Progress and Challenges in the Synthesis of Two-Dimensional Lateral Heterostructures

Abstract

Two-dimensional (2D) lateral heterostructures, an interesting class of nanostructures, have shown great promise in optoelectronics and nanoelectronics due to their unique electronic and optical properties. In recent years, significant progress has been made in the controlled growth of 2D lateral heterostructures. However, challenges remain in areas such as material selection and compatibility, interface quality, and precise control over the growth process. High-quality interfaces are critical for the optoelectronic performance of these heterostructures, yet ensuring uniformity and consistency during fabrication continues to be a major obstacle. This review provides a comprehensive overview of the recent developments in the controlled growth of 2D lateral heterostructures. It examines the fabrication methods for various types of 2D lateral heterostructures and their associated challenges. The review also discusses the properties and potential applications of these heterostructures, aiming to offer a deeper understanding of their preparation, characteristics, and future prospects. By identifying existing challenges and opportunities in the fabrication process, this work seeks to guide future advancements in the field and support the efficient large-scale production of high-quality 2D lateral heterostructures.

1. Introduction

Two-dimensional (2D) materials are a class of materials with nanoscale thickness that have attracted widespread research interest over the past few decades. − These materials have garnered attention due to their unique properties in terms of electronic, optical, and mechanical characteristics, − and are considered important components for future nanodevices and applications. Graphene, as one of the most famous representatives, was first discovered in 2004. It is composed of a single layer of carbon atoms and possesses outstanding electrical conductivity and mechanical performance. Owing to its unique structure and remarkable physical properties, − graphene has shown immense potential in many fields, sparking a research boom on 2D materials and initiating exploration into more 2D materials. − Apart from graphene, many other types of 2D materials have also received significant attention. − To the best of our knowledge, those 2D materials can be broadly divided into two categories, the first ones are single-element 2D materials, of which the most typical ones are listed as graphene, black phosphorus, silicene, germanene, and so on. While the second series are included as transition metal dichalcogenides (TMDs), , hexagonal boron nitride (h-BN), , transition metal carbides (TMCs), entitled as compound 2D materials. ,

With the rapid advancements in 2D materials research, there has been a growing interest in the fabrication of heterostructures by stacking or assembling various 2D materials either vertically or laterally. These heterostructures often exhibit unique functionalities and enhanced properties. − Traditional studies have predominantly focused on vertical heterostructures, where different 2D materials are stacked to form new layered structures. However, more recently, there has been a shift toward lateral heterostructures, where distinct 2D materials are integrated within the same plane, forming stable interfaces. This lateral configuration has attracted considerable attention due to its potential to significantly improve material properties and enable innovative applications. By carefully selecting and designing different 2D materials, it is possible to optimize performance and expand functionality. Notably, compared to vertical heterostructures, lateral heterostructures offer a more direct electron transport pathway within the same plane, which typically leads to superior electronic transport characteristics. −

The core advantage of 2D lateral heterostructures lies in their ability to achieve highly precise interface control at the atomic level, a characteristic that provides significant benefits across various applications. − First, 2D lateral heterostructures can substantially enhance the electronic and optical properties of materials. By carefully selecting material combinations, the bandgap can be tuned, optimizing electron mobility and light absorption characteristics. ,− Furthermore, their layered structure offers advantages for integrated design, which not only reduces device dimensions and material consumption but also improves performance. − 2D lateral heterostructures present opportunities for achieving higher density integrated circuits and more efficient optoelectronic devices, which are of paramount importance for the development of miniaturized and high-performance equipment. Additionally, these heterostructures enable the integration of novel functionalities such as sensing, signal amplification, and processing, thereby driving advancements in multifunctional technologies. In summary, 2D lateral heterostructures possess significant value in fundamental scientific research and demonstrate immense potential in practical applications, laying a solid foundation for the development of the next generation of electronic and optoelectronic devices.

2D lateral heterostructures provide new perspectives and methods for the research and application of 2D materials. They not only offer new material platforms but also can alter the properties of 2D materials and expand their application areas. − However, despite the broad application prospects of 2D lateral heterostructures, there are still challenges and issues that need to be addressed. One major challenge is the preparation of high-quality heterostructures. Due to limitations in the growth and stacking technologies of 2D materials, achieving high-quality heterostructures remains somewhat difficult. Additionally, interface matching and heterostructure stability are crucial factors restricting their applications.

In this review, we discuss the recent advancements in the study of the synthesis of 2D lateral heterostructures. We begin by outlining common methods for fabricating 2D lateral heterostructures. Next, we categorize the various types of these structures and examine their physical properties along with device performance. Finally, we discuss future challenges and opportunities for 2D lateral heterostructures.

2. Synthesis of Lateral Heterostructures

In the early stages of research on the synthesis of 2D materials, monolayer 2D materials were successfully prepared by researchers using mechanical exfoliation methods. In 2004, Andrei Geim and Konstantin Novoselov first applied this method to isolate monolayer graphene. As investigations into graphene deepened, scientists began to explore other 2D materials, thereby enhancing the understanding and application of these materials. By stacking different materials, heterostructures were formed to achieve new functionalities and properties. Currently, based on structural differences, laboratory-synthesized 2D heterostructures can be categorized into two types: 2D vertical heterostructures and 2D lateral heterostructures. ,, 2D vertical heterostructures refer to the stacking of two different types of 2D materials in the vertical direction, creating a new interface. This structure is commonly used to enhance the performance of optoelectronic devices or field-effect transistors. − ,,, Although vertical heterostructures have been successfully fabricated through mechanical exfoliation and transfer techniques, the performance of these 2D devices is limited by interlayer contaminants and stacking orientations that arise during the fabrication process. , To address these limitations, lateral heterostructures have been proposed as an effective solution. In contrast, 2D lateral heterostructures involve the contact of different 2D materials within the same plane, forming a horizontal interface that is typically used to enhance current transport or improve charge carrier separation. −

In recent years, the synthesis of 2D lateral heterostructures has emerged as a highly prominent research direction in the field of materials science. By stacking different types of 2D materials together, novel materials with exceptional properties and unique functions can be created (Figure a). − With the continuous advancement of synthesis methods, the heterostructures of 2D materials can now be precisely controlled and optimized, opening up extensive prospects for various applications.

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(a) Development roadmap of 2D lateral heterostructures. Reproduced with permissions from refs – . Copyright 2012 Spring Nature, 2013 Spring Nature, 2014 Spring Nature, etc. (b) Physical vapor deposition (PVD). (c) Chemical vapor deposition (CVD). (d) Metal–organic chemical vapor deposition (MOCVD). (e) Solution-based synthesis approach. (f) Vapor-phase growth method.

2.1. Physical Vapor Deposition

Physical vapor deposition (PVD) is a straightforward gas-phase technique wherein the material undergoes a phase transition from solid to gas and subsequently deposits onto the substrate surface (Figure b). , In the PVD process, the material is first converted into a gas by heating the solid evaporation source. The deposition rate, crystal structure, and properties of the deposited material can then be influenced by controlling the deposition time and conditions, the atmosphere within the reaction chamber, and adjusting the pressure and gas composition. This precise control facilitates the creation of 2D lateral heterostructures and the attainment of the desired film thickness and structure. Post-deposition treatments, such as annealing and surface treatment, are generally required to enhance the structure and properties of the deposited material and improve its crystal lattice. Another prevalent form of PVD is physical sputtering, where ions in the gas bombard a solid target material, causing the surface material to rapidly release into the gas phase and deposit onto the substrate. This method allows for selective synthesis of materials by choosing specific target materials for sputtering.

2.2. Chemical Vapor Deposition

Chemical vapor deposition (CVD) is a technique utilized for depositing atomic-level thin films onto a substrate surface through chemical reactions (Figure c). − In the CVD process, appropriate precursors and inert gases are selected as carrier gases. The deposition typically occurs at elevated temperatures to promote the thermal decomposition and reactions of the precursors. Within the reaction chamber, the reactive species generated from the decomposition of the precursors react chemically with the substrate surface, resulting in the deposition of the desired 2D material. During the deposition process, the reactive species adsorb onto the substrate, forming a thin film gradually. By controlling variables such as precursor supply, carrier gas, reaction conditions, and post-treatment steps, precise control over the properties and structure of 2D materials is achieved, enabling the fabrication of 2D lateral heterostructures with specific attributes. It should be noted that the success of CVD is influenced by multiple factors, including reaction temperature, precursor concentration, and carrier gas flow rate. Optimization of these parameters is essential for synthesizing high-quality, high-crystallinity 2D lateral heterostructures.

2.3. Metal–Organic Chemical Vapor Deposition

Metal–organic chemical vapor deposition (MOCVD) is a technique that relies on the thermal decomposition and chemical reactions of metal–organic compounds to deposit metals and semiconductor materials onto a substrate surface for the growth of 2D materials (Figure d). ,− In the MOCVD process, metal–organic compounds containing both metal and organic groups are initially selected as precursors. These precursors are evaporated and transported to the substrate surface, where they decompose into reactive species. These reactive species then chemically react with the substrate surface, resulting in the formation of a thin film. By adjusting parameters such as precursor supply, reaction temperature, gas atmosphere composition, and alternating the supply of different precursors, the growth process of 2D lateral heterostructures can be effectively controlled. MOCVD is a highly versatile method capable of synthesizing various 2D materials, including metals, semiconductors, and insulators, thereby facilitating the construction of 2D lateral heterostructures. To ensure the deposited 2D materials exhibit high quality and a well-ordered lattice structure, precise control of the process and meticulous equipment operation are essential for MOCVD.

