Biaxial Strain Field Research Articles

Strain and electric field induced metallization in the GaX (X = N, P, As & Sb) monolayer

We investigate the strain and electric field dependent electronic properties of two dimensional Ga-based group III-V monolayer from the first-principles approach within density functional theory. The energy bandgap of GaX monolayer increases upto the certain value of compressive strain and then decreases. On the other hand, the energy bandgap of GaX monolayer is monotonically decreased with increasing tensile strain and become metallic at the higher value. Furthermore, the perpendicular electric field decreases the energy band gap of unstrained GaX monolayer and shows semiconductor to metal transition. These results suggest that the nature of energy bands and value of energy bandgap in GaX monolayer can be tuned by the biaxial mechanical strain or perpendicular electrical field. Additionally, we have also studied the optical response of unstrained GaX monolayer in term of optical conductivity. These findings may provide valuable information to develop the Ga-based optoelectronic devices and further the understanding of the GaX monolayer.

Electronic Structure and Band Gap Engineering of Two-Dimensional Octagon-Nitrogene

A new phase of nitrogen with octagon structure has been predicted in our previous study, which we referred to as octagon-nitrogene (ON). In this work, we make further investigations of its stability and electronic structures. The phonon dispersion has no imaginary phonon modes, which indicates that ON is dynamically stable. Using ab initio molecular dynamic simulations, this structure is found to be stable up to room temperature and possibly higher, and ripples that are similar to that of graphene are formed on the ON sheet. Based on the density functional theory calculation, we find that single layer ON is a two-dimension wide gap semiconductor with an indirect band gap of 4.7 eV. This gap can be decreased by stacking due to the interlayer interactions. Biaxial tensile strain and perpendicular electric field can greatly influence the band structure of ON, in which the gap decreases and eventually closes as the biaxial tensile strain or the perpendicular electric field increases. In other words, both biaxial tensile strain and a perpendicular electric field can drive the insulator-to-metal transition, and thus can be used to engineer the band gap of ON. From our results, we see that ON has potential applications in many fields, including electronics, semiconductors, optics and spintronics.

Bragg-edge elastic strain tomography forin situsystems from energy-resolved neutron transmission imaging

Technological developments in high resolution time-of-flight neutron detectors have raised the prospect of tomographic reconstruction of elastic strain fields from Bragg-edge strain images. This approach holds the potential to provide a unique window into the full triaxial stress field within solid samples. While general tomographic reconstruction from these images has been shown to be ill-posed, an injective link between measurements and boundary deformations exists for systems subject to in situ applied loads in the absence of residual stress. Recent work has provided an algorithm to achieve tomographic reconstruction for this class of mechanical system. This letter details an experimental proof-of-concept for this algorithm involving the full reconstruction of a biaxial strain field within a non-trivial steel sample. This work was carried out on the RADEN energy resolved neutron imaging instrument within the Japan Proton Accelerator Research Complex, with validation through Digital Image Correlation and constant wavelength neutron strain scans.

Tunable Electronic Properties of Arsenene and Transition-Metal Dichalcogenide Heterostructures: A First-Principles Calculation

The structural and electronic properties of arsenene and monolayer transition-metal dichalcogenides (β-As/MX2) heterostructures have been systematically investigated by density functional theory. It is found that all β-As/MX2 heterostructures with little lattice mismatch possess considerable band gaps. Their electronic properties can be effectively tuned via (biaxial or uniaxial) strain and electric field, but the variation trends are different. The band gaps of the β-As/MX2 heterostructures decrease linearly as the strain arises, while there is a Stark effect of the band gap under suitable electric field due to the spontaneous electric polarization in the heterostructures. Meanwhile, a series change of the semiconductor types of the β-As/MX2 heterostructures could also be obtained by the strain and electric field. These diverse electronic properties may provide a potential application in nanodevices based on arsenene and transition-metal dichalcogenides.

