Vibrational and Electronic Properties of Single-Walled and Double-Walled Boron Nitride Nanotubes

Abstract

We calculated IR, nonresonance Raman spectra and vertical electronic transitions of the zigzag single-walled and double-walled boron nitride nanotubes ((0,n)-SWBNNTs and (0,n) at (0,2n)-DWBNNTs). In the low frequency range below 600 cm-1, the calculated Raman spectra of the nanotubes showed that RBMs (radial breathing modes) are strongly diameter-dependent, and in addition the RBMs of the DWBNNTs are blue-shifted reference to their corresponding one in the Raman spectra of the isolated (0,n)-SWBNNTs. In the high frequency range above ∼1200 cm-1, two proximate Raman features with symmetries of the A<inf>1g</inf> (∼1355 ± 10 cm -1) and E<inf>2g</inf> (∼1330 ± 25 cm-1) first increase in frequency then approach a constant value of ∼1365 and ∼1356 cm-1, respectively, with increasing tubes' diameter, which is in excellent agreement with experimental observations. The calculated IR spectra exhibited IR features in the range of 1200-1550 cm-1 and in mid-frequency region are consistent with experiments. The calculated dipole allowed singlet-singlet and triplet-triplet electronic transitions suggesting a charge transfer process between the outer- and inner-shells of the DWBNNTs as well as, upon irradiation, the possibility of a system that can undergo internal conversion (IC) and intersystem crossing (ISC) processes, besides the photochemical and other photophysical processes. © 2013 Elsevier B.V.