Jiuxiang Dai

MnBi 2 Te 4 /(Bi 2 Te 3 ) n materials system has recently generated strong interest as a natural platform for the realization of the quantum anomalous Hall (QAH) state. The system is magnetically much better ordered than substitutionally doped materials, however, the detrimental effects of certain disorders are becoming increasingly acknowledged. Here, from compiling structural, compositional, and magnetic metrics of disorder in ferromagnetic (FM) MnBi 2 Te 4 /(Bi 2 Te 3 ) n it is found that migration of Mn between MnBi 2 Te 4 septuple layers (SLs) and otherwise non-magnetic Bi 2 Te 3 quintuple layers (QLs) has systemic consequences—it induces FM coupling of Mn-depleted SLs with Mn-doped QLs, seen in ferromagnetic resonance as an acoustic and optical resonance mode of the two coupled spin subsystems. Even for a large SL separation (

2D Ge(110) single crystal is first synthesized via a gallium-associated self-limiting growth mechanism, which exhibits anisotropic honeycomb structure, uniformly incremental lattice, blue-shifted photoluminescence emission, unique phonon modes, and excellent second harmonic generation. Notably, it shows high hole mobility of 724 cm² V⁻¹ s⁻¹, which will provide an excellent candidate for application in electronics and optoelectronics.

Abstract

Germanium, the prime applied semiconductor, is widely used in solid-state electronics and photoelectronics. Unfortunately, since the 3D diamond-like structure with strong covalent bonds impedes the 2D anisotropic growth, only the examples of ultrathin Ge along the (111) plane have been investigated, much less to the controllable synthesis along another crystal surface. Meanwhile, Ge(111) flakes are limited in semiconductor applications because of their gapless property. Here, ultrathin Ge(110) single crystal is synthesized with semiconductive property via gallium-associated self-limiting growth. The obtained ultrathin Ge(110) single crystal exhibits anisotropic honeycomb structure, uniformly incremental lattice, wide tunable direct-bandgap, blue-shifted photoluminescence emission, and unique phonon modes, which are consistent with the previous theoretical predictions. It also confirms excellent second harmonic generation and high hole mobility of 724 cm² V⁻¹ s⁻¹. The realization of ultrathin Ge(110) single crystal will provide an excellent candidate for application in electronics and optoelectronics.

New and in-depth insight into the fundamental mechanism of Fermi level pinning in 2D semiconductor devices is presented in this review. The related device characteristics and contact strategies utilizing both the Fermi level pinning and depinning are introduced.

Abstract

Motivated by the high expectation for efficient electrostatic modulation of charge transport at very low voltages, atomically thin 2D materials with a range of bandgaps are investigated extensively for use in future semiconductor devices. However, researchers face formidable challenges in 2D device processing mainly originated from the out-of-plane van der Waals (vdW) structure of ultrathin 2D materials. As major challenges, untunable Schottky barrier height and the corresponding strong Fermi level pinning (FLP) at metal interfaces are observed unexpectedly with 2D vdW materials, giving rise to unmodulated semiconductor polarity, high contact resistance, and lowered device mobility. Here, FLP observed from recently developed 2D semiconductor devices is addressed differently from those observed from conventional semiconductor devices. It is understood that the observed FLP is attributed to inefficient doping into 2D materials, vdW gap present at the metal interface, and hybridized compounds formed under contacting metals. To provide readers with practical guidelines for the design of 2D devices, the impact of FLP occurring in 2D semiconductor devices is further reviewed by exploring various origins responsible for the FLP, effects of FLP on 2D device performances, and methods for improving metallic contact to 2D materials.

npj 2D Materials and Applications, Published online: 16 December 2021; doi:10.1038/s41699-021-00273-6

Super-Nernstian ion sensitive field-effect transistor exploiting charge screening in WSe₂/MoS₂ heterostructure

Nature Electronics, Published online: 16 December 2021; doi:10.1038/s41928-021-00686-7

A molybdenum disulfide/tungsten diselenide van der Waals heterostructure can exhibit a room-temperature valley Hall effect with electrically tunable magnitude and polarity, which can be used to create a bipolar valleytronic transistor.

Nature, Published online: 16 December 2021; doi:10.1038/s41586-021-04321-5

Selective sulfidation of metal compounds

Publication date: 19 January 2022

Source: Joule, Volume 6, Issue 1

Author(s): Jiawei Yang, Guodong Li, Hangtian Zhu, Nan Chen, Tianbo Lu, Junling Gao, Liwei Guo, Junsen Xiang, Peijie Sun, Yuan Yao, Ronggui Yang, Huaizhou Zhao

Metallic Plasmonic Arrays

Metallic plasmonic array structures provide a powerful platform to control light–matter interactions and show fascinating, rich, and tunable optical properties through morphology and parameter engineering enabled by nanofabrication. In article number 2007988, Bowen Liu, Bin Ren, and co-workers review light-management mechanisms, fabrication techniques, and applications, such as plasmonic sensing, surface-enhanced spectroscopies, nanolasing, and perfect light absorption, for metallic plasmonic array structures.

A novel embedded sensing amplifier and readout scheme is developed for a 2D-layered SnSe₂ CMOS-compatible gas sensor featuring high and adjustable sensitivity. This proposed sensor possesses the ability to operate at room temperature and suitable for low-power applications. Moreover, the calibration method and peripheral circuits proposed in this research endow low error, high density, and high sensitivity responses.

