Biaxial Tensile Strain Research Articles

Strain effect on the physical properties of novel Mg3NI3 perovskite material: First principle DFT analysis

Inorganic perovskite-based substances have become a major attraction to solar technology. Inorganic cubic perovskites have generated a heap of fascination owing to their distinctive optical, electrical, and structural features. The photovoltaic and optoelectronic industries prioritize lead-free, atomically tailored metal halide perovskites due to the need to address lead (Pb) toxicity and instability. This study assessed the optical, structural, and electrical parameters of Pb-free inorganic halide perovskites as a function of biaxial compressive and tensile strain, leveraging first-principles density-functional theory (FP-DFT). Refractive index, absorption coefficient, reflectivity, dielectric function, and tolerance factor are a few additional optical parameters that are computed and processed. The bandgap of the planar molecule is 0.412 eV (PBE) when SOC is not applied. The bandgap reduces to 0.363 eV (PBE) at its Γ(gamma) and R-point when the subjective SOC effect is taken into consideration. This compound's bandgap will narrow under tensile strain and expand under compressive strain, depending on whether the SOC effect is applied or not. Several elastic factors are anticipated, including the bulk modulus, Pugh's ratio, elastic constants, anisotropic factors, and Poisson's ratio. Electronic property calculations using band mechanism and density of states (DOS) suggest that have a bandgap that is indirect and semiconductive. The elastic properties of this material were found to be mechanically stable, anisotropic, and ductile. In the photon energy range suitable for solar cells, the spikes in the dielectric constant of are seen. Our findings point to the prospect of as a non-toxic, high-performance, low-cost material for implementation in solar cells and different semiconductor devices.

First-Principles Study on Strain-Induced Modulation of Electronic Properties in Indium Phosphide.

Indium phosphide (InP) is widely utilized in the fields of electronics and photovoltaics due to its high electron mobility and high photoelectric conversion efficiency. Strain engineering has been extensively employed in semiconductor devices to adjust physical properties and enhance material performance. In the present work, the band structure and electronic effective mass of InP under different strains are investigated by ab initio calculations. The results show that InP consistently exhibits a direct bandgap under different strains. Both uniaxial strain and biaxial tensile strain exhibit linear effects on the change in bandgap values. However, the bandgap of InP is significantly influenced by uniaxial compressive strain and biaxial tensile strain, respectively. The study of the InP bandgap under different hydrostatic pressures reveals that InP becomes metallic when the pressure is less than -7 GPa. Furthermore, strain also leads to changes in effective mass and the anisotropy of electron mobility. The studies of electronic properties under different strain types are of great significance for broadening the application of InP devices.

Two-dimensional Sc2O3 monolayer with tunable ultrawide bandgap for solar-blind ultraviolet photodetector

A novel 2D scandia (Sc2O3) monolayer was identified using an evolutionary algorithm-based crystal structure prediction method. The Sc2O3 monolayer exhibits a P3‾m1 symmetry and excellent energetic, thermal, dynamical, and mechanical stability, as well as good mechanical flexibility. The monolayer possesses an ultrawide indirect band gap of 6.246 eV. The monolayer is transparent in the visible light zone, while the large exciton effect leads to significant absorption in the solar-blind and vacuum ultraviolet regions. The band gap of this monolayer can be reduced monotonically by external biaxial tensile strain, resulting in the absorption spectrum covering the entire solar blind spectral region when the load reaches 5.0 %. Additionally, the monolayer has an ultra-high in-plane dielectric constant of approximately 50. The superior stability, flexibility, and strain-tunable electronic and optical properties, as well as the ultra-high dielectric constant, suggest its potential application in a solar-blind photodetector in harsh environments.

