Ordered cerium oxide thin films grown on Ru(0001) and Ni(111)

Cerium oxide thin films between 1-10 ML thick have been grown in situ on the Ru(0001) and Ni(111) surfaces. The films were highly ordered with an orientation determined by the orientation of the substrate on which they were grown, as shown by ion scattering spectroscopy and low-energy electron diffraction. The principal azimuths of the oxide films were aligned parallel to the principal azimuths of the substrates. The lattice constant of the films was nominally the same as for CeO2 with a fluorite structure. Optimal films were grown by dosing metallic Ce at a rate of ca 3 x 10(14) min(-1) cm(-2) in an oxygen background while the substrate was at 700 K. Fully oxidized films could be grown by using an oxygen pressure near 10(-7) Torr, whereas substoichiometric films could be grown by decreasing the oxygen pressure. 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 of the reduced oxide films was most consistent with a CeO2(111) surface that contained numerous oxygen vacancies. The films grown on Ru(0001) were fully stable in terms of structure and composition at temperatures up to 1000 K. The films grown on Ni(111) lost oxygen upon annealing to 1000 K. (C) 1999 Elsevier Science B.V. All rights reserved.