Absorption spectra of single-walled carbon nanotubes (SWNT) dispersed in dimethylformamide (DMF) have been recorded in the visible to near-infrared range. Besides broad absorption bands, the spectra show a sharp peak at 5187 cm-1, which has been attributed in the literature to the absorption of semiconducting nanotubes with a band gap of 0.64 eV [Ausman et al. J. Phys. Chem. B 2000, 104, 8911]. On the basis of absorbance measurements for samples that show the sharp absorbance peak but do not contain SWNTs, we conclude that the origin of the peak at 5187 cm-1 is not due to semiconducting nanotubes but due to water present in the SWNT/DMF suspension. A comparative study of D2O in DMF reproduces a similar peak that is isotope-shifted into the near-infrared.
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Krupke et al. (2003) studied this question.
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