Strain engineering for optimized hydrogen storage: Enhancing ionic conductivity and achieving near-room-temperature desorption in Mg₂NiH₄

This study investigates strain engineering to optimize hydrogen storage in Mg₂NiH₄, with a focus on enhancing ionic conductivity and approaching room-temperature desorption. Using density functional theory (DFT), we analysed the effects of uniaxial and biaxial tensile and compressive strains on the structural, mechanical, diffusion kinetics, and electronic properties of Mg₂NiH₄. The activation energy for hydrogen diffusion was found to range from 0.38 to 0.45 eV under different strain conditions. The application of strain significantly influences ionic conductivity, with uniaxial strain resulting in values between 1.18 and 25.5 S/m, and biaxial strain yielding values from 12.3 to 18.3 S/m. Mechanical analysis shows that Mg₂NiH₄ exhibits brittle behaviour across all strain conditions. Additionally, electronic structure analysis indicates that the material maintains its metallic properties under both uniaxial and biaxial strain. Although the study did not achieve room-temperature desorption, it demonstrated significant progress, with desorption occurring at approximately 500 K. These results demonstrate that strain engineering can significantly improve ionic conductivity and facilitate hydrogen desorption closer to practical room temperature, providing valuable insights for optimizing Mg₂NiH₄ for practical hydrogen storage applications.

Theoretical insights into the ultrahigh piezoelectric performance of (BiFeO3)n/(BaTiO3)n (n = 1–5) superlattices

Perovskite structures have attracted extensive attention in microelectromechanical systems and nanoelectromechanical systems devices due to the high piezoelectric response and the low dielectric constant. The piezoelectric and dielectric properties of the tetragonal BiFeO3/BaTiO3 superlattices grown along the c-axis direction are investigated using density functional theory (DFT) and density functional perturbation theory. The calculated results demonstrate that the (BiFeO3)n/(BaTiO3)n (n = 1–5) superlattices exhibit a profoundly increased piezoelectric response compared to their bulk structures. The (BiFeO3)2/(BaTiO3)2 possesses the highest piezoelectric d33 of 697 pC/N among known lead-free perovskite systems. Furthermore, the (BiFeO3)2/(BaTiO3)2 superlattice possesses a low dielectric ɛ33, and its d33 at 2% tensile strain is 16 times larger than that of an unstrained equilibrium structure. This demonstrates that biaxial tensile strain significantly enhances the piezoelectric response. Combining the special quasirandom structure method with DFT, the structures of a 0.5BiFeO3–0.5BaTiO3 solid solution are predicted, and its calculated d33 is 58 pC/N, which is much smaller than that of a (BiFeO3)2/(BaTiO3)2 superlattice. The results suggest that the (BiFeO3)2/(BaTiO3)2 superlattice might be a potential candidate for nonvolatile random access memory, transducers and actuators, and nanoscale electronic devices.

Computational screening of Group VⅢ@C5N4 single-atom electrocatalysts for overall water splitting

Single-atom catalysts (SACs) have great potential for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) since their high atomic utilization and strong metal–support interactions. Herein, we develop TM@C5N4 (TM = Fe, Co, Ni, Ru, Rh, Pd, Os, Ir and Pt) catalysts via embedding Group VⅢ TM in holey C5N4 substrate and further evaluate their electrocatalytic activity using density functional theory (DFT) calculations. Systematical studies indicate that Fe@C5N4, Pd@C5N4 and Ir@C5N4 catalysts all exhibit excellent HER performance, which mainly because of their small ΔGH* values of 0.101 eV, -0.114 eV and 0.070 eV, respectively. In parallel, Rh@C5N4 and Ir@C5N4 possess high OER activity along with low overpotential of 0.50 V, which is superior to the commercial IrO2 catalyst (0.56 V). Obviously, Ir@C5N4 could be utilized as bifunctional electrocatalysts both HER and OER in water splitting. Furthermore, we analyze their correlative catalytic mechanisms using the molecular orbitals. Besides, biaxial strain modulation could effectively regulate the catalytic activity of HER and OER. Particularly, 2 % biaxial tensile strain could bring Ir@C5N4 superb HER/OER catalytic performance. Finally, we anticipate that this strain engineering would provide a new perspective for developing high-performance SACs for water splitting.

Fully spin-polarized two dimensional polar semi-metallic phase in Eu substituted GdI2 monolayer

Abstract The coexistence of seemingly mutually exclusive properties such as ferromagnetism, ferroelectricity and metallicity in atomically thin materials is the requirement of the hour in electronics as the Moore’s law faces an impending end. Only a few 2D multiferroic materials have been predicted/realized so far. The polar metals with simultaneous presence of polarity and conductivity are also equally rare. Here, we predict, based on first-principles calculations that an Eu-substituted rare-earth halide GdI2 monolayer showcases ferromagnetism, ferroelasticity while being polar and a fully spin-polarized semi-metal at the same time. The ferroelasticity and polarity are shown to be coupled making it possible to switch the polar direction using external mechanical stress. Further, it is observed that an application of biaxial tensile strain of 5% causes the spin easy-axis to shift from out-of-plane to in-plane direction. Thus, spin easy axis gets coupled with the direction of polarization in the strained monolayer making the switching of magnetization also possible using external strain. Simultaneous coexistence and coupling of the ferroic orders in a metallic 2D material makes the Eu substituted GdI2 monolayer an incredibly rare material for nano-electronics and spintronics applications.

