Characterization of Large Fullerenes in Single-Wall Carbon Nanotube Production by Ion Mobility Mass Spectrometry

Samples from nanotubes produced by various methods are analyzed by laser desorption-ionization ion mobility time-of-flight mass spectrometry (LDI-IM-TOF-MS). The measurements find mostly positive fullerene ions in the mass range from 240 to 10000 Da. These principal contaminants are produced along with single-wall carbon nanotubes, which are too large to be detected in the mass spectra. Large fullerenes in the spectra are identified by their regular pattern of two carbon atom intervals and agreement of their mobility with theory. The distribution of large fullerenes varies among the samples depending on the type of production technique. Large numbers of fullerenes are seen in samples produced by the arc process and by the laser ablation process, whereas relatively few fullerenes are seen in samples produced by CVD processes. Measured drift times are in good agreement with those calculated based on a rigid sphere model. From close examination of the drift time distributions, there appears to be isomers of lower mobility. Agreement of measured with calculated drift times suggest that these isomers may be elongated structures. To assess possible limiting shapes of isomers seen in the mobility spectra, it appears that the shapes of the large fullerenes of a given mass vary from spherical to possibly short cylinders.