Application Of Tensile Strain Research Articles

Electronic and Optical Characteristics of Phosphorus-Doped Two-Dimensional Hexagonal Boron Arsenide: The Effects of Doping Concentration and Mechanical Strain

Abstract The present study investigates the impact of P doping and stretching loads on phonon dispersion, electronic properties, and optical characteristics of P-doped hexagonal boron arsenide (h-BAs(1-x)Px), where the doping level x varies from 0 to 1, employing the density functional theory (DFT) method. The findings reveal that the chemical bonds in h-BAs(1-x)Px monolayers are indeed covalent. Furthermore, an increase in P concentration from 0.0% to 100% leads to enhancement in the band gap, approximately 18.42%. However, regardless of variations in P concentration or the application of tensile strains up to 4%, the electronic nature of h-BAs(1-x)Px remains unaltered. These monolayers continue to exhibit characteristics of a direct band gap semiconductor at the K wave vector. On the other hand, there exists an intricate interplay between strain and optical properties. Investigating the dielectric functions, absorption coefficient, refractive index, and reflectivity coefficient of h-BAs(1-x)Px monolayers provides insights into their behavior in the ultraviolet spectrum.

Theoretical investigation on electronic and photocatalytic properties of MoS2 monolayer with cation incorporation for water-splitting applications

Electronic and photocatalytic properties of cation (Y, Zr and Nb) incorporated MoS2 monolayers have been investigated using density functional theory (DFT). Among the three cations, Nb incorporated MoS2 monolayer (MoNbS2) exhibited a direct band gap of 1.69 eV at K-K direction. Interestingly, MoNbS2 monolayer has suitable band edges for overall water-splitting and CO2 reduction reactions. Furthermore, MoNbS2 monolayer showed indirect bandgap with application of tensile strain, whereas compressive strain-induced monolayer displayed direct bandgap. The MoNbS2 monolayer under 1 % tensile strain and up to 3 % compressive strain have apt band edges for overall water-splitting applications. Hence, strain-modulated MoNbS2 monolayer results in enhanced photocatalytic performance.

A first-principles investigation of the effects of strain and Pd-doping on ion transfer in LSCF bulk of solid oxide cells

Applied strain can be employed to tune ion migration properties in oxygen electrode bulk. Here migration properties of oxygen vacancy in Pd doped La1−xSrxCo1−yFeyO3−δ (LSCF) bulk (LSCFPd) were investigated with density functional theory under 3 % tensile and compressive strains. Formation energies of oxygen vacancy are reduced under tensile strain while they exhibit a nontrivial dependence as a function of compressive strain near Pd-doping sites. Migration barriers of oxygen vacancy in LSCF and LSCFPd bulks are also significantly reduced with tensile strain compared to that with non-strain. However, barriers near Pd-doping site increase greatly under compressive strain. The variation of oxygen vacancy formation and migration properties can be ascribed to the redistribution of atomic charges and local structural distortion caused by Pd-doping and applied strain. Results indicate that Pd-doping and application of tensile strain can significantly improve oxygen vacancy formation and migration properties.

The First Demonstration of Strain-Controlled Periodic Ferroelectric Domains with Superior Piezoelectric Response in Molecular Materials.

Achieving a periodic domain structure in ferroelectric materials to tailor the macroscopic properties or realize new functions has always been a hot topic. However, methods to construct periodic domain structures, such as epitaxial growth, direct writing by scanning tips, and the patterned electrode method, are difficult or inefficient to implement in emerging molecular ferroelectrics, which have the advantages of lightweight, flexibility, biocompatibility, etc. An efficient method for constructing and controlling periodic domain structures is urgently needed to facilitate the development of molecular ferroelectrics in nanoelectronic devices. In this work, it is demonstrated that large-area, periodic and controllable needle-like domain structures can be achieved in thin films of the molecular ferroelectric trimethylchloromethyl ammonium trichlorocadmium (TMCM-CdCl3 ) upon the application of tensile strain. The domain evolution under various tensile strains can be clearly observed, and such processes are accordingly identified. Furthermore, the domain wall exhibits a superior piezoelectric response, with up to fivefold enhancement compared to that of the pristine samples. Such large-area tunable periodic domain structure and abnormally strong piezoresponse are not only of great interests in fundamental studies, but also highly important in the future applications in functional molecular materials.

