Characteristic vibrational modes and electronic structures of carbon nanotubes containing defects

We investigated the geometric structures, vibrational modes, and electronic structures of models of capped (5, 5) carbon nanotubes (CNTs) with four types of defects, namely, V1, V2, V3, and V4, using density functional theory. We found that the defects cause red shifts of the highest peak in infrared (IR) spectra and the highest peak, radial mode, and breathing mode in Raman spectra. There are two IR-active modes localized at V3 and V4 defects. In contrast, the influence of the defects on the electronic structures is considerably case-dependent, with the case of V2 being very special, involving spin polarization and showing a localized feature. The defects cause energy gap change as large as 0.1 eV. By analyzing the density of states of the capped (5, 5) CNT and its four defective structures, we found that at around -7 eV there is a characteristic peak belonging to the pure CNT that could be useful for defect detections. Our results are helpful for understanding the defect effects on the properties of general single-walled CNTs. © 2011 American Chemical Society.