Interlayer Van Der Waals Forces Research Articles

Determining Bandgaps in the Layered Group‐10 2D Transition Metal Dichalcogenide PtSe2

AbstractUnlike traditional group‐6 transition metal dichalcogenides (TMDs), group‐10 TMDs such as PtSe2 and PdTe2 possess highly tuneable indirect bandgaps, transitioning from semiconducting in the near‐infrared to semimetal behavior with a number of monolayers (MLs). This opens up the possibility of TMD‐based mid‐infrared and terahertz optoelectronics. Despite this large potential, the optical properties of such materials have shown an extremely large disparity between that predicted and measured. For example, simulations show that a few MLs is required for the semiconductor–semimetal transition, whilst tens of MLs is found experimentally. This is a result of widely used optical extrapolation methods to determine bandgaps, such as the Tauc plot approach, that are not adapted here owing to i) nearby direct transitions, ii) the material dimensionality and iii) large changes in the non‐parabolic bandstructure with MLs. Here, uniquely combining optical ellipsometry to determine the complex permittivity, terahertz time resolved spectroscopy for the complex conductivity and in‐depth density functional theory (DFT) simulations, it is shown that the optical properties and bandstructure can be determined reliably and demonstrate clearly that the semiconductor‐semimetal transition occurs for PtSe2 layers ≈5 MLs. The microscopic origins of the observed transitions and the crucial role of the Coulomb interaction for thin semiconducting layers, and that of interlayer van der Waals forces for multilayer semimetallic samples are also demonstrated. This work of combining complimentary experimental techniques and extensive simulations avoids the application of constrained extrapolation methods to determine the optical properties of group‐10 TMDs, and will be of importance for future mid‐infrared and terahertz applications.

Stacking-dependent structural and electronic properties of trilayer γ-graphyne: An approach for new 2D carbon allotropes.

Vertical stacks of two-dimensional (2D) materials with interlayer van der Waals (vdW) force have provided a versatile approach for creating hybrid materials and modulating various properties. In this work, the structural and electronic properties of trilayer γ-graphyne, involving different stacking patterns, have been investigated through first-principles approaches. The result indicates that a metal-to-semiconducting transition can be triggered simply by switching the stacking order of trilayer γ-graphyne. More interestingly, in addition to typical vdW homostructures, new 2D carbon allotropes with novel carbon networks can be achieved on the basis of trilayer γ-graphyne, arising from the absence of intralayer acetylene linkages during the structural relaxation. One of the new 2D carbon allotropes possesses an intrinsic semiconducting nature with a wide bandgap of 1.827 eV, coupled with superior structural stability beyond single-layer γ-graphyne. Moreover, the biaxial strain effect on the new 2D carbon allotrope, as well as the trilayer vdW stacks, has also been revealed in this work. Correspondingly, the in-plane tensile strain is demonstrated to further enlarge the electronic bandgaps in these carbon sheets. Therefore, the results of this work imply the great potential of few-layer graphyne in future carbon-based nanoelectronic devices, and simultaneously provide a new approach for developing and synthesizing novel 2D carbon allotropes via the vertical stacking of graphyne with inherent acetylene linkages.

Enhanced colorimetric analysis substrate based on graphene oxide open-close actuator

Traditional colorimetric sensors often suffer from low color resolution and insufficient sensitivity. Therefore, for colorimetric detection to serve as a reliable quantitative analysis technique, an enhanced substrate with high sensitivity and repeatability is required. This strategy employs an interfacial network constructed between two-dimensional graphene oxide (GO) lamellar structures to create a substrate for colorimetric analysis. Under normal conditions, the newly synthesized GO inhibits oxidative activity due to van der Waals forces between the lamellar interfaces, resulting in the GO actuator being in the closed state. During Ag+ colorimetric analysis, the GO interlayer adsorption of silver nanoparticles (AgNPs) disrupts the interlayer van der Waals forces, releasing its oxidase activity and significantly enhancing Ag+ oxidation. The resulting actuator exhibits a faster driving speed (0.045 μM/s), excellent sensitivity, and stability. Additionally, the reducing properties of dopamine (DA) can be utilized to encapsulate the GO actuator with polydopamine, closing the GO actuator. Similarly, the reducing property of ascorbic acid (AA) can be utilized to restore the GO actuator to a closed state. These distinct reduction mechanisms allow for an effective visual distinction between AA and DA. With these advantages, the actuator can be developed into simple analytical tools (such as Ag+ colorimetric test strips and DA and AA test kits), demonstrating significant potential for practical application.

