Interlayer Interaction Research Articles

Moiré pattern modulated topological phase and in-gap edge modes in α-antimonene

Using a simple sequential deposition method, we grow black-phosphorus-like antimonene (α-antimonene) on top of α-bismuthene nanoislands. Due to the lattice mismatch between the α-antimonene overlayer and the bismuthene bases, the heterostructure exhibits a moiré pattern whose periodicitiy (∼8 ± 1 nm) is amongst the largest periodicities ever observed in 2D systems. We use scanning tunnelling microscopy and spectroscopy to show that this moiré pattern modulates both the electronic states in the bulk and the edge states of the α-antimonene, and therefore leads to local modulations of the topological phase. We present calculations which elucidate the effects of strain on the bandstructure of α-Sb and discuss detailed spectroscopy results for the edge states, as well as the effect of interlayer interactions between the α-Sb and α-Bi structures.

Enhanced Layer-Breathing Modes in van der Waals Heterostructures Based on Twisted Bilayer Graphene.

The characterization of interlayer coupling in two-dimensional van der Waals heterostructures (vdWHs) is essential to understand their quantum behaviors and structural functionalities. Interlayer shear and layer-breathing (LB) phonons carry rich information on interlayer interaction, but they are usually too weak to be detected via standard Raman spectroscopy due to the weak electron-phonon coupling (EPC). Here, we report a universal strategy to enhance LB modes of vdWHs based on twisted bilayer graphene (tBLG). In both tBLG/hBN and tBLG/MoS2 vdWHs, the resonantly excited electrons in tBLG can strongly couple to LB phonons extended over the entire layers in the vdWHs, whose resonance condition is tunable by the twist angle of tBLG. In vdWHs containing twisted graphene layers with multiple twisted interfaces, the EPC of LB phonons coming from the collective LB vibrations of entire heterostructure layers can be tuned by resonant excitation of programmable van Hove singularities according to each twisted interface. The universality and tunability of enhanced LB phonons by tBLG make it a promising method to investigate EPC and interlayer interaction in related vdWHs.

Tough and Strong All-Biomass Plastics from Agricultural and Forest Wastes via Constructing an Aggregate of Hydrogen-Bonding Networks

The development of all-biomass materials to replace conventional plastics has been gradually becoming a focus. However, all-biomass plastics, especially those fabricated from agricultural and forestry wastes, have the obstacles of poor formability and/or low toughness. Herein, we demonstrated a facile, efficient, and easy-to-scale method to significantly improve the formability and toughness of biomass materials via constructing an aggregate of hydrogen-bonding networks, where the relatively weak hydrogen bonding could be sacrificed during stretching. After a continuous preparation process that combined a paper-making process with an in situ welding process, the regenerated cellulose material with a layered microstructure was spontaneously formed. The interlayer hydrogen-bonding interactions could dissipate energy during stretching. As a result, the cellulose plastics were tough and strong. The tensile strength, strain, and toughness reached 154.9 MPa, 57.7%, and 81.76 MJ/m3, respectively, which were markedly higher than those of previous cellulose-based materials. The corresponding cellulose hydrogel exhibited an excellent strength of 9.5 MPa and a high strain of 171.4% also. During this scalable process, a 1-ethyl-3-methylimidazolium acetate (EmimAc) aqueous solution worked as a dispersant and a solvent, and a high solid content of cellulose/EmimAc (20 wt %) was used. Based on such an effective method, various agricultural and forestry wastes, including corn straw, wheat straw, grass, and wood powder, could be directly processed into high-tough all-biomass films, indicating a huge potential in ecofriendly materials, environmental protection, and bioresource utilization.

