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