Application Of Biaxial Strain Research Articles

Tunable electronic and optical properties of h-BP/MoS2 van der Waals heterostructures toward optoelectronic applications

The integration of two-dimensional materials (2D) into van der Waals heterostructures (vdWHs) is widely recognized as an effective strategy for the development of multifunctional devices. This study aims to construct stable ultrathin 2D vdWHs using h-BP and MoS2 monolayers, and analyze the impact of strain on the electronic properties of h-BP/MoS2 vdWHs, with a specific focus on the mechanism of biaxial strain regulation. The h-BP/MoS2 vdWHs demonstrate the type II band alignment and possess direct bandgap, which can be effectively controlled through appropriate application of biaxial strain. The power conversion efficiency (PCE) can reach 21.85 % achieved suggests that the material under consideration has potential as a suitable candidate for 2D excitonic solar cells. The observed decrease in effective mass for both electrons and holes implies an enhanced carrier mobility, thereby facilitating the utilization of h-BP/MoS2 vdWHs in the development of high-efficiency excitonic solar cells. These findings indicate that the h-BP/MoS2 vdWHs possess the capability to serve as a reconfigurable system in the construction of highly efficient solar cells.

Multi-level chiral edge states in Janus M2XS2Se2 (M = V, Ti; X = W, Mo) monolayers with high Curie temperature and sizable nontrivial topological gaps.

Quantum anomalous Hall (QAH) insulators with dissipation-less chiral edge channels provide ideal platforms for the exploration of topological materials and low-power spintronic devices. However, the ultralow operation temperature and small nontrivial gaps are the bottlenecks for QAH insulators towards future applications. Here, a new family of QAH insulators, that is, Janus M2XS2Se2 (M = V, Ti; X = W, Mo) monolayers, are proposed to be ferromagnets with large perpendicular magnetic anisotropy (PMA) and high Curie temperature above room temperature. Moreover, the present M2XS2Se2 monolayers hold sizable nontrivial topological gaps, resulting in the 1st chiral edge state with Chern number C = -1. Unexpectedly, there also exists an occupied 2nd chiral edge state below the Fermi level. Although all M2XS2Se2 monolayers retain their PMA characteristics on application of biaxial strain, various topological phase transitions are present. The V2WS2Se2 monolayer preserves the QAH state regardless of strain, while the V2MoS2Se2 and Ti2WS2Se2 monolayers transform from QAH states to metallic states under tensile strains. The present M2XS2Se2 monolayers show competitive advantages among the reported materials for the development of topological electronic devices.

Enhancement of greenhouse gas adsorption on the new α‐type reconstructed structure of two‐dimensional borophene via biaxial strain engineering

AbstractThe adsorption of CO, CO2, and N2O on a newly found α‐type reconstructed form of borophene was investigated via density functional theory calculations. It is revealed that the new α‐type reconstructed borophene structure consists of several large holes, and has the same order of stability as the predicted α1‐borophene in Wu et al. On the pristine reconstructed borophene case, CO and CO2 adsorb moderately and weakly, respectively. Interestingly, N2O spontaneously dissociated on the α‐type reconstructed borophene. Upon the application of biaxial strain, especially at 10%, the adsorption of CO and CO2 on the reconstructed borophene becomes significantly enhanced, and this is attributed to changes in the density of states near the Fermi level of the reconstructed borophene.

A semiconductor Sc2S3 monolayer with ultrahigh carrier mobility for UV blocking filter application.

For humans, ultraviolet (UV) light from sun is harmful to our eyes and eye-related cells. This detrimental fact requires scientists to search for a material that can efficiently absorb UV light while allowing lossless transmission of visible light. Using an unbiased first-principles swarm intelligence structure search, we explored two-dimensional (2D) Sc-S crystals and identified a novel Sc2S3 monolayer with good thermal and dynamical stability. The optoelectronic property simulations revealed that the Sc2S3 monolayer has a wide indirect bandgap (3.05 eV) and possesses an ultrahigh carrier mobility (2.8 × 103 cm2 V-1 s-1). Remarkably, it has almost transparent visible light absorption, while it exhibits an ultrahigh absorption coefficient up to × 105 cm-1 in the ultraviolet region. Via the application of biaxial strain and thickness modulation, the UV light absorption coefficients of Sc2S3 can be further improved. These findings manifest an attractive UV blocking optoelectronic characteristic of the Sc2S3 configuration as a prototypical nanomaterial for the potential application in UV blocking filters.

