Oxygen on Pd(110): Substrate reconstruction and adsorbate geometry by tensor LEED

The c(2 × 4) and (2 × 3) structures formed by oxygen adsorption on Pd(110) were studied in an LEED I-V experiment by employing the tensor LEED method. Adsorption-induced reconstructions occur in both cases, giving rise to respectively (1 × 2) and (1 × 3) periodicities of the Pd atoms. Oxygen removal by H2 treatment leads to clean, metastable, reconstructed phases, which have been studied as starting points for the analysis of the oxygen-covered surfaces. The reconstruction is of the missing-row type in both cases, with the removal of two rows of atoms out of every three for the (1 × 3) surface. In both cases a contraction of the first three interlayer spacings has been observed. The oxygen adatoms are adsorbed on the (111) facets formed as a consequence of the missing-row reconstruction, and form zig-zag chains along the [110] rows. These chains are in antiphase in the c(2 × 4) structure, and with random relative phase in the (2 × 3) structure. Compared to bulk Pd, the c(2 × 4) structure presents a slight increase in the first interlayer distance and a contraction of the second. On the other hand, the (2 × 3) structure shows a relatively large increase in the first interlayer distance and again a reduction in the second. Lateral changes of atomic positions and buckling in the second or third substrate layers have been found in all of the four structures analysed. © 1997 Elsevier Science B.V. All rights reserved.