Search

In-plane heterostructures based on transition metal dichalcogenides are promising for applications in tunnel field-effect transistors (TFETs). However, the transport properties of the in-plane heterostructures have not been fully understood due to the presence of generation current derived from the in-gap state of the heterointerface. For further performance improvement, it is important to identify and suppress the origin of the in-gap states at the heterointerface. In this work, we investigated the transport properties of TFETs based on multilayer NbxMo1−xS2/MoS2 in-plane heterostructures on atomically flat hexagonal boron nitride substrate. We observed a transition from staggered gap to broken gap band alignment by electron doping to MoS2 and that band-to-band tunneling current was dominant below 80 K, a higher temperature compared with the heterostructure on an SiO2 surface. These results indicate that the use of atomically flat substrates helps reduce generation current from strain-derived in-gap states in NbxMo1−xS2/MoS2 in-plane heterostructures. [ABSTRACT FROM AUTHOR]

Tungsten disulfide (WS2) nanotubes exhibit various unique properties depending on their structures, such as their diameter and wall number. The development of techniques to prepare WS2 nanotubes with the desired structure is crucial for understanding their basic properties. Notably, the synthesis and characterization of multi-walled WS2 nanotubes with small diameters are challenging. This study reports the synthesis and characterization of small-diameter WS2 nanotubes with an average inner diameter of 6 nm. The optical absorption and photoluminescence (PL) spectra of the as-prepared nanotubes indicate that a decrease in the nanotube diameter induces a red-shift in the PL, suggesting that the band gap narrowed due to a curvature effect, as suggested by theoretical calculations. [ABSTRACT FROM AUTHOR]

The ability of two-dimensional, layered transition-metal dichalcogenides (TMDs) to promote hydrogen evolution reaction (HER) has attracted much attention for hydrogen-generation applications. Their electrocatalytic active sites originally come from unique electronic properties at the edges. Here, we use scanning electrochemical cell microscopy (SECCM) to visualize and quantify the electrochemical HER activities of tungsten disulfide (WS2) islands. We show that the HER correlated current distribution is affected by the number of WS2 layers. SECCM imaging provides a direction for future designs in TMD-based electrocatalysts. [ABSTRACT FROM AUTHOR]

Two‐dimensional transition metal dichalcogenides (TMDCs) demonstrate great potential in nanoelectronics devices owing to their high carrier mobility in the atomically thin channel regime. However, high contact resistance between source/drain electrodes and TMDC channels hinders the TMDCs applications in the very‐large‐scale integration (VLSI) field. Here, this work reports atomically aligned van der Waals (vdW) junction fabrications through thermal‐induced crystallization of layered Sb2Te3 electrodes on monolayer MoS2 using VLSI‐compatible physical vapor deposition and annealing processes. Due to Fermi‐level unpinning with a small band offset between Sb2Te3 and MoS2 and small density of state of Sb2Te3, better device performance is demonstrated on MoS2 MOSFETs with Sb2Te3/W contact than that of Sb/W contact. Moreover, the ideal vdW junctions are found to demonstrate extreme high‐thermal robustness. No intermixing at the Sb2Te3/MoS2 interface or crystallinity degradation of Sb2Te3 is observed after 450 °C annealing, leading to higher thermal stability than its Sb counterpart. Sb2Te3 is a promising candidate as an n‐type contact material for TMDC‐based devices such as MoS2, MoSe2, and WS2 in future VLSI electronics and various other applications. [ABSTRACT FROM AUTHOR]

Atomically thin transition metal dichalcogenides (TMDCs) are attractive materials for future optoelectronic applications because of their excellent electrical, optical, and quantum (spin‐valley) properties. In particular, in‐plane heterostructures based on TMDC monolayers provide opportunities to directly modulate band structures and lattice strains by the spatial distribution of constituent elements, leading to efficient control of their carrier transport and recombination. However, it is still challenging to create light‐emitting devices using such in‐plane heterostructures because of the technical difficulties associated with sample/device fabrication. This study demonstrated interfacial electroluminescence (EL) in diverse TMDC monolayer in‐plane heterostructures. Various combinations of large‐area, single‐crystalline in‐plane heterostructures with sharp interfaces are grown by chemical vapor deposition, followed by the adoption of electrolyte‐based light‐emitting devices to observe EL. The fine heterostructures enabled the capture of the linear‐shaped EL fixed along the junction interfaces. Significantly, the WS2/WSe2 in‐plane heterostructures exhibited circularly polarized EL with polarizability of 10% at room temperature. This can be explained by the interfacial strain‐mediated electronic structure evolution, in which the combination of electric fields and strain‐induced valley drifts realizes selective EL from the K/K' valley. These findings pave the way for expanding the potential of monolayer in‐plane heterostructures for use in functional optoelectronic devices. [ABSTRACT FROM AUTHOR]

