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Fullerene-assembled low-dimensional materials have been experimentally realized in polymorphic forms and have attracted significant interest very recently. Here, we predict a two-dimensional (2D) honeycomb lattice material TM2(C60)3 (TM = Cr, Mo, and W) assembled from exohedral metallofullerene clusters TM(C60)3 that could exhibit planar triangular geometries. According to first-principles calculations combined with Monte Carlo simulations, we suggest that these 2D assembled materials exhibit various exotic physical properties, including ferromagnetism, ferroelectricity, and quantum anomalous Hall effect. Interestingly, mechanical strains could effectively tune their magnetic moments and switch the conducting spin channel of the Dirac bands at the Fermi level. Our work provides a new cluster-assembly design strategy toward cluster-assembled 2D materials based on fullerene characters. [ABSTRACT FROM AUTHOR]

Spin–orbit coupling induces a current density in the ground state, which consequently requires a generalization for meta-generalized gradient approximations. That is, the exchange–correlation energy has to be constructed as an explicit functional of the current density, and a generalized kinetic energy density has to be formed to satisfy theoretical constraints. Herein, we generalize our previously presented formalism of spin–orbit current density functional theory [Holzer et al., J. Chem. Phys. 157, 204102 (2022)] to non-magnetic and magnetic periodic systems of arbitrary dimension. In addition to the ground-state exchange–correlation potential, analytical derivatives such as geometry gradients and stress tensors are implemented. The importance of the current density is assessed for band gaps, lattice constants, magnetic transitions, and Rashba splittings. In the latter, the impact of the current density may be larger than the deviation between different density functional approximations. [ABSTRACT FROM AUTHOR]

We determine the surface tension of aqueous electrolyte solutions in contact with non-polar dielectric media using a thermomechanical approach, which involves deriving the stress tensor from the thermodynamic potential of an inhomogeneous fluid. To obtain the surface tension, we calculate both the normal and tangential pressures using the components of the stress tensor, recently derived by us [Y. A. Budkov and P. E. Brandyshev, J. Chem. Phys. 159, 174103 (2023)] within the framework of Wang's variational field theory. Using this approach, we derive an analytical expression for the surface tension in the linear approximation. At low ionic concentrations, this expression represents the classical Onsager–Samaras limiting law. By utilizing only one fitting parameter, which is related to the affinity of anions to the dielectric boundary, we successfully approximated experimental data on the surface tension of several aqueous electrolyte solutions. This approximation applies to both the solution–air and solution–dodecane interfaces, covering a wide range of electrolyte concentrations. [ABSTRACT FROM AUTHOR]

Flow-enhanced nucleation (FEN) of n-pentacontahectane (C150) under biaxial extensional flows of varying strain rate ratios is studied using nonequilibrium molecular dynamics simulation. The nucleation rates thus calculated are used to test previously published FEN models based on invariants of the conformation tensor of Kuhn segments and the extra stress tensor. Models based on the conformation tensor provide a more accurate description of FEN observed in biaxial flow simulations than those based on the extra stress tensor. In addition, the formation of nematic domains previously reported to be stabilized by shear or extensional flow is absent in equibiaxial flows. However, such domains do form in non-equibiaxial flows, and nucleation occurs in these domains preferentially. The shape and orientation of nuclei formed under biaxial flows of various strengths and strain rate ratios are also reported. [ABSTRACT FROM AUTHOR]

Stretching or compression can induce significant energetic, geometric, and spectroscopic changes in materials. To fully exploit these effects in the design of mechano- or piezo-chromic materials, self-healing polymers, and other mechanoresponsive devices, a detailed knowledge about the distribution of mechanical strain in the material is essential. Within the past decade, Judgement of Energy DIstribution (JEDI) analysis has emerged as a useful tool for this purpose. Based on the harmonic approximation, the strain energy in each bond length, bond angle, and dihedral angle of the deformed system is calculated using quantum chemical methods. This allows the identification of the force-bearing scaffold of the system, leading to an understanding of mechanochemical processes at the most fundamental level. Here, we present a publicly available code that generalizes the JEDI analysis, which has previously only been available for isolated molecules. Now, the code has been extended to two- and three-dimensional periodic systems, supramolecular clusters, and substructures of chemical systems under various types of deformation. Due to the implementation of JEDI into the Atomic Simulation Environment, the JEDI analysis can be interfaced with a plethora of program packages that allow the calculation of electronic energies for molecular systems and systems with periodic boundary conditions. The automated generation of a color-coded three-dimensional structure via the Visual Molecular Dynamics program allows insightful visual analyses of the force-bearing scaffold of the strained system. [ABSTRACT FROM AUTHOR]