Strain-engineered topological phase transitions in ferrovalley 2H−RuCl2 monolayer

Ferrovalley and topology are two basic concepts in both fundamental research fields and emerging device applications. So far, reports are extremely scarce regarding the coupling of these two scenarios in a single material system. By first-principles calculations and Monte Carlo simulations, we predict a highly stable intrinsic ferrovalley $2H\text{\ensuremath{-}}{\mathrm{RuCl}}_{\text{2}}$ semiconductor with an easy out-of-plane magnetization and a high Curie temperature of 260 K. Due to the combination of exchange interaction and spin-orbit coupling, the system exhibits a spontaneous valley polarization of 240 meV in the top valence band, which is further confirmed by a first-order perturbation theory. Moreover, its out-of-plane ferromagnetic ordering can remain rather robust and survive up to 547 K under $\ensuremath{-}5$% compressive strain well above room temperature. On the other hand, the application of tensile strain can drive the system from the ferrovalley phase into a half-valley-metal state with 100% spin and valley polarizations, followed then by a quantum anomalous Hall (QAH) phase in support of scarce high-temperature QAH effect. Beyond around 2% tensile strain, the system is switched to the in-plane magnetization. If the magnetization is steered to the out-of-plane direction through overcoming the magnetic anisotropy energy barriers, the system is further transitioned from the QAH phase to another half-valley-metal state with the rise of tensile strain, and finally restores to the initial ferrovalley phase. Once synthesized, monolayer $2H\text{\ensuremath{-}}{\mathrm{RuCl}}_{\text{2}}$ would find many important applications in spintronic, valleytronic, and topological electronic nanodevices.

Mechanical strain modulation of domain wall currents across LiNbO3 nanosensors

Recently, studies on low-dimensional conducting domain walls (DWs) in insulating ferroelectrics have opened up new research areas that allow information to be mechanically written and electrically read on the nanoscale. Large strains in thin films can change the polarization gradient across the DW region and thus increasing the DW current significantly. This phenomenon can enable the development of high sensitivity mechanical vibration sensors. In this study, the effects of variable uniaxial strain on the structures of 180° conducting DWs in LiNbO3 (LNO) single-crystal thin films bonded onto Si/SiO2 substrates were investigated. After the creation of antiparallel domains within each LNO nanosensor integrated at the film surface, strain modulation of DW currents was observed through simple mechanical bending of the film. The DW current increases under application of tensile strain along the axis of polarization, but decreases under application of in-plane compression by a factor of approximately 25. Phase field simulations showed the dramatic change in polarization gradients around the DW regions under the increase in tensile strain, which reduced the band gap. Repetitive band-gap narrowing/broadening with change in local electric field intensity under vibrating mechanical forces can periodically modulate both the carrier density and the DW conduction in the sensors. This finding not only provides the new fundamental physics to enrich the ferroelectric theory, but also paves the way to the near-future development of bending actuators, piezolighters, and micro-/nano-manipulators, etc.

Magnetization Reversal and Domain Structures in Perpendicular Synthetic Antiferromagnets Prepared on Rigid and Flexible Substrates

Ferromagnetic (FM) layers separated by nonmagnetic metallic spacer layers can exhibit Ruderman-Kittel-Kasuya-Yosida (RKKY) coupling, which may lead to a stable synthetic antiferromagnetic (SAF) phase. In this article, we have studied magnetization reversal by varying the number of bilayer stacks [Pt/Co] as well as thicknesses of Ir space layer t\(_{Ir}\) on rigid Si(100) and flexible polyimide substrates. The samples with t\(_{Ir}\) = 1.0 nm show a FM coupling, whereas samples with t\(_{Ir}\) = 1.5 nm show an antiferromagnetic (AFM) coupling between the FM layers. At t\(_{Ir}\) = 2.0 nm, it shows a bow-tie shaped hysteresis loop indicating a canting of magnetization at the reversal. Higher anisotropy energy compared to the interlayer exchange coupling (IEC) energy is an indication of the smaller relative angle between the magnetization of lower and upper FM layers. We have also demonstrated the strain-induced modification of IEC as well as magnetization reversal phenomena. The IEC shows a slight decrease upon application of compressive strain and increase upon application of tensile strain, which indicates the potential of SAFs in flexible spintronics.

