Biaxial Compressive Strain Research Articles

Tunable electronic and optical properties of GeC/PtO2 vdW hetero-bilayer using first-principles study

The detailed optical and electronic characteristics of 2D GeC and 2D PtO2 under biaxial strains and electric fields across the plane are studied systematically using the density functional theory (DFT) based first-principles framework. The six different stacking patterns of the stacked van der Waals (vdW) GeC/PtO2 hetero-bilayers were DFT screened, and HBL 4 and HBL 5 are found both dynamically stable and energetically favorable, evident from the non-zero phonon frequency and negative binding energy from phonon dispersion and binding energy calculations, respectively. The bandgap of 2D GeC and 2D PtO2 is found to be ∼2.08 eV (direct) and ∼1.63 eV (indirect), while the bandgaps in vdW HBL 4 (HBL 5) are found to be 0.51 eV (0.49 eV). Biaxial strain lowered the bandgap by ∼11.13 (∼1.81) times at 6% compressive (tensile) biaxial strain in HBL 4 (HBL 5). Semiconductor-to-metal switching is found in both HBLs at ±0.6 V/Å of the cross-plane electric field. All the HBLs show type-II band-alignment, evident from the difference in charge density and projected density of state contour, indicating spatial carrier separation capability. The peak of the optical absorption coefficient is found to be ∼3.1 × 105 cm−1 at 310 nm for both HBL 4 and HBL 5, which is comparable to high-absorbing perovskite material. Moreover, the optical absorption is sensitive to the biaxial strains and electric fields, and increased visible band optical absorption is found for tensile strains in both HBLs. These exceptional findings and engineered bandgap in GeC/PtO2 vdW HBL indicate the promising application of this material in 2D advanced nanoelectronics.

Achieving arbitrary CO2 adsorption energy on χ3 borophene surface by applying electric field or strain: DFT and RSM approaches

The study of χ3 borophene modification was considered finding an applicable technique to achieve more efficient approaches in CO2 capturing. In the framework of density functional theory (DFT), two surface modification methods were described, external electric field or strain application on χ3 borophene, and the effect of them was investigated on CO2 adsorption. All these methods affected the deformation charge density of the surface, which led to an increase in the CO2 binding energy, in the studied range. The turning point in CO2 capturing and structural changes appeared by applying an electric field of −0.030 a.u. strength with −0.48 eV adsorption energy. The uniaxial and biaxial compressive strain resulted in proper adsorption energy of −0.73 to −0.85 eV, although it caused a significant change in the planar structure of the surface. The structural and electronic properties, in addition to the charge density difference analysis, confirmed the chemisorption of CO2 on modified surfaces. Lastly, for the first time, the response surface methodology in the DFT framework was used to evaluate the simultaneous effect of applying an external electric field and strain as well as charge injection on CO2 adsorption. The generated quadratic equation predicts the CO2 adsorption energy with high accuracy as a function of the modification parameters. This result would be very helpful in adjusting the modification parameters to achieve the desired CO2 adsorption energy with lower experimental costs, where the χ3 surface is used for a special application such as CO2 removal or sensing.

Prediction of a monolayer spin-spiral semiconductor: CoO with a honeycomb lattice

The recent successful fabrication of two-dimensional (2D) CoO with nanometer-thickness motivates us to investigate monolayer CoO due to possible magnetic properties induced by Co atoms. Here, we employ first-principles calculations to show that monolayer CoO is a 2D spin-spiral semiconductor with a honeycomb lattice. The calculated phonon dispersion reveals the monolayer's dynamical stability. Monolayer CoO exhibits a type-I spin-spiral magnetic ground state. The spin-spiral state and the direct bandgap character are both robust under biaxial compressive strain (−5%) to tensile strain (5%). The bandgap varies only slightly under either compressive or tensile strain up to 5%. These results suggest a potential for applications in spintronic devices and offer a new platform to explore magnetism in the 2D limit.