Two-dimensional Janus monolayers with tunable electronic and magnetic properties

In the post graphene era, the discovery of magnetism in two-dimensional (2D) intrinsic nanomagnets has opened up exciting possibilities for low-dimensional spintronics. In this article, we have reported three new 2D Janus nanomagnets VBrCl2, VBrI2, and VClBrI for the first time. First-principles based density functional theory calculations reveal that these monolayers are intrinsically magnetic with indirect band gap semiconducting properties and further the magnetic and electronic properties of these monolayers are enhanced with the application of biaxial strain and electric field. We observe interesting electronic and magnetic phase transitions, tunable band gap, and supreme enhancement of the Curie temperature (~ 686%). Large magnetic anisotropic energy (MAE) with high magnetic moment and tunable band gap property make these Janus materials useful candidates for future information storage, optoelectronics, and 2D spin circuit development.

Strain-induced ferroelectricity and piezoelectricity in centrosymmetric binary oxides

First-principles calculations are performed to predict ferroelectricity in the binary rocksalt oxide family ($A\mathrm{O}$ with $A=\mathrm{Cd}$, Ba, Sr, Ca, Mg, etc.) via the application of biaxial strain. The origins of such ferroelectricity are discussed from the lattice dynamics perspective and electronic structure properties. Under compressive strain, the strikingly large longitudinal piezoelectric effect is induced due to the deformation along the $c$ direction as a response to the stress. These findings have the potential to motivate the search of new simple binary oxides possessing ferroelectricity that may lead to novel devices.

Tunable electronic and magnetic properties of two-dimensional magnetic semiconductor VIBr[formula omitted

The recent discovery of two-dimensional (2D) magnetic materials have attracted interest of the scientific community due to their potential applications in spintronics. In this work, we demonstrate by using density functional theory calculations that VIBr2 is a magnetic semiconductor. To tune the electronic and magnetic properties, we consider the application of biaxial strain (η), electric field (Ez) and combination of both. We find the phase transition from semiconductor → half-metal → metal, with ferromagnetic and antiferromagnetic ground states under different excitations. The maximum enhancement in Curie temperature is ∼1126% under application of external stimuli. The presence of various unique properties predicted by our detailed calculations give evidence that VIBr2 can be a promising candidate for future spintronic applications.

Strain and electric field-modulated indirect-to-direct band transition of monolayer GaInS2

The strain- and electric field-dependent electronic and optical properties of monolayer GaInS2 have been calculated using density functional theory (DFT) and time-dependent DFT (TD-DFT) GaInS2 monolayer shows an indirect band gap of 1.79 eV where valence band maxima (VBM) and conduction band maxima (CBM) rest between the K and Γ point and at the Γ point, respectively, while at 4% compressive strain, the material changes from indirect to direct band gap of 2.22 eV having the VBM and CBM at the Γ point. With a further increase in compressive strain, the CBM shifts, from the Γ to the M point, which leads to an indirect band gap again. The electric field also affects the band structure of monolayer GaInS2 and shifts the transition from direct to indirect band gap at a positive electric field of 4 V/nm, which acts normal to the surface. The strain-dependent optical properties are also calculated, which suggests that the absorption coefficient increases with compressive strain. Our work demonstrates a wide range of band gap variation and optical properties improvement upon application of biaxial strain and electric field on the monolayer of GaInS2.

Strain Effects on the Electronic and Optical Properties of Kesterite Cu2ZnGeX4 (X = S, Se): First-Principles Study.

Following the chronological stages of calculations imposed by the WIEN2K code, we have performed a series of density functional theory calculations, from which we were able to study the effect of strain on the kesterite structures for two quaternary semiconductor compounds CuZnGeS and CuZnGeSe. Remarkable changes were found in the electronic and optical properties of these two materials during the application of biaxial strain. Indeed, the band gap energy of both materials decreases from the equilibrium state, and the applied strain is more pronounced. The main optical features are also related to the applied strain. Notably, we found that the energies of the peaks present in the dielectric function spectra are slightly shifted towards low energies with strain, leading to significant refraction and extinction index responses. The obtained results can be used to reinforce the candidature of CuZnGeX(X = S, Se) in the field of photovoltaic devices.