Abstract

A 2D SnSe₂ layered film-based gas detector incorporating a floating-gate device coupled with metal interconnect wiring structures is proposed and demonstrated for the first time. Linear amplification can be readily implemented using a coupling ratio design, which refers to the capacitance ratio between the gate and device in the sense amplifier circuits. A sensitivity of 102 mV ppm⁻¹ can be obtained using the 2D SnSe₂ layered film with a thickness of 10 nm. The 2D SnSe₂ layered film-based complementary metal–oxide–semiconductor (CMOS) gas detector features highly sensitive, wide, and adjustable dynamic ranges with a real-time response of the sub-ppm detection limit on NO₂ gas. In addition, the synthesis process of the SnSe₂ layered film can occur at a low temperature and be operated at room temperature. Furthermore, 3 × 3 gas detector arrays with peripheral circuits demonstrate the functionality of multiple gas detection simultaneously and 16 × 16 arrays with a decoder and other peripheral circuits are constructed and simulated, providing the spatial distribution of the gas concentration in a specific region. The performance of the proposed detector is comparable to that of the other state-of-the-art gas sensors.

Author(s): Laurel Anderson, Austin Cheng, Takashi Taniguchi, Kenji Watanabe, and Philip Kim

Measurements of the Coulomb drag between a nanotube and graphene show subtleties depending on temperature, carrier density, and distance in both linear and nonlinear regimes.

[Phys. Rev. Lett. 127, 257701] Published Mon Dec 13, 2021

Synthesis of new two-dimensional titanium carbonitride Ti₂C_0.5N_0.5T _x MXene and its performance as an electrode material for sodium-ion battery

Abstract

Two-dimensional (2D) layered transition metal carbides/nitrides, called MXenes, are attractive alternative electrode materials for electrochemical energy storage. Owing to their metallic electrical conductivity and low ion diffusion barrier, MXenes are promising anode materials for sodium-ion batteries (SIBs). Herein, we report on a new 2D carbonitride MXene, viz., Ti₂C_0.5N_0.5T _x (T _x stands for surface terminations), and the only second carbonitride after Ti₃CNT _x so far. A new type of in situ HF (HCl/KF) etching condition was employed to synthesize multilayer Ti₂C_0.5N_0.5T _x powders from Ti₂AlC_0.5N_0.5. Spontaneous intercalation of tetramethylammonium followed by sonication in water allowed for large-scale delamination of this new titanium carbonitride into 2D sheets. Multilayer Ti₂C_0.5N_0.5T _x powders showed higher specific capacities and larger electroactive surface area than those of Ti₂CT _x powders. Multilayer Ti₂C_0.5N_0.5T _x powders show a specific capacity of 182 mAh g⁻¹ at 20 mA g⁻¹, the highest among all reported MXene electrodes as SIBs with excellent cycling stability.

The combination of 2D materials and optical sensors has become a hot research topic in recent years. Here, the recent progress of optical biosensors based on various 2D materials (graphene, black phosphorus, and MXenes) is reviewed. Furthermore, the applications of these sensors in biological imaging, food safety, pollution prevention and biomedicine are discussed. Finally, their future development trend is prospected.

Abstract

The combination of 2D materials and optical biosensors has become a hot research topic in recent years. Graphene, transition metal dichalcogenides, black phosphorus, MXenes, and other 2D materials (metal oxides and degenerate semiconductors) have unique optical properties and play a unique role in the detection of different biomolecules. Through the modification of 2D materials, optical biosensor has the advantages that traditional sensors (such as electrical sensing) do not have, and the sensitivity and detection limit are greatly improved. Here, optical biosensors based on different 2D materials are reviewed. First, various detection methods of biomolecules, including surface plasmon resonance (SPR), fluorescence resonance energy transfer (FRET), and evanescent wave and properties, preparation and integration strategies of 2D material, are introduced in detail. Second, various biosensors based on 2D materials are summarized. Furthermore, the applications of these optical biosensors in biological imaging, food safety, pollution prevention/control, and biological medicine are discussed. Finally, the future development of optical biosensors is prospected. It is believed that with their in-depth research in the laboratory, optical biosensors will gradually become commercialized and improve people's quality of life in many aspects.

Recent advances in 2D nanomaterials allow to address scientific and industrial challenges associated with the design of mechanical systems with improved friction and wear performance. In this review, the beneficial properties of layered 2D materials that make them excellent candidates for efficient friction and wear reduction in dry-running and boundary lubricated machine components are summarized.

Abstract

Recent advances in 2D nanomaterials, such as graphene, transition metal dichalcogenides, boron nitride, MXenes, allow not only to discover several new nanoscale phenomena but also to address the scientific and industrial challenges associated with the design of systems with desired physical properties. One of the great challenges for mechanical systems is associated with addressing friction and wear problems in machine elements. In this review, the beneficial properties of layered 2D materials that enable the control of their tribological behavior and make them excellent candidates for efficient friction and wear reduction in dry-running and boundary lubricated machine components are summarized. The recent studies highlighting the successful implementation of 2D structures when used as solid lubricant coatings or reinforcement phases in composites for various machine components including sliding and rolling bearings, gears, and seals are overviewed. The examples presented in the studies demonstrate the great potential for 2D materials to address the energy-saving needs by friction and wear reduction.