Promising 2D Research Articles

Coexisting Ferromagnetic-Antiferromagnetic State and Giant Anomalous Hall Effect in Chemical Vapor Deposition-Grown 2D Cr5Te8.

Two-dimensional (2D) magnets, as an important member of the 2D material family, have emerged as a promising platform for spintronic devices. Herein, we report the chemical vapor deposition (CVD) growth of highly crystalline submillimeter-scale self-intercalated metallic 2D ferromagnetic (FM) trigonal chromium telluride (Cr5Te8) flakes on inert mica substrates. Through magneto-optical and magnetotransport measurements, we unveil the exceptional magnetic properties of these 2D flakes. The trigonal Cr5Te8 flakes exhibit a strong anisotropic FM order with a Curie temperature above 220 K. Notably, an emergent antiferromagnetic (AFM) state is observed in the MOKE signal from ultrathin Cr5Te8 flakes around the Curie temperature. The AFM state has a relatively weak interlayer exchange coupling, allowing a switching between the interlayer AFM and FM states by tuning the temperature. Meanwhile, the trigonal Cr5Te8 flakes exhibit a giant anomalous Hall effect (AHE), with an anomalous Hall conductivity of 710 Ω-1 cm-1 and an anomalous Hall angle of 3.5% at zero magnetic field, surpassing typical itinerant ferromagnets. Further analysis suggests that the AHE in trigonal Cr5Te8 is primarily driven by the skew-scattering mechanism rather than the intrinsic or extrinsic side-jump mechanism. These findings demonstrate the potential of CVD-grown ultrathin Cr5Te8 flakes as a promising 2D magnetic material with exceptional AHE properties for future spintronic applications.

The Impact of Pore Geometry on Frictional Properties of hBN and MoS2 Nanomaterials.

Two-dimensional (2D) nanomaterials hold significant promise for reducing energy consumption in water desalination. This study investigates the influence of pore size and shape on the slip behavior of saline water at the interface of two promising 2D nanomaterials: hexagonal boron nitride (hBN) and molybdenum disulfide (MoS2). Slip length, a key parameter governing fluid flow at the nanoscale, is highly dependent on interfacial properties. Here, we explore how the pore characteristics in these 2D nanomaterials can impact slip length, aiming to gain a fundamental understanding of the role of pore size and shape in optimizing desalination efficiency. We performed quantum mechanical calculations to compute the partial atomic charges on atoms in hBN and MoS2 containing pores. Our DFT calculations reveal a spatially varying charge distribution on these 2D nanomaterials with pores, which we then incorporate into molecular dynamic simulations to elucidate their influence on the 2D nanomaterial-water interface. Our results reveal a significant impact of pore size on friction for nanomaterials containing hexagonal pores, while pore size had no effect on nanomaterials containing triangular pores. Moreover, friction increases with pores in both materials. This research contributes to the development of efficient and energy-saving desalination technologies through the manipulation of interfacial properties in 2D nanomaterials.

Promising 2D Carbon Allotropes with Intrinsic Bandgaps Based on Bilayer α‐Graphyne

2D carbon allotropes with moderated electronic bandgaps are highly desirable for next‐generation carbon‐based nanoelectronics beyond graphene. Herein, the structural and electronic properties of bilayer α‐graphyne have been systematically investigated by using first‐principles calculations. Consequently, in addition to typical van der Waals (vdW) stacks of single‐layer α‐graphyne, new 2D carbon allotropes with purely sp2 or sp3 hybridizations can be achieved, arising from the absence of intralayer acetylene linkages during structural relaxation. Compared to the Dirac semimetallic behavior of monolayer α‐graphyne, the electronic structure of vdW bilayer α‐graphyne can be further modulated by stacking patterns, yet retains metallic characteristics. In contrast, intrinsic semiconducting characteristics can be observed in the proposed new 2D carbon allotropes with tunable bandgaps dependent on the in‐plane biaxial strain. Correspondingly, a pristine 2D carbon sheet with only sp2 hybridization exhibits a promising direct bandgap of 1.062 eV, while the sp3‐hybridized carbon network possesses an indirect bandgap of 1.708 eV, which can be further converted to the direct type under small compressive strains, implying great potential in future carbon‐based nanoelectronic applications beyond graphene. Also, this work provides a new approach for developing novel carbon allotropes via the vertical stacking of graphyne with acetylenic linkages.

