Atomically thin 2D-layered transition-metal dichalcogenides have been studied extensively in recent years because of their intriguing physical properties and promising applications in nanoelectronic devices. Among them, ReSe2 is an emerging material that exhibits a stable distorted 1T phase and strong in-plane anisotropy due to its reduced crystal symmetry. Here, the anisotropic nature of ReSe2 is revealed by Raman spectroscopy under linearly polarized excitations in which different vibration modes exhibit pronounced periodic variations in intensity. Utilizing high-quality ReSe2 nanosheets, top-gate ReSe2 field-effect transistors were built that show an excellent on/off current ratio exceeding 10(7) and a well-developed current saturation in the current-voltage characteristics at room temperature. Importantly, the successful synthesis of ReSe2 directly onto hexagonal boron nitride substrates has effectively improved the electron motility over 500 times and the hole mobility over 100 times at low temperatures. Strikingly, corroborating with our density-functional calculations, the ReSe2-based photodetectors exhibit a polarization-sensitive photoresponsivity due to the intrinsic linear dichroism originated from high in-plane optical anisotropy. With a back-gate voltage, the linear dichroism photodetection can be unambiguously tuned both in the electron and hole regime. The appealing physical properties demonstrated in this study clearly identify ReSe2 as a highly anisotropic 2D material for exotic electronic and optoelectronic applications.

Atomically thin 2D layered transition metal dichalcogenides (TMDs) have been extensively studied in recent years because of their appealing electrical and optical properties. Here, the fabrication of ReS2 field‐effect transistors is reported via the encapsulation of ReS2 nanosheets in a high‐κ Al2O3 dielectric environment. Low‐temperature transport measurements allow to observe a direct metal‐to‐insulator transition originating from strong electron–electron interactions. Remarkably, the photodetectors based on ReS2 exhibit gate‐tunable photoresponsivity up to 16.14 A W−1 and external quantum efficiency reaching 3168%, showing a competitive device performance to those reported in graphene, MoSe2, GaS, and GaSe‐based photodetectors. This study unambiguously distinguishes ReS2 as a new candidate for future applications in electronics and optoelectronics.

Charge-trap memory with high-κ dielectric materials is considered to be a promising candidate for next-generation memory devices. Ultrathin layered twodimensional (2D) materials like graphene and MoS2 have been receiving much attention because of their novel physical properties and potential applications in electronic devices. Here, we report on a dual-gate charge-trap memory device composed of a few-layer MoS2 channel and a three-dimensional (3D) Al2O3/HfO2/Al2O3 charge-trap gate stack. Owing to the extraordinary trapping ability of both electrons and holes in HfO2, the MoS2 memory device exhibits an unprecedented memory window exceeding 20 V. More importantly, with a back gate the window size can be effectively tuned from 15.6 to 21 V; the program/erase current ratio can reach up to 10 4 , far beyond Si-based flash memory, which allows for multi-bit information storage. Furthermore, the device shows a high mobility of 170 cm 2 V -1 s -1 , a good endurance of hundreds of cycles and a stable retention of ~28% charge loss after 10 years which is drastically lower than ever reported MoS2 flash memory. The combination of 2D materials with traditional high-κ charge-trap gate stacks opens up an exciting field of novel nonvolatile memory devices. KEYWORDS. Charge-trap memory, MoS 2 , Memory window, Dual gate, Memory characteristics 3 Atomically thin 2D materials like graphene and MoS 2 has been extensivelystudied recently because of their promising applications in optoelectronics 1, 2 , spintronics 3-7 , transparent and flexible devices [8][9][10][11][12] . Due to its remarkable properties, such as high carrier mobility and mechanical flexibility, graphene has been incorporated into nonvolatile memory structures serving as a floating gate 13,14 or a transparent channel 15 . However, owing to its zero band gap 16 , the graphene channeled memory devices typically possess a low program/erase current ratio, which significantly hinders its application in nonvolatile memory devices. Unlike graphene, MoS 2 has a transition from indirect band gap (1.2 eV) to a direct band gap (1.8 eV) in monolayer 17,18 . Its field effect transistors 19 show a high mobility of 200 cm 2 V -1 s -1 with a high on/off ratio approximately 10 8 . To potentially enhance the program/erase current ratio, attempts were made to replace graphene with MoS 2 as a channel material in a ferroelectric memory 20 or as a charge-trap layer in a graphene flash memory 21 . It was demonstrated that the monolayer MoS 2 is very sensitive to the presence of charges 14 . However, the relatively small memory window, the degraded mobility, and the insufficient trap capability in those devices require further improvement of the chargetrap stack in the MoS 2 memory device.

Recently, layered two-dimensional ferromagnetic materials (2D FMs) have attracted a great deal of interest for developing lowdimensional magnetic and spintronic devices. Mechanically exfoliated 2D FMs were discovered to possess ferromagnetism down to monolayer. It is therefore of great importance to investigate the distinct magnetic properties at low dimensionality. Here, we report the wafer-scale growth of 2D ferromagnetic thin films of Fe 3 GeTe 2 via molecular beam epitaxy, and their exotic magnetic properties can be manipulated via the Fe composition and the interface coupling with antiferromagnetic MnTe. A 2D layer-by-layer growth mode has been achieved by in situ reflection high-energy electron diffraction oscillations, yielding a well-defined interlayer distance of 0.82 nm along {002} surface. The magnetic easy axis is oriented along c-axis with a Curie temperature of 216.4 K. Remarkably, the Curie temperature can be enhanced when raising the Fe composition. Upon coupling with MnTe, the coercive field dramatically increases 50% from 0.65 to 0.94 Tesla. The large-scale layer-by-layer growth and controllable magnetic properties make Fe 3 GeTe 2 a promising candidate for spintronic applications. It also opens up unprecedented opportunities to explore rich physics when coupled with other 2D superconductors and topological matters.

Chiral anomaly, a non-conservation of chiral charge pumped by the topological nontrivial gauge fields, has been predicted to exist in Weyl semimetals. However, until now, the experimental signature of this effect exclusively relies on the observation of negative longitudinal magnetoresistance at low temperatures. Here, we report the field-modulated chiral charge pumping process and valley diffusion in Cd3As2. Apart from the conventional negative magnetoresistance, we observe an unusual nonlocal response with negative field dependence up to room temperature, originating from the diffusion of valley polarization. Furthermore, a large magneto-optic Kerr effect generated by parallel electric and magnetic fields is detected. These new experimental approaches provide a quantitative analysis of the chiral anomaly phenomenon which was inaccessible previously. The ability to manipulate the valley polarization in topological semimetal at room temperature opens up a route towards understanding its fundamental properties and utilizing the chiral fermions.