2.4. Solution-Based Synthesis Approach

The solution-based method is typically employed for the preparation and stacking of 2D materials through the precise control of reaction conditions (Figure e). ,− Techniques such as drop-casting, spray-coating, and spin-coating are used to transfer the solution onto suitable substrates. Once the solution comes into contact with the substrate surface, 2D materials can be precipitated from the solution and grown on the substrate through heat treatment or solvent evaporation. Various 2D materials can be synthesized by selecting different precursor substances. Additionally, the morphology, number of layers, and stacking configuration of the 2D materials can be accurately controlled by adjusting parameters such as solution composition, concentration, and reaction conditions. The solution-based method also facilitates the preparation of large-area, high-quality 2D materials, demonstrating significant scalability.

2.5. Vapor-Phase Growth Method

The sublimation method is employed for the preparation of 2D materials, where the substance transitions directly from a solid state to a gas phase and subsequently deposits onto a substrate surface (Figure f). This technique allows for material growth at relatively high temperatures, facilitating the rapid production of large-sized and high-quality 2D materials. In practical applications, the sublimation method is often integrated with other preparation techniques to achieve enhanced material properties and structural control. Moreover, the sublimation method eliminates the need for solvents, thus circumventing issues related to organic impurities and solvent residues commonly encountered in solution-based methods. The microspacing sublimation method represents an advanced approach used to synthesize 2D lateral heterostructures. Compared to traditional sublimation techniques, the microspacing sublimation method introduces tiny gaps around the source material, allowing for the deposition of raw materials in small dimensions on the substrate. This precise control enhances the production of high-quality materials with superior lattice integrity. Additionally, the microspacing sublimation method simplifies the preparation process and improves scalability by not requiring complex apparatus or high vacuum conditions.

The synthesis methods for 2D lateral heterostructures have undergone rapid development and achieved significant results. These methods have profoundly transformed our understanding of these materials within the realm of 2D materials. However, challenges remain in the current preparation of 2D lateral heterostructures, including the fabrication of high-quality monolayer materials, scalability and cost-effectiveness of synthesis methods, and the advancement of theoretical modeling and characterization techniques. Future research must continue to address these issues, explore novel synthesis techniques and theoretical studies, and establish a solid foundation for the practical applications of 2D lateral heterostructures.

3. Types of Lateral Heterostructures

3.1. Graphene-Based

Graphene, as a 2D material with outstanding electrical properties, holds tremendous potential in the field of electronic devices. In order to achieve more complex functionalities, researchers have begun to explore the combination of graphene with other materials to form 2D lateral heterostructures. Initial research efforts focused on stacking graphene and hexagonal boron nitride (h-BN) using a mechanical exfoliation method. Although this method allowed for atomic-level control, the cumbersome preparation process, low yield, and high cost limited its widespread application. To overcome these limitations, researchers began to employ chemical methods to combine graphene and h-BN.

In 2012, Jiwoong Park et al. reported a versatile and scalable process, which they called “patterned regrowth”, that allowed for the spatially controlled synthesis of lateral junctions between electrically conductive graphene and insulating h-BN, as well as between intrinsic and substitutionally doped graphene. Conductance measurements confirmed that laterally insulating behavior for h-BN regions, while the electrical behavior of both doped and undoped graphene sheets maintain excellent properties, with low sheet resistances and high carrier mobilities. Then in 2013, Pulickel M. Ajayan et al. prepared the creation of graphene and h-BN in-plane heterostructures with controlled domain sizes by using lithography patterning and sequential CVD growth steps. In the experiments, the shapes of the graphene and h-BN domains could be controlled precisely, and sharp graphene/h-BN interfaces could be created.

Currently, researchers primarily utilize CVD techniques to fabricate graphene in conjunction with other 2D materials for the construction of 2D lateral heterostructures. ,− In this process, different 2D materials, such as graphene and semiconductor materials, are typically grown simultaneously on a substrate. By adjusting parameters such as gas flow, temperature, and growth time, the growth of these two materials can be precisely controlled, allowing for their alternate deposition within specific regions of the graphene, thereby forming the desired lateral heterostructure. This heterostructure exhibits excellent optoelectronic properties, demonstrating significant potential for widespread applications in optoelectronic devices and logic circuits. For instance, Xiang Zhang et al. reported a scalable synthesis method with spatial control that successfully overcame the challenges related to precise spatial control during the assembly process, enabling the fabrication of a heterostructure consisting of monolayer molybdenum disulfide and conductive graphene. The research findings indicate that monolayer molybdenum disulfide can effectively nucleate at the edges of graphene, and these chemically assembled atomic-scale transistors exhibit outstanding electrical performance, including high transconductance (10 μS), on–off ratio (∼10⁶) and mobility (∼17 cm² V^–1 s^–1).

Significant progress has been made in the synthesis of 2D lateral heterostructures with graphene. − Graphene can be assembled with various functional materials into heterostructures through different preparation methods, demonstrating remarkable performance in electronic devices, optical devices, and sensors. As research advances, novel synthesis methods and application areas are expected to emerge, presenting both new opportunities and challenges for the development of 2D lateral heterostructures.

3.2. TMDs-Based

TMDs are a class of 2D materials formed by transition metal elements and chalcogen elements (such as sulfur, selenium, and tellurium), typically with the chemical formula MX₂, where M represents the transition metal (e.g., molybdenum, tungsten, tantalum) and X represents a chalcogen element. − TMDs have attracted widespread attention in recent years and have become an important research direction in the field of 2D materials. Due to the presence of many 2D materials with similar crystal structures, TMDs are considered an ideal choice for constructing 2D lateral heterostructures. Lateral heterojunctions, by stacking different material layers in a specific order, enable the tuning of electronic structures, expand carrier transport paths, and offer more possibilities for achieving high-performance electronic and optoelectronic devices. The combination of TMDs with 2D lateral heterostructures not only enriches the application areas of 2D materials but also promotes the development of novel electronic, optoelectronic, and energy devices.

In traditional sequential growth processes, issues such as excessive thermal degradation or uncontrolled uniform nucleation often arise, which may hinder the formation of monolayer heterostructures. To address these challenges, Duan et al. proposed a robust synthesis strategy for growing various lateral heterostructures, multiheterostructures, and superlattices in 2D atomic crystals. In this method, a forward flow from the chemical vapor source is applied at precisely controlled growth temperatures, and reverse flow from the substrate to the source direction is achieved during temperature fluctuations between continuous growth steps. After multiple sequential growth steps, the integrity and quality of the monolayer heterostructures are significantly preserved. This approach offers a versatile and reliable strategy for the growth of various heterostructures, multiheterostructures, and superlattices (Figure a). Additionally, using this technique, a range of 2D heterostructures (such as WS₂–WSe₂ and WS₂–MoSe₂), multiheterostructures (such as WS₂–WSe₂–MoS₂ and WS₂–MoSe₂–WSe₂), and superlattices (such as WS₂–WSe₂–WS₂–WSe₂–WS₂) have been synthesized.

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(a) Robust epitaxial growth of 2D monolayer heterostructures, multiheterostructures, and superlattices with a modified CVD process. Reproduced with permission from ref . Copyright 2017 The American Association for the Advancement of Science. (b) Low-magnification optical image of three-junction heterostructures. The inset shows a larger magnification of the area within the dashed box. (c) Optical images of five-junction heterostructures (left, middle) and seven-junction (right). (d) Photoluminescence intensity maps for the WSe₂ (1.6 eV, left) and MoSe₂ (1.52 eV, right) domains. (e) Composite photoluminescence map for the five-junction heterostructure. (f) Contour color plots of the normalized photoluminescence intensity of three-junction (left) and five-junction (right) heterostructures, along the arrows in the insets. (g) Z-contrast atomic-resolution HAADF-STEM images of pure MoSe₂ (left) and WSe₂ (right). (h) Atomic-resolution HAADF-STEM images of the smooth (left) and sharp (right) interfaces, with their corresponding Fourier-transform patterns and composition profiles (atomic fraction of tungsten per vertical atomic column). (b–h) Reproduced with permission from ref . Copyright 2018 Springer Nature. (i) Schematic of 2D superlattices based on monolayer TMDs. (j) SEM images of three monolayer WS₂/WSe₂ superlattices. (k) The ADF-STEM image at the heterointerface area between WS₂ and WSe₂ (epitaxy direction represented by the arrow; same for all). (l) Inverse FFT of an ADF-STEM image from a larger area near the heterointerface, based on the circled spots in its FFT (inset). (m,n) Spatial maps of normalized lattice constants a _//, a _⊥, and lattice rotation map of superlattice {75 and 60 nm}. (o) Normalized PL spectra of WS₂ for intrinsic WS₂ (dashed line) and superlattices I to V. (Inset) A representative PL spectrum of a WS₂/WSe₂ superlattice. (i–o) Reproduced with permission from ref . Copyright 2018 The American Association for the Advancement of Science.