Microstructure characterization and formability assessment of electron beam welded Nb-10Hf-1Ti (wt.%) refractory alloy sheets

Formability study on welded blanks of Nb-based refractory alloy C-103 (Nb-10Hf-1Ti (wt.%)) has tremendous potential for utilizing smaller sheets for realization of large-size divergent portions of upper-stage liquid engine nozzle of satellite launch vehicles and thrusters of attitude orbital control systems. In this work, vacuum-annealed monolithic C-103 sheets were electron beam welded successfully to obtain defect-free welds and detailed microstructural and mechanical characterizations were investigated. Columnar epitaxial grains were found in fusion zone (FZ) instead of equiaxed grains in base metal (BM). Detailed SEM and HRTEM analyses revealed spherical shape of nano-sized HfO2 precipitates with monoclinic crystal structure in the C-103 sheet. Further, microhardness across the weld cross-section indicated that the FZ had a uniform and maximum hardness of ∼195 HV0.5 due to formation of finer nano-sized HfO2 precipitates with higher number density, followed by a lowering of hardness in a narrow heat-affected zone. A marginal reduction in tensile strength of ∼6% with a considerable decrease in ductility of ∼29% was noticed for the welded sample. However, fracture occurred in the BM region, indicating good weld integrity. Furthermore, formability of the welded blanks was evaluated in terms of limiting dome height (LDH), forming limit diagram, and deep drawn cup depth. The effect of the presence of WZ on the formability of the C-103 sheet was estimated under uniaxial, plane strain, and biaxial tensile strain paths for the first time, and the results were compared with the monolithic sample. It was noted that the failure limit of the welded specimens decreased compared to that of the monolithic sample, resulting in a lower LDH of approximately 69% and 62% when deformed along plane strain and biaxial tensile strain paths, respectively. However, a marginal variation in LDH was observed for the uniaxial strain path. Also, the welded blank had more resistance to material flow into the die cavity due to the harder weld region, resulting in a reduction of deep drawn cup depth by 52% than that of the monolithic blank. The overall results concluded that the presence of the WZ significantly affected the formability of the C-103 sheet, especially in plane strain and biaxial strain paths. However, the fracture was never found to be propagating along the weld line, indicating the ability of the weld to sustain large plastic strains. This study provides insightful information on the formability of electron beam welded C-103 sheets for the successful fabrication of space components.

The impact of mechanical strain on magnetic and structural properties of 2D materials: A Monte Carlo study.

The inherent flexibility of two-dimensional (2D) materials allows for efficient manipulation of their physical properties through strain application, which is essential for the development of advanced nanoscale devices. This study aimed to understand the impact of mechanical strain on the magnetic properties of two-dimensional (2D) materials using Monte Carlo simulations. The effects of several strain states on the magnetic properties were investigated using the Lennard-Jones potential and bond length-dependent exchange interactions. The key parameters analyzed include the Lindemann coefficient, radial distribution function, and magnetization in relation to temperature and magnetic field. The results indicate that applying biaxial tensile strain generally reduces the critical temperature (Tc). In contrast, the biaxial compressive strain increased Tc within the elastic range, but decreased at higher strain levels. Both compressive and tensile strains significantly influence the ferromagnetic properties and structural ordering, as evidenced by magnetization hysteresis. Notably, pure shear strain did not induce disorder, leaving the magnetization unaffected. In addition, our findings suggest the potential of domain-formation mechanisms. This study provides comprehensive insights into the influence of mechanical strain on the magnetic behavior and structural integrity of 2D materials, offering valuable guidance for future research and advanced material design applications.

