Low-energy electron-induced decarbonylation of Fe(CO)5 films adsorbed on Au(111) surfaces

Abstract

The decarbonylation of Fe(CO)5 adsorbed in monolayer and multilayer films on Au(111)/mica substrates has been induced by 0–20 eV electrons and studied by grazing incidence IR spectroscopy. Our results show that the cross sections for the initial stages of this process in as-deposited films range from 60–300 Å2 and show considerable variations with the incident electron energy. The high sensitivity to low-energy electrons is believed to be the result of secondary reactions of anion fragments in the film with the neighbouring Fe(CO)5 moieties, leading to increasingly massive heteronuclear Fen(CO)m species and progressive CO elimination. Continued exposure to the electron beam leads to the slower degradation of these newly created species into an Fe-rich deposit containing traces of CO. These traces are removed by subsequent heating to ~300 K. Fe(CO)5 films that have been subjected to temperatures exceeding 125 K have no measurable sensitivity to the electron beam in the 0–20 eV regime; this is believed to be due to the structural transformation of the as-deposited thin film structure into 3D aggregates. This structural motif presents a very limited quantity of the adsorbed Fe(CO)5 to the incident beam, and may also form a protective layer of the robust Fen(CO)m species during the initial stages of exposure to the electrons.