Electron-phonon coupling superconductivity and tunable topological state in carbon-rich selenide monolayers

The coexistence of Dirac cones and Van Hove singularities (VHSs), as the notable feature on prominent electronic band structure in recently hot-topic Lieb lattice and twisted graphene superlattice materials, has recently drawn tremendous attention since it offers an ideal platform for realizing correlation-driven electronic states (e.g., superconductivity and topological state). Here, we have identified two two-dimensional (2D) crystals, namely ${\mathrm{C}}_{4}\mathrm{Se}$ and ${\mathrm{C}}_{5}\mathrm{Se}$, which exhibit the coexistence of Dirac cones and VHSs. Based on ab initio calculations and the Bardeen-Cooper-Schrieffer theory, we investigated the electron-phonon coupling and possible superconductivity in both structures. The results indicate that ${\mathrm{C}}_{4}\mathrm{Se}$ possesses intrinsic superconducting states, whereas ${\mathrm{C}}_{5}\mathrm{Se}$ exhibits tunable superconductivity when doped. Their superconducting critical temperature (${T}_{c}$) can reach up to 11.6 and 11.2 K, respectively, surpassing the majority of 2D superconductors. Besides, we uncovered an approximate Dirac cone in ${\mathrm{C}}_{6}\mathrm{Se}$ with a small band gap of 0.17 eV. Via the application of a biaxial compressive strain, remarkably, the ${\mathrm{C}}_{6}\mathrm{Se}$ can be transformed into a topological insulator. These findings highlight the potential of carbon-rich C-Se 2D crystals as a promising platform for investigating fascinating band structures and physical states, thus advancing our comprehension of 2D crystals.

Engineering the optical and electronic properties of metal adsorbed Ga2SSe Janus monolayer by applying biaxial tensile and compression strain

Engineering the optical and electronic properties of metal adsorbed Ga2SSe Janus monolayer by applying biaxial tensile and compression strain

Tuning the stability and optoelectronic properties of SnTe/Sb van der Waals heterostructure by biaxial strain effect

Using density functional theory (DFT), we have investigated the structural, stability, and electronic properties of the isolated antimonene, SnTe monolayers, and the structural, stability, and optoelectronic properties of the SnTe/Sb vdW heterostructure. The results show that the atoms in these monolayers have strong cohesion and that the SnTe/Sb vdW heterostructure is stable. The indirect bandgap energies are calculated to be 1.17[Formula: see text]eV (PBE) (2.28[Formula: see text]eV (HSE)), 1.89[Formula: see text]eV (PBE) (2.93[Formula: see text]eV (HSE)), and 0.32[Formula: see text]eV (PBE) (0.89[Formula: see text]eV (HSE)), respectively. However, these physical properties can be modulated by applying biaxial strain, when the compressive and tensile biaxial strain reached more than 4%, the heterostructure turned into metal, and the electronic bandgap decreased as the tensile and compressive biaxial strain increased from 0 to 8%. The phonon dispersion exhibits imaginary modes, notably above the 6% compressive strain, exhibiting its dynamic instability. The formation energy is negative under all biaxial strain, indicating that the heterostructure is still relatively stable during biaxial strain. An enhancement of optical absorption is observed, especially near the UV-visible regions, when the biaxial strain is incorporated, especially for compressive strains of 4% and 2%, which increases the absorption capacity. Therefore, the application of the biaxial strain can improve the stability, optical, and electronic properties of the SnTe/Sb vdW heterostructure, suggesting its potential for photovoltaic and optoelectronic applications.

Theoretical study on the thermal transport and its tunability of a-plane trilayer GaN

Two-dimensional (2D) a-plane gallium nitride, a non-layered 2D material, has promising applications in photoelectric nanodevices due to its direct band bandgap. Herein, employing molecular dynamics simulations, we studied the thermal transport properties of a-plane trilayer GaN, and the temperature, together with strain modulation on the thermal conductivity of the system. The a-plane trilayer GaN shows anisotropic thermal conductivity with 70.22 Wm−1K−1 and 41.81 Wm−1K−1 along zigzag- and armchair- directions respectively at room temperature when extrapolated to infinite size. In addition, the thermal conductivity of trilayer GaN exhibits decreasing trend in response to the increase of temperature. The thermal conductivity decreases monotonically with the increased compressive uniaxial and biaxial strain, while it shows an up-then-down trend under tensile strain. The tunability of thermal conductivity under biaxial strain is much larger than that of uniaxial strain. The phonon density of states is further investigated to understand the behavior of thermal conductivity. The tunability of the system thermal conductivity will expand its applications in thermal management and nanodevices.

