Local structure and chemical reaction of C₆₀ films on Si(111)7 x 7 studied by HREELS-STM

We have investigated the thermal stability and the chemical reactions of C₆₀ thin films on Si(111) 7 x 7 surfaces by the combined measurements of the high-resolution electron-energy-loss spectroscopy (HREELS) and the scanning tunneling microscopy (STM), HREELS-STM. After heating the Si up to 400°C, the molecules did not align perfectly but made local arrangements. The energy shifts of the inelastic electrons indicate that the electrons in the Si dangling bond transfer to the C₆₀ molecules. The value of the charge transfer is estimated to be 1 ± 1 electron(s). After heating the Si up to 800°C, the smooth C₆₀ monolayer film aggregates and forms islands. The nearest neighbouring distance between the C₆₀ molecules is shortened from 10 Å to 9.3 Å. The intensity of the 92 and 101 meV peaks drastically increase. These results indicate the formation of a covalent bond between the C₆₀ molecules. After heating the Si up to 1100°C, an SiC film grows.