Oxygen Adsorbed On The Surface Properties Of Integrity And Defects In Silicon Carbide Nanotubes

Silicon carbide nanotubes (SiCNTs) is a bioinert wide band-gap semiconductors and the energy band gap weakly dependent on their chiarlity compare with carborn nanotubes (CNTs), indicating that SiCNTs have stable properties and more suitable for application in functional apparatus than CNTs. SiCNTs possess thermal stability, chemical inertness, high thermal conductivity, high reactivity of the external (internal) surface and others, which make them candidates for nanodevices that operates in harsh environments. In addation, preciously studies reported that the function and applications of SiCNTs can be improved after appropriate doped, substituted and adsorbed, as well as it is well known that the surface of silicon carbide is oxidized in ambient oxygen. Therefore, in the present paper, the structural and electronic properties of a single oxygen atom or oxygen molecular adsorbed on the exterior surface of pristine as well as Csi and Sic antisite defected or Nc and Bc defected (10,0) and (6,6) SiCNTs have been investigated systematically using the first-principle calculation based on density-functional theory. The following results are obtained:(1) The structural and electronic properties of a single oxygen atom adsorbed on the exterior surface of pristine and antisite defected (6,6) and (10,0) SiCNTs have been investigated systematically. We find that the oxygen atom can adsorb exothermically or spontaneously on the exterior surface of pristine (6,6) and (10,0) SiCNTs and the most favorable adsorbing sites are the bridge site B1 above the Si-C bond perpendicular to the tube axis and the bridge site B2 above the zigzag Si-C bond, respectively. Similar stable configurations are also obtained for CSi or Sic defected (6,6) and (10,0) SiCNTs but the C-C or Si-Si bond below oxygen adatom is broken. Except for B1 site of Csi antisite defected (6,6) SiCNT, shortly CSi(6,6)B1, the Sic(6,6)B1, Cs,(10,0)B2 and Sic(10,0)B2 assist the oxygen adsorption in point of view the binding energy.(2) The structural and electronic properties of oxygen molecular adsorbed on the exterior surface of pristine and NC or BC defected (10,0) or (6,6) SiCNT have been investigated systematically. 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 NC or BC defected (10,0) or (6,6) SiCNT show that the oxygen molecule will dissociate to the pair of oxygen interstitials at the sidewall of NC or BC defected SiCNTs.