The lateral heterostructures of TMDs can be successfully synthesized through single-step, two-step, or multistep growth processes. However, these methods lack flexibility in the in situ control of the growth of individual domains, and challenges remain in the in situ fabrication of high-quality lateral heterostructures with multiple junctions. Prasana K. Sahoo et al. reported a novel method termed “sequential edge-epitaxy” for fabricating 2D lateral heterostructures within a single reaction chamber. This technique enables precise assembly of different 2D materials within one reaction vessel, overcoming the limitations of traditional methods that require multiple steps and complex equipment. The research team selected MoS₂ and WS₂ as model materials and employed CVD to grow these materials in the same reaction chamber. By adjusting the reaction temperature and gas flow rates, the researchers were able to control the growth of different layers on the same substrate. Experimental results indicated that the sequential edge-epitaxy method successfully achieved lateral heterostructures of MoS₂ and WS₂ on a single substrate. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations revealed that the interface layers were of high quality with no significant defects (Figure g,h). Spectral analysis confirmed the formation of the heterostructure and highlighted its exceptional optoelectronic properties (Figure b–f). This method not only simplifies the fabrication process but also significantly enhances the interface quality and consistency of the materials. Compared to traditional multistep processes, it reduces process complexity and lowers material fabrication costs. However, despite its excellent performance in experiments, further validation is needed to address potential issues related to uniformity and reproducibility in large-scale production.

The epitaxial structure with coherent heterogeneous interfaces, in which the lattices of different materials match without dislocations, enables advanced scientific and technological applications. A series of advanced experimental techniques were employed by Jiwoong Park et al. to construct and characterize transition metal dichalcogenide (TMD) superlattices with engineered strain (Figure i). Initially, high-quality monolayer TMD materials were synthesized using CVD methods. Following this, mechanical exfoliation and interlayer transfer techniques were utilized to precisely construct TMD superlattices with highly refined geometries. By controlling the stacking sequence of different TMD layers and the application of strain, superlattices with specific strain characteristics were successfully fabricated. High-resolution characterization of the atomic structure of the superlattices was conducted using TEM and scanning probe microscopy (SPM) (Figure j–l). Additionally, PL and other techniques were combined to investigate the effects of strain on the optical properties of the materials (Figure m–o). The experimental results demonstrated that engineered strain significantly modulated the electronic band structure and optical characteristics of the TMD superlattices. For instance, under specific strain conditions, the materials exhibited enhanced optical emission characteristics and adjusted electronic density of states, providing new avenues for device performance optimization. It was also found that the superlattices maintained high structural coherence and stability under strain control, which is a crucial factor for achieving high-performance devices. This research successfully showcased the construction of high-quality TMD superlattices at the atomic level through precise strain engineering, offering an effective method for tuning the electronic and optical properties of the materials. However, despite the considerable potential demonstrated by the experiments, challenges related to production costs and large-scale manufacturing of the superlattices still need to be addressed.

The controlled growth of 2D heterostructure arrays presents a significant synthetic challenge for exploring exotic physics and developing novel devices. Duan et al. reported a synthetic strategy for fabricate mosaic heterostructure arrays in monolayer 2D atomic crystals. The researchers employed advanced internal and external epitaxial growth techniques to successfully synthesize high-quality monolayer heterostructures through a precisely controlled CVD process in a high-temperature environment (Figure a–d). To achieve mosaic structures, the team meticulously adjusted the deposition times and gas flow rates for different 2D materials to ensure precise alignment and interlayer consistency. Characterization analyses indicated that the synthesized heterostructures demonstrated exceptional crystal quality and interface smoothness, effectively avoiding common interface defects and material mismatches (Figure e,f). Optical property tests further revealed that these heterostructures exhibit significant enhancement in light absorption and superior electron mobility, rendering them suitable for high-performance electronic and optoelectronic devices (Figure g–j). Additionally, by comparing the effects of different deposition conditions on the final structures, the researchers determined the optimal growth parameters and clarified the critical impact of material selection and deposition methods on heterostructure performance (Figure k–p). This study not only extends the scope of epitaxial growth techniques but also provides valuable insights and methods for the design and fabrication of high-performance 2D materials. However, the method is relatively complex and imposes more stringent requirements on the precise control of each experimental step, which presents a challenge to the feasibility of applying the method on a large scale.

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(a–d) Schematic illustration of the lateral endoepitaxial growth of WS₂–WSe₂ monolayer mosaic heterostructures (MMHs). (e) Optical microscopy image of a WS₂–WSe₂ MMHs with triangular WSe₂ domains embedded in monolayer WS₂ matrix. (f) AFM phase of the WS₂–WSe₂ MMH. (g) The PL spectra collected from the locations 1–3. (h–j) PL mapping images of the WS₂–WSe₂ MMHs at different wavelengths: 630 nm (h); 775 nm (i); 769 nm (j). (k) Optical microscopy image of a WS₂–MoS₂ MMH with triangular MoS₂ domains embedded in monolayer WS₂ matrix. (l) AFM phase of the WS₂–MoS₂ MMH. (m–p) PL intensity maps of WS₂–MoS₂ MMHs at different wavelengths: 668 nm (m); 620 nm (n); 627 nm (o); 640 nm (p). (a-p) Reproduced with permission from ref . Copyright 2022 Spring Nature.

Historical technological advancements are often driven by innovations in materials. As research and application of 2D lateral heterostructures have progressed, a growing array of novel fabrication methods has emerged, increasingly coming into view. Jing Kong et al. reported strategies and applications for designing artificial 2D materials using room-temperature atomic-layer substitution (RT-ALS) technology. RT-ALS is a technique that allows for precise material modification at the atomic level by substituting one layer of a 2D material with another. This process typically involves the replacement of atomic layers in existing 2D materials via CVD or other thin-film deposition techniques (Figure a–c). During the fabrication process, various 2D materials, such as graphene and TMDs, were employed as substrates. The precise substitution of atomic layers was achieved by controlling synthesis conditions, such as temperature and gas flow (Figure d,e). Experimental and theoretical calculations revealed the impact of different atomic layer substitutions on material properties (Figure f). For instance, the substitution of sulfides in graphene can significantly alter its conductivity, while atomic layer substitution in TMDs can modulate their optical bandgap. This high-precision control enables materials to exhibit exceptional performance in fields such as electronic devices, optoelectronic devices, and catalytic reactions.

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(a) Schematic illustration of the RT-ALS process from monolayer MoS_2. (b) Schematics of the five key reaction steps for RT-ALS process (cartons from left to right). (c) Free energy of each step in (b) relative to that of the first step. (d) PL spectra of starting monolayer MoS₂, Janus MoSSe, and converted MoSe₂. (Insets) Spatially resolved PL mappings of MoS₂, Janus MoSSe, and converted MoSe₂ flakes at 1.85, 1.72, and 1.60 eV, respectively. (e) RT-ALS with programmable design in dipole/nondipole lateral heterostructures and multiheterostructure. (f) Conduction band minima and valence band maxima energies of MoS₂, Janus MoSSe, and MoSe₂ relative to vacuum, obtained from density functional theory (DFT) calculations. (a–f) Reproduced with permission from ref . Copyright 2021 Proceedings of the National Academy of Sciences of the United States of America. (g–i) OM images of samples on different parts of the same growth substrate. (j) Schematic diagram of the growth mechanism of Mo _x Re_(1–x)S₂-based heterostructures. (k) OM image of a typical Mo _x Re_(1–x)S₂-based heterostructure grown at 750 °C. (l) PL spectra acquired at the interface region of the heterostructure at (k). (g–l) Reproduced with permission from ref . Copyright 2023 Wiley-VCH GmbH.

During the one-step CVD growth process, cross-contamination between the two materials may occur. This possibility allows for the simultaneous achievement of controlled doping and the formation of alloy-based heterostructures by fine-tuning the growth kinetics. Shengxue Yang et al. reported the controllable synthesis of 2H-1T′ Mo _x R_(1–x)S₂ lateral heterostructures and their tunable optoelectronic properties. The 2H phase exhibits semiconductor characteristics, while the 1T′ phase demonstrates metallic properties. By combining these two distinct crystal phases, materials with unique optoelectronic properties can be formed. The researchers successfully synthesized heterostructures with varying 2H and 1T′ phase ratios using CVD technology, achieved by adjusting reaction gas flow, temperature, and deposition time. Optical microscopy and AFM were employed to characterize the composition and structure of the samples, revealing distinct differences in morphology and color contrast between the internal 1T′ Mo _x Re_(1–x)S₂ and external 2H Mo _x Re_(1–x)S₂ phases (Figure g–j). Further characterization using PL spectroscopy confirmed the composition and structure of the samples (Figure k,l), ultimately demonstrating the successful synthesis of 2H-1T′ Mo _x Re_(1–x)S₂ heterostructures. In the study of optoelectronic properties, it was found that as the ratio of the 1T′ phase increased, the light absorption intensity and photoconductivity of the 2H-1T′ Mo _x Re_(1–x)S₂ heterostructures were significantly enhanced. This indicates that adjusting the ratio of 2H to 1T′ phases can effectively modulate the optoelectronic performance of the material, providing new insights for the design and optimization of optoelectronic devices. However, the complexity of the synthesis process and the high cost of materials and equipment pose challenges. Future research should focus on simplifying the synthesis process and reducing costs to facilitate the practical application of these materials.