Unveiling the tunable electronic, optoelectronic, and strain-sensitive gas sensing properties of Janus ZrBrCl: Insights from DFT study

Janus monolayers materials exhibit extraordinary physical and chemical properties because of crystal field changes caused by their asymmetric structures. Here, we investigate the electronic, switching, optoelectronic, and strain-sensitive gas-sensing properties of a Janus ZrBrCl monolayer via density-functional theory and the nonequilibrium Green’s function methods. The electronic properties can be tuned by applying biaxial strain and electric fields. In particular, the band gap can be changed from indirect to direct via applied a + 8 % biaxial tensile strain. It can be transformed from a semiconductor to a metal with an applied −14 % biaxial compressive strain, with a 1011 switching ratio. In addition, a biaxial strain and an electric field can modulate visible light absorption and photocurrents. Under a −12 % biaxial compressive strain, the absorption coefficient increased to 5.26 × 105 cm−1 from the intrinsic 4.08 × 105 cm−1. Across biaxial strains from −4% to + 4 %, the photocurrent density peak displayed red and blue shifts, respectively, with increasing tensile and compressive strains. NH3, NO2, and NO physically adsorb on the Br side of the ZrBrCl monolayer. Maximum gas sensitivity values of a ZrBrCl sensor are 52 % in the zigzag direction and 21 % in the armchair direction. After application of the −14 % biaxial strain, the maximum values respectively increased to 76 % and 179 %. The biaxial compressive strain-sensitive gas-sensing properties are driven by changes in the electrostatic potential difference between the Br and Cl surfaces. These findings indicate promising candidate materials for high-performance switching and optoelectronic devices, and also provide a strategy for improved gas sensors.

Two-dimensional Janus MXTe (M = Hf, Zr; X = S, Se) piezoelectrocatalysts: a comprehensive investigation of its electronic, synthesis feasibility, electric polarization, and hydrogen evolution reaction activity

Abstract We computationally investigated potential piezoelectrocatalysts, two-dimensional (2D) Janus MXTe (M = Hf, Zr; X = S, Se). The structural and electronic properties, synthesis feasibility, piezoelectric properties, and hydrogen evolution reaction were calculated. Our results showed that these 2D Janus MXTe are narrow-gap semiconductors, indicating great conductivity for electrocatalysis. The feasibility of synthesis was comparable to the already synthesized Janus materials. To exhibit a piezoelectrocatalytic effect, the material has to be piezoelectric and catalytically effective simultaneously. As the Janus structure breaks the centrosymmetry, the considered MXTe are intrinsically piezoelectric. We therefore calculated the dipole moments and the variation of out-of-plane polarization upon strain. The computed piezoelectric coefficient e 31 is within the same order of magnitude as that of other Janus 2D materials. Finally, although pristine 2D Janus MXTe were inert to hydrogen evolution reaction, incorporation of single-atom defects was found to boost hydrogen adsorption significantly. The catalytic efficacy can be further tuned by biaxial tensile strain, effectively controlling the Gibbs free energy of adsorption to be close to the thermoneutral value that is indicative of an excellent hydrogen evolution reaction activity, at least for ZrSTe Janus monolayer. In summary, this work proposed and comprehensively investigated a new class of possible piezoelectrocatalysts, 2D Janus materials, which is feasible to be synthesized, catalytically effective, and has great conductivity.

Strain-Controlled Electronic and Magnetic Properties of Janus Nitride MXene Monolayer MnCrNO2

Two-dimensional (2D) van der Waals (vdW) magnetic materials show potential for the advancement of high-density, energy-efficient electronic and spintronic applications in future memory and computation. Here, by using first-principles density functional theory (DFT) calculations, we predict a new 2D Janus nitride MXene MnCrNO2 monolayer. Our results suggest that the optimized MnCrNO2 monolayer possesses a hexagonal structure and exhibits good dynamical stability. The intrinsic monolayer MnCrNO2 exhibits semiconductive properties and adopts a ferromagnetic ground state with an out-of-plane easy axis. It can sustain strain effects within a wide range of strains from −10% to +8%, as indicated by the phonon dispersion spectra. Under the biaxial tensile strain, a remarkable decrease in the bandgap of the MnCrNO2 is induced, which is attributed to the distinct roles played by Mn and Cr in the VBM or CBM bands. Furthermore, when the compressive strain reaches approximately −8%, the magnetic anisotropy undergoes a transition from an out-of-plane easy axis to an in-plane easy axis. This change is mainly influenced by the efficient hybridization of the d orbitals, particularly in Mn atoms. Our study of the Janus MXene MnCrNO2 monolayer indicates its potential as a promising candidate for innovative electronic and spintronic devices; this potential is expected to create interest in its synthesis.

