2D Materials Research Articles

Single-Atom Suture.

In atomically thin two-dimensional (2D) materials, grain boundaries (GBs) are ubiquitous, displaying a profound effect on the electronic structure of the host lattice. The random configuration of atoms within GBs introduces an arbitrary and unpredictable local electronic environment, which may hazard electron transport. Herein, by utilizing the Pt single-atom chains with an ultimate one-dimensional (1D) feature (width of a single atom and length up to tens of nanometers), we realized the suture of the electron pathway at GBs of diversified transition metal dichalcogenides (TMDCs). Theoretical calculations reveal that the construction of Pt single-atom sutures (SAS) prompts the emergence of electronic states proximal to the Fermi level, effectively modulating the transformation of the electronic structure from semiconductivity to metallicity. This transformation underscores the pivotal role of Pt SAS in reconfiguring the electron pathway. Benefiting from this, the Pt SAS-MoS2 emerges as an excellent catalyst, exhibiting an overpotential of 41 mV at 10 mA cm-2 and a Tafel slope of 54 mV dec-1 in hydrogen evolution reaction. Our results offer an understanding of the electron conduction pathway contributed by ultraordered atomic arrangement and the innovative mechanisms for future potential catalysts with an optimized architecture.

2D biphenylene: exciting properties, synthesis & applications.

In the current era of nanotechnology, the isolation of graphene has acted as a catalyst for the study and creation of many innovative two-dimensional (2D) materials with distinctive functions. The recent synthesis of biphenylene (BPN), a porous 2D carbon allotrope, has ignited significant research interest due to its unique and tunable properties, making it a promising candidate for diverse applications in hydrogen storage, batteries, sensing, electrocatalysis, and beyond. Although a considerable amount of research has been carried out on biphenylene, there is hardly any review article on this fascinating material. Therefore, this comprehensive review article focuses on the fascinating properties of the advanced graphene family and 2D biphenylene. Additionally, there has been an in-depth discussion on 2D biphenylene, covering its synthesis process, recent advancements, and its applications in various fields. Moreover, this review will be useful to professionals and researchers in materials science, physics, chemistry, chemical engineering, and related subjects since it provides detailed information on the characteristics, synthesis, and applications of 2D biphenylene.

One-Dimensional Excitonic Insulator of M6Te6 (M = Mo, W) Atomic Wires.

Coulomb attraction with weak screening can trigger spontaneous exciton formation and condensation, resulting in a strongly correlated many-body ground state, namely, the excitonic insulator. One-dimensional (1D) materials natively have ineffective dielectric screening. For the first time, we demonstrate the excitonic instability of single atomic wires of transition metal telluride M6Te6 (M = Mo, W), a family of 1D van der Waals (vdW) materials accessible in the laboratory. The many-body GW and Bethe-Salpeter equation scheme shows giant exciton binding energies up to 1.6 eV for these narrow-gap semiconductors, much exceeding their single-particle band gaps and implying a robust thermal-equilibrium exciton Bose-Einstein condensation with high critical temperatures. The excitonic instability of these single atomic wires is attributed to their small dielectric constant, same parity and ultraflat dispersion for the band edge states. Our work shed light in exploiting the strong excitonic effects in 1D vdW materials to realize macroscopic quantum phenomena.

Clinical applications of 3D printing in spine surgery: a systematic review.

