Recent Advances in Two-Dimensional Materials beyond Graphene

Chalcogen Vacancies as Key Drivers of Distinct Physicochemistry in MoS2, MoSe2, and MoTe2 for Selective Catalysis

The catalytic performance of Mo-based transition-metal-dichalcogenide (TMD) monolayers is intrinsically tied to their physicochemical properties. However, the limited chemical diversity among these materials constrains their versatility for key catalytic processes, including carbon dioxide (CRR), nitrogen (NRR), and oxygen (ORR) reduction reactions. This study employs density functional theory (DFT) calculations to investigate the impact of chalcogen vacancies on the properties ofMoS 2 ${{\rm{MoS}}_2 }$ ,MoSe 2 ${{\rm{MoSe}}_2 }$ , andMoTe 2 ${{\rm{MoTe}}_2 }$ , focusing on the adsorption behaviors of CO, NO, andNO 2 ${{\rm{NO}}_2 }$ . The findings reveal that chalcogen vacancies not only enhance surface reactivity but also impart distinctive physicochemical characteristics to each TMD. These effects arise from intrinsic bonding differences, resulting in distinct charge availability at exposed Mo atoms and variations in vacancy dimensions, which shape specific surface interactions. Hence, while adsorption differences between pristine surfaces are generally negligible for catalysis, vacancies amplify them by over an order of magnitude, resulting in pronounced material-specific behaviors. Moreover, varying vacancy dimensions affect how species incorporate into defects, further enhancing the differences. These characteristics unlock substantial potential of TMD sheets for distinct surface chemistries, transforming them from relatively similar to markedly different as defect density rises. Consequently, our findings provide insights for tailoring these materials toward applications in electro- and photocatalysis.

Unveiling Anomalous Ultrafast Carrier Dynamics of Strong Spectral Overlapping in Few-Layer MoS2

Molybdenum disulfide (MoS2) nanosheets exhibit significant applications in photoelectric devices, and correctly revealing the photogenerated carrier dynamics in the material is crucial for understanding its photophysical response mechanism and optimizing the photoelectric response efficiency of the devices. Herein, we study the ultrafast photogenerated carrier dynamics in MoS2 nanosheets using femtosecond time-resolved transient absorption (TA) microscopy and find that the anomalous rebleaching phenomenon of the TA signals for A- and B-excitons takes place at high pump fluences. By performing a careful quantitative fitting of the time-resolved TA signals, we ascribe the anomalous rebleaching to a result of the superposition of photobleaching and photoinduced absorption induced by the bandgap renormalization effect. This work provides new perspectives for elucidating and comprehending the ultrafast carrier dynamics from the complex TA signals, especially when there is an overlap between positive and negative signals.

Nucleic acid coated photothermal nanoregulator for multiple therapy of drug-resistant breast cancer

Chemotherapy resistance is a leading cause of failure in cancer treatment. A variety of strategies have been investigated to overcome this resistance in cancer therapies. However, the complex microenvironment of tumor cells makes it challenging for any single approach to achieve optimal therapeutic outcomes. In this study, we modified MXene with hyaluronic acid (HA) and coloaded it with doxorubicin (DOX) and the nucleic acid miR489 to address chemotherapy resistance by inhibiting DOX efflux and enabling gene interference. The tumor-targeting capability and biocompatibility of the developed nanosystem, miR489-DOX/Ti3C2@HA-ADH (DTH489), were enhanced through the incorporation of HA. Under near-infrared radiation, MXene not only facilitates photothermal therapy but also reduces the efflux of chemotherapy drugs by down regulating the expression of P-glycoprotein. Additionally, miR489 inhibits epithelial-mesenchymal transition by suppressing the expression of Mothers Against Decapentaplegic Homolog 3, which substantially improves the sensitivity of drug-resistant cancer cells to DOX. In vitro studies confirmed that DTH489 effectively inhibited DOX-resistant breast cancer cells (MCF-7/ADM). Moreover, DTH489 exhibited substantial tumor growth suppression in a mouse model of drug-resistant breast cancer. The results of this research underscore the potential of DTH489 as a multimodal therapeutic platform that effectively reverses chemotherapy resistance in cancer.

Graphendofullerene: a novel molecular two-dimensional ferromagnet

Carbon chemistry has attracted a lot of attention from chemists, physicists and material scientists in the last few decades. The recent discovery of graphullerene provides a promising platform for many applications due to its exceptional electronic properties and the possibility to host molecules or clusters inside the fullerene units. Herein, we introduce graphendofullerene, a novel molecular-based two-dimensional (2D) magnetic material formed by trimetallic nitride clusters encapsulated on graphullerene. Through first-principles calculations, we demonstrate the successful incorporation of the molecules into the 2D network formed by C80 fullerenes, which leads to robust long-range ferromagnetic order with a Curie temperature (T C) of 38 K. Additionally, we achieve a 45% and 18% increase in T C by strain engineering and electrostatic doping, respectively. These findings open the way for a new family of molecular 2D magnets based on graphendofullerene for advanced technologies.

Commensurate, Incommensurate, and Reconstructed Structures of Multilayer Transition Metal Dichalcogenide and Their Applications

Multilayer transition metal dichalcogenides (ML-TMDs) with commensurate, incommensurate, and reconstructed structures, have emerged as a class of 2D materials with unique properties that differ significantly from their monolayer counterparts. While previous research has focused on monolayers, the discovery of various novel properties has sparked interest in multilayers with diverse structures engineered through stacking. These materials are characterized by interactions between layers and exhibit remarkable tunability in their structural, optical, and electronic behaviors depending on stacking order, twist angle, and interlayer coupling. This review provides an overview of ML-TMDs and explores their properties such as electronic band structure, optical responses, ferroelectricity, and anomalous Hall effect. Various synthetic methods employed to fabricate ML-TMDs, including mechanical stacking and chemical vapor deposition techniques, with an emphasis on achieving precise control of the twist angles and layer configurations, are discussed. This study further explores potential applications of ML-TMDs in nanoelectronics, optoelectronics, and quantum devices, where their unique properties can be harnessed for next-generation technologies. The critical role played by these materials in the development of future electronic and quantum devices is highlighted.

Recent Developments of Advanced Broadband Photodetectors Based on 2D Materials

With the rapid development of high-speed imaging, aerospace, and telecommunications, high-performance photodetectors across a broadband spectrum are urgently demanded. Due to abundant surface configurations and exceptional electronic properties, two-dimensional (2D) materials are considered as ideal candidates for broadband photodetection applications. However, broadband photodetectors with both high responsivity and fast response time remain a challenging issue for all the researchers. This review paper is organized as follows. Introduction introduces the fundamental properties and broadband photodetection performances of transition metal dichalcogenides (TMDCs), perovskites, topological insulators, graphene, and black phosphorus (BP). This section provides an in-depth analysis of their unique optoelectronic properties and probes the intrinsic physical mechanism of broadband detection. In Two-Dimensional Material-Based Broadband Photodetectors, some innovative strategies are given to expand the detection wavelength range of 2D material-based photodetectors and enhance their overall performances. Among them, chemical doping, defect engineering, constructing heterostructures, and strain engineering methods are found to be more effective for improving their photodetection performances. The last section addresses the challenges and future prospects of 2D material-based broadband photodetectors. Furthermore, to meet the practical requirements for very large-scale integration (VLSI) applications, their work reliability, production cost and compatibility with planar technology should be paid much attention.

