Increase In Tensile Strain Research Articles

Exploring the impact of strain on the electronic and optical properties of inorganic novel cubic perovskite Sr3PI3

Inorganic perovskite materials have drawn great attention in the realm of solar technology because of their remarkable structural, electronic, and optical properties. Herein, we investigated strain-modulated electronic and optical properties of Sr3PI3, utilizing first-principles density-functional theory (FP-DFT) in detail. The SOC effect has been included in the computation to provide an accurate estimation of the band structure. At its Г(gamma)-point, the planar Sr3PI3 molecule exhibits a direct bandgap of 1.258 eV (PBE). The application of the spin-orbit coupling (SOC) relativistic effect causes the bandgap of Sr3PI3 to decrease to 1.242 eV. Under compressive strain, the bandgap of the structure tends to decrease, whereas, under tensile strain, it tends to increase. Due to its band properties, this material exhibits strong absorption capabilities in the visible area, as evidenced by optical parameters including dielectric function, absorption coefficient, and electron loss function. The increase in compressive or tensile strain also causes a red-shift or blue-shift behavior in the photon energy spectrum of the dielectric function and absorption coefficient. Finally, the photovoltaic (PV) performance of novel Sr3PI3 absorber-based cell structures with SnS2 as an Electron Transport Layer (ETL) was systematically investigated at varying layer thicknesses using the SCAPS-1D simulator. The maximum power conversion efficiency (PCE) of 28.15% with JSC of 34.65 mA cm−2, FF of 87.30%, and VOC of 0.92 V was found for the proposed structure. Therefore, the strain-dependent electronic and optical properties of Sr3PI3 studied here would facilitate its future use in the design of photovoltaic cells and optoelectronics.

Effect of strain on the electronic structure and optical properties of Cr-doped monolayer MoS2.

In this paper, the electronic and optical properties of Cr-doped monolayer MoS2 under uniaxial tensile strain are investigated by first-principle calculations. It is shown that uniaxial tensile strain can significantly change the electronic and optical properties of Cr-doped monolayer MoS2, and the bandgap value of the intrinsic MoS2 system gradually decreases with the increase of tensile strain, while the bandgap value of the Cr-doped MoS2 system is relatively stable. However, when the stretching reaches a certain degree, both the intrinsic and doped systems become metallic. From the analysis of the density of states, it is found that new electronic states and energy levels appear in the intrinsic MoS2 system and all Cr-doped monolayer MoS2 systems with the increase of the tensile strain, but the changes in the density of states diagrams of the Cr-doped monolayer MoS2 system are relatively small, which is mainly attributed to the effect of the Cr-doped atoms. The analysis of optical properties displays that the stretched doped system differs from the intrinsic MoS2 system in terms of dielectric function, absorption and reflection, energy loss function, and refractive index. Our results suggest that uniaxial tensile strain can be used as an effective means to modulate the electronic structure and optical properties of Cr-doped monolayer MoS2. These findings provide a theoretical basis for understanding the optoelectronic properties of MoS2 and its doped systems as well as their applications in optoelectronic devices. Based on the first principle of density functional theory framework and the CASTEP module in Materials Studio software (Perdew et al. in Phys Rev Lett 77(18):3865-3868, 1996). The structure of Cr atom-doped MoS2 systems and MoS2 systems were optimized using the generalized gradient approximation plane-wave pseudopotential method (GGA) and Perdew-Burke-Ernzerhof (PBE) generalized functions under 3%, 6%, and 9% tensile deformation, and the corresponding formation energy, bond length, electronic structure, and optical properties of the models were analyzed. The Grimme (J Comput Chem 27(15):1787-1799, 2006) vdW correction with 400 eV cutoff was used in Perdew-Burke-Ernzerhof (PBE) functional to optimize the geometry until the forces and energy converged to 0.02 eV/Å and 1.0e-5eV/atom, respectively. For each model structure optimization, the K-point grid was assumed to be 4×4×1, using the Monkhorst-Pack special K-point sampling method. After the MoS2 supercell convergence test, the plane-wave truncation energy was chosen to be 400 eV. Following geometric optimization, the iterative accuracy converged to no less than 1.0×10-5 eV/atom for total atomic energy and less than 0.02 eV/Å for all atomic forces. We created a vacuum layer of 18 Å along the Z-axis to prevent the impact of periodic boundary conditions and weak van der Waals forces between layers on the monolayer MoS2. In this paper, a total of 27 atoms were used for the 3×3×1 supercell MoS2 system, which consists of 18 S atoms and 9 Mo atoms.

