Interlayer Interaction Research Articles

Scalable Synthesis and Electrocatalytic Performance of Highly Fluorinated Covalent Organic Frameworks for Oxygen Reduction.

In this study, we present a novel approach for the synthesis of covalent organic frameworks (COFs) that overcomes the common limitations of non-scalable solvothermal procedures. Our method allows for the room-temperature and scalable synthesis of a highly fluorinated DFTAPB-TFTA-COF, which exhibits intrinsic hydrophobicity. We used DFT-based calculations to elucidate the role of the fluorine atoms in enhancing the crystallinity of the material through corrugation effects, resulting in maximized interlayer interactions, as disclosed both from PXRD structural resolution and theoretical simulations. We further investigated the electrocatalytic properties of this material towards the oxygen reduction reaction (ORR). Our results show that the fluorinated COF produces hydrogen peroxide selectively with low overpotential (0.062 V) and high turnover frequency (0.0757 s-1) without the addition of any conductive additives. These values are among the best reported for non-pyrolyzed and metal-free electrocatalysts. Finally, we employed DFT-based calculations to analyse the reaction mechanism, highlighting the crucial role of the fluorine atom in the active site assembly. Our findings shed light on the potential of fluorinated COFs as promising electrocatalysts for the ORR, as well as their potential applications in other fields.

Synthesis of a novel polysiloxane as an inhibitor in water-based drilling fluids and an assessment of the inhibition mechanism

In oil and gas well engineering, shale wellbore stability poses significant challenges. Developing shale inhibitors with high inhibition and resistance to elevated temperatures is crucial to address wellbore stability in deep wells. In this study, an amphoteric polysiloxane known as SC-POTD was synthesized as a heat-resistant shale inhibitor for water-based drilling fluid. The inhibition properties were evaluated using linear swelling, rolling recovery, and rheological tests, and the results were compared with the properties of potassium chloride and commercial polyamines. Various analysis methods were conducted to understand the interaction mechanism between the clay particles and polymer molecules, including X-ray diffraction test, Zeta potential determination, particle size analysis, contact angle measurement, and scanning electron microscope observation. SC-POTD with an amphoteric structure can effectively adsorb on the clay surface through electrostatic force, compressing the electric double layer of clay and forming a hydrophobic layer. Furthermore, SC-POTD can embed in the crystal interlayer, exchange cations and discharge interlayer water, effectively inhibiting hydration. With the flexibility of the Si-O backbone and the small steric hindrance of methyl side groups, SC-POTD may have a better affinity with bentonite containing siloxane tetrahedrons, and cooperate with the quaternary ammonium group to enhance clay interlayer interaction. In addition, the temperature resistance of SC-POTD can be improved by the siloxane backbone with larger bond energy. The results indicated that modified polysiloxane may find a promising application as heat-resistant drilling fluid additives.

Construction of alternating multilayer films with stable absorption-dominated electromagnetic shielding performance and reinforced mechanical properties via interface engineering

As an ideal material to lessen electromagnetic pollution, absorption-dominated electromagnetic interference (EMI) shielding composites still face the problems of complicated structure design and insufficient performance stability. Herein, an alternating multilayer film with stable absorption-dominated EMI shielding effectiveness (SE) and reinforced mechanical properties is fabricated by constructing hydrogen bonding between multilayers interface. When the layers increase to 4, benefiting from the construction of multilayer structure and the stronger interaction, the reflective shielding effectiveness decrease to 2.9 dB, the absorption coefficient of multilayer film increases from 0.13 to 0.52, the retention rate of EMI SE increases from 1.0 % to 97.6 % after bending 1000 cycles, and the tensile strength is enhanced from 5.7 MPa to 27.3 MPa. The calculated binding energies and the experimental results show that the interaction between Pluronic F127 anchored on the porous film and cellulose nanofibers entangled on the carbon nanotubes layer increases the interlayer interaction force and durability of EMI SE.