Two-dimensional BiTeX crystals with persistent luminescence induced by photochemical reactions

Two-dimensional (2D) materials are highly valued for their unique properties and potential applications, as they can display exotic behaviors differing from those of their bulk forms. Research on elementary and binary solids has been making great progress recently, while synthesizing multi-component 2D materials experimentally remains a challenge, despite the possibility of greatly extending the number of members of the 2D realm. In this study, we synthesized ternary BiTeX (X = Cl, Br, I) nanosheets with high crystallinity through an electrochemical exfoliation method. Structural analysis confirmed the retention of bulk composition in these nanosheets. Interestingly, the BiTeX nanosheets display a persistent luminescence effect, where the photogenerated carriers exhibit lifetimes of over 100 seconds. Furthermore, the recovery time increased at lower temperatures. The persistent luminescence in 2D BiTeX, which can be ascribed to reversible bond cleavage and recovery under photoexcitation, exhibits potential for applications in fluorescence and photo-responsive systems.

Elucidating the role of oxidation in two-dimensional silicon nanosheets

We report a synthetic protocol that yields hydrogen-terminated 2D silicon nanosheets with greatly reduced siloxane (e.g., Si-O-Si, OxSi) content. These nanosheets displayed weak, broad photoluminescence centered near 610 nm with a low absolute photoluminescence quantum yield (as low as 0.2%). By intentionally oxidizing the nanosheets, the photoluminescence peak emission wavelength blueshifted to 510 nm, and the quantum yield increased by more than an order of magnitude to 8.5%. These results demonstrate that oxidation of 2D silicon nanosheets modulates the material's bandgap and suggests that previously reported photoluminescence properties for this material resulted, in part, from oxidation.

Double Core-Shell Semiconducting Molecular Chain Halogen-Bridged Metal Complexes with Ohmic Contact Heterojunctions

The fabrication of heterostructures from low-dimensional materials is very challenging, particularly the creation of low-dimensional heterojunctions that can be characterized at an atomic resolution. In a previous work, a two-dimensional (2D) heterostructure made from halogen-bridged metal complexes (MX-Chains), [Ni(chxn)2Br]Br2 (chxn = 1R,2R-diaminocyclohexane) and [Pd(chxn)2Br]Br2, has been synthesized, and the nature of the electronically 1D heterojunction at an atomic resolution was revealed. In the work reported here, we have successfully fabricated double core-shell crystals (Ni-Pd-Ni) from these MX-Chains, using a stepwise electrochemical epitaxial method. Upon cleavage of the heterostructure along the van der Waals layers, a double heterojunction surface is observed. The MX-Chains are aligned in the heterostructure and exhibit anisotropic optical properties based on their 1D electronic systems, as measured using UV-vis-NIR polarized reflectance microscopy. Current-voltage curves at different temperatures are recorded using three probes attached to different areas of the heterostructure and reveal the presence of ohmic conduction through the double 1D heterojunctions. The ohmic contact between the two types of MX-Chains arises from the atomic-scale connection of the MX-Chains at the heterojunction. This work represents the first example of a molecule-based heterostructure that has electronic conductivity and demonstrates electrical conduction through a 1D heterojunction.

Hydrogen adsorption and properties of goldene: a first-principles study

Goldene, a single-atom Au monolayer with a hexagonal lattice in the P6/mmm space group, exhibits interesting hyrdrogen absorption properties, as revealed using density functional theory calculations. This study focuses on H-adsorbed goldene at different coverage ratios, and provides insights into the energetic and electronic properties of this system, distinguishing it from the well-studied pristine goldene. Hydrogen adsorption on goldene, while energetically comparable to bulk gold, shows a slight reduction in energetic favorability and introduces specific scanning tunneling microscopy images, reported here for the first time. Raman spectra of H-adsorbed goldene at a 1/9 coverage ratio are also first reported here, along with a vibrational mode analysis, highlighting distinct atomic displacement patterns. Finally, for completeness, previously reported results on the dynamical and mechanical stability of pristine goldene are reported, with a special emphasis on the quadratic flexural mode characteristic of 2D materials. New insights into the thermodynamic properties of goldene compared to bulk gold are also discussed. Although bulk gold remains thermodynamically more stable at all temperatures, the vibrational contributions to the Helmholtz free energy favor goldene above 175 K, narrowing the stability gap with temperature. Overall, this study validates goldene's robustness and expands its potential for experimental and theoretical exploration in the context of hydrogen adsorption and functionalized 2D materials more broadly.

Data-Driven Studies of Two-Dimensional Materials and Their Nonlinear Optical Properties

We present a data-driven investigation leveraging high-throughput density functional theory calculations and machine learning to expedite the discovery of van der Waals (vdW) materials with nonlinear optical properties. Using the Computational 2D Materials Database, we analyze data from 345 noncentrosymmetric, nonmagnetic semiconductor monolayers, focusing on their second-order susceptibility tensors across multiple energy ranges suitable for various laser applications. By applying data mining techniques to extract key features from second harmonic generation spectra and employing machine learning models, we predict the second-order optical susceptibility for these materials. Our framework for this work facilitates the rapid identification of vdW materials for advanced photonics, optoelectronics, and data storage applications.

1D-(GaN/AlN)/2D-Gr/3D-(SiO2/Si) Combined High-Performance Flash Memory Device

Recent advancements have shown that flash memory devices made from entirely two-dimensional (2D) materials exhibit nice performance in terms of storage window, switching speed, and extinction ratio. However, these devices still face challenges such as low carrier density, environmentally sensitive, and difficulty in integration due to the properties of 2D material channels. Here, we propose a novel nonvolatile memory device based on a floating-gate field effect transistor, which integrates one-dimensional (1D) GaN/AlN microwire with 2D few-layer graphene (Gr) to combine the advantages of both materials. By forming a linear-direction 2D electron gas in the GaN channel layer and precise interface of GaN/AlN/Graphene, our memory device achieves a fast switching speed (5 ms) and demonstrates long-term stability (>12,000 cycles; >600 s). This makes it suitable for high-performance type conversion memory and reconfigurable inverter logic circuits, indicating a promising application potential for the integration device of hybrid-dimensional materials.

Atomic-scale intercalation and defect engineering for enhanced magnetism and optoelectronic properties in atomically thin GeS

We investigate the synergistic effects of chromocene intercalation (GeS-Cr[Formula: see text]) and randomly distributed sulfur vacancies on the optoelectronic properties of atomically thin GeS using advanced first-principles many-body simulations. We demonstrate the emergence of a magnetic ground state in GeS, driven by weak chemical interactions between the GeS host and the intercalated organometallic chromocene. Using large-scale, first-principles many-body simulations that account for randomly distributed sulfur vacancies and the dielectric screening within the hybrid material, we show the tunability of the optoelectronic features. Specifically, we observe enhanced absorption in the range of ∼ 0.21 to 3.5 eV, including absorption below the bandgap threshold as the vacancy concentration is tuned between 1 and 5%. The emergent Lifshitz tails are in excellent agreement with our numerical calculations. The predicted features and tunability underscore the potential of defect engineering for applications in magneto-optics and high-density data storage, where precise manipulation of light with magnetic fields is crucial for advanced applications.

