Smallest Carbon Nanotube Is 3 Å in Diameter

Previous energetic considerations have led to the belief that carbon nanotubes (CNTs) of 4 Å in diameter are the smallest stable CNTs. Using high-resolution transmission electron microscopy, we find that a stable 3 Å CNT can be grown inside a multiwalled carbon nanotube. Density functional calculations indicate that the 3 Å CNT is the armchair CNT(2,2) with a radial breathing mode at 787 cm^-1. Each end can be capped by half of a C₁₂ cage (hexagonal prism) containing tetragons.