Clean WS2 and MoS2 Nanoribbons Generated by Laser-Induced Unzipping of the Nanotubes

Toward Edge Engineering of Two-Dimensional Layered Transition-Metal Dichalcogenides by Chemical Vapor Deposition

The manipulation of edge configurations and structures in atomically-thin transition metal dichalcogenides (TMDs) for versatile functionalization has attracted intensive interest in recent years. The chemical vapor deposition (CVD) approach has shown promise for TMD edge engineering of atomic edge configurations (1H, 1T or 1T'-zigzag or armchair edges) as well as diverse edge morphologies (1D nanoribbons, 2D dendrites, 3D spirals, etc.). These edge-rich TMD layers offer versatile candidates for probing the physical and chemical properties and exploring potential applications in electronics, optoelectronics, catalysis, sensing, and quantum technologies. In this Review, we present an overview of the current state-of-the-art in the manipulation of TMD atomic edges and edge-rich structures using CVD. We highlight the vast range of distinct properties associated with these edge configurations and structures and provide insights into the opportunities afforded by such edge-functionalized crystals. The objective of this Review is to motivate further research and development efforts to use CVD as a scalable approach to harness the benefits of such crystal-edge engineering.

Synthesis and Characterization of Transition Metal Dichalcogenide Nanoribbons Based on a Controllable O2 Etching

Although the synthesis of monolayer transition metal dichalcogenides has been established in the last decade, synthesizing nanoribbons remains challenging. In this study, we have developed a straightforward method to obtain nanoribbons with controllable widths (25-8000 nm) and lengths (1-50 μm) by O₂ etching of the metallic phase in metallic/semiconducting in-plane heterostructures of monolayer MoS₂. We also successfully applied this process for synthesizing WS₂, MoSe₂, and WSe₂ nanoribbons. Furthermore, field-effect transistors of the nanoribbons show an on/off ratio of larger than 1000, photoresponses of 1000%, and time responses of 5 s. The nanoribbons were compared with monolayer MoS₂, highlighting a substantial difference in the photoluminescence emission and photoresponses. Additionally, the nanoribbons were used as a template to build one-dimensional (1D)-1D or 1D-2D heterostructures with various transition metal dichalcogenides. The process developed in this study offers simple production of nanoribbons with applications in several fields of nanotechnology and chemistry.

Ferromagnetism of two-dimensional transition metal chalcogenides: both theoretical and experimental investigations

In recent years, with the fast development of integrated circuit electronic devices and technologies, it has become urgent to improve the density of data storage and lower the energy losses of devices. Under these circumstances, two-dimensional (2D) materials, which have a smaller size and lower energy loss compared with bulk materials, are becoming ideal candidates for future spintronic devices. Among them, 2D transition metal chalcogenides (TMCs), which have excellent electronic and optical properties, have attracted great attention from researchers. However, most of them are intrinsically non-magnetic, which severely hinders their further applications in spintronics. Therefore, introducing intrinsic room-temperature ferromagnetism into 2D TMC materials has become an important issue in spintronics. In this work, we review the introduction of intrinsic ferromagnetism into typical 2D TMCs using various strategies, such as defect engineering, doping with transition metal elements, and phase transfer. Additionally, we found that their ferromagnetism could be adjusted via changing the experimental conditions, such as the nucleation temperature, ion irradiation dose, doping amount, and phase ratio. Finally, we provide some insight into prospective solutions for introducing ferromagnetism into 2D TMCs, hoping to shed some light on future spintronics development.

Borophene: New Sensation in Flatland

Borophene, a 2D allotrope of boron and the lightest elemental Dirac material, is the latest very promising 2D material owing to its unique structural and electronic characteristics of the X₃ and β₁₂ phases. The high atomic density on ridgelines of the β₁₂ phase of borophene provides a substantial orbital overlap, which leads to an excellent electron density in the conduction level and thus to a highly metallic behavior. These unique structural characteristics and electronic properties of borophene attract significant scientific interest. Herein, approaches for crystal growth/synthesis of these unique nanostructures and their potential technological applications are discussed. Various substrate-supported ultrahigh-vacuum growth techniques for borophene, such as molecular beam epitaxy, atomic layer deposition, and chemical vapor deposition, along with their challenges, are also summarized. The sonochemical exfoliation and modified Hummer's technique for the synthesis of free-standing borophene are also discussed. Solution-phase exfoliation seems to address the scalability issues and expands the applications of these unique materials to various fields, including renewable energy devices and ultrafast sensors. Furthermore, the electronic, optical, thermal, and elastic properties of borophene are thoroughly discussed and are compared with those of graphene and its "cousins." Numerous frontline applications are envisaged and an outlook is presented.

Stable edge structures and electronic states in zigzag 1T'-dichalcogenide nanoribbons

Based on first-principles calculations, we studied the various possible edge structures in zigzag 1T'-MoS2and 1T'-WTe2nanoribbons. By the binding energy analysis, there are stable chalcogen S- and Te-terminated edge structures for 1T'-MoS2and 1T'-WTe2nanoribbons, respectively. Unlike 1T'-MoS2nanoribbons, where little edge reconstruction can be found, 1T'-WTe2nanoribbons suffer larger edge reconstruction. Moreover, the new edges of 1T'-WTe2can be magnetized due to the spontaneous strain effect in narrow nanoribbons. Interestingly, there are quantum-well-like states near Fermi level in both 1T'-MoS2and 1T'-WTe2nanoribbons. Our calculations may promote the experimental research for the edge structures and the application of 1T'-dichalcogenide nanoribbons in nanodevices.

Tunable Spin-Polarized Edge Currents in Proximitized Transition Metal Dichalcogenides

We explore proximity-induced ferromagnetism on transition metal dichalcogenides (TMDs), focusing on molybdenum ditelluride ribbons with zigzag edges, deposited on ferromagnetic europium oxide (EuO). A tight-binding model incorporates exchange and Rashba fields induced by proximity to EuO or similar substrates. For in-gap Fermi levels, electronic modes in the nanoribbon are localized along the edges, acting as one-dimensional (1D) conducting channels with tunable spin-polarized currents. TMDs on magnetic substrates can become very useful in spintronics, providing versatile platforms to study the proximity effects and electronic interactions in complex 1D systems.

Unveiling the Structure of MoS x Nanocrystals Produced upon Laser Fragmentation of MoS2 Platelets

Transition-metal dichalcogenide MoS₂ nanostructures have attracted tremendous attention due to their unique properties, which render them efficient nanoscale functional components for multiple applications ranging from sensors and biomedical probes to energy conversion and storage devices. However, despite the wide application range, the possibility to tune their size, shape, and composition is still a challenge. At the same time, the correlation of the structure with the optoelectronic properties is still unresolved. Here, we propose a new method to synthesize various morphologies of molybdenum sulfide nanocrystals, on the basis of ultrashort-pulsed laser fragmentation of MoS₂ platelets. Depending on the irradiation conditions, multiple MoS _x morphologies in the form of nanoribbons, nanospheres, and photoluminescent quantum dots are obtained. Besides the detailed structural analysis of the various crystals formed, the structure-property relation is investigated and discussed.

Towards well-defined MoS2 nanoribbons on a large scale

Massive MoS₂ nanoribbons can be derived from templates, exhibiting well-defined topology and dominated zigzag edge chirality.