Stable Monolayers Research Articles

Fabrication of stable monolayer liquid marbles with reduced particle coverage and locomotion on hydrophilic surface

Liquid marbles are non-wetting, particle-covered microdroplets with a core-shell structure that are used in sample transport, material synthesis, and real-time sensing. Optimizing the distribution of shell particles remains a challenge, due to a tendency for aggregation via spontaneous assembly, which often leads to multilayered structures. Here, we outline a simple method for fabricating water-filled, monolayer liquid marbles with adjustable particle coverage rates, greatly reducing particle consumption. The soft liquid marbles are enclosed by a small quantity of modified polystyrene microspheres and display good atmospheric stability. The rolling behavior of flexible liquid marbles with wide coverage rates is then characterized. Contrary to common perception, the marbles with transparent openings exhibit high maneuverability on hydrophilic surfaces, and also excel in fusion, reaction and surface cleaning, with an elongated operational duration and a wide visualization range. The study provides new insights into the implementation of liquid marble-based miniaturized platforms.

Adjustment of ferromagnetism and improvement of the electronic structure of the TiI3 monolayer by the substitutional doping of 3d transition metal atoms: Ab-initio investigation

Two dimensional Van der Waals materials are very attractive for several researchers because of their distinctive properties and their interesting applications in data storage and spintronic devices. Titanium triiodide (TiI3), which is classified among transition metal trihalides (MX3), has received more attention after CrI3 and VI3 monolayers. Here, we explore the structural, electronic and magnetic properties of pure and 3d TM (TM = Sc, V, Cr, Mn and Fe) doped TiI3 monolayer using first-principles calculations, based on the GGA + Ueff approach. We confirmed the dynamic stability of TiI3 monolayer using phonon calculations and the thermal stability of pure and TM-doped TiI3 monolayers by performing AIMD simulation. We further found that the pure TiI3 monolayer is a stable ferromagnetic semiconductor with intrinsic magnetism. The introduction of vacancy defects in the pristine TiI3 monolayer showed that it is desirable to introduce TM atoms into Ti positions, which led to the improvement of its electronic and magnetic properties. The Sc-doped system keeps its semiconductor behavior with a reduction in the width of the band gap, whereas V-, Cr- and Fe-doped TiI3 monolayers turn into half semiconductors (HSC). Even more impressive, the Mn-doped system is found to be a bipolar ferromagnetic semiconductor (BFMS). We applied spin orbit coupling (SOC) on simulated monolayers, and showed that it affected them by changing their band gaps widths, especially in Fe-doped TiI3 monolayer. Furthermore, we found in all doped systems a ferromagnetic stability, an enhancement of the total magnetic moment, up to 10 μB in Cr- and Fe-doped monolayers, high Curie temperatures, up to 260 K, and high magnetic anisotropic energies, especially in Mn-doped TiI3 monolayer which makes it possess a long range ferromagnetic order. These interesting results concerning the electronic and magnetic properties of pure and transition metals-doped TiI3 monolayers are extremely beneficial for tune and enhance electronic and spintronic devices.

2D Janus ZrSSe/SnSSe Heterostructure: A Promising Candidate for Photocatalytic Water Splitting.

The distinctive physical characteristics and wide range of potential applications in optoelectronic and photovoltaic devices have ignited significant interest in two-dimensional materials. Intensive research attention has been focused on Janus transition metal dichalcogenides due to their unique properties resulting from symmetry disruption and their potential in photocatalysis applications. Motivated by the current fascination with Janus TMD heterostructures, we conducted first-principles calculations to examine the stability, electronic, and optical properties of monolayers consisting of ZrSSe, SnSSe, and the ZrSSe/SnSSe heterostructure. The results indicate that the Janus ZrSSe/SnSSe heterostructure exhibits a structural and mechanical stability. Using the HSE06 functional, the ZrSSe/SnSSe heterostructure shows an indirect band gap of 1.20 eV, and band edge analysis reveals a type-II band alignment. The potential for photo/electrocatalysis in the ZrSSe/SnSSe heterostructure for water splitting or generating reactive oxygen species (ROS) has been explored, and it was found that the oxygen evolution reaction (OER) can spontaneously activate in acidic (pH = 0) media under light irradiation, with a potential of U = 1.82 eV. Additionally, the ZrSSe/SnSSe heterostructure exhibits strong light absorption across a wide range, from visible light to the ultraviolet region, at various levels. These findings open up possibilities for the application of ZrSSe/SnSSe-based materials in optoelectronic devices.