Superior tunable photocatalytic properties for water splitting in two dimensional GeC/SiC van der Waals heterobilayers

The photocatalytic characteristics of two-dimensional (2D) GeC-based van der Waals heterobilayers (vdW-HBL) are systematically investigated to determine the amount of hydrogen (H2) fuel generated by water splitting. We propose several vdW-HBL structures consisting of 2D-GeC and 2D-SiC with exceptional and tunable optoelectronic properties. The structures exhibit a negative interlayer binding energy and non-negative phonon frequencies, showing that the structures are dynamically stable. The electronic properties of the HBLs depend on the stacking configuration, where the HBLs exhibit direct bandgap values of 1.978 eV, 2.278 eV, and 2.686 eV. The measured absorption coefficients for the HBLs are over ~ 105 cm−1, surpassing the prevalent conversion efficiency of optoelectronic materials. In the absence of external strain, the absorption coefficient for the HBLs reaches around 1 × 106 cm−1. With applied strain, absorption peaks are increased to ~ 3.5 times greater in value than the unstrained HBLs. Furthermore, the HBLs exhibit dynamically controllable bandgaps via the application of biaxial strain. A decrease in the bandgap occurs for both the HBLs when applied biaxial strain changes from the compressive to tensile strain. For + 4% tensile strain, the structure I become unsuitable for photocatalytic water splitting. However, in the biaxial strain range of − 6% to + 6%, both structure II and structure III have a sufficiently higher kinetic potential for demonstrating photocatalytic water-splitting activity in the region of UV to the visible in the light spectrum. These promising properties obtained for the GeC/SiC vdW heterobilayers suggest an application of the structures could boost H2 fuel production via water splitting.

Anisotropic Interlayer Exciton in GeSe/SnS van der Waals Heterostructure.

Stacking two or more two-dimensional materials to form a heterostructure is becoming the most effective way to generate new functionalities for specific applications. Herein, using GW and Bethe-Salpeter equation simulations, we demonstrate the generation of linearly polarized, anisotropic intra- and interlayer excitonic bound states in the transition metal monochalcogenide (TMC) GeSe/SnS van der Waals heterostructure. The puckered structure of TMC results in the directional anisotropy in band structure and in the excitonic bound state. Upon the application of compressive/tensile biaxial strain dramatic variation (∓3%) in excitonic energies, the indirect-to-direct semiconductor transition and the red/blue shift of the optical absorption spectrum are observed. The variations in excitonic energies and optical band gap have been attributed to the change in effective dielectric constant and band dispersion upon the application of biaxial strain. The generation and control over the interlayer excitonic energies can find applications in optoelectronics and optical quantum computers and as a gain medium in lasers.

Mechanical manipulation of electronic properties of SnO2 monolayer

A unique and novel SnO2 monolayer structure was introduced and studied by first-principles calculations based on the density functional theory (DFT). Bonding nature and band gap relation to elastic properties were obtained by fitting elastic energy as a function of Green-Lagrangian strain and calculating the elastic constants. The application of uniaxial strain produced a small in-plane stiffness with high Poisson’s ratio. These values revealed no lateral stress was resulted on bonds by the applied longitudinal strain. Area stiffness constant was defined for in-plane area expansion or compression. A higher area stiffness was found for biaxially placed strains, attributed to bending of the Sn-O-Sn bonds, which imposed a direct strain on the Sn-O bonds. Also, the electrons band gap varied from semiconductor energy at equilibrium atomic geometry to narrower gap with the application of biaxial strain. The variance was insignificant for the uniaxial strain case. We Show that the stability in the atomic bonding at strained conditions with fixed unit cell area gave controllability over the electronic state. Interlayer hybridization between O and Sn atoms made the band gap distinctly tunable with biaxial strain.

