Weak Interlayer Research Articles

Tuning the metal–semiconductor contact nature in MXene-based van der Waals heterostructures

Two-dimensional (2D) transition metal carbides, nitrides, or carbonitrides (MXenes) have emerged as promising ultrathin materials for nanoelectronics and optoelectronics. However, the contact barrier at metal–semiconductor (MS) junctions still significantly limits the device's performance. Here, we propose a novel strategy—functionalizing accompanied with external electric fields—to tune the MS contact nature in MXene-based van der Waals (vdW) heterostructures, taking 2D Ti2C as an example, by means of first-principles calculations. Different Ti2CO2/Ti2CX2 (X = OH or S) vdW heterostructures are designed via functionalizing Ti2C metals to contact with 2D Ti2CO2. We reveal that OH functionalized vdW MS heterostructure (Ti2CO2/Ti2C(OH)2) can be tuned to the Ohmic contact owing to the strong interlayer interaction inducing a large number of interlayer transferred electrons; while for the sulfurized vdW MS heterostructure (Ti2CO2/Ti2CS2), its Schottky barrier height and contact type can be effectively tuned by external electric field due to the rather weak interlayer interaction. Our work paves a new way for the construction of 2D MXene-based vdW MS heterostructures and demonstrates the great potential of 2D MXenes in future nanoelectronics and optoelectronics.

Characterizing large-scale weak interlayer shear zones using conditional random field theory

The shear behavior of large-scale weak intercalation shear zones (WISZs) often governs the stability of foundations, rock slopes, and underground structures. However, due to their wide distribution, undulating morphology, complex fabrics, and varying degrees of contact states, characterizing the shear behavior of natural and complex large-scale WISZs precisely is challenging. This study proposes an analytical method to address this issue, based on geological fieldwork and relevant experimental results. The analytical method utilizes the random field theory and Kriging interpolation technique to simplify the spatial uncertainties of the structural and fabric features for WISZs into the spatial correlation and variability of their mechanical parameters. The Kriging conditional random field of the friction angle of WISZs is embedded in the discrete element software 3DEC, enabling activation analysis of WISZ C2 in the underground caverns of the Baihetan hydropower station. The results indicate that the activation scope of WISZ C2 induced by the excavation of underground caverns is approximately 0.5–1 times the main powerhouse span, showing local activation. Furthermore, the overall safety factor of WISZ C2 follows a normal distribution with an average value of 3.697.

Mechanical Analysis of Road Graben Slopes Based on Saturated-Unsaturated Seepage Theory

As the construction of mountainous highways continues to heat up, the stability analysis of road graben slopes becomes one of the current research hotspots. In this paper, based on the saturated-unsaturated seepage theory, the force analysis of the road graben slope under rainfall conditions and its laws are studied. Firstly, the damage mode of the road graben slope and its three damage stages of creeping deformation, sliding damage and tendency to stability are summarized according to the engineering practice and literature survey, and the right side of the road graben slope from K316+439 to K316+859 of Longlian Expressway is monitored, so as to amend the next theoretical analysis. The three stages of rainfall infiltration were analyzed, the state variables and material variables of soil water were selected according to the continuous medium theory and the soil water suction analysis was carried out. Based on the saturated-unsaturated seepage theory, the fluid-structure interaction mathematical model and soil moisture characteristic curve (SWCC) model under rainfall infiltration conditions were established, and the stress of the cutting slope under saturation conditions was analyzed. The experimental results show that for the soil at the foot of the slope, the infiltration depth of rainfall is limited due to the low permeability coefficient, and the change of seepage field is not obvious; the longer the rainfall is held, the deeper the infiltration depth is, and the rainfall will continuously replenish the groundwater, so the force on the slope of the road graben will increase continuously and finally reach the limit of damage. When the rainfall intensity is 5mm-h-1, the decline of stability coefficient for 48 h is 0.121; the initial stability coefficient of the slope is the largest when the dip angle of the weak interlayer is equal to 25∘, and the stability coefficient decreases rapidly with the rainfall time, and when the rainfall reaches 60 h, the stability coefficient tends to be stable and the equilibrium of the slope force no longer changes.

