Behavior Of Monolayers Research Articles

Intercalation-Induced Monolayer Behavior in Bulk NbSe2.

Superconductivity at the 2D limit is significant for advancing fundamental physics, leading to extensive research on monolayer two-dimensional materials. In particular, monolayer transition metal dichalcogenides such as NbSe2 exhibit Ising superconductivity due to broken in-plane inversion symmetry and strong spin-orbit coupling, which has garnered significant attention. In this letter, we adopted an organic cation intercalation technique to modulate the interlayer interaction of NbSe2 by expanding the interlayer distance, thereby making intercalated NbSe2 behave similarly to monolayer NbSe2. The interlayer distances of NbSe2 intercalated with THA+, CTA+, and TDA+ cations are almost double or triple that of pristine NbSe2. The superconducting transition temperature (Tc) of THA-NbSe2 is comparable to that of pristine NbSe2, while the charge density wave (CDW) transition temperature is higher. The Tc of intercalated NbSe2 decreases with a reduced hole concentration, and the enhanced CDW is ascribed to the dimensional reduction. Notably, the in-plane upper critical field of intercalated NbSe2 significantly exceeds the Pauli paramagnetic limit, which is similar to the Ising superconductivity observed in monolayer NbSe2. Our work demonstrates that the organic cations intercalated two-dimensional materials exhibit behavior similar to their monolayer counterparts, providing a convenient platform for exploring and modulating physical phenomena at the two-dimensional limit.

Strain Engineering of ScYCCl2 MXene Monolayer and Intercalation of Metal-ions on MXene Surface: A DFT Study

The present work theoretically examines the influence of bi-axial strain on functionalized ScYCCl2 monolayer. The indirect to direct band gap transition on tensile conditions and the phase transition from semiconductor to metal on compressive strain have been studied. The analysis of extreme conditions of 10% compressive and 10% tensile strain through phonon and AIMD simulations underscore the kinetic and thermal stability, respectively of the monolayer under strain. These findings assure the possibility of experimental synthesis of the ScYCCl2 monolayer. After metallization, ScYCCl2 MXene is used as an anode of metal-ion (−Na, −K, −Li, −Mg) batteries as it has high theoretical storage capacity and low open circuit voltage. Work function engineering and the strain-dependent optical behavior of the ScYCCl2 monolayer have been examined. The work function of the ScYCCl2 monolayer has been raised under compressive strain and decreased under tensile strain. The Crystal Orbital Hamiltonian Population has been simulated under tensile and compressive strain to check the bond- strengths. Hence, the ScYCCl2 monolayer has the capability to alter its characteristics under strain. The improved optical characteristics recommend its applications in low-dimensional photonic devices and metallization after compressive strain recommends its energy storage applications in metal-ion batteries.

Cracking resistance behavior of HVAF-sprayed monolayer and hierarchical Fe-based amorphous coatings under bending stress

The bending strength and fracture toughness are two key indicators that determine the service performance of thermally sprayed Fe-based amorphous coatings (AMCs) in harsh environments. Unfortunately, due to the inherent heterogeneous porosity and limited thickness (typically <1 mm) of the coatings, obtaining these properties is constrained by traditional fracture analysis methods. To address this, a three-point bending combined with the digital image correlation (DIC) method, without prefabricating notch or removing substrate, was proposed in the current work, and the effect of hierarchical structures on the fracture performance of the coatings was successfully revealed. Excitingly, the results show that compared to monolayer coating, hierarchical structures comprising two layers with different porosities can realize the synergistic improvement in the fracture strength and fracture strain of the coatings by alleviating local stress concentration and inducing crack deflection. Further, a finite element method (FEM) was employed to gain insight into the intrinsic relationship between the coating microstructures and the crack evolution behavior. This work not only proposes a simple method for evaluating the fracture performance of Fe-based AMCs sprayed with high velocity air fuel (HVAF), but also presents an innovative idea for optimizing the coating's properties.

