Two-dimensional (2D) ferromagnetic semiconductors have been recognized as the cornerstone for next-generation electric devices, but the development is highly limited by the weak ferromagnetic coupling and low Curie temperature ( T). Here, we reported a general mechanism which can significantly enhance the ferromagnetic coupling in 2D semiconductors without introducing carriers. On the basis of a double-orbital model, we revealed that the superexchange-driven ferromagnetism is closely related to the virtual exchange gap, and lowering this gap by isovalent alloying can significantly enhance the ferromagnetic (FM) coupling. On the basis of the experimentally available two-dimensional CrI and CrGeTe, the FM coupling in two semiconducting alloy compounds CrWI and CrWGeTe monolayers are calculated to be enhanced by 3∼5 times without introducing any carriers. Furthermore, a room-temperature ferromagnetic semiconductor is achieved under a small in-plane strain (4%). Thus, our findings not only deepen the understanding of FM semiconductors but also open a new door for realistic spintronics.

High-temperature ferromagnetic two-dimensional (2D) materials with flat surfaces have been a long-sought goal due to their potential in spintronics applications. Through comprehensive first-principles calculations, we show that the recently synthesized MoN2 monolayer is such a material; it is ferromagnetic with a Curie temperature of nearly 420 K, which is higher than that of any flat 2D magnetic materials studied to date. This novel property, made possible by the electron-deficient nitrogen ions, render transition-metal dinitrides monolayers with unique electronic properties which can be switched from the ferromagnetic metals in MoN2, ZrN2, and TcN2 to half-metallic ones in YN2. Transition-metal dinitrides monolayers may, therefore, serve as good candidates for spintronics devices.

Although graphitic C 3 N 4 (g-C 3 N 4 ) has been demonstrated to be a potential candidate for solar cell absorber and photovoltaic materials, the application has been limited by the low photoconversion efficiency in the visible range. Here, we explored that a g-C 3 N 4 bilayer has much better visible-light adsorption than a single layer via first-principles calculations, and the calculated optical adsorption threshold of bilayer significantly shifts downward by 0.8 eV, which is induced by the interlayer coupling. Additionally, we also found that the optical energy gap of bilayer can be engineered by the external electric field. The insights obtained in this study are general and will be helpful for future studies of twodimensional solar cell absorber and photovoltaic materials.

The formation mechanism of uniform CeO2 structure at the nanometer scale via a wet-chemical reaction is of great interest in fundamental study as well as a variety of applications. In this work, large-scale well-crystallized CeO2 nanorods with uniform diameters in the range of 20-30 nm and lengths up to tens of micrometers are first synthesized through a hydrothermal synthetic route in 5 M KOH solution at 180 degrees C for 45 h without any templates and surfactants. The nanorod formation involves dehydration of CeO2 nanoparticles and orientation growth along the 110 direction in KOH solution. Subsequently, gold nanoparticles with crystallite sizes between 10 and 20 nm are loaded on the surface of CeO2 nanorods using HAuCl4 solution as the gold source and NaBH4 solution as a reducing agent. The synthesized Au/CeO2 nanorods demonstrate a higher catalytic activity in CO oxidation than the pure CeO2 nanorods.

The electronic properties of a graphene–boron nitride (G/BN) bilayer have been carefully investigated by first-principles calculations. We find that the energy gap of graphene is tunable from 0 to 0.55 eV and sensitive to the stacking order and interlayer distances of the G/BN bilayer. By electronic structure analysis and tight-binding simulations, we conclude that the charge redistribution within graphene and charge transfer between graphene and BN layers determine the energy gap of graphene, through modification of the on-site energy difference of carbon p orbitals at two sublattices. On the basis of the revealed mechanism, we also predict how to engineer the band gap of graphene.

No abstract

The valence-shell electron momentum distributions for 1-butene are measured by electron momentum spectroscopy (EMS) employing non-coplanar symmetric geometry. The experimental electron momentum distributions are compared with the density functional theory (DFT) calculations using different-sized basis sets. Although the two conformers of 1-butene in the gas phase, namely the skew and syn, have very close ionization potentials, the electron momentum distributions, especially in the low momentum region, can show prominent differences for some of the valence orbitals. By comparing the experimental electron momentum profiles with the theoretical ones, the skew conformer is found to be more stable than the syn and their relative abundances at room temperature are estimated to be (69 +/- 6)% and (31 +/- 6)%, respectively. It demonstrates that EMS has the latent potential to study the relative stability of conformers.

No abstract