Temperature-dependent Raman spectroscopy studies of the interface coupling effect of monolayer ReSe2 single crystals on Au foils

High-Performance Photoinduced Tunneling Self-Driven Photodetector for Polarized Imaging and Polarization-Coded Optical Communication based on Broken-Gap ReSe2 /SnSe2 van der Waals Heterojunction

Novel 2D materials with low-symmetry structures exhibit great potential applications in developing monolithic polarization-sensitive photodetectors with small volume. However, owing to the fact that at least half of them presented a small anisotropic factor of ≈2, comprehensive performance of present polarization-sensitive photodetectors based on 2D materials is still lower than the practical application requirements. Herein, a self-driven photodetector with high polarization sensitivity using a broken-gap ReSe2 /SnSe2 van der Waals heterojunction (vdWH) is demonstrated. Anisotropic ratio of the photocurrent (Imax /Imin ) could reach 12.26 (635 nm, 179 mW cm-2 ). Furthermore, after a facile combination of the ReSe2 /SnSe2 device with multilayer graphene (MLG), Imax /Imin of the MLG/ReSe2 /SnSe2 can be further increased up to13.27, which is 4 times more than that of pristine ReSe2 photodetector (3.1) and other 2D material photodetectors even at a bias voltage. Additionally, benefitting from the synergistic effect of unilateral depletion and photoinduced tunneling mechanism, the MLG/ReSe2 /SnSe2 device exhibits a fast response speed (752/928 µs) and an ultrahigh light on/off ratio (105 ). More importantly, MLG/ReSe2 /SnSe2 device exhibits excellent potential applications in polarized imaging and polarization-coded optical communication with quaternary logic state without any power supply. This work provides a novel feasible avenue for constructing next-generation smart polarization-sensitive photodetector with low energy consumption.

Anisotropic Phonon Behavior and Phase Transition in Monolayer ReSe2 Discovered by High Pressure Raman Scattering

Re-based transition metal dichalcogenides have attracted extensive attention owing to their anisotropic structure and excellent properties in applications such as optoelectronic devices and electrocatalysis. The present study methodically investigated the evolution of specific Raman phonon mode behaviors and phase transitions in monolayer and bulk ReSe2 under high pressure. Considering the distinctive anisotropic characteristics and the vibration vectors of Re and Se atoms exhibited by monolayer ReSe2, we perform phonon dispersion calculations and propose a methodology utilizing pressure-dependent polarized Raman measurements to explore the precise structural evolution of monolayer ReSe2 under the stress fields. Varied behaviors of the Eg-like and Ag-like modes, along with their specific vector transformations, have been identified in the pressure range 0-14.59 GPa. The present study aims to offer original perspectives on the physical evolution of Re-based transition metal dichalcogenides, elucidating their fundamental anisotropic properties and exploring potential applicability in diverse devices.

General Synthesis of 2D Magnetic Transition Metal Dihalides via Trihalide Reduction

Two-dimensional (2D) transition metal dihalides (TMDHs) have been receiving extensive attention due to their diversified magnetic properties and promising applications in spintronics. However, controlled growth of 2D TMDHs remains challenging owing to their extreme sensitivity to atmospheric moisture. Herein, using a home-built nitrogen-filled interconnected glovebox system, a universal chemical vapor deposition synthesis route of high-quality 2D TMDH flakes (1T-FeCl₂, FeBr₂, VCl₂, and VBr₂) by reduction of their trihalide counterparts is developed. Representatively, ultrathin (∼8.6 nm) FeCl₂ flakes are synthesized on SiO₂/Si, while on graphene/Cu foil the thickness can be down to monolayer (1L). Reflective magnetic circular dichroism spectroscopy shows an interlayer antiferromagnetic ordering of FeCl₂ with a Neel temperature at ∼17 K. Scanning tunneling microscopy and spectroscopy further identify the atomic-scale structures and band features of 1L and bilayer FeCl₂ on graphene/Cu foil.

ReSe2-Based RRAM and Circuit-Level Model for Neuromorphic Computing

Resistive random-access memory (RRAM) devices have drawn increasing interest for the simplicity of its structure, low power consumption and applicability to neuromorphic computing. By combining analog computing and data storage at the device level, neuromorphic computing system has the potential to meet the demand of computing power in applications such as artificial intelligence (AI), machine learning (ML) and Internet of Things (IoT). Monolayer rhenium diselenide (ReSe2), as a two-dimensional (2D) material, has been reported to exhibit non-volatile resistive switching (NVRS) behavior in RRAM devices with sub-nanometer active layer thickness. In this paper, we demonstrate stable multiple-step RESET in ReSe2 RRAM devices by applying different levels of DC electrical bias. Pulse measurement has been conducted to study the neuromorphic characteristics. Under different height of stimuli, the ReSe2 RRAM devices have been found to switch to different resistance states, which shows the potentiation of synaptic applications. Long-term potentiation (LTP) and depression (LTD) have been demonstrated with the gradual resistance switching behaviors observed in long-term plasticity programming. A Verilog-A model is proposed based on the multiple-step resistive switching behavior. By implementing the LTP/LTD parameters, an artificial neural network (ANN) is constructed for the demonstration of handwriting classification using Modified National Institute of Standards and Technology (MNIST) dataset.

