Biaxial Tensile Strain Research Articles

Theoretical predicted Janus SrAlGaTe4: effects of strain and electric field and its topological properties

The asymmetric Janus SrAlGaTe4, constructed from its parent SrGa2Te4 monolayer, was predicted theoretically by first principle calculations. Its stability was confirmed by phonon structure without imaginary frequency and ab initio molecular dynamics (AIMD) simulations. The Janus structure reduces the symmetry of SrGa2Te4 monolayer, which causes the absence of topological states in free-standing Janus SrAlGaTe4. To explore the possible electronic and topological properties, the effects of strain and external electric field, working as effective modulation methods for the electronic properties, were investigated. The SrAlGaTe4 monolayer undergoes a direct-to-indirect bandgap transition when the in-plane biaxial compressive strain is −8%. When the tensile strain is 9% or the electric field is 0.5 V Å−1, the Janus SrAlGaTe4 monolayer exhibits topological insulator (TI) characters, which was confirmed by the evolution of the Wannier charge centers (WCC). And the critical values for the topological transition are 2% for the biaxial tensile strain, and 0.2 V/Å for the applied electric field. The asymmetric Janus structure induces a Rashba spin splitting not only in the valence band but also in the conduction band near the Fermi level when the spin–orbit coupling (SOC) is present. Our findings offer theoretical insights into the exotic physical properties of SrAlGaTe4 and also provide guides to new spintronic device designs.

Theoretical design of Sc2CF2/Ti2CO2 heterostructure as a promising direct Z-scheme photocatalyst towards efficient water splitting

Van der Waals (vdW) heterostructure catalysts with the direct Z-scheme charge transfer path are highly expected for photocatalytic water splitting to address the energy crisis. In this work, the novel Sc2CF2/Ti2CO2 heterostructure has been developed and its photocatalytic utility was evaluated based on the first-principles method. Results indicate the heterostructure is an indirect semiconductor with improved carrier mobilities and absorption. The transfer of photogenerated carriers in this heterostructure follows the Z-scheme path, and the band edge positions confirm its suitability for water splitting. More importantly, the change in Gibbs free energy indicates that solar energy can drive water splitting in Sc2CF2/Ti2CO2 heterostructure with an attractive solar-to-hydrogen efficiency of 41.7%. Besides, biaxial tensile strain can turn Sc2CF2/Ti2CO2 heterostructure into a direct semiconductor, while its photocatalytic performance can be improved. In brief, all findings prove the potential of Sc2CF2/Ti2CO2 heterostructure as a promising direct Z-scheme photocatalyst for efficient water splitting.

A holistic approach of strain-induced and spin-orbit coupling governed structural, optical, electrical and phonon properties of Janus MoSSe heterostructure via DFT theory

Spintronics and optoelectronic equipment benefit from efficient modification of electrical and optical characteristics for Van der Waals heterostructures. Janus MoSSe, in two dimensions, has superior electronic, optical, and phonon properties. Based on these characteristics, we evaluate the effects of biaxial compressive and tensile strain ranges of −6% to +6% on the structural, optical, spin–orbit coupling, and phonon properties of two-dimensional MoSSe employing first-principles-based density functional theory calculations. At K-point, MoSSe possesses a direct band gap of 1.665 eV, making it a semiconductor. Yet, applying tensile strain, we can observe that the bandgap of MoSSe has declined. On the other hand, the bandgap of MoSSe rises due to the compressive strain. From the phonon properties, it is clear that the stability of the monolayer MoSSe is observed in the case of tensile strain. With the increase of compressive strain, it loses its stability. With a photon energy of 2.5 eV, MoSSe exhibits three times greater optical absorption than other photon energy levels. In comparison to two monolayers (MoS2, MoSe2), the MoSSe heterostructure shows an elevated optical absorption coefficient in the visible light band, according to our calculations of its dielectric constant and optical absorptionThe MoSSe dielectric constant’s peaks shift to the stronger photon energy as compressive strain is increased; in contrast, if tensile strain is added, the highest points shift to the less powerful photon energy. This suggests that the spin–orbit coupling (SOC) in MoSSe heterostructures can be enhanced under strain, which has implications for spintronics. The effect of strain can be used to tailor the phonon behaviors of MoSSe, which can be useful for controlling the material’s mechanical and thermal characteristics. The versatility of the electronic and optical properties of the material under strain can be harnessed to design novel devices such as strain sensors, optoelectronic modulators, and detectors.

