Biaxial Compressive Strain Research Articles

MXene monolayer Mn2ZnN2: a promising robust intrinsic half-metallic nanosheet

Two-dimensional half-metallic ferromagnets are promising in spintronics. In recent years, the half-metallicity and the magnetic properties of the MXene materials have been the research hotspots of new materials due to their unique crystal characteristics and wide applications. In this paper, the MXene nanosheet Mn2ZnN2 was predicted as a kind of robust intrinsic half-metallic nanosheet whose magnetic moment per unit is the integer 6.00 μ B based on the first principles calculations. The half-metallic character and the magnetic moment of this nanosheet mainly result from the spin-polarized Mn-ions induced by the crystal field. If the absolute biaxial compression strain is lower than 3.0%, the half-metallicity remains well and the magnetic moment per unit is always 6.00 μ B, indicating that its half-metallicity and magnetic properties are stable within a certain pressure range. More importantly, the magnetic moment per unit is elevated from 6.00 μ B to 9.00 μ B and the half-metallic energy gap increases evidently after an electron is removed from this nanosheet, suggesting that the half-metallicity and magnetic properties of this nanosheet may be improved via tuning its charge state.

Engineering the hydrogen storage properties of the perovskite hydride ZrNiH3 by uniaxial/biaxial strain

In the present work, the bonding length, electronic structure, stability, and dehydrogenation properties of the Perovskite-type ZrNiH3 hydride, under different uniaxial/biaxial strains are investigated through ab-initio calculations based on the plane-wave pseudo-potential (PW-PP) approach. The findings reveal that the uniaxial/biaxial compressive and tensile strains are responsible for the structural deformation of the ZrNiH3 crystal structure, and its lattice deformation becomes more significant with decreasing or increasing the strain magnitude. Due to the strain energy contribution, the uniaxial/biaxial strain not only lowers the stability of ZrNiH3 but also decreases considerably the dehydrogenation enthalpy and decomposition temperature. Precisely, the formation enthalpy and decomposition temperature are reduced from −67.73 kJ/mol.H2 and 521 K for non-strained ZrNiH3 up to −33.73 kJ/mol.H2 and 259.5 K under maximal biaxial compression strain of ε = −6%, and to −50.99 kJ/mol.H2 and 392.23 K for the maximal biaxial tensile strain of ε = +6%. The same phenomenon has been also observed for the uniaxial strain, where the formation enthalpy and decomposition temperature are both decreased to −39.36 kJ/mol.H2 and 302.78 K for a maximal uniaxial compressive strain of ε = - 12%, and to −51.86 kJ/mol.H2 and 399 K under the maximal uniaxial tensile strain of ε = +12%. Moreover, the densities of states analysis suggests that the strain-induced variation in the dehydrogenation and structural properties of ZrNiH3 are strongly related to the Fermi level value of total densities of states. These ab-initio calculations demonstrate insightful novel approach into the development of Zr-based intermetallic hydrides for hydrogen storage practical applications.

Orbital−energy splitting in Ruddlesden−Popper layered halide perovskites for tunable optoelectronic properties

The electronic orbital characteristics at the band edges play an important role in determining the electrical, optical and defect properties of perovskite photovoltaic materials. It is highly desirable to establish the relationship between the underlying atomic orbitals and the optoelectronic properties as a guide to maximize the photovoltaic performance. Here, using first-principles calculations and taking Ruddlesden-Popper (RP) phase layered perovskites Cs n +1 Ge n I n +1 Cl 2n as examples, we demonstrate how to rationally optimize the optoelectronic properties (e.g., band gap, transition dipole matrix elements, carrier effective masses, bandwidth) through a simple band structure parameter. Our results show that reducing the splitting energy |Δ c | between the in-plane p x , y and out-of-plane p z orbitals at the conduction band minimum (CBM) can effectively reduce the band gap and carrier effective masses while greatly improving the optical absorption in the visible region. Thereby, the orbital-property relationship with Δ c is well established through biaxial compressive strain. Finally, it is shown that this approach can be reasonably extended to several other non-cubic halide perovskites with similar p orbitals characteristics at the conduction band edge. Therefore, we believe that our proposed orbital engineering approach will provide atomic-level guidance for understanding the performance limits of layered perovskite solar cells. • Orbital−energy splitting in Ruddlesden−Popper layered halide perovskites. • Optimizing the optoelectronic properties through a simple band structure parameter. • Reducing the splitting energy .|Δ c | can effectively tune the optoelectronic properties.