Novel GaN-based nanocomposites: Effective band structure and optical property tuning by tensile strain or external field

The electronic and optical properties of the GaN monolayer hybrid with ZnO, MoS2 and MoSe2 are studied by means of density functional theory. The lattice mismatches of these three heterobilayers are less than 2.5% and they are stable with the binding energies larger than the ones of bilayer graphene. Despite of the indirect band gap of GaN monolayer, the three heterostructures exhibit direct band gap characteristics and their optical spectrums are broader than those of the isolated constituent layers because of interlayer coupling. Besides, both of biaxial tensile strain and external electric field (E-field) can effectively tune the band gaps of these heterostructures. The band gaps will decrease with the increase of tensile strain or the positive E-field strength while the ones will increase with the increase of the negative E-field intensity. Meanwhile, the adsorption edges of their imaginary parts of the dielectric function display corresponding redshift or blueshift characteristics and the band gaps may undergo direct to indirect transition beyond a critical strain or E-field intensity. The results shows that these GaN heterostructures can be good candidate materials for further investigations on the photo-related applications such as light-emitting diodes (LEDs), photodetection or solar energy conversion.

Independent tuning of excitonic emission energy and decay time in single semiconductor quantum dots

Independent tuning of emission energy and decay time of neutral excitons confined in single self-assembled In(Ga)As/GaAs quantum dots is achieved by simultaneously employing vertical electric fields and lateral biaxial strain fields. By locking the emission energy via a closed-loop feedback on the piezoelectric actuator used to control the strain in the quantum dot, we continuously decrease the decay time of an exciton from 1.4 to 0.7 ns. Both perturbations are fully electrically controlled and their combination offers a promising route to engineer the indistinguishability of photons emitted from spatially separated single photon sources.

The effects of biaxial strain and electric field on the electronic properties in stanene

The effects of biaxial strain (−2% < ε < 6%) and electric field (E-field) on structural and electronic properties in stanene are systematically investigated by first-principles calculations. We find that, with the increase of biaxial strain, the conduction bands at the high symmetric Γ point in the first Brillouin zone shift towards the Fermi level in stanene. In addition, the biaxial strain also affects the position of Dirac cone. The E-field changes the band dispersions near the Γ with a small band gap opening at the K point. Remarkably, the band gap opening in stanene can be effectively modulated by the external E-field and strain. These results present a flexible method toward modulating the electronic and band properties of stanene and shed light on its experimental applications.

Biaxial Strain and Electric Field Dependent Conductivity of Monolayer WTe2 on Top of Fe3O4(111)

The biaxial strain and electric field dependent electronic properties of monolayer WTe2 on top of Fe3O4(111) are investigated by first‐principles calculations. Our results demonstrate that mechanical strain effectively separates the contributions of interface state and valley states to the conductivity of monolayer WTe2. Tensile strain shifts the interface state below Fermi level. The conductivity of WTe2 is dominated by valley states. With compressive strain, the interface state is shifted away from the valley state edge. The conductivity is only subject to the spin‐polarized interface state. Applying perpendicular electric field also yields valley‐state‐dominating conductivity. The valley splitting energy reduces from 139 to −68 meV with an electric field of 0.02 V nm−1. Different from applying strain, valley polarization is robust against wide range of electric field intensity, showing potential applications in spintronic and valleytronic devices.

Effect of biaxial strain and external electric field on electronic properties of MoS2 monolayer: A first-principle study

In this work, making use of density functional theory (DFT) computations, we systematically investigate the effect of biaxial strain engineering and external electric field applied perpendicular to the layers on the band gaps and electronic properties of monolayer MoS2. The direct-to-indirect band gaps and semiconductor-to-metal transition are observed in monolayer MoS2 when strain and electric field are applied in our calculation. We show that when the biaxial strain and external electric field are introduced, the electronic properties including band gaps of monolayer MoS2 can be reduced to zero. Our results provide many useful insights for the wide applications of monolayer MoS2 in electronics and optoelectronics.