Exploring electronic features in monolayer and bilayer MX2 (M = Hf, Zr; X = S, Se) structures under shear strain

This study employed first-principles calculations to investigate the dynamic stability of monolayer, bilayer, and heterostructure systems of four MX2 (M = Hf, Zr and X = S, Se) TMDCs, as well as the influence of shear strain on their electronic properties. The computed binding energies and phonon dispersions demonstrate the excellent dynamic stability of bilayer systems, while the small effective masses of electrons and holes in monolayer systems suggest high carrier mobility. Under shear strain, the bandgap size and type of monolayer MX2 system and their vdW heterostructures are effectively modulated, transitioning to metallic behavior under certain strain conditions. Both types of heterostructures exhibit type-II band alignment, serving as direct bandgap semiconductors, facilitating effective electron-hole separation between different layers and thereby reducing recombination. This study elucidates the tunability of the electronic properties of monolayers, bilayers, and heterostructures of MX2 systems under shear strain, which is important for expanding material functionalities and optimizing device performance.

Beyond Conventional Charge Density Wave for Strongly Enhanced 2D Superconductivity in 1H-TaS2 Superlattices.

Noncentrosymmetric transition metal dichalcogenide (TMD) monolayers offer a fertile platform for exploring unconventional Ising superconductivity (SC) and charge density waves (CDWs). However, the vulnerability of isolated monolayers to structural disorder and environmental oxidation often degrade their electronic coherence. Herein, an alternative approach is reported for fabricating stable and intrinsic monolayers of 1H-TaS2 sandwiched between SnS blocks in a (SnS)1.15TaS2 van der Waals (vdW) superlattice. The SnS block layers not only decouple individual 1H-TaS2 sublayers to endow them with monolayer-like electronic characteristics, but also protect the 1H-TaS2 layers from electronic degradation. The results reveal the characteristic 3 × 3 CDW order in 1H-TaS2 sublayers associated with electronic rearrangement in the low-lying sulfur p band, which uncovers a previously undiscovered CDW mechanism rather than the conventional Fermi surface-related framework. Additionally, the (SnS)1.15TaS2 superlattice exhibits a strongly enhanced Ising-like SC with a layer-independent Tc of ≈3.0 K, comparable to that of the isolated monolayer 1H-TaS2 sample, presumably attributed to their monolayer-like characteristics and retained Fermi states. These results provide new insights into the long-debated CDW order and enhanced SC of monolayer 1H-TaS2, establishing bulk vdW superlattices as promising platforms for investigating exotic collective quantum phases in the 2D limit.

Formation of interfacial molecular film and metal‐trapping function of azacalixarene‐containing copolymers having spherulite‐forming ability

AbstractThe interfacial molecular film behavior of a newly synthesized copolymer having spherulite‐forming ability and consisting of an azacalixarene moiety and a polyethylene glycol linker was investigated. Furthermore, the ability of the azacalixarene ring in the copolymer Langmuir monolayer to trap metals from the subphase was examined. The copolymer formed a monolayer at the air/water interface with high‐density packing. In addition, the corresponding copolymer formed a stable interfacial monolayer whose behavior did not change significantly as the temperature of the subphase changed. The monolayer morphology exhibited a dot‐like crystalline domain. When the subphase contained cadmium ions, the cyclic moiety showed the ability to trap the metal cations. In this case, the distortion angle of the cup‐shaped conformation of the cyclic moiety in the organized molecular film expanded after metal trapping.Highlights LB film of a copolymer containing azacalixarene and PEG units was prepared. The copolymer formed a dense packing in the LB film. Copolymer film formed a surface morphology containing crystalline grains. The copolymer trapped Cd ions in the azacalixarene ring from the subphase. Due to trapping of Cd ions, the distortion angle of the ring widened by 7°.