Photoelectric properties and stability of the single-layer transition metal dichalcogenides under three stress states

In this paper, the electrical and optical properties of single-layer MoS2 and single-layer WS2 in three strain states: biaxial tension, biaxial compression, biaxial tension and compression are systematically studied. All calculations are based on the first-principle of density functional theory. The results show that after biaxial tension strain, biaxial compression strain, and biaxial tension-compression strain are applied, the atomic structure, energy band structure, and optical absorption coefficient will show disparate changing trends. When the biaxial tension and compression strain intensity is less than 15%, the bond length, bond angle, and light absorption peak will have little fluctuation with the increase of strain intensity. However, compared with the other two strain states, these two crystal structures are the most volatile at this time. In addition, when 15% biaxial tensile strain is applied, the two crystals can still maintain their kinetic stability.

Strain tailored thermodynamic stability, electronic transitions, and optoelectronic properties of III (In, Ga and Al)-nitride monolayers

The thermodynamic stability of III-nitride monolayers is calculated using the phonon band structure. Electronic properties are computed using the generalized gradient approximation-Perdew–Burke–Ernzerhof exchange-correlation potentials, which show the semiconducting behavior with bandgap 0.59 eV, 2.034 eV, and 2.906 eV for InN, GaN, and AlN monolayers, respectively. The biaxial tensile and compressive strains are used as external stimuli to understand their impact on the optoelectronic properties of these monolayers. The thermodynamic stability of strained monolayers is investigated to explore the maximum possible strains, i.e. flexibility limit, these monolayers can sustain. These monolayers are more sensitive to compressive strains, showing thermodynamic instability even at 1% compressive strain for all the considered monolayers. Further, the III-nitride monolayers are more robust with the tensile strain. InN, GaN, and AlN monolayers can sustain up to 4%, 16%, and 18% tensile strain, respectively. More interestingly, the electronic transitions, such as direct to indirect and semiconducting to metallic, are noticed with strain in the considered monolayers. The optical properties also exhibit strong strain dependency at the different transition points.

Predicted double perovskite material Ca2ZrTiO6 with enhanced n-type thermoelectric performance

Herein, using first-principles calculations, we studied the electronic and thermoelectric properties of isolated perovskites CaTiO3, CaZrO3 and double perovskite Ca2ZrTiO6 crystal structure under ambient conditions, biaxial compression, and biaxial tensile strain. We used generalized gradient approximation and the Hubbard parameter (GGA ​+ ​U) to calculate exchange and correlation interactions. The isolated perovskite CaTiO3 and CaZrO3 are indirect bandgap (Γ ​− ​R) semiconductors of values 1.90 ​eV, 3.2 ​eV, respectively. The construction of a double perovskite Ca2ZrTiO6 results in a direct (Γ ​− ​Γ) bandgap semiconductor material. The bandgap values under 2% & 5% biaxial tensile strain and compressive strain are in the range of 2.3 ​eV and 2.2 ​eV. We studied the thermoelectric properties by taking the two chemical potential values (μ) equal to CBM and VBM, respectively. The thermoelectric properties of Ca2ZrTiO6 under 2% & 5% biaxial tensile strain were improved at CBM, while thermoelectric properties under 2% & 5% biaxial compression strain were enhanced at VBM as compared to thermoelectric properties under ambient conditions. At CBM, the maximum value of the figure of merit (ZT) is about 4.4 ​at 500 ​K, required for the next generation of the thermoelectric device. The ZT value shows that the novel double perovskite is a very suitable candidate for thermoelectric devices.

