Condensed phase growth of single-wall carbon nanotubes from laser annealed nanoparticulates

Single-wall carbon nanotubes (SWNT) were grown to micron lengths by laser-annealing nanoparticulate soot containing short (∼50 nm long) nanotube "seeds." The "seeded" nanoparticulate soot was produced by restricting the time spent by an ablation plume inside an 800°C oven following laser vaporization of a C-Ni-Co target. The soot collected from the laser vaporization apparatus was placed inside graphite crucibles under argon, and heated by a CO₂ laser. In situ pyrometry was used to estimate the sample temperature. Length distributions of SWNT bundles in the unannealed and annealed samples were measured by transmission electron microscopy and field emission scanning electron microscopy. Annealing treatments exceeding 1600°C produced no increase in nanotube length, while lower temperatures in the 1000-1300°C range were optimal for growth. These experiments indicate that SWNT grow by the conversion of condensed phase nanomaterial during annealing, a similar mechanism to that proposed for growth during normal laser-vaporization production.