Abundance of encapsulated C60 in single-wall carbon nanotubes

Spherical objects (presumably C60 molecules) have been observed inside ∼14 Å diameter single-wall carbon nanotubes. We applied acid etching to access the interior of the tubes, and leaching in toluene to dissolve liberated C60. Quantitative UV–Vis of the 335 nm C60 transition establishes beyond doubt that these are indeed C60, and that their relative abundance in a macroscopic sample can be as high as 5.4% (expressed as the filled fraction of total tube length). Variations in abundance with growth and processing conditions provide clues as to how they form.