Exploration of the two-dimensional transition metal phosphide MoP2 as anode for Na/K ion batteries

Transition metal phosphides are regarded to be potential anode materials for alkali metal ion batteries with abundant availability of the constituent elements. However, the volume changes and resulting structure deterioration during the charge-discharge process are challenges. Using evolutionary search combined with ab initio calculations, we discover a dynamically, thermally, and mechanically stable MoP2 monolayer, which turns out to be an excellent anode material for Na-ion batteries providing a high specific capacity of 339 mA h g−1, low diffusion barrier of 0.12 eV, and low open-circuit voltage of 0.48 V. The volume expansion (125%) is found to be decisively smaller than in the case of black phosphorus (443%), for example.

Band-structure tunability via modulation of planar buckling in ZnO monolayer: Manifestation in optoelectronic and photocatalytic properties

Two-dimensional ZnO materials, with their exceptional characteristics, hold great potential for novel nanoelectronic devices and catalysts. However, the strategy of modulating the electronic properties is still ongoing. To address this challenge, we conducted first-principles calculations to systematically investigate the structural stability, electronic properties and tunability of photocatalytic performance in ZnO monolayers with different planar buckling. The results indicate that ZnO monolayers with different buckling exhibit dynamical and thermal stability. The band edge positions of ZnO monolayers could be effectively controlled by planar buckling, and ZnO monolayers with suitable buckling can serve as potential candidates for visible-light driven water splitting for hydrogen generation. Furthermore, the narrowed band gaps in ZnO monolayers with increasing of planar buckling suggest their potential for use in the design of optoelectronic devices in nanoscale systems. In addition, the stability of buckled ZnO monolayers on Ag/Pt substrates and planar ZnO monolayer on semiconducting blue phosphorus (BlueP) are explored. Interestingly, Ag and Pt metal substrates have been found to be suitable for the growth of buckled ZnO monolayers. While BlueP monolayer is believed to serve as an excellent substrate for the growth of planar ZnO monolayers. These findings offer new strategy for designing planar or buckled ZnO monolayers with potential applications in futuristic nano-optoelectric and photocatalysis systems.

Ultrathick MA2N4(M'N) Intercalated Monolayers with Sublayer‐Protected Fermi Surface Conduction States: Interconnect and Metal Contact Applications

AbstractRecent discovery of ultrathick MoSi2N4(MoN)n monolayers open up an exciting platform to engineer two‐dimensional (2D) material properties via intercalation architecture. In this study, a series of ultrathick MA2N4(M'N) monolayers (M, M' = Mo, W; A = Si, Ge) is computationally investigated under both homolayer and heterolayer intercalation architectures, in which the same and different species of transition metal nitride inner core sublayer are intercalated by outer passivating nitride sublayers, respectively. The MA2N4(M'N) are stable metallic monolayers with excellent mechanical strength. Intriguingly, the metallic states around Fermi level are localized within the inner core sublayer. Carrier conduction mediated by electronic states around the Fermi level is thus spatially insulated from the external environment by the native outer nitride sublayers, suggesting the potential of MA2N4(M'N) in back‐end‐of‐line metal interconnect applications. N and Si (or Ge) vacancy defects at the outer sublayers create ‘punch through’ states around the Fermi level that bridges the carrier conduction in the inner core sublayer and the outer environment, forming an electrical contact akin to the ‘via' structures of metal interconnects. It is further shown that MoSi2N4(MoN) can serve as a quasi‐Ohmic contact to 2D WSe2. These findings reveal the potential of ultrathick MA2N4(MN) monolayers in interconnect and metal contact applications.

Pd-Adsorbed SiN3 Monolayer as a Promising Gas Scavenger for SF6 Partial Discharge Decomposition Components: Insights from the First-Principles Study.

Gas-insulated switchgear (GIS) equipment must be protected by detecting and eliminating the toxic SF6 partial discharge decomposition components. This study employs first-principles calculations to thoroughly investigate the interaction between a Pd-adsorbed SiN3 monolayer (Pd-SiN3) and four typical SF6 decomposition gases (H2S, SO2, SOF2, and SO2F2). The study also investigates the associated geometric, electrical, and optical characteristics along with the sensing sensitivity and desorption efficiency. The ab initio molecular dynamics (AIMD) simulations demonstrated the favorable stability of the Pd-SiN3 monolayer. Furthermore, the Pd-SiN3 monolayer exhibited strong chemisorption behavior toward H2S, SO2, SOF2, and SO2F2 gases because of the higher adsorption energies of -2.717, -2.917, -2.457, and -2.025 eV, respectively. Furthermore, significant changes occur in the electronic and optical characteristics of the Pd-SiN3 monolayer following the adsorption of these gases, resulting in remarkable sensitivity of the Pd-SiN3 monolayer in relation to electrical conductivity and optical absorption. Meanwhile, all of these gas adsorption systems exhibited extremely long recovery times. The aforementioned theoretical findings suggest that the Pd-SiN3 monolayer has the potential to be an effective gas scavenger for the storage or removal of the SF6 decomposition components. Additionally, it might function as a reliable one-time sensor for detecting these gases. The results potentially provide valuable theoretical guidance for maintaining the normal operation of the SF6 insulation devices.