Exploring the transport and optoelectronic properties of silicon diselenide monolayer

A recently predicted hexagonal SiSe2 monolayer is investigated using first-principles calculations to investigate the structural, electronic, transport and optical properties. The electronic structure reveals indirect characteristics with a bandgap of 0.48 eV and 1.17 eV using PBE and HSE06 functional respectively with a valence band in between Γ-M and conduction band at M point. Further, to tune the electronic bandgap, the monolayer is subjected to mechanical strain. The electronic transport show higher electron carrier mobility of about 1.29 × 103 cm2V−1sec−1 and 19.64 × 103 cm2V−1sec−1 along both x- and y-direction respectively as compared to hole. The higher electron mobility as compared to hole is attributed to small values of electron effective mass of about 0.298 m0 and 0.382 m0 along x- and y-direction respectively. The optical properties were also studied under strained conditions and a high absorption coefficient of the order of 104 cm−1 is observed. Small changes in the absorption can be observed on application of biaxial strain. Our study suggests its potential use in optoelectronics and flexible nano-devices for the detection and absorption in the near infrared, visible and ultraviolet regions.

The impact of spin–orbit coupling and the strain effect on monolayer tin carbide

Two-dimensional tin carbide (2D-SnC) has attracted intensive attention from researchers recently due to its superior properties. We focus herein on the impact of the effects of spin–orbit coupling (SOC) and strain on the properties of 2D-SnC by using density functional theory (DFT). The electronic band structure of 2D-SnC confirms that it has an indirect bandgap of ~ 1.246 eV, which decreases to ~ 1.12 eV after introducing the SOC effect. The bandgap widens with increasing applied compressive strain but narrows with increasing applied tensile strain. A transition from an indirect to direct bandgap is observed at 6% compressive strain when excluding the SOC effect, whereas a direct bandgap is formed at 5% compressive strain when including the SOC effect. The structure of 2D-SnC is dynamically robust because it can tolerate a significant amount of biaxial strain. It is found that the peaks of the dielectric constant of 2D-SnC shift to higher photon energy (blue-shift) when the applied compressive strain is increased. In contrast, they shift to lower photon energy (red-shift) when the applied tensile strain is increased. Such strategies for tuning the bandgap of 2D-SnC based on the SOC effect and application of biaxial strain may pave the way for its use in future optoelectronic and spintronic device applications.

Strain-induced energetic and electronic properties of stanene nanomeshes

The energetic and electronic properties of stanene nanomeshes (SnNMs) under biaxial strain are investigated by using first-principles density functional theory. The results of this exploratory study indicate that SnNMs are stable and that, when the width W of the wall between neighboring holes is even, a bandgap can be opened, indicating that SnNMs can be used in logic applications. The value of the bandgap decreases with increasing W and shows a simple relation with the ratio of the removed to total Sn atoms of stanene. It is found that the application of biaxial strain can effectively lower the energy of formation and tune the bandgap of SnNMs. Both compressive and tensile strain can lower the energy of formation, while only compressive strain can increase the bandgap, which is more favorable for use in logic applications. These results reveal that SnNMs have significant potential for use in electronic applications, especially when applying strain engineering.

Exceptional mechano-electronic properties in the HfN2 monolayer: a promising candidate in low-power flexible electronics, memory devices and photocatalysis.

The response of the electronic properties of the HfN2 monolayer to external perturbation, such as strain and electric fields, has been extensively investigated using density functional theory calculations for its device-based applications and photocatalysis. The HfN2 monolayer is found to be a semiconductor showing a direct band gap of 1.44 eV, which is widely tunable by 0.9 eV via application of biaxial strain. Furthermore, the tunability in the band edges of the HfN2 monolayer straddling the water redox potential under a biaxial strain of ±10% makes it suitable for solar energy harvesting via photocatalytic applications over a wide range (0-7) of pH. The band gap can be decreased by 29.8% under a biaxial tensile strain of 10%. Upon incorporation of spin orbit coupling (SOC) a large spin splitting at the conduction band (Δc ∼ 314 meV) and a small splitting at the valence band (Δv ∼ 32 meV) are noted, which is attributable to the orbital composition of the band edges. The spin splitting in the band edges is found to be adjustable via biaxial compressive strain. The strain dependent mechanical properties and stability reveal the ability of the HfN2 monolayer to withstand a large magnitude of strain of up to ±10%, thereby bringing about a giant tunability in its Young modulus (Y) from 66 N m-1 to 283 N m-1, which is gainfully exploitable in flexible electronics. The tunability in Y over such a wide range has not been observed in other 2D materials. Moreover, the HfN2 monolayer undergoes a transition from a semiconducting to a metallic state under the application of a normal electric field or gate voltage of 0.48 V Å-1, which may potentially serve as the OFF (semiconducting) and ON (metallic) state in devices. Interestingly, an electric field of such intensity has been realized experimentally using pulsed ac field technology. Such a small gate voltage will greatly lower its power consumption. The electronic origin of this transition from the OFF to the ON state is found to arise from unoccupied NFEG (Nearly Free Electron Gas) states. A HfN2 monolayer based tunnel field effect transistor (t-FET) is proposed herewith as a model device for low-power digital data storage, thereby paving new avenues in flexible electronics and memory devices.

