Controllable one-step growth of bilayer MoS2-WS2/WS2 heterostructures by chemical vapor deposition

Twist angle-dependent interlayer hybridized exciton lifetimes in van der Waals heterostructures

The interlayer twist angle has a direct effect on exciton lifetimes in van der Waals heterostructures. At small angles, the interlayer and intralayer excitons in MoSe2/WS2 heterostructures are hybridized, resulting in hybridized excitons with long lifetimes and strong resonance. However, the study of twist-angle modulation of hybridized exciton lifetimes is still insufficient, leading to an unclear understanding of the mechanism through which the twist angle between layers influences the lifetime of hybridized excitons. Here, we observed the formation of hybridized excitons by constructing MoSe2/WS2 heterostructures with different twist angles. The exciton lifetime is found to increase from 0.5 ns to 3.3 ns when the twist angle is reduced from 12° to 1°. This work provides a new perspective on the modulation of the exciton lifetime, enabling further exploration in improving the efficiency of optoelectronic devices.

Highly Selective NH3 Sensor Based on MoS2/WS2 Heterojunction

In this paper, the heterostructure of MoS₂/WS₂ was prepared by a hydrothermal method; the n-n heterostructure was demonstrated using TEM combined with Mott-Schottky analysis. The valence and conduction band positions were further identified by the XPS valence band spectra. The NH₃-sensing properties were assessed at room temperature by changing the mass ratio of the MoS₂ and WS₂ components. The 50 wt%-MoS₂/WS₂ sample exhibited the best performance, with a peak response of 23643% to NH₃ at a concentration of 500 ppm, a minimum detection limit of 20 ppm, and a fast recovery time of 2.6 s. Furthermore, the composites-based sensors demonstrated an excellent humidity immune property with less than one order of magnitude in the humidity range of 11-95% RH, revealing the practical application value of these sensors. These results suggest that the MoS₂/WS₂ heterojunction is an intriguing candidate for fabricating NH₃ sensors.

Recent Progress in Fabrication and Physical Properties of 2D TMDC-Based Multilayered Vertical Heterostructures

Two-dimensional (2D) vertical heterojunctions (HSs), which are usually fabricated by vertically stacking two layers of transition metal dichalcogenide (TMDC), have been intensively researched during the past years. However, it is still an enormous challenge to achieve controllable preparation of the TMDC trilayer or multilayered van der Waals (vdWs) HSs, which have important effects on physical properties and device performance. In this review, we will introduce fundamental features and various fabrication methods of diverse TMDC-based multilayered vdWs HSs. This review focuses on four fabrication methods of TMDC-based multilayered vdWs HSs, such as exfoliation, chemical vapor deposition (CVD), metal-organic chemical vapor deposition (MOCVD), and pulsed laser deposition (PLD). The latest progress in vdWs HS-related novel physical phenomena are summarized, including interlayer excitons, long photocarrier lifetimes, upconversion photoluminescence, and improved photoelectrochemical catalysis. At last, current challenges and prospects in this research field are provided.

Recent Progress in Phase Regulation, Functionalization, and Biosensing Applications of Polyphase MoS2

The disulfide compounds of molybdenum (MoS₂ ) are layered van der Waals materials that exhibit a rich array of polymorphic structures. MoS₂ can be roughly divided into semiconductive phase and metallic phase according to the difference in electron filling state of the 4d orbital of Mo atom. The two phases show completely different properties, leading to their diverse applications in biosensors. But to some extent, they compensate for each other. This review first introduces the relationship between phase state and the chemical/physical structures and properties of MoS₂ . Furthermore, the synthetic methods are summarized and the preparation strategies for metastable phases are highlighted. In addition, examples of electronic and chemical property designs of MoS₂ by means of doping and surface modification are outlined. Finally, studies on biosensors based on MoS₂ in recent years are presented and classified, and the roles of MoS₂ with different phases are highlighted. This review offers references for the selection of materials to construct different types of biosensors based on MoS₂ , and provides inspiration for sensing performance enhancement.

Strategies for Controlled Growth of Transition Metal Dichalcogenides by Chemical Vapor Deposition for Integrated Electronics

In recent years, transition metal dichalcogenide (TMD)-based electronics have experienced a prosperous stage of development, and some considerable applications include field-effect transistors, photodetectors, and light-emitting diodes. Chemical vapor deposition (CVD), a typical bottom-up approach for preparing 2D materials, is widely used to synthesize large-area 2D TMD films and is a promising method for mass production to implement them for practical applications. In this review, we investigate recent progress in controlled CVD growth of 2D TMDs, aiming for controlled nucleation and orientation, using various CVD strategies such as choice of precursors or substrates, process optimization, and system engineering. We then survey different patterning methods, such as surface patterning, metal precursor patterning, and postgrowth sulfurization/selenization/tellurization, to mass produce heterostructures for device applications. With these strategies, various well-designed architectures, such as wafer-scale single crystals, vertical and lateral heterostructures, patterned structures, and arrays, are achieved. In addition, we further discuss various electronics made from CVD-grown TMDs to demonstrate the diverse application scenarios. Finally, perspectives regarding the current challenges of controlled CVD growth of 2D TMDs are also suggested.

Synthesis of transition metal dichalcogenide van der Waals heterostructures through chemical vapor deposition

Transition metal dichalcogenide (TMD) van der Waals (vdW) heterostructures show great potential in the exploration of novel physical phenomena and practical applications. Compared to the traditional mechanical stacking techniques, chemical vapor deposition (CVD) method exhibits more advantages in preparing TMD vdW heterostructures. CVD enables the large-scale production of high-quality materials with clean interfaces in the future. Herein, CVD methods for the synthesis of TMD vdW heterostructures are summarized. These methods are categorized in two major strategies, multi-step process and one-step process. The effects of various factors are demonstrated, including the temperature, nucleation, and precursors. Finally, the remaining challenges are discussed.

