Surface intermediates formed during photolytic decarbonylation of iron pentacarbonyl adsorbed on silver surfaces

Abstract

To understand the mechanism of photo-CVD utilized for preparation of a thin Fe film, the photolytic decarbonylation of Fe(CO) 5 adsorbed on silver surfaces at T < 120 K was studied using IR reflection absorption spectroscopy (IRAS), X-ray photoelectron spectroscopy (XPS), and thermal desorption spectroscopy (TDS). Irradiation of adsorbed Fe(CO) 5 with SOR light (λ > 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, indicating significant energy relaxation at the metal surface. XPS analysis indicates that surface intermediates formed by photolytic decarbonylation 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 that the intermediate species is Fe(CO) 4 or Fe 2(CO) 8 at coverages lower than a monolayer, proceeding to higher oligomers as its population increases. The oligomers are dissociated to monomers at T ≃ 280 K. The Fe deposits are found tobe carbon free and inactive for Co adsorption.