The study of these different preparation methods provides new tools and perspectives for exploring the properties of 2D materials and their potential applications. These innovative findings are expected to bring new opportunities and breakthroughs in the fields of energy, optoelectronics, and electronic devices in the future.

2D materials are of great interest due to their atomic-scale thickness and exhibit significant potential in flexible transparent electronics and extreme miniaturization. Although 2D materials can enable the creation of the thinnest devices, precise control of their lateral dimensions remains crucial.

David A. Muller et al. reported a novel method for synthesizing subnanometer-wide one-dimensional (1D) MoS₂ channels embedded within monolayer WSe₂ through dislocation catalysis (Figure a). The edges of these 1D channels are free from dislocations and dangling bonds, forming coherent interfaces with the embedded 2D matrix. The periodic dislocation arrays generated a 2D superlattice containing coherent 1D MoS₂ channels (Figure b). Due to the misalignment of bonds at the epitaxial interfaces, the growth of TMD heterostructures must include strain. To elucidate the strain distribution around the 1D channels within the 2D matrix, the researchers applied geometric phase analysis (GPA) to images obtained via atomic-resolution annular dark-field scanning transmission electron microscopy (ADF-STEM) (Figure c,d). The results indicated that the newly synthesized 1D channels remain coherent with the WSe₂ matrix and are modulated by strain, effectively preventing the formation of misfit dislocations along the channels. Furthermore, the growth of 1D channels is not restricted to interface dislocations between 2D materials. The researchers also explored other possible 2D material combinations through molecular dynamics simulations, finding that various combinations could also yield 1D channels (Figure e). This not only broadens the applicability of this structure but also provides new directions for future research and applications. The electronic band structure of these 1D channels suggests their potential for carrier confinement in direct bandgap materials, indicating significant promise for achieving ultimate length scales and enhancing electronic device performance.

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(a,b) Formation of 1D channels. (c) Geometric phase analysis (GPA) of the 1D MoS₂ with uniaxial strain components ε _xx (left) and ε _yy (right). (d) ADF-STEM image (left) and its ε _xx strain map (right) of a MoS₂ 1D channel formed from an intrinsic 5|7 dislocation in WSe₂, which matches the results found in channels arising from the heterojunction interface. (e) Molecular dynamics (MD) simulation of the 1D channel formation. (a–e) Reproduced with permission from ref . Copyright 2017 Spring Nature. (f–h) STEM-ADF of the entire 65 nm-long WS₂ quantum well and the corresponding strain distribution around the quantum well. (i) Growth mechanism of the WS₂ quantum well in WSe₂. (j) Energy barrier for S_Se substitution under different levels of compressive strain. (f–j) Reproduced with permission from ref . Copyright 2018 The American Association for the Advancement of Science. (k) Formation of ultralong MoS₂ nanochannels. (l) Low-magnification ADF-STEM image showing a straight MoS₂ channel of >600 nm inside single-layer MoSe_2. (m) Low-magnification ADF-STEM image (left) of a winding MoS₂ channels and the superimposed image (right) of the channel and its corresponding rotation map. (n) In-plane strain distribution near a misfit Mo-rich 5|7 dislocation and the corresponding contour plot for the sequence of substitution reaction. (o) A contour plot for the sequence (from blue to light gray) of substitution reaction along a zigzag MoSe₂–MoS₂ interface. (k–o) Reproduced with permission from ref . Copyright 2020 Spring Nature.

In the case of 2D lateral multiheterojunctions and superlattices, the current growth methods are unable to achieve the widths required for quantum confinement effects and quantum well applications, often resulting in rough and defective interfaces along with extensive chemical mixing. Kian Ping Loh et al. reported a growth method driven by misfit dislocations that allows for precise control of growth at the lattice-mismatched sulfide/selenide heterojunction interfaces. This method resulted in the successful fabrication of high-quality sub-2 nm-wide quantum wells within 2D semiconductors such as sulfides (WS₂ or MoS₂) and selenides (WSe₂ or MoSe₂). Characterization results from ADF-STEM indicate that the grown WS₂ quantum well exhibit smooth interfaces and minimal defects. This demonstrates that the dislocation-driven growth method significantly reduces interface roughness and chemical mixing issues (Figure f–h). Furthermore, DFT-calculated band structures reveal that these WS₂ quantum well exhibit type II band alignment, which is highly suitable for quantum well applications (Figure i,j). Type II band alignment signifies that electrons and holes are spatially separated in different materials, which facilitates effective carrier isolation and enhances optoelectronic performance.

The fabrication of nanoscale lateral heterostructures has long posed significant challenges, with researchers actively seeking methods to precisely control the spatial dimensions of the heterostructure regions. Zheng Liu et al. reported a strain-driven synthesis method that successfully produced ultralong MoS₂ nanochannels (Figure k). MoSe₂ was selected as the substrate material, and MoS₂ was synthesized under high-temperature conditions using CVD technology. During the experiment, the strain field in the samples was controlled by adjusting the gas flow and temperature. This strain field not only influenced the growth direction of MoS₂ but also promoted its extension along the grain boundaries, resulting in the formation of ultralong nanochannels (Figure l). Characterization results revealed that these nanochannels were single-layer MoS₂ and were uniformly distributed along the grain boundaries of the MoSe₂ monolayer, exhibiting excellent surface properties, morphology, and structural characteristics (Figure m). Additionally, to further understand the impact of the strain field on the growth of MoS₂ nanochannels, the research team conducted first-principles calculations. The computational results indicated that the strain field facilitated the coherent extension of MoS₂, leading to the growth of nanochannels along the grain boundaries (Figure n,o). This mechanism not only enhanced the quality of MoS₂ but also optimized its performance in catalytic applications.

By rationally designing and controlling the material composition, interface structure, and electrical properties, the customized preparation of 2D lateral heterostructures can be achieved, showcasing excellent performance in nanoelectronic and optoelectronic devices.

MoTe₂ is a TMD with multiple distinct phases. MoTe₂ in different phases possesses different crystal structures and electronic properties, providing an opportunity for the preparation of 2D lateral heterostructures with specific properties. Moon-Ho Jo et al. reported on the polymorphic integration of distinct metallic (1T′) and semiconducting (2H) MoTe₂ crystals within the same atomic planes by heteroepitaxy. The researchers selected high-quality MoTe₂ as the foundational material and successfully achieved the coexistence of the two phases within the same atomic layer by adjusting various growth conditions, such as temperature and atmosphere. Subsequently, a multilayer growth strategy was employed to progressively deposit different phases of MoTe₂ on the substrate (Figure a). Figure b presents representative SEM images that depict the heterostructures between the 1T′ and 2H-MoTe₂ crystals, which represent the first and second types of crystal variants, respectively. Various characterization results demonstrate that the successful coexistence of the metallic and semiconductor phases within the same atomic layer resulted in a highly consistent multiphase structure (Figure c). The study also indicates that, despite the complexities and challenges encountered during the growth process, this synthesis method is applicable to MoTe₂. Furthermore, it can be extended to the multiphase integration of other TMDs, thereby further expanding the applications of 2D materials. Following this, Liying Jiao et al. employed a phase diagram-based growth method that facilitated the chemical synthesis and integration of 2D electronic components. MoTe₂, recognized for its exceptional electronic properties and adaptability, was chosen as the active material for electronic devices in this study. The phase-mode growth technique (Figure d,e), which allows for precise control of atomic layer growth under appropriate conditions, was utilized to ensure the formation of covalent bonds between the components (Figure f). This method enables the simultaneous generation of electronic components with various functionalities, such as semiconductor channels and metallic electrodes, thereby avoiding defects and impurities that may be introduced during traditional stepwise manufacturing processes (Figure g).

6.

(a) Sequential growth scheme for coplanar heteroepitaxy of 1T′/2H MoTe₂ polymorphs. (b) Representative SEM images of the first (left) and second (right) types of crystallographic variants in the heterostructures between 1T′- and 2H-MoTe₂ crystals. (c) Low-magnification TEM image of 1T′/2H-MoTe₂ and their SAED pattern (inset). (a–c) Reproduced with permission from ref . Copyright 2017 Spring Nature. (d) Optical image of the MoO _x pattern (left) and the MoTe₂ heterophase pattern after tellurizing the oxide pattern (right). (e) Raman mapping images of the heterophase pattern with 231 cm^–1 (E_2g mode of 2H MoTe₂, red) and 160 cm^–1 (A_g mode of 1T′ MoTe₂, blue) peak intensities. (f) Typical STEM image of an atomically straight boundary of 2H/1T′ MoTe₂. Inset: large-scale SEM image of the heterophase structures. (g) STEM images of 2H (left) and 1T′ (right) MoTe₂ near the boundary. (d–g) Reproduced with permission from ref . Copyright 2019 Spring Nature. (h) The schematic diagrams for the in-plane 2D epitaxy synthesis of wafer-scale single-crystalline 2H MoTe₂ thin film. (i) Optical image of a 2H MoTe₂ nanoflake assembled in the center of the 1T′ MoTe₂ wafer as a seed to induce the phase transition and recrystallization (top) and the wafer after intermediate growth at 650 °C for 2 h (bottom). Inset shows the seed crystal with a needle probe-punched hole. (j) The cross-sectional HAADF-STEM image and zoomed-in image of the seed region. (k) Electron backscattered diffraction (EBSD) characterization of the wafer-scale single crystalline MoTe₂. (h–k) Reproduced with permission from ref . Copyright 2021 The American Association for the Advancement of Science. (l) Schematic diagrams of the in-plane 2D epitaxy of single-crystal 2H-MoTe₂ on a 3D architecture. (m) Cross-sectional HAADF-STEM images at the interface of the 2H-MoTe₂ film and a fin architecture. (l,m) Reproduced with permission from ref . Copyright 2022 Spring Nature.