Mechanical behavior of sustainable engineered cementitious composites with construction waste powder as binder and sand replacement

The utilization of recycled powder (RP) obtained from construction waste in the development of sustainable engineered cementitious composites (ECC) has significantly improved their sustainability. This study investigated the mechanical strength of sustainable ECC prepared with three different RPs namely recycled brick powder, recycled paste powder, and recycled concrete powder. The results demonstrated that substituting high portion of cement with RP resulted in a loose microstructure in ECC, but the substitution of silica sand with RP led to a denser microstructure in ECC. Replacing 50% cement and 100% fly ash with RP derived from concrete waste led to a marginal decrease of 39.4% and 20.2% in the compressive strength of ECC, but replacing silica sand with such RP slightly increased the strength of ECC. Besides, recycled brick powder blended ECC shows better strength than the recycled concrete powder blended ECC. Under uniaxial tensile load, the incorporation of RP improved the ductility of ECC, regardless of whether it replaced silica sand or binding materials, while simultaneously reducing the ultimate tensile strength of ECC to varying degrees. Specifically, substituting RP from concrete waste for 50% cement, 100% fly ash, and 100% silica sand caused 145.5%, 55.4%, and 43.6% increase in the ultimate tensile strain of blended ECC, respectively. Particularly, the combine substitution of binder and silica sand with RP is feasible in ECC. More sustainable ECC with good mechanical strength and ductility can be achieved by optimizing the content of RP as binder and sand replacement, and the ECC blended with RP shows good environmental and economic benefits.

Processes of mechanical degradation of high-density polyethylene + nanoclay nanocomposites after exposure to an electric field

The paper investigates the mechanical properties of nanocomposites based on high-density polyethylene (PE) with nanoclay (NC) additives after exposure to an electric field and compares them with changes occurring in the structure. It has been shown that C = C groups are formed as a result of the rupture of macromolecules under the action of an electric field. Depending on the exposure time, the mechanical strength of the nanocomposite and PE decreases, while the tensile strain (ε) and optical density (D) increase. The rate of strength reduction in nanocomposite is lower than that of PE.

On the experimental characterization and response modelling of particulate composite: Application to flaky aluminium-epoxy composite

The epoxy-based composites are most commonly used now in the automobile and aerospace industries due to their low weight and high strength. The quasi-brittle nature of epoxy resin, which is not desirable in several applications, can be overcome by adding flaky aluminium additive resulting in a particulate composite. A small volume fraction of flaky aluminium influences the mechanics of epoxy resin in a significant manner (increase in tensile strength and strain at failure by 56 % and 200 %, respectively, comparing with neat epoxy) resulting in a ductile-type failure. The nonlinear, rate-independent (at low loading rate), rate-dependent (at higher loading rate), and inelastic (viscous effect) response, coupled with an internal damage, observed in epoxy-based flaky-aluminium composite is not fully understood due to the complex nature of resulting material. Much of the previous literature focused on modelling, either the rate-dependency or damage at low loading rate, but not capturing everything concurrently.The novelty of present work is a broad framework development for experimental characterization and calibration of particulate composite (flaky aluminium additives in the epoxy matrix) performing uniaxial tension, cyclic loading–unloading, and creep experiments at different displacement loading rates, and subsequent modelling of the constitutive response in a thermodynamically consistent manner. The macro-scale properties of the newly proposed particulate composite are estimated by mean-field homogenization and compared with the corresponding experimental values. The elasto-plastic-damage and visco-plastic-damage material constants are successfully obtained by a novel optimization approach coupling Levenberg–Marquardt algorithm with stress update algorithms. The practical applicability of the obtained material constants is finally demonstrated solving several boundary value problems employing Lemaitre’s ductile damage model.

