Temperature dependent oxidation of thin Ni layers on Cu(1 1 1)

The initial stages of surface oxidation were investigated for pseudomorphic Ni layers (1–3 ML) on Cu(1 1 1) after oxygen adsorption at 150 and 300 K. At 150 K, the oxidation proceeds in a two-step process: first, oxygen chemisorbs on the surface up to a coverage of 0.7 ML leaving the top-most Ni atoms metallic. In the second step these Ni atoms are oxidized parallel to the adsorption of additional sub-surface oxygen (up to 2.0 ML), which is indicated by drastic changes in the Ni 2p3/2 spectra. No bulk oxidation beyond the first layer of metal atoms is observed after adsorption at 150 K. At 300 K, the mobility of the Ni atoms is high enough to allow also the oxidation of the lower lying metal atoms and the formation of NiO clusters on the surface. The sequence of chemisorption and oxidation and the amount of oxygen required for the complete oxidation of 1 ML Ni is the same as for 150 K.