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 structure is indicated to have two layers of O: one forms an overlayer in which 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 tetrahedral hole sires between the first and second metal layers. The stacking sequence, designated as (C)B(A)AB, corresponds to the first three layers of anion-terminated cubic ZrO2, although some lateral compression is needed for superposition on the regular hcp Zr structure. The absorption of O in the tetrahedral holes results in a significant expansion in the first-to-second Zr-Zr interlayer spacing to about 3.44 Angstrom from the bulk vaue of 2.57 Angstrom. The O-Zr bond lengths are estimated to equal 2.07 Angstrom for the overlayer O atoms, and 2.21 Angstrom for the O atoms in tetrahedral hole sites, Comparisons are made with the structures of the corresponding 0.5 and 1 ML surfaces formed by the O/Zr(0001) system. (C) 1997 Elsevier Science B.V.