A significant challenge for graphene nanoplatelet (GNP) suppliers is the characterisation of platelet morphology in industrial environments. This challenge is further exacerbated to platelet surface chemistry when scalable functionalisation processes, such as plasma treatment, are used to modify the GNPs to improve the filler-matrix interphase in nanocomposites. The costly and complex suite of analytical equipment necessary for a complete material description makes quality control and process optimisation difficult. Raman spectroscopy is a facile and accessible characterisation technique, with recent advancements unlocking fast mapping for rapid data collection. In this study, we develop novel techniques to better characterise GNP morphology and changes in surface chemistry using Raman maps of bulk powders. Providing a bespoke algorithmic framework for the analysis of these advanced materials. An unsupervised peak fitting and processing algorithm was used to extract crystallinity data and correlate it with laser-diffraction-derived lateral size values for a commercial set of GNPs rapidly and accurately. Classical machine learning was used to identify the most informative Raman features for classifying the plasma-functionalised GNPs. The initial material properties were found to affect the peak features that were the most useful for classification. In low defect density and low specific surface area GNPs, the D peak full width at half maximum is found to be the most useful, whereas the I2D/IG ratio is the most useful in the opposite case. Finally, a convolutional neural network was trained to discern between different GNP grades with 86% accuracy. This work demonstrates how computer vision could be deployed for rapid and accurate quality control on the factory floor.

We propose that a device composed of two vertically stacked monolayer graphene Josephson junctions can be used for Cooper pair splitting. The hybridization of the Andreev bound states of the two Josephson junction can facilitate non-local transport in this normal-superconductor hybrid structure, which we study by calculating the non-local differential conductance. Assuming that one of the graphene layers is electron and the other is hole doped, we find that the non-local Andreev reflection can dominate the differential conductance of the system. Our setup does not require the precise control of junction length, doping, or super conducting phase difference, which could be an important advantage for experimental realization.

Two-dimensional (2D) MXenes have attracted significant attention in electromagnetic interference (EMI) shielding applications due to their excellent metallic conductivity, high surface area, 2D geometry, tunable surface chemistry, and solution processability. In this study, we present a straightforward way of introducing multiple nanoscale interfaces into Ti3C2T x MXenes using insulating graphene oxide (GO) intercalants to enhance internal scattering, resulting in improved EMI shielding effectiveness (SE). The amine-functionalized MXene with positive surface charge and negatively charged GO flakes are electrostatically self-assembled to form a 2D/2D heterostack of MXene/GO nanosheets. The resultant 2D/2D alternating heterostack of MXene/GO bearing multiple internal interfaces with significant impedance mismatch enhances the internal scattering of incident electromagnetic (EM) waves. Interestingly, despite their inferior electrical conductivity, the MXene/GO heterostack films exhibit higher EMI SE values than the randomly mixed hybrid films, and even outperform pristine MXene films. These MXene/GO heterostack films with enhanced absorption of EM waves via the strong internal scattering effect suggest a valuable pathway toward practical EMI shielding with thin and lightweight features.

Magnetic skyrmions, as topologically protected whirl-like solitons, have been the subject of growing interest in non-volatile spintronic memories and logic devices. Recently, much effort has been devoted to searching for skyrmion host materials in two-dimensional (2D) systems, where intrinsic inversion symmetry breaking and a large Dzyaloshinskii–Moriya interaction (DMI) are desirable to realize a field-free skyrmion state. Among these systems, 2D magnetic Janus materials have become important candidates for inducing a sizable DMI and chiral spin textures. Herein, we demonstrate that layer-dependent DMI and field-free magnetic skyrmions can exist in multilayer MnSTe. Moreover, strong interlayer exchange coupling and Bethe–Slater curve-like behaviors arising from the Mn–Mn double exchange mechanism are found in bilayer MnSTe. We also uncover that the distribution of DMIs in multilayer MnSTe can be understood as making a significant contribution to the intermediate DMI using the three-site Fert–Lévy model. Our results unveil great potential for designing skyrmion-based spintronic devices in multilayer 2D materials.