A Different Perspective on the Solid Lubrication Performance of Black Phosphorous: Friend or Foe?

Black phosphorous (BP), a promising 2D material with exceptional electronic and optical properties, has shown remarkable potential in tribology as an additive in liquid lubrication and a composite in solid lubrication. However, its potential as the standalone solid lubricant is still at its early stage. This study evaluates BP's solid lubrication performance as deposited coating (by drop casting) on a variety of metallic substrates (polished AISI 52 100 steel, aluminum, copper, and iron) under different contact pressures using a ball‐on‐disc linear‐reciprocating test machine in dry conditions. The results demonstrate that BP does not systematically reduce friction and wear. Depending on the contact pressure and the characteristic of the substrate material (particularly surface roughness), its friction and wear behavior vary a great deal. The best results observed are a 33% reduction in friction with increased surface roughness on iron and a 23% reduction in wear on aluminum. While no general trend is observed for contact pressure effects, increased substrate roughness proves beneficial, enhancing lubricant retention and exploiting BP's low interlayer shear mechanism. Therefore, this study demonstrates that while promising, BP's solid lubrication performance is not exceptional. It also highlights the importance of optimizing test conditions and materials for enhanced lubrication.

Enhanced Na-Ion Electrochemical Performance through Cu Doping-Mediated Sb2Se3 Phase Transformation into CuSbSe2 with Improved Kinetics.

This work investigates the influence of structural and electronic modification on the electrochemical performance of conversion and alloying materials. The CuSbSe2, a promising 2D layered conversion-and-alloying material is being investigated with references to parent pristine Sb2Se3 and a doped version of later Sn0.2Sb1.8Se3 for their sodium-ion battery performance. The CuSbSe2 with layered structure is well known to accommodate lattice distortions via inter-layer movement, potentially mitigating distortions brought about by the Alkali ion (Na in this case) insertion. In contrast, the parent conversion-cum-alloying material Sb2Se3 with its one-dimensional crystal structure leads to structural disintegration during battery operation. The Sn-doped analog, Sn0.2Sb1.8Se3, comparatively exhibits enhanced kinetics owing to the reduced long-range order. The 2D layered, CuSbSe2 despite exhibiting2D long-range order exhibits superior electrochemical performance owing to the favorable electronic and structural features. The CuSbSe2 exhibits a reversible capacity of 881 mAh g-1 compared to 516 mAh g-1 for Sn0.2Sb1.8Se3 and 429 mAh g-1 for Sb2Se3, with an improved Coulombic efficiency as well. The transient electrochemical investigations of Electrochemical Impedance Spectroscopy (EIS) and Galvanostatic intermittent titration techniques (GITT) reveal that better performance exhibited by CuSbSe2 may well be attributed to kinetics owing to enhanced diffusion coefficients in the intercalation and conversion regime.

Enhanced spin Hall ratio in two-dimensional semiconductors

The conversion efficiency from charge current to spin current via the spin Hall effect is evaluated by the spin Hall ratio (SHR). Through state-of-the-art ab initio calculations involving both charge conductivity and spin Hall conductivity, we report the SHRs of the III-V monolayer family, revealing an ultrahigh ratio of 0.58 in the hole-doped GaAs monolayer. In order to find more promising 2D materials, a descriptor for high SHR is proposed and applied to a high-throughput database, which provides the fully relativistic band structures and Wannier Hamiltonians of 216 exfoliable monolayer semiconductors and has been released to the community. Among potential candidates for high SHR, the MXene monolayer Sc2CCl2 is identified with the proposed descriptor and confirmed by computation, demonstrating the descriptor validity for high SHR materials discovery.