In this paper, a new Stroh formalism for gradient electro-mechanics is derived for the first time, which is both mathematically concise and numerically powerful, applicable to generally coupled anisotropic material systems. Based on this new formalism, the complicated Lamb wave in flexoelectric and piezoelectric plates is investigated. The dispersion equation is obtained by solving the eigenvalue problem along with the unconditionally stable dual-variable and position method. From the obtained dispersion equation, the dispersion curves and mode shapes of the Lamb wave are calculated by the 1D form of the multidimensional moduli ratio convergence method. Two important and interesting features are observed from our analysis: One is the difference in the mode shape symmetry between the piezoelectric and flexoelectric cases, and the other is the size-dependent property of the flexoelectric effect as observed by nondimensionalization. These features are further illustrated by comparing the dispersion curves and wave-mode shapes among the three different material models (purely piezoelectric, purely flexoelectric, and flexoelectric and piezoelectric coupled). The newly derived Stroh formalism offers a robust, concise, and unified approach for dealing with strain gradient electro-mechanic materials with crystal systems of general anisotropy. The present work also explains the physical mechanism of symmetry breaking observed, as induced by flexoelectric coupling in piezoelectric materials. [ABSTRACT FROM AUTHOR]

In gas gun experiments, a graded density impactor (GDI) is used to achieve quasi-isentropic loading. However, inconsistency between the designed and experimental loading profiles, mainly caused by by-products during preparation, limits the application of GDI for a long time. In this work, a kind of W/Ti GDI with advantages of a wide density range of 4.5–19.3 g/cm3 and high structural designability was designed and synthesized. Each of mid-layers of the W/Ti GDI was composed of W and Ti without the formation of an intermetallic compound, and had good parallelism and flatness. This provides a prerequisite for good agreement between the designed and experimental loading profiles. Due to the high designability of the GDI, quasi-isentropic loading with different stress-paths was achieved by controlling the structure of the GDI. Then, independently controlling peak stress and strain rates of loading was successfully achieved by changing the flyer velocity and the type of the W/Ti GDI. The W/Ti GDI has enormous application potential in studying the dynamic response of materials under quasi-isentropic loading with stress and strain rate controlled. [ABSTRACT FROM AUTHOR]

An extension of a constitutive law for 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) is proposed with a focus on the calibration of a crystal plasticity law. TATB, a highly anisotropic energetic molecular crystal used in explosive formulations, can be subjected to high-pressure and high-temperature conditions, either under high strain-rate deformation or shock loading. The existing thermodynamically consistent model, fully informed by molecular dynamics (MD) simulations, includes nonlinear elasticity as well as a phase-field by reaction pathway formalism under large strain for the modeling of TATB behavior upon pressure as well as its well-known twinning–buckling deformation mechanism. However, it has been observed that TATB single crystal can accommodate large deformations through dislocation-mediated plasticity, a feature not included in the mesoscale model. In the present work, we take advantage of the microscopic flow surface, previously computed through MD calculations, to calibrate a crystal plasticity law, extending the capability of the continuum model currently limited to low velocity impacts and moderate strain rate. Indeed, the microscopic flow surface, defined as a 3D stress-at-first-defect-nucleation contains all information about TATB single crystal mechanical response under directional shear loading, including twinning, buckling, and plastic events. The calibration process uses differential evolution optimization to calibrate TATB basal and transverse slip systems critical stresses to reproduce the microscopic flow surface. Finally, the response of a TATB single crystal to directional loading is investigated in order to evaluate the new model. [ABSTRACT FROM AUTHOR]

In this work, we investigate the possibilities of performing charge and spin current rectifications using graphene nano-ribbon in the presence of Rashba spin–orbit (SO) interaction. More specifically, we explore the specific role of mechanical strain on these two different types of current rectifications. The system is simulated by a tight-binding framework, where all the results are worked out based on the standard Green's function formalism. In order to have current rectification, an asymmetry is required, which is incorporated through uncorrelated disorder among the constituent lattice points. From our extensive numerical analysis, we find that reasonably large charge and spin current rectifications can be obtained under strained conditions, and all the physical pictures are valid for a broad range of tight-binding parameters. The rectification properties are studied mostly for zigzag graphene nano-ribbons; however, an armchair ribbon is also taken into account for a clear comparison. Our work may provide a new direction of getting strain-controlled current rectifications in similar kinds of other physical systems as well. [ABSTRACT FROM AUTHOR]

Ferroelectric materials are widely used in actuators, exciters, and memory devices due to their excellent electromechanical properties. However, the instinctive brittleness of ferroelectric materials makes them easy to fracture under external load. Since giant strain gradient can be easily generated near the crack tip, the flexoelectric effect is indispensable in the research of fracture properties of ferroelectric materials. With the combination of time-dependent Ginzburg–Landau theory and phase-field model, the electromechanical behavior of PbTiO 3 in the vicinity of the crack tip is determined in this work. The simulation results demonstrate that the domain structure near the crack tip becomes asymmetric with the flexoelectric effect. The polarization switching-induced toughening, which is characterized by the J -integral, depends on the direction of the crack relative to the original polarization orientation. Furthermore, the longitude flexoelectric coefficient f 11 has more significant impact on the fracture toughness than that of the transverse flexoelectric coefficient f 12 and the shear flexoelectric coefficient f 44. The results of the present work suggest that the flexoelectric effect must be considered in the reliable design of ferroelectric devices. [ABSTRACT FROM AUTHOR]

