Ab initio study of semiconducting carbon nanotubes adsorbed on the   Si(100) surface: diameter- and registration-dependent atomic configurations   and electronic properties
  We present a first-principles study of semiconducting carbon nanotubes adsorbed on the unpassivated Si(100) surface. We have found metallicity for the combined system caused by n-doping of the silicon slab representing the surface by the SWNT. We confirm this metallicity for nanotubes of different diameters and chiral angles, and find the effect to be independent of the orientation of the nanotubes on the surface. We also present adsorption energetics and configurations which show semiconducting SWNTs farther apart from the surface and transferring less charge, in comparison with metallic SWNTs of similar diameter. 
Salvador Barraza-Lopez, Peter M. Albrecht, Nichols A. Romero and Karl   Hess