W0151

Surface Diffraction from Ultra-Thin Film using X-Ray Energy Dispersive Technique. W. Dmowski, E. Mamontov and T. Egami, Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, PA-19104-6272, USA

The structure evolution of ultra-thin CeO2 overlayers deposited on a single crystal of ZrO2 was studied by in-situ energy dispersive surface x-ray scattering at temperatures up to 900¡C. In order to enhance the surface scattering intensity we applied the energy dispersive mode of x-ray diffraction in the surface scattering experiment [1]. This method uses a white radiation source and the structural information is obtained by the spectroscopy of the diffracted x-rays measured at a fixed diffraction angle.

The synchrotron x-ray scattering experiment was performed at the National Synchrotron Light Source (NSLS) of the Brookhaven National Laboratory beam line X-7A with the grazing angle incidence, in the evanescent wave scattering geometry.

As deposited cerium layer formed most likely amorphous hydroxide. Our in-situ diffraction study showed that as the sample was annealed in air, formation of CeO2 epitaxial layer commenced around 420¡C. The longitudinal and lateral Q dependence of the diffraction intensity indicated formation of epitaxial ceria islands. The lateral coherency was limited to only about 30 _ with the thickness of several atomic layers. While the ceria islands were orientationally matched to the YSZ substrate, their lattice spacing was different from that of YSZ, and was close to that of free standing ceria. Further increase in temperature led to modification of the interface and preferential growth of some ceria grains. Finally at 720¡C total diffusion of cerium into the bulk of the YSZ crystal occurred.

1. W. Dmowski, T. Egami, R. Gorte and J. Vohs, Physica B, 221 (1996) 420.