Morphology of (KC₆₀)_n polymeric fibers

The fibers produced by co-evaporation of C₆₀ and potassium, and subsequent treatment in toluene, have been investigated by electron microscopy and optical spectroscopy. The electron diffraction pattern can be indexed in terms of the known orthorhombic (KC₆₀)_n structure. The frequencies of the vibrational modes indicate charge transfer between K and C₆₀, similar to bulk samples; no anisotropy of optical properties has been observed. The detailed analysis of the electron diffraction and micrographs reveal that, contrary to expectations, the direction of polymerization does not coincide with the direction of the long axis of the fibers. Furthermore, the structure is twinned, explaining the absence of optical anisotropy.