The objective of this systematic review is to present a comprehensive summary of existing research on the use of 3D printing in spinal surgery. The researchers conducted a thorough search of four digital databases (PubMed, Web of Science, Scopus, and Embase) to identify relevant studies published between January 1999 and December 2022. The review focused on various aspects, including the types of objects printed, clinical applications, clinical outcomes, time and cost considerations, 3D printing materials, location of 3D printing, and technologies utilized. Out of the 1620 studies initially identified and the 17 added by manual search, 105 met the inclusion criteria for this review, collectively involving 2088 patients whose surgeries involved 3D printed objects. The studies presented a variety of 3D printed devices, such as anatomical models, intraoperative navigational templates, and customized implants. The most widely used type of objects are drill guides (53%) and anatomical models (25%) which can also be used for simulating the surgery. Custom made implants are much less frequently used (16% of papers). These devices significantly improved clinical outcomes, particularly enhancing the accuracy of pedicle screw placement. Most studies (88%) reported reduced operation times, although two noted longer times due to procedural complexities. A variety of 3DP technologies and materials were used, with STL, FDM, and SLS common for models and guides, and titanium for implants via EBM, SLM, and DMLS. Materialise software (Mimics, 3-Matic, Magics) was frequently utilized. While most studies mentioned outsourced production, in-house printing was implied in several cases, indicating a trend towards localized 3D printing in spine surgery. 3D printing in spine surgery, a rapidly growing area of research, is predominantly used for creating drill guides for screw insertion, anatomical models, and innovative implants, enhancing clinical outcomes and reducing operative time. While cost-efficiency remains uncertain due to insufficient data, some 3D printing applications, like pedicle screw drill guides, are already widely accepted and routinely used in hospitals.

Physical origin and control of exciton spatial localization in high-κ MOene monolayers under external perturbations

Abstract Two-dimensional (2D) materials hold great promise for the next-generation optoelectronics applications, many of which, including solar cell, rely on the efficient dissociation of exciton into free charge carriers. However, photoexcitation in atomically thin 2D semiconductors typically produces exciton with a binding energy of ~500 meV, an order of magnitude larger than thermal energy at room temperature. This inefficient exciton dissociation can limit the efficiency of photovoltaics. In this study, employing the first principles approach - DFT, GW+BSE, and analytical model, we demonstrate the role of asymmetric halogenation, dielectric environment, and magnetic field in 2D Ti2O MOene as an efficient strategy for regulating exciton binding energy towards spontaneous exciton dissociation. Our study goes beyond the exciton ground state and quantifies the degree of spatial delocalisation of exciton in excited states as well. We determine the quantitative impact of varying dielectric screening and magnetic field strength on exciton binding energy for different excited states (1s, 2s, 3s, 4s, and so on). Importantly, we reveal the significant role of orbital orientation (whether in-plane or out-of-plane) and symmetry (related to the angular momentum quantum number) in understanding the spatial localization of excitons and their binding energy. Additionally, a high dielectric constant in 2D MOene enables easier exciton dissociation, similar to that observed in 3D bulk semiconductors, while also harnessing the advantages of 2D materials. This makes it an effective material that combines the best of both 3D bulk and 2D structures. The study offers a promising strategy for designing next-generation optoelectronic devices.

Terahertz Saturable Absorption across Charge Separation in Photoexcited Monolayer Graphene/MoS2 Heterostructure.

Unveiling the nonlinear interactions between terahertz (THz) electromagnetic waves and free carriers in two-dimensional materials is crucial for the development of high-field and high-frequency electronic devices. Herein, we investigate THz nonlinear transport dynamics in a monolayer graphene/MoS2 heterostructure using time-resolved THz spectroscopy with intense THz pulses as the probe. Following ultrafast photoexcitation, the interfacial charge transfer establishes a nonequilibrium carrier redistribution, leaving free holes in the graphene and trapping electrons in the MoS2. When probed with intense THz pulses exceeding 34 kV/cm in a peak electric field, significant THz saturable absorption is observed over a period of 20 ps. Furthermore, the photoinduced change in the transmitted THz waveform, linked to the THz-driven nonlinear current, manifests as a substantial self-phase modulation. These nonlinear responses can be attributed to the competition between rapid carrier heating and slow carrier cooling via electron-electron and electron-phonon scattering in the charge-transfer-induced hole system of the graphene layer. This work demonstrates an integration of advantages arising from robust nonlinear absorption in graphene and enhanced photocarrier harvesting in transition metal dichalcogenides by exploiting heterostructure construction.