Programmable locomotion of molecules inside the carbon nanotube (CNT) has a significant role in controlling the reactions and delivery systems based on nanotubes. Using molecular dynamics (MD) simulations as well as the theoretical approach, we evaluate the oscillation of C60 inside the CNTs that are subjected to strain gradients from both sides. The molecular dynamics simulations are implemented by LAMMPS open-source software. Using this program, the van der Waals (vdW) interactions are established between C60 and nanotube, and the simulations are performed in canonical ensemble. The strain gradient applied on CNT provides the restoring force of the oscillation of C60. The potential energy of fullerene finds the minimum value at the unstrained region of CNT, which makes it the equilibrium point of oscillation. The amplitude of the oscillations is shown to be related to the thermal energy of C60. The frequency of the oscillations depends on the magnitude of the strain gradient applied on the nanotubes. At higher strain gradients of CNTs, we observe the increase in the frequency due to the increase in the restoring force acting on the fullerene molecule. We exploit the strained carbon nanotubes to control the position of C60 inside the nanotube. It has been shown that by changing the strain gradient of CNT, it is possible to steer the locomotion of C60 to different points inside the nanotube. [ABSTRACT FROM AUTHOR]

Low-crosslinked polymer networks have recently been found to behave auxetically when subjected to small tensions, that is, their Poisson's ratio ν becomes negative. In addition, for specific state points, numerical simulations revealed that diamond-like networks reach the limit of mechanical stability, exhibiting values of ν = −1, a condition that we define as hyper-auxeticity. This behavior is interesting per se for its consequences in materials science but is also appealing for fundamental physics because the mechanical instability is accompanied by evidence of criticality. In this work, we deepen our understanding of this phenomenon by performing a large set of equilibrium and stress–strain simulations in combination with phenomenological elasticity theory. The two approaches are found to be in good agreement, confirming the above results. We also extend our investigations to disordered polymer networks and find that the hyper-auxetic behavior also holds in this case, still manifesting a similar critical-like behavior as in the diamond one. Finally, we highlight the role of the number density, which is found to be a relevant control parameter determining the elastic properties of the system. The validity of the results under disordered conditions paves the way for an experimental investigation of this phenomenon in real systems, such as hydrogels. [ABSTRACT FROM AUTHOR]

It has been assumed that the negative divergence of all stress tensors in common use yields the same force. This work finds that this is untrue, and, in fact, can vary wildly. We demonstrate this for the hydrogen atom, the one-particle isotropic harmonic oscillator, and a particle in an infinite spherical well where the exact density, pair-density, and the first order reduced density matrix are known for ground and excited states without any approximation. The Ehrenfest stress-tensor is introduced as any stress-tensor whose negative divergence will yield the corresponding Ehrenfest force for the same system when the exact wave-function is utilized. Stress-tensors within the literature are examined to show those that are Ehrenfest stress-tensors. Those that differ are demonstrated by how they differ within an exact formulation. The proof that the negative divergence of an Ehrenfest stress-tensor yields the Ehrenfest force is summarized. [ABSTRACT FROM AUTHOR]

The topology of the Ehrenfest force field (EhF) is investigated as a tool for describing local interactions in molecules and intermolecular complexes. The EhF is obtained by integrating the electronic force operator over the coordinates of all but one electron, which requires knowledge of both the electron density and the reduced pair density. For stationary states, the EhF can also be obtained as minus the divergence of the kinetic stress tensor, although this approach leads to well-documented erroneous asymptotic behavior at large distances from the nuclei. It is shown that these pathologies disappear using the electron density functions and that the EhF thus obtained displays the correct behavior in real space, with no spurious critical points or attractors. Therefore, its critical points can be unambiguously obtained and classified. Test cases, including strained molecules, isomerization reactions, and intermolecular interactions, were analyzed. Various chemically relevant facts are highlighted: for example, non-nuclear attractors are generally absent, potential hydrogen–hydrogen interactions are detected in crowded systems, and a bifurcation mechanism is observed in the isomerization of HCN. Moreover, the EhF atomic basins are less charged than those of the electron density. Although integration of the EhF over regions of real space can also be performed to yield the corresponding atomic forces, several numerical drawbacks still need to be solved if electron density functions are to be used for that purpose. Overall, the results obtained support the Ehrenfest force field as a reliable descriptor for the definition of atomic basins and molecular structure. [ABSTRACT FROM AUTHOR]

