Two-dimensional (2D) layered inorganic nanomaterials have attracted huge attention due to their unique electronic structures, as well as extraordinary physical and chemical properties for use in electronics, optoelectronics, spintronics, catalysts, energy generation and storage, and chemical sensors. Graphene and related layered inorganic analogues have shown great potential for gas-sensing applications because of their large specific surface areas and strong surface activities. This review aims to discuss the latest advancements in the 2D layered inorganic materials for gas sensors. We first elaborate the gas-sensing mechanisms and introduce various types of gas-sensing devices. Then, we describe the basic parameters and influence factors of the gas sensors to further enhance their performance. Moreover, we systematically present the current gas-sensing applications based on graphene, graphene oxide (GO), reduced graphene oxide (rGO), functionalized GO or rGO, transition metal dichalcogenides, layered III-VI semiconductors, layered metal oxides, phosphorene, hexagonal boron nitride, etc. Finally, we conclude the future prospects of these layered inorganic materials in gas-sensing applications.

Two‐dimensional (2D) materials have attracted extensive research interests due to their excellent properties related to unique structure. Strain engineering, as an important strategy for tuning the lattice and electronic structure of 2D materials, has been widely used in the modulation of physical properties, which broadens their applications in flexible nanoelectronic and optoelectronic devices. In this review, we first summarize the methods of inducing strain to 2D materials and discuss the advantages and problems of various methods. We then introduce the strain‐induced effects on optical, electrical, and magnetic properties, together with the phase transition of 2D materials. Finally, we illustrate the potential applications of strained 2D materials and further look forward to their opportunities and challenges in practical applications in the future.

Anisotropic 2D materials exhibit unique optical, electrical, and thermoelectric properties that open up possibilities for diverse angle‐dependent devices. However, the explored anisotropic 2D materials are very limited and the methods to identify the crystal orientations and to study the in‐plane anisotropy are in the initial stage. Here azimuth‐dependent reflectance difference microscopy (ADRDM), angle‐resolved Raman spectra, and electrical transport measurements are used to systematically characterize the influence of the anisotropic structure on in‐plane optical and electrical anisotropy of 2D GeAs, a novel group IV–V semiconductor. It is proved that ADRDM offers a way to quickly identify the crystal orientations and also to directly characterize the in‐plane optical anisotropy of layered GeAs. The anisotropic electrical transport behavior of few‐layer GeAs field‐effect transistors is further measured and the anisotropic ratio of the mobility is as high as 4.6, which is higher than the other 2D anisotropic materials such as black phosphorus. The dependence of the Raman intensity anisotropy on the sample thickness, excitation wavelength, and polarization configuration is investigated both experimentally and theoretically. These data will be useful for designing new high‐performance devices and the results suggest a general methodology for characterizing the in‐plane anisotropy of low‐symmetry 2D materials.

Heterostructure engineering of atomically thin two-dimensional materials offers an exciting opportunity to fabricate atomically sharp interfaces for highly tunable electronic and optoelectronic devices. Here, we demonstrate abrupt interface between two completely dissimilar material systems, i.e, GaTe-MoS 2 p−n heterojunction transistors, where the resulting device possesses unique electronic properties and self-driven photoelectric characteristics. Fabricated heterostructure transistors exhibit forward biased rectifying behavior where the transport is ambipolar with both electron and hole carriers contributing to the overall transport. Under illumination, photoexcited electron−hole pairs are readily separated by large built-in potential formed at the GaTe−MoS 2 interface efficiently generating self-driven photocurrent within <10 ms. Overall results suggest that abrupt interfaces between vastly different material systems with different crystal symmetries still allow efficient charge transfer mechanisms at the interface and are attractive for photoswitch, photodetector, and photovoltaic applications because of large built-in potential at the interface.

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