Bottom-up constructing of two-dimensional ferromagnets with high Curie temperature by assembling 5d transition metal atom@MnSr8 magnetic superatoms

Abstract The development of advanced spintronic devices requires ultrathin two-dimensional (2D) ferromagnetic (FM) materials with high Curie temperature (T C) and large out-of plane magnetic anisotropy energy (MAE). However, the number of high-T C 2D ferromagnets synthesized through top-down experimental methods is very limited. Here, we propose a bottom-up approach for constructing 2D ferromagnets with high T C by assembling magnetic superatoms. The MnSr9 superatom was first selected as building blocks to construct a series of 2D materials with square, triangular and hexagonal honeycomb lattices. First-principles studies show that all the MnSr9 self-assembled films are thermodynamically stable and exhibit ferromagnetism, unfortunately, they lack the necessary magnetic anisotropy. By substituting one Sr atom with a heavy 5d transition metal (5d-TM) atom, all these 5d-TM@MnSr8 clusters show enhanced stability and symmetry, and their self-assembled hexagonal honeycomb crystals exhibit significant magnetic anisotropy and enhanced ferromagnetism from 5d-TM atoms. Taking the PtMnSr8 superatom as an example, we have demonstrated these characteristics in detail, and the T C and out-of-plane MAE of its honeycomb structure reach up to 253 K and 3.47 meV per unit cell under biaxial tensile strain. Moreover, the PtMnSr8 honeycomb structure on hexagonal boron nitride monolayer substrate exhibit further enhanced ferromagnetism (T C ≈ 327 K) and distinctive antioxidant properties. This study highlights that assembling magnetic superatoms on suitable substrates is an effective way for constructing high-performance 2D FM materials.

MoTe2 Photodetector for Integrated Lithium Niobate Photonics.

The integration of a photodetector that converts optical signals into electrical signals is essential for scalable integrated lithium niobate photonics. Two-dimensional materials provide a potential high-efficiency on-chip detection capability. Here, we demonstrate an efficient on-chip photodetector based on a few layers of MoTe2 on a thin film lithium niobate waveguide and integrate it with a microresonator operating in an optical telecommunication band. The lithium-niobate-on-insulator waveguides and micro-ring resonator are fabricated using the femtosecond laser photolithography-assisted chemical-mechanical etching method. The lithium niobate waveguide-integrated MoTe2 presents an absorption coefficient of 72% and a transmission loss of 0.27 dB µm-1 at 1550 nm. The on-chip photodetector exhibits a responsivity of 1 mA W-1 at a bias voltage of 20 V, a low dark current of 1.6 nA, and a photo-dark current ratio of 108 W-1. Due to effective waveguide coupling and interaction with MoTe2, the generated photocurrent is approximately 160 times higher than that of free-space light irradiation. Furthermore, we demonstrate a wavelength-selective photonic device by integrating the photodetector and micro-ring resonator with a quality factor of 104 on the same chip, suggesting potential applications in the field of on-chip spectrometers and biosensors.

Investigating the Current-Carrying Friction Mechanism of n-Type and p-Type Two-Dimensional TMD under a Positive Electric Field.

Nanofriction plays an important role in the performance and lifetime of n-type or p-type TMD-based semiconductor nanodevices. However, the mechanism of nanofriction in n-type and p-type TMD semiconductors under an electric field is still blurry. In this paper, monolayers of n-MoSe2 and p-WSe2 materials were prepared by chemical vapor deposition (CVD), and their nanofriction behavior under positive electric field was investigated. Atomic force microscopy (AFM) was used to analyze the nanofriction by the positive voltage applied through the needle tip: both the friction and the friction coefficient of MoSe2 increased with the increase of the applied voltage, while the friction and the friction coefficient of WSe2 decreased with the increase of the applied voltage. As the applied voltage increases, the friction force and energy dissipation exhibit corresponding trends in relation to the surface potential. The accumulation and dissipation of carriers represent significant factors influencing friction change. The diverse types of carriers give rise to variations in the friction laws. Our experiments have revealed the differences and mechanisms of friction in TMD materials dominated by different carrier types at positive voltages. It provides guidance for the application and modulation of n- and p-type two-dimensional semiconductor materials in the field of friction.

Precise Preparation of Size-Uniform Two-Dimensional Platelet Micelles Through Crystallization-Assisted Rapid Microphase Separation Using All-Bottlebrush-Type Block Copolymers with Crystalline Side Chains.