Effect of Strain on the Epitaxy of B-Doped Si0.5Ge0.5 Source/Drain Layers

Pseudomorphic B-doped Si1-xGex is commonly used as a source/drain (S/D) material for p-type MOSFETs. The lattice mismatch between the Si1-xGex and the Si substrate induces a compressive strain within the epilayer, which is beneficial to device performance. Indeed, it increases the hole mobility in the channel [1] and increases the B solubility limit in the S/D thanks to a strain compensation effect that enables higher substitutional boron concentrations ([B]sub) compared to pure Si or Ge [2], [3]. However, with device downscaling and a reduction in the active area where epitaxial deposition needs to occur, maintaining the high amounts of strain required is challenging [4]. Most of the compressive strain is released through the elastic relaxation allowed by the presence of free surfaces. This sets the need of assessing the impact of strain on the epitaxy of in-situ doped Si1-xGex and how it affects the material properties.In this study, we investigate these effects through three series of B-doped Si1-xGex films grown on Si(001) substrates whereby three Ge concentrations ranging from 25 to 65% are considered. For each Ge concentration, epilayers of different thicknesses are grown to achieve both fully strained and partially relaxed layers. Subsequently fabricated Ti / Si1-xGex contacts are then evaluated using the multiring circular transmission line method [5]. The resistivity (ρ) and contact resistivity (ρc) are both found to show an enhancement with increasing degree of strain relaxation (Fig. 1a). The thinnest layer in each Ge concentration also yields degraded contact and electrical properties due to a surface scattering effect. Correspondingly, SIMS analyses reveal a decrease in B incorporation during the epitaxial growth upon relaxation, which also coincides with a slight increase in Ge content (Fig. 1b).A similar behavior is observed when B-doped Si0.5Ge0.5 epilayers are grown onto Si1-yGey strain relaxed buffers (SRB) with different Ge contents (Fig. 1c). A change in virtual substrate modifies the magnitude and type of strain in the epilayer. B-incorporation during epitaxial growth is thereby severely impacted. This confirms that the change in adatom incorporation is not linked to the mechanisms of plastic strain-relaxation, but it is determined by the strain status of the growing epilayer.Mechanisms responsible for this behavior are being assessed by ab-initio calculations using Density Functional Theory (DFT). A 128 atoms surface slab of Si0.5Ge0.5 is modelled using Perdew–Burke-Ernzerhof (PBE) exchange-correlation functional. The surface presents a 2x1 reconstruction with all the dangling bonds passivated by H atoms (Fig. 1d). Four strain conditions are applied to the slab, ranging from a fully compressively strained to a fully relaxed Si0.5Ge0.5:B epilayer on unstrained Si. The adsorption and incorporation steps corresponding to B surface doping from a B2H6 molecule are subsequently simulated. The precursor interaction with the surface, its chemisorption and decomposition are found not to be affected by the magnitude of strain. However, the incorporation probability of a B in the first atomic layer of the Si0.5Ge0.5 surface increases with the applied stress, corroborating the observed experimental results.In summary, we report a modified incorporation of adatoms during Si1-xGex epitaxy when the biaxial compressive strain is relaxed. In particular, the B incorporation is reduced, while the Ge concentration is progressively increased. From DFT simulations we get indications that, indeed, a decrease in strain may cause a decrease in the B incorporation probability during the epitaxial deposition.[1] D. Yu et al., Phys. Rev. B, 78 (24), p. 245204, 2008.[2] B. Tillack et al., Appl. Phys. Lett., 67 (8), p. 1143, 1995.[3] R. Loo et al., ECS J. Solid State Sci. Technol. 6 (1), p. 14, 2017.[4] M. Bargallo Gonzalez et al., Mat. Sci. Semicon. Proc. 11 (5), p. 285, 2008.[5] H. Yu, et al., IEEE Electr. Dev . Let. , 36 (6), p. 600, 2015. Figure 1