Computational characterization of novel nanostructured materials: A case study of NiCl[formula omitted

A computational approach combining dispersion-corrected density functional theory (DFT) and classical molecular dynamics is employed to characterize the geometrical and thermomechanical properties of a recently proposed 2D transition metal dihalide NiCl2. The characterization is performed using a classical interatomic force field whose parameters are determined and verified through the comparison with the results of DFT calculations. The developed force field is used to study the mechanical response, thermal stability, melting and solidification of a NiCl2 monolayer on the atomistic level of detail. The 2D NiCl2 sheet is found to be thermally stable at temperatures below its melting point of ∼695 K. At higher temperatures, several subsequent structural transformations of NiCl2 are observed, namely a transition into a porous 2D sheet and a 1D nanowire. The MD simulations of NiCl2 cooling show that the molten NiCl2 system solidifies into an amorphous porous 2D structure at T∼450 K. The resulting structure has lower cohesive energy with respect to the initial 2D sheet. The computational methodology presented through the case study of NiCl2 can also be utilized to study the properties of other novel 2D materials, including recently synthesized NiO2, NiS2, and NiSe2.

Ru-Doped MoS2 Monolayer for Exhaled Breath Detection on Early Lung Cancer Diagnosis: A First-Principles Investigation.

Nanosensor-based patient exhaled breath detection is a practical and effective way to detect lung cancer early. In this paper, a Ru-doped MoS2 monolayer (Ru-MoS2) is proposed as a promising novel biosensor based on first-principles theory for the detection of three typical early stage lung cancer exhaled volatile organic compounds, namely, C3H4O, C3H6O, and C5H8. Replacement of a S atom in the MoS2 monolayer with a Ru dopant atom to form a stable Ru-MoS2 monolayer with a binding energy of -4.78 eV is further demonstrated by the thermostability and chemical stability analysis as well as improving the adsorption performance of the system for three VOCs. The adsorption configuration structures, adsorption properties, and electronic behavior of the Ru-MoS2 monolayer are investigated by electron deformation density and density of states analysis to gain a comprehensive understanding of the physicochemical properties as sensing material. The results show that the adsorption energies of the Ru-MoS2 monolayer for C3H4O, C3H6O, and C5H8 are 3.42, -1.53, and -2.80 eV, respectively, all of which are chemisorption with excellent adsorption performance. The sensitivities for the three VOCs could be up to 1.09, 140.50, and 5.90, respectively, and the band structure and work function further elucidate the sensing mechanism of the Ru-MoS2 monolayer as a resistive gas sensor. The type and concentration of these exhaled breaths may reflect changes in the patient's physiological and biochemical status and may serve as a probe for the diagnosis of lung cancer. The results in this work could provide a guidance for researchers to explore the practical applications in the early diagnosis of lung cancer by gas sensors.

Adsorption and reversible detection of toxic halogens gases at room temperature by two-dimensional Al2SSe for occupational sustainability

