Narrow Results

In this paper, the electrical and optical properties of single-layer MoS₂ and single-layer WS₂ in three strain states: biaxial tension, biaxial compression, biaxial tension and compression are systematically studied. All calculations are based on the first-principle of density functional theory. The results show that after biaxial tension strain, biaxial compression strain, and biaxial tension-compression strain are applied, the atomic structure, energy band structure, and optical absorption coefficient will show disparate changing trends. When the biaxial tension and compression strain intensity is less than 15%, the bond length, bond angle, and light absorption peak will have little fluctuation with the increase of strain intensity. However, compared with the other two strain states, these two crystal structures are the most volatile at this time. In addition, when 15% biaxial tensile strain is applied, the two crystals can still maintain their kinetic stability.

Based on the first principles, the crystal structure, photoelectric properties, and structural stability of two transition metal dichalcogenides (TMDCs) under different strain treatments are systematically calculated. The properties of NbX₂ under tensile and compressive strains are discussed for the first time. Recently, a single-layer 1T structure with X atoms surrounding the transition metal atoms was synthesized in experiments. The 1T multi-forms were octahedral coordination structures, and some of the systems showed excellent semiconductor properties and stability. The results show that NbS₂ has an indirect band gap under different strains and tends to transition to semiconductors which can effectively improve the material activity. NbSe₂ has more excellent properties in the optical field and can be used to manufacture infrared lenses, anti-reflection coatings, and UV reflectors. This study provides a new understanding of the unconventional structure of NbX₂ and provides theoretical guidance for the work in the field of TMDCs.

In this paper, the effects of transition metal doping on the electronic structure of monolayer NbS₂ were studied through the first principles. The electronic structure changes caused by doping transition metal (TM) atoms were recorded, including the energy band, the density of states, binding energy, and optical properties. Studies show that all doping systems are metal. Still, under strain regulation, some doping systems offer an indirect bandgap; NbS₂ transforms into a narrow bandgap diluted semiconductor and can improve the activity. Doping atoms lead to $n(p)$ type doping in NbS₂.

Regarding optical properties, IVB group metals are selected as the typical dopant of three periods. Composite NbS₂ has excellent reflector characteristics and can be applied to infrared and ultraviolet regions. The spectral response and electromagnetic wave absorption range of low-energy areas are also improved. This study effectively solves the problem of impurity states introduced by doping and provides a solution for the doping modification of monolayer NbS₂, which will lay a foundation for nanoelectronics.

Based on the first principle, the change of photoelectric properties of non-metal-doped CrS₂ under biaxial tension was studied. The formation energy indicates that the doping system is stable. Studies have shown that the partial doping system achieves a semiconductor metal phase transition. The strain opens the bandgap of the F-doped system, and the system changes from metal to n-type semiconductor. The Te-doped system realizes the transition from indirect bandgap to direct bandgap under the adjustment of 2% strain. The O and Se doping systems realize the reverse regulation of the bandgap under strain, and the conductivity gradually increases with the increase of strain. The absorption efficiency of Te doping under a certain strain is significantly enhanced, the static dielectric properties of the F doping system are increased by more than two times, the absorption spectrum response range is increased, and the absorption capacity of the system is enhanced. This lays a foundation for applying monolayer CrS₂ in microelectronics and optoelectronics.