Two-dimensional Heterostructures Research Articles

Enhanced photocurrent and spin current in Two-Dimensional MnNCl-MnNI lateral heterostructures

First-principles calculations and quantum transport simulations were performed to investigate the photogalvanic effect (PGE) in the high magnetic transition temperature ferromagnetic two-dimensional (2D) semiconductor MnNCl and the 2D lateral MnNI-MnNCl heterostructure. The MnNI-MnNCl heterostructure exhibits significantly enhanced non-centrosymmetric properties, resulting in increased PGE photocurrent and spin current around 0.4 eV. Compared to MnNCl, the photocurrent is amplified by 4–6 orders of magnitude and demonstrates excellent polarization sensitivity, with an extinction ratio reaching 83.92. These results underscore the potential of MnNCl-MnNI lateral heterostructures for use in self-powered, polarization-sensitive infrared detectors.

Controllable Graphene/MoS2 Heterointerfaces by Perpendicular Surface Functionalization.

Surface chemistry and interface interactions profoundly influence the properties of two-dimensional (2D) materials and heterostructures. Therefore, developing methods to precisely control surfaces and interfaces is crucial for harnessing the properties and functions of 2D materials and heterostructures. Here, we developed a facile approach to tuning the interface distance and properties of graphene/MoS2 heterostructures (G/MoS2) by varying the functional groups attached to the surface of graphene bottom layer. We systematically investigated how different functionalized graphene bottom layers affect the interlayer distance, coupling between the interlayers, and optical properties of resulting G/MoS2 heterostructures. Our findings indicate that both the size and electron-withdrawing/donating properties of functional groups are pivotal in regulating charge transport properties, with size playing a particularly decisive role. Our approach demonstrates an efficient and flexible pathway to regulate the interlayer spacing and charge transport, highlighting the potential of engineering interface chemistry in optimizing properties of van der Waals heterostructures.

Extreme electron–hole drag and negative mobility in the Dirac plasma of graphene

Coulomb drag between adjacent electron and hole gases has attracted considerable attention, being studied in various two-dimensional systems, including semiconductor and graphene heterostructures. Here we report measurements of electron–hole drag in the Planckian plasma that develops in monolayer graphene in the vicinity of its Dirac point above liquid-nitrogen temperatures. The frequent electron–hole scattering forces minority carriers to move against the applied electric field due to the drag induced by majority carriers. This unidirectional transport of electrons and holes results in nominally negative mobility for the minority carriers. The electron–hole drag is found to be strongest near room temperature, despite being notably affected by phonon scattering. Our findings provide better understanding of the transport properties of charge-neutral graphene, reveal limits on its hydrodynamic description, and also offer insight into quantum-critical systems in general.

Suppressed Nonreciprocal Second-Harmonic Generation of Antiferromagnet MnPSe3 in the MnPSe3/Graphene Heterostructure Due to Interfacial Magnon-Plasmon Coupling.

Interfacial coupling is one of the keys to manipulating magnetic/nonmagnetic two-dimensional (2D) heterostructures for novel functionalities. The MnPSe3/graphene heterostructure is a prospective platform for quantum information and metrology. However, how graphene affects MnPSe3 through interfacial coupling is still poorly understood. Herein, second-harmonic generation (SHG) of antiferromagnet MnPSe3 in the MnPSe3/graphene heterostructure is revealed. Surprisingly, it was found that below TN, nonreciprocal or c-type SHG of MnPSe3 disappeared when interfacing with the graphene, suggesting the existence of interfacial couplings and/or interactions. Most interestingly, different from the short-range interfacial proximity interaction, this interfacial interaction could be contactless and long-range and varied from 2D metallic/semiconducting to insulating underlayers. Interfacial magnon-plasmon coupling probably played an important role in suppressing the c-type SHG signals of MnPSe3 in the MnPSe3/graphene heterostructure. This study will improve our understanding of the manipulation of nonlinear optical properties in 2D heterostructures.