We investigated the relationship between porosity and flexoelectricity for aluminum (Al)/polyvinylidene fluoride (PVDF) composites. Neat PVDF, composites of micron aluminum (μAl)/PVDF, and composites of nano aluminum (nAl)/PVDF were 3D printed, and the flexoelectric response was measured using a cantilever beam test setup. Voids (up to 72.4 mm3) were incorporated into the samples by decreasing the infill percent of the 3D printed material. We found that increasing the porosity via millimeter scale voids incorporated into the infill pattern decreased the average effective flexoelectric coefficient relative to the near full-density (100% infill) control samples. This contrasts with other studies that have shown increasing micron scale porosity increases the flexoelectric coefficient. In addition, we measured higher flexoelectric responses for nAl/PVDF than μAl/PVDF as well as for samples printed by the Hyrel 3D SR printer as opposed to the Ender 3 V2 printer. These results indicate that charge generation due to flexoelectricity can be altered by changing parameters such as porosity, particle size of inclusions, or manufacturing method. Smaller voids and fine particles can induce larger strain gradients than larger inhomogeneities, leading to increased flexoelectric coefficients. A competing effect is that more porosity leads to less materials, which can decrease the flexoelectric coefficient. [ABSTRACT FROM AUTHOR]

A study of residual mechanical stresses in the surface layer of the HgCdTe/CdTe/ZnTe/GaAs structure based on the registration of the second harmonic signal characteristics of reflected IR laser radiation from the surface of the studied sample passed through a nonlinear crystal was carried out. It is shown that such a sensitive method makes it possible to obtain information about the anisotropy of the polarization of the reflected radiation, caused by the residual deformation. Observations of the fine structure of the angular sweep of the second harmonic signal suggest a complex structure of residual stresses related to the presence of misoriented areas. The results were compared with data obtained from measurements of the azimuthal dependence of the self-reflected second harmonic signal from the sample surface. [ABSTRACT FROM AUTHOR]

Based on the variational field theory framework, we extend our previous mean-field formalism [Y. A. Budkov and A. L. Kolesnikov, JStatMech 2022, 053205.2022], taking into account the electrostatic correlations of the ions. We employ a general covariant approach and derive a total stress tensor that considers the electrostatic correlations of ions. This is accomplished through an additional term that depends on the autocorrelation function of the local electric field fluctuations. Utilizing the derived total stress tensor and applying the mechanical equilibrium condition, we establish a general expression for the disjoining pressure of the Coulomb fluids, confined in a pore with a slit-like geometry. Using this equation, we derive an asymptotic expression for the disjoining pressure in a slit-like pore with non-electrified conductive walls. Present theory is the basis for future modeling of the mechanical stresses that occur in electrode pores with conductive charged walls, immersed in liquid phase electrolytes beyond the mean-field theory. [ABSTRACT FROM AUTHOR]

The response of plane-parallel 2 mm thick samples of 47.3Ni-52.7Ti alloy was studied in two series of planar impact tests at temperatures between 300 and 473 K and between 473 and 318 K (heating to 473 K followed by cooling). In two additional series, the samples of 0.4–4 mm thickness were tested at 300 and 338 K (after preheating up to 473 K). In all the tests, the samples were loaded by 1 mm thick copper impactors having velocities equal to 314 ± 2 m/s. The velocity of the rear sample surface was continuously monitored by a laser Doppler velocimeter. It was shown that substantial, by an order of magnitude, variation of Hugoniot elastic limit σ H E L and compressive strength Y of the nitinol with temperature are caused by the martensite–austenite transformation and its reversal. The variation of the dynamic tensile (spall) strength σ s p of the nitinol along the heating–cooling path was found similar to that of σ H E L although the difference between σ s p values of austenite and martensite, ∼20%, is much more modest than in the case of σ H E L . The test series performed at constant temperatures with samples of different thicknesses allows one to conclude that the plastic deformation in shocked austenite is presumably realized by dislocation motion and multiplication controlled by phonon viscosity. In the shocked martensite, the plastic deformation mechanism at a stress lower than ∼0.3 GPa is likely a thermally activated combination of deformation twinning and slip of kinking dislocations. [ABSTRACT FROM AUTHOR]

An all-optical photoinduced lensing method is used to excite and monitor acoustic waves in liquids. Following optical absorption, the laser pulse induces a localized temperature gradient that launches pressure waves in the excited region at the nanosecond time scale. This generates a lens-like optical element in the sample. A probe laser beam senses the refractive index change due to the acoustic and thermal effects. Piezo-optic and thermo-optic coefficients govern how the refractive index of a material changes in response to mechanical stress and temperature variations, respectively. These effects are connected to the physical properties of the liquids and can be accessed by theoretically describing the intensity signal. A complete set of physical properties of ten liquids are quantitatively described in this work. These effects find applications in a wide range of fields, from optical communication, ultrasonic imaging, and sensing to adaptive optics and fundamental research. [ABSTRACT FROM AUTHOR]

