Resonance Raman

Single wall carbon nanotubes (SWNT’s) are cylindrical nanostructures, one carbon atom thick, about 20-50 carbon atoms around the circumference, and several microns long ( Fig. 1). They have remarkable electronic properties, insofar as they can be either me-tallic or semiconducting, depending on the nanotube diameter and orientation of the hexagons of the structure with respect to the nanotube axis. SWNT’s also exhibit re-markable Raman spectra, which can provide a wealth of information about the one dimen-sional (1-D) electronic density of states through a strong resonant coupling between the incident and scattered photons and the electronic transitions between the van Hove singularities in the 1-D density of states in the valence and conduction bands. Through the wide range of laser frequencies available in the Raman Laboratory of the Spectrosco-py Laboratory, it has been possible to carry out resonance Raman experiments at many laser excitation energies, thereby allowing study of many novel features. Figure 2 shows the Raman spectrum of a carbon nanotube sample over a wide fre-quency range. The strong feature at ~155 cm-1 is associated with the radial breathing mode, in which every carbon atom vibrates in phase in the radial direction. Since the radial breathing frequency is proportional t