LOCAL-STRUCTURE AND CHEMICAL-REACTION OF C-60 FILMS ON SI(111)7X7 STUDIED BY HREELS-STM

We have investigated the thermal stability and the chemical reactions of C-60 thin films on S(111)7 x 7 surfaces by the combined measurement s of the high-resolution electron-energy-loss spectroscopy (HREELS) an d ihc scanning tunneling microscopy (STM), HREELS-STM. After heating t he Si up to 400 degrees C, the molecules did not align perfectly but m ade local arrangments. The energy shifts of the inelastic electrons in dicate that thr electrons ill the Si dangling bond transfer lit thr C- 60 molecules. The value of the charge transfer is estimated to bt 1 +/ - 1 electron(s). After heating the Si up to 800 degrees C, the smooth C-60 monolayer film aggregates and forms islands. The nearest neighbou ring distance between the C-60 molecules is shortened from 10 Angstrom to 9.3 Angstrom. The intensity or the 92 and 101 meV peaks drasticall y increase. The results indicate the formation of a covalent bond betw een the C-60 molecules. After heating the Si up to 1100 degrees C, nn SiC film grows.