Analysis of the microscopic mechanism of the stacking stability of h-BN on a metal substrate under external force

Nanoelectromechanical systems (NEMS) based on layered materials often rely on mechanical deformation, which involves relative sliding between layers. And the charge distribution between layers is essential for understanding its mechanical and electromechanical behavior. As a typical layered material, h-BN has a small energy difference between different stacks, so it is prone to phase transition under external force. That is, relative sliding between layers. Therefore, analyzing the effect of external forces on the electronic structure of h-BN is crucial for understanding the mechanical deformation of layered materials. In this work, Cu and Ni are used as substrate materials. On the one hand, the influence of different substrates on the electronic structure and stacking stability of h-BN is studied. On the other hand, the microscopic mechanism of the phase of h-BN on the Cu substrate is analyzed and discussed. Through analysis, the stacking stability of h-BN on a metal substrate depends on the hybrid strength of the metal 3d and h-BN p orbitals. That is the adsorption. In addition, the phase transition of h-BN on the Cu substrate is mainly attributed to the difference in the change rate of the total charge density of the h-BN/Cu interface between the two stacks with the external force. However, neither biaxial tensile nor biaxial compressive strain will cause h-BN to undergo transformation on the Ni substrate.

Design and optimization of stress/strain in GAA nanosheet FETs for improved FOMs at sub-7 nm nodes

Stress/strain engineering techniques are employed to boost the performance of Gate-all-around (GAA) vertically stacked nanosheet field-effect transistors (NSFETs) for 7 nm technology nodes and beyond. In this work, we report on the 3D numerical simulation study of the impacts of source/drain epitaxial and uniaxial strained-SiGe channel stresses on p-type NSFETs. It is shown that the uniaxial strained-SiGe channel improves the drive current by up to 107% due to higher compressive stress while the 3-stack NSFET can achieve an enhancement in drive current even up to 187% using a 30% Ge mole fraction. Furthermore, we compare the multiple stacked channel NSFETs and nanowire FETs (NWFETs) considering different strain techniques. As compared to a 3-stack strained-SiGe NWFET, NSFETs show 27% and 10% enhancements in ION and SS, respectively. Vertically stacked NSFETs are shown to be the best option to improve the hole mobility under biaxial and uniaxial compressive strain rather than NWFETs. We also look at how the Ge mole fraction affects various electrical properties in a uniaxial strained-SiGe channel with shrinking dimensions of scaled NSFETs. It is observed that for a fixed Lg, ION/IOFF ratio, SS and DIBL decrease with the increase in Ge mole fraction.

Tuning of optical performance of CrS2 monolayer using strain engineering

In the present manuscript, the compressive and tensile strain in both uniaxial and biaxial directions are used to investigate the electronic and optical properties of CrS2 monolayer. It is revealed that both types of strain have a significant impact on the bandgap. For tensile strain, the value of Eg keeps decreasing but for compressive strain, the bandgap value first rises to 1.196 eV at 8% of uniaxial strain and then subsequently falls to 1.132 eV at 12% strain. The value of Eg in the biaxial case reaches to 1.75 eV at 6% compressive strain, and subsequently decreases to 0.60 eV at 12% compressive strain. The value of Eg for biaxial tensile strain continues to decrease and reached to 0.11 eV at 12% strain. The value of dielectric function i.e., ε2(ω) changes from 2.97 to 1.82 and then to 1.95 under 8% and 12% uniaxial compressive strain. ε2(ω) also changes from 2.97 to 2.52 and then to 3.30 under 4% and 12% biaxial compressive strain, respectively. A blue as well as a red shift in the absorption edge under compressive and tensile strains, respectively are observed. Our results imply that strain can be a useful tool for altering the optoelectronic properties of CrS2 monolayer.

Oxygen-terminated Ti3C2 MXene as an excitonic insulator

Excitonic insulators originate from the formation of bound excitons (electron–hole pairs) in semiconductors and provide a solid-state platform for quantum many-boson physics. We determined the excitonic insulator phase of Ti3C2O2 monolayer from its indirect quasiparticle band structure and from the precise evaluation of the relative value of the fundamental bandgap vs the momentum-indirect excitonic binding energy. The excitonic insulator is stable over the ±4% range of compressive and tensile biaxial strain. The energy region relevant for the optical absorption is strongly strain-dependent.

Magnetic Phase Transition in Strained Two-Dimensional CrSeTe Monolayer

Tunable magnetic phase transition in two-dimensional materials is a fascinating subject of research. We perform first-principle calculations based on density functional theory to clarify the magnetic property of CrSeTe monolayer modulated by the biaxial compressive strain. Based on the stable structure confirmed by the phonon calculation, CrSeTe is determined to be a ferromagnetic metal that undergoes a phase transition from a ferromagnetic state to an antiferromagnetic state with nearly 2.75% compressive strain. We identify the stress-magnetism behavior originating from the changes in interactions between the nearest-neighboring Cr atoms (J 1) and the next-nearest-neighboring Cr atoms (J 2). Through Monte Carlo simulation, we find that the Curie temperature of the CrSeTe monolayer is 160 K. The CrSeTe monolayer could be an intriguing platform for the two-dimensional systems and potential spintronic material.

