Electronic and Structural properties of stained double-walled carbon nanotubes: Density Functional theory study

Abstract

In this work we utilized Density Functional Theory to investigate theoretically the electrical and structural properties of double walled carbon nanotubes (DWCNTs) upon applying uniaxial strain. We used three different types of zigzag single walled carbon nanotubes (SWCNTs) to build the DWCNT cells. These nanotubes are chosen with different sizes and electrical properties including metallic and semiconductors tubes. For all nanotubes we carried out total energy calculations and smooth curves were observed which is a good indication that the nanotubes are intact no fracture occurred. Furthermore we, found that all understudy DWCNTs have total energies less than their constituents SWCNTs before and after applying uniaxial strain. This can be attributed to the presence of Van der Waals forces between the wall to wall layers, which is considered as a reasonable explanation of the DWCNT more stability compared to SWCNT. Interestingly, band gap response to uniaxial strain of DWCNTs has been investigated and analyzed for the three tube types, Furthermore, we have found the band gap of DWCNTs is less than or close to the least band gap of its constituents SWCNT. This was explained by the charge transfer from the outer-tube to the inner-tube in DWCNTs in addition to the overlap between the orbitals of conduction band of the inner nanotube and the valence band of the outer nanotube. We also investigated the dependence of Fermi level on uniaxial strain for all nanotubes. Fermi level show mixed linear and nonlinear downshifts in Fermi level in response to the applied strain on all nanotubes except (8,0)SW. In (8,0)SW we have noted the opposite due to its smallness diameter.