Optical spectroscopic studies of thermally coalesced single-walled carbon nanotubes

Changes in the optical properties of thermally coalesced single-walled carbon nanotubes (SWCNTs) caused by heat treatment between 1300 and 2800 degrees C in argon, have been monitored using optical absorption and photoluminescence spectroscopy. For SWNTs heat treated at 1900 degrees C, we found a complete disapperance of small-diameter tubes (<1.0 nm) as well as the appearance of enlarged, defective tubes. The decreased sp2/sp3 ratio for tubes heat treated below 2100 degrees C suggests that adjacent small-diameter SWNTs transform into energetically stable larger-diameter SWNTs by the presence of structural non sp2 defects.