Quantum spin Hall insulators in functionalized arsenene (AsX, X = F, OH and CH3) monolayers with pronounced light absorption.

The search for new two-dimensional topological insulators (2D-TIs) with large band gaps is of great interest and importance. Our first-principles calculations predicted three candidates for 2D-TIs, arsenene functionalized with F, OH and CH3 groups (AsX, X = F, OH and CH3), which preserved large bulk band gaps from 100 to 160 meV (up to 260 meV) derived from the spin-orbit coupling (SOC) within the px,y orbitals. This picture is similar to what was reported for an AsH monolayer with a band gap of 193 meV. Ab initio molecular dynamic (AIMD) simulations demonstrated the thermal stabilities of the AsX monolayers even at 500 K. The nontrivial topological phase was confirmed by the topological invariant Z2 and topological edge state. The topological electronic bandgap of the AsF monolayer can be effectively modulated by biaxial tensile strain and vertical external electric field. In addition, pronounced light absorption in the near-infrared and visible range of the solar spectrum was expected for the AsX (X = H, F) monolayers from the adsorption peaks at 0.45-1.6 eV, which is attractive for light harvesting. The nontrivial quantum spin Hall (QSH) insulators AsX could be promising candidates for practical room-temperature applications in dissipationless transport devices and photovoltaics.

Energy-tunable single-photon light-emitting diode by strain fields

We report a strain-tunable quantum light-emitting diode for generation of electrically triggered and energy-tunable single photons. The device consists of a p-i-n quantum dots containing nanomembrane integrated onto a piezoelectric actuator. By injecting ultrafast voltage pulses, electrically driven light emission is realized and the quantum nature of single-photon emission is revealed in the second-order time correlation measurements. In addition to electrically pulsed excitation, we achieved a broad tuning range ( $${\sim }$$ 9 meV) to the energy of the emitted single photons by imposing giant biaxial strain fields on quantum dots within the diode. We further show that energy of the single-photon emission emitted from different quantum dots can be tuned to degeneracy, thus rendering the quantum interference on which most of existing photonic quantum technologies rely. The device reported in this work represents an important step toward the realization of quantum repeater by using electrically triggered quantum light sources of indistinguishable photons.

Stanene cyanide: a novel candidate of Quantum Spin Hall insulator at high temperature.

The search for quantum spin Hall (QSH) insulators with high stability, large and tunable gap and topological robustness, is critical for their realistic application at high temperature. Using first-principle calculations, we predict the cyanogen saturated stanene SnCN as novel topological insulators material, with a bulk gap as large as 203 meV, which can be engineered by applying biaxial strain and electric field. The band topology is identified by Z2 topological invariant together with helical edge states, and the mechanism is s-pxy band inversion at G point induced by spin-orbit coupling (SOC). Remarkably, these systems have robust topology against chemical impurities, based on the calculations on halogen and cyano group co-decorated stanene SnXxX′1−x (X,X′ = F, Cl, Br, I and CN), which makes it an appropriate and flexible candidate material for spintronic devices.

Tuning the electronic structure of silicene and germanene by biaxial strain and electric field

We present a first-principles study of effects of small biaxial strain ($|\varepsilon|\le 5\%$) and perpendicular electric field (E-field) on the electronic and phonon properties of low-buckled silicene and germanene. With an increase of the biaxial strain, the conduction bands at the high symmetric $\Gamma$ and $M$ points of the first Brillouin zone shift significantly towards the Fermi level in both silicene and germanene. In contrast, the E-field changes the band dispersions near the $\Gamma$ and open a small band gap at the K point in silicene. We found that the field-induced gap opening in silicene could be enhanced by a compressive strain while mitigated by a tensile strain. This result highlights the tunability of the electronic structures of silicene by combining the mechanical strain and the electric field.