Controllable and fast growth of high-quality atomically thin and atomically flat Bi2O2Se films

As a promising 2D material, bismuth oxyselenide (Bi2O2Se) has demonstrated significant potential to overcome existing technical barriers in various electronic device applications due to its unique physical properties like high symmetry, adjustable electronic structure, and ultra-high electron mobility. However, the rapid growth of Bi2O2Se films down to a few atomic layers with precise control remains a significant challenge. In this work, the growth of two-dimensional (2D) Bi2O2Se thin films by the pulsed laser deposition (PLD) method is systematically investigated. By controlling temperature, oxygen pressure, laser energy density, and laser emission frequency, we finally prepare atomically thin and flat Bi2O2Se (001) thin films on the (001) surface of SrTiO3. Importantly, we provide a fundamental and unique perspective toward understanding the growth process of atomically thin and flat Bi2O2Se films, and the growth process primarily proceeds in four steps. Moreover, the combined results of the crystallinity quality, surface morphology, and the chemical states demonstrate the PLD-growth of high-quality Bi2O2Se films in a controllable and fast mode.

Understanding the Impact of Contact-Induced Strain on the Electrical Performance of Monolayer WS2 Transistors.

Two-dimensional (2D) electronics require low contact resistance (RC) to approach their fundamental limits. WS2 is a promising 2D semiconductor that is often paired with Ni contacts, but their operation is not well understood considering the nonideal alignment between the Ni work function and the WS2 conduction band. Here, we investigate the effects of contact size on nanoscale monolayer WS2 transistors and uncover that Ni contacts impart stress, which affects the WS2 device performance. The strain applied to the WS2 depends on contact size, where long (1 μm) contacts (RC ≈ 1.7 kΩ·μm) show a 78% reduction in RC compared to shorter (0.1 μm) contacts (RC ≈ 7.8 kΩ·μm). We also find that thermal annealing can relax the WS2 strain in long-contact devices, increasing RC to 8.5 kΩ·μm. These results reveal that thermo-mechanical phenomena can significantly influence 2D semiconductor-metal contacts, presenting opportunities to optimize device performance through nanofabrication and thermal budget.

Monolayer Penta-BeAs2: A Promising 2D Materials for Toxic Gas Sensor with High Selectivity.

The discovery of novel materials with high gas sensing selectivity is a key driver of gas sensor technology. Based on the recently reported two-dimensional (2D) pentagonal BeP2, we introduce penta-BeAs2 as a new member of the pentagonal family of materials for toxic gas sensors based on density functional theory (DFT). For electronic applications, a band structure calculation showed that penta-BeAs2 has indirect band gaps of 0.38 and 0.79 eV, using GGA-PBE or HSE functionals. Stability analysis confirmed that penta-BeAs2 is dynamically, mechanically, and thermally stable. The adsorption of toxic gases (CO, NO, and NO2) and nontoxic gases (H2, N2, H2O, and CO2) on the penta-BeAs2 monolayer was studied. The contrasting adsorption behavior observed between toxic and nontoxic gases on penta-BeAs2 (physisorption vs chemisorption) underscores its high selectivity for toxic gas-sensing applications. Adsorption energies for toxic gases fall within a moderate range (0.4-0.8 eV), indicating good reversibility and short recovery times at room temperature. Additionally, the quantum transport properties of penta-BeAs2 were studied using the nonequilibrium Green's function (NEGF) approach, confirming strong sensitivity and selectivity toward toxic gases.

High-throughput screening of 2D materials identifies p-type monolayer WS2 as potential ultra-high mobility semiconductor

Abstract2D semiconductors offer a promising pathway to replace silicon in next-generation electronics. Among their many advantages, 2D materials possess atomically-sharp surfaces and enable scaling the channel thickness down to the monolayer limit. However, these materials exhibit comparatively lower charge carrier mobility and higher contact resistance than 3D semiconductors, making it challenging to realize high-performance devices at scale. In this work, we search for high-mobility 2D materials by combining a high-throughput screening strategy with state-of-the-art calculations based on the ab initio Boltzmann transport equation. Our analysis singles out a known transition metal dichalcogenide, monolayer WS2, as the most promising 2D semiconductor, with the potential to reach ultra-high room-temperature hole mobilities in excess of 1300 cm2/Vs should Ohmic contacts and low defect densities be achieved. Our work also highlights the importance of performing full-blown ab initio transport calculations to achieve predictive accuracy, including spin–orbital couplings, quasiparticle corrections, dipole and quadrupole long-range electron–phonon interactions, as well as scattering by point defects and extended defects.

