxial tensile strain on Pmma BN, the band gap of Pmma BN remains indirect under the uniaxial strain, and its adjustable range reaches 0.64 eV at uniaxial strain along the x direction. When uniaxial strain is applied along the y direction, the positions of the conduction band minimum and valence band maximum change. Pmma BN under uniaxial strain show strong optical absorption capacity in the ultraviolet region. To explore clean energy applications, the thermoelectric properties are also investigated.

Uniaxial Tensile Strain Induced the Enhancement of Thermoelectric Properties in n-Type BiCuOCh (Ch = Se, S): A First Principles Study.

It is well known that the performance of thermoelectric measured by figure of merit ZT linearly depends on electrical conductivity, while it is quadratic related to the Seebeck coefficient, and the improvement of Seebeck coefficient may reduce electrical conductivity. As a promising thermoelectric material, BiCuOCh (Ch = Se, S) possesses intrinsically low thermal conductivity, and comparing with its p-type counterpart, n-type BiCuOCh has superior electrical conductivity. Thus, a strategy for increasing Seebeck coefficient while almost maintaining electrical conductivity for enhancing thermoelectric properties of n-type BiCuOCh is highly desired. In this work, the effects of uniaxial tensile strain on the electronic structures and thermoelectric properties of n-type BiCuOCh are examined by using first-principles calculations combined with semiclassical Boltzmann transport theory. The results indicate that the Seebeck coefficient can be enhanced under uniaxial tensile strain, and the reduction of electrical conductivity is negligible. The enhancement is attributed to the increase in the slope of total density of states and the effective mass of electron, accompanied with the conduction band near Fermi level flatter along the Γ to Z direction under strain. Comparing with the unstrained counterpart, the power factor can be improved by 54% for n-type BiCuOSe, and 74% for n-type BiCuOS under a strain of 6% at 800 K with electron concentration 3 × 1020 cm−3. Furthermore, the optimal carrier concentrations at different strains are determined. These insights point to an alternative strategy for superior thermoelectric properties.

Ab initio calculations on oxygen vacancy defects in strained amorphous silica**Project supported by the Science Challenge Project, China (Grant No. TZ2016003-1-105) and the CAEP Microsystem and THz Science and Technology Foundation (Grant No. CAT201501).

The effects of uniaxial tensile strain on the structural and electronic properties of positively charged oxygen vacancy defects in amorphous silica (a-SiO2) are systematically investigated using ab-initio calculation based on density functional theory. Four types of positively charged oxygen vacancy defects, namely the dimer, unpuckered, and puckered four-fold (4 ×), and puckered five-fold (5 ×) configurations have been investigated. It is shown by the calculations that applying uniaxial tensile strain can lead to irreversible transitions of defect structures, which can be identified from the fluctuations of the curves of relative total energy versus strain. Driven by strain, a positively charged dimer configuration may relax into a puckered 5× configuration, and an unpuckered configuration may relax into either a puckered 4× configuration or a forward-oriented configuration. Accordingly, the Fermi contacts of the defects remarkably increase and the defect levels shift under strain. The Fermi contacts of the puckered configurations also increase under strain to the values close to that of center in a-SiO2. In addition, it is shown by the calculations that the relaxation channels of the puckered configurations after electron recombination are sensitive to strain, that is, those configurations are more likely to relax into a two-fold coordinated Si structure or to hold a puckered structure under strain, both of which may raise up the thermodynamic charge-state transition levels of the defects into Si band gap. As strain induces more puckered configurations with the transition levels in Si band gap, it may facilitate directly the development of oxide charge accumulation and indirectly that of interface charge accumulation by promoting proton generation under ionization radiation. This work sheds a light on understanding the strain effect on ionization damage at an atomic scale.

Effects of external mechanical or magnetic fields and defects on electronic and transport properties of graphene

We report on the results obtained modelling the electronic and transport properties of single-layer graphene subjected to mechanical or magnetic fields and containing point defects. Reviewing, analyzing, and generalizing our findings, we claim that effects of uniaxial tensile strain or shear deformation along with their combination as well as structural imperfections (defects) can be useful for achieving the new level of functionalization of graphene, viz. for tailoring its electrotransport properties via tuning its band gap value as much as it is enough to achieve the graphene transformation from the zero-band-gap semimetal into the semiconductor and even reach the gap values that are substantially higher than for some materials (including silicon) typically used in nanoelectronic devices.

