Effect Of External Strain Research Articles

First-Principles Study of Monolayer GeTe and the Effect of External Strain and Electric Field

First-Principles Study of Monolayer GeTe and the Effect of External Strain and Electric Field

Exploring optoelectronic and thermal characteristics of Janus MoSeTe and WSeTe monolayers under mechanical strain

This paper reveals the effect of external strain on the electronic, thermal and optical properties of Janus MSeTe (M=Mo, W) using first principles. Phonon spectrum calculations confirm the dynamic stability of the system. Biaxial stretching can effectively modulate its thermal properties. Uniaxial, biaxial and shear strains modulate the band structure, structural parameters, averaged differential charge density and optical properties of the MSeTe system to different degrees. The increase of compressive and shear strains leads to a gradual decrease of the band gap and triggers a semiconductor-metal phase transition at the critical point. The intrinsic system exhibits strong light absorption in the visible and ultraviolet regions, while strain induces a redshift of the light-absorbing edge, which enhances the response to the infrared and visible wavelength bands. These findings provide a theoretical basis and application potential for the design of optoelectronic devices and thermoelectric materials.

First-principles prediction of 1H-Na2Se monolayer: effects of external strain and point defects associated with constituent atoms

In this work, a new Na2Se monolayer in 1H-phase, with interesting properties similar to transition metal dichalcogenides (TMDs), has been predicted using first-principles calculations. Results reveal good stability and wide direct gap semiconductor nature, with an energy gap of 0.82(1.45) eV as determined by standard PBE(hybrid HSE06) functional. This two-dimensional (2D) material exhibits poor stability under compressive strain due to the sensitive ZA acoustic phonon mode. In contrast, it only becomes unstable with tensile strain from 9% due to the elongation of chemical bonds reflected in the optical E” phonon mode. Under effects of lattice tension, the direct gap character is preserved and the band gap increases nearly linearly according to increase the strain strength. In addition, the effects of point defects associated with Na and Se atoms, including vacancies, antisites, and atom adsorption are also examined. Results indicate significant magnetization induced by Na single vacancy, Se Na antisite (one Na atom substituted by one Se atom), and Na adsorption on-top of hollow (T H ) site. In these cases, feature-rich magneto-electronic properties as half-metallic and magnetic semiconductor natures are obtained. In contrast, the formation of 2Na+1Se combined vacancies as well as other defects related to Se atoms leads to an effective band gap modification, even metallization in some cases. Results introduces new promising 2D material for optoelectronic applications and proposes point defect engineering to create artificially novel features for spintronic applications.

Extremely promising monolayer materials with robust ferroelectricity and extraordinary piezoelectricity: δ-AsN, δ-SbN, and δ-BiN.

Low-dimensional ferroelectric materials, the mainstay of current high-density non-volatile memory devices, sensors, and nanoscale electronics, have attracted tremendous attention recently. Through employing an evolutionary algorithm and first-principles calculations, we report three novel and stable two-dimensional (2D) ferroelectric materials δ-AsN, δ-SbN, and δ-BiN with spontaneous polarization of up to 5.72 × 10-10, 5.20 × 10-10, and 4.45 × 10-10 C m-1, respectively. The ab initio molecular dynamics (AIMD) simulations further show that the failure temperature of ferroelectricity of δ-AsN, δ-SbN, and δ-BiN is as high as 2000 K, 2000 K, and 1700 K, demonstrating their strong robustness. More interestingly, the three novel materials also exhibit extraordinary piezoelectricity with relaxation ion piezoelectric coefficients d11 of 5.39, 19.55, and 43.87 pm V-1, respectively. The external strain effect found can effectively modulate their spontaneous polarization, ferroelectric switching energy barrier, and piezoelectric properties. These fascinating ferroelectricity and piezoelectricity features endow δ-AsN, δ-SbN, and δ-BiN with significant potential application in future miniaturized and integrated multi-functional electronic devices.

