Seeded 2D epitaxy of large-area single-crystal films of the van der Waals semiconductor 2H MoTe2

A Strategy for Transition Metal Chalcogenide Synthesis Using Sequential Selenium Substitution

The direct synthesis of wafer-scale single-crystal transition metal dichalcogenides (TMDs) remains challenging, albeit with enormous potential applications as semiconductors. In this work, we demonstrate the feasibility of using single-crystal 2H-MoTe2 films as templates, followed by a sequential selenium substitution reaction to synthesize a variety of TMDs and their heterostructures. We also demonstrate the synthesis of a MoTe2/MoSe2 lateral heterostructure with various substitution temperatures for Se substitution in 1T' and 2H phase MoTe2. Computational results illustrate that Se substitution is likely to start at Te vacancy sites, where generated strain lowers the energy barrier for further substitution, leading to a chain reaction that propagates until the entire layer is selenized. The obtained MoSe2 shows a high hole mobility of 32 cm2 V-1 s-1, comparable to the 2.8-31.6 range from mechanically exfoliated samples. Consequently, this MoSe2-based photodetector shows a comparable responsivity of 41 mA W-1 under near-infrared (1060 nm) illumination.

Stoichiometry-engineered phase transition in a two-dimensional binary compound

Due to complex thermodynamic and kinetic mechanism, phase engineering in nanomaterials is often limited by restricted phases and small-scale synthesis, hindering material diversity and scalability. Here, we demonstrate the exploration to unlock the stoichiometry as a degree of freedom for phase engineering in the Pd-Te binary compound. By reducing diffusion rates, we effectively engineer the stoichiometry of the reactants. We visualize the kinetic process, showing the stoichiometry transition from Pd10Te3 to PdTe2 through a sequential multi-step nucleation process. In total, five distinct phases are identified, demonstrating the potential to enhance phase diversity by fine-tuning stoichiometry. By controlling spatially uniform nucleation and halting the phase transition at precise points, we achieve stoichiometry-controllable wafer-scale growth. Notably, four of these phases exhibit superconducting properties. Our findings offer insights into the mechanism of phase transition through stoichiometry engineering, enabling the expansion of the phase library in nanomaterials and advancing scalable applications.

Warm metalworking for plastic manufacturing in brittle semiconductors

Semiconductors are the core of modern electronics1. Because of their brittleness, semiconductors are usually processed by the complicated techniques of sputtering or deposition2-4, instead of the effective and versatile metalworking methods like rolling, extrusion and pressing used with metals5. Here we show that brittle semiconductors can be plastically manufactured with an extensibility as large as ~3,000% using warm metalworking, that is, plastic manufacturing at slightly elevated temperatures (empirically below 500 K). Many bulk brittle semiconductors, such as Cu2Se, Ag2Se and Bi90Sb10, can be processed like metals below 400-500 K into free-standing, large and high-quality films with a thickness from the macro-scale to the micrometre scale. A model based on temperature-dependent collective atomic displacement and thermal vibration is proposed to explain the superior plasticity. The warm-metalworked films can retain the excellent and tunable physical properties of the bulk versions, such as a high carrier mobility up to ~5,000 cm2 V-1 s-1 and tunable electrical conductivities over six orders of magnitude by adjusting the chemical composition. A case study in film thermoelectric devices demonstrates ultra-high normalized output power densities of 43-54 μW cm-2 K-2. This work suggests that brittle semiconductors can be manufactured by warm metalworking for applications in various electronics.

CMOS-Compatible Fabrication of 2D Semiconductor-Based CFETs via High-k Dielectric van der Waals Encapsulation

Two-dimensional (2D) semiconductors are potential candidates for advanced technology nodes, but their integration with silicon lines remains a significant challenge. Here, we present a high-k dielectric van der Waals encapsulation strategy for the fabrication of 2D semiconductor-based complementary field-effect transistors (CFETs) compatible with established processes. This technique, involving the transfer of a high-k dielectric onto 2D semiconductors, protects channels from polymer contamination, enables O2 plasma surface cleaning, and facilitates the following dielectric depositions without doping or damage. The strategy results in heterostructures and devices with reduced surface roughness and is applicable to both p- and n-type semiconductors, including MoS2, WS2, MoTe2, and black phosphorus. Utilizing this method, we have successfully fabricated 2D CFET inverters with a gain of up to 19.54 and power consumption as low as 2.63 nW. Our work paves the way for the integration of 2D semiconductors with silicon technology, therefore accelerating the lab-to-fab transition progress.

Solution-Processable Electronic-Grade 2D WTe2 Enabled by Synergistic Dual Ammonium Intercalation

Tungsten ditelluride (WTe2) exhibits thickness-dependent properties, including magnetoresistance, ferroelectricity, and superconductivity, positioning it as an ideal candidate for nanoelectronics and spintronics. Therefore, the scalable synthesis of WTe2 with defined thicknesses down to the monolayer limit is crucial for unlocking these properties. Here, we introduce a universal electrolyte chemistry utilizing dual-ammonium compounds to exfoliate WTe2, enabling precise control over the intercalation stages and flake thicknesses. This approach achieves an 86% exfoliation yield, producing high-quality flakes averaging 2.83 nm in thickness, in which approximately 10% are monolayers. A solution-processed, single-flake device (10 nm thick) exhibits a magnetoresistance (MR) of 50% at 2 K and 9 T, and piezo-response force microscopy (PFM) indicates ferroelectricity in WTe2 flakes. Additionally, large-area WTe2 thin films (15 × 15 mm2), fabricated using Langmuir-Schaefer deposition, exhibit metallic behavior with a high conductivity of 2.9 × 104 S/m. Overall, the hybrid electrolyte approach facilitates the scalable synthesis of high-quality, solution-processable, two-dimensional (2D) WTe2 flakes with excellent properties. This versatility of the developed method has been further exemplified through the exfoliation of other transition metal dichalcogenides (e.g., MoS2 and MoSe2), expanding the potential for the extensive application of exfoliated 2D materials in printable and flexible nanoelectronics.

2D Materials-Based Field-Effect Transistor Biosensors for Healthcare

The need for accurate point-of-care (POC) tools, driven by increasing demands for precise medical diagnostics and monitoring, has accelerated the evolution of biosensor technology. Integrable 2D materials-based field-effect transistor (2D FET) biosensors offer label-free, rapid, and ultrasensitive detection, aligning perfectly with current biosensor trends. Given these advancements, this review focuses on the progress, challenges, and future prospects in the field of 2D FET biosensors. The distinctive physical properties of 2D materials and recent achievements in scalable synthesis are highlighted that significantly improve the manufacturing process and performance of FET biosensors. Additionally, the advancements of 2D FET biosensors are investigated in fatal disease diagnosis and screening, chronic disease management, and environmental hazards monitoring, as well as their integration in flexible electronics. Their promising capabilities shown in laboratory trials accelerate the development of prototype products, while the challenges are acknowledged, related to sensitivity, stability, and scalability that continue to impede the widespread adoption and commercialization of 2D FET biosensors. Finally, current strategies are discussed to overcome these challenges and envision future implications of 2D FET biosensors, such as their potential as smart and sustainable POC biosensors, thereby advancing human healthcare.

