AGGREGATION MECHANISM IN FULLERENE THIN-FILMS ON SEVERAL SUBSTRATES

Thin films of functional organic compound, fullerene (C60) are fabrica ted on the (001) surfaces of alkali halides (NaCl, KCl and KBr) and mi ca by an organic molecular beam deposition (OMBU) technique. Pure powd er samples are sublimated from the precisely temperature-controlled Kn udsen cell (K-cell) at a pressure of 10(-7) Torr and deposited onto th e substrates kept in the range of 25-350 degrees C for 1-10 min. They tended to grow epitaxially. Dependence of crystal sizes and distances between adjacent fine islands on the temperatures of K-cell and substr ates is evaluated by transmission electron microscope (TEM) and atomic force microscope (AFM). With increasing K-cell temperature and decrea sing substrate temperature, size and distance tend to decrease. The re lationship between these rates and the substrate temperature represent s the activation energies for crystal growth of 6.2-11 kJ/mol and surf ace diffusion of 3.7-11 kJ/mol. Particularly in the case of C60 films formed on the rough surface of alkali halides, although molecules tend ed to start the nucleation at the edge of steps, they formed the lines of nuclei arranging along to the edge on the wide terrace. The numeri cal evaluation of the distances between the neighboring nuclei represe nted the diffusion length of C60 molecules along the one-dimensional s tep edge and along the normal direction to the step edge. (C) 1998 Els evier Science S.A. All rights reserved.