Growth of Ultrathin Iron Oxide Films on Ag(100)

Abstract

Ultrathin iron oxide films are useful model materials for fundamental studies of surface processes and exhibit intriguing properties as catalysts, as demonstrated recently in a number of studies utilizing platinum as a substrate. We report a study of the initial stages of iron oxide film growth on an Ag(100) surface using scanning tunneling microscopy, low energy electron diffraction, X-ray photoelectron spectroscopy, and near-edge X-ray absorption fine structure spectroscopy, with the goal of elucidating the effects of the substrate material on FeO x film growth and physical properties. We demonstrate that a well-ordered, monolayer-thick FeO(111) film can be prepared which is similar to the well-studied structure formed on Pt (111), though with a significantly expanded lattice constant indicative of smaller Fe−O buckling and weaker interactions with the substrate. Increased oxygen pressure during deposition leads to formation of a multilayer phase taking the form of well-ordered islands. Although superficially similar to FeO(111), spectroscopic measurements show a substantial proportion of Fe 3+ in the phase. FeO(100) grains are observed upon deposition at elevated substrate temperatures, which is proposed to result from formation and oxidation of iron clusters embedded in the surface.

Tuning the Reactivity of Ultrathin Oxides: NO Adsorption on Monolayer FeO(111)

“…The average rumpling, calculated as the difference in mean height of the iron‐ and oxygen‐layers, is 0.26 Å, which is roughly one third of the value found for FeO films (ca. 0.7 Å) grown on Pt(111) and Pt(100) and is consistent with the expanded in‐plane lattice parameter observed for the silver‐supported film …”

“…A scanning tunneling microscope (STM) image of the FeO(111) film on Ag(100), grown by reactive deposition of iron in a background of O 2 , is shown in Figure a . The film exhibits a quasi‐hexagonal structure with a moiré modulation arising from coincidence with the substrate.…”

Fe Oxides on Ag Surfaces: Structure and Reactivity

“…One layer thick films were grown by deposition of iron in the presence of oxygen (reactive physical vapor deposition (RPVD)) using an electron beam evaporator at 100°C substrate temperature and 2 9 10 -7 mbar background O 2 pressure with subsequent annealing to 400°C in vacuum according to the procedure developed earlier [33]. The evaporators were calibrated with a reference to a Pt(111) crystal, where the density of one monolayer is known (one closed monolayer of FeO(111) on Pt(111) has the density of 1.2 9 10 15 cm -2 of Fe atoms).…”

Oxidation of Ultrathin FeO(111) Grown on Pt(111): Spectroscopic Evidence for Hydroxylation

“…Previous studies have shown that FeO bilayer films can be grown also on other Pt facets [48], and many other single-crystalline metal substrates such as Pd(111) [35], Ag(100) [41], Ag(111) [49], Mo(100) [50], Ru(0001) [51] and Au(111) [52,53]. In other studies it has been found that FeO(111) films encapsulate Fe 3 O 4 supported Pt particles [54].…”

“…Hence, the overall peak has shifted possibly due to multiple changes on the surface. We did not attempt to explicitly curve fit the Fe 3p peak since both the Fe 2p and 3p curve fitting are non trivial [39][40][41] and beyond the scope of the present study. Instead we used three Doniach-Šunjić (DS) functions to fit the Fe 3p peak in order to determine the integrated area.…”