Hydrogen interaction with native defects in SiC nanotubes

Using spin-polarized density functional theory we investigate the incorporation of hydrogen adatoms on antisites and vacancies present in the zigzag (10,0) and in the armchair (6,6) silicon carbide nanotubes. We find that the presence of antisites Si-C and C-Si increases the incorporation rate of hydrogens adatoms, giving rise to monohydrogenated HSiC and HC-C-Si configurations. In the former structure the H adatom bonds to the Si-C antisite, whereas in the latter the hydrogen adatom bonds to the C atom nearest neighbor to the C-Si antisite. Increasing the coverage of H adatoms, two H adatoms, our binding energy results indicate that the hydrogen adsorption on the neighboring Si and C sites represents the energetically most stable configuration. For carbon vacancies, we obtained binding energies of -2.8 and -3.2 eV/H atom, for monohydrogenated and dihydrogenated silicon dangling bonds, respectively. Those values of binding energies indicate that the hydrogen adsorption on carbon vacancies is exothermic process when compared with the binding energy of an isolated H-2 molecule. For both nanotube chiralities, monohydrogenated silicon vacancies represent the energetically most favorable configuration.