Electronic band structure and magnetism of CoFeV0.5Mn0.5Si

Half-metallic Heusler alloys have attracted significant attention due to their potential application in spin-transport-based devices. We have synthesized one such alloy, CoFeV0.5Mn0.5Si, using arc melting and high-vacuum annealing at 600 °C for 24 hours. First principles calculation indicates that CoFeV0.5Mn0.5Si shows a nearly half-metallic band structure with a degree of spin polarization of about 93%. In addition, this value can be enhanced by the application of tensile strain. The room temperature x-ray diffraction patterns are indexed with the cubic crystal structure without secondary phases. The annealed sample shows ferromagnetic order with the Curie temperature well above room temperature (Tc = 657 K) and a saturation magnetization of about 92 emu/g. Our results indicate that CoFeV0.5Mn0.5Si has a potential for room temperature spin-transport-based devices.

Strain-tunable in-plane ferroelectricity and lateral tunnel junction in monolayer group-IV monochalcogenides

2D ferroelectric materials are promising for designing low-dimensional memory devices. Here, we explore strain-tunable ferroelectric properties of group-IV monochalcogenides MX (M=Ge, Sn; X=S, Se) and their potential application in lateral field tunnel junction devices. We find that these monolayers have in-plane ferroelectricity, with their ferroelectric parameters being on par with other known 2D ferroelectric materials. Among SnSe, SnS, GeSe, and GeS, we find that GeS has the best ferroelectric parameters for device applications, which can be improved further by applying uniaxial tensile strain. We use the calculated ferroelectric properties of these materials to study the tunneling electroresistance (TER) of a 4 nm device based on a lateral ferroelectric tunnel junction. We find a substantial TER ratio of 103–105 in the devices based on these materials, which can be further improved up to a factor of 40 on the application of tensile strain.

A First-principles Study on Strain-induced Change of Adsorption Behaviour of Gas Molecules on Graphene for Multi-gas Detecting Sensor

In order to improve the selectivity, the interaction between graphene and various gas molecules (CO, H2O, and NH3) with and without applied tensile strain were calculated by using first-principles calculation. The changes in adsorption energy and charge transfer (including Bader charge analysis and charge density difference) were further investigated by applying 0%-10% uniaxial tensile strain on the graphene surface. It was found that the adsorption behavior of distinct gas molecules on the graphene surface varied linearly and has different trends under the application of tensile strain. Some gas molecules such as CO and NH3 gradually desorbed, while other gas molecule such as H2O, on the contrary, adsorb more stably with increasing tensile strain. These findings provide feasibility and guidance for further experiments that strain engineering can be used to improve the selectivity of graphene-based gas sensors for further applications in health monitoring.

Strain-tunable triple point Fermions in diamagnetic rare-earth half-Heusler alloys

Topologically non-trivial electronic structure is a feature of many rare-earth half-Heusler alloys, which host atoms with high spin-orbit coupling bringing in the non-triviality. In this article, using the first-principles simulations, rare-earth half-Heusler YPdBi, ScPdBi, LaPdBi, LuPdBi, YPtBi and LuPtBi alloys are studied under strain to reveal multiple band inversions associated with topological phase transitions. From our simulations we find that, as a result of first band-inversion, the Brillouin zone of the diamagnetic half-Heusler alloys hosts eight triple points whereas, the second band inversion causes the emergence of sixteen more triple points. These band-inversions are observed to be independent of the spin-orbit coupling and are the reason behind increasing occupation of bismuth 7s orbitals as volume of the unit cell increases. The surface electronic transport in different triple point semi-metallic phases is found to evolve under strain, as the number of Fermi arcs change due to multiple band inversions. Once the second band inversion occurs, further application of tensile strain does not increase the number of triple points and Fermi arcs. However, increasing tensile strain (or decreasing compressive strain) pushes the triple point crossing to higher momenta, making them more effective as source of highly mobile electrons. These observations make a pathway to tune the bulk as well as surface transport through these semi-metals by application of tensile or compressive strain depending on the unstrained relative band-inversion strength of the material.

