EPITAXY OF COSIX (1-LESS-THAN-X-LESS-THAN-2) SILICIDES ON SI(111) STUDIED BY PHOTOEMISSION AND EXTENDED X-RAY-ABSORPTION FINE-STRUCTURE TECHNIQUES

摘要

Electronic and structural properties of epitaxial CoSix layers have been investigated by means of core-level and valence-band photoemission, x-ray photoelectron diffraction, and extended x-ray-absorption fine-structure (EXAFS) experiments. CoSix layers of various x compositions have been grown on silicon by low rate Co and Si co-deposition onto room-temperature Si(111) substrates, with film thicknesses ranging from 30 to 100 Angstrom. Photoemission shows substantial differences in valence and core-level spectra with respect to those of stable fluorite-type CoSi2 and epsilon-CoSi and indicate that well-defined metastable phases are formed. In particular, core-level photoemission experiments performed with a monochromatized x-ray source show large Si 2p binding-energy shifts (similar to 0.4 eV) in the room-temperature deposited CoSi, (1