Tunable optoelectronic properties of two-dimensional PbSe by strain: First-principles study

Based on first-principles calculations, we studied the band gap, work function and effective mass of two dimensional (2D) PbSe by using applied external in-planed strain. Our results show a linearly decrease trend of band gap under both compressive and tensile axial strain. However, the typical character of direct band gap of 2D PbSe has been changed to indirect with a minimum value about 0.3 eV. In contrast, under biaxial compression, the original type of direct band gap is kept. Under biaxial compression strain, we predict that the optical absorption coefficient of 2D PbSe in the ultraviolet region has significant enhancement. Moreover, we found that the work function of 2D PbSe is sensitive and can be tuned between 3.60 eV and 5.31 eV by applying biaxial strain. In addition, we predict that the decrease of the effective mass of electrons or holes along with the compressive strain can promote the carrier mobility in PbSe monolayer. These results imply that 2D PbSe has potential applications in optoelectronic devices.

First-principles investigation on electronic structure, magnetic states and optical properties of Mn-doped SnS2 monolayer via strain engineering

Two-dimensional magnetic materials are high desirable for realizing advanced optoelectronic and spintronic devices. In this paper, we report systematic studies the effects of strain on the electronic structure, magnetic states and optical properties of Mn-doped SnS2 monolayer (ML) by means of first-principles calculations. Ab-initio molecular dynamics simulations and formation energy reveal that the Mn-doped SnS2 ML is stable at 500 K and can be fabricated under the S-rich condition. The substitution of a Mn for a Sn atom induces 3 μB magnetic moment in nonmagnetic SnS2 ML, which is consistent with the Hund's rule and Aufbau principle. Based on classical Heisenberg model and mean-field approximation the Curie temperature is calculated to be 476.13 K. Due to symmetry reserved crystal structure, the net magnetic moment of Mn-doped SnS2 ML is robust even if considerable strains (−10 to 10%) are applied. The blue-shift and red-shift of the absorption peaks are observed in the optical spectrum by biaxial compressive and tensile strains. The biaxial strain effectively improves the optical properties of Mn-doped SnS2 ML, particularly in the visible light region. This study provide useful guidance for practical application in magnetic and optoelectronic devices.

Effects of artificial stacking configurations and biaxial strain on the structural, electronic and transport properties of bilayer GaSe- A first principle study

The Gallium Selenide (GaSe) is one of the emerging members in the two-dimensional (2D) semiconductor family and being actively explored for electronic and optoelectronic applications. However, to this date, systematic theoretical investigations are yet to be observed on simultaneous effects of interlayer stacking arrangements and applied biaxial strains in few-layer GaSe for realizing tunable electronic and transport properties. In this work, the bilayer (2L) GaSe is considered in its natural as well as three energetically stable artificial interlayer stacking arrangements and is subjected to biaxial compressive and tensile strains. The subsequent modulations in the structural, electronic, and transport properties are systematically analysed from the in-plane, and inter-plane electronic redistributions using density functional theory (DFT) based first principle calculations. In this context, emphasis has been given to the energy bandgaps and effective masses of 2L-GaSe. The results indicate that strain and artificial stacking together can lead to significant changes in the in-plane and interlayer electronic distributions and, thereby, the electronic band structures and transmission spectrum of 2L-GaSe. The applied biaxial compressive strain appears highly effective for linearly tuning the bandgap and effective masses with noticeably different values for different stacking arrangements. Interestingly, under applied biaxial tensile strain, highly nonlinear variations in energy bandgap and effective mass are observed along with characteristic shifts in the position of conduction band minima (CBM) and Valence Band Maxima (VBM) for different stacking orientations. The key findings of this work offer detailed theoretical and design-level insight for strain/stacking co-optimization strategy in 2L-GaSe for realizing high-performance electronic and optoelectronic devices.

