Surface-enhanced Raman spectroscopy and correlated scanning electron microscopy of individual carbon nanotubes

Raman spectra of individual carbon nanotubes are measured by scanning a focused laser spot (0.5μm diameter) over a large area (100μm2) before and after depositing silver nanoparticles. Local regions exhibiting surface enhanced Raman spectroscopy (SERS) were located with respect 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. The data reveals SERS enhancement factors up to 134 000, a consistent upshift in the G band Raman frequency and nanoparticle heating in excess of 600°C.