Bandgap tailoring and optical response of InAlAs/InGaAs/GaAsSb double quantum well heterostructures: the impact of uniaxial strain and well width variations

ABSTRACT In this research work, a theoretical approach has been adopted to study GaAs-based InAlAs/InGaAs/GaAsSb type-II heterostructures. The 6 × 6 k·p Hamiltonian matrix with self-consistent calculations has been carried out to calculate the wavefunctions, localization of the charge carriers (probability density of charge carriers) and their dispersed energy states (Discrete energy level) under variable quantum well width and external strain of the double quantum well heterostructure. Bulk band structures of InAlAs/GaA for different aluminium compositions have been reported. The quantum well size and external strain effect on optical gain have also been explored. Computational analysis showed the generated light has a 1.93 μm NIR lasing wavelength. At 12 GPa, optical gain reaches 7450 cm−1 and wavelength 1.93 μm. Peak gain is 5931 cm−1 for 2 nm well width. The developed type-II structure can be employed in a semiconductor laser diode operating in the NIR range as per the observed results.

Evolution of Symmetrical Grain Boundaries under External Strain in Iron Investigated by Molecular Dynamics Method

In the present work, the evolution of atomic structures and related changes in energy state, atomic displacement and free volume of symmetrical grain boundaries (GB) under the effects of external strain in body-centered cubic (bcc) iron are investigated by the molecular dynamics (MD) method. The results indicate that without external strain, full MD relaxations at high temperatures are necessary to obtain the lower energy states of GBs, especially for GBs that have lost the symmetrical feature near GB planes following MD relaxations. Under external strain, two mechanisms are explored for the failure of these GBs, including slip system activation, dislocation nucleation and dislocation network formation induced directly by either the external strain field or by phase transformation from the initial bcc to fcc structure under the effects of external strain. Detailed analysis shows that the change in free volume is related to local structure changes in these two mechanisms, and can also lead to increases in local stress concentration. These findings provide a new explanation for the failure of GBs in BCC iron systems.

Effects of external strain on electronic and optical properties of β-SnSe: a first-principle study

Strain effects on magnetic and optical properties of β-SnSe have been investigated by the density functional theory (DFT) approach. Under the compressive strain, the band gap of β-SnSe disappears and becomes metal-like system. By comparison, under the tensile strain, the band gap firstly changes from 2.32 to 1.24 eV, and then it rises to 1.92 eV. We further find that the Sn-p and Se-p states at the bottom of conduction band contribute to the variations of the band structures. Moreover, due to the application of the external strain, the absorption strength in visible light might be enhanced.

Thermoelectric performance of silicene under uniform biaxial strain: A first principles study

Whenever a material is grown on a substrate, an external strain is induced on the material due to the lattice mismatch between the substrate and the material. Strain engineering plays an important role in tuning the electronic, vibrational and mechanical properties of a material by proper choice of lattice mismatch. We investigate the effect of biaxial strain on thermoelectric transport coefficients in low-buckled monolayer silicene using first principles study. The compressive strain shows the lattice instability while tensile strain shows stability with a small band-gap opening at the K-point. We systematically estimate the temperature dependent average relaxation time by calculating the electron-phonon coupling in silicene. Incorporation of the relaxation time in transport coefficients along with the effect of external strain increases the practicality of our investigations. The doped behaviour of silicene is also predicted using the rigid-band approximation. We find that with the applied tensile strain, the Seebeck coefficient and electronic thermal conductivity improves while the electrical conductivity and lattice thermal conductivity degrades slightly from its relaxed value. • Lattice mismatch between the substrate and the material induces external strain on the material, and thus affects the material properties. • Effect of biaxial strain on thermoelectric (TE) performance in silicene is predicted using Ab-initio calculations. • For accurate and reliable predictions of band gap, HSE06 functional is used in the calculations. • Simultaneously considered the effect of strain and τ( T ) on TE transport properties for more realistic analysis. • Tensile strain (5%) shows improvement in S, and σ but κ e and κ l degrades slightly from its relaxed value.