Growing wafer-scale single-crystal 2D semiconductors on insulating substrates presents significant challenges. Yu Ye et al. reported a novel method for the large-area epitaxial growth of single-crystal 2H MoTe₂ films on amorphous insulating substrates. This method utilizes a special seed layer to control the growth direction and crystal structure of the films, resulting in the formation of high-quality single crystals over a substantial area. Figure h illustrates the synthesis process of wafer-scale microcrystalline 2H MoTe₂ films. Figure i presents the optical image of 2H MoTe₂ nanosheets assembled at the center of a 1T′ MoTe₂ wafer, serving as a seed for inducing phase transformation and recrystallization. This image also displays the wafer’s optical characteristics after a 2 h intermediate growth at 650 °C, with an inset showing the seed crystal with needle-like probe punctures. The selenization treatment is a critical step for inducing in-plane growth. In this process, the substrate is placed in a high-temperature furnace, where selenium gas is introduced through a vapor-phase reaction. This reaction facilitates the transformation of material surrounding the seed crystal, ultimately forming MoTe₂ crystals. Upon completion of the epitaxial growth, various characterization techniques were employed to demonstrate that the resulting single-crystal 2H MoTe₂ films exhibit excellent crystal structure and uniformity, confirming their suitability for high-quality, single-phase materials (Figure j,k).

The integration of 2D semiconductors with other materials can enhance material functionality and device performance. As a result, the widespread adoption of 2H-MoTe₂ in heterogeneous integration is possible due to its lateral integration with highly lattice-mismatched planar crystals and arbitrary three-dimensional (3D) architectures (Figure l). Yu Ye et al. reported a novel synthetic route that achieves in-plane 2D epitaxial growth via a phase transition, enabling the synthesis of 2H-MoTe₂ films on various substrates, including silicon, GaN, 4H-SiC, and sapphire. In-plane 2D epitaxy is like a diffusion process, where the 2H single-crystal domain can expand and even span arbitrary 3D structures as long as there is a 2H/1T′ interface in a continuous 1T′ film. To exploit this possibility, they prepared silicon fin structures covered with 20 nm atomic layer deposition (ALD) Al₂O₃. Observations revealed that during the growth process, the epitaxially grown 2H-MoTe₂ stacked vertically onto the fin structure, with molybdenum and tellurium atoms at the interface rearranging and advancing along the neighboring 2H-MoTe₂ phase (Figure m). Compared to conventional epitaxial growth that requires substrates with matching lattice structures, this new synthetic route enables the direct synthesis of single-crystal films on substrates with different crystal symmetries, lattice constants, and three-dimensional structures. This method overcomes the limitations of lattice matching and surface flatness, providing new avenues for integration with other functional materials or structures, thus facilitating the fabrication of integrated devices.

By fabricating 2D lateral heterostructures on MoTe₂ with different phases, the interface charge transfer, band structure, and transport properties of the heterostructures can be modulated. Such control of heterostructure allows for a greater range of choices and possibilities in various applications, such as optoelectronic devices, sensors, and energy storage.

3.3. Perovskites-Based

As an emerging family of tunable semiconductors, 2D halide perovskites, due to their inherent soft lattice structure, allow for greater tolerance of lattice mismatches, making them promising candidates for heterostructure formation and semiconductor integration. , In recent years, researchers have developed lateral heterostructures of 2D halide perovskites by manipulating their structures and compositions. With the rise of research on lateral heterostructures of 2D perovskites, the synthesis of these heterostructures has evolved from early studies that focused on single-material heterostructures to successful experiments involving multiple materials, gradually advancing to the stages of interface engineering and performance optimization.

Dou et al. presented an efficient synthesis strategy via a solution-phase sequential growth approach. The study introduces rigid π-conjugated organic ligands to inhibit in-plane ion diffusion in 2D halide perovskites, which contributes to the fabrication of highly stable and tunable lateral epitaxial multiheterostructures and superlattices. There is a possibility of damage because of the instability of the halide perovskites in successive growth steps. In the experiments, it was observed that epitaxial growth occurred in the edge regions of the growing crystals, resulting in the formation of concentric square or rectangular 2D lateral heterostructures directly on SiO₂/Si substrates. Subsequently, π-conjugated ligands were introduced, leading to the final formation of cubic heterostructures. Comparative analysis revealed that the mutual diffusion of Br^– and I^– within the heterostructures was largely suppressed. In contrast, halide heterostructures exhibited a faster mutual diffusion process when utilizing widely used alkyl ligands (Figure c–h). By using molecular dynamics simulations, it can be concluded that in order to stabilize the interface and inorganic framework more effectively, it is necessary to select larger and more rigid conjugated organic ligands. On the other hand, if the selection of smaller organic ligands leads to a softer inorganic lattice, the mismatch of halide sizes can be accommodated and the halide interdiffusion can be facilitated (Figure a,b). Subsequent interface characterization of the lateral heterostructures was conducted, achieving higher spatial resolution at the heterostructure interfaces (Figure j). Analysis of multiple samples indicated that periodic interface misfit dislocations and relaxation mechanisms formed through rippling are expected to occur in order to alleviate accumulated interface strain and stabilize the heteroepitaxy. Based on atomic measurements, it can be concluded that interface dislocations and rippling can effectively maintain coherence at the heterointerface, thereby enhancing control over interface integrity and providing unique insights into the related electronic and optoelectronic properties (Figure i). On this basis, they prepared a series of multiheterostructures and even superlattices by combinations of different halides, metal cations and organic ligands. Moreover, apart from the two-segment concentric heterostructures, the synthesis of (2T)₂PbI₄-(2T)₂PbBr₄ × n (n = 2, 3, 4) superlattices by multiple repeated growth steps has been demonstrated with very high synthetic yields (Figure k,l).

7.

(a,b) Snapshots from the molecular dynamics simulations at 298 K (a) and 800 K (b) for (2T)₂PbI₄-(2T)₂PbBr₄ (left) and (BA)₂PbI₄-(BA)₂PbBr₄ (right) showing the interface between each perovskite domain. (c,d) Optical (c) and photoluminescence (d) images of a (2T)₂PbI₄-(2T)₂PbBr₄ lateral heterostructure. (e,f) Optical (e) and photoluminescence (f) images of a (BA)₂PbI₄-(BA)₂PbBr₄ lateral heterostructure. (g) Photoluminescence image of the (2T)₂PbI₄-(2T)₂PbBr₄ lateral heterostructure after 1 h of heating at 100 °C. (h) Photoluminescence image of the (BA)₂PbI₄-(BA)₂PbBr₄ lateral heterostructure after 1 h of heating at 100 °C. (i) AFM image of the one-pot (2T)₂PbI₄-(2T)₂PbBr₄ lateral heterostructure with clear ripples. (j) TEM characterization of the (2T)₂PbI₄-(2T)₂PbBr₄ heterostructure. (k, l) Schematic illustrations of the (2T)₂PbI₄-(2T)₂PbBr₄ × n lateral superlattice (k; left to right, n = 2, n = 3, n = 4) and (2T)₂SnI₄-(2T)₂PbI₄-(2T)₂PbBr₄ lateral multiheterostructure (l). Top images are optical and bottom images are photoluminescence. (a–l) Reproduced with permission from ref . Copyright 2020 Spring Nature. (m) Schematic illustration of selective anion-exchange process. (n) Photograph of the chessboard-like pattern obtained through area-selective anion-exchange. (o) PL image of the chessboard-like pattern of CsPbBr₃–CsPbI₃ heterostructures. (p) PL taken from the original film and the area after anion exchange. (m–p) Reproduced from ref . Copyright 2021 American Chemical Society.

All-inorganic lead halide perovskites have attracted research interest due to their excellent stability. Wang et al. reported a strategy to grow large-area monocrystalline all-inorganic perovskite thin films via a one-step CVD process and further patterning them into heterostructure arrays. Due to the exceptional stability of all-inorganic lead halide perovskites, CsPbBr₃ microcrystalline domains were able to grow on a mica substrate with good epitaxial relationships, ultimately resulting in large-area, high optical quality single-crystal films. Subsequently, a layer of poly­(methyl methacrylate) (PMMA) was spin-coated onto the CsPbBr₃ films, followed by electron beam lithography (EBL) to generate the desired patterns, thereby facilitating spatially selective anion exchange. Next, anion exchange was performed using a CsI methanol solution, transforming the CsPbBr₃ films into CsPbI₃, which resulted in a CsPbBr₃–CsPbI₃ lateral heterostructure array exhibiting spatially modulated photoluminescent properties (Figure m–p).

