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PRESTO, Japan Science and Technology Corporation, RCAST, The University of Tokyo,
4-6-1 Komaba, Meguro-ku, Tokyo 153-8904, Japan
| Localized graphitization and structural ordering in sputter deposited amorphous carbon films with a small amount of cobalt and rhodium were investigated using transmission electron microscopy, low-energy electron energy-loss spectroscopy and temperature dependent conductivity measurement. Electrons accelerated with 60 kV were irradiated to 100 nm-thick a-C films deposited on Si substrates through a 3-micron-thick Si window. As the result of the electron beam projection, two steps of graphitization occurred at relatively low process temperature in the 15 at.%Co:a-C films. The first one was strongly related to the presence of Co. Spherical graphitic shells formed at the interface of fcc-Co grains following shrinkage of the encapsulated crystals. The second one was independent of the Co catalyst. Large plate-like graphitic structures formed in the region where Co atoms became absent as the result of agglomeration. In the 1 at.%Rh:a-C films, short range structural ordering with formation of graphitic phases was observed and significant change in conductivity mechanism was detected in the temperature range from 15K to RT. |
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