zemin zheng

The optical and optoelectronic properties of 2D Xenes and their applications in photonic devices including all-optical modulators, wavelength converters, ultrafast lasers, and photodetectors are comprehensively reviewed. The article mainly focuses on five most extensively studied Xenes: graphene, black phosphorus, antimonene, bismuthene, and tellurenene. The properties and applications of other Xenes are also briefly introduced.

Abstract

In recent years, tremendous attention has been paid to the investigation of single-element 2D materials. These 2D materials mainly consist of elements from group IV and group V such as silicene, phosphorene, and antimonene. Together with other four elements from groups III and VI, they are classified as 2D Xenes and exhibit rich optical and optoelectronic properties such as broadband optical response, strong nonlinearity, ultrafast recovery time, and layer-dependent bandgap. 2D Xenes can be easily integrated with microfibers and other optical platforms. On the basis of their attracting characteristics, 2D Xenes have been utilized in various functional devices. In this review, the optical and optoelectronic properties of the most intensively studied 2D Xenes are introduced. Their applications in photonic devices including all-optical modulators, wavelength converters, ultrafast lasers, and photodetectors are explicitly explored. Finally, the challenges and future perspectives of photonic devices based on 2D Xenes are discussed.

Recent advances in etching of 2D materials are comprehensively presented and typical etching modes of chemical vapor deposition (CVD) etching are shown. Linear etching usually results in etched lines along specific crystal lattice. Anisotropic etching tends to form etched holes with Euclidean geometric patterns. Fractal etching typically leads to self-similar symmetric patterns, such as snow-like patterns.

Abstract

Etching, considered as the reverse process of growth, has drawn intensive interests in the past decades. Rather from offering building blocks for formation of materials, etching is served as removing basic units from the matrix. Generally, etching plays a critical role in three aspects: first, it can serve as direct top-down method to precisely make designed patterns for electronic devices. Second, it can offer an indirect way to probe the detailed growth mechanism of 2D materials, enhancing understanding of growth process. Finally, it can be an efficient and facile way to visualize grain boundaries. Herein, several commonly used etching techniques for 2D materials are presented of which chemical vapor deposition etching has attracted the most intensive attentions. Thereafter, the typical etching modes of 2D materials are demonstrated, wherein linear etching, anisotropic etching, and fractal etching are comprehensively exhibited, respectively. Furthermore, the etching mechanism of 2D materials is elucidated, thereby offering a guideline for probing their in-depth etching dynamics and kinetics. Finally, relevant concerns regarding uniformity and reproducibility within etching process are discussed and the expected future is envisaged.

Nature Nanotechnology, Published online: 14 July 2022; doi:10.1038/s41565-022-01165-6

This Review elaborates on the recent developments and the future opportunities and challenges of fundamental research on semiconductor moiré materials, with a particular focus on transition metal dichalcogenides.

Nature Communications, Published online: 22 July 2022; doi:10.1038/s41467-022-31851-x

Twisted van der Waals structures represent a versatile platform to investigate topological and correlated electronic states. Here, the authors report the visualization of an electron crystal phase in twisted monolayer-bilayer graphene via scanning tunnelling microscopy, studying the coupling between strong electron correlation and nontrivial band topology.

Nature Communications, Published online: 23 July 2022; doi:10.1038/s41467-022-31954-5

The supercurrent diode effect was recently observed in a Nb/V/Ta superlattice thin film with Rashba-type spin-orbit coupling. Here, the authors observe this effect in few-layer NbSe2 crystals driven by valley-Zeeman-type spin-orbit coupling and find that the effect is proportional to out-of-plane magnetic field.

Nature Communications, Published online: 22 June 2022; doi:10.1038/s41467-022-31225-3

The interplay between chirality and magnetism has been attracting much. Here, the authors show that the movement of bound charges in a chiral dielectric depends on the relative orientation between this movement and an external magnetic field.

Nature Communications, Published online: 27 June 2022; doi:10.1038/s41467-022-31451-9

Harmonic measurements have been used extensively in ferromagnetic/heavy metal heterostructures to characterize the magnetization dynamic; however, it has remained unclear about whether such techniques could be applied to antiferromagnetic devices. Here, Cheng et al demonstrate such a harmonic measurement approach in an antiferromagnet.

Nature Communications, Published online: 05 July 2022; doi:10.1038/s41467-022-31606-8

Bi2O2Se holds potential for the realization of 2D optical modulators due to its broadband nonlinear response, air stability and carrier mobility. Here, the authors report the realization of defect-engineered Bi2O2Se nanoplates as saturable absorbers for femtosecond solid-state lasers, showing improved output power and pulse duration.

