Explore the vast range of titles available.

Two-dimensional (2D) semiconductors have attracted tremendous interest as atomically thin channels that could facilitate continued transistor scaling. However, despite many proof-of-concept demonstrations, the full potential of 2D transistors has yet to be determined. To this end, the fundamental merits and technological limits of 2D transistors need a critical assessment and objective projection. Here we review the promise and current status of 2D transistors, and emphasize that widely used device parameters (such as carrier mobility and contact resistance) could be frequently misestimated or misinterpreted, and may not be the most reliable performance metrics for benchmarking 2D transistors. We suggest that the saturation or on-state current density, especially in the short-channel limit, could provide a more reliable measure for assessing the potential of diverse 2D semiconductors, and should be applied for cross-checking different studies, especially when milestone performance metrics are claimed. We also summarize the key technical challenges in optimizing the channels, contacts, dielectrics and substrates and outline potential pathways to push the performance limit of 2D transistors. We conclude with an overview of the critical technical targets, the key technological obstacles to the ‘lab-to-fab’ transition and the potential opportunities arising from the use of these atomically thin semiconductors. The current status and prospects of two-dimensional transistors are reviewed, and the reliability of widely used device parameters is assessed.

The controllable growth of two-dimensional (2D) heterostructure arrays is critical for exploring exotic physics and developing novel devices, yet it remains a substantial synthetic challenge. Here we report a rational synthetic strategy to fabricate mosaic heterostructure arrays in monolayer 2D atomic crystals. By using a laser-patterning and an anisotropic thermal etching process, we create periodic triangular hole arrays in 2D crystals with precisely controlled size and atomically clean edges, which function as robust templates for endoepitaxial growth of another 2D crystal, to obtain monolayer mosaic heterostructures with atomically sharp heterojunction interfaces. Systematic microstructure and spectroscopic characterizations reveal periodic modulation of chemical compositions, lattice strains and electronic band gaps throughout the mosaic heterostructures. The robust growth of the monolayer mosaic heterostructures with a high level of synthetic control opens a pathway for band structure engineering and spatially modulating the potential landscapes in the atomically thin 2D crystals, establishing a designable material platform for fundamental studies and development of complex devices and integrated circuits from 2D heterostructures. An endoepitaxy approach enables the realization of two-dimensional mosaic heterostructures with atomically sharp heterojunction interfaces.

Strain engineering is a promising method to manipulate the electronic and optical properties of two-dimensional (2D) materials. However, with weak van der Waals interaction, severe slippage between 2D material and substrate could dominate the bending or stretching processes, leading to inefficiency strain transfer. To overcome this limitation, we report a simple strain engineering method by encapsulating the monolayer 2D material in the flexible PVA substrate through spin-coating approach. The strong interaction force between spin-coated PVA and 2D material ensures the mechanical strain can be effectively transferred with negligible slippage or decoupling. By applying uniaxial strain to monolayer MoS 2 , we observe a higher bandgap modulation up to ~300 meV and a highest modulation rate of ~136 meV/%, which is approximate two times improvement compared to previous results achieved. Moreover, this simple strategy could be well extended to other 2D materials such as WS 2 or WSe 2 , leading to enhanced bandgap modulation. Strain engineering is a promising method to manipulate properties of two-dimensional (2D) materials but slippage between material and substrate makes strain transfer inefficient. Here the authors overcome slipping effects by encapsulating a 2D material in a polymer substrate.

We report a general synthetic strategy for highly robust growth of diverse lateral heterostructures, multiheterostructures, and superlattices from two-dimensional (2D) atomic crystals. A reverse flow during the temperature-swing stage in the sequential vapor deposition growth process allowed us to cool the existing 2D crystals to prevent undesired thermal degradation and uncontrolled homogeneous nucleation, thus enabling highly robust block-by-block epitaxial growth. Raman and photoluminescence mapping studies showed that a wide 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) were readily prepared with precisely controlled spatial modulation. Transmission electron microscope studies showed clear chemical modulation with atomically sharp interfaces. Electrical transport studies of WSe₂-WS₂ lateral junctions showed well-defined diode characteristics with a rectification ratio up to 10⁵.