Electrically Controlled Excitons, Charge Transfer Induced Trions, and Narrowband Emitters in MoSe2-WSe2 Lateral Heterostructure.

Controlling excitons and their transport in two-dimensional (2D) transition metal dichalcogenide heterostructures is central to advancing photonics and electronics on-chip integration. We investigate the controlled generation and manipulation of excitons and their complexes in monolayer MoSe2-WSe2 lateral heterostructures (LHSs). Incorporating graphene as a back gate and edge contact in a field-effect transistor geometry, we achieve the precise electrical tuning of exciton complexes and their transfer across interfaces. Photoluminescence and photocurrent maps at 4 K reveal the synergistic effect of the local electric field and interface phenomena in the modulation of excitons, trions, and free carriers. We observe spatial variations in the exciton and trion densities driven by exciton-trion conversion under electrical manipulation. Additionally, we demonstrate controlled narrow-band emissions within the LHS through carrier injection and electrical biasing. Density functional theory calculation reveals significant band modification at the lateral interfaces. This work advances exciton manipulation in LHS and shows promise for next-generation 2D quantum devices.

In Situ Built ZnS/MXene Heterostructure by a Mild Method for Inhibiting Polysulfide Shuttle in Li-S Batteries.

With high specific surface area, excellent polysulfide conversion activity, and fast electron/ion transfer at the interface, MXene-derived heterostructures can be employed as catalysts for lithium-sulfur (Li-S) batteries to accelerate sulfur redox kinetics and suppress shuttle effect. However, the preparation of MXene-derived heterostructures often requires high-temperature reactions, which can easily lead to the oxidation of MXene and sacrifice the electrical conductivity. Herein, a catalytic two-dimensional heterostructure (ZnS/MXene) was successfully synthesized via a mild method. The MXene skeleton retains the original nanosheet structure without oxidation. The in situ-grown ZnS nanospheres prevent the restacking of MXene nanosheets, which not only increases the active sites, but also guarantees channels for the fast passage of lithium ions. The interfacial built-in electric field further promotes electron/ion migration, thereby expediting the polysulfide conversion and suppressing the shuttle effect. Consequently, the batteries using ZnS/MXene modified separators exhibit a high initial discharge capacity of 1230 mAh g-1 at 0.1 C and a low decaying rate of 0.082 % per cycle after 500 cycles at 0.5 C. This work offers a reference for the fabrication of MXene-based heterostructure in Li-S batteries.

Cooperative S-S coupling and H2 production from photocatalytic dehydrogenation of thiols over ReSe2/ZnIn2S4 heterostructure

Photocatalytic anaerobic dehydrogenation provides a new avenue to cooperatively produce clean fuels and fine chemicals, while minimizing waste discharge and reducing environmental impact. Here, we demonstrate an efficient co-production of disulfides and H2 via photocatalytic S-S dehydrogenation of thiols using a two-dimensional (2D) heterostructure of ultrathin ZnIn2S4 (ZIS) nanosheets decorated with dispersed (1T phase) ReSe2 nanoparticles. Experimental characterizations and DFT calculations reveal that integrating ReSe2 with ZIS leads to the formation of a robust internal electric field (IEF) within the ReSe2/ZIS heterostructure. The distorted 1T phase ReSe2 with abundant active Se sites and a high Fermi level induces downward band bending of ZIS at the interface, which promotes charge separation and expedites H2 evolution. Moreover, the introduction of ReSe2 provides more adsorptive sites, increasing the concentration of reactants on the catalyst surface. This enhancement fosters surface interactions between the catalyst and p-toluenethiol (PTT), ultimately accelerating the reaction rate. The optimal H2 and S-S coupling p-tolyl disulfide (PTD) production rates of the 5 wt% ReSe2/ZIS composite reach 2275 and 2303 µmol g−1h−1, respectively, approximately 5 times greater than those of blank ZIS. Importantly, the selectivity of PTD reaches 98.4 %. This visible-light-driven dehydrogenation process aligns with the principles and objectives of green chemistry, realizing high atom economy without generating byproducts. It is anticipated to open new possibilities for sustainable and environmentally friendly routes for synthesizing high-value chemicals and producing clean energy.