We have developed a method of evaluating the photo-induced carrier dynamics of nanostructures by combining optical technologies with multiprobe microscopy techniques. Using multiple probes, measurement can be carried out even for a small sample without complicated pretreatments, such as attaching electrode structures. Using transition metal dichalcogenides as a sample and a continuous laser or an ultrashort pulse laser as the light source, we demonstrated analyses of the carrier dynamics related to trap levels in a millisecond to second time domain and the ultrafast photoexcited carrier dynamics in the picosecond region. [ABSTRACT FROM AUTHOR]

The microscopic structure and photosensitive function of encapsulated dye in the single-wall carbon nanotubes (SWCNTs) are studied. The findings suggest that the photoexcitation of such dyes leads to the enhancement of transient absorption saturation in the nanotubes, which also proves the transfer of ultrafast energy from the dye to SWCNTs.

One-dimensional (1D) transition metal chalcogenides (TMCs) have recently attracted much attention because of their atomically thin, wire structures and superior conducting properties. These wires interact via van der Waals forces, aggregating into 1D crystals of different shapes with desired properties. However, relevant studies on their transport properties remain limited because of the lack of high-quality samples. Herein, we report the formation of a two-dimensional (2D) carrier gas in thin, ribbon-shaped bundles of laterally assembled WTe nanowires grown by chemical vapor deposition. Magnetoresistance measurements reveal that a single WTe bundle exhibits weak antilocalization and Shubnikov-de Haas (SdH) oscillations at low temperatures. Angle-dependent SdH oscillations serve as evidence of the realization of a 2D carrier gas in the WTe bundle. The present findings indicate the versatility of TMC nanowires as building blocks to produce electronic systems of desired dimensionality for future functional electronic and energy-harvesting devices. [ABSTRACT FROM AUTHOR]

The dominant quantum confinement and edge effects in one-dimensional (1D) transition-metal dichalcogenide (TMDC) nanoribbons have given rise to physical properties useful in electronic, optoelectronic, and catalytic applications. Numerous methods of synthesizing TMDC nanoribbons via top-down or bottom-up methods have already been developed. However, controlling the mass growth of these materials remains challenging. We herein describe a predefined growth of zigzag-type TMDC nanoribbons using WTe atomic wires as template precursors. Bundles of WTe wires were annealed in the presence of chalcogen vapors to induce structural transformation into nanoribbons of layered WS2, WSe2, or WTe2. Depending on the stacking arrangement of the WTe wires, vertically or horizontally aligned nanoribbons were generated, forming random or unidirectional networks. The resultant WSe2 nanoribbons showed anisotropic optical responses in Raman and photocurrent measurements, indicating their 1D nature. The present results provide a path for not only the possible structural engineering of TMDC nanoribbons but also their application in sophisticated 1D electronic and optoelectronic devices. [ABSTRACT FROM AUTHOR]

Tungsten ditelluride (WTe2) is a semi-metallic transition metal dichalcogenide (TMDC). WTe2 has attracted a lot of interest for topological properties and various applications such as batteries. In this study, we developed a method to obtain WTe2 nanowires from solution-grown tungsten oxide nanowires. By optimizing the supply of Te vapor, which strongly influences sample composition and structure, and using small-diameter solution-grown nanowires as precursors, we finally synthesized relatively small-diameter WTe2 nanowires with diameters of 15–50 nm. Interestingly, nanowire structures are mainly obtained via tellurization, but when sulfurization and selenization are applied on the same precursors, nanotube structures are obtained. We assume that the volume increase via chalogenization is a key parameter that determines the formation of nanotubes and nanowires. [ABSTRACT FROM AUTHOR]