Plastic deformation of Ag/MgO interface system during tensile fracture: A molecular dynamics study

Fracture experiments on layered metal-ceramic composites show that the plastic dissipation in the metal near the crack tip accounts for most of the macroscopic fracture toughness. In this work we studied the microscopic plastic deformation mechanisms of Ag/MgO interface systems using molecular dynamics (MD) method. As tensile strain increases, lattice dislocations nucleate at interface misfit dislocations and propagate in metal layer. The formation of immobile Hirth dislocations in Ag causes hardening. As the metal layer increases, the yield strength decreases and the hardening range is shortened. Large interface area increases the degree of inhomogeneity of dislocation motion and interface fracture behavior, leading to decreased interface yield strength.

Strain-driven anomalous elastic properties of GeSn thin films

Elastic strain engineering in the GeSn bandgap structure is an attractive area for designing novel material properties. The linear interpolation of the elastic constants of Ge and Sn is commonly used to estimate their respective values for Ge1−xSnx alloys. This work reveals that Young's modulus of Ge1−xSnx epitaxial layers has a non-monotonic dependence on Sn composition. It is shown that the decrease in the elastic modulus correlates with the increase in Sn content in pseudomorphically grown Ge1−xSnx-epilayers with Sn concentration in the range of 1–5 at. % and subcritical thicknesses. An anomalous increase in the elastic modulus is observed with the further increase in Sn content (12 at. %), which is also accompanied by an increase in in-plane tensile strain. Phase separation and a decrease in the elastic modulus are observed for Ge1−xSnx-epilayers grown above the critical thickness with Sn concentration ≥ 12 at. %. A correlation between the experimental elastic moduli and calculated elastic energies explains the complexity of strain-driven anomalous elastic properties of Ge1−xSnx-epilayers. The observed anomalous behavior of the Young's modulus for these GeSn epitaxial layers appears to be related to their recently predicted and observed short-range atomic order.

Two-Dimensional VSi2X2N2 (X = P, As, Sb, Bi) Janus Monolayers: Spin-Polarized Electronic Structure and Perpendicular Magnetic Anisotropy

The discovery of ferromagnetic two-dimensional (2D) materials provides reference value for the exploration of low-dimensional magnetism and new spintronic devices. The VSi2N4 monolayer is ferromagnetic with half-metallic characteristics, which is a new 2D material in the field of spintronics. Here, the electronic structure and magnetic anisotropy of two-dimensional VSi2X2N2 (X = P, As, Sb, Bi) Janus monolayers are studied systematically via first-principles calculations. The results show that VSi2P2N2, VSi2As2N2 and VSi2Bi2N2 are magnetic, but VSi2Sb2N2 is nonmagnetic. At X = P, As and Bi, VSi2X2N2 Janus monolayers are metallic and ferromagnetic. VSi2P2N2 and VSi2As2N2 show the in-plane magnetic anisotropy, while VSi2Bi2N2 shows the perpendicular magnetic anisotropy (PMA). As the tensile strain increases, the spin-down energy band of the VSi2P2N2 monolayer gradually moves up and the spin-up channel moves down. At ε = +12%, the spin-down band shifts above the Fermi level, showing the half-metallic characteristic with a band gap of 0.775 eV calculated using the Perdew–Burke–Ernzerhof (PBE) exchange–correlation function. The magnetic moment of VSi2Sb2N2 is induced at an electric field of −0.4 V/Å and +0.2 V/Å, where PMA appears. These data provide basic theoretical guidance for the development of low-dimensional spintronic devices.