High-Performance Ultra-Broadband Photodetector Based on Fe3O4/CrSiTe3 Heterostructures.

Photodetectors based on advanced materials with a broad spectral photoresponse, high sensitivity, huge integration ability, room-temperature operation, and stable environmental stability are highly desired for diversified applications of imaging, sensing, and communication. Herein, a high-performance ultra-broadband photodetector based on an ultrathin two-dimensional (2D) Fe3O4 nanoflake heterostructure with high sensitivity was designed. The photodetector response light was from visible 405 nm to long-wave infrared (LWIR) 10.6 μm in ambient air. The competitive performances, including a high photoresponsivity (R) of 182.8 A W-1, fast speed with the rise time τr = 8.8 μs, and decay time τd = 4.1 μs, were demonstrated in the visible range. Notably, the device exhibits an excellent uncooled LWIR detection ability, with a high R of 1.4 A W-1 realized at a 1.5 V bias. In the full spectral range, the noise equivalent power is lower than 0.79 pW Hz-1/2, and specific detectivity (D*) is higher than 4.9 × 108 cm Hz1/2 W-1 in ambient air. This work provides alternative ultrathin 2D materials for future infrared optoelectronic devices.

The coupling effect of polarization and lattice strain on charge transfer between quintuple-layer Al2X3/Al2Y3 (X, Y = O, S, Se, Te; X ≠ Y) interfaces

The electronic properties of two-dimensional (2D) polar semiconductor heterostructures are closely related to the degree of interlayer charge transfer. Taking 2D quintuple-layer (QL)-Al2S3 and QL-Al2O3 semiconductor as examples, we study the electronic properties and interlayer charge transfer of QL-Al2S3/Al2O3 interfaces by first-principles calculations. The driving force of the directional interlayer charge transfer is the polarization electric field. The kinetic process of interface charge transfer is related to the charge (strain) distribution of QL-Al2S3 and QL-Al2O3. By changing the strain distribution of QL-Al2S3/Al2O3 interfaces with same polarization arrangement, the electronic properties and interfacial charge transfer of heterojunctions can be adjusted. Our work is an important indicator for understanding the dynamic process of interlayer charge transfer between 2D polar semiconductors. In addition, we propose one method for regulating the electronic properties of heterojunctions by coupling polarization and lattice strain.

Vertical stacking approach for tailoring electronic and optical properties of ultrathin two-dimensional vdW heterostructures of P-MAB (M=Ti, Zr, Hf; A=S, B=Se)

The vertical stacking in the form of heterostructures, is an effective way to enhance the performance of corresponding isolated monolayers. Strong interactions between Janus monolayers (MAB) and Phosphorus (P) monolayers result in significant improvements in both physical and chemical properties compared to single layer configurations. Using first-principle (hybrid) calculations, we explore electronic structure and optical properties of P–MAB (M = Ti, Zr, Hf; A = S, B=Se) van der Waals heterostructures, for potential applications in electronic and optoelectronic devices. Ab initio molecular dynamic (AIMD) simulations confirm the thermal stability, while phonon spectra confirm the dynamical stabilities of these systems. Our analysis reveals that all configurations maintain semiconducting nature with an indirect bandgap. The type-II band alignment in the P–MAB heterostructures is demonstrated through calculations of the partial density of states (PDOS). Bader charge analysis and planar-averaged charge density differences indicate an electron transfer from the P monolayers to the MAB monolayer. Furthermore, our investigation of the dielectric function ϵ2(ω) shows that the lowest energy shift are primarily influenced by excitonic effects.

Ultrafast Charge Transfer-Induced Unusual Nonlinear Optical Response in ReSe2/ReS2 Heterostructure.