Stress and structural damage sensing piezospectroscopic coatings validated with digital image correlation

The piezospectroscopic effect, relating a material’s stress state and spectral signature, has recently demonstrated tailorable sensitivity when the photo-luminescent alpha alumina is distributed in nanoparticulate form within a matrix. Here, the stress-sensing behavior of an alumina-epoxy nanoparticle coating, applied to a composite substrate in an open hole tension configuration, is validated with the biaxial strain field concurrently determined through digital image correlation. The coating achieved early detection of composite failure initiation at 77% failure load, and subsequently tracked stress distribution in the immediate vicinity of the crack as it progressed, demonstrating non-invasive stress and damage detection with multi-scale spatial resolution.

Fluorescence imaging of lattice re-distribution on step-index direct laser written Nd:YAG waveguide lasers

The laser performance and crystalline micro-structural properties of near-infrared step-index channel waveguides fabricated inside Neodymium doped YAG laser ceramics by means of three-dimensional sub-picosecond pulse laser direct writing are reported. Fluorescence micro-mapping of the waveguide cross-sections reveals that an essential crystal lattice re-distribution has been induced after short pulse irradiation. Such lattice re-distribution is evidenced at the waveguide core corresponding to the laser written refractive index increased volume. The waveguides core surroundings also present diverse changes including slight lattice disorder and bi-axial strain fields. The step-index waveguide laser performance is compared with previous laser fabricated waveguides with a stress-optic guiding mechanism in absence of laser induced lattice re-distribution.

Unraveling the effect of boundary conditions and strain monitoring on estimation of the constitutive parameters of elastic membranes by biaxial tests

The purpose of this study is to study the effects of boundary conditions and strain monitoring on the estimation of the constitutive parameters of elastic membranes by biaxial tests. We analyze the effect of geometry, different gripping methods and strain monitoring. Experiments were conducted on membrane silicon using two samples geometries – cruciform and square – of different sizes, two gripping arrangements – clamped and sutured edges – and two strain monitoring methods – displacement between grips and Digital Image Correlation techniques. The strain maps were compared with that produced by a geometrically matched finite element model.We report two important findings. First, as the St Venant principle pointed for medium or large samples the gripping method had no effect on the material parameters and the strain distribution at the center of the sample. However, due to size the restrictions imposed by soft biological tissues, using sutures is the commonly used technique. Secondly, biaxial strain fields measured using surface markers or DIC methodologies are suitable for clamped method and be essential when sutures are used. As conclusion, the parametric study realized can give guidelines for future researchers on biomechanics on the minimum size of samples and an interesting way to extract data from tests.

Biaxial strain effects on adatom surface diffusion on tungsten from first principles

Using first-principles electronic structure calculations, the energy barriers for diffusion mechanisms of adatoms on the tungsten (W) (001) and (110) surfaces under externally applied biaxial strain fields are determined. Adatoms move either by hopping on the surface or by an exchange process with a surface atom, which is found to be completed in one step (direct exchange), or via the formation of a surface crowdion (crowdion-mediated exchange). As a result of the compact atomic stacking, hopping is found to be the major diffusion mechanism on the W(110) surface, irrespective of the surface strain state. On the other hand, the main diffusion mechanism on the less compact W(001) surface is found to be a competition between direct exchange and crowdion-mediated exchange, depending on the magnitude of the surface biaxial strain. Results of the model reveal that, if surface crowdions form, they will be highly mobile and migrate anisotropically. A microscopic explanation is presented by analyzing the charge density associated with surface crowdions. A ``mechanism diagram'' for atomic surface diffusion on the W(001) indicates that the diffusion direction and its rate can both be modulated by an applied biaxial strain. Migration volumes for the three mechanisms are calculated, and the significance of the results to the understanding of surface evolution under plasma or other energetic ion bombardment is highlighted.