Interfacing differently oriented biaxial van der Waals crystals for negative refraction

Abstract Negative refraction has a wide range of applications in diverse fields such as imaging, sensing, and waveguides and typically entails the fabrication of intricate metamaterials endowed with hyperbolic features. In contrast to artificially engineered hyperbolic materials, natural van der Waals (vdW) materials are more accessible owing to their inherent strong in-plane covalent bonding and weak interlayer interactions. However, most vdW materials manifest uniaxial crystal properties, which restrict their behavior solely to out-of-plane hyperbolicity. This characteristic poses a considerable challenge to their seamless integration via planar fabrication techniques, unless a suitable pattern is employed. Recent advances have identified natural biaxial α-MoO3 as a promising vdW material capable of exhibiting in-plane hyperbolicity. In this study, we performed numerical simulations demonstrating that negative refraction could be achieved by interfacing differently oriented α-MoO3 slabs coated with tunable graphene on a gold substrate. Our comprehensive analysis yielded three notable outcomes: negative refraction, simultaneous positive and negative refractions, and diffractionless propagation. These outcomes could be operated in a broad range of frequencies and achieved at all angles to offer a superior platform for the flexible manipulation of mid-infrared polaritons. Our findings provide valuable insights into the potential application of other two-dimensional vdW materials for advances in nanoscale super-resolution imaging, molecular sensing, and on-chip photonic integrated circuits.

Towards skyrmion crystal stabilization in the antiferromagnetic triangular lattice at ambient conditions

We explore possibilities of stabilizing a skyrmion lattice (SkX) phase in the frustrated antiferromagnetic (AF) Heisenberg model with the Dzyaloshinskii–Moriya interaction on a triangular lattice at ambient conditions. We show that by stacking multiple AF layers and coupling them with strong ferromagnetic (F) interaction the SkX phase stability temperature window can be extended by several times. The transition temperature increase is supported by the increasing number of layers and interlayer interaction and thus room-temperature SkX phase could be achievable by proper tailoring of the multilayer structure. Further, we demonstrate that in the sandwich heterostructure, obtained by inserting a stiff F layer in between two AF layers, the required external magnetic field can be completely replaced by the effective field imposed by the F layer. Thus, one can design a heterostructure with the SkX phase stabilized at relatively high temperatures and zero field - the environment favorable for technological applications.

Layer-dependent excellent thermoelectric materials: from monolayer to trilayer tellurium based on DFT calculation.

Monoelemental two-dimensional (2D) materials, which are superior to binary and ternary 2D materials, currently attract remarkable interest due to their fascinating properties. Though the thermal and thermoelectric (TE) transport properties of tellurium have been studied in recent years, there is little research about the thermal and TE properties of multilayer tellurium with interlayer interaction force. Herein, the layer modulation of the phonon transport and TE performance of monolayer, bilayer, and trilayer tellurium is investigated by first-principles calcuations. First, it was found that thermal conductivity as a function of layer numbers possesses a robust, unusually non-monotonic behavior. Moreover, the anisotropy of the thermal transport properties of tellurium is weakened with the increase in the number of layers. By phonon-level systematic analysis, we found that the variation of phonon transport under the layer of increment was determined by increasing the phonon velocity in specific phonon modes. Then, the TE transport properties showed that the maximum figure of merit (ZT) reaches 6.3 (p-type) along the armchair direction at 700K for the monolayer and 6.6 (p-type) along the zigzag direction at 700K for the bilayer, suggesting that the TE properties of the monolayer are highly anisotropic. This study reveals that monolayer and bilayer tellurium have tremendous opportunities as candidates in TE applications. Moreover, further increasing the layer number to 3 hinders the improvement of TE performance for 2D tellurium.