Noble metal modified ReS2 nanocavity for surface-enhanced Raman spectroscopy (SERS) analysis

The rhenium disulphide (ReS₂) nanocavity-based surface enhanced Raman scattering (SERS) substrates ware fabricated on the gold-modified silicon pyramid (PSi) by thermal evaporation technology and hydrothermal method. In this work, the ReS₂ nanocavity was firstly combined with metal nanostructures in order to improve the SERS properties of ReS₂ materials, and the SERS response of the composite structure exhibits excellent performance in sensitivity, uniformity and repeatability. Numerical simulation reveals the synergistic effect of the ReS₂ nanocavity and the plasmon resonance generated by the metal nanostructures. And the charge transfer between the metal, ReS₂ and the analytes was also verified and plays an non-ignorable role. Besides, the plasmon-driven reaction for p-nitrothiophenol (PNTP) to p,p'-dimercaptobenzene (DMAB) conversion was successfully in-situ monitored. Most importantly, it is found for the first time that the SERS properties of ReS₂ nanocavity-based substrates are strongly temperature dependent, and the SERS effect achieves the best performance at 45 °C. In addition, the low concentration detection of malachite green (MG) and crystal violet (CV) molecules in lake water shows its development potential in practical application.

Flexible and highly responsive photodetectors based on heterostructures of MoS2and all-carbon transistors

Heterostructures of graphene and transition-metal dichalcogenides (TMDCs) are promising candidates for high-performance flexible photodetectors because of their high photoresponsivity and detectivity. However, the mechanical stability of current flexible photodetectors is limited, due to a mechanical mismatch between their two-dimensional channel materials and metallic contacts. Herein, we develop a type of mechanically stable, highly responsive, and flexible photodetector by integrating MoS₂and all-carbon transistors. By combining the high mobility of graphene with the strong light-matter interactions of MoS₂, our heterostructure photodetector exhibits a greatly improved photoresponse performance, compared with individual graphene or MoS₂photodetectors. In addition, the mechanical properties of the all-carbon electrodes are a good match for those of the active two-dimensional channels, resulting in greatly improved electrical stability of the heterostructure photodetector under mechanical deformation. These capabilities make our heterostructure photodetector a promising candidate for flexible photodetection and photoimaging applications.

Lattice dynamics, optical and thermal properties of quasi-two-dimensional anisotropic layered semimetal ZrTe2

In this study, an investigation was conducted on the vibrational properties exhibited by 2D layered zirconium ditelluride by employing Raman spectroscopy and confirmed by DFT calculation.

2D Re-Based Transition Metal Chalcogenides: Progress, Challenges, and Opportunities

The rise of 2D transition-metal dichalcogenides (TMDs) materials has enormous implications for the scientific community and beyond. Among TMDs, ReX2 (X = S, Se) has attracted significant interest regarding its unusual 1T' structure and extraordinary properties in various fields during the past 7 years. For instance, ReX2 possesses large bandgaps (ReSe2: 1.3 eV, ReS2: 1.6 eV), distinctive interlayer decoupling, and strong anisotropic properties, which endow more degree of freedom for constructing novel optoelectronic, logic circuit, and sensor devices. Moreover, facile ion intercalation, abundant active sites, together with stable 1T' structure enable them great perspective to fabricate high-performance catalysts and advanced energy storage devices. In this review, the structural features, fundamental physicochemical properties, as well as all existing applications of Re-based TMDs materials are comprehensively introduced. Especially, the emerging synthesis strategies are critically analyzed and pay particular attention is paid to its growth mechanism with probing the assembly process of domain architectures. Finally, current challenges and future opportunities regarding the controlled preparation methods, property, and application exploration of Re-based TMDs are discussed.

Bond-photon-phonon thermal relaxation in the M(X, X2) (M = Mo, Re, Ta, Ge, Sn; X = S, Se, and Te)

We systematically investigated the temperature-dependent bandgap energy and Raman shift on the bond length and bond energy, Debye temperature, and atomic cohesive energy for M(X, X₂) via bond relaxation methods.

Ultrahigh-photoresponsive UV photodetector based on a BP/ReS2 heterostructure p-n diode

The van der Waals (vdW) heterostructure, made up of two dissimilar two-dimensional materials held together by van der Waals interactions, has excellent electronic and optoelectronic properties as it provides a superior interface quality without the lattice mismatch problem. Here, we report the development and photoresponse characteristics of a p-n diode based on a stacked black phosphorus (BP) and rhenium disulfide (ReS2) heterojunction. The heterojunction showed a clear gate-tunable rectifying behavior similar to that of the conventional p-n junction diode. Under UV illumination, the BP/ReS2 p-n diode displayed a high photoresponsivity of 4120 A W-1 and we were able to modify the photoresponse properties by adjusting the back gate voltage. Moreover, an investigation of various channel lengths yielded the highest photoresponsivity of 11 811 A W-1 for a BP length of 1 μm. These results suggested vdW 2D materials to be promising for developing advanced heterojunction devices for nano-optoelectronics.