2D halide perovskite heterostructures have received significant attention due to their exceptional optoelectronic properties and good environmental stability, becoming a focal point of research in the field of materials science. With the continuous advancement of synthesis techniques, including the application of new methods such as solution processing and vapor deposition, notable achievements have been made in enhancing the quality and uniformity of the materials. Furthermore, researchers are dedicated to improving the long-term stability of these materials under various environmental conditions and optimizing the heterojunction structures to enhance carrier separation efficiency and transport performance. These advancements have opened new possibilities for the application of 2D halide perovskites in flexible electronics, optical communications, and other emerging fields.

3.4. Organic-Based

Apart from the already explored lateral heterostructures based on graphene, TMDs and halide perovskites, there are still very few studies on the lateral epitaxial growth of 2D organic heterostructures, which mainly focus on the inorganic components. In the development of semiconductor science, optoelectronics, and photonic integrated circuit technology, organic single crystals, characterized by weak intermolecular interaction force, high crystal structure diversity and good solubility, have occupied an important position. Particularly, 2D organic single crystals have attracted considerable attention as building blocks for optoelectronic devices. Because of the close relationship between 2D organic single crystals and 2D organic lateral heterostructures (2D OLHs), they play a crucial role in the preparation of 2D OLHs. Thus, organic 2D crystals can make full use of the diversity of organic molecules for flexible combination to form a variety of lateral heterostructures. However, the formation of 2D OLHs is only theoretically simple. In fact, the growth of 2D OLHs is still a difficult problem due to lattice mismatches, passivation edges and other conditions.

Jiwoong Park et al. employed the technique of laminar assembly polymerization (LAP) to conduct polymerization reactions at the interface of pentane and water, thereby synthesizing phthalocyanine polymer films with high uniformity and single-layer thickness. In this study, 2D monolayer materials were designed based on porphyrin structural units. A metal–organic framework (MOF) utilizing Cu²⁺ as the linking agent and a covalent organic framework (COF) utilizing terephthalaldehyde as the connecting entity were developed (Figure a). The polymerization process can be divided into three stages: injection, self-assembly, and polymerization (Figure b,c). Initially, the phthalocyanine monomer was dissolved in pentane and then slowly injected into the aqueous phase, resulting in the formation of a monolayer polymer through interfacial polymerization. Subsequently, the formed monolayer polymer was assembled in a specific sequence using laminar assembly techniques to construct the MOF or COF. By selecting different monomers and polymerization chemistries, the researchers were able to directly control the lattice structure and optical properties of these 2D films. Characterization of the synthesized 2D polymers indicated that the prepared 2D polymer films were monolayered and exhibited a uniform, smooth surface (Figure d–g). Furthermore, the synthesized 2D polymers were combined with molybdenum disulfide to form mixed superlattices, which were subsequently utilized in the manufacturing of capacitors. Liao et al. reported a two-step strategy based on a binary solvent system, successfully fabricating Pe-PeO and PeO-Pe 2D OLHs through the combination of liquid-phase and vapor-phase growth. During the preparation process, the nucleation and sequential growth of Pe and PeO crystals can be selectively controlled by adjusting the differences in solubility or sublimation points (Figure h). The single-component α-phase Pe and PeO crystals were prepared by using the liquid-phase growth method on the premise of overcoming the lattice mismatch and passivated edges. In binary solvent system, PeO nucleates first and then epitaxically grows Pe to form Pe-PeO 2D OLHs. The structure of Pe-PeO heterostructures was inverted by a vapor-phase growth processthe microspacing in-air sublimation (MAS) method, and finally PeO-Pe lateral heterostructures was formed on the top substrate. Characterization results indicate that Pe-PeO and PeO-Pe 2D OLHs with excellent performance have been successfully fabricated (Figure i).

8.

(a) Schematic of monolayer 2D polymers (2DPs) and corresponding chemical structures of the molecular precursors. (b) Schematic of a LAP reactor and in situ optical characterization apparatus. MSP, microsyringe pump. (c) Schematic of the LAP synthesis that involves three phases. (d) False-color image of 2DP I/2DP III/2DP II lateral junctions. (Inset) Schematic of generating lateral heterostructures of 2DP I/2DP III/2DP II generated using three nozzles in LAP. (e) False-color images of 2DP I/2DP II lateral junctions with tunable stripe widths. (f) False-color image of overlapped 2DP I and 2DP II stripes. (g) AFM height image of monolayer 2DP I. (a–g) Reproduced with permission from ref . Copyright 2019 The American Association for the Advancement of Science. (h) Schematic illustrating the two-step strategy for synthesizing OLHs from Pe (yellow spheres) and PeO (red spheres), involving a liquid-phase growth method to create Pe-PeO, followed by a vapor-phase growth method to produce PeO-Pe. (i) FM images of Pe-PeO lateral heterostructures and PeO-Pe lateral heterostructures deposited on SiO₂/Si. (h,i) Reproduced with permission from ref . Copyright 2023 Nature Spring.

As a new material structure with potential application prospects, the development process of 2D organic lateral heterostructures has experienced from early material synthesis to modern property modulation and application research. Its research has provided new research directions and application prospects for the fields of materials science and nanotechnology. Particularly, the controllable and sequential integration of organic 2D crystals with tunable optical or electrical properties has expanded the range of lateral heterojunction materials and pointed out new directions for the study of optoelectronic devices. However, the growth of 2D organic lateral heterojunction still faces many challenges, such as crystal quality control and interface engineering. Researchers need to explore new synthesis methods, property modulation mechanisms, and potential application areas further to drive the development of this field and bring about new opportunities.

4. Applications of Lateral Heterostructures

In recent years, research on 2D lateral heterostructures has expanded beyond the scope of preparation and delved into an in-depth exploration of their physical properties. With the continuous deepening of understanding of these properties and the constant improvement of control techniques, this will greatly promote the development of 2D lateral heterostructures in practical applications and facilitate scientific research and technological innovation in related fields. ,, Layered semiconductor materials, particularly TMDs, are regarded as some of the most promising new materials for chips. Lateral junctions composed of various layered semiconductor materials-such as homojunctions, heterostructures, hybrid multilevel junctions, and superlattice junctions-exhibit a range of tunable electrical and optical properties. These advancements provide new research freedoms for the development of next-generation high-performance electronic devices and establish novel research strategies for creating chips that transcend traditional semiconductor materials through innovative principles and structures. −

Liying Jiao et al. reported a phase-patterned growth technique utilizing molybdenum diselenide (MoTe₂) as the active material, successfully achieving covalent connections among device components. Compared to traditionally manufactured devices, the MoTe₂ field-effect transistors (FETs) synthesized using this technique exhibit p-type semiconductor characteristics, with higher mobility (Figure a), lower contact barrier (Figure b) and neater surface (Figure c). In addition to the back-gated FETs, buried local gates and high-κ hafnium oxide (HfO₂) transistors were introduced to optimize gate control. The synthesized FETs demonstrated an on/off current ratio of ∼10⁵, mobility of up to ∼130 cm² V^–1 s^–1 and subthreshold swing down to ∼69 mV dec^–1 (Figure d). Subsequently, the authors explored the chemical synthesis of integrated devices. During the selenization of the chips at 650 °C, channel materials, contacts, and interconnections were formed simultaneously (Figure e,f), successfully producing centimeter-scale logic inverters and RF transistor arrays (Figure g). Based on these advantages, the researchers demonstrated the potential of this method for applications such as ultrashort gate FETs, 3D integration, and flexible electronic devices. Initially, the introduction of carbon nanotubes (CNTs) as gate electrodes facilitated the construction of MoTe₂ FETs with ultrashort gate lengths (Figure h), resulting in increased switching speeds and reduced power consumption. Furthermore, heterogeneously interconnected MoTe₂-based electronic devices were synthesized at different vertical levels (Figure i), successfully creating an array of MoTe₂ FETs (Figure j) and enhancing device integration. Lastly, self-supporting films were obtained by stripping the chemically synthesized device array from the original substrate using polyvinylpyrrolidone (PVP) and polyvinyl alcohol (PVA) films as dielectrics (Figure k). Overall, this research opens new avenues for the application of 2D materials in electronic device manufacturing, with the potential to advance the development of more efficient and flexible electronic devices.

9.

