Application Of Biaxial Tensile Strain Research Articles

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.

Modulation of perpendicular magnetic anisotropy in CoFeB/MgO structure by an application of biaxial tensile strain

The application of %-order biaxial tensile strain can control the perpendicular magnetic anisotropy (PMA) in a CoFeB/MgO system deposited on a flexible substrate. A magnetic anisotropy switch from perpendicular to in-plane was observed when increasing the strain. The reversibility of the anisotropy change has been confirmed. The mechanism of the anisotropy change was discussed based on the strain-induced modulation of the bulk and CoFeB/MgO interfacial anisotropies, which is the origin of the PMA in the system.

Superconductivity of monolayer functionalized biphenylene with Dirac cones.

Monolayer biphenylene is a new two-dimensional (2D) carbon allotrope, which has been experimentally synthesized and theoretically predicted to show superconductivity. In this work, we investigate functionalized biphenylene with the adsorption of Li. The superconducting critical temperature (Tc) can be pushed from 0.59 K up to 3.91 K after Li adsorption. Our calculations confirm that the adsorption pushes the peak showing a high electronic density of states closer to the Fermi level, which usually leads to a larger Tc. Furthermore, the application of biaxial tensile strain can soften phonons and further enhance the Tc up to 15.86 K in Li-deposited biphenylene. Interestingly, a pair of type-II Dirac cones below the Fermi level has been observed, expanding the range of Dirac materials. It suggests that monolayer biphenylene deposited with Li may be a material with potential applications and improves the understanding of Dirac-type superconductors.

Strain-Dependent Polar Optical Phonon Scattering and Drive Current Optimization in Nanoscale Monolayer MoS2 FETs

Recently, microelectromechanical system has been used to dynamically strain atomically thin materials including MoS2. While strain can significantly modulate the electronic and phonon structures of monolayer MoS2, its impact on electron transport, especially in the dissipative regime, has not been well explored. In this paper, using a three-dimensional particle-based quantum-corrected Monte Carlo device simulator, the effects of uniaxial and biaxial strain on room-temperature electron transport in a model monolayer molybdenum disulphide (MoS2) based field-effect transistor have been investigated. In the beginning, the simulator has been validated against recently published experimental results. Overall, strain in monolayer MoS2 strongly affects the polar optical phonon modes as well as the electronic bandstructure. Uniaxial strain breaks the degeneracy of E′ Raman mode and results in phonon softening. In this case, our results show that, for both E+ and E− Raman modes, ON current first increases for up to 3.7% of applied strain and then decreases as the strain is increased further. As for biaxial strain, we consider the effects of both tensile and compressive stresses. We find that the application of biaxial tensile strain boosts the ON current for up to 4% of strain. Especially, biaxial tensile strain leads to ~ 15.56% increase in the ON current, which is highest for any type of applied stress.

Revealing out-of-equilibrium hidden phases in Sr3Ru2O7 by applying stress

We predict that the application of biaxial tensile strain will uncover an antiferromagnetic metallic hidden phase in ${\mathrm{Sr}}_{3}{\mathrm{Ru}}_{2}{\mathrm{O}}_{7}$. By using hybrid density functional theory we applied uniaxial and biaxial strains and identified a variety of phases. We found that tensile strain can reduce by up to half the stress needed to expose hidden phases compared to the use of uniaxial compressive strain. In addition, our results demonstrate that while elongation and compression of the octahedra induce magnetic phase transitions, tilting of the octahedra leads to a metal-to-insulator transition, indicating that the different hidden phases can be accessed by applying strain.

Trilayer TMDC Heterostructures for MOSFETs and Nanobiosensors

Two dimensional materials such as Transition Metal Dichalcogenides (TMDC) and their bi-layer/tri-layer heterostructures have become the focus of intense research and investigation in recent years due to their promising applications in electronics and optoelectronics. In this work, we have explored device level performance of trilayer TMDC heterostructure (MoS2/MX2/MoS2; M=Mo or, W and X=S or, Se) Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) in the quantum ballistic regime. Our simulation shows that device 'on' current can be improved by inserting a WS2 monolayer between two MoS2 monolayers. Application of biaxial tensile strain reveals a reduction in drain current which can be attributed to the lowering of carrier effective mass with increased tensile strain. In addition, it is found that gate underlap geometry improves electrostatic device performance by improving sub-threshold swing. However, increase in channel resistance reduces drain current. Besides exploring the prospect of these materials in device performance, novel trilayer TMDC heterostructure double gate Field Effect Transistors (FETs) are proposed for sensing Nano biomolecules as well as for pH sensing. Bottom gate operation ensures these FETs operating beyond Nernst limit of 59 mV/pH. Simulation results found in this work reveal that scaling of bottom gate oxide results in better sensitivity while top oxide scaling exhibits an opposite trend. It is also found that, for identical operating conditions, proposed TMDC FET pH sensors show super-Nernst sensitivity indicating these materials as potential candidates in implementing such sensor. Besides pH sensing, all these materials show high sensitivity in the sub-threshold region as a channel material in nanobiosensor while MoS2/WS2/MoS2 FET shows the least sensitivity among them.

Band Gap Engineering of Two-Dimensional Nitrogene.

In our previous study, we have predicted the novel two-dimensional honeycomb monolayers of pnictogen. In particular, the structure and properties of the honeycomb monolayer of nitrogen, which we call nitrogene, are very unusual. In this paper, we make an in-depth investigation of its electronic structure. We find that the band structure of nitrogene can be engineered in several ways: controlling the stacking of monolayers, application of biaxial tensile strain, and application of perpendicular electric field. The band gap of nitrogene is found to decrease with the increasing number of layers. The perpendicular electric field can also reduce the band gap when it is larger than 0.18 V/Å, and the gap closes at 0.35 V/Å. A nearly linear dependence of the gap on the electric field is found during the process. Application of biaxial strain can decrease the band gap as well, and eventually closes the gap. After the gap-closing, we find six inequivalent Dirac points in the Brillouin zone under the strain between 17% and 28%, and the nitrogene monolayer becomes a Dirac semimetal. These findings suggest that the electronic structure of nitrogene can be modified by several techniques, which makes it a promising candidate for electronic devices.