Two-dimensional Layer Research Articles

Observation of Ice-Like Two-Dimensional Flakes on Self-Assembled Protein Monolayer without Nanoconfinement under Ambient Conditions

Directly correlating the morphology and composition of interfacial water is vital not only for studying water icing under critical conditions but also for understanding the role of protein-water interactions in bio-relevant systems. In this study, we present a model system to study two-dimensional (2D) water layers under ambient conditions by using self-assembled monolayers (SAMs) supporting the physisorption of the Cytochrome C (Cyt C) protein layer. We observed that the 2D island-like water layers were uniformly distributed on the SAMs as characterized by atomic force microscopy, and their composition was confirmed by nano-atomic force microscopy-infrared spectroscopy and Raman spectroscopy. In addition, these 2D flakes could grow under high-humidity conditions or melt upon the introduction of a heat source. The formation of these flakes is attributed to the activation energy for water desorption from the Cyt C being nearly twofold high than that from the SAMs. Our results provide a new and effective method for further understanding the water-protein interactions.

Transformations of thiocarbonyls into alkenes via Barton-Kellogg olefination.

The transformation of a thiocarbonyl compound into an alkene by stepwise treatment with a diazo compound and triphenylphosphane is known as Barton-Kellogg olefination. As a model reaction, 4,4'-dimethoxythiobenzophenone and diazocyclohexane were used to prepare [bis(4-methoxyphenyl)methylidene]cyclohexane, C21H24O2. The crystal structure of the latter, as well as that of the intermediate thiirane, 2,2-bis(4-methoxyphenyl)-1-thiaspiro[2.5]octane, C21H24O2S, have been determined and their molecular conformations and geometries are generally consistent with those of related structures in the literature. Variations in the influence of four substituents on crowded thiirane rings are minimal and the main differences are noted in the presence of bulky tert-butyl substituents. The conformation of the intermediate thiirane is influenced by weak intramolecular C-H...S interactions. A three-dimensional supramolecular structure of the methylene cyclohexane compound results from the combination of three distinct weak C-H...π interactions. Under similar reaction conditions, 5-phenyl-3H-1,2-dithiole-3-thione has been transformed into 3-[bis(4-methoxyphenyl)methylidene]-5-phenyl-3H-1,2-dithiole, C24H20O2S2, by treatment with bis(4-methoxyphenyl)diazomethane. The crystal structure of the 1,2-dithiole product reveals a molecule with an all-trans 2,4-hexadiene core, in which the Csp2-Csp2 bond lengths display an alternating character that suggests little delocalization of the double bonds. The 1,2-dithiole ring is nearly planar, with just a slight puckering into an envelope form. Two weak C-H...π and one C-H...O interaction link the molecules into thick two-dimensional supramolecular layers.

Photoconductivity Switching in Semiconducting Two-Dimensional Crystals via Molecular Tetris.

Two-dimensional organic materials are mainly constructed by using orthogonal anisotropic connectivity of covalent bonding and π-π stacking. The noncovalent connectivity between building blocks is presumed to be too delicate to stabilize the two-dimensional (2D) layers. Contrary to this assumption, we constructed graphite-like 2D layered material by utilizing pure noncovalent connectivity, i.e., weak intermolecular and π-π interaction via a molecular Tetris strategy. We produce X-ray mountable single crystals comprising polycyclic aromatic heterocycles by employing a single-crystal-to-dissolution-to-single-crystal transformation methodology. The macromechanical analysis of this layered crystal shows shearing behavior, which is quantified using nanoindentation experiments. The 2D lattice's layer space allows reversible intercalation-deintercalation of iodine, which enhances the photoconductivity by 17 folds. Combined efforts of X-ray diffraction, solid-state spectroscopy, and electrochemical studies established the mechanism of intercalation and resulting photoconductivity enhancement.

Five Transition Metal-Mixed Germanium Chalcogenide Materials: Solvothermal Syntheses, Crystal Structures, Photoelectric Response Properties, and Ion-Exchange Properties.

Germanium chalcogenides have attracted wide attention in inorganic chemistry because of their flexible structure and rich properties. Five new germanium chalcogenides containing transition metals such as manganese, zinc, and cadmium were synthesized by solvothermal methods using alkali metals as structural directing agents. Rb2MnGeSe4 (1), Cs2MnGeSe4 (2), and Cs2ZnGeSe4 (3) have a one-dimensional chain structure and Rb2Zn2GeSe4·H2O (4) and Rb2CdGeSe4 (5) have a two-dimensional layer structure. The electronic structure, band gap, and photocurrent response of compounds 1-5 have been comprehensively analyzed. Due to the two-dimensional layered structure of compounds 4 and 5, we studied their ion-exchange properties. Compounds 4 and 5 showed excellent ion-exchange properties and could be used as potential ion-exchange materials for the absorption of radioactive elements in nuclear wastewater.

