Electrolysis method of intercalation of layered transition metal dichalcogenides

A new method of intercalating organic Lewis bases, alkali hydroxides, Cu and Ag metals in to Group V layered dichalcogenide single crystals at room temperature is reported. It involves electrolytic reduction, in a suitable electrolysis cell, using the dichalcogenide as cathode and generation of the fresh intercalate species at the cathode surface. The organic intercalated complexes exhibit superconductivity like the parent dichalcogenides below 4.2°K.     

Lithium intercalation via n-Butyllithium of the layered transition metal dichalcogenides

$\text{n}$-Butyllithium in hexane solution serves as an excellent reagent to effect the intercalation of lithium into the Group IVb and Vb layered dichalcogenides. Under mild conditions, highly crystalline, uncontaminated stoichiometric products are afforded. In addition, the course of the reaction can be monitored by titration of aliquots of the supernatant.     

Structural editing of layered transition metal carbides via chemical scissor-mediated intercalation

<正>Intercalation chemistry is a promising methodology that has been widely used to synthesize two-dimensional(2D) materials and their intercalated layered derivatives, predominantly through introducing non-native species into the van der Waals(vdW) gaps. By tailoring guest-host interaction chemistry, the intercalated materials with tunable properties hold promise for fundamental studies of novel physical phenomena and applications ranging from transistors to supercapacitors, batteries, and...     

Valleytronics in transition metal dichalcogenides materials

Nano Research - Valley degree of freedom in the first Brillouin zone of Bloch electrons offers an innovative approach to information storage and quantum computation. Broken inversion symmetry...     

The lithium intercalates of the transition metal dichalcogenides

The lithium intercalation compounds of the layered transition metal dichalcogenides, prepared by reaction with nbutyl lithium, have been characterised by x-ray analysis. The group IVB and VB compounds are stoichiometric and stable; the intercalation proceeds by simple expansion of the lattice at the Van der Waals gap. The group VIB chalcogenides, SnS₂ and ReSe₂ do not form lithium intercalation compounds with the exception of MoS₂ and that appears to be metastable.     

Two-dimensional square transition metal dichalcogenides with lateral heterostructures

Fabrication of lateral heterostructures (LHS) is promising for a wide range of next-generation devices and could sufficiently unlock the potential of two-dimensional materials.Herein,we demonstrate the design of lateral heterostructures based on new building materials,namely 1S-MX2 LHS,using first-principles calculations.1S-MX2 LHS exhibits excellent stability,demonstrating high feasibility in the experiment.The desired bandgap opening can endure application at room temperature and was confirmed in 1S-MX2 LHS with spin-orbit coupling (SOC).A strain strategy further resulted in efficient bandgap engineering and an intriguing phase transition.We also found that black phosphorus can serve as a competent substrate to support 1S-MX2 LHS with a coveted type-Ⅱ band alignment,allowing versatile functionalized bidirectional heterostructures with built-in device functions.Furthermore,the robust electronic features could be maintained in the 1S-MX2 LHS with larger components.Our findings will not only renew interest in LHS studies by enriching their categories and properties,but also highlight the promise of these lateral heterostructures as appealing materials for future integrated devices.     

Optoelectronic devices based on two-dimensional transition metal dichalcogenides

In the past few years, two-dimensional (2D) transition metal dichalcogenide (TMDC) materials have attracted increasing attention of the research community, owing to their unique electronic and optical properties, ranging from the valley–spin coupling to the indirect-to-direct bandgap transition when scaling the materials from multi-layer to monolayer. These properties are appealing for the development of novel electronic and optoelectronic devices with important applications in the broad fields of communication, computation, and healthcare. One of the key features of the TMDC family is the indirect-to-direct bandgap transition that occurs when the material thickness decreases from multilayer to monolayer, which is favorable for many photonic applications. TMDCs have also demonstrated unprecedented flexibility and versatility for constructing a wide range of heterostructures with atomic-level control over their layer thickness that is also free of lattice mismatch issues. As a result, layered TMDCs in combination with other 2D materials have the potential for realizing novel high-performance optoelectronic devices over a broad operating spectral range. In this article, we review the recent progress in the synthesis of 2D TMDCs and optoelectronic devices research. We also discuss the challenges facing the scalable applications of the family of 2D materials and provide our perspective on the opportunities offered by these materials for future generations of nanophotonics technology.

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Substitutional doping in 2D transition metal dichalcogenides

Nano Research - Two-dimensional (2D) van der Waals transition metal dichalcogenides (TMDs) are a new class of electronic materials offering tremendous opportunities for advanced technologies and...     

Harmonic generation in transition metal dichalcogenides and their heterostructures

Few layered transition metal dichalcogenides (TMD), with an absence of crystal inversion symmetry and outstanding optical characteristics, are frequently applied in studies of nonlinear optics (NLO) for harmonic generation. Related materials are regarded as potential candidates for many optoelectronics applications. In order to enhance and manipulate the intrinsically weak NLO responses, TMD’s have been fabricated into heterostructures in recent years. The basic physics of harmonic generation and of TMD optical responses, as well as the interactions in TMD hybrid structures are introduced briefly, and the current state-of-the-art in the performance of TMDs in harmonic generation are reviewed. A particular focus is made on heterostructure studies to enhance and manipulate the response, which represent the core issues for devices and applications.     

