Photoinduced Spin Injection and Ferromagnetism in 2D Group III Monochalcogenides

The Isoelectronic Dopant in the Z-Scheme SnS2/β-As Heterostructure Enhancing Photocatalytic Overall Water Splitting

The catalytic field aims to decrease reaction barriers, accelerate reaction processes, and enhance the selectivity toward a target product. This study uses first-principles calculations to design a modified direct Z-scheme SnS2/β-As heterostructure as a potential photocatalyst for overall water splitting. Our previous investigations have demonstrated that the SnS2/β-As heterostructure can realize a hydrogen evolution reaction (HER) under light, while the oxygen evolution reaction (OER) follows a pathway involving the intermediate HOOH*. Interestingly, by substituting an S atom of SnS2 with a Se or Te atom, the rate-determining step of the OER is significantly reduced from 3.76 eV to 2.56 or 2.22 eV. Moreover, the OER can occur directly without the transition via HOOH*. Isoelectronic doping effectively trades off the adsorption strength of OER intermediates and promotes the OER process. This work highlights the dual benefits of isoelectronic doping, namely lowering the reaction barrier of the rate-determining step and promoting the selectivity of end products. These findings provide insights into the rational design of high-efficiency photocatalysts for water splitting.

Bilayer hexagonal structure MnN2 nanosheets with room-temperature ferromagnetic half-metal behavior and a tunable electronic structure

Two-dimensional (2D) layered materials have atomically thin thickness and outstanding physical properties, attracting intensive research in the past year. As one of these materials, a 2D magnet is an ideal platform for fundamental physics research and magnetic device development. Recently, a non-MoS2-type geometry was found to be more favorable in 2D transition-metal dinitrides. In this work, driven by this new configuration, we perform a comprehensive first-principles study on the bilayer hexagonal structure of 2D manganese dinitrides. Our results show that 2D MnN2 is a ferromagnetic half-metal at its ground state with 100% spin-polarization ratio at the Fermi energy level. The phonon spectrum calculation and ab initio molecular dynamics simulation show that the 2D MnN2 crystal has a high thermodynamic stability and its 2D lattice can be retained at room-temperature. Monte Carlo simulations based on the Heisenberg model predict a Curie temperature of over 563 K and its electronic properties can be regulated by biaxial strain. The half-metallic states are mainly contributed by Mn d orbitals, and the magnetic exchange of the system mainly comes from the Mn-N-Mn super-exchange. The p-d orbital hybridization will provide a small antiparallel magnetic moment of N atoms, and the p-orbital dangling bond can be eliminated by oxidation to enhance the total magnetic moment of the system. The study of magnetic anisotropy energy indicates that the easy magnetization axis is in-plane and hybridization between Mn dyz and dz2 orbitals gives the largest magnetic anisotropy contribution. In view of these results, we consider that novel 2D MnN2 is one of the most promising two-dimensional materials for nano-spintronic applications.

Two-Dimensional Magnetic Semiconducting Heterostructures of Single-Layer CrI3-CrI2

Single-layer heterostructures of magnetic materials are unique platforms for studying spin-related phenomena in two dimensions (2D) and have promising applications in spintronics and magnonics. Here, we report the fabrication of 2D magnetic lateral heterostructures consisting of single-layer chromium triiodide (CrI₃) and chromium diiodide (CrI₂). By carefully adjusting the abundance of iodine based on molecular beam epitaxy, single-layer CrI₃-CrI₂ heterostructures were grown on Au(111) surfaces with nearly atomic-level seamless boundaries. Two distinct types of interfaces, i.e., zigzag and armchair interfaces, have been identified by means of scanning tunneling microscopy. Our scanning tunneling spectroscopy study combined with density functional theory calculations indicates the existence of spin-polarized ground states below and above the Fermi energy localized at the boundary. Both the armchair and zigzag interfaces exhibit semiconducting nanowire behaviors with different spatial distributions of density of states. Our work presents a novel low-dimensional magnetic system for studying spin-related physics with reduced dimensions and designing advanced spintronic devices.

Ultrafast Light-Induced Ferromagnetic State in Transition Metal Dichalcogenides Monolayers

Ultrafast optical control of magnetism had great potential to revolutionize magnetic storage technology and spintronics, but for now, its potential remains mostly untapped in two-dimensional (2D) magnets. Here, using the state-of-the-art real-time time-dependent density functional theory (rt-TDDFT), we demonstrate that an ultrafast laser pulse can induce a ferromagnetic state in nonmagnetic MoSe₂ monolayers interfaced with van der Waals (vdW) ferromagnetic MnSe₂. Our results show that the transient ferromagnetism in MoSe₂ derives from photoinduced direct ultrafast interlayer spin transfer from Mn to Mo via a vdW-coupled interface, albeit with a delay of approximately a few femtoseconds. This delay was strongly dependent on laser duration and interlayer coupling, which could be used to tune the amplitude and rate spin transfer. Furthermore, we have also shown that ferromagnetic states can be photoinduced in other transition metal dichalcogenides (TMDs), such as PtS₂ and TaSe₂ monolayers. Overall, our findings provide crucial physical insights for exploring light-induced interlayer spin and charge dynamics in 2D magnetic systems.

Family of Two-Dimensional Transition Metal Dichlorides: Fundamental Properties, Structural Defects, and Environmental Stability

A large number of novel two-dimensional (2D) materials are constantly being discovered and deposited in databases. Consolidated implementation of machine learning algorithms and density functional theory (DFT)-based predictions have allowed the creation of several databases containing an unimaginable number of 2D samples. As the next step in this chain, the investigation leads to a comprehensive study of the functionality of the invented materials. In this work, a family of transition metal dichlorides have been screened out for systematic investigation of their structural stability, fundamental properties, structural defects, and environmental stability via DFT-based calculations. The work highlights the importance of using the potential of the invented materials and proposes a comprehensive characterization of a new family of 2D materials.