Shortest double-walled nanotube made

Two carbon nanohoops of different sizes can be made to form Russian doll-style complexes. These structures are the shortest double-walled carbon nanotubes ever made. Double-walled complexes made entirely out of carbon have fascinated chemists for more than three decades. This has led to some unusual structures: bucky onions, C₆₀ buckminsterfullerenes sitting inside larger spherical fullerenes, or fullerene peapods consisting of buckyballs inside carbon nanotubes.