COMPARISON OF LOW-ENERGY SIMS AND AES IN A STUDY OF THE INTERACTION OF OXYGEN WITH POLYCRYSTALLINE NICKEL

A comparison has been made between low-energy SIMS yields and AES intensities during the oxidation of polycrystalline nickel. The AES measurements are in good agreement with earlier work that indicated an initial rapid chemisorption, a plateau in oxygen uptake during which oxide nucleation occurs and the subsequent lateral growth of the oxide layer at its limiting thickness (of 2-3 layers). At 300 K, the SIMS yield data show two regions during the chemisorption stage. In the first, up to about 1 L exposure. Ni+ and Ni+ 2 increase in a parallel fashion and Ni2O+ appears. In the second (1-4 L), the Ni+ increases more rapidly and reaches a maximum at the beginning of the plateau of oxygen uptake after an increase of 120 times over the clean surface yield. During the surface transformation as the oxide nuclei form, the yields of all the ions decrease significantly and particularly that of Ni+ 2. During the lateral growth of the oxide layer, there is a slow decline in all ion yields if the primary energy is in the range 150-500 eV but an increase in Ni+ yields is observed using higher primary energies. Some evidence was found for the incorporation of hydrogen into the oxide layer. The primary ion density must be kept extremely low during the nucleation stage especially at higher temperatures (<1 ion striking the surface per 200 molecules of oxygen) to avoid interference with the oxidation process. Sputtering of the oxidized surface was also examined. © 1979.