Electronic and optical structural manipulation of NbS defects under strain: first-principles calculations.

Context: Monolayer NbS is a promising new two-dimensional material, and it is critical to develop effective methods to make NbS a material for nanodevices and photovoltaic applications. This study studied the strain rule of sulfur-deficient NbS structure by first principles. The results show that all defect structures introduce impurity states to enhance electron transport. The disulfide defect structure produces an indirect band gap under the action of tensile strain, which can reach up to 0.56eV and become a diluted semiconductor. The hybrid NbS exhibits high transparency under infrared, visible, and low-frequency ultraviolet light, improving the material's transmittance, optical response, and catalytic activity. The research results of this paper will provide a basis for the subsequent research of single-layer NbS and accelerate the research process of NbS as a new semiconductor material.

Methods: We are on the surface perpendicular to the 3×3×1 NbS and use a 15 Å vacuum layer to avoid interacting with periodic images. The first-principles simulation uses the CASTEP module in Materials Studio to simulate the hypothetical model and relaxation optimization structure of single-layer NbS under strain and defect state. The calculation function is PBE (Perdew-Burke-Ernzerhof) function under the generalized gradient approximation (GGA) for an approximate calculation to describe the interaction between electrons and the interaction between electrons and ions. The pseudopotentials of 3s3p and 4d5s valence electron configurations were used for S and Nb atoms, respectively. Van der Waals correction is considered in the simulation process. Moreover, it includes spin-orbit coupling (SOC) effects. For the plane wave truncation energy, we set it at 500eV. The arrangement of the Brillouin area is divided by 6×6×1 gamma-centered Monkhorst-Pack grids. The lattice deformation of all hybrid structures is less than 0.05 Gpa, and the interatomic force is less than 0.03 eV/Å.