Boosting photothermal conversion through array aggregation of metalloporphyrins in bismuth-based coordination frameworks.

Materials capable of efficiently converting near-infrared (NIR) light into heat are highly sought after in biotechnology. In this study, two new three-dimensional (3D) porphyrin-based metal-organic frameworks (MOFs) with a sra-net, viz. CoTCPP-Bi/NiTCPP-Bi, were successfully synthesized. These MOFs feature bismuth carboxylate nodes interconnected by metalloporphyrinic spacers, forming one-dimensional (1D) arrays of closely spaced metalloporphyrins. Notably, the CoTCPP-Bi exhibits an approximate Co⋯C distance of 3 Å, leading to enhanced absorption of NIR light up to 1400 nm due to the presence of strong interlayer van der Waals forces. Furthermore, the spatial arrangement of the metalloporphyrins prevents axial coordination at the centers of porphyrin rings and stabilizes a CoII-based metalloradical. These characteristics promote NIR light absorption and non-radiative decay, thereby improving photothermal conversion efficiency. Consequently, CoTCPP-Bi can rapidly elevate the temperature from room temperature to 190 °C within 30 seconds under 0.7 W cm-2 energy power from 808 nm laser irradiation. Moreover, it enables solar-driven water evaporation with an efficiency of 98.5% and a rate of 1.43 kg m-2 h-1 under 1 sun irradiation. This research provides valuable insights into the strategic design of efficient photothermal materials for effective NIR light absorption, leveraging the principles of aggregation effect and metalloradical chemistry.

MXene/Nitrogen-Doped Carbon Nanosheet Scaffold Electrode toward High-Performance Solid-State Zinc Ion Supercapacitor.

While MXene is widely used as an electrode material for supercapacitor, the intrinsic limitation of stacking caused by the interlayer van der Waals forces has yet to be overcome. In this work, a strategy is proposed to fabricate a composite scaffold electrode (MCN) by intercalating MXene with highly nitrogen-doped carbon nanosheets (CN). The 2D structured CN, thermally converted and pickling from Zn-hexamine (Zn-HMT), serves as a spacer that effectively prevents the stacking of MXene and contributes to a hierarchically scaffolded structure, which is conducive to ion movement; meanwhile, the high nitrogen-doping of CN tunes the electronic structure of MCN to facilitate charge transfer and providing additional pseudocapacitance. As a result, the MCN50 composite electrode achieves a high specific capacitance of 418.4 Fg-1 at 1 Ag-1. The assembled symmetric supercapacitor delivers a corresponding power density of 1658.9 Wkg-1 and an energy density of 30.8 Whkg-1. The all-solid-state zinc ion supercapacitor demonstrates a superior energy density of 68.4 Whkg-1 and a power density of 403.5 Wkg-1 and shows a high capacitance retention of 93% after 8000 charge-discharge cycles. This study sheds a new light on the design and development of novel MXene-based composite electrodes for high performance all-solid-state zinc ion supercapacitor.

