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

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 (ωBN) and 804 cm–1 (ωGr). Their intensities almost disappeared at E L = 2.33 eV. We assigned ωBN to the out-of-plane BN phonon mode that coupled with ωGr. 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.