Increase In Tensile Strain Research Articles

First-principles insights into the spin-valley physics of strained transition metal dichalcogenides monolayers

Transition metal dichalcogenides (TMDCs) are ideal candidates to explore the manifestation of spin-valley physics under external stimuli. In this study, we investigate the influence of strain on the spin and orbital angular momenta, effective g-factors, and Berry curvatures of several monolayer TMDCs (Mo and W based) using a full ab initio approach. At the K-valleys, we find a surprising decrease of the conduction band spin expectation value for compressive strain, consequently increasing the dipole strength of the dark exciton by more than one order of magnitude (for strain variation). We also predict the behavior of direct excitons g-factors under strain: tensile (compressive) strain increases (decreases) the absolute value of g-factors. Strain variations of ∼1% modify the bright (A and B) excitons g-factors by ∼0.3 (0.2) for W (Mo) based compounds and the dark exciton g-factors by ∼0.5 (0.3) for W (Mo) compounds. Our predictions could be directly visualized in magneto-optical experiments in strained samples at low temperature. Additionally, our calculations strongly suggest that strain effects are one of the possible causes of g-factor fluctuations observed experimentally. By comparing the different TMDC compounds, we reveal the role of spin–orbit coupling (SOC): the stronger the SOC, the more sensitive are the spin-valley features under applied strain. Consequently, monolayer WSe2 is a formidable candidate to explore the role of strain on the spin-valley physics. We complete our analysis by considering the side valleys, Γ and Q points, and by investigating the influence of strain in the Berry curvature. In the broader context of valley- and strain-tronics, our study provides fundamental microscopic insights into the role of strain in the spin-valley physics of TMDCs, which are relevant to interpret experimental data in monolayer TMDCs as well as TMDC-based van der Waals heterostructures.

Strain-tunable pure H− conduction in one-atom-thick hexagonal boron nitride for high-energy–density fuel cells

After proton conductor, hydride (H−) ion conductor with advantages of suitable-ionic-size fast conduction and strong reducing ability is exceptionally promising for high-energy–density fuel cells, but it is hindered by a very limited number of materials in oxyhydrides, metal hydrides and titanium-nitride thick membranes. So far, pure H– conduction is not demonstrated in two-dimensional (2D) materials. Here, we demonstrated a strain-tunable pure H− conduction in one-atom-thick hexagonal boron nitride (h-BN), being a new-type H− solid electrolyte of high-energy–density fuel cells. We studied adsorption behavior and migration process of H− ion onh-BN monolayer under different strains by using systematic first-principles calculations. It is found that structure ofh-BN primitive unit cell can tolerate compressive strain as big as −6 %. According to Bader charge analysis, H got 0.3eto be H− ion, and H got more charge as the tensile strain increases, which was also proved by electron-localization-function maps. H− ion has the lowest migration energy barrier of 0.730 eV onh-BN monolayer surface without external strain. Overall, the results have demonstrated a large-range strain-tunable fast pure H− conduction in 2D h-BN, and a promise of new-type ultrathin flexible solid electrolytes for next-generation fuel cells with high energy density.

Investigation into Thermomechanical Response of Polymer Composite Materials Produced through Additive Manufacturing Technologies.

This paper presents the static mechanical behavior and the dynamic thermomechanical properties of four market-available reinforced and non-reinforced thermoplastics and photopolymer materials used as precursors in different additive manufacturing technologies. This article proposes a characterization approach to further address development of aeronautic secondary structures via 3D-printed composite materials replacing conventional manufactured carbon fiber reinforced polymer (CFRP) composites. Different 3D printing materials, technologies, printing directions, and parameters were investigated. Experimental results showed that carbon-reinforced ONYX_R material exhibits a transition point at 114 °C, a 600 MPa tensile strength, and an average tensile strain of 2.5%, comparable with conventional CFRP composites manufactured via autoclave, making it a suitable candidate for replacing CFRP composites, in the aim of taking advantage of 3D printing technologies. ONYX material exhibits higher stiffness than Acrylonitrile-Butadiene-Styrene Copolymer (ABS), or conventional Nylon 6/6 polyamide, the flexural modulus being 2.5 GPa; nevertheless, the 27 °C determined transition temperature limits its stability at higher temperature. Daylight High Tensile (further called HTS) resin exhibits a tensile strength and strain increase when shifting the printing direction from transversal to longitudinal, while no effect was observed in HighTemp DL400 resin (further called HTP).

