An ISS and AES study of alkali induced sintering of an iron oxide monolayer adsorbed on Pt(111)

Abstract

An iron oxide monolayer adsorbed on Pt(111) is used as a model system for studying sintering of transition metal oxides. At 1 monolayer (ML) iron oxide coverage only iron and oxigen peaks are observed by ion scattering spectroscopy (ISS). This persists up to 1050 K at which time the iron oxide monolayer decomposes and platinum appears in the ISS spectrum. When 4 ML of sodium oxide, lithium oxide, or potassium oxide are deposited on the iron oxide, only alkali peaks are observed by ISS indicating that the alkali resides in the outermost layer. Heating the sodium oxide covered surface to 850 K induces sintering of the iron oxide monolayer, evidenced by the appearance of a platinum peak in the ISS experiment. Lithium oxide or potassium oxide sinters the iron oxide to a lesser extent than sodium oxide. One monolayer of sodium oxide is found not to induce sintering of the iron oxide adsorbed on Pt(111). A model is proposed in which sintering requires dissolution of iron oxide in an alkali phase.