Strain tuning of the electronic structure and optical properties of novel Janus MgBrI monolayer: Insights from first-principles calculations

Using first-principles calculations in the framework of density functional theory (DFT), we systematically carry out the dynamic stability, electronic and optical properties of the Janus MgBrI monolayer and its parent MgI2 and MgBr2 monolayers. Our findings show that these systems have no imaginary frequencies in the entire Brillouin zone (BZ), which means they are very stable. At the equilibrium state, the results indicate that the Janus MgBrI monolayer is a direct band gap insulator with an energy gap of 3.475 eV, which is smaller than the bandgap of MgI2 and MgBr2 monolayers. The studied optical properties including the complex dielectric function, refractive index, reflectivity, extinction coefficient and absorption coefficient as a function of the photon energy have been investigated. The absorption coefficient shows a strong absorption of the light in the ultraviolet (UV) region. We studied how biaxial strain effects the electronic and optical properties of the Janus MgBrI monolayer. When the strain ranged from −10% to 10%, the Janus MgBrI monolayer showed an insulator characteristic with a direct band gap, which changed to an indirect band gap when the biaxial compressive strain was −10%. In addition, the Janus MgBrI displays an absorption of around 105 cm−1 in the ultra-violet (UV) region. Our results highlight an intriguing new two-dimensional (2D) material that could be used in optoelectronic devices and UV absorbers.

Tight-binding analysis of the effect of strain on the band structure of GaN

The effects of strain on the band structure of GaN are investigated by using an empirical tight-binding method. The impacts on its bandgap, carrier effective mass, and group velocity are discussed. By analyzing the orbital components at the top of the valence band, the cause of the variation of the band structure including effective-mass exchange is discussed. Analysis of the average group velocity indicates that tensile uniaxial or compressive biaxial strain may be beneficial for achieving higher breakdown voltage in vertical GaN devices due to the smaller group velocity of the valence band. For the same reason, we also predict higher breakdown voltages due to tensile biaxial strain for horizontal devices.

Enhancement of Polarization Properties of Bulk PbTiO3 by Engineering Strain

The effect of strain (up to 8%) on the polarization of bulk PbTiO3 is clarified, in which the focus is put on the ferroelectric hysteresis loop. The shell model, a powerful simulation tool for calculating electric polarization, is developed. The results obtained show that the ferroelectric hysteresis loop is expanded or shrunk under the strain. Besides, the study also points out two main results which have potential applications in practice. (1) The remanent polarization is enhanced significantly under the compressive biaxial strain (1.68 times). (2) The ferroelectric-paraelectric phase transition can be achieved under the compressive uniaxial strain (at 8%).

Effect of strain on the thermoelectric properties of three‐dimensional PtS2: A first‐principles study

AbstractThe effect of strain on the electronic structure and thermoelectric properties of three‐dimensional (3D) PtS2 was investigated through ab initio calculations. The phonon dispersion curve has no imaginary frequency under biaxial tensile and compressive strains, indicating that the studied structure is stable. All the studied structures show higher Seebeck coefficients (>400 μV/K), and the Seebeck coefficient of p‐type semiconductors is superior to that of n‐type semiconductors. Tensile strain can decrease the lattice thermal conductivity of PtS2, whereas compressive stress has the opposite effect on the lattice thermal conductivity. The smallest lattice thermal conductivity is 26.7 W/m·K under 6% strain when the temperature is 800 K. The maximum ZT values for the p‐type and n‐type semiconductors are 0.17 and 0.48, respectively. This work provides a guide to studying how strain modulates thermoelectric properties of materials; the relaxation time calculation method in this study is believed to be more accurate due to the fact that the influence of the carrier concentration is considered.

First-Principles Study of Structural and Electronic Properties of Monolayer PtX2 and Janus PtXY (X, Y = S, Se, and Te) via Strain Engineering.