Tunable electronic and magnetic properties of single layer CdS via Li substitutional doping: A first-principle study

A first-principles theoretical study of the enhanced electronic and magnetic properties of a single-layer CdS (denoted as SL-CdS) was conducted via Li substitutional doping at possible sites. Previous work shows that SL-CdS is a non-magnetic and direct bandgap semiconductor. Our work demonstrated that electronic bandgap tuned to smaller and larger values, e.g., the calculated bandgap (pseudo bandgap) for LiCd (Lih) are 1.80 eV and 1.62 eV, respectively. Local magnetic moment induced via Li atomic doping at possible dopants sites except for Lih. The LiCd gives a maximum magnetic moment of 0.98 μB and shows the half-metallic character with a small dispersion for the spin-down channel at the Γ point. Among all the possible sites, the LiCd in SL-CdS is magnetic and being most favorable thermodynamically under both S-rich and Cd-rich conditions. The LiCd in SL-CdS indicates spin polarization with increased bandgap for spin-up and spin-down channels. In contrast, the LiS induces a magnetic moment of 0.86 μB with a reduced bandgap of 0.60 eV for both the spin-up and spin-down channels. The partial magnetic moment is due to the fact small concentration of the dopant. Interestingly, Lih in SL-CdS shows non-magnetic semiconducting nature with decreased bandgap. For further investigation, we considered the most favorable Cd-Site. For room-temperature ferromagnetism, we did ferromagnetic and anti-ferromagnetic calculations. We considered interactions between two Li atoms substituted at far positions (1, 2) and near positions (1, 3) in SL-CdS. It was found that 2LiCd in SL-CdS at near positions (1, 3) has FM order with Curie temperature (Tc) of 339.95 K at − 5% compressive biaxial strain. The effect of Li doping on electronic and magnetic properties of SL-CdS can help to utilize SL-CdS materials in electronics and spintronics devices applications.

First-principles study on the strain-mediated g-C3N4/blue phosphorene heterostructures for promising photocatalytic performance

Well-designed two-dimensional heterogeneous photocatalysts have attracted significant attention due to the enhancement in visible-light absorption and effective charge separation. In this paper, the electronic and optical properties of g-C3N4/BlueP (blue phosphorene) heterojunction under varying strains were investigated systematically by first-principles calculations. The results showed that the type transformation of g-C3N4/BlueP heterojunction can be achieved by suitable biaxial strain. The CBM was found to be composed of g-C3N4 as electron acceptor, while the VBM was contributed by BlueP as electron donor which solved the problem of high electron–hole recombination of type-I heterostructures. The band gap and band edge alignment under −6% to −8% compressive biaxial strain could satisfy the REDOX (reduction-oxidation) potential of photolysis water. A wide optical response range and good absorbance were also observed for the heterostructure under strain, which improved the solar utilization rate compared with individual g-C3N4 and BlueP.

Thermal properties of monolayer MoS2 and WS2/MoS2 heterojunction under three strain states

In this paper, the thermal properties of single-layer MoS2 and WS2/MoS2 heterostructure under three strain states are systematically studied. The first-principles calculation method based on density functional theory is used to obtain the phonon dispersion curves and related thermal parameters of crystals. The results show that Van der Waals cleaves phonons only in the vertical direction. The thermal properties of the two crystals are changed by the application of biaxial compressive strain. Taking the monolayer MoS2 as an example, the curves of the heat capacity and the Debye characteristic temperature of the monolayer MoS2 under the three strain states of biaxial tension, biaxial compression and biaxial tension and compression are comprehensively analyzed. It is found that the thermal properties of the crystal will change differently in different strain states. And at high temperatures, the heat capacity is more sensitive to the effect of strain.