The discovery of intrinsic ferromagnetism in ultrathin two-dimensional van der Waals crystals opens up exciting prospects for exploring magnetism in the ultimate two-dimensional limit. Here, we show that environmentally stable CrSe 2 nanosheets can be readily grown on a dangling-bond-free WSe 2 substrate with systematically tunable thickness down to the monolayer limit. These CrSe 2 /WSe 2 heterostructures display high-quality van der Waals interfaces with well-resolved moiré superlattices and ferromagnetic behaviour. We find no apparent change in surface roughness or magnetic properties after months of exposure in air. Our calculations suggest that charge transfer from the WSe 2 substrate and interlayer coupling within CrSe 2 play a critical role in the magnetic order in few-layer CrSe 2 nanosheets. The highly controllable growth of environmentally stable CrSe 2 nanosheets with tunable thickness defines a robust two-dimensional magnet for fundamental studies and potential applications in magnetoelectronic and spintronic devices. CrSe 2 nanosheets grown on WSe 2 show no apparent change in surface roughness or magnetic properties after months of exposure in air. Calculations suggest that charge transfer from the WSe 2 substrate and interlayer coupling within CrSe 2 play a critical role.

Two-dimensional (2D) semiconductors such as molybdenum disulfide (MoS 2 ) have attracted tremendous interest for transistor applications. However, the fabrication of 2D transistors using traditional lithography or deposition processes often causes undesired damage and contamination to the atomically thin lattices, partially degrading the device performance and leading to large variation between devices. Here we demonstrate a highly reproducible van der Waals integration process for wafer-scale fabrication of high-performance transistors and logic circuits from monolayer MoS 2 grown by chemical vapour deposition. By designing a quartz/polydimethylsiloxane semirigid stamp and adapting a standard photolithography mask-aligner for the van der Waals integration process, our strategy ensures a uniform mechanical force and a bubble-free wrinkle-free interface during the pickup/release process, which is crucial for robust van der Waals integration over a large area. Our scalable van der Waals integration process allows damage-free integration of high-quality contacts on monolayer MoS 2 at the wafer scale and enables high-performance 2D transistors. The van-der-Waals-contacted devices display an atomically clean interface with much smaller threshold variation, higher on-current, smaller off-current, larger on/off ratio and smaller subthreshold swing than those fabricated with conventional lithography. The approach is further used to create various logic gates and circuits, including inverters with a voltage gain of up to 585, and logic OR gates, NAND gates, AND gates and half-adder circuits. This scalable van der Waals integration method may be useful for reliable integration of 2D semiconductors with mature industry technology, facilitating the technological transition of 2D semiconductor electronics. A semirigid stamp and a standard photolithography mask-aligner enable a reliable and scalable pickup and release process for van der Waals materials integration at the wafer scale.

Mulitipe stoichiometric ratio of two-dimensional (2D) transition metal dichalcogenides (TMDCs) attracted considerable interest for their unique chemical and physical properties. Here we developed a chemical vapor deposition (CVD) method to controllably synthesize ultrathin NiS and NiS 2 nanoplates. By tuning the growth temperature and the amounts of the sulfur powder, 2D non-layered NiS and NiS 2 nanoplates can be selectively prepared with the thickness of 2.0 and 7.0 nm, respectively. X-ray diffraction (XRD) and transmission electron microscopy (TEM) characterization reveal that the 2D NiS and NiS 2 nanoplates are high-quality single crystals in the hexagonal and cubic phase, respectively. Electrical transport studies show that electrical conductivities of the 2D NiS and NiS 2 nanoplates are as high as 4.6 × 10 5 and 6.3 × 10 5 S·m −1 , respectively. The electrical results demonstrate that the synthesized metallic NiS and NiS 2 could serve as good electrodes in 2D electronics.

