LEED CRYSTALLOGRAPHIC ANALYSIS FOR THE STRUCTURE FORMED BY 2 ML OF O AT THE ZR(0001) SURFACE

A tensor LEED analysis is reported for the Zr(0001)-(1 x 1)-O surface which involves oxygen at a total coverage of 2 monolayers. The structu re is indicated to have two layers of O: one forms an overlayer in whi ch the O atoms bond to hollow sites of three-fold coordination on the regular metal surface. while the other laver has the O atoms in tetrah edral hole sires between the first and second metal layers. The stacki ng sequence, designated as (C)B(A)AB, corresponds to the first three l ayers of anion-terminated cubic ZrO2, although some lateral compressio n is needed for superposition on the regular hcp Zr structure. The abs orption of O in the tetrahedral holes results in a significant expansi on in the first-to-second Zr-Zr interlayer spacing to about 3.44 Angst rom from the bulk vaue of 2.57 Angstrom. The O-Zr bond lengths are est imated to equal 2.07 Angstrom for the overlayer O atoms, and 2.21 Angs trom for the O atoms in tetrahedral hole sites, Comparisons are made w ith the structures of the corresponding 0.5 and 1 ML surfaces formed b y the O/Zr(0001) system. (C) 1997 Elsevier Science B.V.