Intercellular friction and motility drive orientational order in cell monolayers

Spatiotemporal patterns in multicellular systems are important to understanding tissue dynamics, for instance, during embryonic development and disease. Here, we use a multiphase field model to study numerically the behavior of a near-confluent monolayer of deformable cells with intercellular friction. Varying friction and cell motility drives a solid-liquid transition, and near the transition boundary, we find the emergence of local nematic order of cell deformation driven by shear-aligning cellular flows. Intercellular friction contributes to the monolayer's viscosity, which significantly increases the spatial correlation in the flow and, concomitantly, the extent of nematic order. We also show that local hexatic and nematic order are tightly coupled and propose a mechanical-geometric model for the colocalization of [Formula: see text] nematic defects and 5-7 disclination pairs, which are the structural defects in the hexatic phase. Such topological defects coincide with regions of high cell-cell overlap, suggesting that they may mediate cellular extrusion from the monolayer, as found experimentally. Our results delineate a mechanical basis for the recent observation of nematic and hexatic order in multicellular collectives in experiments and simulations and pinpoint a generic pathway to couple topological and physical effects in these systems.

Thermodynamic Study on Biomimetic Legionella gormanii Bacterial Membranes.

The presented studies were aimed at determining the interactions in model membranes (Langmuir monolayers) created of phospholipids (PL) isolated from Legionella gormanii bacteria cultured with (PL + choline) or without (PL - choline) choline and to describe the impact of an antimicrobial peptide, human cathelicidin LL-37, on PL's monolayer behavior. The addition of choline to the growth medium influenced the mutual proportions of phospholipids extracted from L. gormanii. Four classes of phospholipids-phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylglycerol (PG), cardiolipin (CL), and their mixtures-were used to register compression isotherms with or without the LL-37 peptide in the subphase. Based on them the excess area (Ae), excess (ΔGe), and total (ΔGm) Gibbs energy of mixing were determined. The thermodynamic analyses revealed that the PL - choline monolayer showed greater repulsive forces between molecules in comparison to the ideal system, while the PL + choline monolayer was characterized by greater attraction. The LL-37 peptide affected the strength of interactions between phospholipids' molecules and reduced the monolayers stability. Accordingly, the changes in interactions in the model membranes allowed us to determine the difference in their susceptibility to the LL-37 peptide depending on the choline supplementation of bacterial culture.

Layer-Dependent Gas Sensing Mechanism of 2D Titanium Carbide (Ti3C2Tx) MXene.

Monolayers of Ti3C2Tx MXene and bilayer structures formed by partially overlapping monolayer flakes exhibit opposite sensing responses to a large scope of molecular analytes. When exposed to reducing analytes, monolayer MXene flakes show increased electrical conductivity, i.e., an n-type behavior, while bilayer structures become less conductive, exhibiting a p-type behavior. On the contrary, both monolayers and bilayers show unidirectional sensing responses with increased resistivity when exposed to oxidizing analytes. The sensing responses of Ti3C2Tx monolayers and bilayers are dominated by entirely different mechanisms. The sensing behavior of MXene monolayers is dictated by the charge transfer from adsorbed molecules and the response direction is consistent with the donor/acceptor properties of the analyte and the intrinsic n-type character of Ti3C2Tx. In contrast, the bilayer MXene structures always show the same response regardless of the donor/acceptor character of the analyte, and the resistivity always increases because of the intercalation of molecules between the Ti3C2Tx layers. This study explains the sensing behavior of bulk MXene sensors based on multiflake assemblies, in which this intercalation mechanism results in universal increase in resistance that for many analytes is seemingly inconsistent with the n-type character of the material. By scaling MXene sensors down from multiflake to single-flake level, we disentangled the charge transfer and intercalation effects and unraveled their contributions. In particular, we show that the charge transfer has a much faster kinetics than the intercalation process. Finally, we demonstrate that the layer-dependent gas sensing properties of MXenes can be employed for the design of sensor devices with enhanced molecular recognition.

Sensing-performance improvement of 2D MoSH based gas sensors for detecting NO, NO2, and NH3 gas molecules

Nitrogen group oxide is one of the major pollutants in the air, and its accurate and rapid detection is essential for environmental protection and human health. Therefore, it is of great significance to develop high-performance new line sensor for Nitrogen group oxide. Here, we investigate the potential of monolayer 2D MoSH materials as candidates for NO gas sensing using a combination of density functional theory and non-equilibrium functions to construct nanodevices based on MoSH monolayer, and theoretically study the adsorption behavior of MoSH monolayer to NO, NO2, and NH3 gas molecules. The results indicate that MoSH monolayer exhibit metallicity, and nanodevices based on 2D MoSH monolayer exhibit anisotropic transport properties and significant negative differential resistance effects(NDR). More interestingly, gas sensors based on MoSH monolayers exhibit typical chemical adsorption of NO, NO2, and NH3 gas molecules, and the anisotropic transport properties still maintain, but significant differences of sensitivity appear for these three gas molecules. Specifically, the MoSH based gas sensor has the highest sensitivity to NO, reaching 93.1% and 76.3% along the armchair and zigzag directions, respectively. These results show that 2D MoSH monolayer is an excellent gas-sensing material with excellent application prospects for NO gas detection.

