The electrical and optical measurements, in combination with density functional theory calculations, show distinct layer-dependent semiconductor-to-semimetal evolution of 2D layered PtSe . The high room-temperature electron mobility and near-infrared photo-response, together with much better air-stability, make PtSe a versatile electronic 2D layered material.

Two-dimensional (2D) materials have emerged as promising candidates for various optoelectronic applications based on their diverse electronic properties, ranging from insulating to superconducting. However, cooperative phenomena such as ferroelectricity in the 2D limit have not been well explored. Here, we report room-temperature ferroelectricity in 2D CuInP2S6 (CIPS) with a transition temperature of ∼320 K. Switchable polarization is observed in thin CIPS of ∼4 nm. To demonstrate the potential of this 2D ferroelectric material, we prepare a van der Waals (vdW) ferroelectric diode formed by CIPS/Si heterostructure, which shows good memory behaviour with on/off ratio of ∼100. The addition of ferroelectricity to the 2D family opens up possibilities for numerous novel applications, including sensors, actuators, non-volatile memory devices, and various vdW heterostructures based on 2D ferroelectricity.

Platinum disulfide (PtS2 ), a new member of the group-10 transition-metal dichalcogenides, is studied experimentally and theoretically. The indirect bandgap of PtS2 can be drastically tuned from 1.6 eV (monolayer) to 0.25 eV (bulk counterpart), and the interlayer mechanical coupling is almost isotropic. It can be explained by strongly interlayer interaction from the pz orbital hybridization of S atoms.

The interest in mid-infrared technologies surrounds plenty of important optoelectronic applications ranging from optical communications, biomedical imaging to night vision cameras, and so on. Although narrow bandgap semiconductors, such as Mercury Cadmium Telluride and Indium Antimonide, and quantum superlattices based on inter-subband transitions in wide bandgap semiconductors, have been employed for mid-infrared applications, it remains a daunting challenge to search for other materials that possess suitable bandgaps in this wavelength range. Here, we demonstrate experimentally for the first time that two-dimensional (2D) atomically thin PtSe2 has a variable bandgap in the mid-infrared via layer and defect engineering. Here, we show that bilayer PtSe2 combined with defects modulation possesses strong light absorption in the mid-infrared region, and we realize a mid-infrared photoconductive detector operating in a broadband mid-infrared range. Our results pave the way for atomically thin 2D noble metal dichalcogenides to be employed in high-performance mid-infrared optoelectronic devices.

Due to the intriguing optical and electronic properties, 2D materials have attracted a lot of interest for the electronic and optoelectronic applications. Identifying new promising 2D materials will be rewarding toward the development of next generation 2D electronics. Here, palladium diselenide (PdSe ), a noble-transition metal dichalcogenide (TMDC), is introduced as a promising high mobility 2D material into the fast growing 2D community. Field-effect transistors (FETs) based on ultrathin PdSe show intrinsic ambipolar characteristic. The polarity of the FET can be tuned. After vacuum annealing, the authors find PdSe to exhibit electron-dominated transport with high mobility (µ = 216 cm V s ) and on/off ratio up to 10 . Hole-dominated-transport PdSe can be obtained by molecular doping using F -TCNQ. This pioneer work on PdSe will spark interests in the less explored regime of noble-TMDCs.

The discovery of monolayer superconductors bears consequences for both fundamental physics and device applications. Currently, the growth of superconducting monolayers can only occur under ultrahigh vacuum and on specific lattice-matched or dangling bond-free substrates, to minimize environment- and substrate-induced disorders/defects. Such severe growth requirements limit the exploration of novel two-dimensional superconductivity and related nanodevices. Here we demonstrate the experimental realization of superconductivity in a chemical vapour deposition grown monolayer material—NbSe2. Atomic-resolution scanning transmission electron microscope imaging reveals the atomic structure of the intrinsic point defects and grain boundaries in monolayer NbSe2, and confirms the low defect concentration in our high-quality film, which is the key to two-dimensional superconductivity. By using monolayer chemical vapour deposited graphene as a protective capping layer, thickness-dependent superconducting properties are observed in as-grown NbSe2 with a transition temperature increasing from 1.0 K in monolayer to 4.56 K in 10-layer.

