Paper SS-TuP23
Structural Properties of TbO_x Thin Films Grown on Cu(111)

Tuesday, October 30, 2012, 6:00 pm, Room Central Hall

The oxides of the rare earth metals Tb, Pr and Ce are desirable for several catalytic applications due to their ability to store and release oxygen atoms. In contrast to ceria, terbia surfaces have not been widely investigated, and may exhibit interesting structural behavior since several bulk Tb oxide phases are known to exist. In this study, we investigated the growth of terbium oxide (TbO_x) thin films on Cu(111) in ultrahigh vacuum, using scanning tunneling microscopy (STM) and low energy electron diffraction (LEED) to characterize the surface structures. We used a stepwise procedure to prepare the TbO_x films, with each step involving Tb deposition onto Cu(111) held at 300 K in an O₂ background to produce an ~1 monolayer (ML) film, followed by annealing in O₂ at 750 K. The TbO_­x films grow epitaxially on the Cu(111) substrate to generate TbO_x(111) with unit cell dimensions of about (1.4 x 1.4) relative to the Cu(111) lattice. STM images show that the TbO_x films (~2 - 5 ML) are comprised of large, flat terraces and reveal an atomic-structure consisting of hexagonal, close-packed arrangements of atoms that are separated by rows of oxygen vacancies at a spacing of about 2.2 nm. Estimates of the vacancy concentrations suggest that the oxide stoichiometry corresponds to an O:Tb ratio between 1.67 and 1.71, which agrees well with the composition of the stable iota phase of bulk terbia. The capability of preparing TbO_1.7(111) films with well-defined arrangements of vacancies may provide new opportunities for preparing model catalyst surfaces and studying the interactions of molecular reactants with ensembles of vacancies. Such studies are currently in progress.