TEM STUDY OF C-70 POLYCRYSTALLINE FILMS

Using conventional and high resolution TEM, we have studied the microstructure of C-70 polycrystalline films, prepared by sublimation of C-70 powder onto glass, carbon holey film, and sapphire substrates held at 200 degrees C. An fee structure with lattice parameter 1.50 nm is observed for the films on glass and amorphous carbon. A different structure and stronger adherence to the substrate was observed for the thin film grown on sapphire, suggesting a stronger molecule-substrate interaction in this case. Thicker films on sapphire, however, did have fee structure. In all cases, the film grows in large grains about 100 nm in size, indicating high effective surface mobility of the C-70 molecules. Further analysis of the films on carbon holey substrates indicates a preferred [011]] film growth orientation, the existence of twins, and a high density of stacking faults. Extended exposure of the films to oxygen did not result in visible structural changes, but strong illumination for several hours in atmosphere led to partial annealing of planar defects and higher sensitivity to the electron beam, with film amorphization taking place at much shorter times under the electron beam.