the developing trend of modern electronic technologies, [6] and significant efforts have been devoted to transforming these energy storage systems to their light, flexible, small, and thin counterparts. [7] The flexible battery market is forecast to increase rapidly from $69.6 million in 2015 to $958.4 million in 2022. [8] Lithium-ion batteries (LIBs) historically and presently dominant the markets of rechargeablebattery for portable devices because of the lightness of lithium and high energy density of the battery systems. [9,10] Nonetheless, LIBs are marred by the high cost and the shortage of lithium resources. Moreover, the aprotic electrolytes used in LIBs are generally toxic and flammable. This fact causes great safety issues for LIBs, especially when they are used in wearable/implantable applications in close contact with human body. It is highly challenging to assemble flexible LIBs due to the requirement of a highly reliable protective packaging to avoid the electrolyte leakage and reconcile with the washing need of wearable devices in practical applications. [3] Moreover, due to the high barrier encapsulation, the volumetric performance would be severely restricted, especially when LIBs are miniaturized. In this context, it is highly desirable to prepare flexible "beyond Li-based" batteries with safe, low-cost, and eco-friendly aqueous electrolytes. [11] As alternatives for LIBs, multivalent ion battery technologies (Zn-ion battery, ZIB, Mg-ion battery, and Al-ion battery) are of high interest for electrochemical energy storage. In comparison with LIBs operating with single-electron transfer, multivalent ion batteries employ multielectron transfer during the charge/ discharge processes, thus delivering much higher volumetric energy densities. [12][13][14] Since the first utilization of Zn in batteries in 1799, [15] Zn metal has captured increasing attention as an ideal anode material. In earlier studies, Zn anodes were widely explored in many alkaline battery systems, such as alkaline zinc-MnO 2 batteries, [16] zinc-nickel batteries, [17][18][19][20] zinc-silver batteries, [21] and zinc-air batteries. [22][23][24] Zn metal is able to offering both high gravimetric and high volumetric capacities (820 and 5855 mAh cm −3 ). [25] Moreover, Zn has the merits of low cost, low-toxicity, abundance in earth crust (≈300 times higher than for lithium), environmental benignity, easily recyclable, and intrinsic safety. [14,26] These advantages directly drove the recent renaissance of Zn anode based batteries. [15] However, the use of corrosive alkaline electrolyte leads to the Zn-dendritic (sharp, needle-like metallic protrusions) growth [27,28] and soluble ZnO 2 2− formation on Zn anode, which poison the cathode and result in the rapid capacity To keep pace with the increasing pursuit of portable and wearable electronics, it is urgent to develop advanced flexible power supplies. In this context, Zn-ion batteries (ZIBs) have garnered increasing attention as favorable energy storage devices for flexible electronics, ...

The exponentially growing works on 2D materials have resulted in both high scientific interest and huge potential applications in nanocatalysis, optoelectronics, and spintronics. Of especial note is that the newly emerged and promising family of metal phosphorus trichalcogenides (MPX 3 ) contains semiconductors, metals, and insulators with intriguing layered structures and architectures. The bandgaps of the members in this family range from 1.3 to 3.5 eV, significantly enriching the application of 2D materials in the broad wavelength spectrum. In this review, emphasizing their remarkable structural, physicochemical, and magnetic properties, as well as the numerous applications in various fields, the innovative progress on layered MPX 3 crystals is summarized. Different from other layered materials, these crystals will advance a fascinating frontier in magnetism and spintronic devices with their especially featured atomic layered nanosheets. Thus, their crystal and electronic structures, along with some related researches in magnetism, are discussed in detail. The assortments of growth methods are then summarized. Considering their potential applications, the prominent utilization of these 2D MPX 3 nanoscrystals in catalysis, batteries, and optoelectronics is also discussed. Finally, the outlook of these kinds of layered nanomaterials is provided. Metal Phosphorus Trichalcogenidesions. Friedel [17] and Ferrand [18,19] discovered them in the late 1800s. Based on the interesting structure of these materials, significant research works were reported in the early 2000s. As expected, 2D MPX 3 phases share most of the abovementioned specific properties of 2D TMDs. According to the theoretical and experimental results, MPX 3 compounds are the most sought functional materials for their intermediate bandgaps ranging from 1.3 to 3.5 eV, [20,21] indicating their enhanced light absorption efficiency as compared to the TMD materials. In addition, their unusual intercalation-substitution or intercalation-reduction behavior as well as the incipient ionic conductivity promote their usage in Li-ion batteries, [22,23] gas storage, [24] and photo-electrochemical reactions. [25] Unlike TMDs, several MPX 3 materials show intrinsic anti-ferromagnetism below the Neel temperatures of 78 K for MnPS 3 , 116 K for FePS 3 , and 155 K for NiPS 3 . [26,27] Recently, Li et al. [28] predicted that transformation from the anti-ferromagnetism to ferromagnetism for exfoliated MnPSe 3 nanosheet will be reduced by carrier doping. And the Monte Carlo simulation reveals the Curie temperature of the doped MnPSe 3 nanosheets can reach 206 K, rendering it with potential for utilizations in spintronic devices at high temperature. Therefore, the members in the MPX 3 family have the abovementioned properties along with structural flexibility stemming from their van der Waals nature; thus, it is reasonable to assume that they will contribute to the next major frontier in 2D vdW layered materials.Herein, we emphasize on reviewing the impressive recent progress...