Superhydrophobic, flexible and high thermal stable ANFs/CNTs film for controllable light driven actuators

Superhydrophobic and light-responsive actuators (SLRAs) can be driven to move on water surface remotely and in a non-contact manner, and have shown promising applications in soft robotics, environmental protection, etc. It remains a big challenge to develop high performance SLRAs with excellent thermal stability, fast light responsivity and controllable motion. Here, we propose a layer-by-layer vacuum filtration method to prepare flexible, freestanding and superhydrophobic composite films composed of alternately deposited oleylamine modified acid carbon nanotubes (O-ACNTs) and aramid nanofibers (ANFs). The composite film has excellent thermal stability with the maximum weight loss rate temperature as high as 520 ℃. The closely packed structure and strong interlayer interaction ensure the surface stability and durability of the composite film. The composite film possesses excellent photothermal conversion performance, and can maintain the structure integrity without deformation when its surface temperature reaches 208 °C. When used as a self-propelled actuator, the SLRA film can response to the light quickly and move on the water surface, and the motion speed and direction can be controlled by adjusting the irradiation intensity and position. The outstanding thermal stability guarantees the stability and reliability of the self-propelled motions. The present study opens a new avenue to design high performance SLRAs.

Josephson-like Tunnel Resonance and Large Coulomb Drag in GaAs-Based Electron-Hole Bilayers.

Bilayers consisting of two-dimensional (2D) electron and hole gases separated by a 10nm thick AlGaAs barrier are formed by charge accumulation in epitaxially grown GaAs. Both vertical and lateral electric transport are measured in the millikelvin temperature range. The conductivity between the layers shows a sharp tunnel resonance at a density of 1.1×10^{10} cm^{-2}, which is consistent with a Josephson-like enhanced tunnel conductance. The tunnel resonance disappears with increasing densities and the two 2D charge gases start to show 2D-Fermi-gas behavior. Interlayer interactions persist causing a positive drag voltage that is very large at small densities. The transition from the Josephson-like tunnel resonance to the Fermi-gas behavior is interpreted as a phase transition from an exciton gas in the Bose-Einstein-condensate state to a degenerate electron-hole Fermi gas.

Superconductivity in a breathing kagome metals ROs2 (R = Sc, Y, Lu)

We have successfully synthesized three osmium-based hexagonal Laves compounds ROs2 (R = Sc, Y, Lu), and discussed their physical properties. LeBail refinement of pXRD data confirms that all compounds crystallize in the hexagonal centrosymmetric MgZn2-type structure (P63/mmc, No. 194). The refined lattice parameters are a = b = 5.1791(1) Å and c = 8.4841(2) Å for ScOs2, a = b = 5.2571(3) Å and c = 8.6613(2) Å for LuOs2 and a = b = 5.3067(6) Å and c = 8.7904(1) Å for YOs2. ROs2 Laves phases can be viewed as a stacking of kagome nets interleaved with triangular layers. Temperature-dependent magnetic susceptibility, resistivity and heat capacity measurements confirm bulk superconductivity at critical temperatures, Tc, of 5.36, 4.55, and 3.47 K for ScOs2, YOs2, and LuOs2, respectively. We have shown that all investigated Laves compounds are weakly-coupled type-II superconductors. DFT calculations revealed that the band structure of ROs2 is intricate due to multiple interacting d orbitals of Os and R. Nonetheless, the kagome-derived bands maintain their overall shape, and the Fermi level crosses a number of bands that originate from the kagome flat bands, broadened by interlayer interaction. As a result, ROs2 can be classified as (breathing) kagome metal superconductors.

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.

High-Efficiency Electromagnetic Interference Shielding from Highly Aligned MXene Porous Composites via Controlled Directional Freezing.

Lightweight porous composite materials (PCMs) with outstanding electromagnetic interference (EMI) shielding performances are ideal for aerospace, artificial intelligence, military, and other fields. Herein, a three-dimensional Ti3C2Tx MXene/sodium alginate (SA)/carbon nanotubes (CNTs) (MSC) PCMs was prepared by a controlled directional freezing process. This method constructs a directionally ordered porous structure, which can make the incident electromagnetic waves reflect and scattered several times in the PCMs. The introduction of CNTs into the MSC PCMs can form three-dimensional conductive networks with MXene, thus improving the conductivity and further improving the electromagnetic shielding performance. Furthermore, the SA with abundant hydrogen bonding can strengthen the interlayer interaction between MXene and CNTs. Profiting from the controlled directional freezing and highly aligned porous structure, the MSC PCMs with 75 wt % CNTs exhibit ultrahigh conductivity of 1630 S m-1, an ultrahigh EMI shielding effectiveness of 48.0 dB in X-band for electromagnetic waves incident perpendicular to the hole growth direction, and compressive strength of 72.3 kPa. The as-prepared MSC PCMs show excellent EMI shielding and mechanical properties and have significant applications in the preparation of an entirely novel type of EMI shielding materials with an absorption-based mechanism.

