Identification of a growth defect in solid C60 by electron diffraction

Abstract

The origin of an anomalous sawtooth-shaped feature in x-ray powder diffraction of solid C₆₀ is explained via electron diffraction analysis. Films sublimed on holey carbon crystallize with close-packed (111) planes parallel to the surface. Rods of diffuse scattering are found along the 〈111〉 axis normal to the surface but not along other 〈111〉 axes. Powder averaging of these rods, coupled with the x-ray form factor of spherical shells with 3.5 Å radius, accounts for the sawtooth feature. We attribute this phenomenon to planar defects parallel to close-packed layers, which form during the growth of solid C₆₀ by sublimation. A possibly related consequence of the growth mode is the observation of strong macroscopic (111) preferred orientation in films sublimed on a variety of substrates.