Adsorption of oxygen molecular on pristine and defected SiC nanotubes

The structural and electronic properties of oxygen molecular adsorbed on the exterior surface of pristine and N_C or B_C defected (10,0) or (6,6) SiCNT have been investigated systematically using the first-principles projector-augmented wave potential within the density-functional theory under the generalized-gradient approximation. We find that for both pristine tubes the preferred adsorption sites of the O₂ molecule are above and nearly parallel to armchair Si-C bond whether physisorption or chemisorption. The strong chemical interaction between O₂ molecule and tube leads to not only a vanishing in magnetism of the O₂ molecule but also an outward relaxation of the underlying Si-C bond. The C atom substituted by N or B atom assists O₂ molecule adsorption above and nearly parallel to zigzag Si-N or Si-B bond as well as imparts a metallic character on the SiCNTs with higher concentration of the defects or a magnetism on the SiCNTs with lower concentration of the defects. Therefore, a combination of N or B doping followed by exposure to air may be an effective way to tune the electronic properties of the semiconducting SiCNTs. Furthermore, the lower binding energies for the pair of oxygen interstitials chemisorbed on N_C or B_C defected (10,0) or (6,6) SiCNT show that the oxygen molecule will dissociate to the pair of oxygen interstitials at the sidewall of N_C or B_C defected SiCNTs.