The effect of uniaxial strain on electronic and optical properties of halide double perovskites Cs2AgXCl6 (X=Sb, Bi): a DFT approach

The electronic and optical properties for low toxicity, highly stable lead-free halide double perovskites Cs2AgXCl6 (X = Sb, Bi) under the uniaxial strain from −4 to 4 % were investigated used by density functional theory. It was found that Cs2AgXCl6 perovskites maintained their indirect band gap under uniaxial strains and the bandgap energies decreased (increased) as the compressive (tensile) strain increased. Both lattice parameters and bond lengths increased (decreased) monotonically with increasing tensile (compressive) strain. The effective mass of electrons (holes) decreased (increased) with the strain from −4 to 4 %. Thus, tensile (compressive) strain was more suited to the transport of electrons (holes). The top of the valence band of Cs2AgXCl6 was close to the Fermi energy level and dominated by Cl-3p and Ag-4d orbitals, while the conduction band was dominated by Sb-5p (Bi-6p) and Cl-3p orbitals. The imaginary part ε2(ω) peak intensity decreased with the strain from −4 to 4 %. The edges of optical absorption spectra showed blueshift (redshift) under the tensile (compressive). The reflectivity at 0 eV and reflectivity peak in the visible light range decreased (increased) with the increase of tensile (compressive) strain. Therefore, this study provided a theoretical insight into the photoelectronic properties of Cs2AgXCl6 (X = Sb, Bi) under the uniaxial strain.

High aspect ratio diamond nanosecond laser machining

Laser processing of diamond has become an important technique for fabricating next generation microelectronic and quantum devices. However, the realization of low taper, high aspect ratio structures in diamond remains a challenge. We demonstrate the effects of pulse energy, pulse number and irradiation profile on the achievable aspect ratio with 532 nm nanosecond laser machining. Strong and gentle ablation regimes were observed using percussion hole drilling of type Ib HPHT diamond. Under percussion hole drilling a maximum aspect ratio of 22:1 was achieved with 10,000 pulses. To reach aspect ratios on average 40:1 and up to 66:1, rotary assisted drilling was employed using > 2 M pulse accumulations. We additionally demonstrate methods of obtaining 0.1° taper angles via ramped pulse energy machining in 10:1 aspect ratio tubes. Finally, effects of laser induced damage are studied using confocal Raman spectroscopy with observation of up to 36% increase in tensile strain following strong laser irradiation. However, we report that upon application of 600 °C heat treatment, induced strain is reduced by up to ~ 50% with considerable homogenization of observed strain.

Direct atomic layer deposition of ultra-thin Al2O3 and HfO2 films on gold-supported monolayer MoS2

In this paper, the atomic layer deposition (ALD) of ultra-thin films (<4 nm) of Al2O3 and HfO2 on gold-supported monolayer (1L) MoS2 is investigated, providing an insight on the mechanisms ruling the nucleation in the early stages of the ALD process. A preliminary multiscale characterization of large area 1L-MoS2 exfoliated on sputter-grown Au/Ni films demonstrated: (i) a tensile strain (from 0.1 to 0.3%) and p-type doping (from 1 × 1012 to 4 × 1012 cm−2) distribution at micro-scale; (ii) an almost conformal MoS2 membrane to the Au grains topography, with some locally detached regions, indicating the occurrence of strain variations at the nanoscale; (iii) atomic scale variability (from ∼ 4.0 to ∼ 4.5 Å) in the Mo-Au atomic distances was detected, depending on the local configuration of Au nanograins. Ab initio DFT calculations of a free-standing MoS2 layer and a simplified MoS2/Au(111) interface model showed a significant influence of the Au substrate on the MoS2 energy band structure, whereas small differences were accounted for the adsorption of H2O, TMA (co-reactant, and Al-precursor, respectively) molecules, and a slight improved adsorption was predicted for TDMAHf (Hf-precursor). This suggests a crucial role of nanoscale morphological effects, such as the experimentally observed local curvature and strain of the MoS2 membrane, in the enhanced physisorption of the precursors. Afterwards the nucleation and growth of Al2O3 an HfO2 films onto 1L-MoS2/Au was investigated in detail, by monitoring the surface coverage as a function of the number (N) of ALD cycles, with N from 10 to 120. At low N values, a slower growth rate of the initially formed nuclei was observed for HfO2, probably due to the bulky nature of the TDMAHf precursor as compared to TMA. On the other hand, the formation of continuous films was obtained in both cases for N > 80 ALD cycles, corresponding to ∼ 3.6 nm Al2O3 and ∼ 3.1 nm HfO2. Current mapping on these ultra-thin films by conductive-AFM showed, for the same applied bias, a uniform insulating behavior of Al2O3 and the occurrence of few localized breakdown spots in the case of HfO2, associated to a less compact films regions. Finally, an increase of the 1L-MoS2 tensile strain was observed by Raman mapping after encapsulation with both high-κ films, accompanied by a reduction in the PL intensity, explained by the effects of strain and the higher effective dielectric constant of the surrounding environment.