Current treatment for inhalational halogens poisoning involves providing supportive care, which includes administering humidified oxygen and managing the airway. Since toxic effects of halogens cannot be reversed, sensors with high sensitivity and good reversibility for detecting the relatively lower concentration yet noxious halogens becomes particularly significant and enticing. Herein, the structural and optoelectronic properties of toxic F2 and Cl2 gas molecules adsorbed on highly stable Al2SSe monolayer have been systematically studied by means of first-principles calculations based on density functional theory (DFT). Favorable adsorption sites of said molecules on Al2SSe were carefully examined. The relatively high, negative adsorption energy for F2 and Cl2 indicate that the adsorption process is exothermic and the molecules could be stably adsorbed on Al2SSe monolayer. This characteristic, combined with the substantial charge transfer (0.15–0.55 |e|), drastic change in work function, complete reversibility due to recovery time in 10−1 s scale and distinct optical response, render Al2SSe monolayer a viable option for utilization as either surface work functions transistor or optical chemical resistor for detecting these gases. Pearson correlation coefficient (PCC) analysis of theoretical recovery time and response value indicates that band gap change and electron transfer are the primary influencing factors. Selectivity analysis reveals that common compound forms of halogens and atmospheric molecules such as HF, HCl, N2, O2, H2 and H2O are either physically adsorbed or inert with extremely low adsorption energies on Al2SSe, prompting high F2 and Cl2 selectivity. These outcomes acclaim the exciting prospects of developing Al2SSe monolayer for specific, occupational related ultrahigh-sensitivity F2 and Cl2 sensing nanodevices.

A Sigma1 Receptor Agonist Alters Fluidity and Stability of Lipid Monolayers.

Interactions between the sigma1 receptor agonist PRE-084 and various lipid monolayers, including dipalmitoylphosphatidylcholine (DPPC), DPP-ethanolamine (DPPE), DPP-glycerol (DPPG), DPP-serine (DPPS), palmitoylsphingomyelin (PSM), and cholesterol (Ch), were investigated to elucidate the effects of PRE-084 on membrane fluidity and stability. Their interactions with sigma1 receptor agonists have potential implications for neuroprotection, antidepressant, analgesic, and cognitive enhancement effects. In this study, we observed that the presence of PRE-084 in the subphase led to increased fluidity in DPPC and DPPE monolayers, whereas decreasing fluidity was observed in DPPG, DPPS, and PSM monolayers. The interaction of PRE-084 with Ch monolayers was found to be distinct from its interaction with other lipids. Fluorescence microscopy images revealed changes in the size and shape of liquid-condensed domains in the presence of PRE-084, supporting the notion of altered membrane fluidity. Our findings provide new insights into the interaction of PRE-084 with lipid monolayers and its potential implications for biological and membrane science.

Phonon mode softening and band convergence induced significant enhancement of thermoelectric performance in strained CdI2-type SnI2 monolayer

Monolayer group IVA metal halides have attracted intensive attention for their excellent thermoelectric performance. Recently, the CdI2-type SnI2 monolayer has been successfully fabricated by molecular beam epitaxy for the first time. The universal two-dimensional growth behavior on different substrates, motivates strain engineering on its thermoelectric performance. Herein, the structure stability and thermoelectric properties of SnI2 monolayer under different strains are systematically investigated, based on first-principles calculations combined with Boltzmann transport theory. The investigation shows that the tensile strain can simultaneously induce phonon mode softening and band convergence, resulting in a significant enhancement in thermoelectric performance. The phonon mode softening for ZA and optical branches further enhances lattice anharmonicity and a reduced thermal conductivity of ∼0.14 Wm−1K−1 at 300 K (∼0.05 Wm−1K−1, 800 K) can be obtained. Additionally, band convergence in valence band improves the Seebeck coefficient and increases power factor. Under +2 % tensile strain, the optimal ZT values of SnI2 monolayer for p-type doping are substantially enhanced up to 3.05 (300 K) and 5.06 (800 K), which are increased by ∼98 % and ∼50 % compared to the case without strain. Our results reveal the close relationship between the phonon mode softening and enhanced anharmonicity, and provide the physical insights into the understanding of the modulation of thermoelectric properties of monolayer SnI2, shedding light on substantially optimizing the thermoelectric performance of monolayer group IVA metal halides family.