Anomalous Elastic Evolution Induced by Copper Hopping in van der Waals Ferroelectric CuInP2S6

AbstractVan der Waals (vdW) ferroelectric CuInP2S6 (CIPS) has great potential in post‐Moore's law electronics owing to their advantages of weak interlayer interaction, stable surface with free dangling bonds, and robust switchable spontaneous polarization. The flexoelectric effect is demonstrated as an alternative switching method for the design of ferroelectric domains in layered vdW CIPS. However, the investigation of the correlation between the polarization and elastic properties remains indistinct. Here, an elastic evolution is explored experimentally and theoretically in layered vdW CIPS with temperature, of which Young's modulus (EYoung) is determined by analyzing the force‐indentation responses of vdW ferroelectric CIPS. Interestingly, an anomalous leap in EYoung of CIPS from 35 to 65 GPa occurs when the temperature rises across the Curie temperature TC of ≈315 K. Deep potential molecular dynamic (DPMD) simulations identify that this abnormal behavior can be attributed to temperature‐dependent change of copper distribution and the local copper dynamic hopping, intertwined with the order‐disorder ferroelectric phase transition, which is quite different from the typical decrease of EYoung in the lattice constant due to temperature increasing. The exploration provides an important reference for the analysis of coupled mechanical properties and ferroelectricity in CIPS and its applications in flexible electronics.

Stability and probabilistic assessment of a large asymmetric bedding slope with a weak interlayer.

The mining of open-pit mines has a significant influence on the surrounding ecological environment and safety. Once the slope of an open pit is unstable, it will bring extremely severe disasters to the surrounding environment. The south slope of the Fushun West open-pit mine is a large bedding slope with weak interlayer and asymmetrical features between the eastern and western regions. The different deformation mechanisms are worth further discussion, and the deformation mechanism of the eastern region needs to be systematically investigated. In this study, a comprehensive method combining a numerical model, the limit equilibrium method, and a probabilistic approach is used. The different deformation mechanisms of the slope are explored. Thereafter, the sensitivity of the geometric and mechanical parameters of the slope is determined. Finally, the probability of failure (PF) and slope stability are evaluated. The results illustrate that the difference in geological characteristics and constraint conditions is the fundamental reason for the difference in deformation features of the slope. The sensitivity analysis results show that the friction angle of the weak layer exhibits the most sensitivity and that the unit weight is irrelevant to the slope stability. Taking the friction angle of the weak layer as a variable, when thethickness of the basalt layer is less than 140 m and the height of the slope is more than 360 m, the PF of the slope reaches a high value. When the inclination of the weak layer exceeds 30°, the PF of the slope increases to a high value. When the Ru coefficient exceeds 0.2, the slope presents a high PF. The results illustrate that decision-makers should pay attention to the strength degradation, transitional mining of the basalt layer, and establish a good drainage system. The comprehensive method can also provide an effective way to assess the stability and PF of similar large-scale bedding slopes under complex geological conditions.

Mechanical characterization of intermittent weak interlayer based on DIC and acoustic emission technique

Current research on intermittent structural surfaces tends to concentrate on intermittent joints, often neglecting the abundance of intermittent weak interlayers present in rock structures. To analyze the effect of intermittent weak interlayer on the mechanical properties of rock mass, specimens with varied interlayer thickness and dip angles were prepared and subjected to uniaxial compression tests using an acoustic emission system and Digital Image Correlation (DIC) technique. The results revealed an inverse relationship between the interlayer thickness (t) and dip angle (θ), and the uniaxial compressive strength. Through a nonlinear fitting method, an empirical strength equation for these interlayers was established. Acoustic emission (AE) counts and cumulative acoustic emission counts increased with loading, and the RA-AF values indicated that the specimens were dominated by shear damage, and the larger the thickness and dip angle of the interlayer, the higher the proportion of shear damage. In terms of failure mode, the greater the thickness of the interlayer, the lower the level of development of cracks other than the main crack, and the greater the dip angle of the interlayer, the fewer the number of wing cracks required for specimen failure and the lower the degree of wing crack development. The increase in interlayer thickness and dip angle resulted in a specimen structure that was more susceptible to damage. The actual crack initiation angles agree with the theoretically calculated angles based on the maximum tensile stress theory. These findings emphasize the critical role of these parameters in influencing the failure mode of rocks.