Interlayer Interaction and Coercivity of Three-Layer Films Оbtained bу Chemical Deposition

Abstract—The results of experimental and theoretical studies of the coercivity and the displacement field of the hysteresis loop on the thickness of the nonmagnetic interlayer in magnetic films obtained by electroless plating are presented. With the help of model calculations based on the Landau–Ginzburg equations, the exchange interactions between magnetic layers with the participation of atoms of the nonmagnetic layer are studied. The resulting expression for the displacement field describes well the exponential changes in the displacement field as a function of the interlayer thickness in structures with both magnetically soft layers and layers with significantly different values of the coercivity.

Interlayer Interaction and Coercivity of Three-Layer Films Obtained bу Chemical Deposition

Interlayer Interaction and Coercivity of Three-Layer Films Obtained bу Chemical Deposition

Anisotropic Tunability of Vibrational Modes in Black Phosphorus Under Uniaxial Compressive/Tensile Strain

AbstractStrain engineering is a powerful strategy for tuning the optical, electrical, vibrational properties of 2D nanomaterials. In this work, a four‐point bending apparatus is constructed to apply both compressive and tensile strain on 2D anisotropic black phosphorus flake. Further polarized Raman spectroscopy is used to study the vibrational modes of black phosphorus flakes under uniaxial strain applied along various crystalline orientations. Here, a strong anisotropic blue/redshift of A1g, B2g, and A2g modes is found under compressive/tensile strain, respectively. Interestingly, mode A1g exhibits the maximum/minimum shift while mode B2g and mode A2g present the minimum/maximum shift when the strain is applied along armchair/zigzag direction. Density functional theory calculations are carried out to investigate the anisotropic strain response mechanism, finding that the strain‐induced regulation of the P─P bond angle, bond length, and especially interlayer interaction has a giant influence on the Raman shift.

Nacre‐Inspired Mechanically Robust Films for Osmotic Energy Conversion

AbstractMXene, a new class of 2D layered materials, is considered a candidate for the reverse electrodialysis (RED) film because the laminated MXene nanochannels with charged functional groups provide an excellent ionic selectivity and conductivity. However, the MXene‐based ion‐exchange films suffer from weak mechanical properties and instability in water due to the poor binding force between the nanosheets, which limits their RED performance. Here, inspired by natural nacre structure, a class of cation‐MXene/cation holocellulose nanofibers (C‐MXene/C‐HNF) composite film with high performance for harvesting nanofluidic osmotic is developed. C‐HNF acts as interlocking agent to connect the MXene nanosheets by hydrogen bonding, resulting a mechanically robust and water stable film. The introduction of C‐HNF not only increases the interlayer interaction force, but also enhances the ion transport flux. When the content of C‐HNF is 20%, the tensile stress, fracture strain, and toughness of the composite film reach up to 127.75 ± 1.61 MPa, 3.50 ± 0.1%, and 2.95 ± 0.52 MJ m−3, respectively. Additionally, the composite film can produce an impressive output power density of up to 1.09 W m−2 under a 50‐fold salinity gradient (0.01/0.5 m NaCl), and only decreases by 4.58% after 50 days, demonstrating good stability and durability.

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.