Ferroelectric SrMnO3 Thin Film Grown on (110)‐Oriented PMN‐PT Substrate

Exploring the unique physical properties of oxide perovskites necessitates their growth on diverse single‐crystal substrates. The thin‐film growth of perovskite SrMnO3 (SMO) has been a particular focus of research due to its emerging room‐temperature multiferroicity. Herein, the epitaxial thin films of (110)‐oriented SMO are grown on the piezoelectric (110)‐oriented (1–x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 (PMN‐PT) substrate. The effects of the thickness and oxygen annealing on the crystal structure, stoichiometry, and ferroelectric properties of the SMO thin film are systematically investigated. The tensile strain produced by the lattice mismatch between the bulk SMO and the PMN‐PT substrate causes an expansion of the c‐lattice parallel to the in‐plane direction of the substrate. The films show larger a‐, b‐, and c‐lattice parameters than the bulk material, resulting in volume expansion of the unit cell. This lattice expansion is attributed to the generation of oxygen vacancies driven by the reduced formation energy caused by the high elastic strain. Piezoelectric force microscopy reveals that the SMO film contains domains with strain‐mediated in‐plane and vacancy‐mediated out‐of‐plane polarization. Furthermore, the piezoelectric response of the PMN‐PT substrate effectively modulates the biaxial tensile strain in the SMO film, offering a potential strategy for controlling the crystal structure and ferroelectric properties of SMO.

Intrinsically Stretchable Polymer Semiconductor with Regional Conjugation for Stretchable Electronics

AbstractThe development of intrinsically stretchable polymer semiconductor holds substantial promise in the field of wearable electronics. However, charge transport mobility is typically compromised in existing stretchable semiconductors to achieve the desired stretchability. Herein, a novel “regional conjugation” strategy is proposed to design an intrinsically stretchable polymer semiconductor oligo‐diketopyrrolopyrrole‐thieno[3,2‐b]thiophene (DPPTT)–urethane, in which oligo‐DPPTT conjugated units and alkyl urethane nonconjugated units are introduced. The regional conjugation of oligo‐DPPTT in the polymer backbone endows DPPTT–urethane with good molecular packing, leading to a high mobility of up to 1.7 cm2 V−1 s−1. Additionally, incorporating alkyl urethane nonconjugated units in the backbone can reduce film crystallinity and chain aggregation, which contribute to the stretchability of the polymer thin film. Consequently, fully stretchable transistors retain carrier mobility even at 100% biaxial tensile strain. Furthermore, the fully stretchable organic field‐effect transistor arrays show remarkable charge transport reversibility and durability after 1000 stretch–release cycles at 25% strain. Additionally, the device exhibits extraordinary electrical stability in air atmosphere. Overall, these results indicate that the “regional conjugation” strategy provides an effective and promising methodology to design intrinsically stretchable and high‐performance polymer semiconductor that can advance the development of soft and wearable electronics.

Feeling the strain: Enhancing the thermodynamics characteristics of magnesium nickel hydride Mg2NiH4 for hydrogen storage applications through strain engineering