Strain engineering of the structural, electronic, and optical properties of phosphorene‐like ZnS ceramic nanolayers: Density functional theory study

AbstractStrain engineering is a powerful technique for controlling the performance of semiconductor ceramic systems. In this article, the effect of strain engineering, specifically biaxial compressive and tensile strains, on the bonding characteristics, structure, electronic, and optical properties of nonplanar phosphorene‐like (NPP) ZnS ceramic nanolayers was investigated using density functional theory. It was observed that this ceramic exhibits greater stability under significant tensile strains. The structural stability of NPP‐ZnS ceramic, both with and without biaxial strain, was confirmed by its negative formation energy. Biaxial strain strongly influences the electronic band structure of NPP‐ZnS ceramic nanolayers, leading to a transformation from a direct band gap to an indirect gap under tensile strain. Additionally, the bandgap decreases under compressive strain, while it slightly increases under tensile strain. Various optical properties, including refractive index, extinction coefficient, absorption, reflectivity, optical conductivity, and optical susceptibility, were calculated. Biaxial compressive and tensile strains alter the optical properties, shifting them to higher or lower frequencies. NPP‐ZnS ceramic nanolayers exhibit high optical absorption in the UV range, which can be further enhanced by biaxial strain. Furthermore, under increasing compressive strain, the absorption edge moves toward higher energies. This improvement in optical absorption expands the potential applications of NPP‐ZnS ceramic nanolayers in optoelectronic devices.

Heightening polyoxometalate encapsulation efficiency for biaxial strain-induced catalytic activity boosting

Controllable assembly of polyoxometalates (POMs) in confined nanochannels is crucial to understand the host-guest structures and tailor the emerging properties for applications. Here, we report the encapsulation of polyoxometalates inside single-walled carbon nanotubes (SWNTs) for target catalytic regulation. Theoretical modeling predicts the confined polyoxomolybdates are able to induce biaxial tensile strains of SWNTs for more stable interaction with iron phthalocyanine (FePc) and tailor the charge distribution and coordination environment of targetable FeN4 sites, leading to improved catalytic activity toward oxygen reduction reaction (ORR). The polyoxomolybdates are confined in the SWNTs via redox-driven encapsulation mechanism with a POM encapsulation efficiency of about 21 %. The constructed FePc/SWNT@POM molecule catalyst exhibits a high half-wave potential of 0.90 V, excellent stability and methanol tolerance in alkaline medium. The zinc-air battery also presents prominent charge-discharge ability and long-term durability over 400 h with a peak power density of 190.8 mW cm–2.

Interfacial thermal resistance in stanene/ hexagonal boron nitride van der Waals heterostructures: A molecular dynamics study

Recently, the stanene (Sn)/hexagonal boron nitride (h-BN) van der Waals heterostructure (vdW) has garnered significant attention among the scientific community due to its distinctive electrical, optical, and thermal characteristics. Despite the promising potential of this heterostructure, the interfacial thermal resistance (ITR) between the Sn and h-BN layers remains unexplored. Understanding and modulating this ITR are essential steps towards harnessing the maximum potential of these materials in practical nanodevices. This study aims to investigate the interfacial thermal resistance (ITR) between the Sn and h-BN layers through the use of conventional molecular dynamics (MD) simulation. The transient pump–probe heating technique, commonly referred to as the Fast Pump Probe (FPP) approach, is utilized to analyze the ITR of the Sn/h-BN heterostructure. The estimated ITR value of a 30 × 10 nm2 Sn/h-BN nanosheet is found to be around ∼ 7 × 10-8 K.m2/W at room temperature. This study comprehensively investigates the impact of various internal and external parameters including nanosheet size, system temperature, contact pressure, vacancy concentration, and mechanical tensile strain (uniaxial and biaxial) on ITR, providing an extensive understanding of how these factors collectively affect the thermal resistance between Sn and h-BN layers. The simulationresults demonstrate a consistent decline in ITR by approximately ∼ 93 %, ∼45 %, ∼65 %, and ∼ 33 % with the increasing system size, temperature, contact pressure, and defect concentration, respectively. In contrast, increasing mechanical strain leads to a substantial enhancement in ITR, with a maximum increase of approximately ∼ 47 % under uniaxial tensile strain and almost ∼ 99 % under biaxial tensile strain. Moreover, the pristine Sn/h-BN heterostructure exhibits no significant thermal rectification effect. The Phonon Density of States (PDOS) profile of the Sn and h-BN layer is calculated to elucidate this underlying behavior of ITR. The PDOS analysis reveals that heat is transported from h-BN to the Sn layer through efficient coupling of low-frequency flexural phonons between these two materials. This work will provide both theoretical support and logical guidelines for modulating thermal resistance across diverse dissimilar material interfaces, which will be necessary for the development of advanced nanodevices used in next-generation nanoelectronics, nanophotonic, and optoelectronics applications.