Properties of fragmentation from an explosively driven 316L stainless steel spherical shell section fabricated by a laser powder bed additive manufacturing process with minimal surface finishing are investigated. This shell is driven by an insensitive high explosive, resulting in high strain rate deformation (>8 × 103 s−1) and failure of the stainless steel. Photonic Doppler velocimetry measures the expansion rate; dynamic radiography and high-speed imaging capture the fracture behavior of the stainless steel. The fracture response of the additively manufactured stainless steel shell is compared to published experimental results on additively manufactured 316L stainless steel and conventionally manufactured wrought 316L and 304 stainless steel shell fragmentation. Despite preferred crack orientation, suggesting the influence of surface grooves on fracture time, fragment size is identical to that measured in a similar experiment on wrought 304 stainless steel. Further analysis indicates that the 316L additively manufactured stainless steel shell exhibits comparable spall strength and fragmentation toughness to conventionally manufactured stainless steel yet lower failure strain due to surface stress concentrations. [ABSTRACT FROM AUTHOR]

Rare-earth nickelates (RENiO3: RE≠La) exhibit metal–insulator transition (MIT) properties that enable potential applications, such as critical temperature resistance thermistors, optoelectronic switches, and correlated logical devices. Nevertheless, their abrupt structural distortion across MIT results in mechanical stresses and forms microcracks within the bulk RENiO3, and this irreversibly reduces their resistive change during MIT that further impedes their practical applications. Herein, we demonstrate a compositing strategy that simultaneously improves the MIT performances and mechanical strength of RENiO3 by introducing a secondary phase of perovskite oxides with similar lattice parameters and high resistivity. Despite its much higher resistivity compared to RENiO3 (e.g., RE = Sm or Pr), introducing the LaMnO3 compositing phase under high oxygen pressure surprisingly reduces the matrix resistivity. Furthermore, such a compositing process (e.g., 20% LaMnO3) also effectively improves the mechanical strength of RENiO3 by eight times. Such counterintuitive variations are attributed to the similar structure and lattice parameter between RENiO3 and the perovskite composites that modify the grain boundary. As a result, the resistive change is more abrupt across MIT owing to the reduction in the resistivity associated with the grain boundary, while the defect generation and propagation are also suppressed that improves the mechanical properties. This further pave the way to the application of bulk RENiO3 as discrete devices in correlated electronics. [ABSTRACT FROM AUTHOR]

A comprehensive physics-based modeling framework for electromigration (EM) in copper nano-interconnects is presented. It combines the three stages of stress evolution, void nucleation, and void dynamics in a single fully coupled and consolidated platform. Mechanical stress evolution, pre- and post-void nucleation, and its impact on void dynamics are deciphered, which enables accurate predictions of EM aging processes as validated by dedicated EM experiments. Subsequently, the experimentally validated model is utilized to shed light on the impact of a number of manufacturing variables, namely, line extension, via taper angle, and the effectiveness of the via bottom flux divergence point. A linear correlation between the ion leakage through the via bottom barrier and the peak tensile stress at the cathode was observed in long lines. In short lines, a blocked cathode end with atomic leakage through the anode end weakens the back-stress effect and threatens the Blech effect induced interconnect immortality. Increasing the line extension length was shown to increase the EM lifetime by about 40%. This impact was saturated beyond 1 critical dimension of line extension. On the other hand, the via taper angle increased the upstream EM lifetime by about twofold when the taper angle was increased from 0° to 30°, which indicates that the change of via taper angle has a stronger impact on EM lifetime compared to the line extension. [ABSTRACT FROM AUTHOR]

We present computational results on electronic, magnetic, and structural properties of CoVMnSb, a quaternary Heusler alloy. Our calculations indicate that this material may crystallize in two energetically close structural phases: inverted and regular cubic. The inverted cubic phase is the ground state, with ferrimagnetic alignment, and around 80% spin polarization. Despite having a relatively large bandgap in the minority-spin channel close to the Fermi level, this phase does not undergo a half-metallic transition under pressure. This is explained by the "pinning" of the Fermi level at the minority-spin states at the Γ point. At the same time, the regular cubic phase is half-metallic and retains its perfect spin polarization under a wide range of mechanical strain. Transition to a regular cubic phase may be attained by applying uniform pressure (but not biaxial strain). In practice, this pressure may be realized by an atomic substitution of non-magnetic atoms (Sb) with another non-magnetic atom (Si) of a smaller radius. Our calculations indicate that 25% substitution of Sb with Si results in a half-metallic regular cubic phase being the ground state. In addition, CoVMnSb0.5Si0.5 retains its half-metallic properties under a considerable range of mechanical pressure, as well as exhibits thermodynamic stability, thus making this alloy attractive for potential spintronic applications. We hope that the presented results will stimulate experimental efforts to synthesize this compound. [ABSTRACT FROM AUTHOR]

Slip or twinning is one of the fundamental questions in the deformation studies of metals and alloys. Internal parameters such as generalized stacking fault energy and size and external parameters such as pressure, strain rate, and temperature influence the competition between the full slip and twinning, thus dictating the predominance of one mechanism over the other. In the present investigation, we studied the influence of preloaded stress and temperature on the deformation behavior of BCC-Fe nanowires using molecular dynamics simulations and theoretical analysis. Based on detailed investigations into the energetics associated with slip and twinning, we observed that twinning is the preferred deformation mechanism in BCC-Fe. However, this has been modified by preloaded stresses applied in normal, transverse, and both directions on the nanowire. We observed a slip on {110}, on {112}, and even on {123} planes. The temperature did not alter the inherent twinning nature but linearly decreased the various fault energies. [ABSTRACT FROM AUTHOR]