Numerical Simulation and Experimental Study Regarding the Cross-Sectional Morphology of PEEK Monofilament Deposition During FDM-Based 3D Printing.

Polyether-ether-ketone (PEEK) is widely used in the field of biomedical engineering because of its excellent mechanical properties, chemical stability, and biocompatibility. Fused deposition modeling (FDM), which is a typical 3D printing process, can achieve low-cost and high-efficiency printing of complex PEEK structures. However, poor monofilament deposition quality leads to rough surfaces on macroscopic printed parts, low dimensional accuracy, and weak interlayer bonding, which are urgent problems to be solved. In this study, considering the shear thinning characteristic of PEEK, a numerical model for monofilament deposition was constructed by using the finite volume method. This model revealed the influences of process parameters on the monofilament cross-sectional profiles and achieved predictions of monofilament cross-sectional profiles during FDM-based 3D printing of PEEK. The average relative error of the monofilament cross-sectional area predictions was 7.68%. The average relative error of the monofilament cross-sectional aspect ratio predictions was 12.06%. It was also found that there are three typical deposited monofilament cross-sectional profile shapes, i.e., a capsule shape, a bread shape, and a circular shape. These three shapes occurred because of the combined effect of the layer thickness and the extrusion width during the extrusion and deposition of PEEK. These revealed monofilament cross-sectional profiles provide the basis for accurate nozzle motion trajectory planning, and they lay a foundation for surface roughness predictions and dimensional accuracy control during the FDM-based 3D printing of PEEK.

Self-assembled VS2 microflowers buffering volume change during charging and discharging towards high-performance zinc ion batteries

VS2 has attracted increasing attention as a cathode material for aqueous zinc ion batteries because of its proper large layer spacing, weak interlayer interactions, multiple valence states of V, and excellent electrical conductivity, but its large volume change during charging and discharging leads to poor cycling stability. Herein, we report a one-step hydrothermal synthesis of VS2 microflowers with proper lamellar spacing, which provides a stable framework for the insertion/deinsertion of zinc ions and enhances the cycling stability, delivering an initial charge capacity of 128.3 mAh g−1 at 3 A g−1 and maintains a charge capacity of 100.1 mAh g−1 after 900 cycles. In addition, the optimized VS2 cathode shows specific capacities of 215.7 and 150.5 mAh g−1 at the current densities of 0.1 and 2 A g−1, respectively, demonstrating that the microflower structure with a high specific surface area and a short diffusion distance also significantly enhances the rate performance.

Experimental study on contact erosion at the interface between the weak interlayer and the crushed zone

Contact erosion, one type of internal erosion, is a significant risk to the dam’s safety. Weak interlayer, one of the weakest elements in rock foundations, is vulnerable to contact erosion. In this study, a newly developed triaxial apparatus was employed to investigate the contact erosion at the interface between the weak interlayer and the crushed zone under high triaxial pressure and high water-head. The effects of confining pressure, fines content, and crack width on the initiation of contact erosion were analyzed. The test results reveal that: (1) with increasing confining pressure, the critical hydraulic gradient increased linearly; (2) contact erosion initiated at a relatively low hydraulic gradient in low fines content soil and the critical hydraulic gradient nonlinearly increased with the increase of fines content, which was mainly caused by the contact force distributions of various contact types; (3) increasing crack width linearly reduced the critical hydraulic gradient; (4) the combined effects of confining pressure, fines content, and crack width on the critical hydraulic gradient revealed that fines content had the most significant impact at lower values of fines content, while confining pressure had the most significant impact at higher values of fines content. The experimental results here can be applied to estimate the onset and development of contact erosion at the interface between the weak interlayer and the crushed zone. Furthermore, they also can provide guidance for the embankment dam safety analysis.