Two-Dimensional Cr3Te4/WS2/Fe3GeTe2/WTe2 Magnetic Memory with Field-Free Switching and Low Power Consumption

Spin-orbit torque (SOT) magnetic memory technology has garnered significant attention due to its ability to enable field-free switching of magnets with strong perpendicular magnetic anisotropy (PMA). However, concerns regarding power consumption of SOT-memory are persisting. Here, this work proposes a method to construct magnetic tunnel junction (MTJ) by transferring chemically vapor-deposited two-dimensional (2D) Cr3Te4/WS2 van der Waals (vdW) heterostructures onto 2D Fe3GeTe2 (FGT) magnet. The robustness and tunability of 2D magnets allow MTJs to exhibit non-volatility, multiple output states, and impressive cycling durability. MTJs with thin WS2 barriers (fewer than six layers) exhibit a linear tunneling effect, achieving a low resistance-area product (RA) of 15.5 kΩ·µm2 using bilayer WS2, which facilitats low-power operation. Furthermore, the different 2D magnets display a significant anti-parallel window of up to 8 kOe. SOT-memory based on the typical MTJ demonstrates a low write consumption of 0.3 mJ and read consumption of 9.7 nJ, marking a significant advancement in 2D vdW SOT-memory. This research has pointed out a new direction for constructing low power consumption SOT-memory with PMA field-free switching.

Recent advances in CMOS-compatible synthesis and integration of 2D materials

The upcoming generation of functional electronics in the era of artificial intelligence, and IoT requires extensive data storage and processing, necessitating further device miniaturization. Conventional Si CMOS technology is struggling to enhance integration density beyond a certain limit to uphold Moore's law, primarily due to performance degradation at smaller dimensions caused by various physical effects, including surface scattering, quantum tunneling, and other short-channel effects. The two-dimensional materials have emerged as highly promising alternatives, which exhibit excellent electrical and mechanical properties at atomically thin thicknesses and show exceptional potential for future CMOS technology. This review article presents the chronological progress made in the development of two-dimensional materials-based CMOS devices with comprehensively discussing the advancements made in material production, device development, associated challenges, and the strategies to address these issues. The future prospects for the use of two-dimensional materials in functional CMOS circuitry are outlooked, highlighting key opportunities and challenges toward industrial adaptation.

Unified transmission electron microscopy with the glovebox integrated system for investigating air-sensitive two-dimensional quantum materials

Transmission electron microscopy (TEM) is an indispensable tool for elucidating the intrinsic atomic structures of materials and provides deep insights into defect dynamics, phase transitions, and nanoscale structural details. While numerous intriguing physical properties have been revealed in recently discovered two-dimensional (2D) quantum materials, many exhibit significant sensitivity to water and oxygen under ambient conditions. This inherent instability complicates sample preparation for TEM analysis and hinders accurate property measurements. This review highlights recent technical advancements to preserve the intrinsic structures of water- and oxygen-sensitive 2D materials for atomic-scale characterizations. A critical development discussed in this review is implementing an inert gas-protected glovebox integrated system (GIS) designed specifically for TEM experiments. In addition, this review emphasizes air-sensitive materials such as 2D transition metal dichalcogenides, transition metal dihalides and trihalides, and low-dimensional magnetic materials, demonstrating breakthroughs in overcoming their environmental sensitivity. Furthermore, the progress in TEM characterization enabled by the GIS is analyzed to provide a comprehensive overview of state-of-the-art methodologies in this rapidly advancing field.

Janus Electronic Devices with Ultrathin High-κ Gate Dielectric Directly Integrated on 1T'-MoTe2

Integrating high-quality dielectrics with two-dimensional (2D) transition metal chalcogenides (TMDCs) is crucial for high-performance electronics. However, the lack of dangling bonds on 2D material surfaces complicates direct dielectric deposition. We propose using atomic layer deposition (ALD) to integrate ultrathin high-κ dielectric directly on 1T'-MoTe2 surfaces, facilitating the creation of high-performance back-gated field-effect transistors (FETs). Exploiting 1T'-MoTe2's natural oxidation in ambient conditions, we directly deposit dense and uniform HfO2 dielectric films below 5 nm, achieving an equivalent oxide thickness (EOT) of 0.97 nm. The resulting back-gate transistors, with a monolayer MoSSe on HfO2/1T'-MoTe2, show a current on/off ratio over 105 and operate at low voltages (<1 V), indicating high gating efficiency and a charge carrier mobility of 2.93 cm2V-1s-1. Additionally, we demonstrate a 6 × 5 bottom-gated array of MoSSe transistors using all-1T'-MoTe2 electrodes, achieving an 86.7% sample yield. Our approach also enables the creation of various integrated logic circuits such as inverters, NAND, and NOR gates. This research offers a feasible method for integrating high-κ dielectric films using industrially compatible ALD processes, providing excellent thickness control, uniformity, and scalability for 2D electronic devices.

Revisiting the Epitaxial Growth Mechanism of 2D TMDC Single Crystals

Epitaxial growth of 2D transition metal dichalcogenides (TMDCs) on sapphire substrates has been recognized as a pivotal method for producing wafer-scale single-crystal films. Both step-edges and symmetry of substrate surfaces have been proposed as controlling factors. However, the underlying fundamental still remains elusive. In this work, through the molybdenum disulfide (MoS2) growth on C/M sapphire, it is demonstrated that controlling the sulfur evaporation rate is crucial for dictating the switch between atomic-edge guided epitaxy and van der Waals epitaxy. Low-concentration sulfur condition preserves O/Al-terminated step edges, fostering atomic-edge epitaxy, while high-concentration sulfur leads to S-terminated edges, preferring van der Waals epitaxy. These experiments reveal that on a 2 in. wafer, the van der Waals epitaxy mechanism achieves better control in MoS2 alignment (≈99%) compared to the step edge mechanism (<85%). These findings shed light on the nuanced role of atomic-level thermodynamics in controlling nucleation modes of TMDCs, thereby providing a pathway for the precise fabrication of single-crystal 2D materials on a wafer scale.

Precise p-type and n-type doping of two-dimensional semiconductors for monolithic integrated circuits

The controllable fabrication of patterned p-type and n-type channels with precise doping control presents a significant challenge, impeding the realization of complementary metal-oxide-semiconductor (CMOS) logic using a single van der Waals material. However, such an achievement could offer substantial benefits by enabling continued transistor scaling and unprecedented interlayer interconnect technologies. In this study, we devise a precise method for two-dimensional (2D) semiconductor substitutional doping, which allows for the production of wafer-scale 2H-MoTe2 thin films with specific p-type or n-type doping. Notably, we extend this approach to the synthesis of spatially selective doped 2H-MoTe2 thin films via a one-step growth method, facilitating the monolithic integration of p-type and n-type semiconductor channels. Leveraging this advancement, we successfully fabricate a chip-sized 2D CMOS inverter array that demonstrates excellent device performance and yield. Collectively, these findings represent a significant stride towards the practical incorporation of 2D semiconductors in very large-scale integration technology.

Phase Transformation on Two-Dimensional MoTe2 Films for Surface-Enhanced Raman Spectroscopy

Two-dimensional (2D) transition metal dichalcogenides (TMDs) have recently become attractive candidate substrates for surface-enhanced Raman spectroscopy (SERS) owing to their atomically flat surfaces and adjustable electronic properties. Herein, large-scale 2D 1T'- and 2H-MoTe2 films were prepared using a chemical vapor deposition method. We found that phase structure plays an important role in the enhancement of the SERS performances of MoTe2 films. 1T'-MoTe2 films showed a strong SERS effect with a detection limit of 1 × 10-9 M for the R6G molecule, which is one order of magnitude lower than that of 2H-MoTe2 films. We demonstrated that the SERS sensitivity of MoTe2 films is derived from the efficient photoinduced charge transfer process between MoTe2 and adsorbed molecules. Moreover, a prohibited fish drug could be detected by using 1T'-MoTe2 films as SERS substrates. Our study paves the way to the development and application of high-performance SERS substrates based on TMD phase engineering.