Dynamic Behavior of Above-Room-Temperature Robust Skyrmions in 2D Van der Waals Magnet.

Magnetic skyrmions are swirl-like spin configurations that present topological properties, which have great potential as information carriers for future high-density and low-energy-consumption devices. The optimization of skyrmion-hosting materials that can be integrated with semiconductor-based circuits is the primary challenge for their industrialization. Two-dimensional van der Waals ferromagnets are emerging materials that have excellent carrier mobility and compatibility with integrated circuits, making them an ideal candidate for spintronic devices. Here, we report the realization of skyrmions at above room temperature in the 2D ferromagnet Fe3GaTe2. The thickness tunability of their skyrmion size and the formation of the skyrmion lattice are revealed. Furthermore, we demonstrate that the skyrmions can be moved by a low-density current at room temperature, together with an apparent skyrmion Hall effect, which is consistent with our quantitative micromagnetic simulation. Our work offers a promising 2D material platform for harnessing magnetic skyrmions in practical device applications.

Hexagonal Boron Nitride Quantum Simulator: Prelude to Spin and Photonic Qubits.

The quest for qubit operation at room temperature is accelerating the field of quantum information science and technology. Solid state quantum defects with spin-optical properties are promising spin- and photonic qubit candidates for room temperature operations. In this regard, a single boron vacancy within hexagonal boron nitride (h-BN) lattice such as VB- defect has coherent quantum interfaces for spin and photonic qubits owing to the large band gap of h-BN (6 eV) that can shield a computational subspace from environmental noise. However, for a VB- defect in h-BN to be a potential quantum simulator, the design and characterization of the Hamiltonian involving mutual interactions of the defect and other degrees of freedom are needed to fully understand the effect of defects on the computational subspace. Here, we studied the key coupling tensors such as zero-field splitting, Zeeman effect, and hyperfine splitting in order to build the Hamiltonian of the VB- defect. These eigenstates are spin triplet states that form a computational subspace. To study the phonon-assisted single photon emission in the VB- defect, the Hamiltonian is characterized by electron-phonon interaction with Jahn-Teller distortions. A theoretical demonstration of how the VB- Hamiltonian is utilized to relate these quantum properties to spin- and photonic-quantum information processing. For selecting promising host 2D materials for spin and photonic qubits, we present a data-mining perspective based on the proposed Hamiltonian engineering of the VB- defect in which h-BN is one of four materials chosen to be room temperature qubit candidates.

Bipolar Electrochemistry Enabled Synthesis and Application of 2D Materials

Graphene is a promising 2D material for biosensing and energy storage applications due to its unique properties such as high surface area and high charge mobility. However, there is a significant variation in the high quality graphene contents in commercial products. The conventional wet chemical and electrochemical exfoliation approaches rely on harsh chemicals and can introduce relatively high level of defects in the 2D materials. In our recent research, we have demonstrated a simple and cost-effective bipolar electrochemical (BPE) approach which has the advantages of producing high quality 2D materials such as graphene and phosphorene. Moreover the BPE can simultaneously achieve exfoliation, reduction and deposition which enables the production of high quality microelectrodes based on 2D materials. In one exemplary application, the BPE based graphene electrodes show enhanced areal capacitance and outstanding frequency behavior as supercapacitor electrodes. In another exemplary application, the BPE enabled reduced graphene oxide microelectrodes demonstrated high sensitivity and low detection limit as aptasensors. Furthermore, the mechanistic studies including the temperature effect were conducted in order to further tune the functionality and enhance the exfoliation rate of the 2D materials.

