Sample Preparation and Purification

SWNTs are not soluble in any solvent and they cannot be vaporized by heating at least up to 1450°C in vacuum. In order to measure the optical absorption of SWNTs, the sample can be prepared in two possible forms: one is a solution sample and the other is a thin film. Chen et al. made SWNT solutions by cutting and grinding the nanotube sample [41], and they successfully measured the optical absorption spectra of undoped and of doped SWNTs using a solution sample. Kataura and co-workers have developed a so called "spray method" for thin film preparation [42], whereby the soot containing SWNTs is dispersed in ethanol and then sprayed onto a quartz plate using a conventional air-brush which is normally obtained in a paint store. In this way, the thickness and the homogeneity of the thin film are controlled by the number of spraying and drying processes, but the thickness of the film 300nm with 20% filling) is not precisely controlled.

In the case of the NiY catalyst, a web form of SWNTs which is predominantly in the bundle form is obtained by the electric arc method, and the resulting material can be easily purified by heating in air at 350° C for 30min and by rinsing out metal particles using hydrochloric acid. The purification is effective in removing the nanospheres (soot) and catalyst, and this is confirmed by TEM images and X-ray diffraction. The nanotube diameter distribution of the sample can be estimated by TEM observations [43,44], and the diameter distribution, thus obtained, is consistent with the distribution obtained using resonance Raman spectroscopy of the RBMs.

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