Oxygen adsorption and oxide formation on Co(112̄0)

Adsorption of oxygen on the (112̄0) surface of hexagonal cobalt at 100 and 320 K has been studied by means of low energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS), UV photoelectron spectroscopy (UPS), change of work function (Δφ) and Auger electron spectroscopy (AES). At 100 K, adsorbed oxygen and Co3O4 features are observed, as identified by the UP spectra. During heating, a conversion into CoO takes place. This process is completed at 230 K and followed by dissolution of oxygen in the bulk at temperatures exceeding 450 K. Admission of oxygen at 320 K leads to identical results, but the total amount of adsorbed oxygen is approximately 30% lower. LEED experiments show a (1 × 3) superstructure at low coverages. After higher exposures, CoO formation, as revealed by the photoelectron data, is indicated by a changed diffraction pattern. It is concluded that an epitaxial growth of CoO(100) takes place.