Ultrafast charge transfer in van der Waals heterostructures can effectively engineer the optical and electrical properties of two-dimensional semiconductors for designing photonic and optoelectronic devices. However, the nonlinear absorption conversion dynamics with the pump intensity and the underlying physical mechanisms in a type-II heterostructure remain largely unexplored, yet hold considerable potential for all-optical logic gates. Herein, two-dimensional ReSe2/ReS2 heterostructure is designed to realize an unusual transition from reverse saturable absorption to saturable absorption (SA) with a conversion pump intensity threshold of approximately 170 GW/cm2. Such an intriguing phenomenon is attributed to the decrease of two-photon absorption (TPA) of ReS2 and the increase of SA of ReSe2 with the pump intensity. Based on the characterization results of X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, femtosecond transient absorption spectrum, Kelvin probe force microscopy, and density functional theory calculation, a type-II charge-transfer-energy level model is proposed combined with the TPA of ReS2 and SA of ReSe2 processes. The results reveal the critical role of ultrafast interfacial charge transfer in tuning the unusual nonlinear absorption and improving the SA of ReSe2/ReS2 under different excitation wavelengths. Our finding deepens the understanding of nonlinear absorption physical mechanisms in two-dimensional heterostructure materials, which may further diversify the nonlinear optical materials and photonic devices.

Modeling and Simulation of 2D Transducers Based on Suspended Graphene-Based Heterostructures in Nanoelectromechanical Pressure Sensors.

Graphene-based two-dimensional (2D) heterostructures exhibit excellent mechanical and electrical properties, which are expected to exhibit better performances than graphene for nanoelectromechanical pressure sensors. Here, we built pressure sensor models based on suspended heterostructures of graphene/h-BN, graphene/MoS2, and graphene/MoSe2 by using COMSOL Multiphysics finite element software. We found that suspended circular 2D membranes show the best sensitivity to pressures compared to rectangular and square ones. We simulated the deflections, strains, resonant frequencies, and Young's moduli of suspended graphene-based heterostructures under the conditions of different applied pressures and geometrical sizes, built-in tensions, and the number of atomic layers of 2D membranes. The Young's moduli of 2D heterostructures of graphene, graphene/h-BN, graphene/MoS2, and graphene/MoSe2 were estimated to be 1.001 TPa, 921.08, 551.11, and 475.68 GPa, respectively. We also discuss the effect of highly asymmetric cavities on device performance. These results would contribute to the understanding of the mechanical properties of graphene-based heterostructures and would be helpful for the design and manufacture of high-performance NEMS pressure sensors.

Non-Abelian Fractionalization in Topological Minibands.

Motivated by the recent discovery of fractional quantum anomalous Hall states in moiré systems, we consider the possibility of realizing non-Abelian phases in topological minibands. We study a family of moiré systems, skyrmion Chern band models, which can be realized in two-dimensional semiconductor-magnet heterostructures and also capture the essence of twisted transition metal dichalcogenide homobilayers. We show using many-body exact diagonalization that, in spite of strong Berry curvature variations in momentum space, the non-Abelian Moore-Read state can be realized at half filling of the second miniband. These results demonstrate the feasibility of non-Abelian fractionalization in moiré systems without Landau levels and shed light on the desirable conditions for their realization. In particular, we highlight the prospect of realizing the Moore-Read state in twisted semiconductor bilayers.

Electronic and Optical Properties of 2D Heterostructure Bilayers of Graphene, Borophene and 2D Boron Carbides from First Principles.

