Two-dimensional (2D) metals are appealing for many emergent phenomena and have recently attracted research interests1–9. Unlike the widely studied 2D van der Waals (vdW) layered materials, 2D metals are extremely challenging to achieve, because they are thermodynamically unstable1,10. Here we develop a vdW squeezing method to realize diverse 2D metals (including Bi, Ga, In, Sn and Pb) at the ångström thickness limit. The achieved 2D metals are stabilized from a complete encapsulation between two MoS2 monolayers and present non-bonded interfaces, enabling access to their intrinsic properties. Transport and Raman measurements on monolayer Bi show excellent physical properties, for example, new phonon mode, enhanced electrical conductivity, notable field effect and large nonlinear Hall conductivity. Our work establishes an effective route for implementing 2D metals, alloys and other 2D non-vdW materials, potentially outlining a bright vision for a broad portfolio of emerging quantum, electronic and photonic devices.
Two-dimensional (2D) semiconductors, combining remarkable electrical properties and mechanical flexibility, offer fascinating opportunities for flexible integrated circuits (ICs). Despite notable progress, so far the showcased 2D flexible ICs have been constrained to basic logic gates and ring oscillators with a maximum integration scale of a few thin film transistors (TFTs), creating a significant disparity in terms of circuit scale and functionality. Here, we demonstrate medium-scale flexible ICs integrating both combinational and sequential elements based on 2D molybdenum disulfide (MoS2). By co-optimization of the fabrication processes, flexible MoS2 TFTs with high device yield and homogeneity are implemented, as well as flexible NMOS inverters with robust rail-to-rail operation. Further, typical IC modules, such as NAND, XOR, half-adder and latch, are created on flexible substrates. Finally, a medium-scale flexible clock division module consisting of 112 MoS2 TFTs is demonstrated based on an edge-triggered Flip-Flop circuit. Our work scales up 2D flexible ICs to medium-scale, showing promising developments for various applications, including internet of everything, health monitoring and implantable electronics.
Large-scale, high-quality, and uniform monolayer molybdenum disulfide (MoS2) films are crucial for their applications in next-generation electronics and optoelectronics. Epitaxy is a mainstream technique for achieving high-quality MoS2 films and is demonstrated at a wafer scale up to 4-in. In this study, the epitaxial growth of 8-in. wafer-scale highly oriented monolayer MoS2 on sapphire is reported as with excellent spatial homogeneity, using a specially designed vertical chemical vapor deposition (VCVD) system. Field effect transistors (FETs) based on the as-grown 8-in. wafer-scale monolayer MoS2 film are fabricated and exhibit high performances, with an average mobility and an on/off ratio of 53.5 cm2 V−1 s−1 and 107, respectively. In addition, batch fabrication of logic devices and 11-stage ring oscillators are also demonstrated, showcasing excellent electrical functions. This work may pave the way of MoS2 in practical industry-scale applications.
Magnetic two-dimensional (2D) van der Waals (vdWs) materials are receiving increased attention due to their exceptional properties and potential applications in spintronic devices. Because exchange bias and spin–orbit torque (SOT)-driven magnetization switching are basic ingredients for spintronic devices, it is of pivotal importance to demonstrate these effects in the 2D vdWs material-based magnetic heterostructures. In this work, we employ a vacuum exfoliation approach to fabricate Fe₃GeTe₂ (FGT)/Ir₂₂Mn₇₈ (IrMn) and FGT/Pt bilayers, which have high-quality interfaces. An out-of-plane exchange bias of up to 895 Oe is obtained in the former bilayer, which is larger than that of the previously studied bilayers. In the latter bilayer, the SOT switching of the perpendicularly magnetized FGT is realized, which exhibits higher SOT-driven switching performance compared to the previously studied FGT/Pt bilayer devices with interfacial oxidation.
Electron-electron interactions play an important role in graphene and related systems and can induce exotic quantum states, especially in a stacked bilayer with a small twist angle. For bilayer graphene where the two layers are twisted by the ‘magic angle’, flat band and strong many-body effects lead to correlated insulating states and superconductivity. In contrast to monolayer graphene, the band structure of untwisted bilayer graphene can be further tuned by a displacement field, providing an extra degree of freedom to control the flat band that should appear when two bilayers are stacked on top of each other. Here, we report the discovery and characterization of displacement field-tunable electronic phases in twisted double bilayer graphene. We observe insulating states at a half-filled conduction band in an intermediate range of displacement fields.
Two-dimensional molybdenum disulfide (MoS₂) is an emergent semiconductor with great potential in next-generation scaled-up electronics, but the production of high-quality monolayer MoS₂ wafers still remains a challenge. Here, we report an epitaxy route toward 4 in. monolayer MoS₂ wafers with highly oriented and large domains on sapphire. Benefiting from a multisource design for our chemical vapor deposition setup and the optimization of the growth process, we successfully realized material uniformity across the entire 4 in. wafer and greater than 100 μm domain size on average. These monolayers exhibit the best electronic quality ever reported, as evidenced from our spectroscopic and transport characterizations. Our work moves a step closer to practical applications of monolayer MoS₂.
Atomically thin molybdenum disulfide (MoS₂) is a promising semiconductor material for integrated flexible electronics due to its excellent mechanical, optical and electronic properties. However, the fabrication of large-scale MoS₂-based flexible integrated circuits with high device density and performance remains a challenge. Here, we report the fabrication of transparent MoS₂-based transistors and logic circuits on flexible substrates using four-inch wafer-scale MoS₂ monolayers. Our approach uses a modified chemical vapour deposition process to grow wafer-scale monolayers with large grain sizes and gold/titanium/ gold electrodes to create a contact resistance as low as 2.9 kΩ μm−1. The field-effect transistors are fabricated with a high device density (1,518 transistors per cm2) and yield (97%), and exhibit high on/off ratios (1010), current densities (~35 μA μm−1), mobilities (~55 cm2 V−1 s−1) and flexibility.
