Two-dimensional (2D) transition metal dichalcogenides have been extensively studied due to their fascinating physical properties for constructing high-performance photodetectors. However, their relatively low responsivities, current on/off ratios and response speeds have hindered their widespread application. Herein, we fabricated a high-performance photodetector based on few-layer MoTe₂ and CdS_0.42Se_0.58 flake heterojunctions. The photodetector exhibited a high responsivity of 7221 A/W, a large current on/off ratio of 1.73×10⁴, a fast response speed of 90/120 μs, external quantum efficiency (EQE) reaching up to 1.52×10⁶ % and detectivity (D^*) reaching up to 1.67×10¹⁵ Jones. The excellent performance of the heterojunction photodetector was analyzed by a photocurrent mapping test and first-principle calculations. Notably, the visible light imaging function was successfully attained on the MoTe₂/CdS_0.42Se_0.58 photodetectors, indicating that the device had practical imaging application prospects. Our findings provide a reference for the design of ultrahigh-performance MoTe₂-based photodetectors.

Currently, magnetic storage devices are encountering the problem of achieving lightweight and high integration in mobile computing devices during the information age. As a result, there is a growing urgency for two-dimensional half-metallic materials with a high Curie temperature (T_C). This study presents a theoretical investigation of the fundamental electromagnetic properties of the monolayer hexagonal lattice of Mn₂X₃ (X = S, Se, Te). Additionally, the potential application of Mn₂X₃ as magneto-resistive components is explored. All three of them fall into the category of ferromagnetic half-metals. In particular, the Monte Carlo simulations indicate that the T_C of Mn₂S₃ reachs 381 K, noticeably greater than room temperature. These findings present notable advantages for the application of Mn₂S₃ in spintronic devices. Hence, a prominent spin filtering effect is apparent when employing non-equilibrium Green’s function simulations to examine the transport parameters. The resulting current magnitude is approximately 2 × 10⁴ nA, while the peak gigantic magnetoresistance exhibits a substantial value of 8.36 × 10¹⁶ %. It is noteworthy that the device demonstrates a substantial spin Seebeck effect when the temperature differential between the electrodes is modified. In brief, Mn₂X₃ exhibits outstanding features as a high T_C half-metal, exhibiting exceptional capabilities in electrical and thermal drives spin transport. Therefore, it holds great potential for usage in spintronics applications.

Two-dimensional (2D) ferroelectric materials, which possess electrically switchable spontaneous polarization and can be easily integrated with semiconductor technologies, is of utmost importance in the advancement of high-integration low-power nanoelectronics. Despite the experimental discovery of certain 2D ferroelectric materials such as CuInP₂S₆ and In₂Se₃, achieving stable ferroelectricity at room temperature in these materials continues to present a significant challenge. Herein, stable ferroelectric order at room temperature in the 2D limit is demonstrated in van der Waals SnP₂S₆ atom layers, which can be fabricated via mechanical exfoliation of bulk SnP₂S₆ crystals. Switchable polarization is observed in thin SnP₂S₆ of ~7 nm. Importantly, a van der Waals ferroelectric field-effect transistor (Fe-FET) with ferroelectric SnP₂S₆ as top-gate insulator and p-type WTe_0.6Se_1.4 as the channel was designed and fabricated successfully, which exhibits a clear clockwise hysteresis loop in transfer characteristics, demonstrating ferroelectric properties of SnP₂S₆ atomic layers. In addition, a multilayer graphene/SnP₂S₆/multilayer graphene van der Waals vertical heterostructure phototransistor was also fabricated successfully, exhibiting improved optoelectronic performances with a responsivity (R) of 2.9 A/W and a detectivity (D) of 1.4 × 10¹² Jones. Our results show that SnP₂S₆ is a promising 2D ferroelectric material for ferroelectric-integrated low-power 2D devices.

