AVS 45th International Symposium
    Surface Science Division Thursday Sessions
       Session SS2-ThA

Paper SS2-ThA4
Ordered Cerium Oxide Thin Films Grown on Ru(0001) and Ni(111)@footnote 1@

Thursday, November 5, 1998, 3:00 pm, Room 309

Session: Oxide Growth and Structure
Presenter: D.R. Mullins, Oak Ridge National Laboratory
Authors: D.R. Mullins, Oak Ridge National Laboratory
P.V. Radulovic, Oak Ridge National Laboratory
S.H. Overbury, Oak Ridge National Laboratory
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Ultrathin oxide films grown on single crystal metal substrates are advantageous for studying the adsorption and reaction of gases on oxide surfaces. Ultrathin films have a high surface area relative to their bulk volume. Their composition can be controlled during growth. They can be grown as nearly single crystals, can be readily removed and replenished in situ and they don't suffer from sample charging when using electron or ion probes. Cerium oxide thin films between 1 - 10 ML thick have been grown in situ on the Ru(0001) and Ni(111) surfaces. Well ordered films were grown by dosing metallic Ce in an oxygen ambient of 10@super -8@ - 10@super -7@ torr while the substrate was at 700K. Fully oxidized films could be grown by using a higher oxygen pressure while substoichiometric films were grown by reducing the oxygen pressure. The relative amounts of Ce@super +3@ and Ce@super +4@ were determined by soft x-ray photoelectron spectroscopy. Ion scattering spectroscopy (ISS) and LEED indicate that the cerium oxide films have the same symmetry as the substrate on which they are grown, i. e. six-fold on Ru(0001) and three-fold on Ni(111). The principal azimuths of the oxide films are aligned parallel to the principal azimuths of the substrates. The lattice constant of the cerium oxide is nominally the same as cubic CeO@sub 2@. Angle resolved ISS indicated that the fully oxidized films were predominantly terminated by an oxygen layer, whereas the substoichiometric films had a significant amount of cerium in the top layer. The structure and composition of the films grown on Ru(0001) were stable at temperatures up to 1000K. The films grown on Ni(111) lost oxygen upon annealing to 1000K. @FootnoteText@ @footnote 1@ Research was sponsored by the Division of Chemical Sciences, Office of Basic Energy Sciences, U.S. Department of Energy at Oak Ridge National Laboratory, managed by Lockheed Martin Energy Research Corp. under contract number DE-AC05-96OR22464.