Atomic Layer Deposition of FeO on Pt(111) by Ferrocene Adsorption and Oxidation

We report the synthesis of a submonolayer film of FeO(111) on the Pt(111) surface using atomic layer deposition under well-defined ultrahigh vacuum (UHV) conditions. FeO islands were characterized by scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy, and high-resolution electron energy loss spectroscopy. FeO (111) on Pt(111) was prepared through adsorption and oxidation of ferrocene. Because ferrocene adsorption is crucial to the overall process, it was studied in detail at different exposures and temperatures. At low exposures and at 300 K, ferrocene was found to adsorb dissociatively mainly as Cp (cydopentadienyl ring). At high exposures, molecular adsorption dominated, and the dissociation fragments were replaced with ferrocene molecules. The adsorbed ferrocene desorbed from the Pt(111) surface at a temperature between 473 and 573 K. FeO(111) islands were grown by exposing the ferrocene adlayer to 1 X 10(-6) mbar O-2 at 623 K resulted in islands with the shape of truncated triangles and hexagons. The resulting surface was free of carbon, which presumably oxidized and desorbed as CO2. The FeO islands had a uniform height of 0.15 nm as measured by STM, and the FeO coverage could be controlled by the number of ferrocene adsorption/oxidation cycles. Due to rotational and lattice mismatches between FeO(111) and Pt (111), a pattern with approximately 2 nm periodicity was observed. In UHV, FeO began to decompose at a temperature between 673 and 873 K. Annealing in O-2 at 873 K also resulted in a net decrease of FeO amount through iron dissolution in the platinum bulk.