(a) Typical I _ds–V _gs curves for MoTe₂ FETs with a 1T′ contact measured at various bias voltages. Insets: optical images (lower) and Raman mapping images (upper) for the two FETs. (b) Barrier heights (Φ_b) measured at different gate voltages for FETs with a 1T′ contact. The lavender bands represent the estimated Schottky barrier height. Insets: energy band diagrams for 1T′ contacts to 2H MoTe₂ layers. (c) Surface roughness of the MoTe₂ channels in Pd-contacted (red column) and chemically synthesized (blue column) devices. Error bars represent standard deviation. Insets: AFM images of the two kinds of channels. (d) I _ds–V _gs curves for the chemically synthesized MoTe₂ FETs with 12 nm-thick HfO₂ gates. Inset: schematic illustration of the cross-section of the FET. (e) Illustration of a chemically synthesized inverter. (f) Batch-synthesized devices (∼1500) on a centimeter scale. (g) SEM image of a MoTe₂ inverter. Inset: optical image of the inverter. (h) Schematic of a chemically synthesized 1T′/2H MoTe₂ FET with a CNT gate. (i) Illustration of 3D integrated circuit constructed by the repeated growth of phase-patterned MoTe_2. (j) Cross-sectional TEM image of the multilayered structure in a bilayer circuit. Inset: enlarged images of the first (L1) and second (L2) MoTe₂ layers. (k) Self-supporting film with an array of 144 stretchable transistors (left) and optical and Raman mapping image (right) of a 1T′/2H MoTe₂ junction on PVP/PVA film, respectively. (a–k) Reproduced with permission from ref . Copyright 2019 Spring Nature. (l) Optical images of the 2H-MoTe₂ single-crystal domain grown on 3D fin architectures over time. The 2H-MoTe₂ domain expands over time and spans the 3D fin architectures. (m) Raman mappings of the representative Raman peaks of the 2H-MoTe₂ E_2g ¹ and 1T′-MoTe₂ A_g modes. (n) Local tensile strain deformations and dislocations found in the 2H-MoTe₂ film are marked by the white arrows and triangles, respectively. (o) Photograph and optical image of the wafer-scale 2H-MoTe₂/Si p–n heterojunction array. (l–o) Reproduced with permission from ref . Copyright 2022 Spring Nature.

Yu Ye et al. designed a synthesis route for direct heteroepitaxy of semiconducting 2H-MoTe₂ films on arbitrary substrates with different crystal symmetries, lattice constants and 3D architectures. By preparing silicon fin structures covered with 20 nm atomic layer deposition (ALD) Al₂O₃ and tellurizing sputtered molybdenum film, they successfully obtained the continuous polycrystalline 1T′-MoTe₂ film on the fin substrates. With the supply of tellurium at 620 °C, 2H-MoTe₂ single-crystal domains nucleated in the surrounding 1T′ background and grew through the in-plane 2D-epitaxy process and across the fin structures (Figure l). The crystallinity of the resulting film was characterized by Raman spectroscopy and STEM, and it was found that the 2H-MoTe₂ film grown over the fin structure was uniform (Figure m), and there were a few dislocations around the fin structure (Figure n), locally accommodating strain. Furthermore, they observed that the in-plane 2D-epitaxy process via phase transition was not limited by lattice matching and planar surfaces. And the heteroepitaxial integration of semiconducting 2H-MoTe₂ films onto arbitrary substrates can give rise to enhanced device performances. Therefore, a vertical p–n heterojunction array was fabricated by integrating the 2H-MoTe₂ film (Figure o) with a 2.5 cm silicon wafer. This approach enabled the heterogeneous integration with other functional materials or structures, providing new possibilities for the manufacturing of integrated devices.

Soon-Yong Kwon et al. proposed a scalable synthetic strategy that utilizes thermally stable 2D metal PtTe₂ as a substrate to facilitate the lateral growth of monolayer MoS₂, thereby forming a PtTe₂–MoS₂ metal–semiconductor junction (MSJ) (Figure a). Through the application of gate bias, it was discovered that the source terminal (either Ti or PtTe₂) determines the performance of the FETs with asymmetric contacts. This finding indicates that the electrical characteristics of barriers can be systematically evaluated by controlling the interface. Traditional 2D materials face challenges regarding thermal and chemical stability, which hinder the realization of high-quality edge contacts (Figure d). To address this issue, researchers adopted a scalable synthesis approach, growing MoS₂ on PtTe₂ through techniques such as thermal deposition, achieving high-quality edge contacts and establishing a seamless interface between PtTe₂ and MoS₂. The developed PtTe₂–MoS₂ MSJ features a cleaner interface, effectively preventing further metallization on the MoS₂ surface, resulting in a simple contact component that is solely edge-related (Figure b,c). Observations indicate that the resulting films exhibit excellent quality and thermal stability (Figure e,f). This method also enables the large-scale fabrication of device arrays on wafers while maintaining consistent performance. The seamless atomic-level interface significantly reduces the Schottky barrier, and devices utilizing the PtTe₂–MoS₂ MSJ demonstrate notably decreased contact resistance (Figure g,h). Compared to conventional vertical metal contacts, this advancement further enhances carrier mobility and overall performance. The advantages of this approach in achieving low contact resistance and ultrashort transport lengths open new directions and possibilities for the design and integration of future 2D devices.

10.

(a) Schematic of a device with asymmetric Ti/Au and PtTe₂ electrodes contacted to a monolayer MoS₂. (b) Cross-sectional illustrations of resistance networks of monolayer MoS₂-based MSJ with atomically stitched PtTe₂ lateral contact. (c) Comparison of band alignments with different Schottky barrier heights (SBHs) and Schottky barrier width (SBW) with respect to theMoS₂ conduction band (CB) and valenceband (VB) edges for PtTe₂–MoS₂ heterostructure. (d) Cross-sectional illustrations of resistance networks of monolayer MoS₂-based MSJ with top-contact with Ti/Au. (e) Sheet resistance (R _sh) of as-grown PtTe₂ thin film as a function of the film thickness (H), characterized by four-probe method. (f) (left) XPS-derived atomic ratio of the thin film, showing the nearly ideal stoichiometry of PtTe₂ (at.% (Te/Pt) ≈ 2; dashed red line) irrespective toT up to 825 °C, (right) R _sh of thin films as a function of annealing T, with R _sh ∼ 467 Ω/sq (for T = 500 °C) indicated with a blue dashed line. (g) Representative I _ds–V _ds characteristics ofmonolayer MoS₂ FET with symmetric PtTe₂ and Ti contact electrodes depending on V _g. (h) I _ds–V _g characteristics of corresponding devices on linear (symbols; right) and logarithmic scale (lines; left). (a–h) Reproduced with permission from ref . Copyright 2022 Spring Nature. (i) Schematic diagram of the suspended H-type sensing device. (j) Schematic diagram of the electrical measurement circuit based on the H-type device. (k) Schematic diagram of the thermal measurement circuit based on the H-type sensing device. (l–p) The measured thermal conductivities of samples 1 to 6, respectively, in two opposite heat flow directions within a temperature range of 273 to 378 K. (q) Schematic diagram of the MoSe₂–WSe₂ lateral heterostructure models built for MD simulation with pure materials (I and III) and interface (II). (r) Vibrational density of states (vDOS) for θ = 0° in two directions; (s) Normalized TR ratio (η) and spectra overlap ratio (H) plotted with angle (θ). (i–r) Reproduced with permission from ref . Copyright 2022 The American Association for the Advancement of Science.

Xing Zhang et al. fabricated a MoSe₂–WSe₂ lateral heterojunction monolayer device, designed as an H-type sensor (Figure i), aimed at precisely measuring its electrical rectification (ER) and thermal rectification (TR) characteristics. In the experiments, the monolayer MoSe₂–WSe₂ lateral heterojunction exhibited efficient diode behavior, allowing researchers to switch between electrical and thermal measurement modes by altering the external circuit. Initially, the electrical transport across the interface was characterized using a four-probe method (Figure j). By measuring the drain-source current–drain-source voltage (I _ds–V _ds) curves of various samples under zero back-gate voltage, it was observed that the slanted interface structure resulted in varying ER ratios. Additionally, by investigating the thermodynamic behavior of charge carriers within a specific temperature range, it was found that the influence of temperature on current and rectification ratio was closely related to the angle of the interface. Notably, the reverse current was significantly affected by temperature changes, leading to a decrease in the ER ratio. The role of “heater” and “detector” was interchanged between the two sensors (Figure k), allowing for the measurement of the thermal conductivity of the monolayer MoSe₂–WSe₂ lateral heterostructure in two opposing heat flow directions. The results indicated that the working diode, with atomic-scale thickness, achieved a greater thermal conductivity at elevated temperatures. Consequently, the thermal conductivities of six samples were plotted (Figure l–p). The experimental results demonstrated that the TR effect was dependent on the angle between the heterojunction interface and the heat flow direction. By simply adjusting the angle q, the TR factor could be modulated between its maximum value and zero, providing an effective means for actively controlling phonon transport within the monolayer heterostructure. To elucidate the physical mechanisms behind TR, nonequilibrium molecular dynamics (NEMD) simulations were employed. The schematic representation of the MoSe₂–WSe₂ lateral heterostructure was divided into pure materials (I and III) and interface (II) (Figure q). The findings revealed that heat preferentially transferred from the MoSe₂ domain to the WSe₂ domain, consistent with experimental results. Given that the contribution of the thermal conductivities of individual MoSe₂ and WSe₂ with temperature variation to the TR effect was minimal, attention shifted to the phonon spectra mismatch of regions I and III in both the J⁺ and J^– directions (Figure r). The spectral overlap (S) was subsequently computed to quantify the matching of phonon bands. Experimental data indicated that a larger spectral overlap corresponded to a higher thermal conductivity. Higher thermal conductivity was achieved due to TR effects induced by local temperature gradients at elevated temperatures. Furthermore, by rotating the angle of the monolayer heterojunction interface, the TR factor could be adjusted from its maximum value down to zero. To explain the angle-dependent TR effect, seven different models were established with the angle q varying from 0° to 90°, and their TR ratios, phonon spectra, and spatial energy distributions were calculated. The results indicated that the TR ratio monotonically decreased with increasing angle q, ultimately vanishing when the interface was parallel to the heat flow direction (Figure s). This discovery paves the way for the design of novel nanoelectronic devices with enhanced thermal dissipation capabilities.