Unraveling the interlayer and intralayer coupling in two-dimensional layered MoS[formula omitted] by X-ray absorption spectroscopy and ab initio molecular dynamics simulations

Understanding interlayer and intralayer coupling in two-dimensional layered materials (2DLMs) has fundamental and technological importance for their large-scale production, engineering heterostructures, and development of flexible and transparent electronics. At the same time, the quantification of weak interlayer interactions in 2DMLs is a challenging task, especially, from the experimental point of view. Herein, we demonstrate that the use of X-ray absorption spectroscopy in combination with reverse Monte Carlo (RMC) and ab initio molecular dynamics (AIMD) simulations can provide useful information on both interlayer and intralayer coupling in 2DLM 2Hc-MoS2. The analysis of the low-temperature (10–300 K) Mo K-edge extended X-ray absorption fine structure (EXAFS) using RMC simulations allows for obtaining information on the means-squared relative displacements σ2 for nearest and distant Mo–S and Mo–Mo atom pairs. This information allowed us further to determine the strength of the interlayer and intralayer interactions in terms of the characteristic Einstein frequencies ωE and the effective force constants κ for the nearest ten coordination shells around molybdenum. The studied temperature range was extended up to 1200 K employing AIMD simulations which were validated at 300 K using the EXAFS data. Both RMC and AIMD results provide evidence of the reduction of correlation in thermal motion between distant atoms and suggest strong anisotropy of atom thermal vibrations within the plane of the layers and in the orthogonal direction.

Ultrafast antiferromagnet rearrangement in Co/IrMn/CoGd trilayers

Antiferromagnets offer great potential for high-speed data processing applications, as they can expend spintronic devices from a static storage and gigahertz frequency range to the terahertz range. However, their zero net magnetization makes them difficult to manipulate and detect. In recent years, there has been a lot of attention given to the ultrafast manipulation of magnetic order using ultra-short single laser pulses, but it remains unknown whether a similar scenario can be observed in antiferromagnets. In this work, we demonstrate the manipulation of antiferromagnets with a single femtosecond laser pulse in perpendicular exchange-biased Co/IrMn/CoGd trilayers. We study the dual exchange bias interlayer interaction in quasi-static conditions and competition in ultrafast antiferromagnet rearrangement. Our results show that, compared to conventional ferromagnetic/antiferromagnetic systems, the IrMn antiferromagnet can be ultrafast and efficiently manipulated by the coupled CoGd ferrimagnetic layer, which paves the way for potential energy-efficient spintronic devices.

Scalable Production of 2D Minerals by Polymer Intercalation and Adhesion for Multifunctional Applications.

Natural and sustainable 2Dminerals have many unique properties and may reduce reliance on petroleum-based products. However, the large-scale production of 2D minerals remains challenging. Herein, a green, scalable, and universal polymer intercalation and adhesion exfoliation (PIAE) method to produce 2D minerals such as vermiculite, mica, nontronite, and montmorillonite with large lateral sizes and high efficiency, is developed. The exfoliation relies on the dual functions of polymers involving intercalation and adhesion to expand interlayer space and weaken interlayer interactions of minerals, facilitating their exfoliation. Taking vermiculite as an example, the PIAE produces 2D vermiculite with an average lateral size of 1.83 ± 0.48µm and thickness of 2.40 ± 0.77nm at a yield of ≈30.8%, surpassing state-of-the-art methods in preparing 2D minerals. Flexible films are directly fabricated by the 2D vermiculite/polymer dispersion, exhibiting outstanding performances including mechanical strength, thermal resistance, ultraviolet shielding, and recyclability. The representative application of colorful multifunctional window coatings in sustainable buildings is demonstrated, indicating the potential of massively produced 2D minerals.

Magneto-strain effects in 2D ferromagnetic van der Waal material CrGeTe_3

The idea of strain based manipulation of spins in magnetic two-dimensional (2D) van der Waal (vdW) materials leads to the development of new generation spintronic devices. Magneto-strain arises in these materials due to the thermal fluctuations and magnetic interactions which influences both the lattice dynamics and the electronic bands. Here, we report the mechanism of magneto-strain effects in a vdW material CrGeTe_3 across the ferromagnetic (FM) transition. We find an isostructural transition in CrGeTe_3 across the FM ordering with first order type lattice modulation. Larger in-plane lattice contraction than out-of-plane give rise to magnetocrystalline anisotropy. The signature of magneto-strain effects in the electronic structure are shift of the bands away from the Fermi level, band broadening and the twinned bands in the FM phase. We find that the in-plane lattice contraction increases the on-site Coulomb correlation (U_{eff}) between Cr atoms resulting in the band shift. Out-of-plane lattice contraction enhances the d-p hybridization between Cr–Ge and Cr–Te atoms which lead to band broadening and strong spin-orbit coupling (SOC) in FM phase. The interplay between U_{eff} and SOC out-of-plane gives rise to the twinned bands associated with the interlayer interactions while the in-plane interactions gives rise to the 2D spin polarized states in the FM phase.

