2D Heterostructures Research Articles

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.

Double-pentagon silicon chains in a quasi-1D Si/Ag(001) surface alloy

Silicon surface alloys and silicide nanolayers are highly important as contact materials in integrated circuit devices. Here we demonstrate that the submonolayer Si/Ag(001) surface reconstruction, reported to exhibit interesting topological properties, comprises a quasi-one-dimensional Si-Ag surface alloy based on chains of planar double-pentagon Si moieties. This geometry is determined using a combination of density functional theory calculations, scanning tunnelling microscopy, and grazing incidence x-ray diffraction simulations, and yields an electronic structure in excellent agreement with photoemission measurements. This work provides further evidence of pentagonal geometries in 2D materials and heterostructures and elucidates the importance of surface alloying in stabilizing their formation.

Controllable Synthesis of WSe2-WS2 Lateral Heterostructures via Atomic Substitution.

The atomic substitution in two-dimensional (2D) materials is propitious to achieving compositionally engineered semiconductor heterostructures. However, elucidating the mechanism and developing methods to synthesize 2D heterostructures with atomic-scale precision are crucial. Here, we demonstrate the synthesis of monolayer WSe2-WS2 heterostructures with a relatively sharp interface from monolayer WSe2 using a chalcogen atom-exchange synthesis route at high temperatures for short periods. The substitution was initiated at the edges of monolayer WSe2 and the lateral diffuse along the heterointerface, and the reaction can be controlled by the precise reaction time and temperature. The lateral heterostructure and substitution process are studied by Raman and photoluminescence (PL) spectroscopies, electron microscopy, and device characterization, revealing a possible mechanism of strain-induced transformation. Our findings demonstrate a highly controllable synthesis of 2D layered materials through atom substitutional chemistry and provide a simple route to control the atomic structure.

Ultrasensitive detection of hazardous gas at room temperature enabled by MOF@MXene 0D-2D heterostructure

Achieving high sensitivity in detecting trace concentrations of toxic gases, particularly under room temperature (RT) conditions, remains a significant challenge. Herein, a 0D-2D heterostructure that can detect ppb-level H2S at RT is proposed by self-assembling cobalt-based metal–organic framework (Co-MOF) on Ti3C2Tx MXene. Co-MOFs with high specific surface areas can capture and concentrate target gas molecules, enhancing host-guest interactions and thereby boosting the selectivity and sensitivity. MXene nanosheets with high conductivity enable rapid electron transport at heterointerface, hence efficiently accelerating the reaction kinetics. Thereby, the as-prepared chemiresistive gas sensor based on Co-MOF@MXene 0D–2D heterostructure possessed excellent sensitivity against interfering gases and delivered an excellent response value of 11.1 to 400 ppb H2S at RT. The judicious design of MOF@MXene heterostructure may spur advanced hybrid material systems for superior sensing applications.

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.

Charge Transfer Plasmonics in Bespoke Graphene/α-RuCl3 Cavities.

Surface plasmon polaritons (SPPs) provide a window into the nano-optical, electrodynamic response of their host material and its dielectric environment. Graphene/α-RuCl3 serves as an ideal model system for imaging SPPs since the large work function difference between these two layers facilitates charge transfer that hole dopes graphene with n ∼ 1013 cm-2 free carriers. In this work, we study the emergent THz response of graphene/α-RuCl3 heterostructures using our home-built cryogenic scanning near-field optical microscope. Using phase-resolved imaging, we clearly observe long wavelength, heavily damped THz SPPs in a series of variable-size graphene cavities. From this, we extract the plasmonic wavelength and scattering rate in the graphene/α-RuCl3 heterostructures. We determine that the measured plasmon wavelength and electronic scattering rate match our heterostructures' theoretically predicted values. Our results demonstrate that shaping graphene into bespoke cavity structures enables observation and quantification of SPPs in heavily doped graphene that are largely not addressable with other experimental techniques. Moreover, the manifest lack of metallicity observed in the adjacent doped α-RuCl3 layer provides significant constraints on the nature of the interfacial charge transfer in this 2D heterostructure.

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.