Two-dimensional inverse double sandwich CoB7: strain-induced non-magnetic to ferromagnetic transition

A full-scale structural search was performed using density functional theory calculations and a universal structural prediction evolutionary algorithm. This produced a lowest energy two-dimensional (2D) CoB7 structure. The CoB7-1 global minimum structure has unusual inverse double sandwich features. The structure consists of two outer borophene layers which are held together with a layer of Co atoms. This is a B-Co-B sandwich structure. Density functional theory calculations predict that CoB7-1 has good thermodynamic stability, kinetic stability, and mechanical stability. The overall bonding framework is able to survive molecular dynamics annealing up to 1000 K for 10 ps. The DFT results predict that this structure is very stable and should be amenable to experimental synthesis. Surprisingly, we found that this material can change from a non-magnetic ground state to a ferromagnetic state under the influence of biaxial strain. This unusual property of having a magnetic transition while at the same temperature leads us to conclude that this new 2D CoB7 crystal may have potential applications in future nano-magnetic devices at or near room temperature.

Boosting the Performance of Alkaline Anion Exchange Membrane Water Electrolyzer with Vanadium-Doped NiFe2O4

Developing efficient, economical, and stable catalysts for the oxygen evolution reaction is pivotal for producing large-scale green hydrogen in the future. Herein, a vanadium-doped nickel-iron oxide supported on nickel foam (V-NiFe2O4/NF) is introduced, and synthesized via a facile hydrothermal method as a highly efficient electrocatalyst for water electrolysis. X-ray photoelectron and absorption spectroscopies reveal a synergistic interaction between the vanadium dopant and nickel/iron in the host material, which tunes the electronic structure of NiFe2O4 to increase the number of electrochemically active sites. The V-NiFe2O4/NF electrode exhibited superior electrochemical performance, with a low overpotential of 186 mV at a current density of 10 mA cm-2, a Tafel slope value of 54.45 mV dec-1, and minimal charge transfer resistance. Employing the V-NiFe2O4/NF electrode as an anode in an alkaline anion exchange membrane water electrolyzer single-cell, a cell voltage of 1.711 V is required to achieve a high current density of 1.0 A cm-2. Remarkably, the cell delivered an energy conversion efficiency of 73.30% with enduring stability, making it a promising candidate for industrial applications.

Hypotaxy of wafer-scale single-crystal transition metal dichalcogenides

Two-dimensional (2D) semiconductors, particularly transition metal dichalcogenides (TMDs), are promising for advanced electronics beyond silicon1-3. Traditionally, TMDs are epitaxially grown on crystalline substrates by chemical vapour deposition. However, this approach requires post-growth transfer to target substrates, which makes controlling thickness and scalability difficult. Here we introduce a method called hypotaxy ('hypo' meaning downward and 'taxy' meaning arrangement), which enables wafer-scale single-crystal TMD growth directly on various substrates, including amorphous and lattice-mismatched substrates, while preserving crystalline alignment with an overlying 2D template. By sulfurizing or selenizing a pre-deposited metal film under graphene, aligned TMD nuclei form, coalescing into a single-crystal film as graphene is removed. This method achieves precise MoS2 thickness control from monolayer to hundreds of layers on diverse substrates, producing 4-inch single-crystal MoS2 with high thermal conductivity (about 120 W m-1 K-1) and mobility (around 87 cm2 V-1 s-1). Furthermore, nanopores created in graphene using oxygen plasma treatment allow MoS2 growth at a lower temperature of 400 °C, compatible with back-end-of-line processes. This hypotaxy approach extends to other TMDs, such as MoSe2, WS2 and WSe2, offering a solution to substrate limitations in conventional epitaxy and enabling wafer-scale TMDs for monolithic three-dimensional integration.

First-Principles Investigations of Two-Sided Functionalised MoS2 Monolayer

In this computational study, we investigate two-sided functionalised MoS2 with alkali metal atoms as donors and the organic acceptor molecule F4TCNQ as an acceptor. Characterisation of functionalised MoS2 involves first-principles calculations within the density functional theory (DFT) framework with a PBE+D3 scheme to investigate the electronic structure and quantify the charge transfer in the two-sided functionalised system in comparison to the one-sided functionalised counterpart. Within the two-sided functionalised systems, there is an increase in the overall charge on MoS2 as a result of stronger electron transfer from the donor to the monolayer, additionally controlled by the ability of the acceptor to receive electrons.

P-type doping in edge-enriched MoS2-x nanostructures via RF-generated nitrogen plasma

In this work, we report an intuitive magnetron sputtering technique for the synthesis of vertically aligned MoS2 (v-MS) nanostructures. The morphology and orientation of the as-synthesized nanostructures can be modified by altering the parameters of the sputtering process. This work emphasizes the versatility of magnetron sputtering to synthesize edge-enriched vertically aligned 2D nanostructures. These structures have diverse applications, such as those in optoelectronics, hydrogen evolution, sensing, energy storage and catalysis. The vertically aligned nanostructure of MoS2 was confirmed using the field emission scanning electron microscopy and Raman spectroscopy techniques. Furthermore, we studied the plasma-based nitrogen doping process with minimal damage for introducing nitrogen atoms into 2D nanomaterials. A plasma discharged into a nitrogen environment, assisted by a simple radio frequency (RF) power supply, was employed for p-type doping in v-MS. The successful doping of nitrogen was investigated by Raman spectroscopy and X-ray photoelectron spectroscopy. Atomic force microscopy images confirmed the little surface damage resulting from the nitrogen doping technique. The change in work function resulting from doping was examined by Kelvin probe force microscopy and ultraviolet photoelectron spectroscopy. Optical emission spectroscopy (OES) study revealed the role of nitrogen plasma ions in doping with minimal surface damaging. This work demonstrates the effective alteration of the work function of the MoS2 nanomaterial via plasma treatment.

Wearable Biodevices Based on Two-Dimensional Materials: From Flexible Sensors to Smart Integrated Systems

The proliferation of wearable biodevices has boosted the development of soft, innovative, and multifunctional materials for human health monitoring. The integration of wearable sensors with intelligent systems is an overwhelming tendency, providing powerful tools for remote health monitoring and personal health management. Among many candidates, two-dimensional (2D) materials stand out due to several exotic mechanical, electrical, optical, and chemical properties that can be efficiently integrated into atomic-thin films. While previous reviews on 2D materials for biodevices primarily focus on conventional configurations and materials like graphene, the rapid development of new 2D materials with exotic properties has opened up novel applications, particularly in smart interaction and integrated functionalities. This review aims to consolidate recent progress, highlight the unique advantages of 2D materials, and guide future research by discussing existing challenges and opportunities in applying 2D materials for smart wearable biodevices. We begin with an in-depth analysis of the advantages, sensing mechanisms, and potential applications of 2D materials in wearable biodevice fabrication. Following this, we systematically discuss state-of-the-art biodevices based on 2D materials for monitoring various physiological signals within the human body. Special attention is given to showcasing the integration of multi-functionality in 2D smart devices, mainly including self-power supply, integrated diagnosis/treatment, and human-machine interaction. Finally, the review concludes with a concise summary of existing challenges and prospective solutions concerning the utilization of 2D materials for advanced biodevices.