Effects of uniaxial tensile strain on the electron–phonon scattering limited carrier mobility in an n-type monolayer MoS2 at room temperature: first-principles calculations

In the present work, we theoretically study the strain effect on the room temperature mobility (RTM) of a n-type Monolayer MoS2 limited by electron–phonon (e–ph) scattering. Our numerical results indicate that the RTM along zigzag direction of such a 2D material can be efficiently modulated by a uniaxial tensile strain. Such an RTM, denoted as , has a sizable reduction (enhancement) as a moderate tensile strain is applied in a parallel (perpendicular) direction. For example, when the strain strength amounts to 7%, the two distinct cases of the strain applied in x and y directions differ from each other by roughly two times. In contrast, the RTM in armchair direction is not so sensitive to a tensile strain. The underlying mechanism for such a strain effect on the mobility is then analysed in depth. Our results are obtained completely on the level of first-principles calculations, free from any empirical simplifications. Therefore, our above findings provide reliable and detailed information for experimentally manipulating the RTM of a n-type monolayer MoS2 by simply stretching the sample.

Thermal conductivity of two-dimensional BC3: a comparative study with two-dimensional C3N.

The thermal conductivities of single-layer BC3 (SLBC) sheets and their responses to environmental temperature, vacancy defects and external strain have been studied and compared with those of single-layer C3N (SLCN) sheets by molecular dynamics (MD) simulations. We found that SLBC and SLCN are isotropic in the basal plane and that their predicted thermal conductivities for infinite length sheets are 488.54 W m-1 K-1 and 799.87 W m-1 K-1, respectively. Despite many similar features in the structures of these materials, SLBC exhibits a lower thermal conductivity than SLCN due to stronger flexural acoustic phonon-defect scattering rates and weaker interatomic bonding stiffnesses. The vibrational density of states (VDOS) are calculated in both structures to elucidate their thermal conductivity differences. SLBC exhibits a more substantial redshift phenomenon in the high- and low-frequency domains than SLCN. In addition, the thermal conductivities of these materials exhibit decreasing trends in response to increases in temperature and defect ratio, and the temperature effect in SLBC is more substantial than that in SLCN, while the defect effect in SLBC is less substantial than that in SLCN. The influences of uniaxial compressive and tensile strains on the thermal conductivities of these materials are analysed separately. These two deformation modes cause different effects on the thermal transport behaviours of SLBC and SLCN: the effect of uniaxial compressive strain is slightly negative, while the effect of uniaxial tensile strain is initially positive and then negative. Moreover, the biaxial strains result in a more severe reduction in thermal conductivity than the uniaxial strains. Remarkably, the impact of uniaxial and biaxial tensile strains on thermal transport was stronger in SLBC than in SLCN. We propose that SLBC nanomembranes are promising candidates for various thermal applications.

Flexible germanium nanomembrane metal-semiconductor-metal photodiodes

We demonstrate flexible Ge nanomembrane (Ge NM) based metal-semiconductor-metal photodiodes. The effect of uniaxial tensile strain on Ge NM based photodiodes was investigated using bending fixtures. Dark current density is decreased from 21.5 to 4.8 mA/cm2 at 3 V by a tensile strain of 0.42% while photon responsivity is increased from 0.2 to 0.45 A/W at the wavelength of 1.5 μm. Enhanced responsivity is also observed at longer wavelengths up to 1.64 μm. The uniaxial tensile strain effectively reduces the direct bandgap energy of the Ge NM, leading to a shift of the absorption edge toward a longer wavelength.

Effect of Uniaxial Strain on Low Frequency Raman Modes in Few Layers Molybdenum Disulfide

The effect of uniaxial tensile strain on the shear mode (C mode) and layer breathing mode (LB mode) of few layers MoS2 were studied. The C mode is doubly degenerated into two sub-peaks as applied strain increases. No measurable Raman shift for the LB mode is observed, while its Raman intensity decreases gradually as the strain increases. In addition, the C and LB modes exhibit distinguished thickness dependence. The C mode shows a clear blueshift as the strain increases, while the LB mode is softened in the process. Moreover, the evolution of C mode with thickness follows an enhanced linear-chain model plus a linear component very well. It implies that the C mode is a better thickness navigator as compared to the L mode.