Interfacial self-assembly of Cd2+-tetraphenylethylene coordination polymers and their photophysical properties in Langmuir-Blodgett films

Molecular arrangement and orientation of tetraphenylethylene (TPE) unit in the highly ordered thin films and aggregates can effectively limit its conformation that results in strong effect on the excited energy transfer process and luminescent behaviors under irradiation. We report here an interfacial self-assembly of metal-TPE coordination polymer (CP) ultrathin films and their aggregate-induced emission (AIE) behaviors. After connected with pyridyl or benzimidazole substituents, the tetradentate TPEs as synthesized are used as the multidentate linkers to coordinate with the Cd2+ ions to produce aggregates in the solutions, and to form well-defined two- and three-dimensional organized Cd-TPE CP multilayers at the air-water interfaces by the Langmuir-Blodgett (LB) method. It is revealed that, in addition to the aggregation-induced emission, the following external factors have also large effects on the luminescence of TPEs, including the coordination bonding in the CPs, in plane and interlayer molecular interaction in the LB films; both of them can restrict the intramolecular motion or rotation of TPE unit. Because of these external effects, the emission lifetime of TPEs reaches to approximately 5–10 times longer in some Cd-TPE CP LB films than that in the solutions. Further, the luminescent emission wavelengths and colors of LB films can be tuned to some extent by the in-plane and interlayer molecular interaction. Finally, it is demonstrated that the luminescent emissions and colors of the Cd-TPPE CP LB films is selectively sensing to methanol and formic acid in the gas phase with good reversibility and reproductivity.

Proximity-enhanced valley Zeeman splitting at the WS2/graphene interface

The valley Zeeman physics of excitons in monolayer transition metal dichalcogenides provides valuable insight into the spin and orbital degrees of freedom inherent to these materials. Being atomically-thin materials, these degrees of freedom can be influenced by the presence of adjacent layers, due to proximity interactions that arise from wave function overlap across the 2D interface. Here, we report 60 T magnetoreflection spectroscopy of the A- and B- excitons in monolayer WS2, systematically encapsulated in monolayer graphene. While the observed variations of the valley Zeeman effect for the A- exciton are qualitatively in accord with expectations from the bandgap reduction and modification of the exciton binding energy due to the graphene-induced dielectric screening, the valley Zeeman effect for the B- exciton behaves markedly different. We investigate prototypical WS2/graphene stacks employing first-principles calculations and find that the lower conduction band of WS2 at the valleys (the band) is strongly influenced by the graphene layer on the orbital level. Specifically, our detailed microscopic analysis reveals that the conduction band at the Q point of WS2 mediates the coupling between and graphene due to resonant energy conditions and strong coupling to the Dirac cone. This leads to variations in the valley Zeeman physics of the B- exciton, consistent with the experimental observations. Our results therefore expand the consequences of proximity effects in multilayer semiconductor stacks, showing that wave function hybridization can be a multi-step energetically resonant process, with different bands mediating the interlayer interactions. Such effects can be further exploited to resonantly engineer the spin-valley degrees of freedom in van der Waals and moiré heterostructures.

Impact of electron correlations on the k-resolved electronic structure of PdCrO2 revealed by Compton scattering

Delafossite PdCrO2 is an intriguing material which displays nearly-free electron and Mott insulating behaviour in different layers. Both angle-resolved photoemission spectroscopy (ARPES) and Compton scattering measurements have established a hexagonal Fermi surface in the material’s paramagnetic phase. However, the Compton experiment detected an additional structure in the projected occupancy which was originally interpreted as an additional Fermi surface feature not seen by ARPES. Here, we revisit this interpretation of the Compton data. State-of-the-art density functional theory (DFT) with dynamical mean field theory (DMFT), the so-called DFT+DMFT method, predicts the Mott insulating state along with a single hexagonal Fermi surface in excellent agreement with ARPES and Compton. However, DFT+DMFT fails to predict the intensity of the additional spectral weight feature observed in the Compton data. We infer that this discrepancy may arise from the DFT+DMFT not being able to correctly predict certain features in the shape and dispersion of the unoccupied quasiparticle band near the Fermi level. Therefore, a theoretical description beyond our DFT+DMFT model is needed to incorporate vital electron interactions, such as inter-layer electron coupling interactions which for PdCrO2 gives rise to the Kondo-like so-called intertwined excitation.

