Electron energy spectrum and peculiarities of optical absorption of double-walled carbon nanotubes doped by alkali metals atoms

Abstract

Procedure based on the density functional theory is applied for investigation of the band structure, density of electronic states and optical absorption curves for photon energies less than ≊7 eV of double-walled carbon nanotubes both pristine and doped by alkali metals atoms (Li, Na, K) into the space between the walls. It is shown that in pristine double-walled nanotubes capable for doping by atoms Li, Na and K the radial shift of the inner tube relative to the outer one by ≊3%, 9% and 12% of the outer tube diameter, respectively, take place. It is revealed that the doping process of structures by alkali metals atoms leads to (a) the restoring of coaxial double-walled nanotubes symmetry; (b) the change of electronic band structure and conductivity type; (c) the appreciable shift of the chemical potential level to higher energies by ≊0.9–1.1 eV; (d) the changes in the absorbing capacity (two absorption peaks in the energy region less than 1.3 eV appear, while five absorption peaks which are typical for pristine structures, shifted to high-energy region by ≊0.1–0.2 eV).