Chemisorption and incorporation of oxygen by nickel films

Abstract

Oxygen chemisorbed on nickel can be incorporated into the bulk, the process is activated and sensitive to the initial oxygen coverage. The activation energy increases from about 2 to ∼15 kcal mole^–1as the surface is depleted of chemisorbed oxygen and at 150° the work function is ∼1eV less than the clean metal. The chemical reactivity of surfaces which had incorporated oxygen to carbon monoxide and hydrogen confirmed that the low work function surface was essentially oxide and not metallic.

Oxygen interaction involves competition between oxygen chemisorption and incorporation to form an oxide which may be of high or low work function depending on the temperature and the conditions at the surface. These competitive processes and the ability of chemisorbed oxygen to act as an “anchor” thereby restricting the mobility of nickel and inhibiting the formation of the low work function oxide are suggested to account for the variable work function values observed in the Ni+O₂system. Our results and conclusions are discussed with relation to recent L.E.E.D. and photoelectric data.

The interaction of hydrogen with NiO is complex at 150° two distinct processes were isolated, a fast initial process leading to a decrease in work function of ∼2 eV followed by a somewhat slower process resulting in an increase of work function.