Hybrid material extrusion 3D printing to strengthen interlayer adhesion through hot rolling

Amongst the different categories of additive manufacturing technologies, Fused Deposition Modeling (FDM) has become the most widely adopted owing to its accessibility, low complexity, and high flexibility. Although notable advancements in FDM have been achieved, weak mechanical properties remain a barrier to produce functional components. This limitation is a result of weak interlayer bonding inherent to the layer-by-layer fabrication since the lower layers rapidly cool below glass transition temperature before the next one is deposited. This work presents the installation of a heated roller to compress each layer homogeneously onto the previous one after it has been printed to increase interlayer adhesion. Thermo-mechanical methods are proposed since pressure forces can be used to increase filament surface contact, and heat can be used to enable longer diffusion and neck growth. In this work, the effects of roller pressure, speed, and temperature on bonding strength are analysed through tensile testing, three-point bending, and differential scanning calorimetry. In summary, tensile testing shows a maximum ultimate tensile stress increase of 38.8%, a maximum tensile modulus increase of 19.4%, and a maximum tensile strain increase of 359.6%. Flexural analysis shows a maximum increase in ultimate flexural stress of 13.5%, a maximum increase in flexural modulus of 20.76%, and a maximum increase in flexural strain of 11.9%. Differential scanning calorimetry shows an increase in crystallinity of tested samples from 2.7% to 8.6% Computer tomography scanning indicates a large reduction in porosity and improvement in geometric accuracy. Therefore, this work proposes an inexpensive solution that targets the process of interlayer bond formation to increase the mechanical properties of FDM 3D printed components.

Stability, electronic, and mechanical properties of Si/Ge substitutionally doped T2CO2 (T = Zr and Hf)

The stabilities, electronic properties, and mechanical properties of Si/Ge substitutionally doped T2CO2 (T = Zr and Hf) have been investigated by a first-principles method. The mechanical stability of these systems was verified according to the Born criteria of 2D hexagonal crystals. Thermal stability of Si/Ge substitutionally doped 2 × 2 × 1 T2CO2 (T = Zr and Hf) at room temperature was assured using AIMD simulations. The substitutional doping of Si/Ge elements brings about the band gap narrowing in T2CO2. The most obvious ones are the Si/Ge substitutionally doped 2 × 2 × 1 T2CO2 (T = Zr and Hf). The GGA band gaps for Si-doped Zr2CO2, Ge-doped Zr2CO2, Si-doped Hf2CO2, and Ge-doped Hf2CO2 are direct with the gap value being only 0.026 eV, 0.040 eV, 0.008 eV, and 0.059 eV, respectively. The band gap narrowing is mainly caused by the strong covalent T-Si/Ge bond. Strains can inevitably emerge due to the existence of substrates when using layer materials. For any one of Si/Ge substitutionally doped 2 × 2 × 1 T2CO2, the electronic band gap increases as the tensile strain increases. Hence, it is possible to modulate the electronic properties of T2CO2 (T = Zr and Hf) by Si/Ge substitutional doping and applying further strain. Not so good, the doping elements Si and Ge both reduce the mechanical properties of 2 × 2 × 1 T2CO2 (T = Zr and Hf) to some extent.