In this work, the structural parameters and electronic properties of PtX2 and Janus PtXY (X, Y = S, Se, and Te) are studied based on the density functional theory. The phonon spectra and the Born criteria of the elastic constant of these six monolayers confirm their stability. All PtX2 and Janus PtXY monolayers show an outstanding stretchability with Young's modulus ranging from 61.023 to 82.124 N/m, about one-fifth that of graphene and half that of MoS2, suggesting highly flexible materials. Our first-principles calculations reveal that the pristine PtX2 and their Janus counterparts are indirect semiconductors with their band gap ranging from 0.760 to 1.810 eV at the Perdew-Burke-Ernzerhof level (1.128-2.580 eV at the Heyd-Scuseria-Ernzerhof level). By applying biaxial compressive and tensile strain, the electronic properties of all PtX2 and Janus PtXY monolayers are widely tunable. Under small compressive strain, PtX2 and Janus PtXY structures remain indirect semiconductors. PtTe2, PtSeTe, and PtSTe monolayers undergo a semiconducting to metallic transition when the strain reaches -6, -8, and -10%, respectively. Interestingly, there is a transition from the indirect semiconductor to a quasi-direct one for all PtX2 and Janus PtXY monolayers when the tensile strain is applied.

Thermodynamics modeling of ZrCo-H systems with biaxial compressive strain during desorption

As known, inferior cycling performance and deteriorated de-/hydrogenation kinetics resulting from by hydrogen-induced disproportionation severely impedes engineering applications of zirconium-cobalt (ZrCo) alloys used in the industry of hydrogen isotope storage. In this work, the first principles calculations are conducted to investigate the thermodynamic behavior of ZrCo hydrides with and without biaxial compressive strain during desorption. Importantly, the whole dehydrogenation process is divided into two steps due to the presence of intermediate ZrCoHx (x = 2, 2.25, 2.50, and 2.75). During Step I, the hydrided phase ZrCoH3 is decomposed into ZrCoHx (ZrCoH3 → ZrCoHx), and then the phase transformation from ZrCoHx to ZrCo (ZrCoHx → ZrCo) occurs in Step II. Afterwards, the equilibrium pressures, enthalpy changes, and entropy changes involved in the reactions are determined through the thermodynamic relations. The results demonstrate that compared to the second step, there is a superiority of dehydrogenation performance for the first step, which is derived from higher equilibrium pressure. Moreover, the equilibrium pressure increases with the decrease of the H content in ZrCoHx because of the intensification of vibrational degrees of freedom of H atoms. Further study concerns on the influence of biaxial strain (-3% - 0%) along [010] and [001] on thermodynamics properties of the ZrCo-H systems, indicating that the strain deteriorates the lattice stability and improves the equilibrium pressure. By contrast, it is more favorable to enhancing the dehydrogenation performance when the compressive strain is beyond 1.5%.

Investigating the magnetic, thermoelectric, and thermodynamic properties of the GeCH3 single-layer considering external magnetic field, doping, and strain

Extensive research is ongoing to improve the performance of thermoelectric and thermodynamic properties of the material because preventing energy waste is vital in modern society. Herein, we study the thermoelectric and thermodynamic properties of the GeCH3 single-layer (SL) under the influence of an external magnetic field, electron doping, and tensile and compressive biaxial strain by using the tight-binding and equilibrium Green’s function method. We found that the electronic heat capacity, magnetic susceptibility, and electronic thermal and electrical conductivity increase by employing an external magnetic field, electron doping, and tensile biaxial strain. However, compressive biaxial strain yields a decrease in thermoelectric and thermodynamic properties. The results of our study show that the GeCH3 SL is paramagnetic. The results presented here that the GeCH3 SL is a suitable alternative for use in thermoelectric, spintronic, and valleytronics devices.

First-principles calculations of improving carrier mobility for [formula omitted]CsPbI3

In the past few years, inorganic perovskite CsPbI3 has attracted great interest due to high conversion efficiency in solar cells. Carrier mobility, as an important physical parameter in optoelectronic devices, directly affected power consumption. In this study, the phonon-limited mobilities of β-CsPbI3 were investigated using Boltzmann transport equation based on first-principles calculations. Using the fully relaxed lattice constants of a = 8.829/c = 6.505 Å, we obtained a mobility of μe,x=151/μe,z = 241 cm2V−1s−1 and μh,x=94/μh,z = 163 cm2V−1s−1. Longitudinal optical phonon associated with the relative vibration between Pb and I atoms was revealed to be the main scattering source, and the scattering mechanism was independent of temperature and carrier type. Biaxial compressive strain of in-plane (ab-plane) decreased mobility, which should be avoided in film growth. Since the exchange correlation functional with GGA-PBE form overestimated the lattice constants, the experimental values were used to correct the results. The band gap was mainly determined by the lattice constant of in-plane, and the mobility was extremely sensitive to the lattice constant in out-of-plane (c-axis). Using experimental lattice constants of a = 8.776/c = 6.214 Å, the mobility was improved to μe,x=503/μe,z = 1084 cm2V−1s−1 and μh,x=373/μh,z = 871 cm2V−1s−1.