Automated detection of broiler vocalizations a machine learning approach for broiler chicken vocalization monitoring.

The poultry industry relies on highly efficient production systems. For sustainable food production, where maintaining broiler welfare is crucial, it is essential to have robust data collection systems and automated methods for assessing broiler health and welfare. This paper presents the development and implementation of an acoustic system designed to detect and differentiate between four distinct vocalizations of broiler chickens-pleasure notes, distress calls, short peeps, and warbles-while filtering out background noise and other vocalizations. The vocalization detector is designed as a convolutional neural network with 11 two-dimensional convolutional layers and one one-dimensional convolutional layer. For training, a manually labeled vocalization library was built (>2k samples, with a total duration of 190 minutes), based on a large set of continuous audio recordings of ten male Ross 308 broiler chicks aged from 1 to 36 days. An extension with a subset of the AudioSet dataset was made to include background sounds. With this library, an overall balanced accuracy of 91.1 % was achieved by the neural network-based recognizer.

The analysis of neutron reflectivity from Langmuir monolayers of lipids using molecular dynamics simulations: the role of lipid area.

Biomolecular simulations are increasingly being used to generate detailed structural models to aid interpretation of neutron reflectometry (NR) data obtained from model biological membranes. Unlike globular systems, often studied by small-angle scattering, simulations of two-dimensional layers are sensitive to the simulation cell used which constrains the system laterally. We perform a careful analysis of NR data obtained from a monolayer of the lipid distearoylphosphatidylcholine at the air-water interface and show that the fit of number density profiles obtained from atomistic molecular dynamics simulation to the experimental data is very sensitive to the assumed area per lipid (APL). We propose a protocol for obtaining a realistic isotherm by combining the experimental surface pressure corresponding to a reflectometry measurement with an APL obtained from the simulation that best fits that data. Finally, we demonstrate how downstream interpretation of the experimental sample, derived from structural and dynamic properties of the atomistic model, depends strongly on the correct choice of simulation cell.

Enzymatic bioelectrodes based on ferrocene-modified metal-organic layers for electrochemical glucose detection.

Metal-organic frameworks (MOFs) areoften applied for enzyme immobilization, while they are limited for bioelectrochemical applications due to poor electronic conductivity. Two-dimensional (2D) metal-organic layers (MOLs) with an ultra-thin lamellar structure can effectively shorten the electron transport path and improve the electron transfer rate. In this study, ferrocene as an electron mediator is covalently bound to a 2D-MOL (Fc-NH2-Hf-BTB-MOL) to accelerate electron transferbetween the electrode surface and enzyme. Glucose oxidase (GOx) is immobilized onthe electrode modified with Fc-NH2-Hf-BTB-MOL with the addition of chitosan and carboxylated carbon nanotubes. Electrochemical tests such as cyclic voltammetry are carried outon the glucose biosensor, which showslinear detection ranges of 5 ~ 400μM and 3 ~ 9mM, with a detection limit of 3.9μM (S/N = 3). Therefore, this strategy of construction of an enzyme electrode based on 2D-MOLs withenhanced electron transfer results in a biosensor with excellent specificity and activity for practical glucose detection.

First-Principles Study of the Ga2O3/Metal Interface by Inserting a Boron Nitride Monolayer.

The wide band gap semiconductor Ga2O3 has been well studied in terms of the Schottky diodes. Controlling the Schottky barrier height (SBH) in Ga2O3/metal contacts is essential for achieving desirable, high-performance electronic devices. In this article, based on first-principles calculations, we studied the effect of inserting a two-dimensional dielectric layer of hexagonal boron nitride (h-BN) on the SBH of Ga2O3/metal. Two sets of interface models with and without the BN interlayer, i.e., Ga2O3/Au, Ga2O3/BN/Au, Ga2O3/Mg, and Ga2O3/BN/Mg configurations, were built. As a result, the SBH of high metal work function Au interfaces does not show a significant change after h-BN insertion. In contrast, the SBH of low metal work function Mg interfaces was increased significantly by an h-BN insertion. The reason for this at the atomic level was also explained through electronic structure calculations. They show that inducing a two-dimensional h-BN monolayer can be seen as a transition layer to screen the interface states effectively and weaken the interface interaction greatly. Besides, the effect of the h-BN interlayer on the tunneling barriers was also analyzed. We believe this study will provide insight into improving the performance of wide band gap semiconductor devices with an intercalation structure.