Polymer nanoparticles with low curvature, especially two-dimensional (2D) soft materials, are rich in functions and outstanding properties and have received extensive attention. Crystallization-driven self-assembly (CDSA) of linear semicrystalline block copolymers is currently a common method of constructing 2D platelets of uniform size. Although accompanied by high controllability, this CDSA method usually and inevitably requires a longer aging time and lower assembly concentration, limiting the large-scale preparation of nanoaggregates. In this study, a series of all-bottlebrush-type block copolymers, poly(octadecyl acrylate)-block-poly(oligoethylene glycol methyl ether methacrylate)s are prepared by living polymerization. Driven by the synergistic crystallization of crystalline side chains and the rapid microphase separation of bottlebrush topology, these polymers can assemble into uniform 2D circular platelet micelles in a few minutes, without being affected by a high assembly concentration. In this process, epitaxial growth of the bottlebrush molecules proceeds with rigid cylindrical molecular conformation at the micelle crystallization sites and eventually provides a sandwich-type micelle according to a head-to-head stacking mode. This is explained as a "crystallization-assisted rapid microphase separation" mechanism. The micelle structures are affected by the assembly solvent and temperature, the size of which shows a linear dependence on the assembly temperature below the melting point of the crystalline block, which can be used to precisely control the morphology of these 2D platelets. This study establishes an efficient and rapid method to prepare 2D polymer nanosoft materials, which are promising candidates for further development, preparation, and application of various nanomaterials.

Comparative analysis of modified Johnson-Cook model and artificial neural network for flow stress prediction in BN-reinforced AZ80 magnesium composite.

Boron nitride (BN), renowned for its exceptional optoelectrical properties, mechanical robustness, and thermal stability, has emerged as a promising two-dimensional material. Reinforcing AZ80 magnesium alloy with BN can significantly enhance its mechanical properties. To investigate and predict this enhancement during hot deformation, we introduce two independent modeling approaches a modified Johnson-Cook constitutive model and an artificial neural network (ANN). These models aim to capture both linear and nonlinear deformation characteristics. Hot compression tests conducted across various temperatures and strain rates provided a comprehensive dataset for model validation. The MJCC model, accounting for strain rate and temperature effects, achieved a correlation coefficientRof 0.96 and an average absolute relative error (AARE) of 6.28%. In contrast, the ANN, trained on experimental data, improved the correlation coefficient toRof 0.99 and reduced the AARE to below 1.5%, significantly enhancing predictive accuracy. These results indicate that while the modified J-C model provides reliable predictions under moderate conditions, the ANN more effectively captures complex behaviors under extreme deformation conditions. By comparing these modeling approaches, our study offers valuable insights for accurately predicting the rheological behavior of BN-reinforced AZ80 magnesium composite, aiding process optimization in industrial applications.

Two-Dimensional Materials for Brain-Inspired Computing Hardware.

Recent breakthroughs in brain-inspired computing promise to address a wide range of problems from security to healthcare. However, the current strategy of implementing artificial intelligence algorithms using conventional silicon hardware is leading to unsustainable energy consumption. Neuromorphic hardware based on electronic devices mimicking biological systems is emerging as a low-energy alternative, although further progress requires materials that can mimic biological function while maintaining scalability and speed. As a result of their diverse unique properties, atomically thin two-dimensional (2D) materials are promising building blocks for next-generation electronics including nonvolatile memory, in-memory and neuromorphic computing, and flexible edge-computing systems. Furthermore, 2D materials achieve biorealistic synaptic and neuronal responses that extend beyond conventional logic and memory systems. Here, we provide a comprehensive review of the growth, fabrication, and integration of 2D materials and van der Waals heterojunctions for neuromorphic electronic and optoelectronic devices, circuits, and systems. For each case, the relationship between physical properties and device responses is emphasized followed by a critical comparison of technologies for different applications. We conclude with a forward-looking perspective on the key remaining challenges and opportunities for neuromorphic applications that leverage the fundamental properties of 2D materials and heterojunctions.

