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

Abstract

We present the resonant Raman spectra of a single-wall carbon nanotube inside a multiwall boron nitride nanotube (SWNT@BNNT). At E_L = 1.58 eV, SWNT@BNNT exhibited resonant Raman spectra at 807 (ω_BN) and 804 cm^-1 (ω_Gr). Their intensities almost disappeared at E_L = 2.33 eV. We assigned ω_BN to the out-of-plane BN phonon mode that coupled with ω_Gr. At E_L = 4.66 eV, the G⁺ and G^- bands of the SWNT@BNNT red-shifted 3.8 cm^-1 compared with the SWNT, suggesting the interwall interactions between the in-plane modes of SWNT and BNNT. Moreover, the E_2g mode of the BNNT in SWNT@BNNT appeared at 1370.3 ± 0.1 cm^-1, which is undistinguishable for E_L < 3 eV because of the overlap with the D band frequency. The assignment of the present Raman spectra was confirmed through the first-principles calculations.