Dion-Jacobson perovskite solar cells: Further optimize the performance by SCAPS-1D simulation techniques

With rising global energy demands and the emergence of novel energy forms, perovskite solar cells (PSCs) are becoming increasingly prominent due to their exceptionally high efficiency in converting power. The advantage of Dion-Jacobson (DJ) type 2D layered perovskite materials lies in their lack of interlayer van der Waals forces, coupled with hydrogen bonds at the extremities, necessitating additional external energy to break through their two-dimensional layered configuration, thereby greatly enhancing the materials' structural integrity. This study utilizes DJ type 2D layered perovskite material to tackle the stability problem. This study aimed to uncover the inherent effects of DJ type 2D perovskite substances by simulating the devices with SCAPS-1D (Solar Cells Capacitance Simulator) and modifying appropriate physical parameters to align closely with the outcomes reported in experiments. Simulation results indicate that factors such as the thickness of the absorber layer, the band gap, the operating temperature, and the thickness of the interfacial defect layer uniquely influence the device's performance. The optimal thickness for the absorbing layer was determined by its ability to absorb light. The aim is to boost the sensitivity of DJ type 2D layered perovskite materials to light across various wavelengths and to refine the PCE. During the simulation, the maximum PCE (26.57%) was attained by enhancing both the band gap width in the absorber layer and the hole transport layer. To delve deeper into the fluctuations in device efficiency in environments with low temperatures, this study established the temperature spectrum between 270 and 300 Kelvin. Investigations revealed that at 272 K, the PCE and FF stood at 28.33% and 83.79% respectively, indicating the effectiveness of DJ type 2D layered PSC in low-temperature applications, preserving structural integrity and superior efficiency relative to other PSCs. Consequently, this study offers a viable approach for creating DJ type 2D layered PSC, ensuring high efficiency and enduring stability in cooler conditions.

Morphology design and electronic configuration of MoSe2 anchored on TiO2 nanospheres for high energy density sodium-ion half/full batteries

Molybdenum selenide (MoSe2) has shown potential sodium storage properties due to its large layer spacing (0.646 nm) and high theoretical capacity and narrow band gap. However, as the anode material of sodium ion batteries (SIBs), the MoSe2’s performance is not ideal, especially due to the layer agglomeration and stacking caused by volume expansion and low intrinsic conductivity. Hence, morphology design and electronic configuration of MoSe2 is proposed via building MoSe2 nanosheets and auxiliary sulfur doping on the surface of the TiO2 hollow nanosphere (S-MoSe2@TiO2). The hierarchical shaped S-MoSe2@TiO2 effectively overcomes the shortcomings of high surface energy and weak interlayer van der Waals force of MoSe2. As anode for SIBs, S-MoSe2@TiO2 delivers enhanced cycling life and rate capability (308 mAh/g at 10 A/g after 1000 cycles) with the comparison of MoSe2@TiO2 or pure MoSe2 and TiO2. Such excellent sodium storage performance is due to the fast diffusion kinetics of Na+. When it is applied in sodium ion full batteries, the S-MoSe2@TiO2 anode based cell can reach a high energy density of 187.8 W h kg−1 at 148.3 W kg−1. The design of the new MoSe2-based hybrid provides a novel scheme for the preparation of advanced anode in SIBs.

Preparation of highly dispersed Ni single-atom doped ultrathin g-C3N4 nanosheets by metal vapor exfoliation for efficient photocatalytic CO2 reduction

Single-atom photocatalysts can modulate the utilization of photons and facilitate the migration of photogenerated carriers. However, the preparation of single-atom uniformly doped photocatalysts is still a challenging topic. Herein, we propose the preparation of Ni single-atom doped g-C3N4 photocatalysts by metal vapor exfoliation. The Ni vapor produced by calcining nickel foam at high temperature accumulates in between g-C3N4 layers and poses a certain vapor pressure to destroy the interlayer van der Waals forces of g-C3N4. Individual metal atoms are doped into the structure while exfoliating g-C3N4 into nanosheets by metal vapor. Upon optimization of Ni content, the Ni single atom doped g-C3N4 nanosheets with 2.81 wt% Ni exhibits the highest CO2 reduction performance in the absence of sacrificial agents. The generation rates of CO and CH4 are 19.85 and 1.73 μmol g−1h−1, respectively. The improved photocatalytic performance is attributed to the anchoring Ni of single atoms on g-C3N4 nanosheets, which increases both carrier separation efficiency and reaction sites. This work provides insight into the design of photocatalysts with highly dispersed single-atom.

