IDENTIFICATION OF A GROWTH DEFECT IN SOLID C-60 BY ELECTRON-DIFFRACTION

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 angstrom 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.