Surface structure and segregation of ordered Pt3Co(110) induced by oxygen

We have investigated the surface structure and segregation induced by oxygen adsorption on the ordered Pt3Co(110) ahoy using low-energy electron diffraction(LEED), Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). For the clean Pt3Co(110) surface, two different LEED patterns of 1 x 1 and 2 x 1 were observed depending on the annealing temperature, which had different Pt (237eV)/Co (LMM) AES intensity ratios. With increasing oxygen exposure at the substrate temperature of 300-500 degrees C, the 2 x I LEED pattern of the clean Pt3Co(110) surface changed to c(2 x 4), 1 x 2, and 1 x 2 + 2 x 1 + extra spots patterns, successively, and the Pt/Co AES intensity ratios showed a drastic decrease. Co 2p and O1s core level spectra by XPS and normal emission valence band spectra by UPS indicated that a Co monoxide overlayer is formed due to a reaction with oxygen at a high-temperature substrate. From these results, it was found that the observed several surface structures are due to the reaction between the segregated Co and adsorbed O atoms to form the stoichiometric CoO-typed overlayer. (C) 1998 Elsevier Science B.V. All rights reserved.