Spectroscopic and Scanning Probe Studies of a Nondestructive Purification Method for SWNT Suspensions

A mild method for the bulk enrichment of high-aspect-ratio single-walled carbon nanotubes (SWNTs), while avoiding the damaging effects of acid purification methods, has been developed in this group. Various analytical techniques (atomic force microscopy, Raman microscopy, near IR, and UV−vis spectroscopy) have been used in order to attain a better understanding of the correlation between low-G centrifugation cycles and the quality of the SWNT suspension. Atomic force microscopy data of low-density SWNT networks formed from these suspensions indicate that the size and occurrence of globular impurities is lessened, while small bundles of high-aspect-ratio SWNTs remain. Raman spectroscopy is used to verify that this method produces suspensions of purified SWNTs without significantly damaging them. Near-infrared and UV−vis spectroscopy of these suspensions show prominent semiconducting and metallic interband transitions in the SWNTs and removal of impurities.