Twist angle between adjacent layers of two-dimensional (2D) layered materials provides an exotic degree of freedom to enable various fascinating phenomena, which opens a research direction-twistronics. To realize the practical applications of twistronics, it is of the utmost importance to control the interlayer twist angle on large scales. In this work, we report the precise control of interlayer twist angle in centimeter-scale stacked multilayer MoS₂ homostructures via the combination of wafer-scale highly-oriented monolayer MoS₂ growth techniques and a water-assisted transfer method. We confirm that the twist angle can continuously change the indirect bandgap of centimeter-scale stacked multilayer MoS₂ homostructures, which is indicated by the photoluminescence peak shift. Furthermore, we demonstrate that the stack structure can affect the electrical properties of MoS₂ homostructures, where 30° twist angle yields higher electron mobility.
Van der Waals heterostructures of transition metal dichalcogenides with interlayer coupling offer an exotic platform to realize fascinating phenomena. Due to the type II band alignment of these heterostructures, electrons and holes are separated into different layers. The localized electrons induced doping in one layer, in principle, would lift the Fermi level to cross the spin-polarized upper conduction band and lead to strong manipulation of valley magnetic response. Here, we report the significantly enhanced valley Zeeman splitting and magnetic tuning of polarization for the direct optical transition of MoS₂ in MoS₂/WS₂ heterostructures. Such strong enhancement of valley magnetic response in MoS₂ stems from the change of the spin-valley degeneracy from 2 to 4 and strong many-body Coulomb interactions induced by ultrafast charge transfer. Moreover, the magnetic splitting can be tuned monotonically by laser power, providing an effective all-optical route towards engineering and
Monolayer MoS₂ is an emerging two-dimensional (2D) semiconductor with promise on novel electronics and optoelectronics. Standard micro-fabrication techniques such as lithography and etching are usually involved to pattern such materials for devices but usually face great challenges on yielding clean structures without edge, surface and interface contaminations induced during the fabrication process. Here a direct writing patterning approach for wafer-scale MoS₂ monolayers is reported. By controllable scratching by a tip, wafer-scale monolayer MoS₂ films on various substrates are patterned in an ultra-clean manner. MoS₂ field effect transistors fabricated from this scratching lithography show excellent performances, evidenced from a room-temperature on-off ratio exceeding 1010 and a high field-effect mobility of 50.7 cm2 V−1 s−1, due to the cleanness of as-fabricated devices. Such scratching approach can be also applied to other 2D materials, thus providing an alternate patte
Two-dimensional (2D) material is a new type of materials with thickness ranging from one to several atoms. Atoms within each individual layers are bonded by rather strong covalent bonds while the adjacent layers are usually stacked together by weak van der Waals (vdW) force.
Important factors supporting the vigorous developments of 2D materials are their unique physical properties (associated with interfaces) and potential applications. High-quality 2D crystals play a significant role in exploring new physical phenomena and in further extending their applications in microelectronics and optoelectronics.
Ranging from the initial micro/nano electronic/optoelectronic devices to spin/valley electronic devices, and ranging from optical/electrocatalyst to lithium battery and solar cell and to other areas, 2D materials are expected to be widely used in the new generation of electronic information and energy storage fields.
The emergence of 2D materials opens a brand-new space for exploring various functional material systems and pave the way to overcome various restrictions on the performance of traditional semiconductor devices. Preparation of high quality, wafer-scale monolayer membrane on insulating substrates is crucial for the application of 2D materials in large-scale integrated electronic and optoelectronic devices.
The uniformity of 2D crystals and the unity of their orientations determine the performance of electronic devices so that are decisive in the realization of massive applications of electronic devices based on 2D materials. Moreover, 2D materials can also be used to construct 2D vdW heterostructures in which the interface constructed by vdW force plays a key role in designing and modifying the physical properties and in realizing the application of relevant devices. The combination of the characteristics of two or even more 2D materials in a vdW heterostructure vastly enriches the properties of 2D materials and makes it straightforward to create artificial materials with designed properties.
In recent years, formation of Moire superlattice in the two-dimensional materials by controlling the stacking order between layers has been developed as a new dimension to reshape the physical properties of 2D materials. Controlling the formation of Moire superlattice managed to obtain a variety of exotic states in the twisted graphene system and is developing into another key field of the condensed matter physics and materials science. Promoting the research on the Moire superlattice systems represented by the twisted graphene is of great significance to promote the development of microelectronics and information technologies in our country.
Congratulations to Xingchao Zhang, He won CY23 postdoctoral innovative talent support program
This work shows flexible integrated circuits based on monolayer MoS2 can have both high performance and low power consumption, which provides a technical foundation for the development of two-dimensional semiconductor-based integrated circuits to practical applications
Team developed a large-area flexible multifunctional optoelectronic device based on large-area, high-quality, monolayer MoS2. The optical decay time and persistent photoconductance of the device can be effectively controlled by the gate voltage, so that the functions of optical detection, optical storage and photoelectric synapse can be realized.
The flexible artificial retina device reported in this work has simple device structure, high photoelectric conversion efficiency, ultra-low power consumption and strong adjustability, which provides a new design and idea for the development of artificial retina, and has a great application prospect in the future clinical treatment
Chinese Academy of Sciences University
Hong Kong University of Science and Technology
Hong Kong Polytechnic University
Shanghai University of Science and Technology
Hong Kong university
Southern University of Science and Technology
Hunan University
South China Normal University
Northeast Normal University
University of Macau
University of Electronic Science and Technology of China
The Chinese University of Hong Kong
2D Materials Team