Stretchable Metamaterials with Tunable Infrared Emissivity for Dynamic Thermal Management.

Manipulation of infrared emissivity, which is closely related to surface structure and optical parameters of materials, is a crucial approach for realizing dynamic thermal management. In this study, we design a metamaterial consisting of an array of aluminum disks embedded on a surface of a stretchable elastomeric substrate. Mechanical stretching-induced deformation allows dynamic modification of the surface structure and equivalent optical parameters, thus enabling dynamic control of the emissivity. By utilizing the elastomer polydimethylsiloxane (PDMS) as the substrate, the microstructure interdisk gap can be altered by stretching the PDMS. Through theoretical calculations, the plausibility of this approach is explained by the excitation of plasmon resonance and the variation in the exposed area of highly absorbent PDMS, and the optimal structures for tuning the infrared emissivity are revealed to be 6 μm in diameter and 100 nm in height. Based on this design, we prepare samples with periods of 7 and 7.9 μm and experimentally demonstrate that a change in the period can cause a change in the emissivity and thus tunability in thermal control performance. The temperature difference between the two samples reaches 44.1 °C at a heating power of 0.28 W/cm2 for both samples. Furthermore, we construct a stretching platform that enables in situ mechanical stretching to realize dynamic changes in emissivity. The integral infrared emissivity of the sample increases from 0.32 to 0.5 at a biaxial tensile strain of 13%, achieving a 56% modulation rate of the integral infrared emissivity. The material is expected to enable dynamic thermal management.

Enhanced Carrier Transport Performance of Monolayer Hafnium Disulphide by Strain Engineering.

For semiconducting two-dimensional transition metal dichalcogenides (TMDs), the carrier transport properties of the material are affected by strain engineering. In this study, we investigate the carrier mobility of monolayer hafnium disulphide (HfS2) under different biaxial strains by first-principles calculations combined with the Kubo-Greenwood mobility approach and the compact band model. The decrease/increase in the effective mass of the conduction band (CB) of monolayer HfS2 caused by biaxial tensile/compressive strain is the major reason for the enhancement/degradation of its electron mobility. The lower hole effective mass of the valence bands (VB) in monolayer HfS2 under biaxial compressive strain improves its hole transport performance compared to that under biaxial tensile strain. In summary, biaxial compressive strain causes a decrease in both the effective mass and phonon scattering rate of monolayer HfS2, resulting in an increase in its carrier mobility. Under the biaxial compressive strain reaches 4%, the electron mobility enhancement ratio of the CB of monolayer HfS2 is ~90%. For the VB of monolayer HfS2, the maximum hole mobility enhancement ratio appears to be ~13% at a biaxial compressive strain of 4%. Our results indicate that the carrier transport performance of monolayer HfS2 can be greatly improved by strain engineering.

Prediction of Two-Dimensional Janus Transition-Metal Chalcogenides: Robust Ferromagnetic Semiconductor with High Curie Temperature.

