LEED FROM SURFACE STEPS ON UO2 SINGLE CRYSTALS

A single crystal platelet of uranium dioxide has been prepared with one side very nearly parallel to the (111) plane and the other side inclined approximately 11.4° from the (111) plane. Low energy electron diffraction patterns obtained from the surface parallel to the (111) plane are characteristic of the clean unmodified uranium dioxide structure after the crystal has been vacuum annealed. Diffraction patterns from the inclined surface exhibit more closely spaced beams which are attributed to superstructures of regularly spaced steps. The observed patterns from the inclined surface have been compared to calculated diffraction patterns based on a simple kinematical analysis where it is assumed that the step height and spacing are in accord with a surface parallel to the (553) plane. Calculations have been made for the case in which only the outermost layer of uranium (or oxygen) atoms serve as scattering centers, and also for the case in which the contribution of the second layer equals that of the first. © 1968.