Semiconductor-metal transition induced by combined electric field and external strain in bilayer phosphorene

The gap modulation by effectively external control is an intriguing feature of the black phosphorene which may enable a flexible design and optimization of electronics. In this paper, combined electric field and external strain effects are systematically investigated to tailor the electrical properties of bilayer black phosphorene (BP) in four stacking order by using density functional theory (DFT). The electronic structures and density of states of bilayer black phosphorene can be modulated by the two external controls, the direct semiconductor-indirect semiconductor-metal transitions emerge under uniaxial in-plain strains and vertical electric field. The band gap is more likely to be modulated by the electric field under compressive strain along armchair direction for the AB stacking structures. The greater the compressive strain, the gap closed at a lower electric field. The partial density of states (PDOS) shows the energy band was mainly contributed by p orbital, and the partial charge density of the VBM and CBM further indicates the shifting trend of electrons and holes between the double layers. Our results provide potential reference information for nano-electronic and optoelectronic applications.

External uniaxial and biaxial strains modulated adsorption behaviors of volatile organic compounds on fibrous red phosphorene

For the very first time, we investigate the sensing properties of novel monolayered fibrous red phosphorene nanosheet towards toxic volatile organic compounds using first-principles strategy. Initially, the geometric and electronic features of fibrous red phosphorene are studied. The adsorption energy, charge transfer, density of states, band structure and work function are estimated for the toxic organic vapors, benzo[α]pyrene, benzene, toluene, formaldehyde, m-xylene, o-xylene, and p-xylene adsorbed fibrous red phosphorene. It is clearly enunciated that benzo[α]pyrene chemisorbed on the surface of fibrous red phosphorene, while the other molecules physisorbed to the phosphorene. Furthermore, to understand the effect of external strain, the variations of surface assimilating attributes of benzo[α]pyrene adsorbed fibrous red phosphorene with applied uniaxial and biaxial strains are scrutinized, respectively. The results support that applying external strain is an effective strategy to modulate the sensing performance of fibrous red phosphorene towards benzo[α]pyrene.

Strain effect on the electronic and optical properties of 2D Tetrahexcarbon: a DFT-based study

A new two-dimensional (2D) carbon allotrope, namely Tetrahexcarbon (TH-carbon) semiconductor monolayer with a direct band gap resides in the visible region of the electromagnetic spectra, has been recently proposed theoretically. Herein, the influences of biaxial strains on the electrical and optical aspects of 2D TH-carbon are computationally investigated. To this end, first-principles calculations based on the properties of the density functional theory were employed. According to our simulations, the electronic and optical properties of 2D TH-carbon are effectively sensitive to the external strain effects. This obtained strain sensitivity suggests that this 2D material could be a promising material for usage in new electronic technologies.

Tuning MoSO monolayer properties for optoelectronic and spintronic applications: effect of external strain, vacancies and doping.

Since the successful synthesis of the MoSSe monolayer, two-dimensional (2D) Janus materials have attracted huge attention from researchers. In this work, the MoSO monolayer with tunable electronic and magnetic properties is comprehensively investigated using first-principles calculations based on density functional theory (DFT). The pristine MoSO single layer is an indirect gap semiconductor with energy gap of 1.02(1.64) eV as predicted by the PBE(HSE06) functional. This gap feature can be efficiently modified by applying external strain presenting a decrease in its value upon switching the strain from compressive to tensile. In addition, the effects of vacancies and doping at Mo, S, and O sites on the electronic structure and magnetic properties are examined. Results reveal that Mo vacancies, and Al and Ga doping yield magnetic semiconductor 2D materials, where both spin states are semiconductors with significant spin-polarization at the vicinity of the Fermi level. In contrast, single S and O vacancies induce a considerable gap reduction of 52.89% and 58.78%, respectively. Doping the MoSO single layer with F and Cl at both S and O sites will form half-metallic 2D materials, whose band structures are generated by a metallic spin-up state and direct gap semiconductor spin-down state. Consequently, MoV, MoAl, MoGa, SF, SCl, OF, and OCl are magnetic systems, and the magnetism is produced mainly by the Mo transition metal that exhibits either ferromagnetic or antiferromagnetic coupling. Our work may suggest the MoSO Janus monolayer as a prospective candidate for optoelectronic applications, as well as proposing an efficient approach to functionalize it to be employed in optoelectronic and spintronic devices.