Engineering phonon transport in low-dimensional materials has great significance not only for fundamental research, but also for thermal management applications of electric devices. However, due to the difficulties of micro and nano processing and characterization techniques, the work on tuning phonon transport at nanoscale are scarce. In this work, by introducing Ar⁺ plasma, we probed the phonon transport in two-dimensional (2D) layered semiconductor PdSe₂ under different defect concentrations. By using thermal bridge method, the thermal conductivity was measured to decrease by 50% after a certain Ar⁺ irradiation, which implied a possible phase transition. Moreover, Raman characterizations were performed to show that the Raman sensitive peaks of PdSe₂ was red-shifted and finally became disappeared with the increase of defect concentration. “Defect engineering” proves be a practical strategy in tuning the phonon thermal transport in low-dimensional materials, thus providing guidance for potential application in designing thermoelectric devices with various emerging materials.

Photodetectors based on two-dimensional (2D) semiconductors have attracted many research interests owing to their excellent optoelectronic characteristics and application potential for highly integrated applications. However, the unique morphology of 2D materials also restricts the further improvement of the device performance, as the carrier transport is very susceptible to intrinsic and extrinsic environment of the materials. Here, we report the highest responsivity (172 A/W) achieved so far for a PbI₂-based photodetector at room temperature, which is an order of magnitude higher than previously reported. Thermal scanning probe lithography (t-SPL) was used to pattern electrodes to realize the ultrashort channel (~60 nm) in the devices. The shortening of the channel length greatly reduces the probability of the photo-generated carriers being scattered during the transport process, which increases the photocurrent density and thus the responsivity. Our work shows that the combination of emerging processing technologies and 2D materials is an effective route to shrink device size and improve device performance.

Breaking up bulk crystals of functional materials into nanoscale thinner layers can lead to interesting properties and enhanced functionalities due to the size and interface effects. However, unlike the van der Waals layered crystals, many materials cannot be exfoliated into thin layers by liquid exfoliation. BiFeO₃ is a piezoelectric ceramic material, which is commonly synthesized as bulk crystals, limiting its wider applications. In this contribution, a freeze-drying assisted liquid exfoliation method was adopted to fabricate thin-layered BiFeO₃ nanoplates with lateral sizes of up to 500 nm and thicknesses of 10−20 nm. The freeze-drying process showed a vital role in the preparation process by imposing stress on the dispersed BiFeO₃ crystals during the liquid-to-solid-to-gas transition of the solvent. Such stress resulted in lattice strains in the freeze-dried BiFeO₃ crystals, which enabled their further exfoliation under subsequent ultrasonication. Considering the intrinsic piezoelectric effect of BiFeO₃, pressure sensors based on bulk and thin-layer BiFeO₃ were also fabricated. The pressure sensor based on BiFeO₃ nanoplates exhibited a largely enhanced sensitivity with a wider working range than the bulk counterpart, because of the stronger piezoelectric effect induced and the extra electrical charges at abundant interlayer interfaces. We suggest that the freeze-drying assisted liquid exfoliation method can be applied to other non-van der Waals crystals to bring about more functional material systems.

Interface engineering in atomically thin transition metal dichalcogenides (TMDs) is becoming an important and powerful technique to alter their properties, enabling new optoelectronic applications and quantum devices. Interface engineering in a monolayer WSe₂ sample via introduction of high-density edges of standing structured graphene nanosheets (GNs) is realized. A strong photoluminescence (PL) emission peak from intravalley and intervalley trions at about 750 nm is observed at the room temperature, which indicated the heavily p-type doping of the monolayer WSe₂/thin graphene nanosheet-embedded carbon (TGNEC) film heterostructure. We also successfully triggered the emission of biexcitons (excited state biexciton) in a monolayer WSe₂, via the electron trapping centers of edge quantum wells of a TGNEC film. The PL emission of a monolayer WSe₂/GNEC film is quenched by capturing the photoexcited electrons to reduce the electron-hole recombination rate. This study can be an important benchmark for the extensive understanding of light–matter interaction in TMDs, and their dynamics.