An initial stage of oxidation of a cesium-covered Ni (I 10) surface has been studied by metastable-induced electron spectroscopy (MIES) and low-energy electron diffraction (LEED). The MIES brought spectra with Cs 6s induced peak (P-6s), Cs 5p (P-5p), 0 2p induced peak (P-ox) and a structure related to the substrate Ni 3d states (P-3d). The work function change A p showed an oscillatory behavior in the progress of surface oxidation. The process is divided into three stages: (i) at low O-2 exposures, Delta phi > 0 with unchanging P-5p and P-6s; (ii) at moderate exposures, Delta phi < 0 with a drastic decrease in the P-6s intensity; (iii) at higher exposures, Delta phi > 0 with shifts of peaks P-5p and P-ox to higher energies, together with an appearance of peak P-3d. A three-step model of initial oxidation of alkali-covered Ni (1 1 0) surfaces is presented. (c) 2006 Elsevier B.V. All rights reserved.