Photoinduced dislocation lines on the (111) face of C60 single crystals

We report an atomic force microscopic (AFM) study of photoinduced dislocation lines (DLs) on the (111) face of C-60 Single crystals via excitation of the Frenkel exciton transition of solid C-60. Under illumination, DLs appeared along the [11(2) over bar] direction on the (111) face of the C-60 single crystals. These DLs consist of pairs of substructures that are separated by a hollow region with a width of 30.0 +/- 0.5 nm and a depth of 0.08 +/- 0.02 nm, while the height difference between the topmost regions of the substructures and the surrounding face-centered-cubic (fcc) regions is 0.30 +/- 0.03 nm. The two substructures correspond to ridgelike domain walls enclosing narrow strips of metastable hexagonal-close-packed (hcp) domains on the surrounding fee surface. It was also observed that the pair of substructures constituting the DLs is terminated by a U-shaped growing tip. The photodriven growth of these DLs displayed unique dynamic surface reconstruction behavior. They also exhibited different types of collision processes depending on the growth rate. The driving force for the dynamic process is considered to be the recombination of excitons at surface defects or at the growing tip of each DL. Furthermore, a threshold light intensity value of 0.8 mW/mm(2) was found for the generation of DLs, which indicates that multiexciton relaxation is a prerequisite for the photoinduced dislocation.