Hybrid Density Functional Study on the p-Type Conductivity Mechanism in Intrinsic Point Defects and Group V Element-Doped 2D β-TeO2

The newly discovered two-dimensional (2D) β-TeO2 possesses extraordinarily high p-type carrier mobility and demonstrates immense potential in the electronics field. However, current research on its p-type conductivity mechanisms and the modifications of element doping remains relatively insufficient. In this study, the intrinsic point defects and extrinsic element doping in monolayer β-TeO2 are comprehensively analyzed to probe the potential sources of the intrinsic p-type conductivity and the extrinsic p-type doping possibility in 2D β-TeO2 through hybrid density functional calculations. Our results reveal that the vacancy defects with low formation energies have deep transition levels and thus cannot be used as sources of unintentional p-type conductivity in 2D β-TeO2. The investigations and discussions via Group V element doping modifications in 2D β-TeO2 indicate that bismuth (Bi) doping can easily and significantly enhance the p-type conductivity of 2D β-TeO2 under the presence of O-rich, which can be achieved experimentally. Furthermore, Bi doping can significantly increase carrier mobility without seriously affecting the electronic structure. The finding shows that the Bi element is an ideal dopant candidate for a p-type modification in 2D β-TeO2. Our calculations pave an alternative strategy to achieve the realization of superior p-type conductivity in 2D β-TeO2.

Low-resistivity Ohmic contacts of Ti/Al on few-layered 1T'-MoTe2/2H-MoTe2 heterojunctions grown by chemical vapor deposition

This study explores the phase-controlled growth of few-layered 2H-MoTe2, 1T'-MoTe2, and 2H-/1T'-MoTe2 heterostructures and their impacts on metal contact properties. Cold-wall chemical vapor deposition (CW-CVD) with varying growth rates of MoOx and reaction temperatures with Te vapors enabled the growth of continuous thin films of either 1T'-MoTe2 or 2H-MoTe2 phases on two-inch sapphire substrates. This methodology facilitates the meticulous optimization of chemical vapor deposition (CVD) parameters, enabling the realization of phase-controlled growth of few-layered MoTe2 thin films and their subsequent heterostructures. The study further investigates the influence of a 1T'-MoTe2 intermediate layer on the electrical properties of metal contacts on few-layered 2H-MoTe2. Bi-layer Ti/Al contacts directly deposited on 2H-MoTe2 exhibited Schottky behavior, indicating inefficient carrier transport. However, introducing a few-layered 1T'-MoTe2 intermediate layer between the metal and 2H-MoTe2 layers improved the contact characteristics significantly. The resulting Al/Ti/1T'-MoTe2/2H-MoTe2 contact scheme demonstrates Ohmic behavior with a specific contact resistance of around 1.7 × 10-4 Ω cm2. This substantial improvement is attributed to the high carrier concentration of the 1T'-MoTe2 intermediate layer which could be attributed tentatively to the increased tunneling events across the van der Waals gap and enhancing carrier transport between the metal and 2H-MoTe2.

Wafer-Scale Atomic Layer-Deposited TeOx/Te Heterostructure P-Type Thin-Film Transistors

There is an increasing demand for p-type semiconductors with scalable growth, excellent device performance, and back-end-of-line (BEOL) compatibility. Recently, tellurium (Te) has emerged as a promising candidate due to its appealing electrical properties and potential low-temperature production. So far, nearly all of the scalable production and integration of Te with complementary metal oxide semiconductor (CMOS) technology have been based on physical vapor deposition. Here we demonstrate wafer-scale atomic layer-deposited (ALD) TeOx/Te heterostructure thin-film transistors with high uniformity and integration compatibility. The wafer-scale uniformity of the film is evidenced by spatial Raman mappings and statistical electrical analysis. Furthermore, surface accumulation-induced good ohmic contact has been observed and explained by the unique band alignment of the charge neutrality level inside the Te valence band. These results demonstrate ALD TeOx/Te as a promising p-type semiconductor for monolithic three-dimensional integration in BEOL CMOS applications incorporated with well-established n-type ALD oxide semiconductors.

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.

Roles of Impurity Levels in 3d Transition Metal-Doped Two-Dimensional Ga2O3

Doping engineering is crucial for both fundamental science and emerging applications. While transition metal (TM) dopants exhibit considerable advantages in the tuning of magnetism and conductivity in bulk Ga2O3, investigations on TM-doped two-dimensional (2D) Ga2O3 are scarce, both theoretically and experimentally. In this study, the detailed variations in impurity levels within 3d TM-doped 2D Ga2O3 systems have been explored via first-principles calculations using the generalized gradient approximation (GGA) +U method. Our results show that the Co impurity tends to incorporate on the tetrahedral GaII site, while the other dopants favor square pyramidal GaI sites in 2D Ga2O3. Moreover, Sc3+, Ti4+, V4+, Cr3+, Mn3+, Fe3+, Co3+, Ni3+, Cu2+, and Zn2+ are the energetically favorable charge states. Importantly, a transition from n-type to p-type conductivity occurs at the threshold Cu element as determined by the defect formation energies and partial density of states (PDOS), which can be ascribed to the shift from electron doping to hole doping with respect to the increase in the atomic number in the 3d TM group. Moreover, the spin configurations in the presence of the square pyramidal and tetrahedral coordinated crystal field effects are investigated in detail, and a transition from high-spin to low-spin arrangement is observed. As the atomic number of the 3d TM dopant increases, the percentage contribution of O ions to the total magnetic moment significantly increases due to the electronegativity effect. Additionally, the formed 3d bands for most TM dopants are located near the Fermi level, which can be of significant benefit to the transformation of the absorbing region from ultraviolet to visible/infrared light. Our results provide theoretical guidance for designing 2D Ga2O3 towards optoelectronic and spintronic applications.

Large-Area Epitaxial Growth of Transition Metal Dichalcogenides

Over the past decade, research on atomically thin two-dimensional (2D) transition metal dichalcogenides (TMDs) has expanded rapidly due to their unique properties such as high carrier mobility, significant excitonic effects, and strong spin-orbit couplings. Considerable attention from both scientific and industrial communities has fully fueled the exploration of TMDs toward practical applications. Proposed scenarios, such as ultrascaled transistors, on-chip photonics, flexible optoelectronics, and efficient electrocatalysis, critically depend on the scalable production of large-area TMD films. Correspondingly, substantial efforts have been devoted to refining the synthesizing methodology of 2D TMDs, which brought the field to a stage that necessitates a comprehensive summary. In this Review, we give a systematic overview of the basic designs and significant advancements in large-area epitaxial growth of TMDs. We first sketch out their fundamental structures and diverse properties. Subsequent discussion encompasses the state-of-the-art wafer-scale production designs, single-crystal epitaxial strategies, and techniques for structure modification and postprocessing. Additionally, we highlight the future directions for application-driven material fabrication and persistent challenges, aiming to inspire ongoing exploration along a revolution in the modern semiconductor industry.