This work is based on density functional theory (DFT) and studies the structural, electronic, thermodynamic properties and dehydrogenation kinetics of the hydride Mg2NiH4 under different uniaxial and biaxial strain applied to Mg2Ni or Mg2NiH4. structural properties are first studied based on generalized gradient (GGA) and local density (LDA). Thermodynamic and electronic properties and dehydrogenation kinetics are then studied using the GGA method based on the Perdew-Burke-Ernzerhor (PPE) approximation. The results obtained show that uniaxial/biaxial tensile and compressive strains are capable of inducing structural deformation by increasing the value of the strain step on both Mg2Ni and Mg2NiH4, and that these strains applied to Mg2NiH4 are capable of reducing the stability of the system more than strains applied to Mg2Ni, due to the contribution of strain energy. More specifically, it lowers the enthalpy of formation to −40 kJ/mol.H2 under compressive strain ε = −7.5% or biaxial tensile strain ε = +7.8%, which corresponds exactly to the ideal value suggested by the US Department of Energy (DOE) for materials suitable for hydrogen storage. And the decomposition temperature fell within the fuel cell operating range (PEM) of 289–393 K. On the other hand, under uniaxial and biaxial strains, the activation energy of hydrogen atom diffusion in Mg2NiH4 varied between 0.40 eV and 0.22 eV, resulting in a remarkable improvement in dehydrogenation properties. Analysis of the total (TDOS) and partial (PDOS) density curves shows that the Mg2NiH4 system has a metallic characteristic, and that this characteristic is maintained by increasing the strain pitch, with a variation in the energy width of the valence band.

Strain-tunable elastic, electronic, and thermal transport properties of two-dimensional CaI2 monolayer: A first-principles study

Despite the increasing attention on two-dimensional (2D) metal iodides in recent years for their appropriate bandgaps and exceptional optical properties, there is limited understanding of their intriguing thermal transport properties. Here, the strain-tunable mechanic, electronic, and transport properties of the monolayer CaI2 are calculated in detail by combining first-principles calculations with Boltzmann transport theory. We have checked its thermal, dynamic, and mechanical stability by computing ab-initio molecular dynamics, phonon spectra and elastic constants, respectively. The calculation results from the PBE-GGA and HSE06 methods indicate that the monolayer CaI2 is an indirect semiconductor, with band gaps of 3.92 eV and 5.12 eV, respectively. Additionally, the effective masses and Fermi velocities for both holes and electrons are also obtained, which indicates that the monolayer CaI2 owns the excellent electronic transport property. These mechanical constants and electronic parameters are also highly sensitive to the external strain. The calculated real lattice thermal conductivity of the monolayer CaI2 at 300 K is about 1.01 W/mK, which is rather low among 2D materials, implying its potential application in heat insulation materials or thermal insulation material. With the biaxial tensile strain increasing, its lattice thermal conductivity would further decrease. The difference in lattice thermal conductivities between 0 % and 2 % strain, as well as between 4 % and 6 % strain, is much smaller than that between 2 % and 4 % strains. Subsequently, the group velocities, phonon scattering rates, and cumulative lattice thermal conductivities of the monolayer CaI2 are discussed under the different strains.

Ab-initio study of strain-tunable g-GaN/BN nanoheterostructure for optoelectronic and photocatalytic applications.

Two-dimensional (2D) nanoheterostructures of materials, integrating various phase or materials into a single nanosheet have stimulated large-scale research interest for designing novel two dimensional devices. In contemporary analysis present work, we examined the structural and electronic properties of the isolated 2D BN and GaN monolayers. We have investigated the structural stability and optoelectronic and photocatalytic response of the g-GaN/BN nanoheterostructure along with its response to strain. Nanoheterostructure g-GaN/BN is predicted to be a direct bandgap semiconductor with wide gap of 4.45eV, whose value can be effectively modulated by applied strain ( , ranging from 4.55 ( = - 4%) to 3.58eV ( = 8%). We also discovered that the tensile strain of 8% can substantially tune the direct bandgap of nanoheterostructure to indirect band gap nature. Even more important, the biaxial tensile strain engineering accentuates an enhancement of optical absorption in the UV region, broadening the light harvesting of the g-GaN/BN nanoheterostructure with the shifting of first absorption peak from 4.64 ( = - 4%) to 3.71eV ( = 8%). Furthermore, strain-tuned band edge potentials arrangement perfectly fits the water reduction and oxidation redox potentials. Our findings portend that the g-GaN/BN nanoheterostructure has application in prospective nanoscale optoelectronic devices and photocatalytic hydrogen evolution system. First principles calculations in this study are performed using density functional theory. Generalized gradient approximation within PBEsol functional employed to address the electron-electron exchange-correlation effects. For avoiding periodic interactions between the layers, we have inserted a vacuum region of thickness 10Å in the z-direction. For ensuring the convergence accuracy of the computed results, convergence criteria of the iteration process is set to be 0.0001eV. Local modified Becke-Johnson, a semi local functional, is applied for calculating electronic and optical properties for more accuracy of results. As in layered 2D nanoheterostructure, a factual depiction of the van der Waals interactions cannot be provided by conventional DFT techniques. Accordingly, in order to incorporate these interactions, we had employed the dispersion correction method of Grimme's.

