The role of oxide substrate with respect to O2 adsorption induced changes in the Raman spectra of individual metallic carbon nanotubes is examined. A chiral metallic nanotube suspended over a trench exhibits a relatively simple two-peak G -band feature with no observable D -band intensity. On the other hand, a much more complex Raman G -band feature along with significant D -band intensities are observed on the part of the nanotube resting on the oxide substrate. O2 adsorption induced charge transfer and enhancement of physical disorder are considered to explain the differences observed. Spectral changes upon Ar annealing/ O2 exposure cycles on the on-substrate segment of a single nanotube are compared with those on the suspended part of the same nanotube. Complexity of the line shape and narrower linewidths are much more pronounced in the on-substrate part of the nanotube but continued annealing/ O2 adsorption cycle eventually leads to similar (but smaller) changes in the suspended part as well. Direct correlation between D -band intensity enhancements and the changes in the G -band (increasing complexity and the removal of phonon softening via the Kohn anomaly) suggest that O2 adsorption not only causes charge transfer and physical disorder but also leads to otherwise not observable double-resonance G -band phonon modes to have significant intensities.
|Original language||English (US)|
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|State||Published - Sep 29 2008|
ASJC Scopus subject areas
- Condensed Matter Physics
- Electronic, Optical and Magnetic Materials