Tension-induced phase transformation and anomalous Poisson effect in violet phosphorene

Two-dimensional violet phosphorene (VP) nanosheets are promising semiconductor materials with unique cross structures distinct from those of their allotropes such as black phosphorene and blue phosphorene, but their mechanical behaviors remain almost unexplored. By using the first-principles calculations, in this paper we investigate the mechanical behaviors of monolayer, bilayer, and bulk VP under uniaxial tension. A phase transformation from the open-pore phase to closed-pore phase is observed in VP structures when under a specific tensile strain. It is revealed that the phase transformation is attributed to the competition between the rotation and elongation of sub-nano rods in VP structures during the loading process. Due to the phase transformation, the in-plane Poisson's ratio of monolayer VP can become greater than 1.2, while the bulk VP possesses a negative out-of-plane Poisson's ratio with a magnitude up to -0.3 at a certain strain. These results indicate that Poisson effects in VP are superior to those in any other existing two-dimensional materials. In addition, based on the tensor analysis of elastic constants, a strong mechanical anisotropy is observed in VP structures both before and after the phase transformation. Besides the mechanical properties, the band gap of all VP structures decreases as the applied tensile strain increases, which can eventually transform into the metallic state prior to their fracture. The combination of unique phase transformation, anomalous Poisson effect, strong mechanical anisotropy and tunable electronic properties render VP be a novel nanoscale metamaterial with multifunctional applications.

Tailoring the electronic and optical properties of ZrS2/ZrSe2 vdW heterostructure by strain engineering

Under framework of first-principles calculation, we construct ZrS2/ZrSe2 heterostructure and explore the effects of the uniaxial and biaxial strains on its electronic and optical properties. Band structure shows the unstrained ZrS2/ZrSe2 heterostructure has a type-II band alignment. The large binding energy and small interface distance indicate there is a chemical combination between ZrS2 and ZrSe2 layers beyond the van der Waals interaction. Due to the redistribution of charge, a built-in electric field from ZrSe2 to ZrS2 is formed on the interface of the ZrS2/ZrSe2 heterostructure. In addition, constructing the ZrS2/ZrSe2 heterostructure can enhance light absorption intensity. Then we investigate the effects of uniaxial and biaxial strains in the range of −8%∼8% on the electronic and optical properties of the ZrS2/ZrSe2 heterostructure. The band gap of the ZrS2/ZrSe2 heterostructure increases (decreases) with the increase of tensile (compressive) strain, this tunable band gap shows its potential applications in electronic devices. The band type is very sensitive to strain, because the type-II alignment can be converted to type-I alignment. In addition, under uniaxial (−4% and −2%) and biaxial (−2%) compressive strains, a red-shift phenomenon is occurred compared to the unstrained ZrS2/ZrSe2 heterostructure, indicating the better optical gas sensitivity and can be used in infrared light detectors. These findings make possible the application of two-dimensional ZrS2/ZrSe2 heterostructure in multifunctional electronic and optoelectronic devices.

Effect of uniaxial tensile strain on binding energy of hydrogen atoms to vacancy-carbon-hydrogen complexes in α-iron

• The hydrogen binding energy to vacancies under uniaxial tensile strain was calculated. • The binding energy of hydrogen atoms to vacancies decreased with increasing strain. • The binding energy of hydrogen to vacancy-C complexes increased with increasing strain. • The hydrogen retention was estimated under uniaxial tensile strain. The hydrogen binding energy to vacancies or vacancy-carbon complexes in α -Fe under uniaxial tensile strain was calculated using the density functional theory. The solution energies of hydrogen and carbon decreased with an increase in the uniaxial tensile strain. With increasing strain, the binding energy of hydrogen atoms to vacancies also decreases; however, the binding energy of the vacancy-carbon complexes increases. The hydrogen retention was estimated under exposure to hydrogen gas. In the strained area, both the hydrogen concentration of the interstitial hydrogen atoms and the number of hydrogen atoms trapped in the vacancies increased. Therefore, hydrogen retention increased with increasing strain; however, the change in the hydrogen binding energy did not have a strong impact on the hydrogen retention. The presence of vacancies affects hydrogen retention more strongly. Although the binding energy of hydrogen atoms to vacancy-carbon complexes increased, the hydrogen retention in the Fe-C alloy was lower than that in pure Fe.

