Stability of carbon nanotubes: How small can they be?

Experimental evidence has been found for the existence of small single wall carbon nanotubes with diameters of 0.5 and 0.33 nn? by high resolution tra nsmission electron microscopy, and their mechanical stability was investiga ted using tight-binding molecular dynamics simulations. It is shown that, w hile the carbon tubes with diameters smaller than 0.4 nm are energetically less favorable than a graphene sheet, some of them are indeed mechanically stable at temperatures as high as 1100 degrees C. The 0.33 nm carbon tube o bserved is likely a (4, 0) tube and is indeed part of a compound nanotube s ystem that forms perhaps the smallest metal-semiconductor-metal tubular jun ction yet synthesized.