Sub-micro Organosolv lignin as bio-based epoxy polymer component: A sustainable curing agent and additive.

Sub-micro organosolv lignin (OBs) isolated from beechwood biomass, comprising of sub-micro sized particles (570 nm), with low molecular weight (Mw) and dispersity (Ð), and relatively high total phenolic -OH content, was successfully utilized for the production of bio-based epoxy polymer composites. OBs lignin was incorporated in the glassy epoxy system based on diglycidyl ether of bisphenol A (DGEBA) and aliphatic polyoxypropylene α,ω-diamine (Jeffamine D-230), being utilized both as curing agent replacing partially D-230 as well as an additive, substituting part of both petroleum derived components. Up to 12 wt.% replacement of D-230 by OBs lignin was achieved, while a total of ~17 wt.% of OBs effectively replaced the conventional epoxy polymer. The incorporation of OBs lignin in the polymeric matrix was achieved without the use of any solvent or previous functionalization. Enhanced properties were obtained, with substantial increase of tensile strength, strain, and stiffness, Tg, antioxidant activity and resistance to solvents.

Experimental Tests on Lightweight Cement Mortar and Concrete with Recycled Plastic Wastes

The management of plastic waste has become a fundamental issue in recent decades and several studies have focused on finding proper solutions to recycle and reuse these secondary raw materials in different sectors. Using plastic waste in the building sector allows for long-term application and reduces the number of times the recycling process is needed. This research focuses on experimenting with two building products, namely lightweight screed and concrete, with the addition of plastic waste in the form of irregular granules. The screed was produced by adding plastic granules of different sizes, while the concrete was produced by replacing different percentages of the coarse and fine aggregates with plastic granules and pulverized plastic. The screed has been tested under compressive and three-point bending tests, while the concrete has only been tested under compressive tests. The results have shown that the addition of plastic waste in both products led to the desired weight reduction. On one hand, plastic waste have provided a decrease in both tensile (−16%) and compressive (−25%) strengths of the screed with an increase of ultimate tensile strain (+60%). On the other hand, the only acceptable concrete mixture resulted to be the one with 25% of aggregates substitution, which exhibited a decrease in compressive strength (−40%) and an increase of ultimate strain (+38%), whereas samples with higher percentages of plastic aggregates have been not considered to be suitable as building materials.

Effect of strain on the spin-polarization, mechanical and magnetic properties of Co[formula omitted]TiGe heusler alloy: A First Principle Study

In our work, we studied the effect of isotropic strain from −6% to 8% (compressive to tensile) on the Band gap, Elastic, Spin-polarization and Magnetic properties of Co2TiGe heusler alloy. We found that the half-metallicity (100% Polarization) is maintained under uniform strain from −2% to 4% but for the strain −4% to −6% the Spin-polarization drops quickly from 94% to 5.363%. From the study of electronic band structure we found that the energy band gap decreases with the increase of tensile strain and increase with the increase of compressive strain. For strain free compound the calculated magnetic moment of the material is 2.00 μB. We have found that under −4% to 8% uniform strain the total magnetic moment of the compound remains constant. But for strain −6% it decreases to 1.91 μB. We have calculated the mechanical properties of the material under different uniform strain. So, from the computed values we found the Bulk modulus, Young modulus, Shear modulus, Pugh’s ratio and Poisson ratio decreases with the tensile strain and increases with the compressive strain. With the increase of tensile strain (up to 8%) brittle nature of the material increases but with the increase of compressive strain (up to −6%) ductile of the material increases.