Effect of Co doping on structural and magnetic properties of kagome like La based cuprate francisite Cu3La(SeO3)2O2Cl

The effects of Co doping on the structural and magnetic properties of a frustrated layered rare earth based synthetic analog of mineral francisite [Cu3La(SeO3)2O2Cl;(LaCufr)] have been investigated experimentally with a prior theoretical input. We have estimated intra-layer and inter-layer exchange interactions from density functional theory, which reveals the strong antiferromagnetic (AFM) nature of the studied compounds. 10 at. % Co-doped CuLafr confirms incorporation of Co2+ at the Cu2+ site with the local environment around dopant Co nearly similar around that of host Cu. An observed field-induced meta-magnetic transition and a spin reorientation transition have been interpreted considering magnetic exchange interactions. Co-doped LaCufr exhibits a decrease in the AFM ordering temperature and the critical field corresponding to a meta-magnetic spin-flip type transition. The competition and modulation among different intra-layer exchange interactions upon incorporation of Co into the Cu site may lead to such situations. The evidence of spin–phonon coupling from Raman analysis in both compounds is noteworthy and enriches their magnetic properties.

Interlayer expanded VS2 nanosheet for efficient sodium storage

An interlayer-expanded vanadium disulfide (VS2) electrode has been developed to enhance the performance of sodium ion batteries. The interlayer expansion of the (001) plane from the standard 5.7 Å to 9.5 Å improves capacity by 2–3 times at various current densities even over long cycles. This advancement is credited to the optimized kinetics of Na+ diffusion, as the intrinsic structure of VS2 with weak van der Waals interlayer interactions leads to minimal resistance along 2D ionic diffusion routes. Our findings highlight the significance of interlayer engineering in designing efficient energy storage electrodes.

Exciton Emission in Molybdenum Telluride Homobilayers with Fine‐Tuned Twist‐Angles

AbstractLayered 2H‐molybdenum ditelluride (MoTe2) is a promising near‐infrared material with optical activity, which enables hybrid‐integrated with silicon photonics for communication purposes. The use of various artificial hetero‐stacking or twist‐stacking techniques can further expand the emission bandwidth and offer more choices of optical‐active materials used as building blocks in on‐chip optoelectronic devices. However, while the twisting technique is an effective tool for adjusting interlayer interaction in van der Waals materials, a systematic experimental study of twisted MoTe2 homobilayers is currently lacking. Here, a series of MoTe2 homobilayers were prepared with precisely controlled twist‐angles from 0° to 60°, with a particular focus on the small‐twist region. Conducting photoluminescence measurements at low temperatures enabled observation of the evolution of exciton emission as the twist angle increases. Neutral and charged excitons were also identified in a dual‐gated 1.4° twisted MoTe2 through gate‐dependent and field‐dependent photoluminescence measurements. Furthermore, spatially‐resolved photoluminescence measurements revealed the critical role of the interface conditions, including interlayer spacing and strain, in addition to the twist‐angle, in determining the excitonic behavior of the material. This study provides compelling experimental evidence for understanding the twist‐angle‐dependent excitonic behaviors in atomically thin semiconductors.

A Revisit of Superconductivity in 4Hb-TaS2−2xSe2x Single Crystals

Previous investigations of 4$H_b$-TaS$_{2-2x}$Se$_{2x}$ mainly focused on the direct competition between superconductivity and charge density wave (CDW). However, the superconductivity itself, although has been prominently enhanced by isovalent Se substitution, has not been adequately investigated. Here, we performed a detailed electrical transport measurement down to 0.1 K on a series of 4$H_b$-TaS$_{2-2x}$Se$_{2x}$ single crystals. A systematic fitting of the temperature-dependent resistance demonstrates that the decreased Debye temperatures ($\Theta_{D}$) and higher electron-phonon coupling constants ($\lambda_{e-p}$) at the optimal Se doping content raise the superconducting transition temperature ($T_c$). Additionally, we discovered that the incorporation of Se diminishes the degree of anisotropy of the superconductivity in the highly layered structure. More prominently, a comprehensive analysis of the vortex liquid phase region reveals that the optimally doped sample deviates from the canonical 2D Tinkham prediction but favors a linear trend with the variation of the external magnetic field. These findings emphasize the importance of interlayer interaction in this segregated superconducting-Mott-insulating system.