Van der Waals quantum dots on layered hexagonal boron nitride

Semiconductor quantum dots (QD) promise unique electronic, optical, and chemical properties, which can be exquisitely tuned by controlling the composition, size, and morphology. Semiconductor QDs have been synthesized primarily via two approaches, namely, epitaxial growth and wet-chemical synthesis. However, the properties of epitaxial QDs (eQDs) are susceptible to wetting layer formation and substrate dislocations, while colloidal QDs (cQDs) face fluorescence intermittency issues. Here, we report on the synthesis of a class of QDs that can overcome the fundamental limitations of eQDs and cQDs. By exploiting the sp2 bonding of layered hexagonal boron nitride (hBN), we show that GaN QDs can be epitaxially grown through a weak van der Waals (vdW) interaction without two-dimensional wetting layer formation. The photoluminescence intensity of GaN van der Waals quantum dots (vQDs) is more than six times stronger than that of conventional GaN eQDs and no optical blinking was observed from vQDs. We show that the interadatom bond strength is about one order of magnitude stronger compared with that between the adatoms and the hBN substrate. This work shows that vQDs have unique properties that are difficult to achieve using existing QDs synthesis methods and thus can potentially enable new classes of high-performance optoelectronic and quantum devices.

Training State-of-the-Art Deep Learning Algorithms with Visible and Extended Near-Infrared Multispectral Images of Skin Lesions for the Improvement of Skin Cancer Diagnosis.

An estimated 60,000 people die annually from skin cancer, predominantly melanoma. The diagnosis of skin lesions primarily relies on visual inspection, but around half of lesions pose diagnostic challenges, often necessitating a biopsy. Non-invasive detection methods like Computer-Aided Diagnosis (CAD) using Deep Learning (DL) are becoming more prominent. This study focuses on the use of multispectral (MS) imaging to improve skin lesion classification of DL models. We trained two convolutional neural networks (CNNs)-a simple CNN with six two-dimensional (2D) convolutional layers and a custom VGG-16 model with three-dimensional (3D) convolutional layers-using a dataset of MS images. The dataset included spectral cubes from 327 nevi, 112 melanomas, and 70 basal cell carcinomas (BCCs). We compared the performance of the CNNs trained with full spectral cubes versus using only three spectral bands closest to RGB wavelengths. The custom VGG-16 model achieved a classification accuracy of 71% with full spectral cubes and 45% with RGB-simulated images. The simple CNN achieved an accuracy of 83% with full spectral cubes and 36% with RGB-simulated images, demonstrating the added value of spectral information. These results confirm that MS imaging provides complementary information beyond traditional RGB images, contributing to improved classification performance. Although the dataset size remains a limitation, the findings indicate that MS imaging has significant potential for enhancing skin lesion diagnosis, paving the way for further advancements as larger datasets become available.

Thiophene-fused aromatic belts

Aromatic belts, ultrashort carbon nanotubes, and related structures, are emerging molecular entities in the fields of organic electronics and supramolecular chemistry owing to their structural rigidity, fully fused π-conjugation, and well-defined cavity. Synthesis of aromatic belts with embedded thiophene structures, which manifest significant optoelectronic and conductive properties, has not yet been achieved. Herein, we report the synthesis of thiophene-fused aromatic belts (thiophene belts) via one-step sulfur cross-linking reaction of partially fluorinated cycloparaphenylenes. Their structural features, including unidirectional columnar stacking with high dipole moment in crystals, two-dimensional layer assembly on metal surfaces, and photophysical properties, such as long-lifetime phosphorescence, are uncovered. These distinctive features of the thiophene belts should inspire a range of applications such as optoelectronic devices and polar materials.

Multi-valley band and low thermal conductivity in two-dimensional Mg3Bi2 mono layer: A method for improving thermoelectric performance of Mg3Bi2 based on First-principles calculations

Multi-valley band and low thermal conductivity in two-dimensional Mg3Bi2 mono layer: A method for improving thermoelectric performance of Mg3Bi2 based on First-principles calculations

Melting Heat Transfer Effects on MHD Chemically Thermally Radiative Micropolar Fluid Flow towards Stretching Exponentially Sheet with Heat Sink/Source

The effective use of non-Newtonian fluids is vital for situations involving heat and mass transfer. For instance, we employ thermal paste, a non-Newtonian fluid, to cool the CPU. By means of a computational approach, the behaviour of non-Newtonian on the surface of a two-dimensional steady MHD boundary layer flow and melting heat and mass transfer over a micropolar fluid is presented here, in conjunction with a partially slipper sheet at the surface providing heat generation/absorption. Further, heat radiation as well as chemical reactions are considered. Using similarity parameters, the governing nonlinear partial differential equations for heat, mass and flow are converted into a series of coupled nonlinear ordinary differential equations, then solved using the Runge–Kutta fourth order integration scheme and the shooting method. For various parameters defining the flow within the boundary layer, the new findings for velocity, microrotation, temperature and concentration are graphed. Graphic representations of local skin friction, Nusselt number and Sherwood number are provided. Boosting the melting parameter decreases fluid velocity, microrotation and temperature significantly. An intensification in slip near the boundary decreases both fluid velocity and microrotation, but opposite effects are observed on temperature.

