Oxygen adsorption on binary Co50Pd50 alloy surfaces

The interaction of O-2 with polycrystalline Co-50 Pd-50 alloy samples was s tudied by Auger electron spectroscopy (AES) and thermal desorption spectros copy (TDS). The samples were oxidised in the temperature range of 300-773 K with oxygen exposure up to 405 L. AES studies revealed surface segregation of Co due to dissociative oxygen chemisorption on the CoPd surface. This i s in contrast to the behaviour of Co-Pd alloys heated in UHV when the surfa ce layer was enriched in Pd. The cobalt enriched at the surface was simulta neously oxidised to an oxide form. TDS spectra of oxygen exhibited one or t wo peaks, depending on the adsorption temperature and oxygen exposure. The low-temperature peak (T-m approximate to 430K) was attributed to the oxygen chemisorbed phase. The initial sticking coefficient was estimated to be 0. 01 +/- 0.003, the adsorption energy 129 +/- 3 kJ/mol. Decomposition of surf ace cobalt oxide and removal of absorbed oxygen resulted in the broad featu re (T > 585 K) characteristic for the high-temperature exposure of the allo y to oxygen. (C) 2001 Elsevier Science Ltd. All rights reserved.