Electrical properties of double-walled silicon nanotubes with Stone-Wales defect modulated by external electric field

The effects of the electric field on the geometrical and electronic properties of zigzag double-walled silicon nanotubes (DWSiNTs (5,0)@(9,0) and (6,0)@(10,0)) with three different orientations of Stone-Wales (SWI, SWII and SWIII) defective were investigated by the self-consistent charge density functional tight-binding (SCC-DFTB) method. Variations in tube diameter can alter the warping pattern of the outer wall, which subsequently induces changes in the geometric configuration of the inner wall's cross-section. The inner wall with SW defects can influence the corresponding local structural changes in the outer wall, whereas the outer wall with SW defects does not affect the structure of the inner wall. The impact of the external electric field on the geometric structure is localized, with local positions exhibiting the breakage and distortion of Si-Si bonds. The changes in bond length distribution further confirm the localized modulating effect of the electric field on the structure. For (5,0)@(9,0), the proportion of longer bond lengths increases, while for (6,0)@(10,0), the ratio of shorter bond lengths increases. Compared with SWI defects, SWII and SWIII defects in (5,0) @ (9,0) have higher structural stability. The electric field significantly increases the stability of (5,0)@(9,0), but the stability with double SW defects is lower than single SW defect. An external electric field can effectively open the bandgap of (5,0)@(9,0), while defect types play a crucial role in opening the bandgap of (6,0)@(10,0). The bandgap of SWII defective tubes is notably modulated by the applied electric field, achieving transitions from semiconductor to semimetal properties and from metal to semimetal properties. The charge redistribution induced by the external electric field primarily occurs between the defect region and the perfect region. Different types of defects also exhibit different charge distributions with different electric field strengths. Their combined effect leads to changes in the band structure and density of states.