Two-Dimensional Organic-Inorganic van der Waals Hybrids

Two-dimensional organic-inorganic (2DOI) van der Waals hybrids (vdWhs) have emerged as a groundbreaking subclass of layer-stacked (opto-)electronic materials. The development of 2DOI-vdWhs via systematically integrating inorganic 2D layers with organic 2D crystals at the molecular/atomic scale extends the capabilities of traditional 2D inorganic vdWhs, thanks to their high synthetic flexibility and structural tunability. Constructing an organic-inorganic hybrid interface with atomic precision will unlock new opportunities for generating unique interfacial (opto-)electronic transport properties by combining the strengths of organic and inorganic layers, thus allowing us to satisfy the growing demand for multifunctional applications. Here, this review provides a comprehensive overview of the latest advancements in the chemical synthesis, structural characterization, and numerous applications of 2DOI-vdWhs. Firstly, we introduce the chemistry and the physical properties of the recently rising organic 2D crystals (O2DCs), which feature crystalline 2D nanostructures comprising carbon-rich repeated units linked by covalent/noncovalent bonds and exhibit strong in-plane extended π-conjugation and weak interlayer vdWs interaction. Simultaneously, representative inorganic 2D crystals (I2DCs) are briefly summarized. After that, the synthetic strategies will be systematically summarized, including synthesizing single-component O2DCs with dimensional control and their vdWhs with I2DCs. With these synthetic approaches, the control in the dimension, the stacking modes, and the composition of the 2DOI-vdWhs will be highlighted. Subsequently, a special focus will be given on the discussion of the optical and electronic properties of the single-component 2D materials and their vdWhs, which will be closely relevant to their structures, so that we can establish a general structure-property relationship of 2DOI-vdWhs. In addition to these physical properties, the (opto-)electronic devices such as transistors, photodetectors, sensors, spintronics, and neuromorphic devices as well as energy devices will be discussed. Finally, we provide an outlook to discuss the key challenges for the 2DOI-vdWhs and their future development. This review aims to provide a foundational understanding and inspire further innovation in the development of next-generation 2DOI-vdWhs with transformative technological potential.

A cutting-edge neural network approach for predicting the thermoelectric efficiency of defective gamma-graphyne nanoribbons

This study predicts the thermoelectric figure of merit (ZT) for defective gamma-graphyne nanoribbons (γ-GYNRs) using binary coding, convolutional neural networks (CNN), long short-term memory networks (LSTM), and multi-scale feature fusion. The approach accurately predicts ZT values with only 500 initial structures (3% of 16,512 candidates), achieving an R2 above 0.91 and a mean absolute error (MAE) of 0.05 to 0.06. The use of artificial feature extraction combined with an attention mechanism reveals that the number and distribution of defects are crucial for achieving high ZT values. γ-GYNRs with moderate and evenly distributed defect count show superior thermoelectric performance. This demonstrates the effectiveness of neural networks in designing low-dimensional materials like γ-GYNRs and offers insights into exploring other materials with excellent thermoelectric properties.

Impact of grain boundaries on the electronic properties and Schottky barrier height in MoS2@Au heterojunctions

Using density functional theory (DFT) calculations we thoroughly explored the influence of grain boundaries (GBs) in monolayer MoS2 composed of S-polar (S5|7), Mo-polar (Mo5|7), and (4|8) edge dislocation, as well as an edge dislocation-double S vacancy complex (S4|6), and a dislocation-double S interstitial complex (S6|8), respectively, on the electronic properties of MoS2 and the Schottky barrier height (SBH) in MoS2@Au heterojunctions. Our findings demonstrate that GBs formed by edge dislocations can significantly reduce the SBH in defect-free MoS2, with the strongest effect for zigzag (4|8) GBs (-20% reduction) and the weakest for armchair (5|7) GBs (-10% reduction). In addition, a larger tilt angle in the GBs leads to a more pronounced decrease in the SBH, suggesting that the modulation of SBH in the MoS2@Au heterostructure and analogous systems can be accomplished by GB engineering. Our findings also suggest that planar defects with high mobility in MoS2 may contribute to the memory switching effect observed in MoS2-based memtransistors and the reduction caused by the presence of planar defects can partially contribute to the discrepancy observed between experimental measurements and theoretical SBH predictions at the MoS2@Au heterojunction.

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.

Atomistic Study on the Mechanical Properties of HOP-Graphene Under Variable Strain, Temperature, and Defect Conditions

HOP-graphene is a graphene structural derivative consisting of 5-, 6-, and 8-membered carbon rings with distinctive electrical properties. This paper presents a systematic investigation of the effects of varying sizes, strain rates, temperatures, and defects on the mechanical properties of HOP-graphene, utilizing molecular dynamics simulations. The results revealed that Young's modulus of HOP-graphene in the armchair direction is 21.5% higher than that in the zigzag direction, indicating that it exhibits greater rigidity in the former direction. The reliability of the tensile simulations was contingent upon the size and strain rate. An increase in temperature from 100 K to 900 K resulted in a decrease in Young's modulus by 7.8% and 2.9% for stretching along the armchair and zigzag directions, respectively. An increase in the concentration of introduced void defects from 0% to 3% resulted in a decrease in Young's modulus by 24.7% and 23.1% for stretching along the armchair and zigzag directions, respectively. An increase in the length of rectangular crack defects from 0 nm to 4 nm resulted in a decrease in Young's modulus for stretching along the armchair and zigzag directions by 6.7% and 5.7%, respectively. Similarly, an increase in the diameter of the circular hole defect from 0 nm to 4 nm resulted in a decrease in Young's modulus along both the armchair and zigzag directions, with a corresponding reduction of 11.0% and 10.4%, respectively. At the late stage of tensile fracture along the zigzag direction, HOP-graphene undergoes a transformation to an amorphous state under tensile stress. Our results might contribute to a more comprehensive understanding of the mechanical properties of HOP-graphene under different test conditions, helping to land it in potential practical applications.

Effects of transition metal substitution doping on the structure and magnetic properties of biphenylene

This study employed first-principles calculations to comprehensively explore the structural, electronic, and magnetic properties of transition metal-doped biphenylene networks (BPNs). Initially, we optimized the most stable structures of biphenylene doped with various transition metals (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn) and analysed their doping energies and electronic structures in detail. The results indicate that the introduction of transition metals induces varying degrees of spin polarization. Specifically, the Cr-doped BPN exhibits almost 100% spin polarization at the Fermi level, exhibiting the properties of a half-metal or a spin-gapless semiconductor. In contrast, V-doped, Mn-doped and Co-doped BPNs show incomplete spin polarization, and exhibit antiferromagnetic like properties on the C atom. Furthermore, an analysis of the energy differences between the spin states and the non-spin states confirmed the stability of spin states, providing theoretical support for the application of BPNs as a new class of magnetic materials. In summary, through transition metal doping, BPNs exhibit promising applications, particularly in the fields of magnetic storage and magnetic sensors, highlighting their significant potential.