Quasi-equilibrium growth of inch-scale single-crystal monolayer α-In2Se3 on fluor-phlogopite

Epitaxial growth of two-dimensional (2D) materials with uniform orientation has been previously realized by introducing a small binding energy difference between the two locally most stable orientations. However, this small energy difference can be easily disturbed by uncontrollable dynamics during the growth process, limiting its practical applications. Herein, we propose a quasi-equilibrium growth (QEG) strategy to synthesize inch-scale monolayer α-In2Se3 single crystals, a semiconductor with ferroelectric properties, on fluor-phlogopite substrates. The QEG facilitates the discrimination of small differences in binding energy between the two locally most stable orientations, realizing robust single-orientation epitaxy within a broad growth window. Thus, single-crystal α-In2Se3 film can be epitaxially grown on fluor-phlogopite, the cleavage surface atomic layer of which has the same 3-fold rotational symmetry with α-In2Se3. The resulting crystalline quality enables high electron mobility up to 117.2 cm2 V-1 s-1 in α-In2Se3 ferroelectric field-effect transistors, exhibiting reliable nonvolatile memory performance with long retention time and robust cycling endurance. In brief, the developed QEG method provides a route for preparing larger-area single-crystal 2D materials and a promising opportunity for applications of 2D ferroelectric devices and nanoelectronics.

High Electron Mobility in Si-Doped Two-Dimensional β-Ga2O3 Tuned Using Biaxial Strain

Two-dimensional (2D) semiconductors have attracted much attention regarding their use in flexible electronic and optoelectronic devices, but the inherent poor electron mobility in conventional 2D materials severely restricts their applications. Using first-principles calculations in conjunction with Boltzmann transport theory, we systematically investigated the Si-doped 2D β-Ga2O3 structure mediated by biaxial strain, where the structural stabilities were determined by formation energy, phonon spectrum, and ab initio molecular dynamic simulation. Initially, the band gap values of Si-doped 2D β-Ga2O3 increased slightly, followed by a rapid decrease from 2.46 eV to 1.38 eV accompanied by strain modulations from -8% compressive to +8% tensile, which can be ascribed to the bigger energy elevation of the σ* anti-bonding in the conduction band minimum than that of the π bonding in the valence band maximum. Additionally, band structure calculations resolved a direct-to-indirect transition under the tensile strains. Furthermore, a significantly high electron mobility up to 4911.18 cm2 V-1 s-1 was discovered in Si-doped 2D β-Ga2O3 as the biaxial tensile strain approached 8%, which originated mainly from the decreased quantum confinement effect on the surface. The electrical conductivity was elevated with the increase in tensile strain and the enhancement of temperature from 300 K to 800 K. Our studies demonstrate the tunable electron mobilities and band structures of Si-doped 2D β-Ga2O3 using biaxial strain and shed light on its great potential in nanoscale electronics.

Van der Waals mid-wavelength infrared detector linear array for room temperature passive imaging

Passive imaging for mid-wave infrared (MWIR) is resistant to atmospheric pollutants, guaranteeing image clarity and accuracy. Arrayed photodetectors can simultaneously perform radiation sensing to improve efficiency. Room temperature van der Waals (vdWs) photodetectors without lattice matching have evolved rapidly with optimized stacking methods, primarily for single-pixel devices. The urgent need to implement arrayed devices aligns with practical demands. Here, we present an 8 by 1 black phosphorus/molybdenum sulfide (BP/MoS2) vdWs photodetector linear array with a fill-factor of ~77%, fabricated using a temperature-assisted sloping transfer method. The flat interface and uniform thickness facilitate carrier transport and minimize pixel nonuniformities, showing an average peak detectivity (D*) of 2.34 × 109 cm·Hz1/2·W-1 in the mid-wave infrared region. Compared to a single pixel, push-broom scanning passive imaging is eight times more efficient and further enhanced through mean filtering and fast Fourier transform filtering for strip noise correction. Our study offers guidance on vdWs arrayed devices for engineering applications.

Growth of Single Crystalline 2D Materials beyond Graphene on Non-metallic Substrates

The advent of 2D materials has ushered in the exploration of their synthesis, characterization and application. While plenty of 2D materials have been synthesized on various metallic substrates, interfacial interaction significantly affects their intrinsic electronic properties. Additionally, the complex transfer process presents further challenges. In this context, experimental efforts are devoted to the direct growth on technologically important semiconductor/insulator substrates. This review aims to uncover the effects of substrate on the growth of 2D materials. The focus is on non-metallic substrate used for epitaxial growth and how this highlights the necessity for phase engineering and advanced characterization at atomic scale. Special attention is paid to monoelemental 2D structures with topological properties. The conclusion is drawn through a discussion of the requirements for integrating 2D materials with current semiconductor-based technology and the unique properties of heterostructures based on 2D materials. Overall, this review describes how 2D materials can be fabricated directly on non-metallic substrates and the exploration of growth mechanism at atomic scale.

Silk-based intelligent fibers and textiles: structures, properties, and applications

Multifunctional fibers represent a cornerstone of human civilization, playing a pivotal role in numerous aspects of societal development. Natural biomaterials, in contrast to synthetic alternatives, offer environmental sustainability, biocompatibility, and biodegradability. Among these biomaterials, natural silk is favored in biomedical applications and smart fiber technology due to its accessibility, superior mechanical properties, diverse functional groups, controllable structure, and exceptional biocompatibility. This review delves into the intricate structure and properties of natural silk fibers and their extensive applications in biomedicine and smart fiber technology. It highlights the critical significance of silk fibers in the development of multifunctional materials, emphasizing their mechanical strength, biocompatibility, and biodegradability. A detailed analysis of the hierarchical structure of silk fibers elucidates how these structural features contribute to their unique properties. The review also encompasses the biomedical applications of silk fibers, including surgical sutures, tissue engineering, and drug delivery systems, along with recent advancements in smart fiber applications such as sensing, optical technologies, and energy storage. The enhancement of functional properties of silk fibers through chemical or physical modifications is discussed, suggesting broader high-end applications. Additionally, the review addresses current challenges and future directions in the application of silk fibers in biomedicine and smart fiber technologies, underscoring silk's potential in driving contemporary technological innovations. The versatility and sustainability of silk fibers position them as pivotal elements in contemporary materials science and technology, fostering the development of next-generation smart materials.

Constrained patterning of orientated metal chalcogenide nanowires and their growth mechanism

One-dimensional metallic transition-metal chalcogenide nanowires (TMC-NWs) hold promise for interconnecting devices built on two-dimensional (2D) transition-metal dichalcogenides, but only isotropic growth has so far been demonstrated. Here we show the direct patterning of highly oriented Mo6Te6 NWs in 2D molybdenum ditelluride (MoTe2) using graphite as confined encapsulation layers under external stimuli. The atomic structural transition is studied through in-situ electrical biasing the fabricated heterostructure in a scanning transmission electron microscope. Atomic resolution high-angle annular dark-field STEM images reveal that the conversion of Mo6Te6 NWs from MoTe2 occurs only along specific directions. Combined with first-principles calculations, we attribute the oriented growth to the local Joule-heating induced by electrical bias near the interface of the graphite-MoTe2 heterostructure and the confinement effect generated by graphite. Using the same strategy, we fabricate oriented NWs confined in graphite as lateral contact electrodes in the 2H-MoTe2 FET, achieving a low Schottky barrier of 11.5 meV, and low contact resistance of 43.7 Ω µm at the metal-NW interface. Our work introduces possible approaches to fabricate oriented NWs for interconnections in flexible 2D nanoelectronics through direct metal phase patterning.

