Date of Award

5-2007

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Physics

Advisor

Rao, Apparao M

Abstract

Anharmonic effects in two different quasi-1D systems were probed via micro-Raman spectroscopy. In the first system, we observed upshifts of peaks in the Raman spectra for b-Ga2O3 nanowires grown along the [110] growth direction compared those present in bulk b-Ga2O3. Contrary to our Raman studies on -Ga2O3 nanowires, downshifts in the Raman spectrum for b-Ga2O3 nanowires grown along [401] direction has also been reported by other research groups. We attribute these Raman shifts to the growth direction-induced lattice strains (compressive and tensile) present in the nanowires, and present a model based on the quasi-harmonic density functional theory to support our hypothesis.
In the second study, the anharmonic phonon lifetime in suspended single-walled carbon nanotubes was measured using high-resolution micro-Raman spectroscopy. Previous studies on suspended nanotubes performed with scanning tunneling microscopy (STM) reported phonon lifetimes of the order of nanoseconds for the radial breathing mode (RBM). However, the longest phonon lifetimes measured from Raman spectroscopy is of the order of picoseconds. Our study also showed the RBM lifetime to be in the picosecond regime, and we sought to explain this discrepancy with the STM study by invoking an anharmonic model for phonon decay in carbon nanotubes.

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