Strained phonon–phonon scattering in carbon nanotubes

Focusing on three-phonon processes, the effect of uniaxial tensile strain on the phonon–phonon scattering rates is studied for (10,10) single-walled carbon nanotube at room temperature. Longitudinal optical (LO) and longitudinal acoustic (LA) phonon scattering rates are reported at 0%, 2.5%, 5%, 10%, 15% and 20% strains. Results show that the presence of strain can change the phonon–phonon scattering rates by as much as three orders of magnitude. For LO phonons, the mean scattering rate increases monotonically with the increasing axial strain. For LA phonons, the mean scattering rate also increases with the increasing strain. However, it decreases significantly at 10% strain. The anomaly observed in the mean scattering rate of LA at 10% strain is explained in light of the effect of strain on the density of states. It is also shown that pre-straining a CNT at 5% or less can improve the decay rate of hot phonons into lower energy phonons.

Understanding the effect of uniaxial tensile strain on the early stages of sensitization in AISI 304 austenitic stainless steel

In the present study, an attempt has been made to understand the effect of different competing mechanisms controlling the overall degree of sensitization (DOS) of deformed austenitic stainless steel at the early stage of sensitization. The Double Loop Electrochemical Potentiokinetic Reactivation (DL-EPR) studies were performed to characterize the Degree of Sensitization (DOS) as a function of both pre-defined strain and sensitization temperature. X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) were used to explain the phenomena qualitatively. A non monotonous behaviour in the variation of DOS has been observed with deformation and sensitization temperature. The presence of Deformation Induced Martensites (DIM) and their transformation into tempered martensites (α + M23C6) at higher temperatures was found to play major roles in controlling the overall sensitization and desensitization processes.

Mechanical characterization of human mesenchymal stem cells subjected to cyclic uniaxial strain and TGF-β1

Human mesenchymal stem cells (hMSCs) have shown promising potential in the field of regenerative medicine particularly in vascular tissue engineering. Optimal growing of MSCs into specific lineage requires a thorough understanding of the role of mechanobiology in MSC metabolism. Although effects of external physical cues (mechanical stimuli through external loading and scaffold properties) on regulation of MSC differentiation into Smooth muscle (SM) lineage have attracted widespread attention, fewer studies are available on mechanical characterization of single engineered MSCs which is vital in tissue development through proper mechanotransductive cell–environment interactions. In this study, we investigated effects of uniaxial tensile strain and transforming growth factor-β1 (TGF-β1) stimulations on mechanical properties of engineered MSCs and their F-actin cytoskeleton organization. Micropipette aspiration technique was used to measure mechanical properties of MSCs including mean Young׳s modulus (E) and the parameters of standard linear viscoelastic model. Compared to control samples, MSCs treated by uniaxial strain either with or without TGF-β1 indicated significant increases in E value and considerable drop in creep compliance curve, while samples treated by TGF-β1 alone met significant decreases in E value and considerable rise in creep compliance curve. Among treated samples, uniaxial tensile strain accompanied by TGF-β1 stimulation not only caused higher stimulation in MSC differentiation towards SM phenotype at transcriptional level, but also created more structural integrity in MSCs due to formation of thick bundled F-actin fibers. Results can be applied in engineering of MSCs towards functional target cells and consequently tissue development.

Analytical modeling of uniaxial strain effects on the performance of double-gate graphene nanoribbon field-effect transistors

The effects of uniaxial tensile strain on the ultimate performance of a dual-gated graphene nanoribbon field-effect transistor (GNR-FET) are studied using a fully analytical model based on effective mass approximation and semiclassical ballistic transport. The model incorporates the effects of edge bond relaxation and third nearest neighbor (3NN) interaction. To calculate the performance metrics of GNR-FETs, analytical expressions are used for the charge density, quantum capacitance, and drain current as functions of both gate and drain voltages. It is found that the current under a fixed bias can change several times with applied uniaxial strain and these changes are strongly related to strain-induced changes in both band gap and effective mass of the GNR. Intrinsic switching delay time, cutoff frequency, and Ion/Ioff ratio are also calculated for various uniaxial strain values. The results indicate that the variation in both cutoff frequency and Ion/Ioff ratio versus applied tensile strain inversely corresponds to that of the band gap and effective mass. Although a significant high frequency and switching performance can be achieved by uniaxial strain engineering, tradeoff issues should be carefully considered.