Two-dimensional Porcine Intestinal Organoids Reflecting the Physiological Properties of Native Gut.

The gastrointestinal tract (GIT) serves both in the digestion of food and the uptake of nutrients but also as a protective barrier against pathogens. Traditionally, research in this area has relied on animal experiments, but there's a growing demand for alternative methods that adhere to the 3R principles-replace, reduce, and refine. Porcine organoids have emerged as a promising tool, offering a more accurate in vitro replication of the in vivo conditions than traditional cell models. One major challenge with intestinal organoids is their inward-facing apical surface and outward-facing basolateral surface. This limitation can be overcome by creating two-dimensional (2D) organoid layers on transwell inserts (from here on referred to as insert(s)), providing access to both surfaces. In this study, we successfully developed two-dimensional cultures of porcine jejunum and colon organoids. The cultivation process involves two key phases: First, the formation of a cellular monolayer, followed by the differentiation of the cells using tailored media. Cellular growth is tracked by measuring transepithelial electrical resistance, which stabilizes by day 8 for colon organoids and day 16 for jejunum organoids. After a 2-day differentiation phase, the epithelium is ready for analysis. To quantify and track active electrogenic transport processes, such as chloride secretion, we employ the Ussing chamber technique. This method allows for real-time measurement and detailed characterization of epithelial transport processes. This innovative in vitro model, combined with established techniques like the Ussing chamber, provides a robust platform for physiologically characterizing the porcine GIT within the 3R framework. It also opens opportunities for investigating pathophysiological mechanisms and developing potential therapeutic strategies.

2.5-dimensional topological superconductivity in twisted superconducting flakes

Multilayer flakes of two-dimensional materials were recently shown to be tunable by twisting monolayers on their surface. This raises the question whether qualitatively new phenomena can occur in such finite-thickness moiré systems. Here we demonstrate the emergence of distinct topological phases and transitions in N-layered flakes of nodal superconductors with a single monolayer twisted on top of it. We show that a c-axis current transforms the whole system into a chiral topological superconductor. Increasing the current drives a sequence of topological transitions between states characterized by a Chern number increasing from ~O(N) up to ~O(N2), well beyond the additive effect of stacking N layers. We predict thickness-independent signatures of these states in the thermal Hall and tunneling microscopy measurements. Twisted superconductor flakes thus provide an example of a “2.5-dimensional” material where the synergy of two-dimensional layers extended in a third dimension realize states inaccessible in either monolayer or bulk materials.

High-Performance Ti3C2Tx-MXene/Mycelium Hybrid Membrane for Efficient Lead Remediation: Design and Mechanistic Insights.

This study presents a hybrid microfiltration technology designed for high-performance lead (Pb(II)) remediation, especially from aqueous solutions with high Pb(II) concentrations, by utilizing two-dimensional (2D) Ti3C2Tx-MXene layers deposited on dry mycelium membranes. The hybrid Ti3C2Tx-MXene/mycelium (MyMX) membranes were fabricated via a single-step electrochemical deposition (ECD) technique, which enabled a uniform coating of 2D Ti3C2Tx-MXene onto individual hyphal fibers of a prefabricated mycelium membrane. Optimized ECD parameters for high Pb(II) uptake were identified using scanning electron microscopy and energy-dispersive X-ray spectroscopy. In immersion-based (no-flow) Pb(II) remediation experiments, MyMX membranes demonstrated significantly high Pb(II) removal efficiency (>87-99%) and rapid sorption kinetics across an initial Pb(II) concentration range of 60-1500 ppm in both single-ion and co-ion solutions. The enhanced Pb(II) sorption was attributed to electrostatic interactions and surface complexation assisted by hyphal surface proteins and Ti3C2Tx-MXene functional groups, as confirmed by infrared and X-ray photoelectron spectroscopies. In cross-flow studies, the MyMX membranes achieved a Pb(II) sorption capacity of ∼1347 mg/g while maintaining a high permeation rate of 51,800 L m-2 bar-1 h-1 at 1500 ppm Pb(II), surpassing the performance of various polymer-based and MXene-based microporous membranes for heavy metal remediation. The biomaterial-based hybrid MyMX membrane represents a significant advancement in water treatment technology, providing a cost-effective, sustainable solution for Pb(II) remediation in contaminated water sources.