Effects of strain and electric fields on the electronic transport properties of single-layer β12-borophene nanoribbons.

Motivated by recent experimental and theoretical research on a monolayer of boron atoms, borophene, the transmission probability and current-voltage characteristics of β12-borophene nanoribbons (BNRs) with zigzag and armchair edges have been calculated using the five-band tight-binding calculation, the Green's function approach, and the Landauer-Büttiker formalism. We focus on the effects of the geometrical parameters, perpendicular electric field, and external strain on the electronic transport properties of β12-BNRs by considering the effects of the substrate. Our calculations show that the transmission coefficient and current of the system decrease by increasing the channel length, whereas increasing ribbon width leads to an increment in the transmission probability as well as the I-V characteristic of β12-BNRs. Besides, the application of tensile strain causes a decrement in the current of the inversion symmetric model of the armchair β12-BNR, whereas the current increases in the presence of compressive strain. We also observed a dip in the transmission spectrum of the biased β12-BNR along the armchair direction which shows a metal-to-n-doped semiconductor phase transition in the device when applying a strong enough electric field. Moreover, the current of the inversion symmetric model of the β12-BNR with zigzag and armchair edges increases with the application of a perpendicular electric field, while in the case of the homogeneous model, the application of an electric field enhances the current of the β12-BNR only in the zigzag direction. These results provide insights for future experimental research and show that β12-BNRs are potential candidates for next-generation electronic devices.

Strain modulated carrier mobility and optical properties of graphene nanowiggles

Recently, synthesized Chevron graphene nanoribbons (CGNRs) and its laterally extended counterpart known as extended CGNRs (ECGNR) are constructed by making alternated regular cuts in pristine graphene nanoribbons (GNRs). First-principles calculations demonstrate that these GNRs are super-ductile and possess width-dependent mechanical properties. The Young’s modulus is calculated to be 389.4 GPa and 414.6 GPa for CGNR and ECGNR, respectively. The bandgap of these nanoribbons decreases on the application of tensile strain. The carrier effective masses are found to be highly sensitive towards mechanical strains. The holes (electrons) mobility of ECGNR is calculated to be 7.68 × 104 cm2 V−1 s−1 (1.69 × 104 cm2 V−1 s−1), which is higher than that of CGNR can be further enhanced by elongation. The prominent peaks of the imaginary part of dielectric function and electron energy loss spectra show redshift on increasing the tensile strain. The electron energy loss spectra show intense plasmonic structure in low energy spectrum indicating GNRs to be more sensitive to the visible region than ultra violet spectrum. Our results provide insight about the possible applications of GNRs in the fields of high-speed transistors, sensors, photonics, and optoelectronics.

Effects of Compressive and Tensile Strain on Macrophages during Simulated Orthodontic Tooth Movement.