Liquid exfoliation of a series of expanded layered Cu(II)-paddlewheel metal-organic frameworks to form nanosheets

Ultrasonic liquid exfoliation provides a convenient route for converting layered materials into nanosheets. However, the relationship between the structure and morphology of the bulk materials and the properties of the resulting nanosheets remains poorly understood. In this work, we prepare an isoreticular series of layered metal-organic frameworks (MOFs) based on linear aromatic dicarboxylate derivatives (L1, L2, L3) with three different linker lengths (L3 > L2 > L1) and using copper(II) nitrate and acetate as metal ion sources. Liquid exfoliation of large crystals of all three MOFs [Cu2(L)2](solvent)2, synthesised from Cu(NO3)2, produced monolayer nanosheets with longer linkers leading to larger lateral dimensions. Exfoliation of smaller MOF crystals, formed using the copper(II) acetate salt under identical conditions, produced a much higher concentration of multi-layer nanosheets with smaller lateral dimensions. These results indicate that the initial crystal size plays an important role in determining both the lateral dimensions and the thicknesses of nanosheets. Such insights contribute to a deeper understanding of the design principles governing metal-organic framework nanosheets (MONs) and other two-dimensional materials.

Nontrivial Raman Characteristics in 2D Non-Van der Waals Mo5N6

Resonant Raman spectra of a two-dimensional (2D) non-van der Waals (vdW) material, molybdenum nitride (Mo5N6), are measured across varying thicknesses, ranging from a few to tens of nanometers. Fifteen distinct Raman peaks are observed experimentally, and their assignments are made using first-principles calculations for the most stable AABB-stacking structure of Mo5N6. The assignments are further supported by angular-dependent Raman measurements for all peaks, except the most intense one at 215 cm-1. Calculations reveal that the 215 cm-1 peak does not appear for three-dimensional molybdenum nitrides and is not a first-order Raman-active mode. We further investigated the origin of the 215 cm-1 peak and assigned it as a defect-induced double-resonance peak. Moreover, thickness-dependent Raman measurements reveal that both the 215 and 540 cm-1 peaks─assigned to out-of-plane and in-plane modes, respectively─blue shift as thickness increases, reaching a plateau around 20 nm. This thickness-dependent Raman shift over a wide thickness range is nontrivial compared to other common vdW 2D materials and is attributed to the much stronger stacking interaction between the constituent layers in non-vdW materials. This finding highlights Raman spectroscopy as a valuable tool for characterizing the thickness of 2D non-vdW materials.

Multiple Weyl fermions and topological phase transition in two-dimensional ferromagnetic CrS2

The study of topological states in two-dimensional (2D) systems, especially with magnetic properties, has recently gained significant attention owing to their potential in spintronics and nanotechnology. Here, we propose a 2D ferromagnetic (FM) material, CrS2, which hosts multiple Weyl points (WPs) and can undergo a topological phase transition by rotating the magnetization direction. Based on first-principles calculations, we identify distinct Weyl points around the Fermi level: W1, W2, and W3. These points appear in both spin channels and include various types: type-I, type-II and type-III WPs. Corresponding Fermi arcs are clearly observed at the material edges. CrS2 displays a FM ground state with the easy magnetization direction along the c-axis. When the magnetization direction is rotated in the x-y plane, the W1 and W3 points open gaps, with the gap values remaining the same in all magnetization directions. The W2 can maintain a crossing at specific in-plane magnetization directions, indicating that the material retains its Weyl state. Additionally, we examine the effects of biaxial and uniaxial strains on electronic properties. Weyl points remain stable under biaxial strain of less than ±5%, but they disappear under uniaxial strain. In summary, our work proposes a 2D FM material with multiple coexisting Weyl fermions, where the topological states can be tuned by an external magnetic field.

First Principles Study of p-Type Transition and Enhanced Optoelectronic Properties of g-ZnO Based on Diverse Doping Strategies

By utilizing first principles calculations, p-type transition in graphene-like zinc oxide (g-ZnO) through elemental doping was achieved, and the influence of different doping strategies on the electronic structure, energy band structure, and optoelectronic properties of g-ZnO was investigated. This research study delves into the effects of strategies such as single-acceptor doping, double-acceptor co-doping, and donor-acceptor co-doping on the properties of g-ZnO. This study found that single-acceptor doping with Li and Ag elements can form shallow acceptor levels, thereby facilitating p-type conductivity. Furthermore, the introduction of the donor element F can compensate for the deep acceptor levels formed by double-acceptor co-doping, transforming them into shallow acceptor levels and modulating the energy band structure. The co-doping strategy involving double-acceptor elements and a donor element further optimizes the properties of g-ZnO, such as reducing the bandgap and enhancing carrier mobility. Additionally, in terms of optical properties, g-Zn14Li2FO15 demonstrates outstanding performance in the visible-light region compared with other doping systems, especially generating a higher absorption peak around the wavelength of 520 nm. These findings provide a theoretical foundation for the application of g-ZnO in optoelectronic devices.

The quantum anomalous Hall effect and strong robustness in two-dimensional p-state Dirac half-metals Y3X2 (Y = Li, Na; X = Se, Te)

Based on first-principles calculations, we have predicted a novel group of 2D p-state Dirac half-metal (DHM) materials, Y3X2 (Y = Li, Na; X = Se, Te) monolayers. All the monolayers exhibit intrinsic ferromagnetism. Among them, Li3Te2 and Na3Se2 open topologically nontrivial band gaps of 4.0 meV and 5.0 meV considering spin-orbit coupling (SOC), respectively. The Curie temperature of Li3Te2 is 355 K. The non-zero Chern number and the presence of edge states further confirm that the Li3Te2 monolayer is a room-temperature ferromagnetic material and a quantum anomalous Hall (QAH) insulator. Additionally, it is found that Y3X2 (Y = Li, Na; X = Se, Te) monolayers exhibit strong robustness against strain and electric fields. Finally, we have proposed the growth of Y3X2 (Y = Li, Na; X = Se, Te) monolayers on h-BN substrates, which shows promise for experimental synthesis. Our research indicates that Y3X2 (Y = Li, Na; X = Se, Te) monolayers exhibit strong robustness as DHMs, showcasing significant potential for realizing the intrinsic quantum anomalous Hall effect (QAHE).

Advancements and Challenges in the Integration of Indium Arsenide and Van der Waals Heterostructures

The strategic integration of low-dimensional InAs-based materials and emerging van der Waals systems is advancing in various scientific fields, including electronics, optics, and magnetics. With their unique properties, these InAs-based van der Waals materials and devices promise further miniaturization of semiconductor devices in line with Moore's Law. However, progress in this area lags behind other 2D materials like graphene and boron nitride. Challenges include synthesizing pure crystalline phase InAs nanostructures and single-atomic-layer 2D InAs films, both vital for advanced van der Waals heterostructures. Also, diverse surface state effects on InAs-based van der Waals devices complicate their performance evaluation. This review discusses the experimental advances in the van der Waals epitaxy of InAs-based materials and the working principles of InAs-based van der Waals devices. Theoretical achievements in understanding and guiding the design of InAs-based van der Waals systems are highlighted. Focusing on advancing novel selective area growth and remote epitaxy, exploring multi-functional applications, and incorporating deep learning into first-principles calculations are proposed. These initiatives aim to overcome existing bottlenecks and accelerate transformative advancements in integrating InAs and van der Waals heterostructures.

