AVS 64th International Symposium & Exhibition | |
Surface Science Division | Tuesday Sessions |
Session SS-TuP |
Session: | Surface Science Poster Session |
Presenter: | Christopher Lee, University of Florida |
Authors: | C. Lee, University of Florida V. Mehar, University of Florida S. Keil, University of Bremen, Germany V. Zielasek, University of Bremen, Germany M. Bäumer, University of Bremen, Germany J.F. Weaver, University of Florida |
Correspondent: | Click to Email |
Within the family of rare earth oxides (REOs), the terbium oxides exhibit favorable properties in selective oxidation catalysis due to the flexibility in the storage and release of oxygen within the lattice, specifically through structural rearrangement into well-ordered intermediates between the Tb2O3 and TbO2 stoichiometries. We investigated the growth and structures of TbOx films grown on Pt(111) in ultra-high vacuum (UHV) as well as the oxidation of the films by plasma-generated gaseous atomic oxygen. LEED and STM show that the deposition produces crystalline Tb2O3 films that adopt an oxygen deficient cubic fluorite structure where the film conforms to the hexagonal registry of the Pt(111) substrate. This is characterized by initial surface wetting up to 2 ML of Tb2O3 followed by 3D Stranski-Krastanov island growth at higher coverages.
We also find that the terbia film undergoes isomeric reorganization into the longer-order bixbyite Tb2O3 conformation when subject to a combination of atomic oxygen exposure along with subsequent annealing at 1000 K. LEED and TPD show that coexisting, ordered intermediates between Tb2O3 and TbO2 may then be created by further oxidizing the bixbyite Tb2O3 film via atomic oxygen beam exposure. In particular, two distinct O2 desorption peaks in TPD spectra provide evidence of the sequential phase stabilization of Tb7O12 (ι-phase) and Tb11O20 (δ-phase) along with lower temperature peaks corresponding with more weakly bound surface oxygen. The rapid reorganization of oxygen and oxygen vacancies within this intermediate regime is promising in that it suggests that specific structural arrangements of the terbia lattice may readily adjust to accommodate dissimilar metal cations into the metallic lattice to stabilize ordered, substitutionally doped films. The future outlook is to characterize structure and promoted surface chemistry of doped terbium oxide films, particularly the changes in oxidation induced by the incorporation of high valence dopants and low valence dopants into the metallic framework of the oxide. The larger implication is that the substitutional doping of terbium oxides can provide fundamental insight into doped oxide catalysis, which can provide the additional degree of tuneability towards increased reactivity or selectivity towards partial oxidation pathways required for an effective oxidative coupling of methane (OCM) catalyst.