Trace B doping Fe50Mn30Co10Cr10 high entropy alloy: Mechanical response and multi-microstructure evolution under TWIP and TRIP effects

Face-centered cubic (FCC) high entropy alloy has attracted extensive attention because of its excellent mechanical response, while its poor strength limits its application in practical engineering. In this work, the Fe50Mn30Co10Cr10 alloy doped with 30 ppm B atoms and proper thermo-mechanical processing (cold rolling and annealing) has achieved excellent synthetic strength and plasticity. It was found that the grain refinement strengthening introduced by B doping and the strong dislocation strengthening of inhomogeneity structure produced by the annealing treatment contribute to enhanced yield strength. The multiple structure evolution during the deformation process contribute to the excellent ductility. With the increase of tensile strain, dislocations, FCC deformation twins, strain-induced close packed hexagonal structure (HCP) phase, HCP deformation twins and reverse FCC phase appear successively, implying an interesting mechanism that the FCC and HCP phases bear plastic deformation by twinning-induced plasticity (TWIP) and transformation-induced plasticity (TRIP) effects successively. FCC twinning, FCC→HCP phase transformation, HCP twinning, HCP→FCC reverse transformation occurred successively, which simultaneously leads to the high plasticity of the alloy. Interstitial atoms doping combined with the TWIP and TRIP effects can lead to the overall improvement of the yield strength and plasticity of the alloy, which provides a feasible way for the subsequent design of high-strength plastic alloys.

Influence of Cu Concentration on Structure, Mechanical Properties and Corrosion Resistance of Ti–Ni–Cu Shape Memory Alloy Ribbons

The paper presents the results of investigating the influence of Cu concentration on structure, mechanical properties and corrosion resistance of Ti50Ni50−xCux (x = 0, 5, 10, 15 and 20) alloy ribbons. The ribbons with a thickness of about 25 µm were prepared by using melt-spinning method with a tangential velocity of copper wheel of 40 m.s−1. All the ribbons reveal a single crystalline phase of (Ni,Cu)Ti with the martensitic-B19 structure at room temperature when Cu substitutes for Ni. The structural transformations temperature, tensile strain and elastic modulus increase with increasing Cu concentration whereas the hardness and dislocation density trendly decrease. The corrosion potential Ecorr in 3.5% NaCl aqueous solution increases from −0.67 V (for x = 0) to −0.46 V (for x = 20) indicating the better resistance against electrochemical corrosion by Cu addition.

Exploring the basal/prismatic slip transfer at grain boundaries in magnesium: A molecular dynamic simulation

This study utilized the molecular dynamics method to investigate the slip transfer behaviors of edge and screw dislocations in magnesium at basal/prismatic grain boundaries (BPGBs), where the Burgers vectors and the slip planes are parallel across the GBs. The results demonstrate that when shear stress increases, the initially introduced basal dislocation migrates toward, interacts with a BPGB, and is transmuted to a prismatic dislocation and vice versa. The critical resolved shear stress for the basal screw dislocation transmutation is considerably higher than edge dislocation. The slip transfer from basal to prismatic slip has a higher resistance than the slip transfer from prismatic to basal slip. The influence of normal strain perpendicular to the slip plane and temperature was also analyzed to better understand the process of the interactions. Moreover, as the tensile strain increases, the basal to prismatic slip transfer is more easily facilitated.