Chemical bonding within AIIIBVI materials under uniaxial compression.

The work provides a comprehensive explanation of the nature of chemical bonding through quantum chemical topology for multilayers of AIIIBVI compounds, such as GaSe, InSe, and GaTe, spanning pressures from 0 GPa to 30 GPa. These compounds are subjected to pressure orthogonal to the multilayers. Quantum chemical topological indices indicate that uniaxial pressure induces changes in hybridisation, leading to the disappearance of interlayer van der Waals forces. The distinct nature of the elements within the compounds results in different pressures at which van der Waals interactions disappear, as revealed by non-covalent interaction analysis. The presence or absence of chemical bonding is assessed by quantum topological indices as Espinosa indices, charge density distribution difference, and crystal orbital Hamilton populations. The varying changes in hybridisation, as indicated by topological indices, are corroborated by variations in the population of the electronic projected density of states. Ultimately, the type of chemical bonding is identified through the Espinosa indices in the field of Bader theory. This analysis confirms the existence of shared shell bonds between AIII and BVI atoms in vacuum that goes to an intermediate bond between shared and closed shells called the transition zone with increasing pressure. The implications and importance of this work extend beyond the presented results. It suggests that many other classes of two-dimensional materials may undergo phase transitions under uniaxial stress, leading to the formation of new phases with potentially interesting electronic properties.

WS2 nanosheets vertically grown on Ti3C2 as superior anodes for lithium-ion batteries

Tungsten disulfide (WS2) is considered as a promising anode material for high-performance lithium-ion batteries (LIBs) result from its inherent characteristics such as high theoretical capacity, large interlayer spacing and weak interlayer Van der Waals force. Nevertheless, WS2 has the drawbacks of easy agglomeration, severe volume expansion and high Li+ migration barrier, which lead to rapid capacity degradation and imperfect rate ability. In this work, a novel two-dimensional (2D) hierarchical composite (Ti3C2/WS2) consisting of WS2 nanosheets vertically grown on titanium carbide (Ti3C2) nanosheets is prepared. Thanks to this distinctive hierarchical structure and synergy between WS2 and Ti3C2, the Ti3C2/WS2 composite demonstrates exceptional electrochemical performance in LIBs. In addition, we investigate the effect of the mass proportion of WS2 in Ti3C2/WS2 composite on the electrochemical performance, and find that the optimal mass ratio of WS2 is 60%. As expected, the optimal electrode exhibits a high specific capacity (650 mAh/g at 0.1 A/g after 100 cycles) and ultra-long cycle stability (400 mAh/g at 1.0 A/g after 5000 cycles).

A Universal Chelation-Induced Selective Demetallization Strategy for Bioceramic Nanosheets (BCene).

The emergence of nanosheet materials like graphene and phosphorene, which are created by breaking the interlayer van der Waals force, has revolutionized multiple fields. Layered inorganic materials are ubiquitous in materials like bioceramics, semiconductors, superconductors, etc. However, the strong interlayer covalent or ionic bonding in these crystals makes it difficult to fabricate nanosheets from them. In this study, we present a simple technique to produce nanosheets from layered crystals by selectively exfoliating their interlayer metal atoms using the metal-chelation reaction. As a proof of concept, we successfully produced bioceramic nanosheets (BCene) by extracting Ca layers from Akermanite (AKT). The 3D-printed BCene scaffolds exhibited superior mechanical strength and in vitro bioactivity compared to the scaffolds made from AKT nanopowders. Our findings demonstrate the outstanding potential of BCene nanosheets in tissue engineering. Additionally, the selective demetallization technique for nanosheet production could be applied to other inorganic layered crystals to optimize their performance.

