Phonon Coupling between Layers in Hetero-Nanotubes

Desman Perdamaian Gulo^1*, Nguyen Tuan Hung^2,3, Wei-Liang Cheng⁴, Shuhui Wang⁵, Ming Liu⁵, Esko I. Kauppinen⁶, Shigeo Maruyama⁵, Yu-Ming Chang⁴, Riichiro Saito^1,2, Hsiang-Lin, Liu¹

¹Physics, National Taiwan Normal University, Taipei, Taiwan
²Physics, Tohoku University, Sendai, Japan
³Frontier Research Institute for Interdisciplinary Sciences, Tohoku University, Sendai, Japan
⁴Center for Condensed Matter Sciences, National Taiwan University, Taipei, Taiwan
⁵Department of Mechanical Engineering, School of Engineering, The University of Tokyo, Tokyo, Japan
⁶Department of Applied Physics, Aalto University School of Science, Aalto, Finland

* Presenter:Desman Perdamaian Gulo, email:desmanpgulo@ntnu.edu.tw

We present the resonant Raman spectra of a hetero-nanotube of single-wall carbon nanotube inside multi-walls boron nitride nanotube (SWNT@BNNT) with a laser excitation energy EL ranging from 1.58 to 4.66 eV. For EL = 1.58 eV, the SWNT@BNNT exhibited resonant at 807 and 804 cm-1, which we denote as ωBN and ωGr, respectively. With increasing EL, the ωBN redshifted to 801 cm-1 whereas the ωGr blueshifted to 809 cm-1. Because the ωGr is also appeared in the SWNT, we assigned ωGr as the double-resonance Raman spectra of the out-of-plane mode. Additionally, the intensities of ωBN+ωGr in the SWNT@BNNT almost disappeared at EL = 2.33 eV, we designated ωBN to out-of-plane BN phonon mode that coupled with ωGr. For EL = 4.66 eV, we observed a redshift of 3.8 cm-1 in the G+ and G- bands of the SWNT@BNNT compared with the SWNT, suggesting the interwall interactions of the in-plane modes between the SWNT and BNNT. Moreover, the E2g mode of the BNNT in SWNT@BNNT appeared at 1370.3 ± 0.1 cm-1, which is undistinguishable for EL < 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.

Keywords: Resonant Raman spectra, Phonon Interactions, First-Principles Calculations