The atomic structure of the UO2+x(110) surface and the effects of interstitial oxygen: an elevated-temperature STM study

The (110) surface of uranium dioxide (UO2+x) single crystals has been studied by elevated-temperature scanning tunneling microscopy (STM). STM images of stoichiometric UO2(110) surfaces display a row structure which corresponds to a (1 x 1) bulk termination with missing rows along the [ITO] direction. Uranium sites are visible with atomic resolution in empty-states images above similar to 1.6 V sample bias. Interstitial oxygen in hyperstoichiometric UO2+x leads to a local redistribution of charge which appears in the STM image as dimer pairs. After dosing a UO2(110) surface with oxygen, another type of superstructure was observed which results from oxygen adsorption at surface interstitial sites. (C) 1998 Elsevier Science B.V. All rights reserved