Biaxial strain effects on electronic, transport, and thermoelectric properties of SnX[formula omitted] (X = Se, Te) and Janus SnSeTe 1T-monolayers

Biaxial strain in two-dimensional materials plays a crucial role in degenerating the valence and conduction bands, leading to energy dispersion in the band structure and causing changes in transport properties, such as carrier mobility, Seebeck coefficient, and electrical conductivity. Herein, we investigated the effects of biaxial strain on SnX2 (X = Se, Te) and the Janus SnSeTe 1T-monolayer using density functional theory, deformation potential, and semiclassical Boltzmann transport theory. Our findings reveal that the studied 1T-monolayers exhibit high and directionally isotropic electron mobility. Biaxial tensile strain has the effect of increasing the bandgap, predominantly reducing the effective mass of electrons while increasing that of holes. This results in an enhanced electron mobility along with a simultaneous reduction or increase in the concentration of electron carriers or holes, respectively. Especifically, in the case of the Janus SnSeTe 1T-monolayer, we observed a remarkable 68% increase in electron mobility, reaching a value of 1588 cm2V−1s−1. This increase contributes to higher thermoelectric performance due to elevated electrical conductivity and a simultaneous rise in the Seebeck coefficient when subjected to biaxial strain. Our study underscores that strain engineering is an effective strategy for achieving improved thermoelectric properties, particularly exemplified by the SnSeTe 1T-monolayer, which achieved a maximum value of 2.25 for n-type due the ultralow thermal conductivity of 0.359 Wm−1K−1 as result of strong phonon anharmonicity on acoustical and optical modes.

A hybrid density functional study of tensile-induced changes in phonon dispersion, electronic structure and optical absorption of bilayer BN for optoelectronic applications

The electronic, phonon dispersion and optical properties of bilayer BN have been investigated with density functional theory (DFT) calculations. Interestingly, applying the biaxial strain of 4% converts the indirect band gap of bilayer BN to a direct band gap. We show that the interaction between the BN layers results in the removal of two-fold degeneracy and separation of ZA and ZO phonon modes near the Γ point. Across the entire range of applied biaxial tensile strains, the bilayer BN exhibits a dynamically stable behavior. The phonon bandgap of bilayer BN decreases under tensile strain. The bilayer BN has strong adsorption in the UV region and the optical absorption peaks are red-shifted by applying the tensile strain. These findings are essential for the strain engineering of bilayer BN and future fabrication of flexible electronic and optoelectronic devices.

Biaxial strain modulation of the optoelectronic properties of F-doped defective monolayer SnS2

Abstract The first principles approach calculates the geometrical structure, stability, and optoelectronic properties of F-atom doped S vacancy defective SnS2 systems under biaxial tensile and compressive deformation. The calculations show that all systems can be formed stably, and defects and F doping cause a tiny increase in the average bond length of the systems. The formation of defects converts an indirect bandgap system into a direct one. Substitutional doping of F atoms transforms the SnS2 structure into a p-type semiconductor. The doped system's valence band mainly originates from S-3p orbitals, Sn-5p orbitals, and F-2p orbitals. The conduction bands mainly originate from the S-3p, Sn-5s, and F-2p orbitals. The absorption and reflection peaks of the doped system with applied strain are blueshifted at the maximum peak. The biaxial compressive strain increases the band gap and decreases the doped system's refractive index and extinction coefficient. The biaxial tensile strain increases the band gap of the doped system, the hybridization of the valence band of the system is enhanced, the conductivity of the real part of the complex dielectric function of the system is increased, and the refractive index of the system is elevated. The biaxial stretching strain can better change the sensitivity of the F-doped system to visible light.