Mutually Activated 2D Ti0.87O2/MXene Monolayers Through Electronic Compensation Effect as Highly Efficient Cathode Catalysts of Li–O2 Batteries

Abstract2D materials exhibit remarkable electrochemical performance as the cathode catalyst in lithium–oxygen batteries (LOBs). Their catalytic capability mainly derives from their 2D surface with tunable surface chemistry and unique electronic states. Herein, Ti0.87O2 and Ti3C2 MXene monolayers are applied to construct a face/face 2D heterostructure to enhance the catalytic performance in LOBs. It is demonstrated that electronic compensation from the O‐terminated MXene to Ti0.87O2 side is achieved through the built‐in electric field and the overlap of Ti 3d and O 2p orbitals between Ti0.87O2 and MXene units. As a result, the ORR/OER catalytic activity is improved in Ti0.87O2/MXene heterojunction due to the modulated p‐band center that optimizes the s–p coupling with the key intermediate LiO2. The Ti0.87O2/MXene cathode presents a structural stability and long‐term cycling life of 425 cycles (2534 h) at 200 mA g−1 and 407 cycles at 1000 mA g−1 with a fixed capacity of 600 mAh g−1, being nearly five and three times higher than that of pure Ti0.87O2 and MXene cathodes, respectively.

Photonic Synapse of CrSBr/PtS2 Transistor for Neuromorphic Computing and Light Decoding

Abstract Field effect transistors based on 2D layered material have gained significant potential in emerging technologies, such as neuromorphic computing and ultrafast memory response for artificial intelligence applications. This study proposes a facile approach to fabricate an optoelectronic artificial synapse for neuromorphic computing and light‐decoding information system by utilizing the 2D heterostructure of CrSBr/PtS2 to overcome circuit complexity. The CrSBr layer serves as a trapping layer, while PtS2, mounted on top of CrSBr, acts as a channel layer. PtS2 exhibits n‐type semiconductor behavior with a hysteresis that varies with the thickness of the underlying CrSBr layer. The heterostructure device, featuring a 96.3 nm thick CrSBr layer, exhibited a large memory window of 11.9 V when the gate voltage is swept from −10 V to +10 V. Various synaptic behaviors are effectively demonstrated, including paired‐pulse facilitation, excitatory postsynaptic current, optical spike number and intensity‐dependent plasticity using laser light at a wavelength of 365 nm. The device achieves 26 distinct output signals depending on the intensity of the incident laser light, ranging from 10 to 385 mW cm−2, enabling its applications for light‐decoded information security systems. Thus, the investigation presents a unique approach to artificial intelligence and cybersecurity systems.

Progress and challenges in the synthesis of two-dimensional Van der Waals ferroic materials and heterostructures

Abstract Two-dimensional ferroelectric and magnetic van der Waals materials are emergent platforms for the discovery of novel cooperative quantum phenomena and development of energy-efficient logic and memory applications as well as neuromorphic and topological computing. This review presents a comprehensive survey of the rapidly growing 2D ferroic family from the synthesis perspective, including brief introductions to the top-down and bottom-up approaches for fabricating 2D ferroic flakes, thin films, and heterostructures as well as the important characterization techniques for assessing the sample properties. We also discuss the key challenges and future directions of the field, including scalable growth, property control, sample stability, and integration with other functional materials.

Revealing Intrinsic Functionalization, Structure, and Photo-Thermal Oxidation in Hexagonal Antimonene.

Antimonene is one of the more exciting members of the post-graphene family with promising applications in optoelectronics, energy storage and conversion, catalysis, sensing or biomedicine. Efforts have been focused on developing a large-scale production route, and indeed, through a colloidal approach, high-quality few-layers antimonene (FLA) hexagons have been recently obtained. However, their oxidation behavior remains unexplored, as well as their interface, inner structure, and photothermal properties. Herein, it is revealed that the hexagons have an intrinsic surface functionalization with alkyl thiols that protects the core of the hexagonal flake against oxidation, and displayed inner defects related to the crystal formation during synthesis, as confirmed by cross-sectional scanning transmission electron microscopy energy dispersive X-ray spectroscopy (STEM-EDX) and temperature-dependent X-ray photoelectron spectroscopy (XPS) and selected area electron diffraction (SAED) analysis. A comprehensive study of temperature and laser power-dependent Raman spectroscopy on varying FLA hexagon thicknesses is carried out. Thinner flakes (<20nm) exhibited a blueshift and intensity decrease, contrasting with thicker ones resembling typical exfoliated flakes with a redshift. This work addresses a literature gap, providing insights into hexagonal FLA structure and characterization, and highlighting the influence of surface functional groups on oxidation behavior. Additionally, it emphasizes the potential of antimonene hexagons as building blocks for 2D heterostructures, including combinations with antimonene oxides and other 2D materials.

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.

