First-principles calculations of carbon nanotubes adsorbed on diamond (100) surfaces

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 stablegeometries for the nanotubes are on top of dimer rows and between two consecutive dimerrows where C–C chemical bonds between carbons of the nanotubes and the surface dimersare formed. The binding energies for a (3, 3) nanotube at the two sites are 2.26 and0.83 eV Å−1, while theyare 1.74 and 0.36 eV Å−1 for a (4, 4) nanotube. Our results show that to reach the stable geometrythe nanotubes initially experience weakly adsorbed states at the position∼2.6 Å above the surface and then overcome a barrier of∼0.7 eV. Concerning the electronic properties, the most noticeable feature is that for the moststable geometry the electronic structure of the adsorbed metallic nanotube becomessemiconducting, i.e. a small band gap appears, due to the formation of C–C bonds betweenthe nanotube and the dimer atoms. As a result, the adsorbed metallic nanotubes arerealized in a metal-to-semiconductor transition. In contrast, on the fully hydrogenatedC(100) surface, the nanotubes are weakly adsorbed on the surface, preserving an almostunchanged metallic character.