Metallic nature of T-graphene sheet and nanotubes

The band structure, density of states (DOS), and Pauli magnetic susceptibility (PMS) of T-graphene nanotubes (TGNTs) with varying chiralities and diameters are investigated using the tight-binding Hamiltonian model and Green's function formalism. We analyze two edge types: zigzag (zTGNT) and armchair (aTGNT). Our findings reveal that both zTGNTs and aTGNTs exhibit metallic behavior regardless of diameter. Notably, aTGNTs feature Dirac points in their band structure, with their abundance increasing with nanotube diameter. As compared to graphene, when the diameter of the nanotube increases, aTGNTs reveal more Dirac points at the Fermi level. Additionally, increasing the diameter leads to the emergence of additional sub-bands in the band structure and van-Hove singularities in the DOS diagrams. Consequently, the PMS curves exhibit a crossover, dividing into distinct regimes at varying temperatures. The metallic properties of both TGNT types are apparent in the PMS curves, attributed to the proportional relationship between PMS and DOS. Furthermore, the DOS curves converge towards monolayer behavior as the TGNT diameter increases significantly.

First-principles design of PtPd bimetal dispersed WTe2 monolayer for sensing thermal runaway gases: Enhanced performance against single Pt or Pd dispersion

To conduct the early-monitoring of thermal runaway for the Li-ion battery (LIBs), this work purposes PtPd bimetal dispersed WTe2 (PtPd-WTe2) monolayer as a promising sensing material to realize the high-sensitive detection of thermal runaway gases (H2, CO, CO2, C2H2 and C2H4). The adsorption behavior of PtPd-WTe2 monolayer upon such five gas molecules are compared with single Pt- and Pd-dispersed WTe2 monolayer from the first-principles insight to highlight the combined catalytic property of two noble metal atoms. Results reveal that Pt-, Pd- and PtPd-WTe2 monolayer all behave good chemical and thermal stability at 498 K with good binding force between the noble metal atom(s) and the pristine WTe2 surface. Besides, PtPd-WTe2 monolayer behaves much enhanced adsorption performance with more negative adsorption energy and much higher sensing response with larger bandgap changing rate than Pt- and Pd-WTe2 monolayer upon five typical gas molecules. Moreover, the desorption property analysis manifests the necessity conducting the heating process to realize the reusability of PtPd-WTe2 monolayer for gas sensing. These findings manifest the strong potential of PtPd-WTe2 monolayer as a resistive gas sensor for detections of the thermal runaway gas species thus evaluating the operation status of the LIBs, which may stimulate the further deeper investigations about WTe2-based materials for gas sensing applications across multiple fields.

Unveiling thermally driven photoluminescence in CVD grown MoS[formula omitted] dendritic flake

High-quality MoS2 nanostructures were fabricated via chemical vapor deposition technique on SiO2/Si substrate. In this paper, the effect of temperature on the photoluminescence behavior of MoS2 dendritic flake is addressed. We scrutinized the photoluminescence spectra of monolayer and multilayer regions of MoS2 in the temperature range 300 K–680 K. Monolayer and multilayer behavior of MoS2 flakes are confirmed by Raman and Photoluminescence spectroscopy. The excitonic peaks from the multilayer regime become less intense and show a red shift compared to the monolayer PL spectra. Thermally-induced bandgap modulation of MoS2 is demonstrated. The excitonic intensity and peak positions reveal pronounced temperature-dependent changes. These changes are explicable through the increased electron–phonon interaction and lattice rearrangements. Furthermore, first principle calculations are employed to glean insight into the impact of atomic rearrangements on the band gap behavior of MoS2. Our research presents a detailed understanding of thermally driven band gap modulation of monolayer and multilayer MoS2, which is essential for designing optoelectronic devices.

