A LEED CRYSTALLOGRAPHIC ANALYSIS FOR THE HALF MONOLAYER STRUCTURE FORMED BY O AT THE ZR(0001) SURFACE

A tensor LEED analysis has been made for the half monolayer structure formed by O absorbed at the Zr(0001) surface. The analysis uses intensity-versus-energy curves for eight independent diffracted beams measured at normal incidence. The best correspondence with the experimental intensity data is for a model in which O atoms occupy octahedral holes in an unreconstructed metallic structure, with 0.25 ML between the first and second metal layers, and another 0.25 ML between the second and third metal layers. These two (2 X 2)-O arrays are displaced laterally from one another by an unit translational vector of the Zr(0001) substrate. The O atoms induce both vertical and lateral relaxations in the three topmost Zr layers; the largest displacements being found in the second Zr layer. The averaged O-Zr bond length is 2.28 Angstrom, about 0.02 Angstrom shorter than the value in bulk ZrO.