A Generic Hybrid Model for Bulk Elastodynamics, With Application to Ultrasonic Nondestructive Evaluation

Monolayer two-dimensional transitional metal dichalcogenides, such as MoS₂, WS₂, and WSe₂, are direct band gap semiconductors with large exciton binding energy. They attract growing attentions for optoelectronic applications including solar cells, photodetectors, light-emitting diodes and phototransistors, capacitive energy storage, photodynamic cancer therapy, and sensing on flexible platforms. While light-induced luminescence has been widely studied, luminescence induced by injection of free electrons could promise another important applications of these new materials. However, cathodoluminescence is inefficient due to the low cross-section of the electron–hole creating process in the monolayers. Here for the first time we show that cathodoluminescence of monolayer chalcogenide semiconductors can be evidently observed in a van der Waals heterostructure when the monolayer semiconductor is sandwiched between layers of hexagonal boron nitride (hBN) with higher energy gap. The emission intensity shows a strong dependence on the thicknesses of surrounding layers and the enhancement factor is more than 500-fold. Strain-induced exciton peak shift in the suspended heterostructure is also investigated by the cathodoluminescence spectroscopy. Our results demonstrate that MoS₂, WS₂, and WSe₂ could be promising cathodoluminescent materials for applications in single-photon emitters, high-energy particle detectors, transmission electron microscope displays, surface-conduction electron-emitter, and field emission display technologies

Controlled Synthesis of High-Quality Monolayered α‑In₂Se₃ via Physical Vapor Deposition

In this work, we have demonstrated the synthesis of high-quality monolayered α-In₂Se₃ using physical vapor deposition method under atmospheric pressure. The quality of the In₂Se₃ atomic layers has been confirmed by complementary characterization technologies such as Raman/photoluminescence spectroscopies and atomic force microscope. The atomically resolved images have been obtained by the annular dark-field scanning transmission electron microscope. The field-effect transistors have been fabricated using the atomically layered In₂Se₃ and exhibit p-type semiconducting behaviors with the mobility up to 2.5 cm²/ Vs. The In₂Se₃ layers also show a good photoresponsivity of 340A/W, as well as 6 ms response time for the rise and 12 ms for the fall. These results make In₂Se₃ atomic layers a promising candidate for the optoelectronic and photosensitive device applications

One-Step Synthesis of Metal/Semiconductor Heterostructure NbS₂/MoS₂

Chemical vapor deposition (CVD) has proven its surpassing advantages, such as larger scale, interlayer orientation control, and clean interface, in the synthesis of transitional metal dichalcogenide (TMDC) semiconductor/semiconductor van der Waals (vdW) heterostructures. However, it is suffering problems of high melting points and low chemical reactivity of metal oxide feedstocks in the preparation of high-quality metal/semiconductor (M/S) TMDC vdW heterostructures. Here, for the first time, we report the synthesis of the M/S TMDC vdW heterostructure NbS₂/MoS₂ via a one-step halide-assisted CVD method, which effectively overcomes the drawbacks of metal oxide precursors. This one-step method provides the high quality and clean interface of the NbS₂/MoS₂ heterostructure, which has been proved by the transmission electron microscopy characterization. A mechanism that MoS₂ finishes the growth first and subsequently serves as a superior substrate for the growth of NbS₂ is proposed. This novel method will open up new opportunities in the syntheses of other M/S TMDC vdW heterostructures and will facilitate the research of the TMDC M/S interface