Investigation of Nanometric Thin-Film Bismuth Piezoresistors Deposited on Silicon Substrates

ABSTRACTThin film bismuth piezoresistors, defined on oxidized silicon wafers, are investigated as a function of their orientation for their eventual integration on micro-electro-mechanical (MEMS) microsensors. Bismuth’s piezoresistance (or elasto-resistance) is experimentally investigated to accurately determine its longitudinal and transverse strain sensitivities. Whisker-shaped resistive elements defined on different orientations (from 0o, the beam’s main strain axis, to 90o, perpendicular to that axis) undergo changes of resistance (ΔR), associated with the induced strains on silicon cantilevers beam’s surface when these are mechanically loaded under pure bending stress conditions. For Bi-resistors, the traditional gage factor concept, (ΔR/Ro)/εl, is found to be equal to +16 and +33, for elements oriented along 0 and 90o, respectively, considerably larger than those for metals or metal alloys. These high sensitivity values and the “unusual” positive, higher value for the 90o (perpendicular) resistors can be of considerable interest for microsensors applications. The results of this study enable us to precisely determine the bismuth’s longitudinal and transverse strain sensitivities that are calculated to be equal to +26 and +40.5 respectively. This experimental study is extended to explore the Bi-films’ response to bi-axial strain fields.

Anisotropic Biaxial Stretch Slows Longitudinal and Transverse Conduction in Micropatterned Mouse Ventricular Myocyte Cultures

The effects of stretch on cardiac conduction velocity are controversial, and several counteracting mechanisms have been proposed. Conflicting reports of conduction velocity increase and decrease under cardiac loading have been reported. These changes have been attributed to stretch modulation of ion channels, cell-cell junctions, cell capacitance, and properties of the interstitium. To separate the effects of tissue geometrical changes from intrinsic changes in myocyte conduction and to eliminate effects of stretch on interstitial electrical properties, neonatal murine cardiomyocytes were cultured on micropatterned stretchable substrates for optical mapping of excitation conduction velocity. A homogeneous anisotropic biaxial strain field of 14% in the primary direction and 3.6% in the secondary direction was applied to these substrates, where the primary direction of stretch was oriented either parallel or perpendicular to the longitudinal axis of the aligned cell culture. When the primary direction of strain was oriented parallel to the longitudinal cell culture axis, the longitudinal conduction velocity slowed to 72% ± 3% and recovered to 95% ± 14% of baseline conduction following unloading, while the transverse conduction velocity slowed to 75% ± 3% and recovered to 137% ± 19% (n=3, mean ± SEM). When the primary direction of strain was oriented along the transverse cell culture axis, the transverse conduction velocity slowed to 77% ± 6%, while the longitudinal conduction velocity slowed to 84% ± 9%, neither recovering following unloading (n=3, mean ± SEM). Conduction velocity slowed in both longitudinal and transverse directions under biaxial strain and substantially recovered following unloading in the case of primarily axial stretch.

Quantification and significance of fluid shear stress field in biaxial cell stretching device

A widely used commercially available system for the investigation of mechanosensitivity applies a biaxial strain field to cells cultured on a compliant silicone substrate membrane stretched over a central post. As well as intended substrate strain, this device also provides a fluid flow environment for the cultured cells. In order to interpret the relevance of experiments using this device to the in vivo and clinical situation, it is essential to characterise both substrate and fluid environments. While previous work has detailed the substrate strain, the fluid shear stresses, to which bone cells are known to be sensitive, are unknown. Therefore, a fluid structure interaction computational fluid dynamics model was constructed, incorporating a finite element technique capable of capturing the contact between the post and the silicone substrate membrane, to the underside of which the pump control pressure was applied. Flow verification experiments using 10-μm-diameter fluorescent microspheres were carried out. Fluid shear stress increased approximately linearly with radius along the on-post substrate membrane, with peak values located close to the post edge. Changes in stimulation frequency and culture medium viscosity effected proportional changes in the magnitude of the fluid shear stress (peak fluid shear stresses varied in the range 0.09-3.5Pa), with minor effects on temporal and spatial distribution. Good agreement was obtained between predicted and measured radial flow patterns. These results suggest a reinterpretation of previous data obtained using this device to include the potential for a strong role of fluid shear stress in mechanosensitivity.