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A significant problem in the area of rechargeable alkali ion battery technologies is the exploration of anode materials with overall high specific capacities and superior physical properties. By using first-principles calculations, we have determined that monolayer TiSi2N4 is precisely such a potential anode candidate. Its demonstrated dynamic, thermal, mechanical, and energetic stabilities make it feasible for experimental realization. An important benefit of the electrode conductivity is that the electronic structure reveals that the pristine system experiences a change from a semiconductor to a metal throughout the entire alkali adsorption process. What's more interesting is that monolayer TiSi2N4 can support up to double-sided 3-layer ad-atoms, resulting in extremely high theoretical capacities for Li, Na, Mg, and K of 1004, 854, 492 and 531 mA h g−1 and low average open-circuit voltages of 0.55, 0.25, 0.55, and −1.3 V, respectively. Alkali diffusion on the surface has been demonstrated to occur extremely quickly, with migration energy barriers for Li, Na, Mg, and K as low as 0.25, 0.14, 0.10, and 0.07 eV, respectively. The results reveal that the migration barrier energy is the lowest for Li and Mg from path-2 and Na and K from path-1. Overall, these findings suggest that monolayer TiSi2N4 is a suitable anode candidate for use in high-performance and low-cost metal-ion batteries. [ABSTRACT FROM AUTHOR]

Recently, by forming a P‐rich P–S system, the P3S monolayer has been predicted to have good resistance to air oxidation, large band gap, high absorption, and superior mobility. Inheriting this prediction, a series of ternary Janus P6XY (X/Y = S, Se, and Te; X ≠ Y) monolayers based on P3X nanosheet are designed and studied. The structures of P6XY monolayers are confirmed to be stable based on the evaluation of calculated results for phonon spectra, ab initio molecular dynamic simulations. It is also found that P6XY compounds possess anisotropic mechanical characteristics. All Janus structures are indirect semiconductors with large energy gaps varying from 2.12 to 2.60 eV calculated by the hybrid functional. Besides, biaxial strain significantly affects the electronic properties of the P6XY monolayers. In particular, the biaxial strains can induce a transition from indirect to direct bandgap in all three P6XY structures. The carrier mobility in the three proposed structures exhibits directional anisotropy and high electron mobility value, up to 1.27 × 103 cm2 V−1 s−1, which are suitable for applications in high‐performance and direction‐dependent nanoelectronic devices. [ABSTRACT FROM AUTHOR]

Since the recent successful experimental synthesis of MoSi2N4 [Science, 369 (2020), 670], the "MA2Z4 family" has been of particular interest to the scientists in the field of materials science due to its outstanding physical properties. In this paper, the first‐principles calculations are performed to study the structural, elastic, and electronic properties of novel two‐dimensional (2D) Janus MSiGeN4 monolayers (M = Ti, Zr, Hf). The calculations of phonon spectra indicate that monolayers MSiGeN4 are dynamically stable and can be experimentally synthesized. The obtained Young's modulus and Poisson's ratio of the Janus structures MSiGeN4 are much larger than that of other binary 2D materials and meet the mechanical stability criteria suggested by Born and Huang. In the calculations using either PBE or HSE06 functionals, the Janus MSiGeN4 structures exhibit indirect semiconductor characteristics with larger band gaps than that of similar septuple‐atomic‐layer materials, such as MoSiGeN4 and WSiGeN4. In addition, the influences of biaxial strain and external electric field on the electronic structure of MSiGeN4 are investigated. It is found that the biaxial strain tunes the electronic characteristics more significantly than the external electric field. The obtained results can provide insights into novel Janus monolayers with potential applications in electronic devices. [ABSTRACT FROM AUTHOR]

In this work, we investigate the tunable structural and electronic properties of SnAs monolayer through chlorinated functionalization and the SnAs/SnAsCl heterostructure construction. Through chlorinated functionalization, we observe a remarkable transformation of the SnAs monolayer into a semiconducting SnAsCl monolayer with a direct band gap of 1.32 eV. This demonstrates the potential for controlling and tuning the electronic properties of SnAs through surface functionalization. Moreover, depending on the specific stacking patterns in the SnAs/SnAsCl heterostructure, we observe the formation of either Ohmic contact or Schottky contact. Particularly noteworthy is the presence of ultra-low Schottky barriers, measured at 0.03 eV, charge transport efficiency and improving device performance. The SnAs/SnAsCl heterostructure exhibits small tunneling probability, indicating a relatively low electron transparency. These findings pave the way for the development of high-performance electronic devices utilizing these heterostructures and offer promising opportunities for future technological advancements. • Structural and electronic properties of SnAs monolayer through Cl-functionalization and the construction of SnAs/SnAsCl heterostructure are investigated. • Metallic SnAs and semiconducting SnAsCl presents an intriguing phenomenon in terms of the metal–semiconductor contact. • SnAs/SnAsCl heterostructure forms either Ohmic contact or Schottky contact with ultra-low Schottky barriers. • SnAs/SnAsCl heterostructure exhibit small tunneling probability, indicating a relatively low electron transparency. • These findings pave the way for the development of high-performance electronic devices. [ABSTRACT FROM AUTHOR]

