Effect of strain on the electronic structure and optical properties of Cr-doped monolayer MoS.

Context: In this paper, the electronic and optical properties of Cr-doped monolayer MoS under uniaxial tensile strain are investigated by first-principle calculations. It is shown that uniaxial tensile strain can significantly change the electronic and optical properties of Cr-doped monolayer MoS, and the bandgap value of the intrinsic MoS system gradually decreases with the increase of tensile strain, while the bandgap value of the Cr-doped MoS system is relatively stable. However, when the stretching reaches a certain degree, both the intrinsic and doped systems become metallic. From the analysis of the density of states, it is found that new electronic states and energy levels appear in the intrinsic MoS system and all Cr-doped monolayer MoS systems with the increase of the tensile strain, but the changes in the density of states diagrams of the Cr-doped monolayer MoS system are relatively small, which is mainly attributed to the effect of the Cr-doped atoms. The analysis of optical properties displays that the stretched doped system differs from the intrinsic MoS system in terms of dielectric function, absorption and reflection, energy loss function, and refractive index. Our results suggest that uniaxial tensile strain can be used as an effective means to modulate the electronic structure and optical properties of Cr-doped monolayer MoS. These findings provide a theoretical basis for understanding the optoelectronic properties of MoS and its doped systems as well as their applications in optoelectronic devices.

Methods: Based on the first principle of density functional theory framework and the CASTEP module in Materials Studio software (Perdew et al. in Phys Rev Lett 77(18):3865-3868, 1996). The structure of Cr atom-doped MoS systems and MoS systems were optimized using the generalized gradient approximation plane-wave pseudopotential method (GGA) and Perdew-Burke-Ernzerhof (PBE) generalized functions under 3%, 6%, and 9% tensile deformation, and the corresponding formation energy, bond length, electronic structure, and optical properties of the models were analyzed. The Grimme (J Comput Chem 27(15):1787-1799, 2006) vdW correction with 400 eV cutoff was used in Perdew-Burke-Ernzerhof (PBE) functional to optimize the geometry until the forces and energy converged to 0.02 eV/Å and 1.0e-5eV/atom, respectively. For each model structure optimization, the K-point grid was assumed to be 4×4×1, using the Monkhorst-Pack special K-point sampling method. After the MoS supercell convergence test, the plane-wave truncation energy was chosen to be 400 eV. Following geometric optimization, the iterative accuracy converged to no less than 1.0×10 eV/atom for total atomic energy and less than 0.02 eV/Å for all atomic forces. We created a vacuum layer of 18 Å along the Z-axis to prevent the impact of periodic boundary conditions and weak van der Waals forces between layers on the monolayer MoS. In this paper, a total of 27 atoms were used for the 3×3×1 supercell MoS system, which consists of 18 S atoms and 9 Mo atoms.