Synthesis of large-area, atomically thin transition metal dichalcogenides (TMDs) on diverse substrates is of central importance for the large-scale fabrication of flexible devices and heterojunction-based devices. In this work, we successfully synthesized a large area of highly-crystalline MoSe₂ atomic layers on SiO₂/Si, mica and Si substrates using a simple chemical vapour deposition (CVD) method at atmospheric pressure. Atomic force microscopy (AFM) and Raman spectroscopy reveal that the as-grown ultrathin MoSe₂ layers change from a single layer to a few layers. Photoluminescence (PL) spectroscopy demonstrates that while the multi-layer MoSe₂ shows weak emission peaks, the monolayer has a much stronger emission peak at ∼1.56 eV, indicating the transition from an indirect to a direct bandgap. Transmission electron microscopy (TEM) analysis confirms the single-crystallinity of MoSe₂ layers with a hexagonal structure. In addition, the photoresponse performance of photodetectors based on MoSe₂ monolayer was studied for the first time. The devices exhibit a rapid response of ∼60 ms and a good photoresponsivity of ∼13 mA/W (using a 532 nm laser at an intensity of 1 mW mm⁻² and a bias of 10 V), suggesting that MoSe₂ monolayer is a promising material for photodetection applications.

Anisotropic layered semiconductors have attracted significant interest due to the huge possibility of bringing new functionalities to thermoelectric, electronic and optoelectronic devices. Currently, most reports on anisotropy have concentrated on black phosphorus and ReS₂, less effort has been contributed to other layered materials. In this work, two-dimensional (2D) orthorhombic SnS flakes on a large scale have been successfully synthesized via a simple physical vapor deposition method. Angle-dependent Raman spectroscopy indicated that the orthorhombic SnS flakes possess a strong anisotropic Raman response. Under a parallel-polarization configuration, the peak intensity of A_g (190.7 cm⁻¹) Raman mode reaches the maximum when incident light polarization is parallel to the armchair direction of the 2D SnS flakes, which strongly suggests that the A_g (190.7 cm⁻¹) mode can be used to determine the crystallographic orientation of the 2D SnS. In addition, temperature-dependent Raman characterization confirmed that the 2D SnS flakes have a higher sensitivity to temperature than graphene, MoS₂ and black phosphorus. These results are useful for the future studies of the optical and thermal properties of 2D orthorhombic SnS.

Development of high‐performance and cost‐effective non‐noble metal electrocatalysts is pivotal for the eco‐friendly production of hydrogen through electrolysis and hydrogen energy applications. Herein, the synthesis of an unconventional nickel nitride nanostructure enriched with nitrogen vacancies (Ni₃N_1−x) through plasma‐enhanced nitridation of commercial Ni foam (NF) is reported. The self‐supported Ni₃N_1−x/NF electrode can deliver a hydrogen evolution reaction (HER) activity competitive to commercial Pt/C catalyst in alkaline condition (i.e., an overpotential of 55 mV at 10 mA cm⁻² and a Tafel slope of 54 mV dec⁻¹), which is much superior to the stoichiometric Ni₃N, and is the best among all nitride‐based HER electrocatalysts in alkaline media reported thus far. Based on theoretical calculations, it is further verified that the presence of nitrogen vacancies effectively enhances the adsorption of water molecules and ameliorates the adsorption–desorption behavior of intermediately adsorbed hydrogen, which leads to an advanced HER activity of Ni₃N_1−x/NF.