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In this paper, the effects of Al doping and equibiaxial strain on monolayer h-BN were investigated by first-principles calculations. The results show that with tensile strain applied, the structure of the material is more stable, while the structural stability of the material decreases when compressive strain is applied. When the monolayer h-BN is doped with Al, the band gap decreases, and the higher the doped Al concentration, the lower the band gap. Equibiaxial strain is very effective for band gap tuning of monolayer h-BN. The optical calculation results show that the peaks of dielectric function and optical constant of the material decrease after Al doping, and the peaks decrease with the increase of Al concentration. When the strain is tensile, the optical properties of the material will be red-shifted as a whole, and the optical properties of the material will be blue-shifted when compressive strain is applied. After the monolayer h-BN was doped with two Al atoms and a strain of −9% was applied, the optical properties of the material were significantly affected. Our study provides some theoretical implications for the application of monolayer h-BN in the field of spintronic devices and optoelectronic devices. • The effect of equbiaxial strain and Al doping on monolayer h-BN were investigated. • Using first principles based on density functional theory. • Compared with the compression strain, the structure of the material is more stable under the tensile strain. • Band gap decreases with increasing Al doping concentration. • Optical properties of the material are red-shifted with tensile strain and blue-shifted with compressive strain. [ABSTRACT FROM AUTHOR]

In this paper, the effects of biaxial [110] strain synergistic vacancy defects on the binding energy, electronic structure, and optical properties of monolayer MoS 2 were investigated using first-principles based on density functional theory. The results show that the monolayer MoS 2 is the most stable in the unstressed state, when it has vacancy defects, the stability decreases slightly, and the binding energy decreases with the increase of the absolute value of the strain. Monolayer MoS 2 is a semiconductor with a direct band gap of 1.73 ​eV. When Mo-vacancy appears, the band gap decreases significantly and the metallicity increases. When S-vacancy appears, the direct band gap transforms into an indirect band gap and the forbidden bandwidth decreases. The optical properties of the material are red-shifted by tensile strain, and blue-shifted by compressive strain. The strain coordinated vacancy defects have a significant effect on the regulation of the optical properties of monolayer MoS 2. The synergistic strain effect of vacancy provides some theoretical support for the application of monolayer MoS 2 in optics and other fields. The first principle calculation method based on density functional theory is used to study the electronic structure of monolayer MoS 2 and its vacancy structure. Different strains are applied to three different systems to improve the optical properties. The optical properties of materials can be significantly improved by strain synergetic vacancy. [Display omitted] • Effects of strain and vacancy defects on monolayer MoS 2 were investigated. • Using first principles based on density functional theory. • Results show that the synergistic strain of vacancy can effectively tune the optical properties of monolayer MoS 2. • Band gap of monolayer MoS 2 decreases when vacancy defects appear. • The strain will make the optical parameters of the material red shift or blue shift. [ABSTRACT FROM AUTHOR]

The effects of uniaxial strain on the binding energy, band structure, and optical properties of monolayer MoS 2 were investigated using first principles based on density functional theory. Monolayer MoS 2 is more stable in the absence of strain, and exhibits elastic behavior after applying strain. As the strain increases, the band gap is transformed from a direct band gap to an indirect band gap, and the band gap decreases with increasing strain. The influence of strain on the optical properties of materials mainly exists in the low-energy region. The changing trends of tensile strain and compressive strain are relative, and the optical properties of materials are obviously improved by strain, which can further provide theoretical reference for the study of optical properties of monolayer MoS 2 and other fields. [ABSTRACT FROM AUTHOR]

A Janus monolayer can be described as a two-dimensional material with distinct anions on either side of each layer. Two of these distinct chalcogen atoms are situated in the mirror-symmetric lattice positions of the transition metal atoms and are referred to as Janus transition metal dichalcogenides (TMDs). This material breaks the out-of-plane mirror symmetry and thus has excellent properties not found in conventional TMDs. However, during material synthesis, it can generate a number of defects that can substantially alter its properties. Therefore, in this article, the changes in the electronic structure and optical properties of Janus WSeTe when generating single vacancy defects, double vacancy defects and antisite defects have been investigated using first principles study. Assess the stability of the material through computations of its phonon spectrum, AIMD simulation and defect formation energy. Analyse its bandstructure, projected density of states, and optical absorption coefficient to present the change in its properties. The results show that the easiest and most stable form of defect is the substitution of Se atom for Te atom. These defect types change the bandgap value in different ways in Janus WSeTe, which further changes the peak optical absorption coefficient. The lattice constants undergo alterations during the defect generation process. For this purpose, we also investigated the changes in the properties of Janus WSeTe and its defects when subjected to biaxial tensile and compressive strains ranging from −9% to 9 %. As the tensile and compressive strains increase, a gradual decrease in the band gap value is observed. Our findings may serve as a theoretical basis for experiments in the synthesis of Janus WSeTe and the development of electronic devices using monolayer Janus WSeTe. • The photoelectric properties of Janus WSeTe in the presence of vacancy defects have been investigated using first principles. • With increasing strain, Janus WSeTe and its band gap with vacancy defects gradually decrease. • We found that the peak light absorption coefficient can be significantly modulated by defects and strains. • This study can provide some theoretical references for the synthesis of Janus WSeTe and the design of optoelectronic devices. [ABSTRACT FROM AUTHOR]