In the present work the atomic, electronic and optical properties of two-dimensional graphene, borophene, and boron carbide heterojunction bilayer systems (Graphene-BC3, Graphene-Borophene and Graphene-B4C3) as well as their constituent monolayers are investigated on the basis of first-principles calculations using the HSE06 hybrid functional. Our calculations show that while borophene is metallic, both monolayer BC3 and B4C3 are indirect semiconductors, with band-gaps of 1.822 eV and 2.381 eV as obtained using HSE06. The Graphene-BC3 and Graphene-B4C3 bilayer heterojunction systems maintain the Dirac point-like character of graphene at the K-point with the opening of a very small gap (20-50 meV) and are essentially semi-metals, while Graphene-Borophene is metallic. All bilayer heterostructure systems possess absorbance in the visible region where the resonance frequency and resonance absorption peak intensity vary between structures. Remarkably, all heterojunctions support plasmons within the range 16.5-18.5 eV, while Graphene-B4C3 and Graphene-Borophene exhibit a π-type plasmon within the region 4-6 eV, with the latter possessing an additional plasmon at the lower energy of 1.5-3 eV. The dielectric tensor for Graphene-B4C3 exhibits complex off-diagonal elements due to the lower P3 space group symmetry indicating it has anisotropic dielectric properties and could exhibit optically active (chiral) effects. Our study shows that the two-dimensional heterostructures have desirable optical properties broadening the potential applications of the constituent monolayers.

Modulating electronic by construction WS2/WN heterostructure coupled with N-doped carbon to boost alkaline seawater hydrogen production

The development of an efficient and durable non-precious electrocatalyst for alkaline seawater electrolysis is of great significance. Herein, two-dimensional (2D) lamellar heterostructure WS2/WN was dispersed on the carbon matrix (marked as WS2/WN@CM). The obtained WS2/WN@CM catalysts demonstrate exceptional performance in the hydrogen evolution reaction (HER) in alkaline freshwater (1.0 M KOH), alkaline simulated seawater (1.0 M KOH + 0.5 M NaCl) and alkaline natural seawater (1.0 M KOH + seawater), respectively, which achieved a low overpotential (92 mV, 95 mV and 113 mV) at 10 mA cm−2 and outstanding long-term durability at 200 mA cm−2 for 100 h. The catalyst benefits from the 3D carbon skeleton, which not only effectively prevents stacking of the 2D lamellar WS2/WN to fully utilize the active material, but also provides rapid electron transport. Moreover, stress effects at WS2/WN interfaces lead to distortions of torsion angles in the WS2 lattice, thereby increasing crystal surface defects accompanied by an enhancement of electrical conductivity. Density functional theory (DFT) calculations combined with XPS evidence confirm the electronic structure reorganization of WS2/WN at interfaces, which optimizes the adsorption energy of specific intermediates. Additionally, WN captures many electrons from WS2, so the WN region favors the reduction reaction and thus enhances the HER process.

Prediction of multiferroicity in the layered hydrogen-bonded system α-CrOOH: Proton transfer ferroelectricity and strain-tunable magnetic transition

Ferroelectric materials with vertical polarization could provide ground-breaking device applications, compatible with electric-field switching even in the presence of a surface-depolarizing field. Herein, we present theoretical evidence that rhombohedral chromium oxide hydroxide α-CrOOH, which has been synthesized experimentally, is a type-Ⅰ multiferroic. First-principles calculations plus Monte Carlo simulations indicate that α-CrOOH is a room temperature proton transfer ferroelectricity semiconductor with robust electric polarization as large as 24.6 μC/cm2. Moreover, the system exhibits an anti-ferromagnetism ground state with a Neel temperature of 340 K, where strain can modulate the transition from antiferromagnetic to ferromagnetic. Finally, a two-dimensional (2D) heterostructure model was designed, composed of monolayer α-CrOOH and functional MXene, for various applications such as non-volatile memory (NVM). The remarkable properties may enable the system to hold great potential for the development of future multifunctional devices.

Constructing the Fulde-Ferrell-Larkin-Ovchinnikov State in a CrOCl/NbSe2 van der Waals Heterostructure.

