Raman spectroscopy of double- and triple-walled carbon nanotubes: fundamental, combination, and overtone modes

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University of Alabama Libraries

A single-walled carbon nanotube (SWNT) is a graphene sheet rolled up into a tube. Double-walled (DWNT) and triple-walled carbon nanotubes (TWNT) are two and three coaxial SWNTs respectively. Isolated species of DWNTs and TWNTs were only recently probed and it can be considered as a new branch in carbon nanotube science. Phonons, and the combination of phonons and overtones are fundamental to understanding optical processes, transport and thermoelectricity in carbon nanotubes. To study these phonons, resonance Raman spectroscopy is employed on DWNT and TWNT bundles, as well as isolated TWNTs. The phonon modes of interest to this dissertation are the radial breathing mode (RBM), the G-band, and the M-band. From the RBM, it is learnt that for inner tubes with a tube diameter less than 1.2 nm, the curvature effects are dominant. Evidence for intertube interactions was found, although for outer tubes the environmental effects dominate. There was also evidence for commensurate and incommensurate tubes. Studying the G-band allowed for possible chiral indices to be identified for the middle and outer tubes of isolated TWNTs. In addition, the frequency shifts of TWNT G-band frequencies relative to SWNT G-band frequencies were studied and compared to TWNT G-band frequency shifts. As for the M-bands, phonon mode assignments for peaks between 1680 cm-1 to 1850 cm-1 were attempted.

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Condensed matter physics, Materials science