Integration of polycrystalline diamond heat spreader with AlGaN/GaN HEMTs using a dry/wet combined etching process

A 1.5-μm polycrystalline diamond was deposited on the AlGaN/GaN heterojunction on SiC substrate with a 20-nm SiN dielectric layer. A (5.8 ± 0.1)% increase in 2DEG density after the diamond growth due to the increase in tensile strain of GaN layer was confirmed by micro-Raman measurements. Top-side integration of polycrystalline diamond heat spreader with AlGaN/GaN high electron mobility transistors was demonstrated. Using a dry/wet combined etching process for the removal of the diamond and SiN interlayer, the integration fabrication of diamond heat spreader and GaN HEMTs with low surface damage was achieved. After the diamond growth, Off-state drain current shows no degradation. Besides, both the drain current and peak transconductance of the GaN HEMTs were enhanced. Temperature reduction of 25 °C at power density of 20 W/mm was achieved by electro-thermal simulation using the thermal properties determined by TDTR measurements.

The electronic and optical properties of multi-layer Bi2O2X (X = S, Se, Te) by first-principles calculations

Two-dimensional (2D) Bi2O2X (X = S, Se, Te) have been reported to be promising optoelectronic materials, which have attracted immense attention from researchers. Adjustable optoelectronic materials are very important for the design and application of the device, but how to design its electronic and optical properties is rarely studied. In this research, we have systematically investigated the electronic and optical properties of 2D Bi2O2X (X = S, Se, Te), especially the response based on the number of layers and the strength of strain. We have found the lattice constants and the band gaps of the H-Bi2O2X and Z-Bi2O2X decrease as the number of layers increases, and finally approach the values of the bulk phase. Moreover, the adjustment of the number of layers can change the range of H-Bi2O2S band gap very much, and can even be adjusted from blue light energy to infrared light energy. As the layer numbers increase, the peaks of the imaginary part of the dielectric function and the absorption spectrum of H-Bi2O2S shift to low-energy region (redshift). Furthermore, the band gaps of H-Bi2O2X (X = S, Se, Te), Z-Bi2O2S, and Z-Bi2O2Se increase first and decrease with the increasing compress strain, and that decrease linearly with the increasing tensile strain. Surprisingly, with the increase of tensile strain, the band gap of Z-Bi2O2Te increases first and then decreases instead of the linear decrease like other materials, which may be due to the heavier Te atoms. Our HSE06 calculation results show that the Bi2O2X is a promising tunable photodetector with a broadband photoresponse in the visible light range.

A Proof-of-Concept Study of Auxetic Composite Foams with Negative Poisson’s Ratio for Enhanced Strain-Stable Performance of Electromagnetic Shielding

Stretching of conductive polymer composite (CPC) foams always results in a severe reduction in electromagnetic interference shielding effectiveness (EMI SE) mainly due to the destruction of conductive networks and the decrement of sample thickness. Therefore, it is desirable to develop a novel strategy for preparing CPC foams with strain-stable EMI SE under moderate stretching. Herein, a strategy of constructing an auxetic structure to stabilize the EMI SE of CPC foams during stretching is proposed for the first time. Lightweight auxetic polyurethane/carbon nanotube (APU/CNT) composite foams were prepared by a solution dip-coating approach and triaxial volumetric compression. Compared with nonauxetic PU/CNT foam, the APU/CNT foam with similar filler loading and density of around 0.035 g/cm3 showed more stable SE values with the increase of tensile strain (especially within the first 20% strain, the SE/SE0 reduction of the APU/CNT foam is less than ∼5%), exhibiting enhanced strain-stable EMI-shielding behavior in the stretching process. The underlying reason is that the presence of auxetic structure with a negative Poisson’s ratio could not only slightly increase the thickness of the foam but also avoid the serious destruction of the conductive networks under stretching, which is beneficial to attenuate EM waves more stably. Moreover, the outstanding and more stable Joule-heating performance could also be observed in the stretched APU/CNT foam. This work reveals the potential of auxetic structures to solve the challenging problem of how to stabilize the EMI-shielding (or Joule-heating) performance of CPC foams during moderate stretching.