• Janus Al 2 SSe monolayer is dynamically and thermally stable at room temperature. • Al 2 SSe monolayer is an indirect semiconductor with band gap of 2.079 eV. • Electronic properties of Al2SSe monolayer depend strongly on biaxial strain. • Al 2 SSe monolayers can strongly absorb the near-ultraviolet light. • Optical absorbance intensity of Al2SSe can be enhanced by strain. Motivated by the successful experimental fabrication of Janus structures recently, a systematic study of the structural, electronic, and optical properties of the Janus Al 2 SSe monolayer has been done through first-principles approach. Through phonon spectrum and ab initio molecular dynamics analysis, Al 2 SSe was confirmed to be dynamically and thermally stable. The Janus Al 2 SSe monolayer exhibits a semiconducting characteristics with indirect band gap of 2.079 eV at equilibrium. While biaxial strain can significantly alter band gap, the influence of electric field on electronic as well as optical properties is negligible. The optical absorbance of Al 2 SSe is activated in the visible light region and its intensity can be enhanced by strain. Our findings only highlight the physical properties but also provide an effective way for tuning the electronic and optical properties of Al 2 SSe monolayer by strain engineering. [ABSTRACT FROM AUTHOR]

MoS 2 can exist in many different polytypes, such as trigonal prismatic, distorted octahedral, or octahedral. The 2 H -phase of MoS 2 has been extensively studied in recent times, but there are very few studies focusing on the remaining phases, especially the distorted octahedral T ′)-phase. Here, we design the MoS 2 monolayer and Janus MoSSe structure in the 1 T ′ phase and study their electronic properties within the framework of first-principles calculations. Both 1 T ′ -MoS 2 and 1 T ′ -MoSSe monolayers are confirmed to have structural stability and anisotropic mechanical characteristics. Interestingly, while the 1 T ′ -MoS 2 monolayer exhibits metallic characteristics, Janus MoSSe in the 1 T ′ phase is a semiconductor with a small band gap of 0.04 eV. More interestingly, a tiny bandgap of 0.05 eV has opened up in the 1 T ′ -MoS 2 monolayer due to the spin–orbit coupling effect. We also study the mobility of carriers in the semiconductor Janus 1 T ′ -MoSSe monolayer. 1 T ′ -MoSSe monolayer exhibits a high anisotropic carrier mobility due to its high anisotropic crystal structure. Surprisingly, 1 T ′ -MoSSe monolayer possesses extremely high electron mobility, up to 4. 58 × 1 0 3 cm 2 V−1 s−1. Our findings give a deeper insight into the 1 T ′ -phase of transition metal dichalcogenide and its Janus structure. • MoS 2 and MoSSe monolayers are structurally stable in the 1T' crystal phase. • 1T' -MoS 2 and 1T' -MoSSe monolayers exhibit anisotropic mechanical characteristics. • A small band gap of 0.05 eV has opened up in 1T' -MoS 2 due to the spin–orbit coupling effect. • 1T' -MoSSe monolayer possesses anisotropic transport characteristics with electron mobility exceeding 4 × 103 cm2 V−1 s−1. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) materials with high specific capacities and superior physical properties are essential for designing rechargeable metal-ion batteries. In this study, first-principles calculations were performed to evaluate the potential of a WSSe monolayer as an electrode material for rechargeable lithium (Li), sodium (Na), and potassium (K) ion batteries. Our results showed that all alkali adsorptions were energetically stable and caused a semiconductor-to-metal transition, improving electronic conductivity. The calculated open-circuit voltage (OCV) for Li ions (0.48 V), Na ions (0.57 V), and K ions (0.37 V) was less than 1 V, which is critical for high charge and discharge rates. The maximum theoretical capacities for Li, Na, and K atoms adsorbed on the Janus WSSe monolayer were 477.8, 371.5, and 156.0 mAh/g, respectively. Our calculated migration energy barriers for Li, Na and K on S layer (Se layer) are (0.25, 0.07 and 0.07 (0.18, 0.04 and 0.038) eV, respectively, suggesting that the Se layer experiences faster Li-ion diffusion than the S layer. The ion diffusion potential for Li, Na, and K on the S layer (Se layer) for path 1 was considerably lower than paths 2 and 3, suggesting that the Se layer has faster Li-ion diffusion than the S layer. These findings provide a promising avenue for designing high-performing anode materials for rechargeable metal-ion batteries. [Display omitted] • Potential of a WSSe monolayer as an electrode material for rechargeable metal ion batteries is considered. • Alkali adsorption improves conductivity via semiconductor-to-metal transition. • The OCV is less than 1 V, which is critical for high charge and discharge rates. • The maximum TSC for Li, Na, and K atoms adsorbed on WSSe monolayer are 477.8, 371.5, and 156.0 mAh/g, respectively. • WSSe monolayer a potential candidate for high-performance electrodes. [ABSTRACT FROM AUTHOR]