The magnetoresistance (MR) of spin values usually displays a symmetric dependence on the magnetic field. An antisymmetric MR phenomenon has been discovered recently that breaks the field symmetry and has the potential to realize multi-bit memory. In this work, we report a controllable switch between the antisymmetric and symmetric MRs and propose a multi-bit memory performance in Fe3GeTe2 (FGT)/graphite/FGT trilayer with modified vertical geometry. Via investigating the evolution of the antisymmetric MR depending on the spatial distribution, current direction, and magnetization configuration, we demonstrate that the antisymmetric MR results from the local nonequilibrium current through the trilayer. Furthermore, an exchange bias effect is induced which modifies the antisymmetric MR. A stable multi-bit memory is presented in the heterostructure. Such architecture for multi-state memory provides insights into other spin-valve structures to improve storage density.

The substrate is one of the key components that determines the quality of the epitaxial layers. However, the implications of growing two-dimensional layers on three-dimensional bulk substrates have not yet been fully understood, and these implications need to be studied for different combinations of materials and substrates. Here, we present a study that addresses the influence of the sapphire substrate off-cut angle on the final growth of two-dimensional layers of hexagonal boron nitride (h-BN) by metal-organic vapor phase epitaxy (MOVPE). A two-step wafer-scale process was used in one epitaxial MOVPE procedure. The main process starts with a self-limiting continuous growth of a BN buffer followed by flow-modulated epitaxy in the second step, and is used to study substrates with different off-cuts angles, pre-growth nitridation steps, and post-growth annealing. An initial nitridation step at the growth temperature allowed for the growth of an AlN sublayer. This layer is shown to smooth out the underlying sapphire and establishes an ‘effective’ sapphire/AlN substrate. This step is also responsible for enforcing a specific growth of the BN layer in a crystallographic orientation, which is shown to strongly deviate from the substrate for off-cut angles larger than 0.3°. A substrate with off-cut angle of 1° clearly yields the highest quality of h-BN layers as evidenced by the lowest amount of debris on the surface, most intense x-ray diffraction signal, minimal Raman phonon line width and thinnest amorphous BN (a-BN) at the interface with the effective substrate. Our study shows that the off-cut angles of sapphire substrates strongly influence the final epitaxial h-BN, clearly indicating the importance of optimal substrate preparation for the growth of two-dimensional BN layers. Post-growth annealing in N2 atmosphere at 800 °C improves the top surface morphology of the final stack, as well as suppresses further the presence of a-BN.

In the past decade, flexible strain sensors have attracted much attention in the fields of health care, soft robots and other flexible electronics due to their unique flexibility, high stability, and strong mechanical properties. To further meet the requirements of the excellent performance for electronic equipment, carbon-based conductive sensitive materials have become one of the first choice for the preparation of flexible strain sensors due to their excellent electrical conductivity, mechanical properties, and high compatibility. Herein, based on different strain behaviors, this paper analyzes the working mechanism of tensile and compressive strain sensors, focusing on the latest research progress of carbon-based conductive materials in strain sensors with different dimensions. The applications of carbon-based sensitive materials with multifunctional strain sensing in the areas of physiological information detection, human motion, human–machine interaction, and visual display have also been summarized. Furthermore, it has been attempted to discuss the current challenges of carbon-based strain sensors as well as the prospect of flexible strain sensors. This review is aimed to provide appropriate references for further exploitation of multi-functional flexible carbon-based strain sensors.

Abstract The capability to structure two-dimensional materials (2DMs) at the nanoscale with customizable patterns and over large areas is critical for a number of emerging applications, from nanoelectronics to 2D photonic metasurfaces. However, current technologies, such as photo- and electron-beam lithography, often employing masking layers, can significantly contaminate the materials. Large-area chemical vapour deposition-grown graphene is known to have non-ideal properties already due to surface contamination resulting from the transferring process. Additional contamination through the lithographic process might thus reduce the performance of any device based on the structured graphene. Here, we demonstrate a contactless chemical-free approach for simultaneous patterning and cleaning of self-supporting graphene membranes in a single step. Using energetic ions passing through a suspended mask with pre-defined nanopatterns, we deterministically structure graphene with demonstrated feature size of 15 nm, approaching the performance of small-area focused ion beam techniques and extreme ultraviolet lithography. Our approach, however, requires only a broad beam, no nanoscale beam positioning and enables large area patterning of 2DMs. Simultaneously, in regions surrounding the exposed areas, contaminations commonly observed on as-grown graphene targets, are effectively removed. This cleaning mechanism is attributed to coupling of surface diffusion and sputtering effects of adsorbed surface contaminants. For applications using 2DMs, this simultaneous patterning and cleaning mechanism may become essential for preparing the nanostructured materials with improved cleanliness and hence, quality.