G-C3N4 sheet nanoarchitectonics with island-like crystalline/amorphous homojunctions towards efficient H2 and H2O2 evolution

Photocatalystic evolution of H2O2 from water and oxygen has attracted significant attention because of environmentally friendly. The absorption in visible and hydrophilic feature of graphitic carbon nitride (g-C3N4) make it a good candidate. In this paper, a rapid post-treatment at high temperature was developed to obtain g-C3N4 nanosheets with abundant crystalline/amorphous interfaces to form homojunctions, which optimized uniplanar carrier mobility dynamics. The conversion from bulk to two-dimensional g-C3N4 resulted from the breakage of interplanar hydrogen bonds and interlayer Van der Waals force. The unique morphology not only rendered photocatalyst with larger specific surface area but also inhibited the robust volume recombination of charge carriers. The accelerated charge carriers flow at the interface, interplane and interlayer together ameliorated the separation and transfer of electrons and holes. A new-emerged n→π* transition ameliorated the poor light utilization efficiency. Beyond the increased photocatalytic H2 evolution property (779.2 μmol g−1 h−1), optimized sample displayed a H2O2 evolution activity as high as 4877.1 μM g−1 h−1 under visible light illumination, which was ∼5.8 times of that of bulk g-C3N4. Detailed photocatalytic mechanism investigation manifested that the two-step single-electron oxygen reduction process occupied the dominant status in H2O2 evolution. This work proposed a novel strategy for obtaining g-C3N4 homojunctions as a promising bi-functional metal-free catalyst to be applied in clean energy production field.

Monolayer MoS2 Fabricated by In Situ Construction of Interlayer Electrostatic Repulsion Enables Ultrafast Ion Transport in Lithium-Ion Batteries

HighlightsIn-situ construction of electrostatic repulsion between MoS2 interlayers is first proposed to successfully prepare Co-doped monolayer MoS2 under high vapor pressure.The doped Co atoms radically decrease bandgap and lithium ion diffusion energy barrier of monolayer MoS2 and can be transformed into ultrasmall Co nanoparticles (~2 nm) to induce strong surface-capacitance effect during conversion reaction.The Co doped monolayer MoS2 shows ultrafast ion transport capability along with ultrahigh capacity and outstanding cycling stability as lithium-ion-battery anodes.High theoretical capacity and unique layered structures make MoS2 a promising lithium-ion battery anode material. However, the anisotropic ion transport in layered structures and the poor intrinsic conductivity of MoS2 lead to unacceptable ion transport capability. Here, we propose in-situ construction of interlayer electrostatic repulsion caused by Co2+ substituting Mo4+ between MoS2 layers, which can break the limitation of interlayer van der Waals forces to fabricate monolayer MoS2, thus establishing isotropic ion transport paths. Simultaneously, the doped Co atoms change the electronic structure of monolayer MoS2, thus improving its intrinsic conductivity. Importantly, the doped Co atoms can be converted into Co nanoparticles to create a space charge region to accelerate ion transport. Hence, the Co-doped monolayer MoS2 shows ultrafast lithium ion transport capability in half/full cells. This work presents a novel route for the preparation of monolayer MoS2 and demonstrates its potential for application in fast-charging lithium-ion batteries.