Investigation of acoustic characterization of ultrasonic air coupling testing of NEPE propellant under strain control

To explore the acoustic characterization of composite solid propellant materials, the wave equation of the viscoelastic body was derived based on the linear viscoelastic constitutive model, and the theoretical relationship between ultrasonic sound velocity and attenuation coefficient, which are closely related to mechanical properties, such as elastic modulus, viscosity coefficient, and complex modulus, was obtained. Ultrasonic air-coupled testing experiments of the NEPE (Nitrate Ester Plasticized Polyether) propellant under different tensile strain states were carried out to obtain the variation law of ultrasonic transmission wave peak amplitude, sound velocity, and attenuation coefficient with strain variables in combination with the variation in propellant porosity under tensile strain. Furthermore, the acoustic parameters with strain and porosity were fitted by the regression equation, and the effect of mesoscopic damage on macroscopic mechanical properties was analyzed. The results show that with the increase in NEPE propellant tensile strain, the porosity increases exponentially. With the increase in porosity, the sound velocity decreases by first polynomials, the wave amplitude decreases by second polynomials, and the attenuation coefficient increases by third polynomials.

Mechanical strain modulation of domain wall currents across LiNbO3 nanosensors

Recently, studies on low-dimensional conducting domain walls (DWs) in insulating ferroelectrics have opened up new research areas that allow information to be mechanically written and electrically read on the nanoscale. Large strains in thin films can change the polarization gradient across the DW region and thus increasing the DW current significantly. This phenomenon can enable the development of high sensitivity mechanical vibration sensors. In this study, the effects of variable uniaxial strain on the structures of 180° conducting DWs in LiNbO3 (LNO) single-crystal thin films bonded onto Si/SiO2 substrates were investigated. After the creation of antiparallel domains within each LNO nanosensor integrated at the film surface, strain modulation of DW currents was observed through simple mechanical bending of the film. The DW current increases under application of tensile strain along the axis of polarization, but decreases under application of in-plane compression by a factor of approximately 25. Phase field simulations showed the dramatic change in polarization gradients around the DW regions under the increase in tensile strain, which reduced the band gap. Repetitive band-gap narrowing/broadening with change in local electric field intensity under vibrating mechanical forces can periodically modulate both the carrier density and the DW conduction in the sensors. This finding not only provides the new fundamental physics to enrich the ferroelectric theory, but also paves the way to the near-future development of bending actuators, piezolighters, and micro-/nano-manipulators, etc.

Biaxial strain tuned electronic structure, lattice thermal conductivity and thermoelectric properties of MgI2 monolayer

We systematically investigate the effect of strain engineering on the thermodynamic stability, electronic structure, Seebeck coefficient and other properties of two-dimensional (2D) MgI2 monolayer on the basis of first-principles. The increasing stress causes the maximum phonon frequency of the MgI2 monolayer to decrease gradually. With the increase of tensile strain, although the indirect-band structure remains the same from the Perdew-Burke-Eruzerhof (PBE) and Heyd-Scuseria-Ernzerhof (HSE06) levels with considering the spin-orbital coupling, the peaks of conduction band and valence band are closer of the MgI2 monolayer. In the process of tensile strain from 2% to 4%, the number of band valleys increases, and the multiple valley pockets caused by such strain increase the Seebeck coefficient. It is found that the Seebeck coefficient increased from 140.86 μV/K without strain to 231.58 μV/K under 4% tensile strain. It also makes the power factor reach its peak at 4% strain of the MgI2 monolayer. However, the lattice thermal conductivity of the MgI2 monolayer is 0.89 W/mK at 300 K in the case of no strain, and it decreases linearly with the increase of tensile strain. The results showed that the ZT value increased gradually with the increasing tensile strain, and it reaches 1.39 at 300 K for the MgI2 monolayer under the 9% tensile strain. Greatly stimulated further theoretical and experimental research on strain engineering and wish to improve thermoelectric conversion efficiency of two-dimensional (2D) materials.