Optimization of the aqueous electrolyte concentration is a significant issue in the development of high-performance aqueous rechargeable magnesium ion batteries (MIBs). In this study, a novel magnesium ion-based hybrid electrolyte composed of 2 M magnesium sulfate (MgSO4)/2 M acetate (MgOAc) was designed, and its corresponding physiochemical properties were systemically investigated by simply tuning their molar ratios. Additionally, a δ-MnO2/reduced graphene oxide (rGO) composite cathode material was successfully synthesized and delivered a high specific capacity and excellent rate capability in the optimized hybrid electrolyte. The as-fabricated device based on the δ-MnO2/rGO composite cathode exhibited a high operating voltage of up to 2 V and delivered a maximum energy density of 29.8 Wh kg−1 at the power density of 823 W kg−1. More importantly, the device showed impressive discharge capacity and excellent cycling stability even at the low temperature of −20 °C. In view of the outstanding electrochemical properties of the δ-MnO2/rGO composite cathode in an optimized hybrid electrolyte of MgSO4/MgOAc, it could be regarded as a novel prototype for low-cost aqueous MIBs.

The frequent oil spill accidents during oil exploration and transportation have caused large economic loss and catastrophic environmental disasters. Due to low cost and simplicity, adsorption and filtration materials are often chosen to deal with oil spills, but the outcomes are not satisfactory mainly because of the awfully high viscosity of crude oil. Herein a photothermal ultra-high molecular weight polyethylene/MXene composite aerogel with a high light absorption (99.97%) and water repellency (water contact angle >148°) is developed by thermally induced phase separation method. The composite aerogel endows durable hydrophobicity with which the water contact angle is more than 142° in acidic/alkaline environments, and the maximum absorption capacity of 81 g g−1. In addition, it exhibits an excellent photothermal performance, rising surface temperature to 70 °C within 60 s under 1 sun irradiation, that can drastically reduce the crude oil absorption time from 60 min to 60 s, saving 98% of absorption time and reaching a crude oil absorption capacity of 21 g g−1. More interestingly, the designed solar evaporation device with the obtained composite aerogel can achieve an evaporation rate of 1.15 kg m−2h−1 and evaporation efficiency of 74%. The designed composite aerogel opens a possible pathway for solar-powered crude oil adsorption applications.

The synthesized MoSi2N4 marks a new-born two-dimensional MA2Z4 family. In this work, we present a comprehensive study on the MA2Z4 family as anodes for Li- and Na-ion batteries (LIBs and SIBs) based on first-principle calculations. There exists a linear relationship between the ion adsorption energy Eads and the energy level of the lowest unoccupied states ELUS of MA2Z4, and a lower ELUS leads to more energetically favorable electron occupation and hence stronger adsorption. ELUS acts as a simple and useful descriptor, which allows for the straightforward prediction of ion adsorption based solely on the substrate electronic properties. Through evaluating the theoretical capacities and diffusion barriers, NbGe2N4 is predicted to be the most promising candidate for LIBs while VSi2P4 is better for SIBs, with maximum theoretical capacities of 547 mAh g−1 and 696 mAh g−1 and ion diffusion barriers of 0.34 eV and 0.10 eV, respectively. Moreover, NbGe2N4 and VSi2P4 show good phase stabilities by the analysis of their phase transformations. This study explores the application prospects of novel MA2Z4 in LIBs and SIBs and provides a deep understanding of intrinsic electronic mechanisms.

Achieving efficient nitrogen reduction reaction (NRR) under mild conditions is desirable but still challenging due to the lack of high-performance catalysts. Herein, we report the feasibility of a new type of two-dimensional conjugated metal–organic frameworks (cMOFs) featuring dense single-metal-atom sites, namely TM3(HAT)2 monolayers (TM = transition metal from groups 4 to 10, HAT = 1,4,5,8,9,12-hexaazatriphenylene), as NRR catalysts. We construct an efficient four-step screening strategy and identify the W3(HAT)2 monolayer as a candidate with considerable stability, activity, and selectivity based on density functional theory (DFT) computations. The analysis of bonding, integrated-crystal orbital Hamilton population, and Bader charge uncovers the NRR activity origin of the TM3(HAT)2 monolayers and elucidates the structure–performance correlations. Meanwhile, our results show that a simple descriptor ϕ based on the inherent nature of the TM atoms can be applied to accelerate the screening of candidates without explicit DFT calculations. This work highlights a feasible strategy to prescreen and design high-performance cMOF-based electrocatalysts.