Highly reversible extrinsic electrocaloric effects over a wide temperature range in epitaxially strained SrTiO3 films

Electrocaloric effects have been experimentally studied in ferroelectrics and incipient ferroelectrics, but not incipient ferroelectrics driven ferroelectric using strain. Here we use optimally oriented interdigitated surface electrodes to investigate extrinsic electrocaloric effects in low-loss epitaxial SrTiO3 films near the broad second-order 243 K ferroelectric phase transition created by biaxial in-plane coherent tensile strain from DyScO3 substrates. Our extrinsic electrocaloric effects are an order of magnitude larger than the corresponding effects in bulk SrTiO3 over a wide range of temperatures including room temperature, and unlike electrocaloric effects associated with first-order transitions they are highly reversible in unipolar applied fields. Additionally, the canonical Landau description for strained SrTiO3 films works well if we set the low-temperature zero-field polarization along one of the in-plane pseudocubic <100> directions. In future, similar strain engineering could be exploited for other films, multilayers and bulk samples to increase the range of electrocaloric materials for energy efficient cooling.

Gradient‐Strained Van Der Waals Heterojunctions for High‐Efficient Photodetectors

AbstractMaximizing light‐to‐electricity conversion efficiency is a crucial challenge for the practical applications of 2D material photodetectors. However, due to the lack of stable and precise electronic structure control methods for 2D materials, the driving force of photogenerated carriers is insufficient that severely hinders the efficiency of separation and transport. Herein, a gradient‐modulated, stable and precise strain applied strategy for 2D materials is designed and constructed, which results in a significant improvement in the detect efficiency of ZnO/WSe2/graphene van der Waals heterojunction photodetectors. Different from the overall strain of all‐component materials in typical photodetectors, biaxial tensile strain is applied to WSe2 that can be precisely modulated by controlling the height of ZnO nanorods, while the strain is nearly unaffected to ZnO. As the strain modulation increases from 1.3% to 4.0%, the external quantum efficiency (EQE) of the heterojunction increases from 11.4% to 35.3%, representing a threefold increase. Furthermore, with increasing strain, the EQE can reach higher levels. Moreover, the strain‐enhanced conversion efficiency mechanism is elucidated that results from the synergistic effect of the strain‐induced WSe2 exciton convergence and the strain‐increased ZnO/WSe2 interface barrier, which enhances the carrier interface separation efficiency.

Piezoelectric response and ferromagnetic order in 2D Janus FeGeN3

Two-dimensional (2D) materials with ferromagnetism and piezoelectricity have drawn great attention due to their promising application and fundamental significance. Using first-principles swarm structure search calculations, we have predicted a 2D Janus FeGeN3, with quintet atomic layers of N–Fe–N–Ge–N, demonstrating a desirable coexistence of ferromagnetism and piezoelectricity. It has an out-of-plane piezoelectric response of −0.31 pm/V, a robust ferromagnetic order with a Curie temperature (TC) of 302 K, and an excellent semiconductivity with a bandgap of 1.99 eV. Its ferromagnetic coupling is derived from the super-exchange interaction between Fe atoms mediated by multi-type N atoms. Moreover, the biaxial tensile strain is in the favor of the enhancement of ferromagnetism. These intriguing properties make Janus FeGeN3 an attractive candidate for spintronic devices with multifunctionality.