Characteristics of thermal- and strain-induced ε-martensite in Fe50Mn30Co10Cr10 multi-component alloy: Effect of grain size

Electron backscatter diffraction technique is used to systematically investigate the characteristics of thermal- and strain-induced ε-martensite in Fe50Mn30Co10Cr10 multi-component alloy, focusing on the grain size effect. Results show that a clear morphological distinction between thermal- and strain-induced ε-martensite cannot be made, both exhibiting laminate- and blocky-shaped features. The amount of thermal-induced ε-martensite dependence of initial γ-austenite grain sizes is evidenced, revealing the formation of multiple initial ε variants in coarse γ-austenite grains, rather than in fine γ-austenite grains. The external strain effect is advantageous of the formation of secondary ε variants and εtwins, but not the thermal effect. Decreasing γ-austenite grain size hinders the activation of secondary ε variants and εtwin, confirming secondary ε variants and εtwin can be produced in coarse γ-austenite grains under the small strain, rather than in fine γ-austenite grains. Furthermore, under the heavy strain, the saturated ε-martensite is almost dominated by one persisting ε variant in coarse and fine γ-austenite grains.

Two-dimensional blue-phase CX (X = S, Se) monolayers with high carrier mobility and tunable photocatalytic water splitting capability

Photocatalytic water splitting utilizing solar energy is considered as one of the most ideal strategies for solving the energy and environmental issues. Recently, two-dimensional (2D) materials with an intrinsic dipole show great chance to achieve excellent photocatalytic performance. In this work, blue-phase monolayer carbon monochalcogenides (CX, X = S, Se) are constructed and systematically studied as photocatalysts for water splitting by performing first-principles calculations based on density functional theory. After confirming the great dynamical, thermal, and mechanical stability of CX monolayers, we observe that they possess moderate band gaps (2.41 eV for CS and 2.46 eV for CSe) and high carrier mobility (3.23 × 104 cm2 V−1 s−1 for CS and 4.27 × 103 cm2 V−1 s−1 for CSe), comparable to those of many recently reported 2D photocatalysts. Moreover, these two monolayer materials are found to have large intrinsic dipole (0.43 D for CS and 0.51 D for CSe), thus the build-in internal electric field can be self-introduced, which can effectively drive the separation of photongenerated carriers. More importantly, the well-aligned band edge as well as rather pronounced optical absorption in the visible-light and ultraviolet regions further ensure that our proposed CX monolayers can be used as high efficient photocatalysts for water splitting. Additionally, the effects of external strain on the electronic, optical and photocatalytic properties of CX monolayers are also evaluated. These theoretical predictions will stimulate further work to open up the energy-related applications of CX monolayers.

Prediction of a new 2D B2CO monolayer from density functional theory

In this study, a novel two-dimensional (2D) B2CO monolayer is theoretically predicted. According to our results 2D B2CO monolayer indicates significant structural, energetically and kinetically stabilities. These stabilities are confirmed by calculating its cohesive energy and phonon dispersion spectra. It is found that fully relaxed and optimized unit cell of the predicted monolayer possesses a buckled hexagonal crystal structure (space group: 156_P3m1) and is an indirect semiconductor with a band gap of 1.69 eV (2.81 eV) calculated by DFT-PBE (HSE06) level of theory. We further examined the effects of biaxial strains on the electronic properties of the monolayer and found its electronic properties can be effectively modulated by external strain effects. The optical aspects of the monolayer and found that proposed 2D material were also investigated. It has been shown that the monolayer shows very low absorption in visible region of electromagnetic spectra while it exhibits high absorption and reflection characters in UV region. These obtained results propose that the monolayer can be considered as a transparent material for the visible lights and a useful shielding material in ultra violet region.

Strain tunable band structure of a new 2D carbon allotrope C568

Recently, C568 has emerged as a new carbon allotrope, which shows semiconducting properties with a band gap around 1 eV and has attracted much attention. In this work, the external strain effects on the electronic properties of C568 have been studied theoretically through first-principle calculations. The numerical results show that while in-plane uniaxial and biaxial strains both reduces the band gap of C568 in case of tensile strain, their effects are quite different in the case of compressive strain. With increasing compressive uniaxial strain, the band gap of C568 first increases, and then dramatically decreases. In contrast, the application of compressive biaxial strain up to –10% only leads to a slight increase of band gap. Moreover, an indirect-to-direct gap transition can be realized under both types of compressive strain. The results also show that the optical anisotropy of C568 can be induced under uniaxial strain, while biaxial strain does not cause such an effect. These results indicate good strain tunability of the band structure of C568, which could be helpful for the design and optimization of C568-based nanodevices.

