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A transmission electron microscopy study of epitaxial C60 and C70 films grown on a GeS (001) surface is presented. The relationship between the orientation of the substrate and the films and structural defects in the films, such as grain boundaries, unknown in bulk C60 and C70 crystals, are studied. Small misalignments of the overlayers with respect to the orientation of the substrate, so-called epitaxial rotations, exist mainly in C70 films, but also sporadically in the C60 overlayers. A simple symmetry model, previously used to predict the rotation of hexagonal overlayers on hexagonal substrates, is numerically tested and applied to the present situation. Some qualitative conclusions concerning the substrate-film interaction are deduced. ©1996 American Institute of Physics.

The energy-dependant cross sections of the impact-excited intramolecular vibrations in an epitaxial C60(111) film have been measured by High Resolution Electron Energy Loss Spectroscopy (HREELS). A Negative Ion Resonance (NIR) behaviour is evidenced by a dramatic cross-section enhancement at a primary energy of ∼2.9 eV together with some fine structures on the high energy side. Through comparison with experimental results on the unoccupied states and on the electronic excitations of solid C60, these NIR structures can be correlated to a temporary trapping of the probing electron in the LUMO+3-derived state in the framework of an 'electronic excitation associated' NIR process. © 1995.