Tight-binding model of Pt-based jacutingaites as combination of the honeycomb and kagome lattices

We introduce a refined tight-binding (TB) model for Pt-based jacutingaite materialsPt2NX3, (N= Zn, Cd, Hg; X = S, Se, Te), offering a detailed representation of the low-energy physics of its monolayers. This model incorporates all elements with significant spin-orbit coupling contributions, which are essential for understanding the topological energy gaps in these materials. Through comparison with first-principles calculations, we meticulously fitted the TB parameters, ensuring an accurate depiction of the energy bands near the Fermi level. Our model reveals the intricate interplay between the Pt 3eandNmetal orbitals, forming distinct kagome and honeycomb lattice structures. Applying this model, we explore the edge states of Pt-based jacutingaite monolayer nanoribbons, highlighting the sensitivity of the topological edge states dispersion bands to the nanostructures geometric configurations. These insights not only deepen our understanding of jacutingaite materials but also assist in tailoring their electronic properties for future applications.

i-PHAOS: An Overview with an Open-Source Collaborative Database on Miniaturized Integrated Spectrometers

On-chip spectrometers are increasingly becoming tools that might help in everyday life needs. The possibility offered by several available integration technologies and materials to be used to miniaturize spectrometers has led to a plethora of very different devices, that in principle can be compared according to their metrics. Having access to a reference database can help in selecting the best-performing on-chip spectrometers and being up to date in terms of standards and developments. In this paper, an overview of the most relevant publications available in the literature on miniaturized spectrometers is reported and a database is provided as an open-source project to which researchers can have access and participate in order to improve the share of knowledge in the interested scientific community.

Two-Dimensional MoSi2N4 Family: Progress and Perspectives Form Theory

Recently, a new two-dimensional (2D) layered MoSi2N4 has been successfully synthesized by chemical vapor deposition without knowing the 3D counterparts [ Science 2020, 369, 670-674]. The unique septuple-atomic-layer structure and diverse composition of MoSi2N4 have drawn tremendous interest in studying 2D MA2Z4 systems based on the MoSi2N4 structure. As an emerging family of 2D materials, MA2Z4 materials exhibit a wide range of properties and excellent tunability, making them highly promising for various applications. Herein, we summarize recent significant progress in property characterization of the MA2Z4 family. The electronic, magnetic, thermal transport, and superconducting properties, including their tunability through strain engineering and elemental substitution, are presented and elaborated in detail. Further perspectives and new opportunities of the emerging MA2Z4 family are presented at the end of this Perspective.

Computational screening of single-atom transition metals on boron-rich boron nitride nanosheets for efficient hydrogen evolution catalysis in all pH range

Low-cost and high-efficiency catalysts are of crucial importance for the electrocatalytic hydrogen evolution reaction (HER). Two-dimensional (2D) boron nitride (B-N) compounds formed by the combination of boron and nitrogen atoms of group III and V elements are promising candidates for electrocatalytic HER due to their significant electronic properties. Hence, an electrocatalyst is computer-aided designed with isolated single atoms of 3d, 4d, and 5d transition metals supported on 2D B-N (B2N, B5N3, and B7N5) monolayers to fabricate single-atom catalysts (SACs) with an excellent HER performance. Moreover, pH modulations are considered to improve the HER activity theoretically based on first-principles calculation. Our results indicate that B-N compounds surface doping with transition metal atoms can effectively enhance the HER catalytic performance over a wide range of pH. Among all SACs studied, Co-, Ti-, V-, Nb-, Ru-, Tc-, Zr-, and Os-embedded B2N, Sc-, Cr-, Mn-, Ti-, and Y-embedded B5N3, and Sc- and Mn-embedded B7N5 have excellent catalytic activity under acidic conditions, while Mo-, Ir-, Re-, Ta-, and W-embedded B2N and Ti- and Fe-embedded B7N5 show high catalytic activity under alkaline conditions. Interestingly, Hf@B2N and V@B5N3 systems exhibit promising catalytic activity under acidic, neutral, and alkaline conditions. Our work offers cost-effective candidates with a wide pH range HER performance for exploring ideal electrocatalysts.

Sub-1 nm Materials Chemistry: Challenges and Prospects

Subnanometer materials (SNMs) refer to nanomaterials with a feature size close to 1 nm, similar to the diameter of a single polymer, DNA strand, and a single cluster/unit cell. The growth and assembly of subnanometer building blocks can be controlled by interactions at atomic levels, representing the limit for the precise manipulation of materials. The size, geometry, and flexibility of 1D SNMs inorganic backbones are similar to the polymer chains, bringing excellent gelability, adhesiveness, and processability different from inorganic nanocrystals. The ultrahigh surface atom ratio of SNMs results in significantly increased surface energy, leading to significant rearrangement of surface atoms. Unconventional phases, immiscible metal alloys, and high entropy materials with few atomic layers can be stabilized, and the spontaneous twisting of SNMs may induce the intrinsic structural chirality. Electron delocalization may also emerge at the subnanoscale, giving rise to the significantly enhanced catalytic activity. In this perspective, we summarized recent progress on SNMs, including their synthesis, polymer-like properties, metastable phases, structural chirality, and catalytic properties, toward energy conversion. As a critical size region in nanoscience, the development of functional SNMs may fuse the boundary of inorganic materials and polymers and conduce to the precise manufacturing of materials at atomic levels.

When van der Waals Met Kagome: A 2D Antimonide with a Vanadium-Kagome Network

2D materials showcase unconventional properties emerging from quantum confinement effects. In this work, a "soft chemical" route allows for the deintercalation of K+ from the layered antimonide KV6Sb6, resulting in the discovery of a new metastable 2D-Kagome antimonide K0.1(1)V6Sb6 with a van der Waals gap of 3.2 Å. The structure of K0.1(1)V6Sb6 was determined via the synergistic techniques, including X-ray pair distribution function analysis, advanced transmission electron microscopy, and density functional theory calculations. The K0.1(1)V6Sb6 compound crystallizes in the monoclinic space group C2/m (a = 9.57(2) Å, b = 5.502(8) Å, c = 10.23(2) Å, β = 97.6(2)°, Z = 2). The [V6Sb6] layers in K0.1(1)V6Sb6 are retained upon deintercalation and closely resemble the layers in the parent compound, yet deintercalation results in a relative shift of the adjacent [V6Sb6] layers. The magnetic properties of the K0.1(1)V6Sb6 phase in the 2-300 K range are comparable to those of KV6Sb6 and another Kagome antimonide KV3Sb5, consistent with nearly temperature-independent paramagnetism. Electronic band structure calculation suggests a nontrivial band topology with flat bands and opening of band crossing afforded by deintercalation. Transport property measurements reveal a metallic nature for K0.1(1)V6Sb6 and a low thermal conductivity of 0.6 W K-1 m-1 at 300 K. Additionally, ion exchange in KV6Sb6 via a solvothermal route leads to a successful partial exchange of K+ with A+ (A = Na, Rb, and Cs). This study highlights the tunability of the layered structure of the KV6Sb6 compound, providing a rich playground for the realization of new 2D materials.