Time reversal symmetry breaking in superconductors, resulting from external magnetic fields or spontaneous magnetization, often leads to unconventional superconducting properties. In this way, an intrinsic phenomenon called the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state may be realized by the Zeeman effect. Here, we construct the FFLO state in an artificial CrOCl/NbSe2 van der Waals (vdW) heterostructure by utilizing the superconducting proximity effect of NbSe2 flakes. The proximity-induced superconductivity demonstrates a considerably weak gap of about 0.12 meV, and the in-plane upper critical field reveals the behavior of the FFLO state. First-principles calculations uncover the origin of the proximitized superconductivity, which indicates the importance of Cr vacancies or line defects in CrOCl. Moreover, the FFLO state could be induced by the inherent large spin splitting in CrOCl. Our findings not only provide a practical scheme for constructing the FFLO state but also inspire the discovery of an exotic FFLO state in other two-dimensional vdW heterostructures.

Unraveling the enhanced sodium-storage mechanism in a strongly bonded 2D honeycomb borophene/boron phosphide heterostructure

The growing modern demand for battery capacity is driving the development of high-capacity metal-ion battery anodes for future energy storage. Two-dimensional (2D) material-based heterostructures have shown advantages as alternative anodes due to their enhanced adsorption capacity. The lightweight nature of honeycomb borophene (HB) is beneficial for serving as a high-capacity anode but is constrained by structural instability arising from electron deficiency. In this study, using first-principles calculations, we propose a HB/boron phosphide (BP) heterostructure as an anode for both lithium-ion batteries and sodium-ion batteries (SIBs). The heterostructure engineering not only stabilizes the HB structure but also leads to a bonding heterostructure instead of common van der Walls type. The HB/BP demonstrates robust structural stability and reversibility when multiple ions are stored. In addition, the HB/BP offers stable storage sites and low diffusion barriers for lithium (0.31 eV) and sodium (0.28 eV), indicating rapid charging–discharging performance. Notably, the predicted maximum sodium storage capacity reaches 2402 mAh/g, surpassing that of the constituent monolayers and most 2D heterostructures. The underlying mechanism for high storage capacity is elucidated through detailed charge image model analysis, offering atomistic-scale insights for constructing high-capacity anodes. All results suggest that the presented HB/BP is a promising anode candidate for SIBs and opens an avenue for stabilizing HB in energy storage.

Proximity-induced ferromagnetism of platinum thin film on magnetic insulating CrI3 nanoflakes

The induced magnetization of Pt holds significant promise for the development of spintronic devices. In this study, we constructed a two-dimensional heterostructure consisting of a ferromagnetic insulating CrI3 nanoflake and metallic Pt thin films. The observation of anomalous Hall effect suggests the emergence of a ferromagnetic long-range order in the Pt thin film induced by the magnetic proximity effect. Density functional theory calculations were performed to investigate the underlying mechanisms. We propose that the spontaneous magnetization of Pt in Pt/CrI3 stems from an intensified exchange interaction between Pt 5d and Cr 3d electrons, which is facilitated by the interface coupling and the formation of interfacial hybrid orbitals. These results contribute to a deeper understanding of spin-based phenomena and have potential implications for advancements in the field of spintronics.

Two-dimensional heterostructure of MXene-derived V2O5·H2O and graphene with enhanced Zn-ion storage capability

Aqueous rechargeable zinc-ion batteries (ZIBs) are promising candidates for gird-scale energy storage with economic and environmental advantages. Layered hydrated vanadium oxides with multivalent and “lubricating” effect receive much attention in ZIBs. However, the application of them is suffering from the poor intrinsic conductivity and the unstable structure. Herein, a unique 2D/2D heterostructure of δ-V2O5·H2O nanobelts (VO) and reduced graphene oxide (rGO) is designed as cathode for ZIBs (denoted as VOG). The stronger interface coupling and the shorter ion transport pathways impart the VOG electrode impressive stability and fast ions diffusion kinetics. Specifically, the VOG cathode delivers a superior capacity of 342 mAh g−1 at 1 A g−1 and a remarkable rate capability of 280 mAh g−1 at a quite high rate of 10 A g−1. The energy storage mechanism involved is investigated by systematical characterizations. The exploration of such 2D/2D heterostructure materials with strong synergy sheds light on the rational design of high performanced AZIBs.