Fe Oxides on Ag Surfaces: Structure and Reactivity

Abstract

One layer thick iron oxide films are attractive from both applied and fundamental science perspectives. The structural and chemical properties of these systems can be tuned by changing the substrate, making them promising materials for heterogeneous catalysis. In the present work, we investigate the structure of FeO(111) monolayer films grown on Ag(100) and Ag(111) substrates by means of microscopy and diffraction techniques and compare it with the structure of FeO(111) grown on other substrates reported in literature. We also study the NO adsorption properties of FeO(111)/Ag(100) and FeO(111)/Ag(111) systems utilizing different spectroscopic techniques. We discuss similarities and differences in the data obtained from adsorption experiments and compare it with previous results for FeO(111)/Pt(111). Keywords FeO Á Ag Á Surface X-ray diffraction Á Reactivity Á Single crystal surfaces Á Surface structure This article originally listed an author (J. F. Weaver) incorrectly. The article has been updated.

Stability, magnetic order, and electronic properties of ultrathin Fe3O4 nanosheets

“…In this approach, the effective Hubbard parameter U eff is specified, which is the difference between the on-site Coulombic (U ) and the effective on-site exchange parameter (J). In the literature, numerous different U eff values have been employed for modeling iron oxides, typically ranging from 3.6 to above 5.0 eV [8,33,34,[36][37][38][39][40][41]. We evaluated the bandgap of bulk FeO for values of U eff in the range 3.6-4.5 eV and found that this property increases monotonically from 1.9 to 2.6 eV, with an approximate agreement with the experimental value of ∼2.4 eV for U eff = 4.2 eV [42].…”

2D Oxide Nanomaterials to Address the Energy Transition and Catalysis

“…This behavior originates from charge transfer through the film to adsorbed oxygen, making the system a promising low temperature CO oxidation catalyst. Another example where the atomistic scale structure of the UTF is coupled to its chemical properties comes from Merte and co‐workers, who used DFT+U calculations to explain the experimentally observed difference in adsorption affinity toward NO between FeO(111)/Ag(100) and FeO(111)/Pt(111) surfaces . The calculations showed that the weaker FeO adsorption over Ag(100) drives a decrease in layer buckling, which in turn increases the accessibility of the iron atoms toward NO adsorption.…”

On the Structure of Ultrathin FeO Films on Ag(111)

“…Among the substrates used, Ag(111) has always been considered a promising candidate for iron oxides growth, as it has the same surface symmetry as FeO(111), only ~5% lattice mismatch (much smaller than the commonly used Pt(111) [ 3 , 4 ]), is considered a weakly-interacting substrate and is relatively resistant to oxidation. There have been several reports on the growth of ultrathin and thin iron oxide films on differently oriented silver single crystal supports [ 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 ]. An overview of these works is presented in the Supplementary Materials file, Section 1 (SM1) .…”

“…More recently, Lundgren, Weaver and co-workers grew the films using different procedure, i.e. by depositing iron onto a slightly heated silver substrate and in an oxygen ambient [ 17 , 18 , 19 ]. The authors employed STM and observed the formation of a p(9×9) Moiré superstructure with a significantly expanded FeO surface lattice constant (to 3.25 Å) and very small separation between iron and oxygen layers (0.26 Å—meaning that the iron and oxygen atoms are almost in-plane).…”

“…[ 8 ] did not employ STM (or any other atomic-resolution technique) to determine the exact structure of their films and (3) the authors of Refs. [ 17 , 18 , 19 ] were clearly stating that their films are not uniform and consist of a mixture of well-defined Moiré-reconstructed FeO (majority phase) and ill-defined “FeO x ” species (minority phase).…”