SURFACE INTERMEDIATES FORMED DURING PHOTOLYTIC DECARBONYLATION OF IRON PENTACARBONYL ADSORBED ON SILVER SURFACES

To understand the mechanism of photo-CVD utilized for preparation of a thin Fe film, the photolytic decarbonylation of Fe(CO), adsorbed on s ilver surfaces at T < 120 K was studied using IR reflection absorption spectroscopy (IRAS), X-ray photoelectron spectroscopy (XPS), and ther mal desorption spectroscopy (TDS). Irradiation of adsorbed Fe(CO)5 wit h SOR light (lambda > 150 nm) leads to the evolution of CO without the photodesorption of molecular Fe(CO)5. The yield of CO photo-evolution increases with increasing coverage of Fe(CO)5 up to 15 monolayers, in dicating significant energy relaxation at the metal surface. XPS analy sis indicates that surface intermediates formed by photolytic decarbon ylation of Fe(CO)5 adsorbed at coverages less than one monolayer have an average composition of CO/Fe = 4. In overlayers of adsorbed Fe(CO)5 , photodecarbonylation proceeds further. The intermediates are stable under prolonged irradiation, but undergo thermal decarbonylation at T > 300 K, depositing Fe on the surface. The results of IRAS suggest tha t the intermediate species is Fe(CO)4 or Fe2(CO)8 at coverages lower t han a monolayer, proceeding to higher oligomers as its population incr eases. The oligomers are dissociated to monomers at T congruent-to 280 K. The Fe deposits are found to be carbon free and inactive for CO ad sorption.