Role of Density and Conformational Composition in the Surface-to-Bulk Molecular Dosing of Photosensitive Surfactant Monolayers.

Poorly water-soluble photosensitive monolayers might enable very precise control of the rate and number of desorbing molecules by controlling both the monolayer density and conformational composition. In this perspective, we systematically characterized the interfacial behavior of Langmuir monolayers consisting of a poorly water-soluble azobenzene-containing surfactant as a function of its trans/cis ratio. Precise control of the conformational ratio was achieved by controlling the UV irradiation time, allowing researchers to investigate compositions spanning from 100% trans to 90% cis. Our results demonstrate that in 100% trans monolayers, molecules do not desorb with compression until a threshold area is reached. Instead, the number of molecules desorbing in mixed trans-cis monolayers can be modulated by controlling both the composition and the compression rate. Additionally, the desorption rate at constant density is also strongly composition-dependent, and it accounts for two different regimes with two different characteristic times. We will show that trans molecules mostly desorb according to the slow regime while cis molecules conform to the fast one, but the two conformers mutually influence each other.

Impact of wrinkle orientation on the nanotribological properties of chemical vapor deposited TMD monolayers using AFM

Structural defects in two-dimensional (2D) materials are ubiquitous and can influence their physical and chemical properties. The presence of structural defects in single atom thick 2D materials such as graphene is detrimental to the tribological properties and is well documented; however, their effects on various other 2D materials such as transition metal dichalcogenides (TMDs) remain largely unexplored. Here, we report the role of wrinkles’ orientation on the nanoscale tribological behavior of the chemical vapor deposited (CVD) tungsten disulfide (WS2) monolayers. Our molecular dynamics (MD) simulations reveal the underlying atomistic mechanism which indicates the presence of wrinkles exhibiting various orientations, and maximum damage occurred when the tip moved at a 45-degree angle to the wrinkle. This underscores the significant influence of wrinkles’ orientation on the wear behavior of WS2 monolayers.

Impact of cholesterol on the structure and phase separation of DPPC Langmuir monolayers: Experiments and simulations

Cholesterol is a lipid that plays a key role mainly in the plasma membrane of animal cells, determining their structural and mechanical properties. While Langmuir monolayers have been a traditional model for studying these membranes, they may not fully capture microscopic phenomena. We studied mixed Langmuir monolayers of DPPC and cholesterol in various proportions, using a Langmuir trough for surface compression isotherms and micro-Brewster Angle Microscopy (MicroBAM) for imaging. Furthermore, atomistic Molecular Dynamics (MD) simulations were used to examine molecular distributions, geometric conformations, and emergence of a gas phase in the monolayers. Both experimental and simulation results were compared to obtain a comprehensive understanding. The results reveal strong attraction between DPPC tails and cholesterol, increasing monolayer stiffness and density. These interactions align the lipid tails more perpendicularly to the water surface, effectively minimizing their projected area and preventing tail entanglement. Consequently, the reduced flexibility triggers a phase separation in the monolayer at smaller areas per lipid, with low-density voids and denser regions, as observed in both MicroBAM and simulations. These outcomes emphasize the critical role of cholesterol in biological membranes. Finally, the consistency of MD simulations with experiments validate them as a valuable tool for investigating lipid monolayer behavior.

Sustainable water sterilization by nano-ZnO using anisotropic polysaccharide columns derived from agro-waste stalk

The escalating demand for clean water and proliferation of microbial contamination in water have challenged ecosystems and human health safety. ZnO NPs are widely used as environmental restoration agents, but their efficacy in water decontamination is hindered by low biological toxicity. In order to enhance its sterilization efficiency, we propose a top-down strategy utilizing the unique maze structure of corn stalk pith (CSP) as a germ trapper for ZnO. The in-situ delignified CSP offers abundant active sites for the adsorption of Zn2+, exhibiting the typical behaviors of monolayer, physisorption, endothermicity, spontaneity, and randomness. This adsorption behavior exerts an influence on microscopic morphology of the composite column, consequently resulting in alterations to antibacterial properties. The results show that the hybrid column fabricated under the Zn2+ initial dosage of 1.00 mol/L at 30 h for 40 °C, possesses such optimal features as stacked grain-shaped ZnO NPs of 669.3 mg/g loading amount with adhesion coefficients of 0.73 ∼ 0.86 for bacterial microparticles. Consequently, the assembled bio-filter can eliminate E. coli and S. aureus as high as 99.7 % and 96.5 % respectively, attributed to CSPP labyrinth structure to enhance pathogen capture from water and facilitate ZnO-mediated inactivation. The collective findings emphasize the viability of agro-waste stalks as bio-filters for water purification.

