Smallest Nanotube: Breaking the Symmetry of sp3 Bonds in Tubular Geometries

We describe how sp² carbon, threefold coordinated by other carbons, can be replaced by sp³ carbon, also threefold carbon coordinated, to produce extremely small-diameter ( ~0.4 nm) carbon nanowires with only minimal bond-angle distortion. Under a naming convention analogous to that for ordinary carbon nanotubes, the smallest sp³ tubes have wrapping indices (3,0) and (2,2). These systems have large band gaps and a stiffness larger even than that of traditional sp²-bonded carbon nanotubes. They therefore form the stiffest one-dimensional systems known.