Semiconductor industry is experiencing unprecedented growth, still driven by Moore's law, which is continually delivering devices with improved performance at lower costs. The continuation of this development places the industry in a divergent trade-off between economic attractiveness, technological feasibility, and the need for further performance improvement. Since the mainstream semiconductor technologies are silicon-based, new disruptive innovations are needed to gain additional performance margins. The use of nanowires is the preferred approach for preserving electrostatic control in the MOS transistor channel, and the application of mechanical stress is a booster of carrier mobility. It is in this context that this paper presents the design, fabrication, theoretical modeling, and characterization of a measurement platform to characterize the mechanical tensile stress of extremely narrow Si nanowires as small as 14.2 ± 1.12 nm in width. The proposed measurement platform enables a precise control of uniaxial strain, in terms of both amplitude and location, through the implementation of a stoichiometric Si3N4 pulling strand exerting a high tensile force on silicon nanowires. Reported devices are fabricated using a silicon-on-insulator wafer with fully complementary metal–oxide–semiconductor-compatible processing and top-down approach. It is observed that the mechanical strength of nanostructured Si is size-dependent and increases with miniaturization. Characterization revealed a record tensile strength value of 7.53 ± 0.8% (12.73 ± 1.35 GPa) for the narrowest nanowires fabricated using a top-down approach. [ABSTRACT FROM AUTHOR]

Flexoelectricity is a universal phenomenon in all dielectrics, which couples electrical polarizations with strain gradients. However, limited by the size effects, the intensity of the flexoelectric effect becomes appreciable at the micro- and nano-scale, which suppresses its applications at the macroscale. To amend this inconvenience in applications, we innovatively propose replacing the traditional pure dielectric film with flexoelectret film containing quasi-permanent electrical charges in crumpling deformation. The crumpled flexoelectret film can give a considerable flexoelectric-like response at the macroscale. Specifically, we establish a theoretical model for the crumpled flexoelectret film, derive the analytical solution of the electromechanical coupling under the bi-directional bending conditions, and analyze the flexoelectric-like response under different thicknesses, charge densities, and scales. The results show that when the flexoelectret film's thickness H = 1 mm and the charge density q = − 0.2 mC ⋅ m − 2 , the intensity of its flexoelectric-like response is nearly 100 times of that of pure dielectric film's intrinsic flexoelectricity. [ABSTRACT FROM AUTHOR]

Piezoelectric semiconductor (PS) materials have attracted much attention in recent years due to their unique properties. This paper explores the electromechanical coupling behavior of bent piezoelectric semiconductor fibers with non-uniform cross-sectional areas. The study uses the generalized differential quadrature method to numerically solve the field equations with variable coefficients derived from piezoelectric theory. The research examines the mechanical and electrical field distribution of bent variable cross-sectional fibers, comparing the performances of non-uniform fibers with different profiles. The study reveals that the variable cross-sectional profile of the fiber changes the characteristic of the uniform fiber's electrical distribution along the axis, and it exhibits a more sensitive and stronger electrical response to the same external force. The research also shows that the concavity and convexity of the radius distribution function of the non-uniform fibers determine whether there are extreme points of surface potential. Finally, the study suggests that by designing extreme points of the PS fiber profile, surface potential extreme points can be artificially created at the same location. These results offer a theoretical direction for creating advanced piezoelectric semiconductor nanodevices and present novel insights into designing higher-efficiency nanogenerators and mechanical strain sensors in the future. [ABSTRACT FROM AUTHOR]

Demonstration of acoustically improving charge transport characteristics of regioregular poly(3-hexylthiophene) (rrP3HT) based organic field effect transistor (OFET) fabricated on YZ lithium niobate piezoelectric substrate has been presented and analyzed. Owing to the acoustoelectric (AE) effect, a surface acoustic wave (SAW) propagating through the substrate transfers its momentum and energy to the charges in the rrP3HT channel, reducing the effective energy gap between the charge hopping states, which leads to a decrease in charge trapping and an increase in path conductivity and number of paths for charge transport. Hence, a significant increase in drain current and mobility and a substantial reduction in gate voltage were observed in the presence of SAW. The AE effect has been especially predominant in devices with smaller channel width, depicting that gate voltage brought down by 30 V provided drain current equivalent to that obtained in the absence of SAW. The bias stress analysis of the devices showed an increase in current instead of the decrease, generally seen with respect to time, reinforcing that the long term charge trapping effect in OFETs can be compensated with the propagation of SAW leading to enhanced device stability. [ABSTRACT FROM AUTHOR]

