Abstract
We report first-principles total-energy calculations on the adsorption of (3, 3) and (4, 4)
single-walled carbon nanotubes (SWCNTs) on clean and hydrogenated diamond (100) surfaces.
For the nanotubes adsorbed on the clean surface we find that the stable geometries for the
nanotubes are on top of dimer rows and between two consecutive dimer rows where C–C
chemical bonds between carbons of the nanotubes and the surface dimers are formed. The
binding energies for a (3, 3) nanotube at the two sites are 2.26 and 0.83 eV ˚A
−1, while they are
1.74 and 0.36 eV ˚A
−1 for a (4, 4) nanotube. Our results show that to reach the stable geometry
the nanotubes initially experience weakly adsorbed states at the position ∼2.6 ˚A above the
surface and then overcome a barrier of ∼0.7 eV. Concerning the electronic properties, the most
noticeable feature is that for the most stable geometry the electronic structure of the adsorbed
metallic nanotube becomes semiconducting, i.e. a small band gap appears, due to the formation
of C–C bonds between the nanotube and the dimer atoms. As a result, the adsorbed metallic
nanotubes are realized in a metal-to-semiconductor transition. In contrast, on the fully
hydrogenated C(100) surface, the nanotubes are weakly adsorbed on the surface, preserving
an almost unchanged metallic character.