Strong band engineering in two-dimensional (2D) materials can be achieved by introducing moiré superlattices, leading to the emergence of various novel quantum phases with promising potential for future applications. Presented works to create moiré patterns have been focused on a twist embedded inside channel materials or between channel and substrate. However, the effects of a twist inside the substrate materials on the unaligned channel materials are much less explored. In this work, we report the realization of superlattice multi-Dirac cones with the coexistence of the main Dirac cone in a monolayer graphene (MLG) on a ∼0.14° twisted double-layer boron nitride (tBN) substrate. Transport measurements reveal the emergence of three pairs of superlattice Dirac points around the pristine Dirac cone, featuring multiple metallic or insulating states surrounding the charge neutrality point. Displacement field tunable and electron–hole asymmetric Fermi velocities are indicated from temperature dependent measurements, along with the gapless dispersion of superlattice Dirac cones. The experimental observation of multiple Dirac cones in MLG/tBN heterostructure is supported by band structure calculations employing a periodic moiré potential. Our results unveil the potential of using twisted substrate as a universal band engineering technique for 2D materials regardless of lattice matching and crystal orientations, which might pave the way for a new branch of twistronics.

Optical spectroscopy is indispensable for research and development in nanoscience and nanotechnology, microelectronics, energy, and advanced manufacturing. Advanced optical spectroscopy tools often require both specifically designed high-end instrumentation and intricate data analysis techniques. Beyond the common analytical tools, deep learning methods are well suited for interpreting high-dimensional and complicated spectroscopy data. They offer great opportunities to extract subtle and deep information about optical properties of materials with simpler optical setups, which would otherwise require sophisticated instrumentation. In this work, we propose a computational approach based on a conventional tabletop optical microscope and a deep learning model called ReflectoNet. Without any prior knowledge about the multilayer substrates, ReflectoNet can predict the complex refractive indices of thin films and 2D materials on top of these nontrivial substrates from experimentally measured optical reflectance spectra with high accuracies. This task was not feasible previously with traditional reflectometry or ellipsometry methods. Fundamental physical principles, such as the Kramers–Kronig relations, are spontaneously learned by the model without any further training. This approach enables in-operando optical characterization of functional materials and 2D materials within complex photonic structures or optoelectronic devices.

A potential application of two-dimensional (2D) MXenes, such as Ti2CT x and Ti3C2T x , is energy storage devices, such as supercapacitors, batteries, and hydride electrochemical cells, where intercalation of ions between the 2D layers is considered as a charge carrier. Electrochemical cycling investigations in combination with Ti 1s x-ray absorption spectroscopy have therefore been performed with the objective to study oxidation state changes during potential variations. In some of these studies Ti3C2T x has shown main edge shifts in the Ti 1s x-ray absorption near-edge structure. Here we show that these main edge shifts originate from the Ti 4p orbital involvement in the bonding between the surface Ti and the termination species at the fcc-sites. The study further shows that the t 2g –eg crystal field splitting (10Dq) observed in the pre-edge absorption region indicate weaker Ti–C bonds in Ti2CT x and Ti3C2T x compared to TiC and the corresponding MAX phases. The results from this study provide information necessary for improved electronic modeling and subsequently a better description of the materials properties of the MXenes. In general, potential applications, where surface interactions with intercalation elements are important processes, will benefit from the new knowledge presented.