Design and fabrication OF Cu2O@MoS2/r-Go dendrite binary electrode for quasi – Symmetric capacitor- sustainable approach

Modified hummers method to synthesise GO from powdered graphite and sodium molybdate, then green synthesised Cu2O/MoS2/rGO nanostructure prepared by economical microwave approach. XRD analysis proved that Cu2O and MoS2/rGO were present in the sample. FTIR spectra revealed a Cu2O group at around 620 cm−1, whilst EDAX analysis revealed Mo, Cu, S, O, and C characteristic bands. rGO material resembles the SEM image of Cu2O/MoS2-rGo in appearance, with dendritic morphologies of Cu2O and MoS2 sheets on its exterior. When applied to nearby r-GO sheet formations, MoS2 thins down the layers. Incorporating rGO, a conductive material, into the MoS2/rGO composite greatly enhanced its capacity to store charges. Improved storage properties of the composite led to charge-discharge curves that were more symmetrical than those of pure MoS2. The significant heterostructure of 2D materials is responsible for their remarkable cyclic stability. Supercapacitors with a Cu2O/MoS2/r-GO nanostructure as manufactured are safe for use with batteries. Building 2D and 3D heterostructures to improve energy storage systems of the future is the goal of this endeavor.

Covalently Linked 2D-Co3O4/GO Heterostructures: Catalytic and Electrochemical Properties.

Covalently cross-linked 2D heterostructures may represent a ground-breaking approach to creating materials with multifunctionalities. To date, however, this field still remains relatively unexplored. In the present work, Co3O4/GO covalently linked heterostructures (Co3O4/GO-CL) were produced using 2D-Co3O4 functionalized with (3-aminopropyl)triethoxysilane (APTES) to react with the carboxyl groups of graphene oxide (GO). The surface and interface properties of the final material were assessed through electrochemical and catalytic studies. We found that the covalent bonds lead to a self-standing and ordered final structure, not observed for the noncovalent material (Co3O4/GO-nCL), also produced for comparison. The catalytic activity of Co3O4/GO-CL over the degradation of Rhodamine 6G showed great performance and the possibility of recycling the catalyst. Electrochemical evaluation stated higher specific capacitance for the covalently bonded material (468 F g-1 against 110 F g-1). Overall, results showed that the covalent bonds may be improving charge-transfer and interfacial area features, thus leading to enhanced catalytic and electrochemical performances.

Editorial for two-dimensional materials-based heterostructures for next-generation nanodevices.

Heterostructures, such as van der Waals (vdW) heterostructures, provide a versatile platform for engineering the physical properties of two-dimensional (2D) layered materials, spanning electronics, mechanics, optics, as well as electron-phonon couplings. Furthermore, vdW heterostructures, which are composed of metal/semiconductor or semiconductor/semiconductor combinations, not only maintain the unique properties of their individual constituents but also exhibit tunable physical and chemical properties that can be externally adjusted through strain, heat, and electric fields. These externally tunable properties offer significant advances in the fields of solid-state devices and renewable energy applications. Additionally, 2D material-based heterostructures, such as those composed of 0D clusters or quantum dots, as well as 1D nanotubes/wires in combination with 2D materials, also show immense potential for advancing next-generation nanodevices. The vast design space of vdW heterostructures enables their versatile applications spanning numerous fields, such as light-emitting diodes, field-effect transistors, photocatalysis, solar cells, photodetectors, and so on.&#xD;In the Special Issue of Journal of Physics: Condensed Matter, entitled "Two-dimensional Materials-based Heterostructures for Next-generation Nanodevices", we have gathered a comprehensive collection of 14 articles, presenting the latest achievements in the fields of designing novel 2D materials and 2D heterostructures. Below, we have briefly condensed the essential research findings from these studies.&#xD.

Facile synthesis of dual-MOF ultrathin nanosheets supported on layered double hydroxides heterostructure: Electron modulation strategy for enhanced electrocatalytic water splitting

In this study, we achieved electron environment modulation of MOF-based electrocatalyst by creating a dual-functional heterostructure using two-dimensional (2D) MOFs and layered double hydroxides (LDH), to enhance its electrocatalytic performance. Through a self-sacrificial template method, ultrathin hybrid dual-MOF (CoBDC and MIL-100(Fe)) nanosheets were grown on LDH, forming DM@CoFeRu-LDH, a 2D heterostructure benefiting from interference co-growth on the 2D scaffold. The thickness of dual-MOF nanosheets can be controlled by regulating the nucleation and reaction kinetics. Specifically, with a thickness ranging from 1–1.5 nm, it effectively exposes more active sites and accelerate electron and mass transfer. Additionally, electron transfer occurred between the dual-MOF and LDH heterostructures, leveraging synergistic effects from multi-metal centers to achieve an optimal electron structure. DM@CoFeRu-LDH exhibited the lowest energy barrier for the rate-determining step in the oxygen evolution reaction, along with a favorable hydrogen adsorption energy for the hydrogen evolution reaction. As a result, the DM@CoFeRu-LDH demonstrated efficient electrocatalytic activity, requiring only a voltage of 1.50 V to achieve a current density of 10 mA cm−2.