On understanding the mechanical properties and damage behavior of Cf/SiC composites by indentation method

Carbon fiber reinforced silicon carbide ceramic matrix (Cf/SiC) composites have the advantages of high temperature resistance, wear resistance, low density, high hardness as well as specific strength. They have been applied extensively in hot-end components of aerospace and braking systems of trains. Nevertheless, grappling with the anisotropy, non-homogeneity, and weak interlayer bonding of Cf/SiC composites presents a major challenge for achieving efficient and low-damage processing. This paper is primarily intended to investigate comprehensively the mechanical properties and damage behavior of Cf/SiC composites by nanoindentation and Vickers indentation tests. The behaviors of indentation damage on the longitudinal section of fiber (LSF), the cross-section of fiber (CSF) and matrix under different loads and the deflection mechanism of matrix crack were analyzed. The findings reveal a pronounced anisotropy between the radial and axial orientations of the fiber, and plastic deformation exists in the matrix. Furthermore, the matrix has the largest hardness and elastic modulus, while the LSF displays the lowest values among the composites. The main forms of indentation damage on the LSF are fiber crack, fiber peel off, fiber cocked up and squamous crack. The main manifestations of indentation damage on CSF are fiber crushing and fiber debonding, with the total surface damage area being comparatively limited. The fiber orientation and interface are influential factors in the crack propagation path of matrix. Notably, the fibers effectively inhibit the crack propagation of the matrix. This investigation provides valuable theoretical guidance for the formation mechanism and suppression strategy of machining damage in Cf/SiC composites.

Towards layer-selective quantum spin hall channels in weak topological insulator Bi4Br2I2

Weak topological insulators, constructed by stacking quantum spin Hall insulators with weak interlayer coupling, offer promising quantum electronic applications through topologically non-trivial edge channels. However, the currently available weak topological insulators are stacks of the same quantum spin Hall layer with translational symmetry in the out-of-plane direction—leading to the absence of the channel degree of freedom for edge states. Here, we study a candidate weak topological insulator, Bi4Br2I2, which is alternately stacked by three different quantum spin Hall insulators, each with tunable topologically non-trivial edge states. Our angle-resolved photoemission spectroscopy and first-principles calculations show that an energy gap opens at the crossing points of different Dirac cones correlated with different layers due to the interlayer interaction. This is essential to achieve the tunability of topological edge states as controlled by varying the chemical potential. Our work offers a perspective for the construction of tunable quantized conductance devices for future spintronic applications.

Influential factors on mechanical properties and microscopic characteristics of underwater 3D printing concrete

Underwater 3D Printing Concrete (U3DPC) technology can be a promising approach to address the challenges of renewable marine energy and coastal protection. Conducting extensive research on the mechanical properties of U3DPC is crucial for its successful implementation. This study investigates various factors, including printing environment, construction methods (mold-cast and printing), curing age, and material composition, regarding their significance on the mechanical properties of U3DPC. The compressive strength, anisotropy, interlayer bonding, and interface microstructure are evaluated. The research findings reveal that compared to casting specimens in air, the printing method and water environmental factors result in approximately 20% and 15.1% reduction in the compressive strength of U3DPC, respectively. U3DPC exhibits different anisotropic variations compared to specimens printed in air, attributed to weak interlayer bonding interfaces caused by external water. The influence of material components on the interlayer bonding strength of U3DPC has a critical threshold that should not be exceeded; otherwise, it weakens the interlayer bonding. The variation in fine aggregate types and fibers leads to changes in interlayer interface roughness, where excessive roughness captures more ambient water due to the “dog-tooth overlapping” structure, thereby reducing the adhesive capacity. The pore distribution reveals the underlying mechanism of how interface roughness affects interlayer bonding.

Numerical Simulation Analysis of Wellbore Stability in Weak Interlayer of Igneous Rock

Numerical Simulation Analysis of Wellbore Stability in Weak Interlayer of Igneous Rock

Study on the risk of seepage field of Qiantang River underground space excavated in water-rich rheological rock area

Abstract With the rapid development of underwater space construction, the theoretical research is at the initial stage. At present, the theoretical research methods mainly include mirror image method and conformal transformation method. At present, almost all the research objects in analytical research are homogeneous soil layers. However, in practical engineering, soil layers are often distributed in layers. In this study, the seepage field of layered soil layers is analyzed, and the analytical derivation method of seepage field in heterogeneous media based on traditional conformal transformation method is given, which is verified by numerical simulation. The hydraulic head loss of the medium with better permeability in shallow layer is very small, and the streamline is vertically distributed. In the weak interlayer, the hydraulic head loss is huge, and the streamline bends greatly, showing a strong horizontal distribution and converging towards the center. It can provide theoretical basis for the design of water and soil pressure in practical engineering.