Nature Communications, Published online: 06 July 2022; doi:10.1038/s41467-022-31685-7

The study of the mechanical properties of twisted van der Waals structures can provide important information about their interlayer coupling and electronic behaviour. Here, the authors report a nanoindentation-based technique to determine the interlayer shear stress in bilayer MoS2, showing its independence as a function of the twist angle.

Nature Communications, Published online: 12 July 2022; doi:10.1038/s41467-022-31612-w

CrGeTe3 is a van der Waals honeycomb ferromagnet, known for exhibiting strong coupling between lattice and spin degrees of freedom. Here, Chen et al perform neutron scattering on CrGeTe3, find a broadened spin-wave excitation resulting from zero-temperature motion of the atoms in the lattice.

Nature Communications, Published online: 18 July 2022; doi:10.1038/s41467-022-31886-0

Chemical vapor deposition enables the scalable production of 2D semiconductors, but the grown materials are usually affected by high defect densities. Here, the authors report a hydroxide vapour phase deposition method to synthesize wafer-scale monolayer WS2 with reduced defect density and electrical properties comparable to those of exfoliated flakes.

Nature Communications, Published online: 26 May 2022; doi:10.1038/s41467-022-30676-y

A Ni-based MOF catalyst is reported to facilitate the photocatalytic reduction of CO2 to CO, a low-value product. In tandem, the as-produced CO is used as a reactant in the Pd-catalyzed carbonylation of aryl halides and other fine organic chemicals.

The electronic and magnetic response of the magnetic topological insulator MnBi₂Te₄ is shown to be controllable by manipulating the surface chemistry in epitaxial thin films. This results in a dramatic reversal of the sign of the anomalous Hall effect driven by a change in the effective film thickness due to the non-compensated magnetic moment.

Abstract

Understanding the effects of the interfacial modification to the functional properties of magnetic topological insulator thin films is crucial for developing novel technological applications from spintronics to quantum computing. Here, a large electronic and magnetic response is reported to be induced in the intrinsic magnetic topological insulator MnBi₂Te₄ by controlling the propagation of surface oxidation. It is shown that the formation of the surface oxide layer is confined to the top 1–2 unit cells but drives large changes in the overall magnetic response. Specifically, a dramatic reversal of the sign of the anomalous Hall effect is observed to be driven by finite thickness magnetism, which indicates that the film splits into distinct magnetic layers each with a unique electronic signature. These data reveal a delicate dependence of the overall magnetic and electronic response of MnBi₂Te₄ on the stoichiometry of the top layers. This study suggests that perturbations resulting from surface oxidation may play a non-trivial role in the stabilization of the quantum anomalous Hall effect in this system and that understanding targeted modifications to the surface may open new routes for engineering novel topological and magnetic responses in this fascinating material.

Nature Communications, Published online: 27 May 2022; doi:10.1038/s41467-022-30738-1

Van der Waals heterostructures offer the potential of integrating multiple material layers into a single device to achieve new functionalities. Here, Ou et al combine ZrTe2, a topological semimetal, with CrTe2, a 2D ferromagnet, in a single heterostructure and demonstrate spin-orbit torque switching of the 2D ferromagnet by current in the topological semimetal.

A facile approach is developed for constructing high-quality metal-2D semiconductor junctions through the edge-guided electrodeposition. Cross-sectional imaging and transport measurements confirm the seamless contact of Pd with each layer of MoS₂ greatly reduces the contact barrier to ≈20 meV and contact resistance to ≈290 Ω µm and thus significantly increases the performance of FETs with Pd nanowire edge contacts.

Abstract

2D semiconductors, such as MoS₂ have emerged as promising ultrathin channel materials for the further scaling of field-effect transistors (FETs). However, the contact barrier at the metal-2D semiconductor junctions still significantly limits the device's performance. By extending the application of electrochemical deposition in 2D electronics, a distinct approach is developed for constructing metal-2D semiconductor junctions in an edge-contacted configuration through the edge-guided electrodeposition of varied metals. Both high-resolution microscopic imaging and electrical transport measurements confirm the successful creation of high-quality Pd-2D MoS₂ junctions in desired geometry by combining electrodeposition with lithographic patterning. FETs are fabricated on the obtained Pd-2D MoS₂ junctions and it is confirmed that these junctions exhibit a reduced contact barrier of ≈20 meV and extremely low contact resistance of 290 Ω µm and thus increase the averaged mobility of MoS₂ FETs to ≈108 cm² V ⁻¹ s⁻¹. This approach paves a new way for the construction of metal-semiconductor junctions and also demonstrates the great potential of the electrochemical deposition technique in 2D electronics.