In this work, a novel Ti3C2T x MXene/chitosan/lignosulfonate adsorbent (MCL), was prepared via a facile decoration of Ti3C2T x MXene sheets with chitosan/lignosulfonate nanospheres as a renewable and biodegradable additive that can improve the biocompatibility and aqueous stability of MXenes. Chitosan/lignosulfonate nanospheres were stabilized on the surface of MXne sheets, endowing them with a variety of surface functionalities, high specific surface area, and antioxidant characteristics. The competitive adsorption of multi-metal systems revealed that MCL had a preferential adsorption affinity toward various heavy metal ions; the MCL removal efficiency for the quinary-metal ions adsorption followed a trend of Pb(II) > Cr(VI) ≈ Cu(II) > Ni(II) ≈ Co(II) in neutral pH conditions. A moderate reduction was observed for Cu(II) and Cr(VI) ions. For all metals, the kinetics data fitted well with the pseudo-second-order model, and the adsorption equilibrium was best described by the Langmuir model. The adsorption mechanism is suggested to be a synergic combination of electrostatic interaction, surface complexation, and ion exchange. The findings of this study provide a new approach for eco-friendly MXene surface modification and give a general pattern of metal pollutants interactions during adsorption.

We report the epitaxial growth of PdTe2 ultrathin films on a topological insulator Bi2Se3. A prominent moiré pattern was observed in scanning tunneling microscope measurements. The moiré periodicity increases as film thickness decreases, indicating a lattice expansion of epitaxial PdTe2 thin films at lower thicknesses. In addition, our simulations based on a multilayer relaxation technique reveal uniaxial lattice strains at the edge of PdTe2 domains, and anisotropic strain distributions throughout the moiré supercell with a net change in lattice strain up to ∼2.9%. Our density functional theory calculations show that this strain effect leads to a narrowing of the band gap at Γ point near the Fermi level. Under a strain of ∼2.8%, the band gap at Γ closes completely. Further increasing the lattice strain makes the band gap reopen and the order of conduction band and valence bands inverted in energy. The experimental and theoretical results shed light on a method for constructing quantum grids of topological band structure under the modulation of moiré potentials.

In this letter, we propose a mechanism to control the magnetic properties of topological quantum material (TQM) by using magnetoelectric coupling: this mechanism uses a heterostructure of TQM with two-dimensional (2D) ferroelectric material, which can dynamically control the magnetic order by changing the polarization of the ferroelectric material and induce possible topological phase transitions. This concept is demonstrated using the example of the bilayer MnBi2Te4 on ferroelectric In2Se3 or In2Te3, where the polarization direction of the 2D ferroelectrics determines the interfacial band alignment and consequently the direction of the charge transfer. This charge transfer, in turn, enhances the stability of the ferromagnetic state of MnBi2Te4 and leads to a possible topological phase transition between the quantum anomalous Hall (QAH) effect and the zero plateau QAH. Our work provides a route to dynamically alter the magnetic ordering of TQMs and could lead to the discovery of new multifunctional topological heterostructures.

Hybrid organic/inorganic Van der Waals heterostructures have emerged recently with enormous potential applications in nanotechnology and industrial areas. In these heterostructures, the interfacial effects can modulate the final properties, creating further possibilities in the design and operation of innovative devices. With this perspective in mind, we report on an experimental investigation of a hybrid organic/inorganic heterostructure of coronene and a few-layers MoS2 . We observe a local enhancement of MoS2 optical properties using both far-field and near-field Raman scattering and photoluminescence. Mainly located at MoS2 edges and defects, the local enhancement is due to the assembling of coronene molecules in MoS2 , as confirmed by atomic force microscopy. Quantum semi-empirical and fully atomistic molecular dynamics simulations were also used to gain further insights into these phenomena. Our results pave the way to engineer molecules in two-dimensional (2D) layered nanomaterials and control and modulate optical phenomena.

Graphdiyne (GDY) is a new carbon allotrope with excellent properties due to its unique structure and highly conjugated system. In this work, GDY/CuMoO4 (CMO)/CuO tandem S-scheme heterojunction was constructed using the cross-coupling method. Among them, CuI is not only used as a coupling catalyst to obtain easily collected GDY, but also as a precursor for more active composite catalysts. 2D GDY provides a substrate for the loading of CMO and CuO, while the highly conjugated system and excellent electrical conductivity allow the composites to form a unique system with strong charge distribution and transport. The step-by-step progressive S-scheme heterojunctions constructed based on the one-step calcination strategy have stronger reducing activity and carrier transfer capability. The intrinsic charge transfer mechanism of the catalyst was investigated by photoelectrochemical characterization and in situ x-ray photoelectron spectroscopy analysis, and the mechanism of the photocatalytic hydrogen production reaction was proposed. This work provides a viable approach for the development of GDY in photocatalysis and the design of S-scheme heterojunctions.