Double-sided van der Waals epitaxy of topological insulators across an atomically thin membrane.

Atomically thin van der Waals (vdW) films provide a material platform for the epitaxial growth of quantum heterostructures. However, unlike the remote epitaxial growth of three-dimensional bulk crystals, the growth of two-dimensional material heterostructures across atomic layers has been limited due to the weak vdW interaction. Here we report the double-sided epitaxy of vdW layered materials through atomic membranes. We grow vdW topological insulators Sb2Te3 and Bi2Se3 by molecular-beam epitaxy on both surfaces of atomically thin graphene or hexagonal boron nitride, which serve as suspended two-dimensional vdW substrate layers. Both homo- and hetero-double-sided vdW topological insulator tunnel junctions are fabricated, with the atomically thin hexagonal boron nitride acting as a crystal-momentum-conserving tunnelling barrier with abrupt and epitaxial interfaces. By performing field-angle-dependent magneto-tunnelling spectroscopy on these devices, we reveal the energy-momentum-spin resonance of massless Dirac electrons tunnelling between helical Landau levels developed in the topological surface states at the interfaces.

Chemical Reaction and Activation Energy Impacts on Unsteady Radiative Flow of Sisko Fluid

In this work, we study the two-dimensional boundary layer flow of Sisko fluid over stretching surface. Further we have observed, the effect of chemical reaction and activation energy on unsteady radiative flow of Sisko fluid. The suitable transformations are used to convert non-linear partial differential equations (PDEs) into ordinary differential equations (ODEs). Numerical solutions are obtained for the velocity, temperature and concentration profiles by utilizing the bvp4c technique. The effect of various parameters on the heat transfer and concentration profiles are depicted in the graphs and tables are briefly discussed.

Spin transport properties in a topological insulator sandwiched between two-dimensional magnetic layers

Non-trivial band topology along with magnetism leads to different novel quantum phases. When time-reversal symmetry is broken in three-dimensional topological insulators (TIs) through, e.g., the proximity effect, different phases such as the quantum Hall phase or the quantum anomalous Hall(QAH) phase emerge, displaying interesting transport properties for spintronic applications. The QAH phase displays sidewall chiral edge states, which leads to the QAH effect. We have considered a heterostructure consisting of a TI, namely BiSe, sandwiched between two two-dimensional ferromagnetic monolayers of CrI, to study how its topological and transport properties change due to the proximity effect. Combining DFT and tight-binding calculations, along with non-equilibrium Green’s function formalism, we show that a well-defined exchange gap appears in the band structure in which spin-polarised edge states flow. In a finite slab, the nature of the surface states depends on both the cross-section and thickness of the system. Therefore, we also study the width and finite-size effects on the transmission and topological properties of this magnetised TI nanoribbon.

Two-Dimensional Layer {P4Mo6} Clusters Constructed with N-Ligands for Bifunctional Properties of Proton Conduction and Supercapacitors.

Proton exchange membrane fuel cells (PEMFCs) are developing into very meaningful clean energy to fundamentally address environmental pollution. Among which the most studied Nafion series membranes are limited under large-scale use, and some strong oxidizing groups such as hydrogen peroxide will attack the structure of Nafion, shortening the lifespan of PEMFCs. Therefore, it is crucial to develop a proton-conductive material with strong stability and broad application. In this study, a novel hourglass-type P4Mo6-based POMOFs denoted as (H2timb)2[Mn3(H3P4Mo6O31)2]·4H2O was synthesized using 1,3,5-tri(1H-imidazole-1-yl)benzene (timb) as a ligand. It was found that CUST-577 exhibited an excellent proton conductivity of 8.9 × 10-3 S cm-1 at 80 °C and 98% RH (relative humidity), proving that CUST-577 was conducted by protons. In addition, CUST-577 also had a greater H2O2 decomposition ability, thereby improving the longevity of fuel cells. In a three-electrode system, CUST-577 displayed a specific capacitance (Cs) value of 308 F g-1 at a current density of 0.15 A g-1, with a capacitance retention of 88.3% after 2000 cycles. Since the proton-conductive electrolyte can deliver protons for the redox reaction of various pseudocapacitor (PC) electrode materials, CUST-577 may be a promising polyacid-based proton conductor material and PC electrode material.