On the optical properties and dynamical and mechanical stability of 1T PdSSe, PdSTe, and PdSeTe monolayers under biaxial strain

In this work, the effects of compressive and tensile biaxial strain, applied to monolayered 1T Pd Janus PdSSe, PdSTe, and PdSeTe structures are investigated. For tensile strengths larger than 4%, the valence band maxima no longer occur at the high symmetry Γ point; this phenomenon is accompanied by the emergence of a quasi-direct bandgap, where Dirac-like cones develop for large enough strain. A semiconductor-semimetal phase transition takes place for compressive strain strengths of −8%, −4%, and −2% in PdSSe, PdSTe, and PdSeTe respectively. Phonon dispersion calculations show that the Janus structures, subject to tensile strains, are dynamically stable; yet under compressive strains, they are only stable for values not exceeding −6% in PdSSe, −4% in PdSTe, and −2% in PdSeTe. All structures are mechanically stable except for PdSTe under a 14% tensile strain, registering negative in-plane stiffness constants of −9.36 and −7.62 N/m along the x and y directions respectively. Optical absorption/emission within the infrared region is possible when the materials are exclusively subject to tensile strain. Once the Pd Janus structures are synthesized, the results presented here can serve as a guide for the fabrication of optoelectronic devices of optimal performance.

Two-Dimensional Janus FeXY (X, Y = Cl, Br, and I, X ≠ Y) Monolayers: Half-Metallic Ferromagnets with Tunable Magnetic Properties under Strain.

Two-dimensional (2D) ferromagnetic materials with high spin polarization are highly desirable for spintronic devices. 2D Janus materials exhibit novel properties due to their broken symmetry. However, the electronic structure and magnetic properties of 2D Janus magnetic materials with high spin polarization are still unclear. Inspired by the successful synthesis of a ferromagnetic FeCl2 monolayer and 2D Janus MoSSe and WSSe, we systematically study the electronic structure and magnetic properties of Janus FeXY (X, Y = Cl, Br, and I, X ≠ Y) monolayers. Based on the Goodenough-Kanamori-Anderson theory, the ferromagnetism stems from the superexchange interaction mediated by Fe-X/Y-Fe bonds. The band gaps of spin-up channels are large enough (>4 eV) to prevent spin flipping, which is beneficial for spintronic devices. Additionally, the sizable magnetocrystalline anisotropy energy (MAE) indicates that Janus FeXY monolayers are suitable for information storage. More importantly, the half-metallic character is still kept in Janus FeXY monolayers, and their magnetic properties are enhanced by the biaxial compressive strain. The MAE of FeClI and FeBrI increases by 1 order of magnitude, and the Curie temperature of FeXY monolayers enhances by 100%. These results provide an example of the 2D Janus half-metallic materials and enrich the 2D magnetic material library.

Ferroelectricity in strained Hf2CF2 monolayer

Low dimensional ferroelectrics are highly desired for applications and full of exotic physics. Here a functionalized MXene Hf$_2$CF$_2$ monolayer is theoretically studied, which manifests a nonpolar to polar transition upon moderate biaxial compressive strain. Accompanying this structural transition, a metal-semiconductor transition occurs. The in-plane shift of unilateral fluorine layer leads to a polarization pointing out-of-plane. Such ferroelectricity is unconventional, similar to the recently-proposed interlayer-sliding ferroelectricity but not identical. Due to its specific hexapetalous potential energy profile, the possible ferroelectric switching paths and domain walls are nontrivial, which are mediated via the metallic paraelectric state. In this sense, the metallic walls can be manipulated by reshaping the ferroelectric domains.

Strain Effects on the Electronic and Thermoelectric Properties of n(PbTe)-m(Bi2Te3) System Compounds.