Bi-based bracelet-like monolayer with negative in-plane Poisson’s ratio and enhanced photocatalytic performance: a first-principles study

Auxetic materials are in high demand for advanced applications due to their relatively rare negative Poisson’s ratio in two-dimensional materials. This study investigates the structural, mechanical, electronic, optical and photocatalytic properties of the AsBiTe3 monolayer(ML) using first-principles calculations. Through analysis of phonon dispersion curves, ab-initio molecular dynamics simulations, and Born conditions, we have confirmed the thermal, dynamic, and mechanical stability of the AsBiTe3 monolayer. The study of the mechanical properties of this material revealed significant anisotropy and a bidirectional in-plane negative Poisson’s ratio (NPR). In addition, electronic band structures calculated, with and without spin–orbit coupling (SOC) using the HSE functional, indicate that this monolayer exhibits the characteristics of an indirect-gap semiconductor around 1.17 and 1.32 eV, respectively. Notably, by assessing the optical properties of AsBiTe3 monolayer, it has been found that this monolayer has a strong light-harvesting capability with an absorption coefficient higher than 105 cm −1 in the visible region. Fascinatingly, under a biaxial 1 % and 4 % tensile and −2% compressive strain, the band edge of the AsBiTe3 monolayer extends across the redox potential of water at pH = 0, 7 and 14, respectively. This suggests that this monolayer holds promise as a potential material for catalytic water splitting. These results should inspire further experimental and theoretical research, aimed at fully exploring the potential applications of this new class of 2D materials.

Janus HfSSe monolayer: a promising candidate for SO2 and COCl2 gas sensing

Janus monolayers based on transition metal dichalcogenides have garnered significant interest as potential materials for nano electronic device applications due to their exceptional physical and electronic properties. In this study, we investigate the stability of the Janus HfSSe monolayer using ab initio molecular dynamics simulations and analyze the electronic properties in its pristine state. We then examine the impact of adsorbing toxic gas molecules (AsH3, COCl2, NH3, NO2, and SO2) on the monolayer’s structure and electronic properties, testing their adsorption on different active sites on top of hafnium, selenium, and sulfur. The sensitivity of the gas molecules is quantified in terms of their adsorption energy, with the highest and lowest energies being observed for SO2 (−0.278 eV) and NO2 (−0.095 eV), respectively. Additionally, we calculate other properties such as recovery time, adsorption height, Bader charge, and charge difference density to determine the sensitivity and selectivity of the toxic gas molecules. Our findings suggest that the Janus HfSSe monolayer has the potential to function as SO2 and COCl2 gas sensor due to its high sensitivity for these two gases.

Two-dimensional Strontium Tantalate: 2D-Sr[formula omitted]TaO[formula omitted

We propose and characterize a novel 2D material with a perovskite structure, Sr2TaO4 monolayer. Using a first principles approach, we study the stability, elastic and electronic properties of the 2D-Sr2TaO4 system. In this metallic monolayer system, the tantalum atom is surrounded by six oxygen atoms in an octahedral configuration. The rotation of the octahedra structures yields antiferrodistortive distortions favoring a phase transition. We have demonstrated the stability of this perovskite-like monolayer using phonons, molecular dynamics, and elasticity criteria.

Strain effects of stability, transport, and electro-optical properties of novel Ga2TeS monolayer

Strain effects of stability, transport, and electro-optical properties of novel Ga2TeS monolayer

First-principle study on the photoelectric properties of monolayer h-BN under different strain types.

Two-dimensional materials are a new and promising research field in materials science. This is mainly attributed to their unique photoelectric and chemical properties. In addition to possessing unique optoelectronic and chemical properties, two-dimensional materials also have important application prospects in the field of field-effect devices. Based on density functional theory, the effects of uniaxial strain and equibiaxial strain on the mechanical properties, electronic structure, and optical properties of monolayer h-BN were studied using first principles. The results indicate that compressive strain has a significant impact on the stability of monolayer h-BN. The band gap width of monolayer h-BN decreases with increasing strain, and the optical properties of monolayer h-BN exhibit a relative trend under tensile and compressive strains. The influence of biaxial strain on the mechanical properties, electronic structure, and optical properties of monolayer h-BN is greater than that of uniaxial strain. All the calculations were done by the VASP software based on density functional theory. The interaction between atomic nuclei and electrons is described by the projected added wave pseudopotential (PAW), using the generalized gradient approximation (GGA) to exchange the Perdew-Burke-Ernzerhof (PBE) of the functional. To avoid interlayer interactions, a 15-Å vacuum layer was set up. The Brillouin zone selects the Monkhorst-Pack method to generate 9 × 9 × 1 of k-point grid, the cut off energy is set to 500eV, the energy convergence standard of the system is 1 × 10-5eV, and the interaction force between atoms is 0.01eV/Å.