Strongly enhanced electromechanical coupling in atomically thin transition metal dichalcogenides

Flexoelectricity in thin films has emerged as an effective electromechanical response owing to appealing scaling law and universal existence. However, current studies show limited out-of-plane converse flexoelectric effect (CFE) of ultra-thin transition metal dichalcogenides (TMDs) when compared to their conventional in-plane piezoresponse. Here, we report converse flexoresponse of atomically thin TMDs such as molybdenum disulfide (MoS₂) and tungsten diselenide (WSe₂) which exceeds their intrinsic in-plane piezoresponses. Our piezoresponse force microscopy (PFM) measurements revealed strongly enhanced CFE of the atomically thin MoS₂ and WSe₂ than their bulk counterpart (∼700% enhancement in MoS₂, ∼400% enhancement in WSe₂). We observed an anomalous reduction in converse flexoresponse in the monolayer structure attributed to a puckering deformation. By inducing a built-in in-plane tension to reduce puckering, we estimated the CFE of monolayer WSe₂ to be 8.14 pm/V, the highest among the atomically thin TMDs.     

Recent progress of flexible electronics by 2D transition metal dichalcogenides

Flexible electronics is the research field with interdisciplinary crossing and integration.It shows the promising advantages of novel device configurations,low-...     

Cathodic reduction of layered transition metal chalcogenides

Layered binary transition metal chalcogenides MX₂ (M = transition metal, X=S, Se) may be reduced electrochemically in aqueous electrolyte solutions to give hydrated polyelectrolyte compounds (A_x)^x+ (H₂O)_y [MX₂]^x? (I). The latter consist of negatively charged layers [MX₂]^x? with hydrated cations A⁺ positioned between the metal chalcogenide sheets. The interlayer cations may be exchanged against other mono- or polyvalent inorganic or organic cations. Reductions may also be carried out in nonaqueous electrolyte solutions. Galvanostatic and potentiostatic measurements show clearly the reversibility of the electrode process and provide evidence for the occurrence of intermediate reaction steps.     

Exploration of channel width scaling and edge states in transition metal dichalcogenides

We explore the impact of edge states in three types of transition metal dichalcogenides (TMDs), namely metallic Td-phase WTe₂ and semiconducting 2H-phase MoTe₂ and MoS₂, by patterning thin flakes into ribbons with varying channel widths. No obvious charge depletion at the edges is observed for any of these three materials, in contrast to observations made for graphene nanoribbon devices. The semiconducting ribbons are characterized in a three-terminal field-effect transistor (FET) geometry. In addition, two ribbon array designs have been carefully investigated and found to exhibit current levels higher than those observed for conventional one-channel devices. Our results suggest that device structures incorporating a high number of edges can improve the performance of TMD FETs. This improvement is attributed to a higher local electric field, resulting from the edges, increasing the effective number of charge carriers, and the absence of any detrimental edge-related scattering.

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Reversible topotactic redox reactions of layered dichalcogenides

The twodimensional MX₂-slabs of titanium, niobium and tantalum dichalcogenides present in contact with electrolyte solutions matrix units of highly flexible and reversible solid state redox systems. In the reduced polyelectrolyte state (negative charge density of layers = 0.1–0.3 e^?/unit cell) exchangeable solvated cations are located in the interlayer space. Cation density is coupled with the redox state of the layers. In the oxidized state (charged density = 0) layers are held together by van der Waals bonding. A high degree of cooperativity is found for these topotactic systems. It is shown in addition that many so-called intercalation compounds of dischalcogenides are reduced forms with exchangeable cations in the interlayer space.     

Preparation and characterization of ionic liquid intercalation compounds into layered zirconium phosphates

In this work, immobilizing a series of ionic liquids (ILs) 1-alkyl-3-methylimidazolium chloride [C _n mim]Cl (n = 2, 4, 6, 8) on the layered zirconium phosphates were investigated. [C₄mim]Cl was used to explore in detail the factors affecting intercalation. By comparing several starting materials including α-zirconium phosphate (α-ZrP), γ-zirconium phosphate (γ-ZrP) and the corresponding alkylamine preintercalated composites, it was found that the α-ZrP · 2BA (i.e., preintercalated BA were arranged in a bilayer mode at the galleries of α-ZrP) was a suitable host for intercalating ILs. Intercalation was verified with X-ray diffraction (XRD), Raman, UV–Vis and other instrumental approaches. pH effect on immobilization was investigated. Other ionic liquids including [C _n mim]Cl (n = 2, 6, 8) intercalation compounds were prepared. Based on XRD data, the interlayer distances of the studied intercalation compounds were similar, suggesting that the ionic liquids were arranged in an approximately planar manner, as confirmed by molecular modeling.