During orthodontic tooth movement (OTM) to therapeutically correct the position of misaligned teeth, thus improving oral health and quality of life, fibroblasts, macrophages, and other immune cells within the periodontal ligament (PDL), which connects a tooth to its surrounding bone, are exposed to compressive and tensile strain. While it is known that PDL fibroblasts are critically involved in the biological regulation of OTM by a mechanotransductively triggered release of cytokines, it is unclear whether macrophages also react to pressure and tension in a similar manner thus impacting on or mediating OTM. RAW264.7 macrophages were seeded onto conventional 6-well cell culture plates for pressure or on Bioflex plates for tension assays and preincubated for 24 h. For in vitro simulation of physiological orthodontic compressive or tensile strain for 2 h, 4 h, 24 h, and 48 h, glass discs (2 g/cm2) were placed or adherent macrophages isotropically stretched for 16%, respectively. We determined cell number, cytotoxicity, and gene/protein expression of Vegf-a/VEGF-A (macrophage-mediated angiogenesis), Mmp-8/9 (extracellular matrix reorganization), and Cox-2/PG-E2, Il-6/IL-6, and Tnf-α/TNF-α (proinflammatory mediators) by RT-qPCR and ELISA. Compressive but not tensile strain resulted in a significant reduction in cell number after only 2 h. Mmp-8 and Mmp-9 expression was significantly enhanced within 24 h of compressive and in part tensile strain. Significantly increased Vegf-a/VEGF-A expression was detected within 4 h of pressure, but not during application of tensile strain. Expression of proinflammatory mediators Cox-2/PG-E2, Il-6/IL-6, and Tnf-α/TNF-α was significantly increased as early as 2-4 h after application of compressive or tensile strain. Our results indicate that macrophages respond early on to compressive and tensile strain occurring during OTM with an enhanced gene expression of proinflammatory cytokines, which could affect PDL fibroblasts, osteoblasts, and immune cells triggering or enhancing the biological mechanisms and osteoclastogenesis underlying OTM.

Strain engineering of ferroelectric KNbO3 for bulk photovoltaic applications: an insight from density functional theory calculations

A large ferroelectric (FE) polarization and low bandgap are essential to improving the bulk photovoltaic response which is the generation of photocurrent in the polar non-centrosymmetric materials such as FE perovskite oxides. Among various perovskite oxides, Potassium Niobate (KNbO3, KNO) is a promising FE material for bulk photovoltaic applications as its bandgap and polarization can be tuned effectively by strain, doping, or by applying an electric field. In this work, using the density functional theory calculations, we present an insight into the strain engineering of polarization, band structure, and optical properties of the cubic (C), tetragonal (T), and orthorhombic (O) structures of KNO. The tensile and compressive strain under the triaxial, biaxial, and uniaxial conditions are applied along the direction parallel and perpendicular to the polar axis of KNO structures. We find that the bandgap decreases along with a substantial increment of polarization on the application of tensile strain along the direction parallel to the polar axis. In T (O) phase at +2% strain, the polarization increases by 18 µC cm−2 (14 µC cm−2) in triaxial, 26 µC cm−2 (16 µC cm−2) in biaxial, and 29 µC cm−2 (29 µC cm−2) in uniaxial conditions with a considerable decreasing of bandgap with respect to zero strain condition. Therefore, wisely applying the tensile strain along the direction parallel to the polar axis, the photovoltaic efficiency of KNO can be improved.

Optimizing the thermoelectric transport properties of Bi2O2Se monolayer via biaxial strain.

Recent studies have shown that the two-dimensional semiconductor Bi2O2Se is a promising thermoelectric (TE) material, whereas its TE performance needs to be further improved. By using first-principles methods combined with semi-classical Boltzmann transport theory, we systemically investigate the effects of biaxial strain on the TE transport properties of Bi2O2Se monolayer. Under -2-2% strain, the maximum power factors of 3.63-3.79 and 1.43-1.79 mW m-1 K-2 are found for p-type and n-type doped Bi2O2Se monolayer, respectively. The figure of merit ZT of p-type doped Bi2O2Se monolayer is enhanced to 1.14 by 2% tensile strain at 300 K and it reaches as high as 4.22 at 800 K (as compared with the highest value of 1.42 for bulk Bi2O2Se at 800 K). This study demonstrates that the TE performance of Bi2O2Se can be significantly improved by application of tensile strain and the Bi2O2Se monolayer has great potential as a TE material.

