Raman frequency shift in oxygen-functionalized carbon nanotubes

Based on density functional theory, the geometrical and electronic structures of oxygen-functionalized single-wall carbon nanotubes (O-SWCNs) are obtained, of which the vibrational properties are calculated in terms of lattice dynamics theory. Both bond expansion and contraction are found to coexist in O-SWCNs. A distinct Raman shift is observed in the radial breathing mode (RBM) and the G modes, depending not only on the tube diameter and chirality but also on oxygen coverage and adsorption configurations. With the oxygen coverage increasing, interestingly, a nonmonotonic upshift and downshift is observed in the G modes, which is attributed to the competition between the bond expansion and contraction. In addition, the resonance Raman effect at different oxygen coverage, which may be observable in O-SWCNs, is discussed.