P/N-Type Conversion of 2D MoTe2 Controlled by Top Gate Engineering for Logic Circuits

Two-dimensional (2D) transition-metal dichalcogenides (TMDCs) are regarded as promising materials for next-generation logic circuits. Top gate field-effect transistors (FETs) have independent gate control ability and can be fabricated directly on TMDC materials without a transfer process. Therefore, it has the merits of device reliability and complementary metal-oxide semiconductor (CMOS) process compatibility, which are demanded in practical circuit-level integration. However, the fabrication of the top gate FET involves depositing an insulating dielectric layer and a gate electrode in sequence on the TMDC channel material, which may affect the device performance. Insightfully investigating the influences of different top-gate-deposition methods on the electrical properties of the TMDC channel and further harnessing these influences to realize a homogeneous CMOS device on an identical 2D TMDC platform are with practice significance. In this work, p/n-type controllable top gate FET arrays based on 2H-MoTe2 are fabricated by using different top-gate-deposition methods. The electron-beam evaporation (EBE) of top metal gate exhibits an obvious n-doping effect on the 2H-MoTe2 channel and converts it from p-type to n-type, whereas the thermal evaporation of top gate affects little to the channel. High-resolution transmission electron microscopy (HR-TEM) analysis reveals that the high-energy metal atoms from the EBE process can penetrate through the 30 nm gate dielectric layers (including 10 nm Al2O3 seeding layer), leading to multiple atomic defects in both MoTe2 and the interface between MoTe2 and Al2O3. Furthermore, by utilizing the top gate engineering, a large-scale double-top-gate MoTe2 homogeneous CMOS inverter array is fabricated. The CMOS inverters exhibit clear logic swing, negligible hysteresis, and high device yield (∼93%), indicating high device reliability and stability. Notably, the fabrication process is facile, free from transfer procedure, and compatible with traditional silicon technology. This work promotes the application of 2D TMDCs in nanoelectronics integration.

Understanding epitaxial growth of two-dimensional materials and their homostructures

The exceptional physical properties of two-dimensional (2D) van der Waals (vdW) materials have been extensively researched, driving advances in material synthesis. Epitaxial growth, a prominent synthesis strategy, enables the production of large-area, high-quality 2D films compatible with advanced integrated circuits. Typical 2D single crystals, such as graphene, transition metal dichalcogenides and hexagonal boron nitride, have been epitaxially grown at a wafer scale. A systematic summary is required to offer strategic guidance for the epitaxy of emerging 2D materials. Here we focus on the epitaxy methodologies for 2D vdW materials in two directions: the growth of in-plane single-crystal monolayers and the fabrication of out-of-plane homostructures. We first discuss nucleation control of a single domain and orientation control over multiple domains to achieve large-scale single-crystal monolayers. We analyse the defect levels and measures of crystalline quality of typical 2D vdW materials with various epitaxial growth techniques. We then outline technical routes for the growth of homogeneous multilayers and twisted homostructures. We further summarize the current strategies to guide future efforts in optimizing on-demand fabrication of 2D vdW materials, as well as subsequent device manufacturing for their industrial applications.

Van der Waals Epitaxial Growth of Ultrathin Indium Antimonide on Arbitrary Substrates through Low-Thermal Budget

III-V semiconductors possess high mobility, high frequency response, and detection sensitivity, making them potentially attractive for beyond-silicon electronics applications. However, the traditional heteroepitaxy of III-V semiconductors is impeded by a significant lattice mismatch and the necessity for extreme vacuum and high temperature conditions, thereby impeding their in situ compatibility with flexible substrates and silicon-based circuits. In this study, a novel approach is presented for fabricating ultrathin InSb single-crystal nanosheets on arbitrary substrates with a thickness as thin as 2.4 nm using low-thermal-budget van der Waals (vdW) epitaxy through chemical vapor deposition (CVD). In particular, in situ growth has been successfully achieved on both silicon-based substrates and flexible polyimide (PI) substrates. Notably, the growth temperature required for InSb nanosheets (240 °C) is significantly lower than that employed in back-end-of-line processes (400 °C). The field effect transistor devices based on fabricated ultrathin InSb nanosheets exhibit ultra-high on-off ratio exceeding 108 and demonstrate minimal gate leakage currents. Furthermore, these ultrathin InSb nanosheets display p-type characteristics with hole mobilities reaching up to 203 cm2 V-1 s-1 at room temperatures. This study paves the way for achieving heterogeneous integration of III-V semiconductors and facilitating their application in flexible electronics.

Low Temperature Synthesis of 2D p-Type α-In2Te3 with Fast and Broadband Photodetection

2DA 2 III B 3 VI ${\mathrm{A}}_2^{{\mathrm{III}}}{\mathrm{B}}_3^{{\mathrm{VI}}}$ compounds (A = Al, Ga, In, and B = S, Se, and Te) with intrinsic structural defects offer significant opportunities for high-performance and functional devices. However, obtaining 2D atomic-thin nanoplates with non-layered structure on SiO2/Si substrate at low temperatures is rare, which hinders the study of their properties and applications at atomic-thin thickness limits. In this study, the synthesis of ultrathin, non-layered α-In2Te3 nanoplates is demonstrated using a BiOCl-assisted chemical vapor deposition method at a temperature below 350 °C on SiO2/Si substrate. Comprehensive characterization results confirm the high-quality single crystal is the low-temperature cubic phase α-In2Te3 , possessing a noncentrosymmetric defected ZnS structure with good second harmonic generation. Moreover, α-In2Te3 is revealed to be a p-type semiconductor with a direct and narrow bandgap value of 0.76 eV. The field effect transistor exhibits a high mobility of 18 cm2 V-1 s-1, and the photodetector demonstrates stable photoswitching behavior within a broadband photoresponse from 405 to 1064 nm, with a satisfactory response time of τrise = 1 ms. Notably, the α-In2Te3 nanoplates exhibit good stability against ambient environments. Together, these findings establish α-In2Te3 nanoplates as promising candidates for next-generation high-performance photonics and electronics.

Room-Temperature Growth of Square-Millimeter Single-Crystalline Two-Dimensional Metal Halides on Silicon

Silicon is the cornerstone of electronics and photonics. In this context, almost all integrated devices derived from two-dimensional (2D) materials stay rooted in silicon technology. However, as the growth substrate, silicon has long been thought to be a hindrance for growing 2D materials through bottom-up methods that require high growth temperatures, and thus, indirect routes are usually considered instead. Although promising growth of large-area 2D materials on silicon has been demonstrated, the direct growth of single-crystalline materials using low-thermal-budget synthesis methods remains challenging. Here, we report the room-temperature growth of millimeter-scale single-crystal 2D metal halides on silicon substrates with a hydroxyl-terminated surface. Theoretical calculations reveal that the activation energy for surface diffusion can be reduced by an order of magnitude by terminating the surface with hydroxyl groups, from which on-silicon growth is greatly facilitated at room temperature and enables a 4-order-of-magnitude increase in area. The high quality and uniformity of the resulting single crystals are further evidenced. The optoelectronic devices employing the as-grown materials show an ultralow dark current of 10-13 A and a high detectivity of 1013 Jones, thereby corroborating a weak-light detection ability. These results would point to a rich space of surface modulation that can be used to surmount current limitations and demonstrate a promising strategy for growing 2D materials directly on silicon at room temperature to produce large single crystals.