Single‐Layered MoS2 Fabricated by Charge‐Driven Interlayer Expansion for Superior Lithium/Sodium/Potassium‐Ion‐Battery Anodes

Single-layered MoS2 is a promising anode material for lithium-ion batteries (LIBs), sodium-ion batteries (SIBs), and potassium-ion batteries (PIBs) due to its high capacity and isotropic ion transport paths. However, the low intrinsic conductivity and easy-agglomerated feature hamper its applications. Here, a charge-driven interlayer expansion strategy that Co2+ replaces Mo4+ in the doping form to endow MoS2 layers with negative charges, thus inducing electrostatic repulsion, together with the insertion of gaseous groups, to drive interlayer expansion which once breaks the confinement of interlayer van der Waals force, single-layered MoS2 is obtained and uniformly dispersed into carbon matrix arising from the transformation of carbonaceous gaseous groups under high vapor pressure, is proposed. Co atom doping helps enhance the intrinsic conductivity of single-layered MoS2 . Carbon matrix effectively prevents agglomeration of single-layered MoS2 . The doped Co atoms can be fully transformed into ultrasmall Co nanoparticles during conversion reaction, which enables strong spin-polarized surface capacitance and thus significantly boosts ion transport and storage. Consequently, the prepared material delivers superb Li/Na/K-ion storage performances, which are best in the reported MoS2 -based anodes. The proposed charge-driven interlayer expansion strategy provides a novel perspective for preparing single-layered MoS2, which shows huge potential for energy storage.

Synthesis of Crystalline Phosphine-Graphdiyne with Self-Adaptive p-π Conjugation.

"Dynamic" behavior materials with high surface activity and the ability of chemical bond conversion are the frontier materials in the field of renewable energy. The outstanding feature of these materials is that they have adaptive electronic properties that external stimuli can adjust. An original discovery in a new crystalline two-dimensional phosphine-graphdiyne (P-GDY) material is described here. Although the p-π conjugation of most trivalent phosphorus π-systems is insignificant because of the pyramidal configuration, the lone pair electrons of phosphorus atoms participate strongly in the delocalization under the influence of the interlayer van der Waals forces in P-GDY. Due to the dynamically reversible nature of noncovalent interactions (p-π conjugation), P-GDY exhibits a specific adaptive behavior and realizes the responsive reversible transport of a lithium ion by regulating p-π interactions. Our findings would provide the potential to develop a new family of responsive materials with tunable structures.

Recent progress in mid-infrared photodetection devices using 2D/nD (n=0, 1, 2, 3) heterostructures

Mid-infrared (MIR) photodetection plays an important role in a variety of modern technologies, such as biomedical devices, free-space communication and security. In the past decade, 2D materials and heterostructures have been widely utilized in MIR photodetectors because of the tunable bandgaps, high carrier mobility and strong light absorption. Apart from 2D/2D heterostructures, 2D material can also form mixed-dimensional heterostructures with other dimensional materials thanks to the interlayer van der Waals forces, which presents a much broader group and greatly expands the research of MIR photodetectors due to the synergistic advantages. In this review, the recent progress of MIR photodetectors based on van der Waals (vdWs) heterostructures, including all-2D and mixed-dimensional heterostructures is systematically summarized. First, the common synthesis strategies to realize vdWs heterostructures are presented. Then, the motivation, device design, mechanism and performance of MIR photodetectors are presented and discussed in classification of various kinds of vdWs heterostructures. Finally, the current challenges and some future prospects in this research field are suggested.

Dimethyl 2‐Methylglutarate (Iris): A Green Platform for Efficient Liquid‐Phase Exfoliation of 2D Materials

AbstractLiquid‐phase exfoliation of bulk crystals of layered materials, held together by weak interlayer van der Waals forces, is an ideal platform for scalable synthesis of nanosheets. However, it is mandatory to substitute existing solvents, regrettably displaying severe limitations due to toxicity. Here, dimethyl 2‐methylglutarate (Rhodiasolv Iris) is validated for efficient liquid‐phase exfoliation of selected van der Waals materials, namely, MoS2, WS2, GeSe, and graphite. Here, we show that Iris‐assisted liquid phase exfoliation provides high yield (up to 52%) of flakes of 2D materials with aspect ratio as high as 500. Considering the various advantages of Iris over the state‐of‐the‐art solvents, including the absence of toxicity and its biodegradability, this work opens new possibilities for the ecofriendly production of 2D materials and for their extensive usage in industrial processes hitherto semi‐unexplored, owing to the toxicity of state‐of‐the‐art solvents (including the production of drinkable water or fruit juice concentration). Accordingly, the validation of Iris for sustainable liquid‐phase exfoliation of van der Waals crystals has intrinsic outstanding potential commercial impact. Moreover, here the values of the surface tension, Hansen solubility parameter, and viscosity of Rhodiasolv Iris are reported for the first time, which will be relevant also for any other sustainable process based on this new green solvent.