Modulation of contact type in BAs/Hf3C2 heterostructure via surface functionalization and strain

The exploration of contact property is greatly vital to improve the performance of transistors based on two-dimensional (2D) materials. In this work, we construct 2D BAs/Hf3C2 vdW heterostructure to explore its contact property based on first-principles calculations. We find that the BAs layer shows metallic feature in the BAs/Hf3C2 heterostructure, suggesting Hf3C2 destroys the band dispersion of BAs due to the appearance of strong interfacial coupling. Therefore, the pristine Hf3C2 is not ideal electrode material. The functionalization of Hf3C2 can weaken the interlayer interaction and make BAs maintain its semiconductor feature. Here, we select chalcogens and halogens to functionalize the Hf3C2, forming Hf3C2X2 (X = O, S, Se, Te, F, Cl, Br, and I). Furthermore, we investigate the contact type, Schottky barrier, charge transfer, and tunneling probability of BAs/Hf3C2X2 heterostructures. Ohmic contact is formed in the most BAs/Hf3C2X2 systems, suggesting that they possess high performance with a view to the application for the transistors. The biaxial strain and external electric field are utilized to modulate the contact type and barrier height in the BAs/Hf3C2O2 and BAs/ Hf3C2F2 heterostructures.

Wafer‐Scale Synthesis of Mixed‐Dimensional Heterostructures via Manipulating Platinization Conditions

Abstract2D van der Waals (vdW) hetero integration, which features exotic interplanar interactions derived from mixed‐dimensional heterostructures, is an emergent platform for implementing high‐performance electronics and broadband/wavelength‐tunable photodetectors. However, the production of large‐area 2D spatially homogeneous transition‐metal dichalcogenides (TMDs) and elucidation of the electrostatic dynamics governing the interlayer interactions are two paramount prerequisites for realizing practical 2D‐TMD‐heterostructure‐based photodetectors. Here, a wafer‐scale synthesis of mixed‐dimensional Pt–MoS2‐based vdW heterostructures is unprecedentedly demonstrated by manipulating the platinization conditions. The rationally designed platinization yields dimensionality‐tailored Pt, including Pt nanofilm, Pt nanoparticles, and Pt atoms, with MoS2 as host platform. From density functional theory calculations, this study insights that Mo vacancy sites on the MoS2 surface are thermo‐dynamically favorable sites for Pt with an adsorption energy of −2.25 eV, then Pt clusters are sequentially formed neighboring the specific Pt‐substituted position with a formation energy of 1.30 eV. Intensive microscopic and spectroscopic analyses reveal the structural, chemical, and electrical features, validating the proposed dynamics‐related mechanism. The dimensionality‐tailored vdW heterostructures exhibit outstanding optoelectrical properties with excellent photoresponsivity (2.04 mA W−1) and highly sensitive detectivity (9.82 × 106 cm Hz1/2 W−1).

Numerical solution for nonlimit-state earth pressure considering interlayer shear stress and the soil arching effect

The earth pressure of multilayer cohesive soils is affected by interlayer interaction and the soil arching effect. However, only the soil arching effect is considered in the existing methods for calculating earth pressure, and the interlayer shear stress caused by principal stress deflection is ignored. For a vertical rigid retaining wall with a horizontal backfill surface, the trajectory of the minor principal stresses in the soil behind the wall takes the form of an arc of a circle. On this basis, the horizontal and vertical stress equilibrium equations of the differential soil elements behind the wall are derived. The interlayer shear stress, wall displacement and soil arching effect are incorporated into the horizontal slice model, and the numerical scheme of the nonlimit-state earth pressure, the resultant force and the location of the action point are determined with the numerical solution method. Furthermore, the rationality of the proposed solution is demonstrated through comparison with experimental data and other solutions.

Pressure Dependence of Intra- and Interlayer Excitons in 2H-MoS2 Bilayers.

The optical and electronic properties of multilayer transition metal dichalcogenides differ significantly from their monolayer counterparts due to interlayer interactions. The separation of individual layers can be tuned in a controlled way by applying pressure. Here, we use a diamond anvil cell to compress bilayers of 2H-MoS2 in the gigapascal range. By measuring optical transmission spectra, we find that increasing pressure leads to a decrease in the energy splitting between the A and the interlayer exciton. Comparing our experimental findings with ab initio calculations, we conclude that the observed changes are not due to the commonly assumed hydrostatic compression. This effect is attributed to the MoS2 bilayer adhering to the diamond, which reduces the in-plane compression. Moreover, we demonstrate that the distinct real-space distributions and resulting contributions from the valence band account for the different pressure dependencies of the inter- and intralayer excitons in compressed MoS2 bilayers.