Size-Dependent Correlations between Strain and Phonon Frequency in Individual ZnO Nanowires

The effect of uniaxial tensile strain on individual ZnO nanowires with diameters ranging from 500 nm to 2.7 μm and the effect of pure bending strain on ZnO microwires are systematically investigated by Raman spectroscopy. It is found for the first time that the tensile and compressive strains result in a linear downshift and upshift of the phonon frequencies of the E2L, E2H, E1TO, and second-order modes compared with the strain-free state, respectively, while the A1TO mode is not influenced by the strain. Furthermore, the strain modulation on phonons depends strongly on the nanowire diameter. The E2H phonon deformation potential is ~3 cm(-1)/% for the 500 nm nanowire, while 1% tensile strain results only in ~1 cm(-1) downward frequency shift for the 2.7 μm ZnO wire. The results provide a versatile "local-self-calibration" and nondestructive method to measure and monitor the local strains in ZnO micro/nanostructures.

Strain-Tunable Spin Moment in Ni-Doped Graphene

Graphene, due to its exceptional properties, is a promising material for nanotechnology applications. In this context, the ability to tune the properties of graphene-based materials and devices with the incorporation of defects and impurities can be of extraordinary importance. Here, we investigate the effect of uniaxial tensile strain on the electronic and magnetic properties of graphene doped with substitutional Ni impurities (Nisub). We have found that, although Nisub defects are nonmagnetic in the relaxed layer, uniaxial strain induces a spin moment in the system. The spin moment increases with the applied strain up to values of 0.3–0.4 μB per Nisub, until a critical strain of ∼6.5% is reached. At this point, a sharp transition to a high-spin state (∼1.9 μB) is observed. This magnetoelastic effect could be utilized to design strain-tunable spin devices based on Ni-doped graphene.

Characteristics of the SiN Uniaxial Strained NMOSFET with Channel Fluorine Implantation

Channel fluorine implantation (CFI) has been successfully integrated with silicon nitride contact etch stop layer (SiN CESL) to further improve the channel hot electron stress (CHES) and constant voltage stress (CVS) reliability of n-channel metal-oxide-semiconductor field-effect-transistor with HfO2/SiON gate stack. Although the improvement of transconductance, drain current and subthreshold swing due to the fluorine passivation is screened out by the effect of uniaxial tensile strain, the result clearly demonstrates that integrating the CFI process in the SiN CESL-strained device can further suppress the CHES- and CVS-induced threshold voltage shift.

Molecular dynamics simulation of resonance properties of strain graphene nanoribbons

Starting from the energy conversion and energy conservation law in the constant-NVE ensemble, the molecular dynamics method using the COMPASS force field was applied to investigate the dynamic properties of graphene nanoribbons (GNRs) together with the GNR-based strain sensors. The following results were obtained: (a) the nonlinear response dominates the dynamic behavior of GNRs, and their ultra-high fundamental frequencies are closely related with the length and boundary conditions; (b) the effect of uniaxial tensile strain on the fundamental frequencies of GNRs is significant and strongly depends on boundary conditions, and the GNR-based strain sensor clamped on four edges has a higher frequency shift, and its sensitivity is up to 7800 Hz / nanostrain, much higher than that of carbon nanotube-based strain sensor with the same length; (c) the resonant characteristics of GNRs and GNR-based strain sensors are insensitive to the chirality. The obtained results suggest that, through cutting the appropriate size and setting the boundary conditions, the GNRs could be used to design a new generation of nanoelectromechanical system (NEMS) resonators and strain sensors, owing to their ultra-low density and ultra-high fundamental frequencies as well as ultra-high sensitivity without considering the impact of chirality.

Effects of Mechanical Strain on Characteristics of Polycrystalline Silicon Thin-Film Transistors Fabricated on Stainless Steel Foil

The effects of uniaxial tensile strain on the performance of polycrystalline silicon thin-film transistors (poly-Si TFTs) is reported. Longitudinal strain increases the electron mobility and decreases the hole mobility, while transverse strain decreases the electron mobility and slightly decreases the hole mobility. Under longitudinal strain the off current decreases for both NMOS and PMOS TFTs and shifts in threshold voltage and substhreshold slope are observed for p-channel TFTs. A strong dependence on channel length for both electron and hole mobilities under longitudinal strain indicates the presence of a series resistance. For poly-Si TFTs, the mobility changes under strains are related to the strain effects on single crystalline silicon devices.