Raman spectroscopy of carbon nanotubes under axial strain and surface-enhanced Raman spectroscopy of individual carbon nanotubes

UnrestrictedIn this thesis, I present resonant Raman spectroscopy of individual carbon nanotube bundles under axial strains up to 17%. The main effect of this strain is to cause nanotube debundling. The G band Raman spectra of metallic and semiconducting nanotubes are found to respond differently to strain and debundling, giving insight into the nature of the broad metallic G- band lineshape. For metallic nanotubes, the G- band upshifts and becomes narrower with strain, making it appear more semiconductor-like. Surprisingly, this metal to semiconductor transition is irreversible with strain, indicating that nanotube-nanotube coupling plays a significant role in the observed G- band of metallic nanotubes. The vibrational and electronic properties of these nanotubes under strain are modeled using tight-binding calculations.; This thesis also presents a systematic study of surface enhanced Raman spectroscopy (SERS) of carbon nanotubes. Raman spectra of individual carbon nanotubes are measured by scanning a focused laser spot (0.5 um diameter) over a large area (100 um2) before and after depositing silver nanoparticles. Local regions exhibiting SERS enhancement were located relative to a lithographically patterned grid, allowing subsequent scanning electron microscopy to be performed. The uniquely large aspect ratio of carbon nanotubes enables imaging of the nanoparticle geometry together with the SERS active molecule. By measuring the same individual carbon nanotube before and after metal nanoparticle deposition, the SERS enhancement factor is determined unambiguously. SERS enhancement factors up to 134,000, a consistent upshift in the G band Raman frequency and nanoparticle heating in excess of 600°C are revealed.; Nanotubes are also strained through top-down microprocessing. By straining nanotubes to the bottom of a trench made deeper through etching, we induce changes in nanotubes' resonance with an incident laser. This causes increases in intensity for all the bands, most notably the radial breathing mode. From the radial breathing mode intensity, we calculate the changes to the density of states. Furthermore, we observe two peaks in the G' band spectrum, which also reflects changes in the density of states. All nanotubes measured experienced irreversible changes in their D bands, indicating the build up of residue on the nanotube surface from etching