Wafer-Scale Synthesis of Highly Oriented 2D Topological Semimetal PtTe2 via Tellurization

Platinum ditelluride (1T-PtTe2) is a two-dimensional (2D) topological semimetal with a distinctive band structure and flexibility of van der Waals integration as a promising candidate for future electronics and spintronics. Although the synthesis of large-scale, uniform, and highly crystalline films of 2D semimetals system is a prerequisite for device application, the synthetic methods meeting these criteria are still lacking. Here, we introduce an approach to synthesize highly oriented 2D topological semimetal PtTe2 using a thermally assisted conversion called tellurization, which is a cost-efficient method compared to the other epitaxial deposition methods. We demonstrate that achieving highly crystalline 1T-PtTe2 using tellurization is not dependent on epitaxy but rather relies on two critical factors: (i) the crystallinity of the predeposited platinum (Pt) film and (ii) the surface coverage ratio of the Pt film considering lateral lattice expansion during transformation. By optimizing the surface coverage ratio of the epitaxial Pt film, we successfully obtained 2 in. wafer-scale uniformity without in-plane misalignment between antiparallelly oriented domains. The electronic band structure of 2D topological PtTe2 is clearly resolved in momentum space, and we observed an interesting 6-fold gapped Dirac cone at the Fermi surface. Furthermore, ultrahigh electrical conductivity down to ∼3.8 nm, which is consistent with that of single crystal PtTe2, was observed, proving its ultralow defect density.

A Mini Review: Phase Regulation for Molybdenum Dichalcogenide Nanomaterials

Atomically thin two-dimensional transition metal dichalcogenides (TMDCs) have been regarded as ideal and promising nanomaterials that bring broad application prospects in extensive fields due to their ultrathin layered structure, unique electronic band structure, and multiple spatial phase configurations. TMDCs with different phase structures exhibit great diversities in physical and chemical properties. By regulating the phase structure, their properties would be modified to broaden the application fields. In this mini review, focusing on the most widely concerned molybdenum dichalcogenides (MoX2: X = S, Se, Te), we summarized their phase structures and corresponding electronic properties. Particularly, the mechanisms of phase transformation are explained, and the common methods of phase regulation or phase stabilization strategies are systematically reviewed and discussed. We hope the review could provide guidance for the phase regulation of molybdenum dichalcogenides nanomaterials, and further promote their real industrial applications.

Monolithic three-dimensional tier-by-tier integration via van der Waals lamination

Two-dimensional (2D) semiconductors have shown great potential for monolithic three-dimensional (M3D) integration due to their dangling-bonds-free surface and the ability to integrate to various substrates without the conventional constraint of lattice matching1-10. However, with atomically thin body thickness, 2D semiconductors are not compatible with various high-energy processes in microelectronics11-13, where the M3D integration of multiple 2D circuit tiers is challenging. Here we report an alternative low-temperature M3D integration approach by van der Waals (vdW) lamination of entire prefabricated circuit tiers, where the processing temperature is controlled to 120 °C. By further repeating the vdW lamination process tier by tier, an M3D integrated system is achieved with 10 circuit tiers in the vertical direction, overcoming previous thermal budget limitations. Detailed electrical characterization demonstrates the bottom 2D transistor is not impacted after repetitively laminating vdW circuit tiers on top. Furthermore, by vertically connecting devices within different tiers through vdW inter-tier vias, various logic and heterogeneous structures are realized with desired system functions. Our demonstration provides a low-temperature route towards fabricating M3D circuits with increased numbers of tiers.

Coplanar MoS2-MoTe2 Heterojunction With the Same Crystal Orientation

Two-dimensional (2D) coplanar heterostructure enables high-performance optoelectronic devices, such as p-n heterojunctions. However, realizing site-controllable and shape-specific 2D coplanar heterojunctions composed of two semiconductors with the same crystal orientation still requires the development of new growth methods. Here, a route to fabricate MoS2-MoTe2 coplanar heterojunctions with the same crystal orientation is reported by exploiting the properties of phase transition and atomic rearrangement during the growth of 2H-MoTe2. Raman spectroscopy and electron microscopy techniques reveal the chemical composition and lattice structure of the heterostructure. Both MoS2 and MoTe2 in the heterojunction are single crystals and have the same lattice orientation, and their shapes can be arbitrarily defined by electron beam lithography. Electrical measurements show that the MoS2 and MoTe2 channels exhibit n-type and p-type transfer characteristics, respectively. The coplanar epitaxy technology can be used to prepare more coplanar heterostructures with novel device functions.

Solution-Processable and Printable Two-Dimensional Transition Metal Dichalcogenide Inks

Two-dimensional (2D) transition metal dichalcogenides (TMDs) with layered crystal structures have been attracting enormous research interest for their atomic thickness, mechanical flexibility, and excellent electronic/optoelectronic properties for applications in diverse technological areas. Solution-processable 2D TMD inks are promising for large-scale production of functional thin films at an affordable cost, using high-throughput solution-based processing techniques such as printing and roll-to-roll fabrications. This paper provides a comprehensive review of the chemical synthesis of solution-processable and printable 2D TMD ink materials and the subsequent assembly into thin films for diverse applications. We start with the chemical principles and protocols of various synthesis methods for 2D TMD nanosheet crystals in the solution phase. The solution-based techniques for depositing ink materials into solid-state thin films are discussed. Then, we review the applications of these solution-processable thin films in diverse technological areas including electronics, optoelectronics, and others. To conclude, a summary of the key scientific/technical challenges and future research opportunities of solution-processable TMD inks is provided.

Adsorption and Sensing Mechanism of a nTiO2 Particle (n = 1-3)-Doped MoTe2 Monolayer to Faulty and Hazardous Gases in the Underground Cableway

With the rapid growth of the economy and industrial technology, vigoroso and stable power distribution networks have gradually been established worldwide. Among these networks, underground cables play a crucial role in the distribution process, determining the overall electrical stability of entire cities. Based on density functional theory, this paper first proposes a TiO2 particle-doped MoTe2 monolayer to detect and eliminate these faults and hazardous gases within the underground cableway. The band structure, total density of states, projected density of states, and differential charge density are analyzed. The results demonstrate that the presence of TiO2 particles significantly enhances the adsorption capacity of MoTe2, diminishes the electrical conductivity of the doping system, and heightens electron activity in the doping reaction zone. The best adsorption performance is achieved in the case of two-particle doping. Furthermore, the modified MoTe2 exhibits an enhanced capability for capturing SO2 and SOF2, with the adsorption mechanism classified as physical-chemical adsorption. This work not only introduces a novel surface modification method for a MoTe2 monolayer but also provides a substantial data set to support the design and production of efficient sensors used in the underground cableway. These contributions further enhance the safety and stability of power systems and ensure human health.

Biomimetic wafer-scale alignment of tellurium nanowires for high-mobility flexible and stretchable electronics

Flexible and stretchable thin-film transistors (TFTs) are crucial in skin-like electronics for wearable and implantable applications. Such electronics are usually constrained in performance owing to a lack of high-mobility and stretchable semiconducting channels. Tellurium, a rising semiconductor with superior charge carrier mobilities, has been limited by its intrinsic brittleness and anisotropy. Here, we achieve highly oriented arrays of tellurium nanowires (TeNWs) on various substrates with wafer-scale scalability by a facile lock-and-shear strategy. Such an assembly approach mimics the alignment process of the trailing tentacles of a swimming jellyfish. We further apply these TeNW arrays in high-mobility TFTs and logic gates with improved flexibility and stretchability. More specifically, mobilities over 100 square centimeters per volt per second and on/off ratios of ~104 are achieved in TeNW-TFTs. The TeNW-TFTs on polyethylene terephthalate can sustain an omnidirectional bending strain of 1.3% for more than 1000 cycles. Furthermore, TeNW-TFTs on an elastomeric substrate can withstand a unidirectional strain of 40% with no performance degradation.