Nonlinear Optics in Two-Dimensional Magnetic Materials: Advancements and Opportunities.

Nonlinear optics, a critical branch of modern optics, presents unique potential in the study of two-dimensional (2D) magnetic materials. These materials, characterized by their ultra-thin geometry, long-range magnetic order, and diverse electronic properties, serve as an exceptional platform for exploring nonlinear optical effects. Under strong light fields, 2D magnetic materials exhibit significant nonlinear optical responses, enabling advancements in novel optoelectronic devices. This paper outlines the principles of nonlinear optics and the magnetic structures of 2D materials, reviews recent progress in nonlinear optical studies, including magnetic structure detection and nonlinear optical imaging, and highlights their role in probing magnetic properties by combining second harmonic generation (SHG) and multispectral integration. Finally, we discuss the prospects and challenges for applying nonlinear optics to 2D magnetic materials, emphasizing their potential in next-generation photonic and spintronic devices.

A Novel Molecularly Imprinted Electrochemiluminescence Sensor Based on Mxene Quantum Dots for Selective Detection of Oseltamivir in Biological Samples.

Oseltamivir is a drug that has been widely used to prevent and treat influenza A and B. In this work, an ultrasensitive, simple, and novel electrochemiluminescence (ECL) sensor combined with molecularly imprinted polymers (MIP-ECL) based on a graphene-like two-dimensional material, Mxene quantum dots (MQDs) was constructed to selectively detect oseltamivir. A molecularly imprinted polymer membrane containing an oseltamivir template was constructed by electropolymerization and elution of modified MQDs on a glassy carbon electrode. Under optimized experimental conditions, the MIP-ECL sensor could detect oseltamivir in the range of 10-10 to 10-6 M (R2 = 0.9816), with a low limit of detection of 6.5 × 10-11 M (S/N = 3), and the recovery rates of oseltamivir in biological samples were 92.21-104.2%, with relative standard deviations of 3.70%~5.70%. The developed MIP-ECL sensor provides a new idea for detecting oseltamivir, which was successfully applied to the determination of oseltamivir in serum samples, indicating great potential for application in clinical diagnostics.

Mechanical properties of two-dimensional material-based thin films: a comprehensive review.

Two-dimensional (2D) materials are materials with a thickness of one or a few atoms with intriguing electrical, chemical, optical, electrochemical, and mechanical properties. Therefore, they are deemed candidates for ubiquitous engineering applications. Films and three-dimensional (3D) structures made from 2D materials introduce a distinct assembly structure that imparts the inherent properties of pristine 2D materials on a macroscopic scale. Acquiring the adequate strength and toughness of 2D material structures is of great interest due to their high demand for numerous industrial applications. This work presents a comprehensive review of the mechanical properties and deformation behavior of robust films composed of 2D materials that help them to attain other extraordinary properties. Moreover, the various key factors affecting the mechanical performance of such thin films, such as the lateral size of nanoflakes, fabrication technique of the film, thickness of the film, post-processing, and strain rate, are elucidated.

Recent progress in two-dimensional Bi2O2Se and its heterostructures.

Ever since the identification of graphene, research on two-dimensional (2D) materials has garnered significant attention. As a typical layered bismuth oxyselenide, Bi2O2Se has attracted growing interest not only due to its conventional thermoelectricity but also because of the excellent optoelectronic properties found in the 2D limit. Moreover, 2D Bi2O2Se exhibits remarkable properties, including high carrier mobility, air stability, tunable band gap, unique defect characteristics, and favorable mechanical properties. These properties make it a promising candidate for next-generation electronic and optoelectronic devices, such as logic devices, photodetectors, sensors, energy technologies, and memory devices. However, despite significant progress, there are still challenges that must be addressed for widespread commercial use. This review provides an overview of progress in Bi2O2Se research. We start by introducing the crystal structure and physical properties of Bi2O2Se and a compilation of methods for modulating its physical properties is further outlined. Then, a series of methods for synthesizing high-quality 2D Bi2O2Se are summarized and compared. We next focus on the advancements made in the practical applications of Bi2O2Se in the fields of field-effect transistors (FETs), photodetectors, neuromorphic computing and optoelectronic synapses. As heterostructures induce a new degree of freedom to modulate the properties and broaden applications, we especially discuss the heterostructures and corresponding applications of Bi2O2Se integrated with 0D, 1D and 2D materials, providing insights into constructing heterojunctions and enhancing device performance. Finally, the development prospects for Bi2O2Se and future challenges are discussed.