Mechanical and electronic behaviour of TMDC nanotubes and monolayers: molecular simulations

ABSTRACT Transition metal dichalcogenides (TMDCs) are among the most exciting materials in nano-size particles. In this study, MX2 (M = Mo and W; X = S, Se, and Te) nanotubes and monolayers were evaluated to show the structural, mechanical, and electronic properties. The results showed that the stability of MX2 monolayers changes similarly to nanotubes with the sequence of MS2 > MSe2 > MTe2 (M = Mo and W). Besides, MX2 nanotubes and monolayers are semiconductors, and the band gap energy increases with a similar sequence with stability properties. The structural stability and band gap energy of WX2 structures are more than MoX2 structures. Young's modulus of nanotubes was studied with density functional theory (DFT) and molecular dynamics (MD) simulations with Stillinger-Weber (SW) potential methods. The results are similar to the formation and band gap energy showing that Young's modulus of the MX2 structures is in order of MS2 > MSe2 > MTe2 (M = Mo and W) and WX2 > MoX2 (X = S, Se or Te). Structural defects in monolayers, which were M-vacancy (VM), X2-vacancy (VX2), M-X2-vacancy (VM-X2), and M-X4-vacancy (VM-X4), were studied and it showed that the mechanical properties could be decreased. However, the defects do not affect electronic properties.

Corrosion behavior of TiN monolayer and CrN/TiN multilayer coatings: Impact of immersion time and saline solution type

AbstractThe corrosion behavior of the TiN monolayer and CrN/TiN multilayer coatings deposited via cathodic arc evaporation physical vapor deposition (CAE‐PVD) on the Ti–6Al–4V substrates were evaluated in Ringer's and Hank's physiological saline electrolytes. XRD (x‐ray diffractometry) and scanning electron microscopy (SEM) analysis were used to characterize the coatings. The corrosion behavior of coatings was assessed by impedance spectroscopy and potentiodynamic polarization techniques. The results showed that the corrosion resistance of coatings was increased in the order of TiN‐Ringer's &lt; TiN‐Hank's &lt; CrN/TiN‐Ringer's &lt; CrN/TiN‐Hank's. Therefore, it can be concluded that the CrN/TiN coating, due to having a large number of interfaces and a smoother surface with fewer macroparticles and pinholes, is more efficient in raising the corrosion resistance properties of titanium than TiN monolayer coating. Moreover, it was observed that Ringer's solution is a more severe environment than Hank's solution. Both coatings, because of the precipitation of a protective corrosion products layer on their surface, showed an enhancement in corrosion resistance with increasing the immersion time from 1 to 14 days in Hank's. The results suggest TiN monolayer and CrN/TiN multilayer coatings as promising candidates for biomedical applications.

Adsorption of NH3, HCHO, SO2, and Cl2 gasses on the o-B2N2 monolayer for its potential application as a sensor

The adhesion behaviour of the o-B2N2 monolayer (OBNML) onto the toxic gasses, namely NH3, HCHO, SO2, and Cl2, was scrutinized through DFT. The adhesion attributes, stet density, differential charge density and the optimal structure of the adhesion systems were investigated, and the findings indicated the stability of the OBNML. Furthermore, to further investigate the gas adhesion attributes, the workfunction, sensitivity, recovery time (RT) and the energy gap were examined. Based on the results, the optimal RT for the OBNML at high temperatures was easier, and the higher sensitivity and the more change in the workfunction also reflected the better adhesion capability of the OBNML. The findings also showed that the OBNML was capable of acting as an adsorbent of these toxic gasses, and it can be useful in practically purifying the air and protecting the environment.