Nanoscale Channel Length MoS2 Vertical Field-Effect Transistor Arrays with Side-Wall Source/Drain Electrodes

Two-dimensional transition metal dichalcogenides (TMDCs) have natural advantages in overcoming the short-channel effect in field-effect transistors (FETs) and in fabricating three-dimensional FETs, which benefit in increasing device density. However, so far, most reported works related to MoS2 FETs with a sub-100 nm channel employ mechanically exfoliated materials and all of the works involve electron beam lithography (EBL), which may limit their application in fabricating wafer-scale device arrays as demanded in integrated circuits (ICs). In this work, MoS2 FET arrays with a side-wall source and drain electrodes vertically distributed are designed and fabricated. The channel length of the as-fabricated FET is basically determined by the thickness of an insulating layer between the source and drain electrodes. The vertically distributed source and drain electrodes enable to reduce the electrode-occupied area and increase in the device density. The as-fabricated vertical FETs exhibit on/off ratios comparable to those of mechanically exfoliated MoS2 FETs with a nanoscale channel length under identical VDS. In addition, the as-fabricated FETs can work at a VDS as low as 10 mV with a desirable on/off ratio (1.9 × 107), which benefits in developing low-power devices. Moreover, the fabrication process is free from EBL and can be applied to wafer-scale device arrays. The statistical results show that the fabricated FET arrays have a device yield of 87.5% and an average on/off ratio of about 1.7 × 106 at a VDS of 10 mV, with the lowest and highest ones to be about 1.3 × 104 and 1.9 × 107, respectively, demonstrating the good reliability of our fabrication process. Our work promises a bright future for TMDCs in realizing high-density and low-power nanoelectronic devices in ICs.

Metal telluride nanosheets by scalable solid lithiation and exfoliation

Transition metal tellurides (TMTs) have been ideal materials for exploring exotic properties in condensed-matter physics, chemistry and materials science1-3. Although TMT nanosheets have been produced by top-down exfoliation, their scale is below the gram level and requires a long processing time, restricting their effective application from laboratory to market4-8. We report the fast and scalable synthesis of a wide variety of MTe2 (M = Nb, Mo, W, Ta, Ti) nanosheets by the solid lithiation of bulk MTe2 within 10 min and their subsequent hydrolysis within seconds. Using NbTe2 as a representative, we produced more than a hundred grams (108 g) of NbTe2 nanosheets with 3.2 nm mean thickness, 6.2 µm mean lateral size and a high yield (>80%). Several interesting quantum phenomena, such as quantum oscillations and giant magnetoresistance, were observed that are generally restricted to highly crystalline MTe2 nanosheets. The TMT nanosheets also perform well as electrocatalysts for lithium-oxygen batteries and electrodes for microsupercapacitors (MSCs). Moreover, this synthesis method is efficient for preparing alloyed telluride, selenide and sulfide nanosheets. Our work opens new opportunities for the universal and scalable synthesis of TMT nanosheets for exploring new quantum phenomena, potential applications and commercialization.

Highly Robust Room-Temperature Interfacial Ferromagnetism in Ultrathin Co2Si Nanoplates

The reduced dimensionality and interfacial effects in magnetic nanostructures open the feasibility to tailor magnetic ordering. Here, we report the synthesis of ultrathin metallic Co2Si nanoplates with a total thickness that is tunable to 2.2 nm. The interfacial magnetism coupled with the highly anisotropic nanoplate geometry leads to strong perpendicular magnetic anisotropy and robust hard ferromagnetism at room temperature, with a Curie temperature (TC) exceeding 950 K and a coercive field (HC) > 4.0 T at 3 K and 8750 Oe at 300 K. Theoretical calculations suggest that ferromagnetism originates from symmetry breaking and undercoordinated Co atoms at the Co2Si and SiO2 interface. With protection by the self-limiting intrinsic oxide, the interfacial ferromagnetism of the Co2Si nanoplates exhibits excellent environmental stability. The controllable growth of ambient stable Co2Si nanoplates as 2D hard ferromagnets could open exciting opportunities for fundamental studies and applications in Si-based spintronic devices.

Wafer scale growth of single crystal two-dimensional van der Waals materials

Two-dimensional (2D) van der Waals (vdW) materials, including graphene, hexagonal boron nitride (hBN), and metal dichalcogenides (MCs), form the basis of modern electronics and optoelectronics due to their unique electronic structure, chemical activity, and mechanical strength. Despite many proof-of-concept demonstrations so far, to fully realize their large-scale practical applications, especially in devices, wafer-scale single crystal atomically thin highly uniform films are indispensable. In this minireview, we present an overview on the strategies and highlight recent significant advances toward the synthesis of wafer-scale single crystal graphene, hBN, and MC 2D thin films. Currently, there are five distinct routes to synthesize wafer-scale single crystal 2D vdW thin films: (i) nucleation-controlled growth by suppressing the nucleation density, (ii) unidirectional alignment of multiple epitaxial nuclei and their seamless coalescence, (iii) self-collimation of randomly oriented grains on a molten metal, (iv) surface diffusion and epitaxial self-planarization and (v) seed-mediated 2D vertical epitaxy. Finally, the challenges that need to be addressed in future studies have also been described.

Two-Dimensional Semiconductors and Transistors for Future Integrated Circuits

Silicon transistors are approaching their physical limit, calling for the emergence of a technological revolution. As the acknowledged ultimate version of transistor channels, 2D semiconductors are of interest for the development of post-Moore electronics due to their useful properties and all-in-one potentials. Here, the promise and current status of 2D semiconductors and transistors are reviewed, from materials and devices to integrated applications. First, we outline the evolution and challenges of silicon-based integrated circuits, followed by a detailed discussion on the properties and preparation strategies of 2D semiconductors and van der Waals heterostructures. Subsequently, the significant progress of 2D transistors, including device optimization, large-scale integration, and unconventional devices, are presented. We also examine 2D semiconductors for advanced heterogeneous and multifunctional integration beyond CMOS. Finally, the key technical challenges and potential strategies for 2D transistors and integrated circuits are also discussed. We envision that the field of 2D semiconductors and transistors could yield substantial progress in the upcoming years and hope this review will trigger the interest of scientists planning their next experiment.

Dual-Limit Growth of Large-Area Monolayer Transition Metal Dichalcogenides

The large-scale growth of monolayer transition metal dichalcogenide (TMDC) films is a determinant for the implementation of two-dimensional materials in industrial applications. However, the simultaneous realization of uniform monolayer thickness and large-area coverage is still a challenge, because it requires precise control of reaction kinetics in both space and time dimensions. Herein, we achieve a variety of large-area monolayer TMDCs films by a dual-limit growth (DLG) that is realized through nanoporous carbon nanotube (CNT) films. In the DLG, a precursor-loaded CNT film placed face-to-face with a substrate provides a space-limited environment facilitating the monolayer growth, while the byproducts formed in the CNT film timely limits the supply of precursors released from nanopores of the CNT film, inhibiting the growth of multilayer TMDCs on the substrate. Consequently, large-area monolayer TMDC films are grown in a wide range of reaction times and show good homogeneity in thickness, optical properties, and device performance over the entire substrate. The DLG strategy is widely applicable for the growth of a variety of TMDC films including WSe2, MoS2, MoSe2, WS2, and ReS2. Our work provides a universal strategy to attain large-area monolayer TMDC films that can be used in practical applications of integrated circuits.

