Effects of Stone-Wales and applied electric fields on the structure and electrical properties of silicene nanoribbons by SCC-DFTB calculations

Stone-Wales (SW) defects are widespread in graphene-like materials, which can affect electrical properties of nanostructures. In this paper, the effects of SW defects and applied vertical electric fields of different strengths on the geometric structure and electrical properties of zigzag silicene nanoribbons with different period widths (widths = 2, 3, 4) were studied by using a self-consistent charge density functional tight-binding (SCC-DFTB) method. The presence of SW defects leads to the reconstruction of silicon atoms, the enhancement of the interaction between atoms and the change of bond lengths and bond angles at the location of defects, and the influence of SW-II type defects on the geometric structure of nanoribbons is greater than that of SW-I type defects. The changing trend of the binding energy of perfect structure nanoribbon is related to its period width, regardless of types and the number of defects, while the size of the energy gap changes with the number and position of defects, and the transition between semi-metallic and semiconductor properties occurs. Meanwhile, at the same defect concentration, the effect of SW-I defects on the band structure is more obvious than that of SW-II defects. The electric field breaks the mirror symmetry at the SW defect, and the electronegativity of some atoms changes with the increase of the electric field strength. The defect types do not affect the charge transfer rule of nanoribbons, however, change the amount of charge transfer of the nanoribbons.