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

The c(2 x 4) and (2 x 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 x 2) and (1 x 3) periodicities of the Pd atoms. Oxygen removal by H-2 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 x 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 [1 (1) over bar 0] rows. These chains are in antiphase in the c(2 x 4) structure, and with random relative phase in the (2 x 3) structure. Compared to bulk Pd, the c(2 x 4) structure presents a slight increase in the first interlayer distance and a contraction of the second. On the other hand, the (2 x 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. (C) 1997 Elsevier Science B.V.