Two-dimensional layered semiconductors present a promising material platform for band-to-band-tunneling devices given their homogeneous band edge steepness due to their atomically flat thickness. Here, we experimentally demonstrate interlayer band-to-band tunneling in vertical MoS2/WSe2 van der Waals (vdW) heterostructures using a dual-gate device architecture. The electric potential and carrier concentration of MoS2 and WSe2 layers are independently controlled by the two symmetric gates. The same device can be gate modulated to behave as either an Esaki diode with negative differential resistance, a backward diode with large reverse bias tunneling current, or a forward rectifying diode with low reverse bias current. Notably, a high gate coupling efficiency of ∼80% is obtained for tuning the interlayer band alignments, arising from weak electrostatic screening by the atomically thin layers. This work presents an advance in the fundamental understanding of the interlayer coupling and electron tunneling in ...

Dual-gated MoS2/WSe2 van der Waals tunnel diodes and transistors.

Highly active and low-cost catalysts for electrochemical reactions such as the hydrogen evolution reaction (HER) are crucial for the development of efficient energy conversion and storage technologies. Theoretical simulations have been instrumental in revealing the correlations between the electronic structure of materials and their catalytic activity, and guide the prediction and development of improved catalysts. However, difficulties in accurately engineering the desired atomic sites lead to challenges in making direct comparisons between experimental and theoretical results. In MoS2, the Mo-edge has been demonstrated to be active for HER whereas the S-edge is inert. Using a computational descriptor-based approach, we predict that by incorporating transition metal atoms (Fe, Co, Ni, or Cu) the S-edge site should also become HER active. Vertically standing, edge-terminated MoS2 nanofilms provide a well-defined model system for verifying these predictions. The transition metal doped MoS2 nanofilms show an increase in exchange current densities by at least two-fold, in agreement with the theoretical calculations. This work opens up further opportunities for improving electrochemical catalysts by incorporating promoters into particular atomic sites, and for using well-defined systems in order to understand the origin of the promotion effects.

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Transition-metal Doped Edge Sites in Vertically Aligned MoS2 Catalysts for Enhanced Hydrogen Evolution

Recent explosion of interest in two-dimensional (2D) materials research has led to extensive exploration of physical and chemical phenomena unique to this new class of materials and their technological potential. Atomically thin layers of group 6 transition metal dichalcogenides (TMDs) such as MoS2 and WSe2 are remarkably stable semiconductors that allow highly efficient electrostatic control due to their 2D nature. Field effect transistors (FETs) based on 2D TMDs are basic building blocks for novel electronic and chemical sensing applications. Here, we review the state-of-the-art of TMD-based FETs and summarize the current understanding of interface and surface effects that play a major role in these systems. We discuss how controlled doping is key to tailoring the electrical response of these materials and realizing high performance devices. The first part of this review focuses on some fundamental features of gate-modulated charge transport in 2D TMDs. We critically evaluate the role of surfaces and interfaces based on the data reported in the literature and explain the observed discrepancies between the experimental and theoretical values of carrier mobility. The second part introduces various non-covalent strategies for achieving desired doping in these systems. Gas sensors based on charge transfer doping and electrostatic stabilization are introduced to highlight progress in this direction. We conclude the review with an outlook on the realization of tailored TMD-based field-effect devices through surface and interface chemistry.

Electronic transport properties of transition metal dichalcogenide field-effect devices: surface and interface effects

Traditional lithium-ion batteries that are based on layered Li intercalation electrode materials are limited by the intrinsically low theoretical capacities of both electrodes and cannot meet the increasing demand for energy. A facile route for the synthesis of a new type of composite nanofibers, namely carbon nanofibers decorated with molybdenum disulfide sheets (CNFs@MoS2), is now reported. A synergistic effect was observed for the two-component anode, triggering new electrochemical processes for lithium storage, with a persistent oxidation from Mo (or MoS2) to MoS3 in the repeated charge processes, leading to an ascending capacity upon cycling. The composite exhibits unprecedented electrochemical behavior with high specific capacity, good cycling stability, and superior high-rate capability, suggesting its potential application in high-energy lithium-ion batteries.

Carbon Nanofibers Decorated with Molybdenum Disulfide Nanosheets: Synergistic Lithium Storage and Enhanced Electrochemical Performance

Infrared photodetectors are currently subject to a rapidly expanding application space, with an increasing demand for compact, sensitive and inexpensive detectors. Despite continued advancement, technological factors limit the widespread usage of such detectors, specifically, the need for cooling and the high costs associated with processing of iii–v/ii–vi semiconductors. Here, black phosphorous (bP)/MoS2 heterojunction photodiodes are explored as mid-wave infrared (MWIR) detectors. Although previous studies have demonstrated photodiodes using bP, here we significantly improve the performance, showing that such devices can be competitive with conventional MWIR photodetectors. By optimizing the device structure and light management, we demonstrate a two-terminal device that achieves room-temperature external quantum efficiencies (ηe) of 35% and specific detectivities (D*) as high as 1.1 × 1010 cm Hz1/2 W−1 in the MWIR region. Furthermore, by leveraging the anisotropic optical properties of bP we demonstrate the first bias-selectable polarization-resolved photodetector that operates without the need for external optics.

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Papers

An innovative way of etching MoS2： Characterization and mechanistic investigation