GeC monolayer: A promising 2D material for reusable SO2 and NO2 gas sensor with high sensitivity

Gas sensors are crucial in various fields such as environmental monitoring, industrial production, and healthcare due to their ability to detect harmful gases in real-time. This study investigates GeC monolayer as a potential material for gas sensors targeting sulfur-containing toxic gases (SO2, H2S, SF4) and nitrogen-containing toxic gases (NO, NH3, NO2). The electronic and adsorption properties of GeC monolayer were explored using density functional theory (DFT) calculations. The adsorption of SO2 and nitrogen dioxide significantly affects the band structure and work function of GeC monolayer, indicating that compared to other toxic gases, GeC monolayers exhibit higher sensitivity and selectivity towards SO2 and NO2. The electron localization function analysis indicates that the adsorption process is characterized by physical adsorption. In addition, GeC monolayer exhibits good desorption behavior towards SO2 and NO2 at room temperature. These findings suggest that GeC monolayer is a promising material for developing efficient gas sensors for detecting SO2 and NO2.

GeP3 monolayer as a promising 2D sensing materials in detecting SO2, H2S, SOF2 and SO2F2

The detection of SF6 decomposition components using gas-sensitive sensors is significantly important for characterizing internal insulation failures and assessing the operational status of SF6 gas-insulated equipment. In this paper, the adsorption properties of GeP3 monolayers for SO2, H2S, SOF2 and SO2F2 gases were investigated based on density functional theory. Four gas adsorption systems were constructed, and the adsorption mechanisms and sensing characteristics of GeP3 monolayers on target gases were investigated by calculating parameters such as adsorption energy, charge transfer, density of states, and recovery time, along with their potential application as resistive gas sensors and field-effect transistor sensors. It is demonstrated that GeP3 monolayers were suitable for the detection of SO2, H2S, SOF2 and SO2F2 gases, all of which exhibited good chemisorption with adsorption energies of −1.36 eV, −0.78 eV, −1.82 eV and −2.91 eV, respectively. The adsorption of SO2 and H2S is found to cause a significant change in the conductivity of the GeP3 monolayers, and desorption is achieved at the optimal operating temperature in only 54.428 s and 10.686 s, respectively. Also the adsorption of SOF2 and SO2F2 can make the work function of the GeP3 monolayers significantly larger. Consequently, the GeP3 monolayers have the potential to be used as a resistive gas sensor for SO2 and H2S gases, or as a field effect transistor sensor for SOF2 and SO2F2 gases. This study provides theoretical guidance for the development of GeP3-based sensors for monitoring the insulation status and operational conditions of SF6 gas-insulated equipment.

Impact of dimensionality on the magnetocaloric effect in two-dimensional magnets

Magnetocaloric materials, which exploit reversible temperature changes induced by magnetic field variations, are promising for advancing energy-efficient cooling technologies. The potential integration of two-dimensional materials into magnetocaloric systems represents an emerging opportunity to enhance the magnetocaloric cooling efficiency. In this study, we use atomistic spin dynamics simulations based on first-principles parameters to systematically evaluate how magnetocaloric properties transition from three-dimensional (3D) to two-dimensional (2D) ferromagnetic materials. We find that 2D features such as reduced Curie temperature, sharper magnetic transition, and higher magnetic susceptibility are beneficial for magnetocaloric applications, while the relatively higher lattice heat capacity in 2D can compromise achievable adiabatic temperature changes. We further propose GdSi2 as a promising 2D magnetocaloric material. Our calculation predicts that GdSi2 exhibits an isothermal entropy change ΔSM of 22.5 J kg−1 K−1 and an adiabatic temperature change ΔTad of 6.2 K, near the hydrogen liquefaction temperature (TC≈25 K). Our analysis offers valuable theoretical insights into the magnetocaloric effect in 2D ferromagnets and demonstrates that 2D ferromagnets hold promise for cooling and thermal management applications in compact and miniaturized nanodevices.