Two-dimensional (2D) ferromagnetic semiconductors (FM SCs) provide an ideal platform for the development of quantum information technology in nanoscale devices. However, many developed 2D FM materials present a very low Curie temperature (TC), greatly limiting their application in spintronic devices. In this work, we predict two stable 2D transition metal chalcogenides, V3Se3X2 (X = S, Te) monolayers, by using first-principles calculations. Our results show that the V3Se3Te2 monolayer is a robust bipolar magnetic SC with a moderate bandgap of 0.53 eV, while V3Se3S2 is a direct band-gap FM SC with a bandgap of 0.59 eV. Interestingly, the ferromagnetisms of both monolayers are robust due to the V-S/Se/Te-V superexchange interaction, and TCs are about 406 K and 301 K, respectively. Applying biaxial strains, the FM SC to antiferromagnetic (AFM) SC transition is revealed at 5% and 3% of biaxial tensile strain. In addition, their high mechanical, dynamical, and thermal stabilities are further verified by phonon dispersion calculations and ab initio molecular dynamics (AIMD) calculations. Their outstanding attributes render the V3Se3Y2 (Y = S, Te) monolayers promising candidates as 2D FM SCs for a wide range of applications.

Mechanical strain effect on the optoelectronic properties and photocatalysis applications of layered AlN/GaN nanoheterostructure.

The aim of this work is to use first principles calculations to examine the effects of different mechanical strains on the optoelectronic and photocatalytic capabilities of the 2D/2D nanoheterostructure of AlN/GaN. By utilizing the lmBJ (Meta-GGA) and PBEsol (GGA) functional, the bandgap of the nanoheterostructure is calculated and found to be 4.89eV and 3.24eV. Simulated 2D AlN/GaN nanoheterostructure exhibits exceptional optical and electronic characteristics under applied biaxial tensile and compressive strains. The band gap changes from 4.89 to 3.77eV, while the energy gap nature transitions from direct to indirect during tensile strain fluctuations of 0% to 8%. Strain is also found to have a significant effect on the optical absorption peaks. And a 0-8% rise in tensile strain causes the initial absorption peak of the 2D AlN/GaN nanoheterostructure to shift from 4.88 to 4.20eV, which results in a 14% red shift in photon energy for every 2% change in strain. Furthermore, the optimum bandgap and band edge positions of the 2D AlN/GaN nanoheterostructure enable the water redox process to produce hydrogen and oxygen for wide range of pH. Thus, modification via strain may be an effective method for altering the optical as well as electronic characteristics of a 2D AlN/GaN nanoheterostructure, and this study may pave the way for new applications of this material in optoelectronic devices in the future. In the current work, density functional theory is used to explore every attribute of the 2D AlN/GaN nanoheterostructure. To characterize the electronic exchange-correlation, we used the PBEsol functional. In order to prevent any interlayer contact between periodicity of images, a vacuum is produced along the z-direction of approximately 10 Å. To increase the precision of bandgap prediction, the electronic and optical characteristics were computed using the meta-GGA lmBJ functional. To account for interlayer van der Waals interactions, nanoheterostructure computations were performed using the DFT-D3 functional.

High Electron Mobility in Si-Doped Two-Dimensional β-Ga2O3 Tuned Using Biaxial Strain.

Two-dimensional (2D) semiconductors have attracted much attention regarding their use in flexible electronic and optoelectronic devices, but the inherent poor electron mobility in conventional 2D materials severely restricts their applications. Using first-principles calculations in conjunction with Boltzmann transport theory, we systematically investigated the Si-doped 2D β-Ga2O3 structure mediated by biaxial strain, where the structural stabilities were determined by formation energy, phonon spectrum, and ab initio molecular dynamic simulation. Initially, the band gap values of Si-doped 2D β-Ga2O3 increased slightly, followed by a rapid decrease from 2.46 eV to 1.38 eV accompanied by strain modulations from -8% compressive to +8% tensile, which can be ascribed to the bigger energy elevation of the σ* anti-bonding in the conduction band minimum than that of the π bonding in the valence band maximum. Additionally, band structure calculations resolved a direct-to-indirect transition under the tensile strains. Furthermore, a significantly high electron mobility up to 4911.18 cm2 V-1 s-1 was discovered in Si-doped 2D β-Ga2O3 as the biaxial tensile strain approached 8%, which originated mainly from the decreased quantum confinement effect on the surface. The electrical conductivity was elevated with the increase in tensile strain and the enhancement of temperature from 300 K to 800 K. Our studies demonstrate the tunable electron mobilities and band structures of Si-doped 2D β-Ga2O3 using biaxial strain and shed light on its great potential in nanoscale electronics.