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The relevant fundamental properties of Janus WSSe monolayers to photocatalytic water-splitting performance are presented here and investigated using density functional theory. The Janus WSSe monolayer with a direct band gap of 1.75 eV is subjected to biaxial strain, and related optoelectronic properties are investigated. The effect of strain is reflected in band gap change from direct to indirect. Hydrogen evolution reaction (HER) is active all over, whereas oxygen evolution reaction (OER) is active only at 4% and 6% compressive strains. The red- and blue-shifts under tensile and compressive strains, respectively, substantiate possible control over exciton-phonon interaction making it suitable for the water-splitting application. Graphic Abstract Upon being irradiated by sunlight with sufficient energy, the biaxially strained Janus WSSe monolayer complying with HER/OER requirement produces hydrogen gas along with oxygen as a secondary product.

Highlights Janus MoSSe-based floating-gate memory exhibits ultrafast charge-trapping dynamics and stable charge retention exceeding 10 8  s under low-voltage operation. The intrinsic out-of-plane dipole moment in Janus MoSSe effectively suppresses leakage current and enlarges the memory window, even with ultrathin h-BN tunneling layers. The proposed all-van der Waals heterostructure provides a scalable platform for high-speed, energy-efficient, and reliable nonvolatile memory applications. The continued scaling of flash memory technologies faces challenges such as limited operation speed, poor data retention, and interface defects inherent to conventional three-dimensional architectures. Two-dimensional (2D) materials, with van der Waals interfaces and atomic-scale thickness, offer a promising pathway to overcome these limitations by enabling efficient charge modulation while minimizing surface defects. In this work, a nonvolatile 2D flash memory device is developed employing monolayer Janus MoSSe as the charge-trapping layer and hexagonal boron nitride (h-BN) as an ultrathin tunneling barrier. The intrinsic structural asymmetry of Janus MoSSe induces a strong vertical dipole moment, resulting in enhanced charge trapping, deeper energy barriers, and directional polarization compared with symmetric 2D materials. Consequently, the devices exhibit outstanding retention times exceeding 10 4  s, endurance beyond 10 4 program/erase cycles, and large memory window ratios (Δ V / V G,max of 50%–70% for 10 and 6 nm h-BN, respectively), with charge-trapping rates up to 8.96 × 10 14  cm −2  s −1 . In addition, Janus MoSSe-based devices show synaptic characteristics under electrical pulses and perform recognition simulations in artificial neural networks. These findings establish a design paradigm for 2D memory devices, enabling ultrathin, flexible, and energy-efficient nonvolatile memories.

The 2D Janus transition‐metal dichalcogenides (TMDs) and alloyed TMDs are a widely studied emerging class of 2D materials that have been extensively used in electronic devices because of their excellent electronic, optical, and mechanical properties. The properties and behaviors of 2D‐materials‐based devices, such as the electrical breakdown caused by structural failure, are significant issues that have drawn considerable attention. In this study, the electrical behavior of polymorphic molybdenum sulfide selenide (MoSSe) devices is studied via in situ biasing experiments and recorded using transmission electron microscopy (TEM) at the atomic scale. The selenization temperature is a key factor in the phase transition of the material, which further affects the electrical and mechanical properties of MoSSe. The effects of electron‐beam irradiation and bias voltage are also discussed through a combination of experiments and theory. Quantifying the defect coverage and defect size also helps us to understand the behavior of material degradation. Furthermore, Cs‐corrected scanning TEM is utilized to identify the evolution of the morphology. The fracture morphology of the synthesized structure also varies with the application of high voltage. The cracks and defects caused by Joule heating are studied in terms of fracture type and size. Janus and alloy polymorphic monolayer molybdenum sulfide selenide (MoSSe) prepared at different selenization temperatures exhibits different electrical and mechanical properties after biasing. In the structural degradation of MoSSe, powerful in situ transmission electron microscope (TEM) and annular dark‐field scanning TEM are used to understand the individual effects of electron beams and bias.

Based on density functional theory, we theoretically investigate the electronic structures of free-standing armchair Janus MoSSe nanoribbons (A-MoSSeNR) with width up to 25.5 nm. The equilibrium structures of nanoribbons with spontaneous curling are obtained by energy minimization in molecular dynamics (MD). The curvature is 0.178 nm−1 regardless of nanoribbon width. Both finite element method and analytical solution based on continuum theory provide qualitatively consistent results for the curling behavior, reflecting that relaxation of intrinsic strain induced by the atomic asymmetry acts as the driving force. The non-edge bandgap of curled A-MoSSeNR reduces faster with the increase of width compared with planar nanoribbons. It can be observed that the real-space wave function at the non-edge VBM is localized in the central region of the curled nanoribbon. When the curvature is larger than 1.0 nm−1, both edge bandgap and non-edge bandgap shrink with the further increase of curvature. Moreover, we explore the spontaneous curling and consequent sewing process of nanoribbon to form nanotube (Z-MoSSeNT) by MD simulations. The spontaneously formed Z-MoSSeNT with 5.6 nm radius possesses the lowest energy. When radius is smaller than 0.9 nm, the bandgap of Z-MoSSeNT drops rapidly as the radius decreases. We expect the theoretical results can help build the foundation for novel nanoscale devices based on Janus TMD nanoribbons.

Lubrication induced by a vertical electric field or bias voltage is typically not applicable to two-dimensional (2D) van der Waals (vdW) crystals. By performing extensive first-principles calculations, we reveal that the interlayer friction and shear resistance of Janus transition metal dichalcogenide (TMD) MoXY (X/Y = S, Se, or Te, and X ≠ Y) bilayers under a constant normal force mode can be reduced by applying vertical electric fields. The maximum interlayer sliding energy barriers between AA and AB stacking of bilayers MoSTe, MoSeTe, and MoSSe decrease as the positive electric field increases because of the more significant counteracting effect from the electric field energy and the more significant enhancement in interlayer charge transfer in AA stacking. Meanwhile, the presence of negative electric fields decreases the interlayer friction of bilayer MoSTe, because the electronegativity difference between Te and S atoms reduces the interfacial atom charge differences between AA and AB stacking. These results reveal an electro-lubrication mechanism for the heterogeneous interfaces of 2D Janus TMDs.

The exponential growth of population and industrial development necessitates the deployment of monitoring and sensing devices to curb the rising concentration of toxic gases in the environment. In the present work, the density functional theory approach has been employed on the chromium selenosulfide (CrSSe) monolayer. The structural stability of CrSSe monolayer was verified from the calculation of cohesive energy ( - 2.11 eV/atom) and dynamical stability was stated based on the phonon dispersion curves with no imaginary frequencies. CrSSe monolayer has metallic behaviour which can verified from the electronic band structure and density of states (DOS). Apart from that, gas sensing properties of CrSSe monolayer for some oxide gases such as NO 2 , CO were calculated. From the selected gas molecules for the current study, it has been analysed that NO 2 gas molecule having adsorption energy - 0.772 eV, acts as acceptor with 0.112e charge transferred from the CrSSe monolayer and work function difference is - 0.0541 eV. Majority of the contribution by NO 2 gas molecule is in the valence band which can be checked from projected density of states (PDOS). In the investigation of CrSSe monolayer as a sensing material it has been verified that material shows remarkable sensitivity for the NO 2 gas molecule.