Adsorption behavior of Rh-VSe2 monolayer upon dissolved gases in transformer oil and the effect of applied electric field

Dissolved gas analysis (DGA) in transformer oil is an effective method to monitor the operating status of transformers. Based on fundamental principles, the adsorption behavior of decomposed gases from transformer oil (CO, CH4, C2H2, C2H4, and C2H6) on intrinsic and Rh-doped VSe2 monolayers is examined. The adsorption structure, adsorption energy, charge transfer, density of state, electron density difference, work function, and desorption properties are discussed to evaluate the potential applications of VSe2 monolayers as scavengers and gas-sensing materials for transformer oil decomposed gases. The results show that Rh dopant can be stably adsorbed on the surface of VSe2 monolayer, and the minimum binding energy is −4.957 eV. The adsorption behavior of oil-dissolved gases on the intrinsic VSe2 monolayer is weak. The sensing performance of VSe2 monolayer for oil-dissolved gas molecules is significantly enhanced after the introduction of Rh dopant. The sensing performance of Rh-VSe2 monolayer for CO, C2H2, C2H4 and C2H6 gases is stronger than that of CH4. Furthermore, in order to improve the applicability of the Rh doped VSe2 monolayer for the detection of oil-dissolved gases molecules. The effect of electric field on the sensing properties of gas molecules on Rh doped VSe2 monolayers is also investigated. Finally, the desorption performance of the system is evaluated based on the transition state theory and Van’t-Hoff-Arrhenius expression. The findings of the study not only disclose the method by which the Rh doped VSe2 monolayer detects the breakdown gasses in transformer oil, but they also offer theoretical recommendations for the advancement of VSe2-based sensors and scavengers.

Enhance Carrier Diffusion of Monolayer MoSe2 by Interface Engineering.

Two-dimensional materials hold great potentials for beyond-CMOS (complementary metal-oxide-semiconductor) electronical and optoelectrical applications, and the development of field effect transistors (FET) with excellent performance using such materials is of particular interest. How to improve the performance of devices thus becomes an urgent issue. The performance of FETs depends greatly on the intrinsic electrical properties of the channel materials, meanwhile the device interface quality, such as extrinsic scattering of charged impurities, charge traps, and substrate surface roughness have a great influence on the performance. In this paper, the impact of the interface quality on the carrier diffusion behaviors of monolayer (ML) MoSe2 has been investigated by using an in situ ultrafast laser technique to avoid the surface contamination during device fabrication process. Two types of self-assembled monolayers (SAMs) are introduced to modify the gate dielectric surface through an interface engineering approach to obtain chemical-stable interfaces. The results showed that the transport properties of ML MoSe2 were enhanced after interface engineering, for example, the carrier mobility of ML MoSe2 was improved from ∼59.4 to ∼166.5 cm2 V-1 s-1 after the SAM modification. Meanwhile, the photocarrier dynamics of ML MoSe2 before and after interfacial engineering were also carefully studied. Our studies provide a feasible method for improving the carrier diffusion behaviors of such materials, and making them suited for application in future integrated circuit.

Modulated bandgap and gas adsorption behavior on two-dimensional SrAl2S4 monolayer: Potential applications for photovoltaic and energy storage

The structure of a novel two-dimensional layered material SrAl2S4 monolayer has been proposed, and its kinetic and thermodynamic stability has been confirmed. Researches have shown that SrAl2S4 monolayer is a semiconductor material with a bandgap of 1.630 eV for PBE and 2.798 eV for HSE06 at the ground state. Under biaxial strain, SrAl2S4 monolayer can complete the transition from a direct bandgap semiconductor to an indirect bandgap semiconductor, and its bandgap can vary between 0.187 eV and 1.712 eV. In addition, We have considered the adsorption behavior of SrAl2S4 monolayer for hydrogen and oxygen molecules, and the results show that SrAl2S4 monolayer adsorbed H2 molecules remains a direct bandgap semiconductor, whereas SrAl2S4 monolayer adsorbed O2 molecules show indirect bandgap semiconductor properties. At the same time, the adsorption of O2 molecules causes a flat band near the Fermi level, which increases the electrical conductivity. The few charges transfer observed between the SrAl2S4 monolayer and gas molecules confirms that the adsorption process of gas molecules on SrAl2S4 monolayer is physical adsorption. The tunable bandgap characteristics and good adsorption behavior of hydrogen and oxygen exhibited by SrAl2S4 monolayer make it a promising candidate material in the fields of photovoltaics and energy storage.