Ab initio study of semiconducting carbon nanotubes adsorbed on the Si(100) surface: Diameter- and registration-dependent atomic configurations and electronic properties

We present an ab initio study of semiconducting carbon nanotubes adsorbed on an unpassivated Si(100) surface. Despite the usual gap underestimation in density functional theory, a dramatic reduction of the semiconducting gap for these hybrid systems as compared with the electronic gaps of both their isolated constitutive components has been found. This is caused by the changes in the electronic structure as the surface reconstructs due to tube's proximity, the concomitant electronic charge transfer from the nanotubes, and the band hybridization with silicon and carbon states resulting in the appearance of states within the energy gap of the formerly isolated nanotube. Furthermore, it is determined that semiconducting nanotubes exhibit weaker adsorption energies and remain at a greater distance from the Si(100) surface as compared to metallic nanotubes of similar diameter. This effect may be useful for the solid-state separation of metallic and semiconducting nanotubes. (c) 2006 American Institute of Physics.