In the context of the failure of Moore’s Law, new avenues must be explored to achieve higher performance in electronic devices. The exceptional electron transport properties and tunable band structures of 2D lateral heterostructures offer promising opportunities for the design and fabrication of advanced nanoelectronic devices. −

The 2D lateral heterostructures exhibit significant potential in the optoelectronic field. ,,,,− With the advancement of information technology, the applications of optoelectronic devices in communications, energy conversion, and sensing are becoming increasingly widespread. The tunable band structures and active surface sites of 2D lateral heterostructures provide unique advantages in optoelectronic devices. Anlian Pan et al. reported the growth of 2D layered semiconductor heterostructures achieved through controlled layer-selective atomic substitution, focusing on the compositional regulation of MoS₂–MoS_2(1–x)Se_2x . Microscopic structural characterization revealed that these heterostructures possess well-defined interfaces, with the composition of the monolayer regions transitioning smoothly from MoS₂ to MoSe₂ while maintaining high-quality crystallinity. Photoluminescence and Raman imaging studies indicated that the monolayer regions of the heterostructures exhibit tunable optical properties. This research offers a straightforward pathway for the development of high-quality layered semiconductor heterostructures, demonstrating broad application potential in integrated nanoelectronic and optoelectronic devices. Yongjun Tian et al. investigated the synthesis and properties of 2D heterostructures composed of different layered semiconductors. The researchers successfully prepared large-scale lateral bilayer (LBL) WS₂–MoS₂ heterostructures using a two-step chemical vapor deposition method. The results demonstrated that the optoelectronic detectors based on LBL WS₂–MoS₂ heterostructures exhibited exceptionally high photodetectivity and response rates, significantly outperforming single-crystal MoS₂ and WS₂. These outstanding performances position LBL WS₂–MoS₂ heterostructures as promising candidate materials for the next generation of optoelectronic devices.

2D lateral heterostructures can also be applied in the field of flexible electronics. With the rise of smart wearable devices, flexible sensors, and bendable electronic products, the demand for flexible electronic devices has been increasing significantly. 2D heterostructures based on the combination of TMDs and transition metal oxides (TMOs) have aroused growing attention due to their integrated merits of both components and multiple functionalities. Kai Liu et al. proposed a novel strategy for the lithography-free fabrication of TMD-TMO heterostructures, enabling the development of high-performance sensors. These sensors demonstrated exceptional performance in terms of bending and flexibility, showcasing immense potential for future applications in portable and wearable electronic devices. The inherent flexibility and bendability of 2D materials establish a foundation for the fabrication of flexible electronic devices, while the unique properties of 2D lateral heterostructures introduce new possibilities in the realm of flexible electronics.

Additionally, 2D lateral heterostructures exhibit excellent catalytic activity and stability in electrochemical catalytic reactions, making them suitable for the fabrication of efficient devices for water electrolysis, fuel cells, and supercapacitors in energy conversion and storage. ,, Zheng Liu et al. reported the synthesis of ultralong MoS₂ nanotubes within monolayer MoSe₂, where the nanotubes can reach lengths of several micrometers and widths ranging from 2 to 30 nm, formed at internal grain boundaries (GBs). Research indicated that the spontaneous strain of MoS₂ nanotubes further enhances the hydrogen production activity at the grain boundaries, providing new insights for the design of efficient TMD catalysts based on grain boundaries. Furthermore, Zesheng Li et al. conducted theoretical studies on various systems, including seven monolayer XP₃ (X = Al, Ga, Ge, As, In, Sn, Sb) and their combined vertical and lateral heterostructures. The study demonstrated that the lateral heterostructure AlP₃–GaP₃ possesses all the ideal characteristics required for photocatalytic water splitting, positioning it as a promising photocatalyst for this reaction. This research offers new strategies for the design and fabrication of high-performance photocatalysts for water splitting, thereby advancing the application of lateral heterostructures.

2D lateral heterostructures demonstrate significant potential in various application domains, contributing to advancements in information processing systems, sensors, and bioelectronic actuators. By skillfully combining different 2D materials, these devices are capable of achieving efficient computational capabilities and outstanding performance. As materials science and interface engineering technologies continue to evolve, it is expected that these heterostructures will play an increasingly important role in future electronics and nanotechnology, fostering innovation and transformation across multiple industries. In summary, 2D lateral heterostructures possess important application prospects for the development of information technology and electronic devices in the post-Moore era. Their unique properties and advantages offer new ideas and solutions to address the challenges posed by the limitations of Moore’s Law, thereby driving innovation in this field. With the deepening research into 2D materials and heterostructures, it is believed that 2D lateral heterostructures will assume an even more critical role in the post-Moore era.

5. Outlook and Challenge

As the development pace of silicon-based CMOS integrated circuits slows down, the necessity and urgency for the development of new chip materials, innovative device structures, integrated processes, and specialized system architectures in the post-Moore era have increased significantly. Researchers have begun to actively explore new materials and structures to address this challenge. Meanwhile, notable progress has also been made in areas such as layered semiconductors, lateral epitaxial heterostructures, and integrated biochips in the development of advanced devices. These advancements provide a solid foundation for achieving more energy-efficient and high-speed signal processing, storage, detection, communication, and system functions. Through in-depth exploration of these emerging materials and devices, semiconductor technology in the post-Moore era is expected to attain higher performance and a wider range of applications, thereby driving innovation and development across various fields (Figure ). ,

11.

Development path of 2D lateral heterostructures in device applications.

In this context, 2D lateral heterostructures have garnered significant attention due to their unique electronic and optical properties. Through the vertical stacking of various 2D materials to create heterostructures, both the functional properties of the materials are enhanced, and precise control over the interactions of electrons and photons is achieved. This structure facilitates more efficient energy transfer, flexible bandgap tuning, and enhanced quantum effects, thereby promoting the development of next-generation ultralow-power electronic devices, wearable technology, and high-performance optoelectronic applications. Furthermore, 2D lateral heterostructures provide new possibilities for the design of quantum computing and novel sensors, showcasing immense potential for various applications. This innovative material design not only paves the way for technological breakthroughs in the post-Moore era but also opens new avenues for achieving higher-performance devices. However, numerous difficulties and challenges are still encountered during the fabrication process.

• (1)Material integrity and purity: nsuring the integrity and purity of materials during the fabrication of 2D lateral heterostructures presents a significant challenge. The stringent requirements for fabrication processes and equipment are necessary to prevent contamination or the introduction of impurities, which can adversely affect the structural and functional properties of the heterostructures.
• (2)Interface quality control: The interfaces between different 2D materials often face challenges such as lattice mismatches or discontinuities in electronic energy levels. Precise control over the interface quality is critical to optimizing the performance of the heterostructures and ensuring reliable device functionality.
• (3)Structural stability: Due to the inherent flexibility and thin-film nature of 2D materials, fabricated lateral heterostructures are particularly susceptible to structural instability. Stress and thermal expansion can lead to deformation or degradation, negatively impacting the performance and lifespan of devices. Addressing these issues requires careful design and stabilization strategies.
• (4)Exploration of intrinsic properties: Despite the development of dozens of 2D material structures, the exploration of their intrinsic physical properties remains limited. This underdevelopment is primarily constrained by the scarcity of certain materials, which hinders their broader utilization in studying novel physical phenomena and applications.
• (5)Development of novel devices: The creation of new optoelectronic devices based on 2D lateral heterostructures represents a critical area of research. Beyond the design of individual devices, the integration of these heterostructures into complex electronic circuits poses a significant challenge. Such advancements are essential for achieving scalable and efficient systems in next-generation technologies.

Despite numerous challenges, the significant potential of 2D lateral heterostructures across various application fields cannot be overlooked. In optoelectronics, 2D heterostructures enable efficient light absorption and emission, thereby meeting the demand for high-performance photodetectors and light sources. In the realm of electronic devices, these materials are driving the development of next-generation ultrafast electronic devices due to their superior electron mobility and switching performance. Additionally, in the fields of catalysis and energy storage, 2D heterostructures exhibit impressive catalytic activity and electrochemical performance, effectively enhancing energy conversion and storage efficiency.

Looking ahead, as science and technology continue to advance, 2D lateral heterostructures are expected to find applications in a broader range of fields. Researchers are actively exploring the possibilities of integrating these materials with existing technologies to foster a new wave of technological innovation. As emerging materials, 2D lateral heterostructures are becoming a significant focus in scientific research and industrial applications due to their unique physical properties and extensive potential. Despite facing multiple challenges related to fabrication processes, material stability, and device reliability, it is anticipated that future 2D lateral heterostructures will overcome these obstacles. Through ongoing research and technological innovation, they are expected to promote rapid development across various relevant fields. With the in-depth exploration of these materials, there is good reason to believe that they will have a profound impact on modern technology and play a crucial role in future innovations.

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R.Y. and Z.Z. contributed equally to this work.

The authors declare no competing financial interest.