In this paper, we present a covariant approach that utilizes Noether's second theorem to derive a symmetric stress tensor from the grand thermodynamic potential functional. We focus on the practical case where the density of the grand thermodynamic potential is dependent on the first and second coordinate derivatives of the scalar order parameters. Our approach is applied to several models of inhomogeneous ionic liquids that consider electrostatic correlations of ions or short-range correlations related to packing effects. Specifically, we derive analytical expressions for the symmetric stress tensors of the Cahn–Hilliard-like model, Bazant–Storey–Kornyshev model, and Maggs–Podgornik–Blossey model. All of these expressions are found to be consistent with respective self-consistent field equations. [ABSTRACT FROM AUTHOR]

Flexoelectricity is often studied at the macroscopic scale for energy conversion and harvesting. The fact that microstructural heterogeneities can have a profound impact on a material's flexoelectric response has been under-appreciated and largely unexplored. To capture the effects of microstructure on both the macroscopic flexoelectric behavior and the development of microscopic electric field that drives such microscale processes, we develop a computational framework that enables the quantification of how the microstructure can influence the flexoelectric behavior of heterogeneous materials. The specific material evaluated is a porous composite of tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride polymer and aluminum (Al) particles. The models explicitly resolve the Al particles and voids within the microstructure. The focus of the analysis is on assessing the physical mechanisms that enhance the macroscopic flexoelectric output and determining the effective flexoelectric coefficient of the inhomogeneous material. The approach also allows the contributions of individual strain gradient components to the effective flexoelectric coefficient to be delineated and offers a method of determining the flexoelectric coefficients associated with individual strain gradient components using measurements of the macroscopic flexoelectric responses of microstructures with different concentrations of Al particles and voids. It is concluded that the enhancement of local strain gradients near the Al particles and voids and the activation of contributions from multiple strain gradient components are the primary mechanisms for the increase in the macroscopic flexoelectric output of the composites. The macroscopic flexoelectric coefficient under cantilever beam bending is found to rise linearly with the Al content, consistent with the experimental measurements. [ABSTRACT FROM AUTHOR]

Dedicated coating materials for anechoism and furtivity in underwater acoustics must exhibit a strong reliability regarding their mechanical resistance to hydrostatic pressure. Soft porous materials, especially, a distribution of soft porous beads within a polyurethane matrix, have been previously proposed as an acoustic insulator device. The purpose of the present letter is to investigate the attenuation efficiency of soft porous silicone beads-based materials while being exposed to uniaxial loads mimicking hydrostatic pressures encountered in underwater acoustics. The acoustic performance of this locally resonant material is then compared to the classical coating technology using micro-balloons. The use of an adapted surfactant (a silicone alkyl polyether compound) in the fabrication process of the soft porous silicone-based beads, obtained through an emulsion templating process, leads to particles exhibiting an open porosity. The (resonant) attenuation of the soft porous beads-based material remains greater than the micro-balloons-based material until several bars. Above this critical resilience value, the mechanical stress irreversibly damages the soft porous beads. [ABSTRACT FROM AUTHOR]

The composition and thickness of the interphase are critical factors affecting the strength of SiC/SiC materials. Therefore, SiC/(BN/PyC)/SiC ceramic matrix composites with varying PyC thicknesses were fabricated, and the mechanism by which thickness influences the mechanical properties of the materials was investigated. During the fracture process of the composites, debonding and crack deflection predominantly occurred at the BN/PyC interface. The PyC interphase thickness emerged as a critical factor influencing the mechanical performance of composites. The residual stresses within the PyC and its adjacent SiC matrix were determined by analyzing shifts in Raman peak positions. The findings indicate that a reduction in PyC thickness leads to an increase in residual compressive stress within the PyC and a corresponding increase in residual tensile stress within the SiC matrix, which increases the interfacial shear stress and improves the mechanical properties of the composites. [ABSTRACT FROM AUTHOR]

To understand the differences in material removal behavior during grinding for different ceramics, scratching of Al 2 O 3 , AlN, Si 3 N 4 and ZrO 2 (3Y-TZP) ceramics by a cube-corner diamond indenter was investigated in this paper. Scratching characteristics, including material deformation, scratching force, coefficient of friction (COF) and scratching damage of different ceramics were compared and analyzed. Elastic recovery rate model and stress field model were built to analyze the mechanism of material deformation and scratching damage during scratching on different ceramics. The results demonstrated that material deformation behaviors vary significantly, and depend on mechanical properties of the ceramics. Ceramics with higher hardness exhibit shallower penetration depth of scratching, while higher fracture toughness results in shorter maximum surface damage distance. Elastic recovery rate model can predict the extent of material deformation. The ceramic with the highest elastic recovery rate is Al 2 O 3 , followed by Si 3 N 4 , ZrO 2 , and finally AlN. Elastic recovery rate decreases with increase in force. In stress field model, AlN exhibits the highest maximum principal stress, followed by Al 2 O 3 and Si 3 N 4 , with ZrO 2 displaying the lowest stress. These distribution patterns are consistent with the results of scratching damage pattern. [ABSTRACT FROM AUTHOR]