Non-metallic doped GeC monolayer: tuning electronic and photo-electrocatalysis for water splitting

We conducted a first-principles study on the electronic, magnetic, and optical characteristics of non-metallic atoms (B, C, F, H, N, O, P, S, and Si) doped in single-layer carbon germanium (GeC). The findings indicate that the introduction of various non-metallic atoms into the monolayer GeC leads to modifications in its band structure properties. Different non-metallic atoms doped in single-layer GeC will produce both magnetic and non-magnetic properties. B-, H-, N-, and P-doped GeC systems exhibit magnetic properties, while C-, F-, O-, S-, and Si-doped single-layer GeC systems exhibit non-magnetic properties. Different non-metallic-doped single-layer GeC systems will produce semiconductor, semimetallic, and metallic properties. The C-, N-, O-, P-, S-, and Si-doped GeC systems still exhibit semiconductor properties. The H-doped GeC system exhibits semimetallic properties, while the B- and F-doped GeC systems exhibit metallic properties. Other than that, the doping of B, H, N, and P atoms can modulate the magnetism of single-layer GeC. Subsequently, we studied the influence of the doping behavior on the work function, where the work function of the single-layer GeC system doped with P atoms is very small, indicating that its corresponding doping system (P-doped GeC system) can produce a good field emission effect. In the optical spectrum, the doped systems have a certain influence in the far ultraviolet region. Furthermore, our results showed that S- and Si-doped single-layer GeC systems are conducive to photocatalysis compared to the single-layer GeC system.

Gamma rays impact on 2D-MoS2 in water solution

Two-dimensional transition metal dichalcogenides, particularly MoS2, are interesting materials for many applications in aerospace research, radiation therapy and bioscience more in general. Since in many of these applications MoS2-based nanomaterials can be placed in an aqueous environment while exposed to ionizing radiation, both experimental and theoretical studies of their behaviour under these conditions is particularly interesting. Here, we study the effects of tiny imparted doses of 511 keV photons to MoS2 nanoflakes in water solution. To the best of our knowledge, this is the first study in which ionizing radiation on 2D-MoS2 occurs in water. Interestingly, we find that, in addition to the direct interaction between high-energy photons and nanoflakes, reactive chemical species, generated by γ-photons induced radiolysis of water, come into play a relevant role. A radiation transport Monte Carlo simulation allowed determining the elements driving the morphological and spectroscopical changes of 2D-MoS2, experimentally monitored by SEM microscopy, DLS, Raman and UV-vis spectroscopy, AFM, and X-ray photoelectron techniques. Our study demonstrates that radiolysis products affect the Molybdenum oxidation state, which is massively changed from the stable + 4 and + 6 states into the rarer and more unstable + 5. These findings will be relevant for radiation-based therapies and diagnostics in patients that are assuming drugs or contrast agents containing 2D-MoS2 and for aerospace biomedical applications of 2DMs investigating their actions into living organisms on space station or satellites.

Effects of size and shape of hole defects on mechanical properties of biphenylene: a molecular dynamics study

The distinctive multi-ring structure and remarkable electrical characteristics of biphenylene render it a material of considerable interest, notably for its prospective utilization as an anode material in lithium-ion batteries. However, understanding the mechanical traits of biphenylene is essential for its application, particularly due to the volumetric fluctuations resulting from lithium ion insertion and extraction during charging and discharging cycles. In this regard, this study investigates the performance of pristine biphenylene and materials embedded with various types of hole defects under uniaxial tension utilizing molecular dynamics simulations. Specifically, from the stress‒strain curves, we obtained key mechanical properties, including toughness, strength, Young's modulus and fracture strain. It was observed that various near-circular hole (including circular, square, hexagonal, and octagonal) defects result in remarkably similar properties. A more quantitative scaling analysis revealed that, in comparison with the exact shape of the defect, the area of the defect is more critical for determining the mechanical properties of biphenylene. Our finding might be beneficial to the defect engineering of two-dimensional materials.

Advancements in Surfactant Carriers for Enhanced Oil Recovery: Mechanisms, Challenges, and Opportunities

Enhanced oil recovery (EOR) techniques are crucial for maximizing the extraction of residual oil from mature reservoirs. This review explores the latest advancements in surfactant carriers for EOR, focusing on their mechanisms, challenges, and opportunities. We delve into the role of inorganic nanoparticles, carbon materials, polymers and polymeric surfactants, and supramolecular systems, highlighting their interactions with reservoir rocks and their potential to improve oil recovery rates. The discussion includes the formulation and behavior of nanofluids, the impact of surfactant adsorption on different rock types, and innovative approaches using environmentally friendly materials. Notably, the use of metal oxide nanoparticles, carbon nanotubes, graphene derivatives, and polymeric surfacants and the development of supramolecular complexes for managing surfacant delivery are examined. We address the need for further research to optimize these technologies and overcome current limitations, emphasizing the importance of sustainable and economically viable EOR methods. This review aims to provide a comprehensive understanding of the emerging trends and future directions in surfactant carriers for EOR.

Aqueous Graphene Dispersion and Biofunctionalization via Enzymatic Oxidation of Tripeptides

Graphene, a 2D carbon material, possesses extraordinary mechanical, electrical, and thermal properties, making it highly attractive for various biological applications such as biosensing, biotherapeutics, and tissue engineering. However, the tendency of graphene sheets to aggregate and restack hinders its dispersion in water, limiting these applications. Peptides, with their defined amino acid sequences and versatile functionalities, are compelling molecules with which to modify graphene-aromatic amino acids can strengthen interactions through π-stacking and charged groups can be chosen to make the sheets dispersible and stable in water. Here, a facile and green method for covalently functionalizing and dispersing graphene using amphiphilic tripeptides, facilitated by a tyrosine phenol side chain, through an aqueous enzymatic oxidation process is demonstrated. The presence of a second aromatic side chain group enhances this interaction through non-covalent support via π-π stacking with the graphene surface. Futhermore, the addition of charged moieties originating from either ionizable amino acids or terminal groups facilitates profound interactions with water, resulting in the dispersion of the newly functionalized graphene in aqueous solutions. This biofunctionalization method resulted in ≈56% peptide loading on the graphene surface, leading to graphene dispersions that remain stable for months in aqueous solutions outperforming currently used surfactants.

Molecular donor-acceptor linked systems as models for examining their interactions in excited states

Molecular donor-acceptor (D-A) linked systems have attracted significant attention due to their potential to address D-A interactions in excited states. In these systems, it is crucial to understand the interplay between electrons and spin behaviors, atomic nucleus movements (including vibration, rotation, fluctuation, and transfer), and collective motion (electron-phonon coupling) over time. Through intentional manipulation of locally excited, charge-transfer excited, and charge-separated states, along with modulation of dynamic effects (enhancement or restraint), we expect to unlock the full potential of D-A systems for photofunctions in electronics, energy, healthcare, and functional materials. In this perspective, we present our recent examples of D-A linked systems and related ones that address the aforementioned issues as part of our "Dynamic Exciton" research project in Japan.