Fabrication Strategies and Optoelectronic Applications of Perovskite Heterostructures

Metal halide perovskites (MHPs) are emerging low‐cost and multifunctional semiconductor materials. They have been widely used in optoelectronic devices such as perovskite solar cells, light‐emitting diodes, photodetectors, memristors, and lasers. Developing new MHPs, defects passivation, optimizing device structures, and packaging techniques are all effective methods to improve photoelectric performance and stability of perovskite devices. Particularly, the fabrication of perovskite/perovskite heterostructures (PPHSs) is a novel and arresting method to obtain stable and high‐performing optoelectronic perovskite devices since it can passivate defects, regulate energy gaps, and provide new carrier transmission modes of MHPs for multiple semiconductor applications. In this paper, representative fabrication strategies of PPHSs including films and single‐crystal heterostructures are reviewed, and their applications in optoelectronic devices are summarized. Furthermore, the challenges and prospects of PPHSs are discussed based on the current status.

Hot carrier dynamics in MoS2/WS2heterostructure

TMDs based heterostructure have drawn much attention for its potential application in photoelectric devices benefiting from the rapid and effective carrier separation and ultra-long interlayer exciton lifetime. Recent studies on carrier dynamics of TMDs based heterostructures are mainly focused on the transfer process of photo-generated carriers across the interface and lifetime of interlayer exciton but little attention is paid on the dynamics of hot carriers. Here, the carrier dynamics of hot carriers in MoS₂/WS₂heterostructure is investigated by transient absorption spectra. Rapid separation of electron and hole is observed. More importantly, hot carriers of C exciton, which contribute to the absorption of most of the visible light, could compensate for the carrier loss in the band edge exciton energy band through the intervalley transfer process. This re-injection process of hot carriers of C exciton could compensate for carrier depletion in photoelectric devices, thus may greatly improve the light utilization in optoelectronic devices.

Two-dimensional biomaterials: material science, biological effect and biomedical engineering applications

To date, nanotechnology has increasingly been identified as a promising and efficient means to address a number of challenges associated with public health. In the past decade, two-dimensional (2D) biomaterials, as a unique nanoplatform with planar topology, have attracted explosive interest in various fields such as biomedicine due to their unique morphology, physicochemical properties and biological effect. Motivated by the progress of graphene in biomedicine, dozens of types of ultrathin 2D biomaterials have found versatile bio-applications, including biosensing, biomedical imaging, delivery of therapeutic agents, cancer theranostics, tissue engineering, as well as others. The effective utilization of 2D biomaterials stems from the in-depth knowledge of structure-property-bioactivity-biosafety-application-performance relationships. A comprehensive summary of 2D biomaterials for biomedicine is still lacking. In this comprehensive review, we aim to concentrate on the state-of-the-art 2D biomaterials with a particular focus on their versatile biomedical applications. In particular, we discuss the design, fabrication and functionalization of 2D biomaterials used for diverse biomedical applications based on the up-to-date progress. Furthermore, the interactions between 2D biomaterials and biological systems on the spatial-temporal scale are highlighted, which will deepen the understanding of the underlying action mechanism of 2D biomaterials aiding their design with improved functionalities. Finally, taking the bench-to-bedside as a focus, we conclude this review by proposing the current crucial issues/challenges and presenting the future development directions to advance the clinical translation of these emerging 2D biomaterials.

Recent progress in the CVD growth of 2D vertical heterostructures based on transition-metal dichalcogenides

This review summarizes recent advances in the controllable CVD growth of 2D TMDC vertical heterostructures under four different strategies.

Induced Magnetism of the MoS2 Monolayer during the Transition Metal (Fe/Ni) Bombardment Process: A Nonadiabatic Ab Initio Collision Dynamics Investigation

The source of induced magnetism in the MoS2 monolayer induced by transition metal (Fe/Ni) collision is investigated using nonadiabatic ab inito molecular dynamics simulations that take into account high-spin and low-spin energy states during trajectory integration. By considering various metal firing angles, a strong interaction between the Fe/Ni atom and the MoS2 surface can be observed because of enormous increase in the kinetic energy of the metal atom. When firing along the Mo-S bond, the Fe bullet is pulled more strongly than when firing along the S-Mo-S bisector. Spin polarization of MoS2 is gradually induced when Fe approaches the surface and eliminated when Fe roams around a potential energy trap on the MoS2 layer. We observe that there is charge transfer between Fe and Mo atoms, which enhances the probability of electron pairing and leads to instantaneous vanishing of total magnetization. The Ni-MoS2 system is found to establish a total magnetization of 1.5-4 μB when Ni is 2.0 Å above the surface. Interestingly, the strong bonding attachment of Ni suppresses the band gap to at least 40%.

Controlled fractal growth of transition metal dichalcogenides

We report controlled fractal growth of atomically thin transition metal dichalcogenides (TMDCs) by chemical vapor deposition, with morphological evolution from dendritic to triangular. Several important growth parameters controlling the fractal dimensions were identified, including the relaxation rate, adhesion coefficient, diffusion anisotropy and growth time. A model based on nucleation, diffusion limited aggregation and relaxation was proposed to explain the morphological evolution. The results of the computational simulation based on this model are in good agreement with the experimental results. Our study sheds light on the growth mechanism of TMDCs and paves the way for growth of TMDCs with improved controllability.