Constructing van der Waals heterostructures by dry-transfer assembly for novel optoelectronic device

Since the first successful exfoliation of graphene, the superior physical and chemical properties of two-dimensional (2D) materials, such as atomic thickness, strong in-plane bonding energy and weak inter-layer van der Waals (vdW) force have attracted wide attention. Meanwhile, there is a surge of interest in novel physics which is absent in bulk materials. Thus, vertical stacking of 2D materials could be critical to discover such physics and develop novel optoelectronic applications. Although vdW heterostructures have been grown by chemical vapor deposition, the available choices of materials for stacking is limited and the device yield is yet to be improved. Another approach to build vdW heterostructure relies on wet/dry transfer techniques like stacking Lego bricks. Although previous reviews have surveyed various wet transfer techniques, novel dry transfer techniques have been recently been demonstrated, featuring clean and sharp interfaces, which also gets rid of contamination, wrinkles, bubbles formed during wet transfer. This review summarizes the optimized dry transfer methods, which paves the way towards high-quality 2D material heterostructures with optimized interfaces. Such transfer techniques also lead to new physical phenomena while enable novel optoelectronic applications on artificial vdW heterostructures, which are discussed in the last part of this review.

Universal Principle for Large-Scale Production of a High-Quality Two-Dimensional Monolayer via Positive Charge-Driven Exfoliation

On the basis of the intrinsic characteristics of the layered materials, here we report a universal principle for the production of intact monolayers via layer-by-layer exfoliation from their bulk via positive charge doping. At experimental accessible densities (nc) of ∼1014 cm-2, various multilayer crystals, including graphite, hexagonal boron nitride, transition metal dichalcogenides, MXenes, and black phosphorus, can be exfoliated into the corresponding monolayers through ab initio density functional theory stimulations. The carrier critical thresholds for exfoliating are found to be nearly independent of thickness but dependent on surface size. The universality of positive charge-driven exfoliation originates from the common intrinsic characteristics of electronic structures for layered materials. The positively doped charges that preferentially accumulate near the surface induce interlayer repulsion, leading to layer-by-layer exfoliation when repulsion surpasses interlayer van der Waals force. This strategy may open the possibility of producing diverse high-quality two-dimensional monolayers with a small number of defects toward large-scale manufacturing.

A discrete-continuum mosaic model for the buckling of inner tubes of double-walled carbon nanotubes under compression

In this paper, the discrete-continuum mosaic (DCM) method is applied for predicting buckling of inner tubes of double-walled carbon nanotubes (DWNTs). The moving least squares (MLS) approximation is used for linking discrete atomic model and the corresponding continuum counterpart. Actual atomic positions are used as interaction points for the interlayer van der Waals (vdW) force of DWNTs, which can accurately capture the discreteness of non-bonded interactions, and a DCM contact model is constructed. A variationally consistent meshless computational scheme based on the DCM contact model is developed for simulating the buckling of inner tubes of DWNTs upon compression. Results show that both the lengths and radii of outer tubes can influence the buckling patterns of the corresponding inner tubes. The inner tubes of DWNTs with the interlayer spacing of 0.2034 nm have strongest buckling resistance for the case that the outer tubes are not extremely short. The local critical axial compression ratio of the inner tube increases with the lengths of the inner and outer tube increasing given that the interlayer spacing of a DWNT is less than 0.34 nm.