Tuning electronic and transport properties of MoS2/Ti2C heterostructure by external strain and electric field

We investigated the effects of external strain and electric field on the electronic, transport, and thermoelectric properties of MoS2/Ti2C heterostructure by using the first-principles method. Its electronic properties can be effectively tuned by applying uniaxial tensile strain, biaxial tensile strain, and vertical electric field, and exhibits different behaviour. An obvious band gap between the valence bands I and II is observed under external field. Upon application of tensile strain, energy bands become more dispersive, inducing the increase in conductivity. However, when the coupling of tensile strain and vertical electric field was imposed, energy bands become more flat, leading to the decrease in conductivity. Based on the calculated energy bands, the effect of external field on the carrier effective mass was also discussed. Furthermore, the change in electronic properties affects the transport and thermoelectric properties of MoS2/Ti2C heterostructure. Tensile strain enhances its transport properties. However, the transport properties of MoS2/Ti2C heterostructure is weakened under the application of vertical electric field. Comparing with no external field, the thermoelectric power factor is decreased under external field.

High intrinsic dissipation of graphyne nanotubes

We utilize molecular-dynamics simulations to report the first investigation of energy dissipation of two different doubly clamped graphyne nanotubes (GNTs), where the point of emphasis is to compare their dissipation characteristics with those of carbon nanotube (CNT). The obtained results demonstrate that: (a) GNTs exhibit significantly higher energy dissipation, and thus lower quality (Q) factor which is generally five times lower than that of CNT; (b) the Q factor of GNT further reduces with the increasing percentage of acetylenic linkages, which originates from the larger vibrational mismatch between the acetylenic linkage (sp C-C bonds) and the hexagonal ring (sp2 C-C bonds); (c) the application of tensile strain is found to be highly beneficial to improving the Q factor of GNTs, especially for those with higher percentage of acetylenic linkages. These findings enable a first insight into the damping behavior of GNTs and also offer a significant guideline for the future design of GNT-based devices.

Computational exploration of two-dimensional silicon diarsenide and germanium arsenide for photovoltaic applications.

The properties of bulk compounds required to be suitable for photovoltaic applications, such as excellent visible light absorption, favorable exciton formation, and charge separation are equally essential for two-dimensional (2D) materials. Here, we systematically study 2D group IV–V compounds such as SiAs2 and GeAs2 with regard to their structural, electronic and optical properties using density functional theory (DFT), hybrid functional and Bethe–Salpeter equation (BSE) approaches. We find that the exfoliation of single-layer SiAs2 and GeAs2 is highly feasible and in principle could be carried out experimentally by mechanical cleavage due to the dynamic stability of the compounds, which is inferred by analyzing their vibrational normal mode. SiAs2 and GeAs2 monolayers possess a bandgap of 1.91 and 1.64 eV, respectively, which is excellent for sunlight harvesting, while the exciton binding energy is found to be 0.25 and 0.14 eV, respectively. Furthermore, band-gap tuning is also possible by application of tensile strain. Our results highlight a new family of 2D materials with great potential for solar cell applications.

MoS2 edges and heterophase interfaces: energy, structure and phase engineering

The transition metal dichalcogenides exhibit polymorphism; i.e. both 2H and 1T′ crystal structures, each with unique electronic properties. These two phases can coexist within the same monolayer microstructure, producing 2H/1T′ interfaces. Here we report a systematic investigation of the energetics of the experimentally most important MoS2 heterophase interfaces and edges. The stable interface and edge structures change with chemical potential (these edges/interfaces are usually non-stoichiometric). Stable edges tend to be those of highest atomic density and the stable interfaces correspond to those with local atomic structure very similar to the 2H crystal. The interfacial energies are lower than those of the edges, and the 1T′ edges have lower energy than the 2H edges. Because the 1T′ edges have much lower energy than the 2H edges, a sufficiently narrow 1T′ ribbon will be more stable than the corresponding 2H ribbon (this critical width is much larger in MoTe2 than in MoS2). Similarly, a large 2H flake have an equilibrium strip of 1T′ along its edge (again this effect is much larger in MoTe2 than in MoS2). Application of tensile strains can increase the width of the stable 1T′ strip or the critical thickness below which a ribbon favors the 1T′ structure. These effects provide a means to phase engineer transition metal dichalcogenide microstructures.