Owing to their low lattice thermal conductivity, many compounds of the n(PbTe)-m(BiTe) homologous series have been reported in the literature with thermoelectric (TE) properties that still need improvement. For this purpose, in this work, we have implemented the band engineering approach by applying biaxial tensile and compressive strains using the density functional theory (DFT) on various compounds of this series, namely BiTe, PbBiTe, PbBiTe and PbBiTe. All the fully relaxed BiTe, PbBiTe, PbBiTe and PbBiTe compounds are narrow band-gap semiconductors. When applying strains, a semiconductor-to-metal transition occurs for all the compounds. Within the range of open-gap, the electrical conductivity decreases as the compressive strain increases. We also found that compressive strains cause larger Seebeck coefficients than tensile ones, with the maximum Seebeck coefficient being located at −2%, −6%, −3% and 0% strain for p-type BiTe, PbBiTe, PbBiTe and PbBiTe, respectively. The use of the quantum theory of atoms in molecules (QTAIM) as a complementary tool has shown that the van der Waals interactions located between the structure slabs evolve with strains as well as the topological properties of BiTe and PbBiTe. This study shows that the TE performance of the n(PbTe)-m(BiTe) compounds is modified under strains.

Reduced thermal conductivity of epitaxial GaAsSb on InP due to lattice mismatch induced biaxial strain

High-quality lattice-matched and mismatched strained GaAs1−xSbx (0.37 < x < 0.57) sub-micrometer epilayers are grown on InP by molecular beam epitaxy. Based on a heat conduction model regarding the heat transfer process between the thin GaAsSb films and thick InP substrates, the corresponding thermal conductivity of GaAsSb epilayers was accurately extracted from the power and temperature micro-Raman measurement. Combined with time-domain thermoreflectance measurements, we found that in comparison to the lattice-matched sample with Sb = 47.7%, a significant reduction in thermal conductivity of the lattice-mismatched sample with Sb = 37.9% and Sb = 56.2% is observed. With the help of diffraction reciprocal space maps and temperature-dependent photoluminescence results, the reduction in thermal conductivity is attributed to lattice-mismatch-induced biaxial tensile and compressive strain that can cause the breakage of the cubic crystal symmetry and provoke more defects.

Morphologies of compressed active epithelial monolayers.

Using a three-dimensional active vertex model, we numerically study the shapes of strained unsupported epithelial monolayers subject to active junctional noise due to stochastic binding and unbinding of myosin. We find that while uniaxial, biaxial, and isotropic in-plane compressive strains do lead to the formation of longitudinal, herringbone pattern, and labyrinthine folds, respectively, the villus morphology characteristic of, e.g., the small intestine appears only if junctional tension fluctuations are strong enough to fluidize the tissue. Moreover, the fluidized epithelium features villi even in the absence of compressive strain provided that the apico-basal differential surface tension is large enough. We analyze several details of the different epithelial forms including the role of strain rate and the modulation of tissue thickness across folds. Our results show that even unsupported, non-patterned epithelia can form nontrivial morphologies.

Strain tuning of the Curie temperature and valley polarization in two dimensional ferromagnetic WSe2/CrSnSe3 heterostructure

Magnetic proximity effect can be used to tailor the magnetic ground state and valley polarization in the monolayer of transition metal dichalcogenides. Thus, we explore the effect of biaxial tensile and compressive strain on valley polarization in the WSe2/CrSnSe3 heterostructures with different stacking orders systematically. The indirect band gaps in the two most stable stackings; hollow (0.27 eV) and top (0.33 eV) were further enhanced to 0.35 eV under tensile strain while suppressed to almost 0.13 eV under compressive strain. The heterostructures had a FM ground state with a total magnetic moment per unit cell of 6 μ B in pristine as well as strained structures. In hollow stacking and compressively strained structures, we obtained a perpendicular magnetocrystalline anisotropy, while the top stacking and tensile strain structures had small in-plane anisotropy. An enhancement was found in Curie temperature from 73 K in pristine to 128 K in a 6% tensile strained structure. The valley splittings found in pristine hollow (4 meV) and top (9 meV) stacked heterostructures were further enhanced to 29 meV and 22 meV at 5% compressive strain respectively. This enhancement was attributed to the increased spatial dependence of the charge density along K+ and K− directions of the Brillouin zone, which give rise to the different local dipolar fields at these valleys. Our results suggest that strain could be an effective way to control or tune the valley splitting in WSe2/CrSnSe3 heterostructures.