Tuning electronic and optical properties of SnSe by external strain

By employing the first-principles calculations, the effects of external strain upon α-SnSe have been investigated. Different phenomena appear while the strain is applied. Under the tensile strain, the α-SnSe always shows an indirect band gap of about 1.06 eV. By comparison, an indirect to direct transform of band gap appears while the compressive is loaded, and the system shows a large gap of 2.51 eV. We further study density of electronic states in these systems. The Sn-p state at the bottom of conduction band contributes to the variations of the band structures. Moreover, due to the application of the external strain, especially the compressive strain, the absorption strength in visible light might be enhanced. These results show that the strain induced α-SnSe might give some potential applications in spintronic devices and optical fields.

A comprehensive investigation on electronic structure, optical and thermoelectric properties of the HfSSe Janus monolayer

Electronic structure, optical and thermoelectric properties of the HfSSe Janus monolayer have been comprehensively investigated using first-principles calculations based on the full-potential linearized augmented plane-wave (FP-LAPW) method. Results show that the HfSSe Janus monolayer is dynamically stable. Electronic properties features indicate that the two-dimensional (2D) material at hand is an indirect gap semiconductor with a band gap of 0.756 eV calculated by the Wu-Cohen scheme within generalized gradient approximation (GGA-WC). The spin-orbit coupling (SOC) inclusion in the calculations breaks the degeneracy in both valence and conduction bands, and gives a smaller band gap of 0.653 eV. Additionally, the external strain effect on the electronic structure is also examined. The metallization can be achieved when a compressive strain of −8% is applied. Optical properties results suggest that the studied 2D monolayer may be a promising candidate to be applied in nano-optoelectronic devices provided that it displays a wide absorption band from visible to ultraviolet with high absorption coefficient of the order of 103/cm. Finally, the thermoelectric properties including electrical conductivity, Seebeck coefficient, electronic thermal conductivity and power factor are calculated using the semi-classical Boltzmann transport theory. Results indicate that the electron doping may be favorable for the thermoelectric performance of the HfSSe Janus monolayer due to large power factor values as compared with those of the hole doping.

Structural stability and optoelectronic properties of tetragonal MAPbI3 under strain

In recent years, organic–inorganic hybrid perovskites have attracted wide attention due to their excellent optoelectronic properties in the application of optoelectronic devices. In the manufacturing process of perovskite solar cells, perovskite films inevitably have residual stress caused by non-stoichiometry components and the external load. However, their effects on the structural stability and photovoltaic performance of perovskite solar cells are still not clear. In this work, we investigated the effects of external strain on the structural stability and optoelectronic properties of tetragonal MAPbI3 by using the first-principles calculations. We found that the migration barrier of I− ion increases in the presence of compressive strain and decreases with tensile strain, indicating that the compressive strain can enhance the structural stability of halide perovskites. In addition, the light absorption and electronic properties of MAPbI3 under compressive strain are also improved. The variations of the band gap under triaxial and biaxial strains are consistent within a certain range of strain, resulting from the fact that the band edge positions are mainly influenced by the Pb–I bond in the equatorial plane. Our results provide useful guidance for realizing the commercial applications of MAPbI3-based perovskite solar cells.

Helium bubble growth under strain fields in tungsten investigated by atomic method

The evolution of helium (He) bubble and dislocation loop from loop punching process affected by external strain field have been studied at atomic scale with hydrostatic strains of around −2% to 2%. The 1st maximal displacements of tungsten atoms around HenV, the formation energy of HenV clusters and the binding energy between the clusters and He are calculated, indicating that the number of He atoms needed to form the 1st self-interstitial atom (SIA) increases from tensile state to compressive state, and the configurations of the 1st SIAs are all in the form of 〈1 1 1〉 crowdion, independent of applied strains. Comparing to the case without external strain effect, the tensile and compressive strains affect not only the critical number of He atoms to punch the 1st loop in loop-punching process but also the Burgers vectors of formed loops. All these results provide a new understanding to radiation damages related with He bubble growth in nuclear materials.