The underlying mechanism of the strain-induced reversible magnetic state transition in MXene nanosheets

MXenes have emerged as one of the most promising members among the two-dimensional (2D) material family owing to their unique physical-chemical properties and outstanding application prospects. Here, we investigated the unique magnetic properties of Ti2C MXenes monolayer by means of the first-principles calculations combining with the Heisenberg spin Hamiltonian approach. A strain-induced reversible magnetic transition for the Ti2C monolayer could be found in our study. When the strain is applied to the Ti2C monolayer, the magnetic configuration of the Ti2C monolayer transforms from the A-type antiferromagnetic (A-AFM) phase to the ferromagnetic (FM) phase with the biaxial tensile strain larger than 6%. Furthermore, the transition from the A-AFM phase to the FM phase was found to be closely related with the change of the Ti and C atomic magnetic moments. The direct magnetic coupling between Ti and C atoms with the increased Ti and C magnetic moments is able to stabilize the structure due to the weakened superexchange interaction between Ti and C atoms under large tensile strain. This is the underlying driving force for the transition from the A-AFM phase to the FM phase. This work provides a promising pathway to better understand the existence of magnetic reversal behavior in the Ti2C MXenes monolayer and opens the door to future magnetic applications of MXenes.

Effect of tensile and compressive strains on the electronic structure of O-atom-doped monolayer MoS2

We investigate the effects of biaxial tensile and compressive strains on the electronic structure of O-doped monolayer MoS2 by density functional theory (DFT) in this paper. O-doped monolayer MoS2 is an exothermic reaction. The doping of O leads to the transformation of the system from direct bandgap to indirect, and the bonding of Mo and O causes a large amount of charge transfer. The application of tensile strain leads to a decrease in the stability of the doped system, and the system always maintains the nature of indirect bandgap. The degree of interatomic charge transfer and bandgap value gradually decrease with the increase of tensile strain. The application of compression strain improves the stability of the doped system, and as the compressive strain increases, the bandgap of the doped system completes the indirect–direct–indirect transformation. The bandgap value shows a trend of increasing and then decreasing. Additionally, the degree of charge transfer between atoms is strengthened.

Effect of non-metallic doping on the electronic structure and optical properties of ZrSe2

The optoelectronic properties of non-metal (B, N, O, C, F) doped and biaxial tensile strain in the x–y direction of O-doped and N-doped ZrSe2, including energy band structure, density of states, dielectric function, and absorption coefficients, have been calculated by a first-principles approach based on density-functional theory. It is shown that the doped system has a low formation energy, indicating that the structure can exist stably. The B, C, and N atom-doped systems show impurity energy levels near the Fermi energy level, narrowing the bandgap, enhancing the electron transport ability, and increasing the electrical conductivity. Biaxial stretching was applied to the ZrSe2 structure before and after O and N doping, and it was found that the stability of the ZrSe2, Zr9Se[Formula: see text]O[Formula: see text] and Zr9Se[Formula: see text]N1 structures was found to decrease gradually with increasing strain. The energy bandwidth of the doped system in the Zr9Se[Formula: see text] O1system at a tensile strain of 4% is a maximum of 0.924[Formula: see text]eV; from the density of states, it is found that there is a very obvious orbital hybridization of Se-4p and Zr-d. The doped system has the largest effect on the dielectric function at 6% tensile strain and on the absorption coefficient at 8%. In the Zr9Se[Formula: see text]N1 system, stretching 8% energy bandwidth is a maximum of 0.788[Formula: see text]eV, the tensile strain of 8% has the greatest effect on the dielectric function, and a tensile strain of 6% has the most significant effect on the absorption coefficient.

Hydrogen generation from direct Z-scheme for photocatalytic overall water splitting with the SiSe/SnSe2 and SiSe/SnSSe heterostructures

The direct Z-schemes of the photocatalytic overall water splitting with the SiSe/SnSe2, SiSe/SnSSe-I, and SiSe/SnSSe-II heterostructures are constructed based on the density functional theory calculations and nonadiabatic molecular dynamics (NAMD) simulations. The maximum solar-to-hydrogen efficiency (ηʹSTH) reaches 19.18% and can be promoted to 28.71% under tensile biaxial strains. NAMD simulations indicate the transfer of the electron for hydrogen evolution reaction (HER) and hole for oxygen evolution reaction (OER) for SiSe/SnSe2 are apparently slower than those for the other two heterostructures, implicating the reduction and oxidation activities of this heterostructure are well-protected. Moreover, the shortest electron-hole recombination time is attributed to SiSe/SnSSe-I, indicating that it holds the best photocatalytic performance. Remarkably, the Gibbs free energies indicate that HER and OER with SiSe/SnSSe-I can spontaneously proceed, while OERs can but HERs cannot spontaneously proceed with the other two heterostructures. Therefore, the newfound heterostructures, especially SiSe/SnSSe-I, are promising candidates in photocatalytic overall water splitting.