Molecular dynamics study on the microscopic mechanism of in-service welding damage and failure

The risk of burn-through is a major concern when conducting in-service welding repair for oil-gas pipelines. The governing mechanism of burn-through has not hitherto been studied systematically. During in-service welding, different micro-zones of the pipe wall metal below the molten pool have different crack initiation mechanisms due to different temperature and stress conditions. This paper uses molecular dynamics to study the initiation and evolution of micro-defects in different micro-zones of the pipe wall under the in-service welding pool and reveals the microscopic mechanism of in-service welding damage and failure. The research found that the pipe wall under the in-service welding pool is divided into a fusion zone and a coarse grain zone. For the coarse grain zone, the grain boundary region is subjected to large deformations and causes high strain. The stress concentration at the grain boundary (especially the triple junctions) is caused by the arrest of grain boundary slip, which leads to the initiation and propagation of microcracks in the grain boundary region. The displacement vector of atoms at the grain boundaries is generally larger than that of the atoms in the crystal, further indicating that grain boundary slip is the primary mechanism of microcrack initiation in the coarse grain zone. Compared with the coarse grain zone, the grain boundary width of the fusion zone increases, and the grain boundary atoms show apparent disorder. The peak value of the radial distribution function decreases, and the peak becomes wider, indicating that the grain boundary pre-melting phenomenon occurs in the fusion zone. In addition, as the tensile strain increases, the instability of the pre-melting zone expands rapidly and advances into the crystal grain. During in-service welding, the high-temperature deformation of the coarse grain zone and the fusion zone of the tube wall are mainly controlled by the intergranular mechanism. Through molecular dynamics, the mechanism of grain boundary slip in coarse grain zone and grain boundary pre-melting in fusion zone were studied from the microscopic scale. Thereby the microscopic mechanism of in-service welding damage failure was further clarified.

Tunable electronic structure and CO2 adsorption of hb-Sb/graphene van der Waals heterostructure

The van der Waals (vdW) heterostructure combining different 2D materials stimulates broad research interests. Novel chemical and electronic properties can be obtained via building vdW heterostructures. In this paper, the CO2 adsorption properties of buckled honeycomb antimonene/graphene (hb-Sb/G) vdW heterostructure are examined by first-principles calculation, which provides theoretical insights into the enhanced electrocatalytic activity for CO2 reduction of hb-Sb/G heterostructure reported in a recent experimental study. Furthermore, by applying in-plane biaxial strains, the tunable Schottky barrier and transition of contact property are observed. As compressive strain decreases or tensile strain increases, the catalytic activity of hb-Sb/G heterostructure is predicted to be enhanced as a result of the increased interlayer coupling. Our work reveals the origin of electrocatalytic activity of hb-Sb/G heterostructure for CO2 reduction and proposes a strain engineering method to enhance its catalytic activity via tuning its electronic structure. This work uncovers promising applications of hb-Sb/G heterostructure in green energy and ultra-thin devices.

Strain-induced tunability of the optoelectronic properties of inorganic lead iodide perovskites APbI3 (A= Rb and Cs)

Herein we investigate the influence of biaxial strain ranges from −2% to +2% on the optoelectronic properties of APbI3 (A = Rb and Cs) perovskites through first-principles density functional theory calculations. It has been explored that the biaxial strain in APbI3 (A = Rb and Cs) can significantly increase their absorbance, both in the visible and ultraviolet light energy range. The electronic band structure shows that the RbPbI3 and CsPbI3 compounds are all semiconductors with a direct bandgap of 1.05 eV and 1.28 eV, respectively, at the R-point. However, the bandgap of APbI3 (A = Rb and Cs) reveals a decreasing trend and has a tendency towards the metallic condition when the compressive strain is applied. Besides, due to the increase of tensile strain, the bandgap of APbI3 exhibits an increasing trend. Therefore, this study would provide a systematic way to satisfy the requirements of different optoelectronic device applications through biaxial strain.