Tuning the electronic transport properties of p-type GaS monolayer by the application of biaxial strain

The first-principles calculations based on Density Functional Theory are performed in order to investigate the effect of strain on the electronic structure and transport properties of the p-type GaS monolayer. Our calculations show that unstrained GaS monolayer is semiconducting in nature having an indirect energy band gap of 2.35 eV. The application of compressive or tensile strain modifies the electronic band structure and energy band gap which further modifies the electronic transport coefficients of GaS monolayers. The energy band gap of GaS monolayer increases (decreases) under the application of compressive (tensile) strain. The Seebeck coefficient of p-type GaS monolayer is increased by applying strain, giving rise to the increase in the power factor.

Tunable electronic properties in bismuthene/2D silicon carbide van der Waals heterobilayer

A comprehensive analysis of the structural and electronic properties of a novel 2D bismuthene and silicon carbide (SiC) van der Waals heterostructure is performed using first-principles calculation. The electronic structure of the proposed heterobilayer can be effectively tuned by changing the interlayer distance as well as upon the application of biaxial strain. The inclusion of spin–orbit coupling results in the splitting in the CB and VB with a greater reduction in the band gap. The calculated projected density of states and space-charge distribution near the CB and VB reveals the carrier confinement at the bismuthene layer only, indicating the prospect of 2D-SiC as a potential substrate for the realization of bismuthene-based heterostructure. Lower electron effective mass is computed, which dictates the higher electron mobility on the heterobilayer. These intriguing findings will manifest a new path for the realization of bismuthene-based high-speed nanoelectronic devices.

A strain tunable single-layer MoS2 photodetector

Strain engineering, which aims to tune the bandgap of a semiconductor by the application of strain, has emerged as an interesting way to control the electrical and optical properties of two-dimensional (2D) materials. Apart from the changes in the intrinsic properties of 2D materials, the application of strain can be also used to modify the characteristics of devices based on them. In this work, we study flexible and transparent photodetectors based on single-layer MoS2 under the application of biaxial strain. We find that by controlling the level of strain, we can tune the photoresponsivity (by 2-3 orders of magnitude), the response time (from <80 ms to 1.5 s) and the spectral bandwidth (with a gauge factor of 135 meV/% or 58 nm/%) of the device.

Strain and layer modulated electronic and optical properties of low dimensional perovskite methylammonium lead iodide: Implications to solar cells

In the present work we report the effect of quantum confinement, biaxial and uniaxial strains on electronic properties of two dimensional (2D), one dimensional (1D) and layered system of Methylammonium lead iodide (MAPI) in cubic phase using first principles calculations based on density functional theory for its implications to solar cell. Our studies show that the bandgap of MAPI is dimension dependent and is maximum for 1D. We also found that the band gap of 2D MAPI can be modulated through application of biaxial strain, which shows linear relation with strain; compressive strain decreases the band gap whereas tensile strain increases the band gap. 1D MAPI shows near parabolic response towards strain which increases with compressive and tensile strain. Our studies show that the 2D MAPI is better for a solar cell due to lower effective mass of electron and hole arising from the strong s-p anti-bonding coupling. The calculated solar cell parameters suggest that the 2D MAPI is best suited for solar cell applications. The calculated open circuit voltage, fill factor and efficiency are highest for 2D MAPI. The highest theoretical efficiency of 2D MAPI is 23.6% with mesoporous (mp)-TiO2 electrode.