HighlightsThe large-sheet holey graphene framework/SiO (LHGF/SiO) composite displays notably high recoverable strain, suggesting considerably improved mechanical flexibility and robustnessThe LHGF/SiO anode with a mass loading of 44 mg cm−2 delivers a high areal capacity of 35.4 mAh cm−2 at current density of 8.8 mA cm−2 and retains a capacity of 10.6 mAh cm−2 at 17.6 mA cm−2The LHGF/SiO anode with an ultra-high mass loading of 94 mg cm−2 delivers an extraordinary areal capacity up to 140.8 mAh cm−2, about 1–2 order of magnitude higher than those in typical commercial devicesSilicon monoxide (SiO) is an attractive anode material for next-generation lithium-ion batteries for its ultra-high theoretical capacity of 2680 mAh g−1. The studies to date have been limited to electrodes with a relatively low mass loading (< 3.5 mg cm−2), which has seriously restricted the areal capacity and its potential in practical devices. Maximizing areal capacity with such high-capacity materials is critical for capitalizing their potential in practical technologies. Herein, we report a monolithic three-dimensional (3D) large-sheet holey graphene framework/SiO (LHGF/SiO) composite for high-mass-loading electrode. By specifically using large-sheet holey graphene building blocks, we construct LHGF with super-elasticity and exceptional mechanical robustness, which is essential for accommodating the large volume change of SiO and ensuring the structure integrity even at ultrahigh mass loading. Additionally, the 3D porous graphene network structure in LHGF ensures excellent electron and ion transport. By systematically tailoring microstructure design, we show the LHGF/SiO anode with a mass loading of 44 mg cm−2 delivers a high areal capacity of 35.4 mAh cm−2 at a current of 8.8 mA cm−2 and retains a capacity of 10.6 mAh cm−2 at 17.6 mA cm−2, greatly exceeding those of the state-of-the-art commercial or research devices. Furthermore, we show an LHGF/SiO anode with an ultra-high mass loading of 94 mg cm−2 delivers an unprecedented areal capacity up to 140.8 mAh cm−2. The achievement of such high areal capacities marks a critical step toward realizing the full potential of high-capacity alloy-type electrode materials in practical lithium-ion batteries.

The development of next-generation electronics requires scaling of channel material thickness down to the two-dimensional limit while maintaining ultralow contact resistance 1 , 2 . Transition-metal dichalcogenides can sustain transistor scaling to the end of roadmap, but despite a myriad of efforts, the device performance remains contact-limited 3 – 12 . In particular, the contact resistance has not surpassed that of covalently bonded metal–semiconductor junctions owing to the intrinsic van der Waals gap, and the best contact technologies are facing stability issues 3 , 7 . Here we push the electrical contact of monolayer molybdenum disulfide close to the quantum limit by hybridization of energy bands with semi-metallic antimony ( 01 1 ̅ 2 ) through strong van der Waals interactions. The contacts exhibit a low contact resistance of 42 ohm micrometres and excellent stability at 125 degrees Celsius. Owing to improved contacts, short-channel molybdenum disulfide transistors show current saturation under one-volt drain bias with an on-state current of 1.23 milliamperes per micrometre, an on/off ratio over 10 8 and an intrinsic delay of 74 femtoseconds. These performances outperformed equivalent silicon complementary metal–oxide–semiconductor technologies and satisfied the 2028 roadmap target. We further fabricate large-area device arrays and demonstrate low variability in contact resistance , threshold voltage, subthreshold swing, on/off ratio, on-state current and transconductance 13 . The excellent electrical performance, stability and variability make antimony ( 01 1 ̅ 2 ) a promising contact technology for transition-metal-dichalcogenide-based electronics beyond silicon. The electrical contact of two-dimensional transistors is pushed close to the quantum limit by hybridization of the energy bands with antimony; the contacts have low contact resistance and excellent stability.

Two-dimensional layered semiconductors such as MoS 2 and WSe 2 have attracted considerable interest in recent times. Exploring the full potential of these layered materials requires precise spatial modulation of their chemical composition and electronic properties to create well-defined heterostructures. Here, we report the growth of compositionally modulated MoS 2 –MoSe 2 and WS 2 –WSe 2 lateral heterostructures by in situ modulation of the vapour-phase reactants during growth of these two-dimensional crystals. Raman and photoluminescence mapping studies demonstrate that the resulting heterostructure nanosheets exhibit clear structural and optical modulation. Transmission electron microscopy and elemental mapping studies reveal a single crystalline structure with opposite modulation of sulphur and selenium distributions across the heterostructure interface. Electrical transport studies demonstrate that the WSe 2 –WS 2 heterojunctions form lateral p–n diodes and photodiodes, and can be used to create complementary inverters with high voltage gain. Our study is an important advance in the development of layered semiconductor heterostructures, an essential step towards achieving functional electronics and optoelectronics. Different two-dimensional materials can be grown epitaxially side by side to create one-layer-thick p–n junctions.