Mapping of cracking sequence of polyvinyl alcohol-steel hybrid fiber reinforced high-strength engineered cementitious composite under uniaxial tension

In the present paper, cracking sequence of high-strength engineered cementitious composite with the characteristic of low drying shrinkage (LSECC) under tension was experimentally studied by continually photographing during loading. The specific objective is to investigate the development of crack opening of each individual crack occurred during loading. Four Engineered cementations composite mixtures with water to binder ratio of 0.20, 0.25, 0.30, and 0.35 (LSECC-0.20, LSECC-0.25, LSECC-0.30, and LSECC-0.35) were used in the tests. Using the photographers taken during the test, crack width of each crack occurred during loading are determined according to the difference between solid material and crack on gray level. The test results show that cracks in ECC under tensile load are formed according to a temporal sequence. The opening width of each crack grows in a controllable and gradual manner with the increase of tensile strain. At a given strain level, crack width of different crack is not equal and the distribution of crack width is affected by matrix strength of the composite. Maximum crack width and the tensile strain capacity at the moment may be utilized to characterize the tensile performance of the composite that can guarantee both of tensile ductility and long-term durability. As maximum crack width equals 60 μm, at which the permeability of ECC may not be influenced by the cracks, higher strength ECC with water to binder ratio of 0.20 and 0.25 (LSECC-0.20 and LSECC-0.25) shows obvious higher tensile strain capacity and more cracks of narrow opening. By contrast, lower strength ECC with water to binder ratio of 0.30 and 0.35 (LSECC-0.30 and LSECC-0.35) shows relatively lower tensile strain and fewer cracks of narrow crack opening as crack width is limited below 60 μm. With the increase of tensile strain and the maximum crack width, much wider cracks (larger than 60 μm) are formed in lower strength ECC comparing to that of higher strength ECC.

Ballistic response of woven glass fabric-epoxy composites at low temperatures: Experimental investigation

The ability of Glass Fabric Reinforced Polymer (GFRP) composites in arresting a projectile during a ballistic impact is dependent on climatic conditions such as temperature since their mechanical properties vary with the same. In the present work, ballistic impact experiments were carried out on plain weave GFRP composites to evaluate their performance in low-temperature environments. Square sheets of plain weave GFRP were impacted by cylindrical projectiles at four different temperatures viz. -35°C, -15°C, 0°C, and at Room temperature. A gas gun was used to propel the projectiles and the velocities were measured using a High-speed camera while the temperatures were monitored using a Resistance Temperature Detector (RTD). Strain gauges were also attached at different locations on the samples to quantify the strains due to the projectile impact. The ballistic limit obtained from the test data was found to increase linearly with reducing temperature contrary to the general expectation of degradation in the ballistic performance of GFRP at low temperatures. The Lambert-Jonas equations were fit to the experimental data and the parameters were estimated. The results obtained also indicated a decrease in stress wave attenuation and an increase in tensile strains with the decrease in temperature.

Atomistic understanding of the anisotropic tensile response and zero-stiffness of carbon honeycomb nanostructure

ABSTRACT Carbon honeycomb (CHC) is a novel carbon allotrope with excellent mechanical and physical properties and has great potentials for various energy and environmental applications. In this work, the tensile response of the CHC nanostructure is re-examined via molecular dynamics simulation to provide an atomistic understanding of its anisotropic mechanical properties and zero-stiffness as reported previously. The simulation results obtained demonstrate that the tensile response of CHC is closely related to the deformation of its constitutive graphene nanoribbons. To illustrate the underlying deformation mechanisms of the nanoribbons, the evolution of their atomic structure during the deformation is characterised by calculating several characteristic bond lengths and angles, and the atomic stress distribution. It is found that when tensile loading is applied in the armchair direction, the graphene nanoribbons undergo severe distortion and subsequent distortion flattening as the tensile strain increases, which leads to the zero-stiffness behaviour. For the tensile loading applied in the zigzag direction, the graphene nanoribbons are mainly stretched without distortion, giving rise to the anisotropic tensile response of CHC. In addition to the zero-stiffness and anisotropic behaviour, the negative Poisson’s effect is also observed when a tensile loading is applied in the armchair direction.