Thickness-dependent surface reconstructions in non-van der Waals two-dimensional materials.

Bismuth oxychalcogenides (Bi2O2X, X = S, Se, Te), a family of non-van der Waals (non-vdW) two-dimensional (2D) semiconductors, are attracting significant attention due to their outstanding semiconducting properties and huge potential in various applications of electronic and optoelectronic devices. Surface imperfections (e.g., surface vacancies) and surface reconstructions are more likely to appear and may cause intriguing physical properties and novel phenomena in the non-vdW 2D materials than the vdW cases. Here, we explore the impacts of surface vacancies and surface reconstructions on the properties of the surfaces and 2D structures of Bi2O2X by using the first-principles method. We find that the dimerization of surface X-vacancies occurs in Bi2O2S and Bi2O2Te (001) surfaces, like that happening in Bi2O2Se. Unexpectedly, the electronic structures of Bi2O2X (001) surfaces show strong tolerance to the order of surface X-vacancies. Furthermore, we find a phenomenon of thickness-dependent surface reconstructions for non-vdW Bi2O2X ultrathin films. For a monolayer, the zipper-surface is more stable, while the dimer-surface is generally more stable for thicker films. Calculated exfoliation energies of the Bi2O2X monolayer and multi-layers are close to those of common vdW 2D materials, indicating that 2D Bi2O2X belong to easily fabricated 2D materials, even though the inter-layer binding interaction is of the non-vdW type. Our results suggest that non-vdW 2D materials can possess intriguing properties because of surface imperfections and reconstructions in comparison with vdW 2D materials.

Atomically thin 2D materials for solution-processable emerging photovoltaics.

Atomically thin 2D materials, such as graphene and graphene oxide, covalent organic frameworks, layered carbides, and metal dichalcogenides, reveal a unique variability of electronic and chemical properties, ensuring their prospects in various energy generation, conversion, and storage applications, including light harvesting in emerging photovoltaic (ePV) devices with organic and perovskite absorbers. Having an extremely high surface area, the 2D materials allow a broad variability of the bandgap and interband transition type, conductivity, charge carrier mobility, and work function through mild chemical modifications, external stimuli, or combination with other 2D species into van-der-Waals heterostructures. This review provides an account of the most prominent "selling points" of atomically thin 2D materials as components of ePV solar cells, including highly tunable charge extraction selectivity and work function, structure-directing and stabilizing effects on halide perovskite light absorbers, as well as broad adaptability of 2D materials to solution-based manufacturing of ePV solar cells using sustainable and upscalable printing technologies. A special focus is placed on the large potential of the materials discovery and design of ePV functionalities based on van-der-Waals stacking of atomically thin 2D building blocks, which can open a vast compositional domain of new materials navigable with machine-learning-based accelerated materials screening.

Photoinduced charge separation at heterojunctions between two-dimensional layered materials and small organic molecules.

p-n heterojunctions are fundamental components for electronics and optoelectronics, including diodes, transistors, sensors, and solar cells. Over the past few decades, organic-inorganic p-n heterojunctions have garnered significant interest due to the diverse properties they exhibit, which are a result of the limitless combinations of organic molecules and inorganic materials. This review article concentrates on photoinduced charge separation and photocurrent generation at heterojunctions between two-dimensional layered materials and structurally well-defined organic small molecules. We highlight representative examples, including our work, and critically discuss their potential and perspectives.

Unlocking recent progress in niobium and vanadium carbide-based MXenes for sodium-ion batteries

This review examines the potential capability of Nb–C and VC MXenes as advanced anode materials for enhancing the performance of Na-ion batteries (SIBs). The crucial challenges and future prospects of these SIB electrodes have elaborated in detail.