Oxygen adsorption on binary Co50Pd50 alloy surfaces

The interaction of O-2 with polycrystalline Co-50 Pd-50 alloy samples was studied by Auger electron spectroscopy (AES) and thermal desorption spectroscopy (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 is in contrast to the behaviour of Co-Pd alloys heated in UHV when the surface layer was enriched in Pd. The cobalt enriched at the surface was simultaneously oxidised to an oxide form. TDS spectra of oxygen exhibited one or two 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 surface cobalt oxide and removal of absorbed oxygen resulted in the broad feature (T > 585 K) characteristic for the high-temperature exposure of the alloy to oxygen. (C) 2001 Elsevier Science Ltd. All rights reserved.