Tunable Ultrafast Charge Transfer across Homojunction Interface

Charge transfer at heterojunction interfaces is a fundamental process that plays a crucial role in modern electronic and photonic devices. The essence of such charge transfer lies in the band offset, making charge transfer uncommon in a homojunction. Recently, sliding ferroelectricity has been proposed and confirmed in two-dimensional van der Waals stacked materials such as bilayer boron nitride. During the sliding of these layers, the band alignment shifts, creating conditions for charge separation at the interface. We employ ab initio nonadiabatic molecular dynamics simulations to elucidate the excited state carrier dynamics in bilayer boron pnictides. We propose that, akin to ferroelectric polarization flipping, the precise modulation of the distribution of excited state carriers can also be reached by sliding. Our results demonstrate that sliding induces a reversal of the frontier orbital distribution on the upper and lower layers, facilitating a robust interlayer carrier transfer. Notably, the interlayer carrier transfer is more pronounced in boron phosphide than in boron nitride, attributed to strong electron scattering in momentum space in boron nitride. We propose this novel method to manipulate carrier distribution and dynamics in a homojunction exhibiting sliding ferroelectricity, in general, paving a new way for developing advanced electronic and photonic devices.

First-Principles Studies of the Electronic and Optical Properties of Two-Dimensional Arsenic-Phosphorus (2D As-P) Compounds

In this work, we propose the construction of a two-dimensional system based on the stable phases previously reported for the 2D arsenic and phosphorus compounds, with hexagonal and orthorhombic symmetries. Therefore, we have modeled one hexagonal and three possible orthorhombic structures. To ensure the dynamical stability, we performed phonon spectra calculations for each system. We found that all phases are dynamically stable. To ensure the thermodynamic and mechanical stabilities, we have calculated cohesive energies and elastic constants. Our results show that the criteria for the stabilities are all fulfilled. For these stable structures, we computed the electronic and optical properties from first-principles studies based on density functional theory. The computation of electronic band gaps was performed by using the GW approximation to overcome the underestimation of the results obtained from standard DFT approaches. To study the optical properties, we have computed the dielectric function imaginary part within the BSE approach, which takes into account the excitonic effects and allows us to calculate the exciton binding energies of each system. The study was complemented by the computation of the absorption coefficient. From our calculations, it can be established that the 2D As-P systems are good candidates for several technological applications.

Advances in Inorganic Foam Materials Fabricated Via Blowing Strategy: A Comprehensive Review

Two-dimensional (2D) materials with excellent properties and widespread applications have been explosively investigated. However, their conventional synthetic methods exhibit concerns of limited scalability, complex purification process, and incompetence of prohibiting their restacking. The blowing strategy, characterized by gas-template, low-cost, and high-efficiency, presents a valuable avenue for the synthesis of 2D-based foam materials and thereby addresses these constraints. Whereas, its comprehensive introduction has been rarely outlined so far. This review commences with a synopsis of the blowing strategy, elucidating its development history, the statics and kinetics of the blowing process, and the choice of precursor and foaming agents. Thereafter, we dwell at length on across-the-board foams enabled by the blowing route, like BxCyNz foams, carbon foams, and diverse composite foams consisting of carbon and metal compounds. Following that, a wide-ranging evaluation of the functionality of the foam products in fields such as energy storage, electrocatalysis, adsorption, etc. is discussed, revealing their distinctive strength originated from the foam structure. Finally, after concluding the current progress, we provide some personal discussions on the existing challenges and future research priorities in this rapidly developing method.

A clean transfer approach to prepare centimetre-scale black phosphorus crystalline multilayers on silicon substrates for field-effect transistors

Recently reported direct growth of highly crystalline centimetre-sized black phosphorus (BP) thin films on mica substrates by pulsed laser deposition (PLD) has attracted considerable research interest. However, an effective and general transfer method to incorporate them into (opto-)electronic devices is still missing. Here, we show a wet transfer method utilizing ethylene-vinyl acetate (EVA) and an ethylene glycol (EG) solution to transfer high-crystalline large-area PLD-BP films onto SiO2/Si substrates. The transferred films were used to fabricate BP-based bottom-gate field-effect transistor (FET) arrays exhibiting good uniformity and continuity, with carrier mobility and current switching ratios comparable to those obtained in as-grown BP films on mica substrates. Our work presents a promising transfer strategy for scalable integration of on-substrate grown 2D BP into devices with more complex structures and further investigation of material properties.

Growth of Single Crystalline 2D Materials beyond Graphene on Non-metallic Substrates

The advent of 2D materials has ushered in the exploration of their synthesis, characterization and application. While plenty of 2D materials have been synthesized on various metallic substrates, interfacial interaction significantly affects their intrinsic electronic properties. Additionally, the complex transfer process presents further challenges. In this context, experimental efforts are devoted to the direct growth on technologically important semiconductor/insulator substrates. This review aims to uncover the effects of substrate on the growth of 2D materials. The focus is on non-metallic substrate used for epitaxial growth and how this highlights the necessity for phase engineering and advanced characterization at atomic scale. Special attention is paid to monoelemental 2D structures with topological properties. The conclusion is drawn through a discussion of the requirements for integrating 2D materials with current semiconductor-based technology and the unique properties of heterostructures based on 2D materials. Overall, this review describes how 2D materials can be fabricated directly on non-metallic substrates and the exploration of growth mechanism at atomic scale.

Magnon gap excitations in van der Waals antiferromagnet MnPSe3

Magneto-spectroscopy methods have been employed to study the zero-wavevector magnon excitations in MnPSe3. Experiments carried out as a function of temperature and the applied magnetic field show that two low-energy magnon branches of MnPSe3 in its antiferromagnetic phase are gapped. The observation of two low-energy magnon gaps (at 1.70 ± 0.05 meV and 0.09 ± 0.01 meV) implies that MnPSe3 is a biaxial antiferromagnet. A relatively strong out-of-plane anisotropy imposes the spin alignment to be in-plane whereas the spin directionality within the plane is governed by a factor of 2.5 × 10-3 weaker in-plane anisotropy.

Dias A, Janotti A, Da Silva JLF, Lima MP. Tuning Excitonic Properties of Monochalcogenides via Design of Janus Structures

Two-dimensional (2D) Janus structures offer a unique range of properties as a result of their symmetry breaking, resulting from the distinct chemical composition on each side of the monolayers. Here, we report a theoretical investigation of 2D Janus Q'A'AQ P3m1 monochalcogenides from group IV (A and A' = Ge and Sn; Q, Q' = S and Se) and 2D non-Janus QAAQ P3̅m1 counterparts. Our theoretical framework is based on density functional theory calculations combined with maximally localized Wannier functions and tight-binding parametrization to evaluate the excitonic properties. The phonon band structures exhibit exclusively real (nonimaginary) branches for all materials. Particularly, SeGeSnS has greater energetic stability than its non-Janus counterparts, representing an outstanding energetic stability among the investigated materials. However, SGeSnS and SGeSnSe have higher formation energies than the already synthesized MoSSe, making them more challenging to grow than the other investigated structures. The electronic structure analysis demonstrates that materials with Janus structures exhibit band gaps wider than those of their non-Janus counterparts, with the absolute value of the band gap predominantly determined by the core rather than the surface composition. Moreover, exciton binding energies range from 0.20 to 0.37 eV, reducing band gap values in the range of 21% to 32%. Thus, excitonic effects influence the optoelectronic properties more than the point-inversion symmetry breaking inherent in the Janus structures; however, both features are necessary to enhance the interaction between the materials and sunlight. We also found anisotropic behavior of the absorption coefficient, which was attributed to the inherent structural asymmetry of the Janus materials.