Structural and thermal analysis of polycrystalline diamond thin film grown on GaN-on-SiC with an interlayer of 20 nm PECVD-SiN

A 1.5-μm polycrystalline diamond was deposited on the AlGaN/GaN heterojunction on the SiC substrate with a 20-nm SiN dielectric. A 4.9% increase in 2DEG density after the diamond growth due to the increase in tensile strain of the GaN layer is confirmed by micro-Raman measurements. The interfacial analysis through the transmission electron microscopy and electron energy loss spectroscopy shows a thickness reduction in the SiN layer of ∼1.7 nm, which converts to a thin SiC layer at the diamond/SiN interface, and no carbon diffusion is found in the SiN layer after the diamond growth. Device simulation using the thermal properties extracted by time domain thermoreflectance predicts a temperature drop of 17.1 °C when the diamond only covers the device access region and reveals that the improvement of thermal boundary resistance is much more effective than that of the diamond thermal conductivity for the top-side heat spreading, which is mainly due to the limited thickness of the top diamond film.

Molecular-level characterization of changes in the mechanical properties of wood in response to thermal treatment

Thermal treatment can improve the dimensional stability of wood, but it also decreases wood’s toughness, or increases its brittleness. In this paper, combining FTIR spectroscopy and mechanical analysis were used to monitor wood molecular straining and deepen the micromechanical understanding of thermally-treated wood. The degradation of hemicellulose increased as the thermal treatment temperature increase, and the 220 °C treatment also led to cellulose microfibrils reorientation. The results of static tension FTIR spectra of thermally-treated wood indicated that the absorption peak of cellulose glycosidic bond underwent a substantial bandshift to lower wave numbers as the tensile strain increase, but the characteristic peak position of the lignin was no obvious change during stretching. For the 160–200 °C treated samples, the bandshift ratios of cellulose C–O–C glycosidic bond increased upon increasing the temperature; Furthermore, the intensities of the two split peaks of cellulose at 1169 cm−1 and 1435 cm−1 in 0° polarization dynamic FTIR spectra decreased upon increasing the treatment temperature, indicating the elastic-like response of cellulose for thermally-treated wood decrease. For the 220 °C treated sample, the bandshift ratio of cellulose glycosidic bond decreased compared with other thermal treatment samples, but the intensities of the two split peaks of cellulose increased again. Those results indicated that the shear slipping between cellulose microfibrils decrease and microfibrils reorientation due to hemicellulose degradation after thermal treatment may cause the toughness of the thermally-treated wood decrease, or the brittleness increase.Graphical abstract

Impact of strain on the electronic, phonon, and optical properties of monolayer transition metal dichalcogenides XTe2 (X = Mo and W)

Here, we provide a systematic assessment of biaxial strain effects on the electronic, phonon, and optical properties of monolayer transition metal dichalcogenides (TMDs) XTe2 (X = Mo and W) using density functional theory calculations. We observed a large direct bandgap of 1.163 eV and 0.974 eV for MoTe2 and WTe2, which reduced to 1.042 eV and 0.824 eV in the spin–orbit coupling ambient. The XTe2 structures show a tunable bandgap with the variation of the applied biaxial strains. Due to the breaking of inversion symmetry, a large spin-valley coupling emerged at the valance band edges for both MoTe2 and WTe2 monolayers under applied biaxial strain. The phonon properties with different biaxial strains reveal that monolayer MoTe2 is more stable than the WTe2 structure. The calculated optical properties demonstrate that the dielectric constant and absorption coefficient of MoTe2 and WTe2 move to higher photon frequencies when the compressive strain is increased. On the other hand, with the increase in tensile strain, a red-shift behavior is found in the calculated optical properties, indicating the suitability of the XTe2 monolayer for different infrared and visible light optical applications.