DIAMETER DOUBLING OF SINGLE-WALL NANOTUBES

High-yield single wall nanotube (SWNT) material consisting primarily o f zero-helicity armchair tubes was annealed at 1400 or 1500 degrees C under medium-high vacuum, flowing argon and flowing hydrogen atmospher es, As many as 60% of the nanotubes so treated coalesced with neighbor s, the proportion depending on the atmosphere, resulting in nanotubes with twice (2.7 nm) and occasionally three times (4.1 nm) the diameter of the (10, 10) tube that is the dominant armchair tube in these samp les. Since only nanotubes with equal helical pitch angle and chirality can coalesce seamlessly, the high conversion ratio adds support to ot her recent evidence that no type of SWNT is formed in these samples in greater numbers than the (10,10) tube.