Controllable growth of 2D ReS2 flakes and their surface Raman enhancement effects

Two-dimensional (2D) ReS2 has received widespread attention because of its unique anisotropic properties, weak interlayer interactions and broad application prospects. Therefore, the controllable and repeatable growth of 2D ReS2 flakes is very important for studying their properties and practical applications. In this work, 2D single-crystalline ReS2 flakes with different layer numbers were synthesized on mica substrates using chemical vapor deposition (CVD) by adjusting the distance between the mica substrate and Re source, and the growth mechanism was further discussed. The fluorescence quenching effect and surface-enhanced Raman scattering (SERS) effect of 2D ReS2 flakes were investigated using rhodamine B (RhB), crystal violet (CV) and malachite green (MG) dye molecules as Raman probes. The results show that the fluorescence quenching effect and SERS effect of 2D ReS2 flakes are enhanced with decreasing layer number. The lowest detection limits on monolayer ReS2 flake substrates are 10−10 M, 10−9 M and 10−8 M for RhB, CV and MG under 532 nm laser excitation, respectively. 2D ReS2 flakes used as a sensitive SERS-active substrate have excellent uniformity and stability. The surface Raman enhancement mechanism of 2D ReS2 flakes was discussed.

Strong Ti3 C2 Tx MXene-Based Composite Films Fabricated through Bioinspired Bridging for Flexible Energy Storage Devices.

Flexible energy storage device is one of the most critical components as power source for wearable electronics. The emergence of MXenes, a growing family of 2D nanomaterials, has demonstrated a brand-new possibility for flexible energy storage. However, the fabrication of MXene films with satisfactory mechanical, electrical, and electrochemical reliabilities remains challenging due to the weak interlayer interactions and self-restacking of MXene sheets. Sequential bridging of polydopamine/polyethyleneimine-functionalized (PDA/PEI)-coated MXene sheets to induce synergistically covalent and hydrogen binding connections of MXene-based films is demonstrated here. By interrupting self-hydrogen bonding and π-π stacking interactions, the introduction of long-chain PEI can not only inhibit the massive aggregation of PDA, but also improve the continuity of the interconnection network of PDA/PEI between MXene layers. Hence, the as-prepared MXene/PDA/PEI composite film displays high mechanical strength (≈366MPa) which achieves 12-fold improvement compared with pure MXene film, as well as superior energy storage capability (≈454Fg-1 at 5mVs-1 ) and rate performance of ≈48% at 10000mV s-1 . This modulation of inserted polymer between MXene layers can provide an avenue for assembling high performance MXene films, and can even be extended to the fabrication of other 2D platelets for varied applications.

Stacking and thickness effects on cross-plane thermal conductivity of hexagonal boron nitride

Recently, the in-plane thermal transport in van der Waals (vdW) materials such as graphene, hexagonal boron nitride (h-BN), and transition metal dichalcogenides (TMDs) has been widely studied. Whereas, the cross-plane one is far from sufficient. Based on the non-equilibrium molecular dynamics simulations and Boltzmann transport equation, here we reveal the stacking and thickness effects on the cross-plane thermal conductivity (κ) of h-BN. We find that κ can be significantly modulated by both the stacking structure and thickness (d) of h-BN, which is unexpected from the viewpoint of its smooth in-plane structure and weak interlayer interaction. In the small thickness region (d < 6 nm), κ of h-BN at room temperature significantly increases with thickness, following a power law of κ∝dβ withβ = 0.84, 0.66, and 0.92 for AA', AB, and AB' stacking structures, respectively. Moreover, κ of AB' structure reaches up to 60% larger than that of AA' and AB structures with d = 5.3 nm, showing the remarkable stacking effect. We also find that the stacking effect on κ changes dramatically with d increasing, where AA' stacking has the largest κ with d > 200 nm. We finally clarify that such exotic stacking and thickness dependence of κ is owing to the competing effect of excited number of phonons and phonon relaxation time, both of which directly affect the thermal conductivity. Our findings may provide new insights into the cross-plane thermal management in vdW materials.