Strain-tuned electronic and valley-related properties in Janus monolayers of SWSiX2 (X = N, P, As)

Abstract Exploring novel two-dimensional (2D) valleytronic materials has an essential impact on the design of spintronic and valleytronic devices. Our first principles calculation results reveal that the Janus SWSiX2 (X = N, P, As) monolayer has excellent dynamical and thermal stability. Owing to strong spin-orbit coupling (SOC), the SWSiX2 monolayer exhibits a valence band spin splitting of up to 0.49 eV, making it promising 2D semiconductor for valleytronic applications. The opposite Berry curvatures and optical selection rules lead to the coexistence of valley and spin Hall effects in the SWSiX2 monolayer. Moreover, the optical transition energies can be remarkably modulated by the in-plane strains. Large tensile (compressive) inplane strains can achieve spin flipping in the SWSiN2 monolayer, and induce both SWSiP2 and SWSiAs2 monolayers transit from semiconductor to metal. Our research provides new 2D semiconductor candidates for designing high-performance valleytronic devices.

Novel ultrastable 2D MOF/MXene nanofluidic membrane with ultralow resistance for highly efficient osmotic power harvesting

Two-dimensional (2D) materials have shown great potential in harvesting osmotic power due to their high membrane selectivity, but the high resistance from tortuous pathways of 2D nanofluidic membranes still impedes the further improvement in output performance. Here, we report an innovative 2D MXCT (MXene/Cu-TCPP) lamellar membrane with ultralow resistance for highly efficient osmotic power generation. The incorporation of 2D Ti3C2Tx MXene with rich functional groups not only resolves the water-stability issue of 2D metal-organic framework (MOF) Cu-TCPP, but provides large surface charges for selective ion transport. The orderly sub-2 nm framework channels of Cu-TCPP provide much shorter permeation pathways for fast ion transport, thus endowing the MXCT membrane with ultralow resistance. Consequently, the MXCT membrane reaches an ultrahigh power output of ∼8.29 W/m2 by mixing seawater and river water, which is ∼275 % higher than that of the pristine MXene membrane. Additionally, it outperforms all the reported single-layer 2D nanosheet-based osmotic power generators under the same experimental conditions in terms of output power and internal resistance (9 kΩ). This work presents a reliable strategy for stabilizing 2D Cu-TCPP MOF in electrolytes, opening new avenues for designing promising 2D nanofluidic membranes for efficient blue energy harvesting and ionic devices.

Hydrogenated h-CSe as a promising 2D direct semiconductor for optoelectronic applications

Hydrogenated h-CSe as a promising 2D direct semiconductor for optoelectronic applications

Transparent Multilayer Acrylic Composites Reinforced with Poly(Acrylated Urethane) Filled Low Grammage Bacterial Cellulose Nanopaper.

Cellulose nanopaper is a material structure that possesses high mechanical performance and is widely regarded as a promising 2D reinforcement for polymer matrix composites. This work explores the use of low grammage bacterial cellulose (BC) nanopaper as reinforcement for poly(acrylated urethane) interlayer adhesive to increase the impact performance of multilayer acrylic composites. The BC nanopaper is impregnated with an acrylated urethane resin and laminated between acrylic sheets to create BC/acrylic composites consisting of one, three, and five layers of BC nanopaper-reinforced poly(acrylated urethane) interlayer adhesive(s). Both the poly(acrylated urethane)-filled BC nanopaper interlayer adhesive and the resulting laminated acrylic composites are optically transparent. The incorporation of BC nanopaper into the poly(acrylated urethane) interlayer adhesive improves the tensile modulus by eightfold and the single-edge notched fracture toughness by 60% compared to neat poly(acrylated urethane). It is also found that using poly(acrylated urethane)-filled BC nanopaper interlayer adhesive proves beneficial to the impact properties of the resulting laminated acrylic composites. In Charpy impact testing, the impact strength of the multilayer acrylic composites increases by up to 130% compared to the "gold-standard" impact-modified monolithic acrylic, with a BC loading of only 1.6wt%.