On the Origin of Preferential Growth of Semiconducting Single-Walled Carbon Nanotubes

A correlation is observed between the diameters (d) of single-walled carbon nanotubes and the percentages of metallic and semiconducting tubes synthesized at 600 °C by plasma-assisted chemical vapor deposition. Small tubes (d ≈ 1.1 nm) show semiconductor percentages that are much higher than expected for a random chirality distribution. Density functional theory calculations reveal differences in the heat of formation energies for similar-diameter metallic, quasi-metallic, and semiconducting nanotubes. Semiconducting tubes exhibit the lowest energies and the stabilization scales with ∼1/d 2. This could be a thermodynamic factor in the preferential growth of small semiconducting nanotubes.