Increased interlayer bonding strength of short carbon fiber composite fabricated by material extrusion via warm isostatic pressing (WIP) process

Recently, short carbon fiber-reinforced plastic (SFRP) has been selected as a filament material to improve the strength of components fabricated by material extrusion (ME). However, despite the improved material properties, the weak interlayer bonding and voids present in the microstructure constitute defects that cause anisotropy in the SFRP composite and deteriorate its mechanical properties such as the tensile, compressive, and flexural strengths. In this study, warm isostatic pressing (WIP) was investigated as a means to increase the interlayer bonding force and reduce the voids. To increase the efficiency of WIP, vacuum packing was investigated as a means to promote interfacial strength and diffusion between the layers. The WIP process improved the tensile, compressive, and flexural properties, and the anisotropy decreased with increasing interlayer bonding force. In addition, the thermal properties improved with an increase in the degree of crystallinity, and the voids in the microstructure were effectively reduced. These results indicate that WIP is a promising post-processing treatment for ME-fabricated SFRP parts.

Magnetic bubbles with alternating chirality in domain walls

In magnetic multilayers with perpendicular anisotropy, the competition of short-range and long-range interactions gives rise to the stability of cylindrical magnetic domains, also known as magnetic bubbles. The presence of Dzyaloshinsky-Moriya interaction induced by asymmetric interfaces between magnetic and nonmagnetic layers may lead to the formation of cylindrical bubble domains with Neel-type domain walls across the whole thickness of the multilayer. Such domain walls produce no contrast in Lorentz TEM under the normal incidence of the electron beam to the film. The latter is often used as an argument for the presence of Dzyaloshinskii-Moriya interaction in the system. Here we show that in magnetic multilayers, the absence of the Lorentz TEM contrast might also have another origin. In particular, in the absence of interfacial Dzyaloshinskii-Moriya interaction and weak interlayer exchange coupling, the magnetic bubbles might have Bloch-type domain walls of alternate chirality in adjacent layers. Such domain walls also do not produce magnetic contrast in Lorentz TEM at normal incidence of the electron beam. We show that, in the absence of interlayer exchange coupling, the magnetic bubble domains with the domain walls of fixed and alternate chirality have nearly identical energies and can coexist in the same range of magnetic fields. Using the geodesic nudged elastic band method, we prove that these states are separated by finite energy barriers. Furthermore, we demonstrate that magnetic multilayers with only dipolar coupling, besides the magnetic bubbles with nontrivial topology in all layers, can accommodate solutions with trivial topology within the internal layers.

The effects of weak interlayers on the dynamic mechanical properties and failure behaviours of rocks: A combined numerical and experimental analysis

Rock strata often contain weak interlayers, and it is vital to understand how rocks respond to dynamic loads for predicting natural disasters such as earthquakes and landslides. In this paper, a combined numerical and experimental analysis is carried out to investigate the dynamic properties and failure behaviours of specimens with and without a weak interlayer. Specifically, split Hopkinson pressure bar tests are employed, and numerical simulations of these tests are developed in the framework of the extended finite element method. Additionally, the feasibility of the proposed numerical method for modelling the split Hopkinson pressure bar is verified by comparison with laboratory tests. The results demonstrate that the existence of a material interface or a weak interlayer in the specimen can cause stress concentrations under dynamic stress waves and that the failure behaviours of the specimen can also be changed. Evidently, the failure pattern in the intact specimen consists of a compression‒shear failure pattern and a tensile failure pattern. The failure pattern in the specimen containing a persistent flaw is the compression‒shear failure pattern, and the failure pattern in the specimen containing a weak interlayer consists of a compression‒shear failure pattern and a tensile failure pattern, in which the number of tensile cracks increases with increasing thickness of weak interlayers in the specimen.