Technology and Integration Roadmap for Optoelectronic Memristor

Optoelectronic memristors (OMs) have emerged as a promising optoelectronic Neuromorphic computing paradigm, opening up new opportunities for neurosynaptic devices and optoelectronic systems. These OMs possess a range of desirable features including minimal crosstalk, high bandwidth, low power consumption, zero latency, and the ability to replicate crucial neurological functions such as vision and optical memory. By incorporating large-scale parallel synaptic structures, OMs are anticipated to greatly enhance high-performance and low-power in-memory computing, effectively overcoming the limitations of the von Neumann bottleneck. However, progress in this field necessitates a comprehensive understanding of suitable structures and techniques for integrating low-dimensional materials into optoelectronic integrated circuit platforms. This review aims to offer a comprehensive overview of the fundamental performance, mechanisms, design of structures, applications, and integration roadmap of optoelectronic synaptic memristors. By establishing connections between materials, multilayer optoelectronic memristor units, and monolithic optoelectronic integrated circuits, this review seeks to provide insights into emerging technologies and future prospects that are expected to drive innovation and widespread adoption in the near future.

Recent Strategies for the Synthesis of Phase-Pure Ultrathin 1T/1T' Transition Metal Dichalcogenide Nanosheets

The past few decades have witnessed a notable increase in transition metal dichalcogenide (TMD) related research not only because of the large family of TMD candidates but also because of the various polytypes that arise from the monolayer configuration and layer stacking order. The peculiar physicochemical properties of TMD nanosheets enable an enormous range of applications from fundamental science to industrial technologies based on the preparation of high-quality TMDs. For polymorphic TMDs, the 1T/1T' phase is particularly intriguing because of the enriched density of states, and thus facilitates fruitful chemistry. Herein, we comprehensively discuss the most recent strategies for direct synthesis of phase-pure 1T/1T' TMD nanosheets such as mechanical exfoliation, chemical vapor deposition, wet chemical synthesis, atomic layer deposition, and more. We also review frequently adopted methods for phase engineering in TMD nanosheets ranging from chemical doping and alloying, to charge injection, and irradiation with optical or charged particle beams. Prior to the synthesis methods, we discuss the configuration of TMDs as well as the characterization tools mostly used in experiments. Finally, we discuss the current challenges and opportunities as well as emphasize the promising fields for the future development.

2D Materials in Flexible Electronics: Recent Advances and Future Prospectives

Flexible electronics have recently gained considerable attention due to their potential to provide new and innovative solutions to a wide range of challenges in various electronic fields. These electronics require specific material properties and performance because they need to be integrated into a variety of surfaces or folded and rolled for newly formatted electronics. Two-dimensional (2D) materials have emerged as promising candidates for flexible electronics due to their unique mechanical, electrical, and optical properties, as well as their compatibility with other materials, enabling the creation of various flexible electronic devices. This article provides a comprehensive review of the progress made in developing flexible electronic devices using 2D materials. In addition, it highlights the key aspects of materials, scalable material production, and device fabrication processes for flexible applications, along with important examples of demonstrations that achieved breakthroughs in various flexible and wearable electronic applications. Finally, we discuss the opportunities, current challenges, potential solutions, and future investigative directions about this field.

Robust multiferroic in interfacial modulation synthesized wafer-scale one-unit-cell of chromium sulfide

Multiferroic materials offer a promising avenue for manipulating digital information by leveraging the cross-coupling between ferroelectric and ferromagnetic orders. Despite the ferroelectricity has been uncovered by ion displacement or interlayer-sliding, one-unit-cell of multiferroic materials design and wafer-scale synthesis have yet to be realized. Here we develope an interface modulated strategy to grow 1-inch one-unit-cell of non-layered chromium sulfide with unidirectional orientation on industry-compatible c-plane sapphire. The interfacial interaction between chromium sulfide and substrate induces the intralayer-sliding of self-intercalated chromium atoms and breaks the space reversal symmetry. As a result, robust room-temperature ferroelectricity (retaining more than one month) emerges in one-unit-cell of chromium sulfide with ultrahigh remanent polarization. Besides, long-range ferromagnetic order is discovered with the Curie temperature approaching 200 K, almost two times higher than that of bulk counterpart. In parallel, the magnetoelectric coupling is certified and which makes 1-inch one-unit-cell of chromium sulfide the largest and thinnest multiferroics.

Heteroepitaxial Growth of Black Phosphorus on Tin Monosulfide

Black phosphorus (Black P), a layered semiconductor with a layer-dependent bandgap and high carrier mobility, is a promising candidate for next-generation electronics and optoelectronics. However, the synthesis of large-area, layer-precise, single crystalline Black P films remains a challenge due to their high nucleation energy. Here, we report the molecular beam heteroepitaxy of single crystalline Black P films on a tin monosulfide (SnS) buffer layer grown on Au(100). The layer-by-layer growth mode enables the preparation of monolayer to trilayer films, with band gaps that reflect layer-dependent quantum confinement.

Non-Steady-State Symmetry Breaking Growth of Multilayered SnSe2 Nanoplates

The use of non-equilibrium growth modes with non-steady dynamics is extensively explored in bulk materials such as amorphous and polycrystalline materials. Yet, research into the non-steady-state (NSS) growth of two-dimensional (2D) materials is still in its infancy. In this study, multilayered tin selenide (SnSe2 ) nanoplates are grown by chemical vapor deposition under NSS conditions (modulating carrier gas flow and temperature). Given the facile diffusion and inherent instability of SnSe2 , it proves to be an apt candidate for nucleation and growth in NSS scenarios. This leads to the emergence of SnSe2 nanoplates with distinct features (self-growth twisting, symmetry transformation, interlayer decoupling, homojunction, and large-area 2D domain), exhibiting pronounced second harmonic generation. The authors' findings shed light on the growth dynamics of 2D materials, broadening their potential applications in various fields.

Substrate Engineering for Chemical Vapor Deposition Growth of Large-Scale 2D Transition Metal Dichalcogenides

The large-scale production of 2D transition metal dichalcogenides (TMDs) is essential to realize their industrial applications. Chemical vapor deposition (CVD) has been considered as a promising method for the controlled growth of high-quality and large-scale 2D TMDs. During a CVD process, the substrate plays a crucial role in anchoring the source materials, promoting the nucleation and stimulating the epitaxial growth. It thus significantly affects the thickness, microstructure, and crystal quality of the products, which are particularly important for obtaining 2D TMDs with expected morphology and size. Here, an insightful review is provided by focusing on the recent development associated with the substrate engineering strategies for CVD preparation of large-scale 2D TMDs. First, the interaction between 2D TMDs and substrates, a key factor for the growth of high-quality materials, is systematically discussed by combining the latest theoretical calculations. Based on this, the effect of various substrate engineering approaches on the growth of large-area 2D TMDs is summarized in detail. Finally, the opportunities and challenges of substrate engineering for the future development of 2D TMDs are discussed. This review might provide deep insight into the controllable growth of high-quality 2D TMDs toward their industrial-scale practical applications.