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

Paper SS2-ThA8
The Effects of High Temperature Annealing on the Surface Reconstruction of NiO(111)

Thursday, November 5, 1998, 4:20 pm, Room 309

Session: Oxide Growth and Structure
Presenter: M.A. Schofield, University of Wisconsin, Milwaukee
Authors: M.A. Schofield, University of Wisconsin, Milwaukee
A.K. Hicks, University of Wisconsin, Milwaukee
M. Gajdardziska-Josifovska, University of Wisconsin, Milwaukee
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NiO is an ionically bonded solid with a rocksalt structure. In the <111> crystallographic direction, NiO consists of alternating close-packed planes of nickel and oxygen. The bulk terminated (111) surface, therefore, is a polar surface with theoretically predicted infinite surface energy. Consequently, adsorption of charged species at the surface or a considerable rearrangement of the atomic ordering is expected to occur to stabilize the surface. While microscopic faceting into neutral planes has been the accepted model for polar oxide surfaces, recent theoretical and experimental studies have reported a 2x2 reconstruction as a stabilization mechanism for the NiO(111) surface. In essence, the 2x2 structure (also known as octapolar, or nanofaceting structure) is the smallest possible scaling of the faceting model. In the present work we report two new reconstructions of annealed NiO(111) surfaces which cannot be readily explained by nanofaceting. Electron transparent single-crystal NiO samples were prepared for study of the (111) surface in plan view by transmission electron microscopy (TEM) and diffraction (TED) techniques. Annealing experiments were performed under high vacuum and atmospheric conditions over a wide range of temperatures and times. Under high vacuum annealing conditions a preferential desorption of oxygen from the sample surface resulted in the formation of epitaxial nickel islands. Conversely, for annealing experiments performed under atmospheric conditions, the NiO(111) samples exhibited surface reconstructions. Two reconstructions were observed and identified as having (@sr@3x@sr@3)R30° and (2@sr@3x2@sr@3)R30° surface periodicities from TED patterns obtained after annealing above 800°C in air. Both reconstructions were stable in air even after prolonged exposure of several weeks to atmospheric conditions.