Enhanced Alkali-Ion Adsorption in Strongly Bonded Two-Dimensional TiS2/MoS2 van der Waals Heterostructures

Despite their remarkable properties, many two-dimensional (2D) materials do not possess the desired characteristics to enhance the energy density, rate performance, and cycle life of batteries when used as standalone materials for battery electrodes. However, engineering 2D van der Waals (vdW) heterostructures by stacking different 2D materials offers new opportunities for battery electrodes, combining desirable features and overcoming the limitations of the constituent 2D layers. In this work, using first-principles calculations, we investigated the electronic structure, thermal stability, stress–strain response, alkali (Li/Na/K)-ion adsorption, and diffusion characteristics of 2D heterostructures of titanium disulfide (TiS2) and molybdenum disulfide (MoS2) monolayers with attractive applications in alkali-metal ion batteries (AMIBs). This work revealed relatively strong interlayer interactions in the heterostructure, resulting in significant enhancements in the adsorption of alkali ions compared to the respective monolayers. This work demonstrates that TiS2/MoS2 heterostructures offer excellent mechanical flexibility, increased strength, and greater strain endurance. The results indicate that TiS2/MoS2 heterostructures are promising materials for next-generation flexible anodes for AMIBs.

Nanoscale Ni-NiO-ZnO Heterojunctions for Switchable Dehydrogenation and Hydrogenation through Modulation of Active Sites.

Catalysts consisting of metal-metal hydroxide/oxide interfaces are highly in demand for advanced catalytic applications as their multicomponent active sites will enable different reactions to occur in close proximity through synergistic cooperation when a single component fails to promote it. To address this, herein we disclosed a simple, scalable, and affordable method for synthesizing catalysts consisting of nanoscale nickel-nickel oxide-zinc oxide (Ni-NiO-ZnO) heterojunctions by a combination of complexation and pyrolytic reduction. The modulation of active sites of catalysts was achieved by varying the reaction conditions of pyrolysis, controlling the growth, and inhibiting the interlayer interaction and Ostwald ripening through the efficient use of coordinated acetate and amide moieties of Zn-Ni materials (ZN-O), produced by the reaction between hydrazine hydrate and Zn-Ni-acetate complexes. We found that the coordinated organic moieties are crucial for forming heterojunctions and their superior catalytic activity. We analyzed two antagonistic reactions to evaluate the performance of the catalysts and found that while the heterostructure of Ni-NiO-ZnO and their cooperative synergy were crucial for managing the effectiveness and selectivity of the catalyst for dehydrogenation of aryl alkanes/alkenes, they failed to enhance the hydrogenation of nitro arenes. The hydrogenation reaction was influenced by the shape, surface properties, and interaction of the hydroxide and oxide of both zinc and nickel, particularly accessible Ni(0). The catalysts showed functional group tolerance, multiple reusabilities, broad substrate applicability, and good activity for both reactions.

Macromolecular rearrangement caused by CO2 adsorption in coal

Macromolecule rearrangement is an important reason for coal adsorption induced deformation. The process of carbon dioxide (CO2) sequestration in a coal seam induces coal deformation, which yields challenges in terms of the injectability of CO2 and the safety of sequestration. We report the molecular rearrangement characteristics of coal with adsorbed CO2 that is completely different from macroscopic coal deformation. In-situ spectroscopy was used to monitor the Raman and infrared responses during the CO2 injection process in coal. The interlayer characteristics and defects of coal macromolecules were highly responsive to the adsorption process. The adsorption of CO2 could lead to the increase of interlayer shear vibration intensity and cause irreversible damage to the defective part of coal. Quantum chemistry simulations showed that CO2 can adsorb on the edge of the coal aromatic nucleus (AN) and cause layer slip in the AN. In the rearrangement process, the AN of coal macromolecules tend to increase the layer spacing and slip to the direction of more overlapping between layers. Our study reveals a potential molecular mechanism for coal deformation via CO2 adsorption; provides a new insight into coal adsorption deformation, and indicates that coal macromolecular rearrangement can be attributed to the change of interlayer interaction.

