Photon- versus electron-induced decomposition of Fe(CO)5 adsorbed on Ag(111): Iron film deposition

Abstract

The photon- and electron-induced decomposition of monolayer and multilayer Fe(CO)5 on a Ag(111) surface were examined with temperature-programmed desorption, Auger electron spectroscopy, and low-energy electron diffraction. In the absence of photon or electron exposure, Fe(CO)5 thermally desorbs from Ag(111) in monolayer (181 K) and multilayer (168 K) states with minimal decomposition. The small temperature difference between these states (13 K) suggests that the monolayer is physisorbed on Ag(111). Both ultraviolet (UV) photon (3.4 and 4.8 eV) and low-energy electron (3–132 eV) irradiation convert adsorbed Fe(CO)5 into a new species, presumably a Fex(CO)y cluster. The new species thermally decomposes at 330 K with the desorption of CO and the deposition of carbon- and oxygen-free Fe. Also, the new species is much less susceptible to photon- or electron-induced decomposition than is adsorbed Fe(CO)5. In contrast, substantial carbon and oxygen deposition occurs when high-energy electrons (2 keV) bombard adsorbed Fe(CO)5. From a practical viewpoint, low-energy electron-induced decomposition of Fe(CO)5 exhibits higher cross sections than UV photolysis, and is therefore a more effective means of depositing pure iron films on silver.