Interacting Phonons between Layers in Raman Spectra\nof Carbon Nanotubes inside Boron Nitride Nanotubes

Abstract

We\npresent the resonant Raman spectra of a single-wall carbon nanotube\ninside a multiwall boron nitride nanotube (SWNT@BNNT). At <i>E</i>_L = 1.58 eV, SWNT@BNNT exhibited resonant Raman\nspectra at 807 (ω_BN) and 804 cm^–1 (ω_Gr). Their intensities almost disappeared at <i>E</i>_L = 2.33 eV. We assigned ω_BN to the out-of-plane BN phonon mode that coupled with ω_Gr. At <i>E</i>_L = 4.66 eV, the G⁺ and G^– bands of the SWNT@BNNT red-shifted\n3.8 cm^–1 compared with the SWNT, suggesting the\ninterwall interactions between the in-plane modes of SWNT and BNNT.\nMoreover, the <i>E</i>_2g mode of the BNNT in\nSWNT@BNNT appeared at 1370.3 ± 0.1 cm^–1, which\nis undistinguishable for <i>E</i>_L < 3 eV\nbecause of the overlap with the D band frequency. The assignment of\nthe present Raman spectra was confirmed through the first-principles\ncalculations.