Valence Band Splitting on Multilayer MoS₂: Mixing of Spin–Orbit Coupling and Interlayer Coupling

Understanding the origin of valence band splitting is important because it governs the unique spin and valley physics in few-layer MoS₂. We explore the effects of spin–orbit coupling and interlayer coupling on few-layer MoS₂ using first-principles methods. We find spin–orbit coupling has a major contribution to the valence band splitting at K in multilayer MoS₂. In double-layer MoS₂, the interlayer coupling leads to the widening of the gap between the already spin–orbit split states. This is also the case for the bands of the K-point in bulk MoS₂. In triple-layer MoS₂, the strength of interlayer coupling of the spin-up channel becomes different from that of spin-down at K. This combined with spin–orbit coupling results in the band splitting in two main valence bands at K. With the increase of pressure, this phenomenon becomes more obvious with a decrease of main energy gap in the splitting valence bands at the K valley

Nitrogen/Boron Doping Position Dependence of the Electronic Properties of a Triangular Graphene

We investigate the effect of N/B doping on the electronic properties for a zero-dimensional zigzag-edged triangular graphene, wherein two sets of sublattices are unbalanced, using density functional theory (DFT). We find that the substitutional N/B atom energetically prefers to distribute in the major sublattice. After the N/B doping, the net spin for triangular graphene is reduced and full or partial depolarization occurs depending on doping sites. Our DFT calculations show that the triangular graphene with N/B doped in the major sublattice has a larger energy gap, and the electronic properties depend on the doping position. There is an impurity state below or above the Fermi level for the N/B-doped triangular graphene, depending on the sublattice at which the dopant locates. The dependence of the electronic properties on doping position is attributed to the competition between the Coulomb attraction of N+ (B−) and the correlation with nonbonding states for the extra charge introduced by the N/B atom

Calculated band structure of cubic BaSnO₃ using the TB-mBJ potential.

<p>Calculated band structure of cubic BaSnO₃ using the TB-mBJ potential.</p

Calculated conduction band structure of the relaxed (KTaO₃)//(CaSnO₃) supercell (see text) using the TB-mBJ potential.

<p>The Fermi energy is at 0 eV. Spin orbit is included.</p

Calculated band gap of BaSnO₃ as a function of lattice parameter with the TB-mBJ potential.

<p>Calculated band gap of BaSnO₃ as a function of lattice parameter with the TB-mBJ potential.</p

Modulation of Hydrogen Evolution Catalytic Activity of Basal Plane in Monolayer Platinum and Palladium Dichalcogenides

With an appropriate catalyst, hydrogen evolution reaction (HER) by water splitting can be used to produce hydrogen gas. Recently, layered transition-metal dichalcogenides have been proposed as alternative HER catalysts. However, a significant challenge is how to obtain the high-density active sites. With first-principle calculations, we explore the possibility of defect engineering to trigger the HER catalytic activity of basal plane by analyzing monolayer PdSe2, PtSe2, PdTe2, and PtTe2. It is found that the double-vacancy DVSe (DVTe) and B-doping can modulate appropriately the interaction between H and basal plane and improve the HER activity of these transition-metal dichalcogenides. Especially, the B-doping with high concentration can increase enormously the density of active sites on basal plane

Highly Ordered Periodic Au/TiO₂ Hetero-Nanostructures for Plasmon-Induced Enhancement of the Activity and Stability for Ethanol Electro-oxidation

The catalytic electro-oxidation of ethanol is the essential technique for direct alcohol fuel cells (DAFCs) in the area of alternative energy for the ability of converting the chemical energy of alcohol into the electric energy directly. Developing highly efficient and stable electrode materials with antipoisoning ability for ethanol electro-oxidation remains a challenge. A highly ordered periodic Au-nanoparticle (NP)-decorated bilayer TiO₂ nanotube (BTNT) heteronanostructure was fabricated by a two-step anodic oxidation of Ti foil and the subsequent photoreduction of HAuCl₄. The plasmon-induced charge separation on the heterointerface of Au/TiO₂ electrode enhances the electrocatalytic activity and stability for the ethanol oxidation under visible light irradiation. The highly ordered periodic heterostructure on the electrode surface enhanced the light harvesting and led to the greater performance of ethanol electro-oxidation under irradiation compared with the ordinary Au NPs-decorated monolayer TiO₂ nanotube (MTNT). This novel Au/TiO₂ electrode also performed a self-cleaning property under visible light attributed to the enhanced electro-oxidation of the adsorbed intermediates. This light-driven enhancement of the electrochemical performances provides a development strategy for the design and construction of DAFCs

Calculated conduction band structure of the relaxed (KNbO₃)//(ZnSnO₃) supercell (see text) using the TB-mBJ potential.

<p>The Fermi energy is at 0 eV.</p

Structures of supercells, left to right (a) KNbO₃//CaSnO₃, (b) KNbO₃//ZnSnO₃, (c) KTaO₃//CaSnO₃, and (d) KTaO₃//ZnSnO₃.

<p>As seen, the structures containing ZnSnO₃ have noticeable cation offcentering in the coordinating O cages in both the ZnSnO₃ and K(Nb,Ta)O₃ parts of the supercells. This corresponds to a ferroelectric polarization. The direction of this is indicated by the arrows on the left of the corresponding structure figures.</p

Calculated absorption spectrum of CaSnO₃ using the TB-mBJ potential.

<p>The Cartesian directions are along the crystallographic , and orthorhombic lattice parameters. A Lorentzian broadening of 0.025 eV was applied.</p