A SOFT-X-RAY PHOTOEMISSION-STUDY OF IRON DEPOSITION ON SI(111)2X1 BY SYNCHROTRON RADIATION-EXCITED PHOTODECOMPOSITION OF ADSORBED FE(CO)5

We report a soft-X-ray photoemission investigation of the adsorption behaviour of Fe(CO)5 on Si(111)2 x 1 and of its photodecomposition to metallic Fe on Si. The system has been studied as a function of temperature in the 20-300 K range and at exposures in the 100-1000 langmuir range. Valence band and Si 2p, C 1s, O 1s, Fe 3p core level photoemission spectra are discussed, together with XAS (X-ray absorption spectroscopy) measurements at the Fe L2,3 edges, recorded in total electron yield (TEY) mode. In the present experimental conditions, we show that the initial adsorption of Fe(CO)5 is partially dissociative in the investigated temperature range. The reacted surfaces have been exposed to unmonochromatized synchrotron light ("white light") for different extents of time. At all investigated temperatures, the resulting product is metallic Fe on silicon, as clearly recognized from the appearance of a Fermi edge in the valence band, and by the XAS Fe L2,3 spectra. The process is shown to be locally excited by synchrotron light. The Fe overlayers obtained at low T's are stable, after room temperature (RT) annealing.