  The length of single-walled carbon nanotubes (SWCNTs) is an important metric
for the integration of SWCNTs into devices and for the performance of
SWCNT-based electronic or optoelectronic applications. In this work we propose
a rather simple method based on electric-field induced differential absorption
spectroscopy (EFIDAS) to measure the chiral-index-resolved average length of
SWCNTs in dispersions. The method takes advantage of the electric-field induced
length-dependent dipole moment of nanotubes and has been verified and
calibrated by atomic force microscopy. This method not only provides a low
cost, in-situ approach for length measurements of SWCNTs in dispersion, but due
to the sensitivity of the method to the SWCNT chiral index, the chiral index
dependent average length of fractions obtained by chromatographic sorting can
also be derived. Also, the determination of the chiral-index resolved length
distribution seems to be possible using this method.
