Raman Imaging and Spectroscopy of Heterogeneous Individual Carbon Nanotubes

Isolated single-walled carbon nanotubes (CNTs) were grown by chemical vapor deposition methods on Fe/Mo/Al 2 O 3 catalysts, which were patterned by microcontact printing. The pattern allowed us to trace back and investigate the same isolated CNT by atomic-force (AFM) and confocal Raman microscopy with different excitation wavelengths. A change of the Raman intensity could be correlated with structural defects revealing that the molecular structure of the tubes is changing along the tube axis. By investigating the same tube segments with different excitation energies, we found that the D-line of isolated tubes shows a strong dispersive effect of 45−50 cm -1 /eV. In contrast, the spectral position of the G-line shows no frequency shift with changing excitation energy but is different for various tube segments.