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.

Enhanced dopamine detection using Ti3C2Tx/rGO/Pt ternary composite synthesized via microwave-assisted hydrothermal method

A novel electrochemical sensing platform for dopamine (DA) detection was developed by fabricating the ternary composite of Ti3C2Tx MXene (M) and reduced graphene oxide (rGO) with platinum nanoparticles (Pt NPs) through microwave-assisted hydrothermal heating. The exceptional electrical conductivity and rich surface chemistry of MXene provide abundant active catalytic sites for electrochemical reactions, while the large surface area of rGO facilitates ion and electron pathways. The integration of rGO in the MXene sheet, forming MXene-rGO (M_rGO) heterostructure composite, imparts long-term stability to the 2D heterostructure while providing additional electron pathways and significantly enhancing conductivity. Pt NPs synergistically increased the electrocatalytic activity of the electrochemical sensor's performance. Ternary nanocomposites were fabricated with different weight percentages (wt.%) of Pt NPs, ranging from 5 to 20. Characterizations of the samples (rGO, M, M_rGO, and 5–20 wt% Pt@M_rGO) were conducted through X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX), Raman spectroscopy (RAMAN), and X-ray spectroscopy (XPS). Electrochemical evaluations of the samples were investigated in 0.1 M phosphate buffer solution (PBS) using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) analyses. The analysis revealed that the ternary composite with 5 wt% of Pt NPs (5% Pt@M_rGO) exhibited a uniform well-distribution of Pt NPs and the highest oxidation peak for DA oxidation in CV studies. The presence of metal nanoparticles, aided by the synergistic effects between the MXene and rGO, resulted in an excellent DA sensor with a 0.147 μM detection limit from 1 to 14 μM linearity range. The sensor demonstrated outstanding selectivity, reproducibility (RSD values of 8.10%), repeatability (RSD value of 2.46%) and, excellent stability over 14 days. In human urine samples, the sensor exhibited excellent DA recovery (88.62–110.65%). This study significantly advances the development of electrochemical sensors for DA detection by introducing a rapid, facile and, efficient method for fabricating ternary composites. The fabricated sensor exhibited high sensitivity, excellent selectivity, and robust electrochemical performance, offering valuable insights into human and behavioral health advancements.

2D heterostructures in photocatalysis for emerging applications: Current Status, challenges, and Prospectives

Photocatalysts for energy conversion and production, pollutants degradation, CO2 reduction, organic synthesis, biomedical, are especially important in a renewable energy-based energy and economic landscape. Due to their larger surface area and efficient capacity to segregate photogenerated electrons and holes, 2D van der Waals (vdW) heterostructures are being investigated to overcome the critical challenge of the short lifespan of photogenerated charges. This study presents the most recent research on 2D photocatalysts, specifically vdW heterostructures, for energy conversion and production, pollutants degradation, CO2 reduction, organic synthesis, biomedical. After presenting the core concepts of the light-driven redox reaction for aforementioned applications, we address a number of interesting 2D vdW heterostructures, highlighting transition metal dichalcogenides and graphene oxide heterostructures from both theoretical and experimental perspectives. In this review, we address the prospects and difficulties within this field of study. The enhanced understanding of 2D vdW heterostructures in photocatalysis presented in this research opens up new possibilities for increasing the efficiency of hydrogen generation. The key issues and future developments in the applications of 2D/2D layered heterojunctions and heterostructures in photocatalysis are explored.

Towards the scalable synthesis of two-dimensional heterostructures and superlattices beyond exfoliation and restacking.

Two-dimensional transition metal dichalcogenides, which feature atomically thin geometry and dangling-bond-free surfaces, have attracted intense interest for diverse technology applications, including ultra-miniaturized transistors towards the subnanometre scale. A straightforward exfoliation-and-restacking approach has been widely used for nearly arbitrary assembly of diverse two-dimensional (2D) heterostructures, superlattices and moiré superlattices, providing a versatile materials platform for fundamental investigations of exotic physical phenomena and proof-of-concept device demonstrations. While this approach has contributed importantly to the recent flourishing of 2D materials research, it is clearly unsuitable for practical technologies. Capturing the full potential of 2D transition metal dichalcogenides requires robust and scalable synthesis of these atomically thin materials and their heterostructures with designable spatial modulation of chemical compositions and electronic structures. The extreme aspect ratio, lack of intrinsic substrate and highly delicate nature of the atomically thin crystals present fundamental difficulties in material synthesis. Here we summarize the key challenges, highlight current advances and outline opportunities in the scalable synthesis of transition metal dichalcogenide-based heterostructures, superlattices and moiré superlattices.