Interlayer Electrons Polarization of Asymmetric Metal Nanoclusters/g-C3 N4 for Enhanced Microwave Therapy of Pneumonia.

Interlayer interactions in two dimensional (2D) materials promote catalytic performance but often depend on the transport of inter rather than intralayer electrons. In this study, it is found that asymmetric metal-nanocluster-doped 2D g-C3 N4 greatly enhances catalytic performance by inducing microwave excitation of interlayer electron delocalization, resulting in a polarization of interlaminar charge transport for microwave disinfection and pneumonia therapy. Asymmetric Fe and Cu nanocluster doping (DCN-FeCu) enables g-C3 N4 to generate interlayer electrons under microwave irradiation, leading to interlayer polarization processes and electron delocalization effects, thus enhancing the interlayer migration efficiency of electrons. It also improves impurity energy levels and leads to a decrease in work function, allowing DCN-FeCu to produce microwave carriers across the photoelectric potential barrier under low-energy microwave radiation (2.45GHz). This asymmetric doping modulation produces layer number-dependent microwave electron excitations that are verified using multi-metal doping. Therefore, structurally modulated asymmetric doping of 2D materials with interfacial spatial effects can provide efficient microwave disinfection and pneumonia therapy.

Electronic structure of cuprate–nickelate infinite-layer heterostructure

The discovery of superconductivity in Sr/Ca-doped infinite-layer nickelates Nd(La)NiO2 thin films inspired extensive experimental and theoretical research. However, research on the possibilities of enhanced critical temperature by interface heterostructure is still lacking. Due to the similarities of the crystal structure and band structure of infinite-layer nickelate LaNiO2 and cuprate CaCuO2, we investigate the crystal, electronic and magnetic properties of LaNiO2:CaCuO2 heterostructure using density functional theory and dynamical mean-field theory. Our theoretical results demonstrate that, even a very weak inter-layer z-direction bond is formed, an intrinsic charge transfer between Cu-3d x 2–y 2 and Ni-3d x 2–y 2 orbitals is obtained. The weak interlayer hopping between Cu and Ni leaves a parallel band contributed by Ni/Cu-3d x 2–y 2 orbitals near the Fermi energy. Such an infinite-layer heterostructure with negligible interlayer interaction and robust charge transfer opens a new way for interface engineering and nickelate superconductors.

Flexible and alternately layered high electrochemical active electrode based on MXene, carboxymethylcellulose, and carbon nanotube for asymmetric micro-supercapacitors

Recent studies have shown that Ti-based MXene has great potential for electrochemical energy storage applications, including Li-ion batteries and micro-supercapacitors. However, self-stacking and weak interlayer interactions lead to poor electrochemical properties. Herein, a simple one-step vacuum filtration method was used to prepare a MXene/carboxymethylcellulose/carbon nanotube (Ti3C2Tx/CMC/CNT) hybrid membrane. Due to the unique adhesion and flexibility of CMC, it can be interwoven with CNT to form an interconnected mesh structure, which on the one hand mitigates the self-aggregation of CNT, and on the other hand, the CNT entangled on the surface of CMC imparts its electrical conductivity. Moreover, the –OH of CMC can form hydrogen bonds with the reactive terminal groups (-O, –OH, -F) of Ti3C2Tx, resulting in the tight anchoring of CMC and CNT to Ti3C2Tx nanosheet layers and bridging adjacent Ti3C2Tx nanosheets to form a complete conductive pathway. As a result, the mechanical property test indicates that the Ti3C2Tx/CMC/CNT hybrid film could achieve a maximum tensile strength of 64.9 MPa. Furthermore, an asymmetric micro-supercapacitor (MSC) using Ti3C2Tx/CMC/CNT as the cathode and reduced graphene oxide/carboxymethylcellulose/polypyrrole (RGO/CMC/PPy) as the anode was fabricated, which exhibited a high energy density of 258.8 μWh cm−2 at a power density of 750 μW cm−2, and an ultra-long cycle life (93.2% capacitance retention after 15,000 GCD cycles). The simple and scalable preparation process makes this MSC device very promising for commercial electronics applications.