Strain-induced modification in thermal properties of monolayer 1T-ZrS2 and ZrS2/ZrSe2 heterojunction.

This paper systematically analyzes the phonon dispersion curves of single-layer ZrS2, ZrSe2, and ZrS2/ZrSe2 heterostructures under different strains. The phonon spectra and thermal parameters of the three structures were obtained based on the density functional perturbation theory method. The upper limits of strain that different monolayers and heterojunctions can withstand were studied. The monolayers ZrSe2 and ZrS2 can withstand up to 8% biaxial tensile strain, and the ZrS2/ZrSe2 heterojunction can withstand up to 6% biaxial tensile strain. In addition, the van der Waals force of the heterojunction may cause phonon tearing in the vertical direction. The application of biaxial tensile strain can adjust the thermal properties of the system to a large extent, which is similar to the strain effect in the pristine case. When the temperature rises, the entropy enthalpy of the three structures also gradually increases, the free energy gradually decreases, and the heat capacity of the system gradually increases until it tends to be stable. Taking single-layer ZrS2 as an example, we analyzed the change curve of thermal properties of single-layer ZrS2 under tensile strain. The results show that with the gradual increase of strain, the crystal's entropy, enthalpy, and free energy change differently. In addition, the heat capacity increases slowly under high temperatures. When all systems reach the limit strain, the phonon spectrum appears to have an imaginary frequency, and the thermal properties decrease significantly. This paper uses the first-principle calculation method based on density functional theory, and the PBE exchange-correlation function based on generalized gradient approximation (GGA) is selected for a specific calculation. The density functional perturbation theory (DFPT) calculates the full kinetic matrix. Because the lattice constants of ZrS2 and ZrSe2 are similar and have similar periodicity, the corresponding unit cells are used for structural optimization and property calculation. The Brillouin zone is integrated using the K points generated by the Monkhorst-pack method. For single-layers ZrS2 and ZrSe2, 8 × 8 × 1K-point grid is selected, and for ZrS2/ZrSe2 heterojunction, 8 × 8 × 2K-point grid is selected. A vacuum layer of 30Å was added in the vertical direction to avoid interlayer interaction. The non-conservative pseudopotential method is used to optimize the structure, and the optimization convergence is set as follows: the cutoff energy is set to 700eV, the convergence threshold of the maximum force between atoms is 0.01eV/Å, the convergence threshold of the maximum energy change is set to 1 × 10-9eV, and the convergence threshold of the maximum displacement is 0.001Å.

The local electronic interaction and strain effects on transverse dynamical spin susceptibility of [formula omitted]-graphyne

We present the behaviors of dynamical transverse spin susceptibilities of undoped β-graphyne monolayer using the Green’s function approach in the context of Hubbard model Hamiltonian. Such dynamical spin susceptibility is proportional to inelastic cross section of neutron beam from the layer. Specially, the effects of magnetic field, on-site coulomb repulsion strength and strain parameter on the spin excitation modes of β-graphyne monolayer are investigated via calculating correlation function of transverse components of spin density operators. Our results show the increase of absolute value of compressive strain parameter leads to move the magnetic excitation modes to higher energies. Also the intensity of peaks in inelastic cross section reduces with absolute value of compressive strain parameter. We also show that applying biaxial tensile strain causes to decrease the intensity of peaks in dynamical transverse spin susceptibility. Finally the effects of magnetic field and on-site coulomb repulsion interaction strength on frequency dependence of dynamical spin structure factor of β-graphyne layer are studied. Moreover the frequency positions of spin excitation mode of β-graphyne monolayer have been investigated due to the effects of biaxial strains, applied magnetic field and Hubbard parameter strength in details.