The adhesion stability of a film on its substrate is essential for enhancing and maintaining the protective performance of the film. In this study, titanium nitride (TiN) films were deposited on Mg alloy (ZM21) substrates with roughness values (Ra) of 200, 400, and 600 nm by magnetron sputtering. The effects of the substrate roughness on the film residual stress, adhesion strength, and wear resistance were studied. The results indicated that the residual stress of the film decreased as the substrate roughness increased. Adhesion is affected by a combination of the balance of film residual stresses and mechanical anchorage and the distribution of stresses on the rough surface. The TiN film on a substrate with a Ra of approximately 400 nm exhibited optimal adhesion strength. The wear resistance decreased with increasing Mg substrate roughness. Both the film residual stress and adhesion strength of the TiN film deteriorated after natural storage for 60 d, and the TiN film on the substrate with a Ra of 400 nm had optimal adhesion stability. [Display omitted] • The compressive residual stress of the TiN films decreased with increasing Mg substrate roughness. • Adhesion is affected by film residual stresses, mechanical anchorage, and the distribution of stresses on the rough surface. • The TiN film with a substrate roughness of approximately 400 nm exhibited the best adhesion strength and stability. [ABSTRACT FROM AUTHOR]

Structural analysis is a challenge for the application of ceramic matrix composite at present. On one hand, the macro-homogenization method cannot consider mesoscopic non-periodicity, therefore it is difficult to ensure accuracy. On the other hand, directly performing finite element calculations on the mesoscopic model is unacceptable since the model is too large to be solved. The super-element method is developed in the present study to balance the calculation accuracy and efficiency. The modification of the stress-strain field by the material properties is considered, and the modified strain method and the modified stress method are proposed. Establishment of the super-element method for weighted averaging of the two methods according to the degree of damage. The simulation calculations of the super-element model for the non-periodic CMC dovetail were carried out, which verified that the super-element method proposed is accurate. [ABSTRACT FROM AUTHOR]

In this paper, nonlinear vibrational behaviors of doubly-curved functionally graded piezoelectric (FGP) microshells in thermal environments have been studied. The doubly-curved microshell has been modeled by using modified couple stress and thin shell theories. The microshell has two material constituents which are piezoelectric materials and their gradation is described using power-law functions. Temperature fields are considered to be uniform, linear, and nonlinear. A closed-form of nonlinear vibration frequency has been obtained by analytically solving the governing equations using the Harmonic balance method. It will be demonstrated that nonlinear vibrational frequency of doubly-curved microshell relies on couple stress influence, material gradation, curvature radius, center deflection, and electrical field. [ABSTRACT FROM AUTHOR]

Considering the importance of correctly understanding the dynamics of microstructure materials for their applications in related technologies, by eliminating the shortcomings and some overlooked physical concepts in the existing asymmetric elastic theories, we have presented an asymmetric elastodynamic model based on a $ U(1) $ U (1) gauge theory with quantum electrodynamics (QED) structure. Accordingly, we have shown that there is a correspondence between an elastic theory, which can explain the behavior of elastic waves within an asymmetric elastic medium and QED. More specific, we have indicated that the corresponding elastic wave equations are somehow analogous to QED ones. In this regard, by adding vibrational degrees of freedom and introducing a gauge property of the waves of displacement for the waves of rotation, we have generalized and modified the related Cosserat theory (CT) for an elastic environment. Thus on macro scales, the elastic waves can possess the QED treatment. This analogy provides a new paradigm of fermions and bosons. Also, from experimental point of view, we have shown that the behavior of elastic waves in a granular medium is equivalent to behavior of light in dispersive media, which can be explained using QED. Hence, contrary to the Cosserat and discrete models, this amended CT has qualitatively been indicated to be consistent with the corresponding empirical observations. [ABSTRACT FROM AUTHOR]

In the current report, wave propagation analysis of a sandwich doubly curved nanopanel considering a laminated composite core and a couple of face sheets of magneto-electro-elastic (MEE) in the framework of nonlocal strain gradient theory (NSGT) is investigated. The higher-order-shear-deformable (HSD) model is employed to obtain the formulation of strain–stress equations. Maxwell equations are employed for modeling the behaviors of MEE materials. By considering Hamiltonian, the current model's governing equations have been extracted. Afterward, in order to analyze the influence of wavenumber, inserted ampere, inserted voltage, the laminated structure's geometry, nano-sized mechanics impact on the smart sandwich nano-scaled panel's phase velocity, a parametric study has been considered. It is also observed that by raising the electric potential, the number of critical waves could be likely to be increased. A useful suggestion of this study is that the influence of the magnetic field on the phase velocity is more than the influence of the electric field of the MEE panel on the wave propagation of the smart panel. Besides, the nonlocal parameter and phase velocity have an exponential negative relation, while the length scale parameter and phase velocity have a linear direct relation. [ABSTRACT FROM AUTHOR]