Study on the structures and electronic properties of double-walled silicon nanotubes (4,min)@(8,mout) under external electric field by SCC-DFTB calculations

Abstract

The geometric structural optimization and electronic properties of double-walled silicon nanotubes (DWSiNTs) (4,min)@(8,mout) (min = 0 to 4, mout = 0 to 8) are studied in terms of the self-consistent charge density functional tight binding (SCC-DFTB) method. Calculations demonstrate that the regularity of the atomic arrangement, the diameter of the inner and outer walls, the degree of buckling, stability, energy gap, Fermi energy level, quantum molecular descriptors, and charge distribution strongly depend on the chiral index of the tube. In particular, the possibility of tuning the band structure by changing the chiral index has been demonstrated to help for the performance needs of different devices, inducing a metal–semiconductor transition and direct–indirect band gap transition. In addition, the influence of adding an external electric field on electronic properties of the zigzag DWSiNT (4,0)@(8,0) has been investigated. The tube applied electric field transforms from semiconductor to semi-metallic property. The tube becomes metallic upon the critical electric field strength of 0.7 V/nm and 1.0 V/nm. As increasing the external field strengths, the stability of the tube is reduced and the EF level is increased. The direction of charge transfer is always in the reverse of the field direction, which is different from the case of absent field.